A STEEL REBAR AND A PRODUCTION METHOD THEREOF

Abstract

The present invention relates to a steel rebar comprising the following ingredients: 0.005%-0.030% of C, 0.3%-0.6% of Si, 1.2%-2.5% of Mn, 0.01% or less of P, 0.01% or less of S, 8.0%-10.0% of Cr, 1.0%-3.0% of Mo, 0.2%-0.4% of Sn, 0.01%-0.05% of Rare Earth element, and the remainder being Fe and unavoidable impurities. The present invention also provides a production method of steel rebar. The steel rebar of the present invention has excellent comprehensive mechanical properties and corrosion resistance performance, while meeting the requirements of anti-knock, the service life in sea water of the steel rebar is increased, thus it can be widely used in reinforced concrete structures in ocean environment.

Claims

1. A steel rebar, wherein, comprising the following ingredients calculated in weight percentage: 0.005%-0.030% of C, 0.3%-0.6% of Si, 1.2%-2.5% of Mn, 0.01% or less of P, 0.01% or less of S, 8.0%-10.0% of Cr, 1.0%-3.0% of Mo, 0.2%-0.4% of Sn, 0.01%-0.05% of Rare Earth element, and the remainder being Fe and unavoidable impurities.

2. The steel rebar in accordance with claim 1, wherein, comprising the following ingredients calculated in weight percentage: 0.005%-0.030% of C, 0.3%-0.6% of Si, 1.2%-1.8% of Mn, 0.01% or less of P, 0.01% or less of S, 8.0%-10.0% of Cr, 1.0%-1.6% of Mo, 0.2%-0.4% of Sn, 0.01%-0.05% of Rare Earth element, and the remainder being Fe and unavoidable impurities.

3. A steel rebar, wherein, comprising the following ingredients calculated in weight percentage: 0.005%-0.030% of C, 0.3%-0.6% of Si, 1.2%-2.5% of Mn, 0.01% or less of P, 0.01% or less of S, 8.0%-10.0% of Cr, 1.0%-3.0% of Mo, 0.2%-0.4% of Sn, 0.01%-0.05% of Rare Earth element, 0.04%-0.18% of V and/or 0.010%-0.030% of Ti, and the remainder being Fe and unavoidable impurities.

4. The steel rebar in accordance with claim 3, wherein, comprising the following ingredients calculated in weight percentage: 0.005%-0.030% of C, 0.3%-0.6% of Si, 1.7%-2.5% of Mn, 0.01% or less of P, 0.01% or less of S, 8.0%-10.0% of Cr, 1.5%-2.0% of Mo, 0.2%-0.4% of Sn, 0.01%-0.05% of Rare Earth element, 0.04%-0.08% of V, and the remainder being Fe and unavoidable impurities.

5. The steel rebar in accordance with claim 3, wherein, comprising the following ingredients calculated in weight percentage: 0.005%-0.030% of C, 0.3%-0.6% of Si, 1.7%-2.5% of Mn, 0.01% or less of P, 0.01% or less of S, 8.0%-10.0% of Cr, 1.8%-3.0% of Mo, 0.2%-0.4% of Sn, 0.01%-0.05% of Rare Earth element, 0.10%-0.18% of V, 0.010%-0.030% of Ti, and the remainder being Fe and unavoidable impurities.

6. The steel rebar in accordance with claim 5, wherein, the steel rebar has a microscopic structure composed of ferrite and bainite, with the ferrite accounting for a percentage of 50%-70%.

7. The steel rebar in accordance with claim 5, wherein, the steel rebar has a ratio of tensile strength to yield strength at greater than 1.25, a maximum stress total elongation percentage greater than 9%, an after-fracture elongation percentage greater than 18%, a corrosion rate by cyclic immersion corrosion test at less than 0.45 m.sup.2h, and a corrosion rate by salt spray corrosion test at less than 0.45 m.sup.2h.

8. A production method of steel rebar, wherein, comprising the following steps: S1: performing preliminary desulfurization of molten iron to control the sulfur content at no more than 0.01%; S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping; S3: performing steel tapping, during the process of which, alloying elements of Si and Mn are added for deoxygenation and carbon powder and slag former are also added; S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen in an RH vacuum refining furnace so as to control the Cr and C contents within the range in accordance with claim 1; carrying out deoxygenation with an LF furnace, adding the required alloying elements of Mn, Mo, Sn and Rare Earth into the steel after deoxygenation, and then adding calcium-ferrum alloy under soft stirring by blowing inert gas, so as to control contents of these elements within the range in accordance with claim 1; raising the temperature of the molten steel and adding a cover agent; S5: performing continuous casting, by casting the molten steel under protective casting with a continuous casting machine to form a continuous casting slab; S6: performing rolling, by heating the continuous casting slab to a temperature higher than its austenitization temperature in a heating furnace, rough rolling, moderate rolling, precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling, so as to produce a finished product of steel rebar with ingredients in accordance with claim 1.

9. A production method of steel rebar, wherein, comprising the following steps: S1: performing preliminary desulfurization of molten iron to control the sulfur content at no more than 0.01%; S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping; S3: performing steel tapping, during the process of which, alloying elements of Si and Mn are added for deoxygenation and carbon powder and slag former are also added; S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen in an RH vacuum refining furnace so as to control the Cr and C contents within the range in accordance with claim 5; carrying out deoxygenation with an LF furnace, adding the required alloying elements of Mn, Mo, Sn, Rare Earth, as well as V and/or Ti, into the steel after deoxygenation, and then adding calcium-ferrum alloy under soft stirring by blowing inert gas, so as to control contents of these elements within the range in accordance with claim 5; raising the temperature of the molten steel and adding a cover agent; S5: performing continuous casting, by casting the molten steel under protective casting with a continuous casting machine to form a continuous casting slab; S6: performing rolling, by heating the continuous casting slab to a temperature higher than its austenitization temperature in a heating furnace, rough rolling, moderate rolling, precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling, so as to produce a finished product of steel rebar with ingredients in accordance with claim 5.

10. The production method in accordance with claim 9, wherein, in Step S2, the steel for steel tapping has a temperature no higher than 1690 C.

11. The production method in accordance with claim 9, wherein, in Step S3, a protective gas is blown into the molten steel for stirring during the process of steel tapping.

12. The production method in accordance with claim 9, wherein, in Step S4, the decarburization by blowing oxygen is performed at a temperature no lower than 1605 C. during refining in the RH vacuum refining furnace, the deoxygenation is performed at a temperature no lower than 1575 C. during refining in the LF furnace to control the oxygen content at no more than 50 ppm, the soft stirring is performed for a duration no less than 5 min, and the temperature of the molten steel is raised to 1570-1600 C.

13. The production method in accordance with claim 9, wherein, in Step S6, the continuous casting slab is heated to 1100-1200 C. in the heating furnace, the start rolling temperature before the rough rolling is 1030-1100 C., the temperature during the precision rolling is 950-1050 C., and the temperature when the rolled steel is initially placed onto the cooling bed is 900-960 C.

14. The steel rebar in accordance with claim 1, wherein, the steel rebar has a microscopic structure composed of ferrite and bainite, with the ferrite accounting for a percentage of 50%-70%.

15. The steel rebar in accordance with claim 1, wherein, the steel rebar has a ratio of tensile strength to yield strength at greater than 1.25, a maximum stress total elongation percentage greater than 9%, an after-fracture elongation percentage greater than 18%, a corrosion rate by cyclic immersion corrosion test at less than 0.45 m.sup.2h, and a corrosion rate by salt spray corrosion test at less than 0.45 m.sup.2h.

16. The production method in accordance with claim 8, wherein, in Step S2, the steel for steel tapping has a temperature no higher than 1690 C.

17. The production method in accordance with claim 8, wherein, in Step S3, a protective gas is blown into the molten steel for stirring during the process of steel tapping.

18. The production method in accordance with claim 8, wherein, in Step S4, the decarburization by blowing oxygen is performed at a temperature no lower than 1605 C. during refining in the RH vacuum refining furnace, the deoxygenation is performed at a temperature no lower than 1575 C. during refining in the LF furnace to control the oxygen content at no more than 50 ppm, the soft stirring is performed for a duration no less than 5 min, and the temperature of the molten steel is raised to 1570-1600 C.

19. The production method in accordance with claim 8, wherein, in Step S6, the continuous casting slab is heated to 1100-1200 C. in the heating furnace, the start rolling temperature before the rough rolling is 1030-1100 C., the temperature during the precision rolling is 950-1050 C., and the temperature when the rolled steel is initially placed onto the cooling bed is 900-960 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to make the present invention easy and clear to understand, hereinafter, the present invention will be further described in detail according to specific embodiments of the present invention and with reference to the appended drawings, wherein:

[0040] FIG. 1 is a microstructure view of a steel rebar of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0041]

TABLE-US-00001 TABLE 1 Steel rebar ingredients of Embodiments 1-10 as well as comparison examples 1-3 (wt. %) C Si Mn Cr Mo RE Sn V Ti P S Embodiment 1 0.005 0.60 2.5 9.0 1.0 0.05 0.20 <0.01 <0.01 Embodiment 2 0.030 0.45 1.2 10.0 3.0 0.01 0.40 <0.01 <0.01 Embodiment 3 0.015 0.30 1.8 8.0 1.6 0.03 0.30 <0.01 <0.01 Embodiment 4 0.020 0.5 2.3 8.5 2.2 0.02 0.25 0.04 <0.01 <0.01 Embodiment 5 0.025 0.55 1.7 8.2 2.3 0.02 0.35 0.18 0.01 <0.01 <0.01 Embodiment 6 0.009 0.35 1.8 8.5 2.5 0.04 0.36 0.1 0.03 <0.01 <0.01 Embodiment 7 0.012 0.40 2.2 9.5 1.5 0.03 0.28 0.02 <0.01 <0.01 Embodiment 8 0.012 0.57 1.8 9.7 2.0 0.03 0.21 0.08 <0.01 <0.01 Embodiment 9 0.018 0.50 1.9 9.0 1.7 0.02 0.30 0.06 <0.01 <0.01 Embodiment 10 0.026 0.50 2.3 8.1 1.8 0.05 0.40 0.15 0.02 <0.01 <0.01 Comparison 0.23 0.54 1.5 <0.01 <0.01 Example 1 Comparison 0.015 0.48 1.9 9.1 1.8 0.02 0.60 <0.01 <0.01 Example 2 Comparison 0.024 0.52 2.0 9.8 2.0 0.02 <0.01 <0.01 Example 3

Embodiment 1

[0042] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0043] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping step with a steel tapping temperature of 1680 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1605 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1575 C. until the oxygen content in the molten steel reaches 40 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 5 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 1 in Table 1; raising the temperature of the molten steel to 1580 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1100 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1030 C. and the precision rolling temperature at 950 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 900 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 2

[0044] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0045] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1690 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1625 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1600 C. until the oxygen content in the molten steel reaches 20 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 6 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 2 in Table 1; raising the temperature of the molten steel to 1600 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1200 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1100 C. and the precision rolling temperature at 1050 C. without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 960 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 3

[0046] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0047] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1685 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1610 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1585 C. until the oxygen content in the molten steel reaches 30 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 6 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 3 in Table 1; raising the temperature of the molten steel to 1570 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1120 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1050 C. and the precision rolling temperature at 960 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 910 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 4

[0048] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, V, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0049] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1690 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, performed by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1620 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1590 C. until the oxygen content in the molten steel reaches 20 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth, V into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 6 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 4 in Table 1; raising the temperature of the molten steel to 1585 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1180 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1040 C. and the precision rolling temperature at 990 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 950 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 5

[0050] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, V, Ti, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0051] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1675 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1615 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1580 C. until the oxygen content in the molten steel reaches 25 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth, V, Ti into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 7 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 5 in Table 1; raising the temperature of the molten steel to 1580 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1190 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1095 C. and the precision rolling temperature at 1030 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 950 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 6

[0052] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, V, Ti, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0053] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1670 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1610 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1580 C. until the oxygen content in the molten steel reaches 20 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth, V, Ti into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 7 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 6 in Table 1; raising the temperature of the molten steel to 1590 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1185 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1085 C. and the precision rolling temperature at 1035 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 955 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 7

[0054] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, Ti, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0055] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1685 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1615 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1580 C. until the oxygen content in the molten steel reaches 20 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth, Ti into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 7 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 7 in Table 1; raising the temperature of the molten steel to 1585 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1180 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1080 C. and the precision rolling temperature at 1020 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 940 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 8

[0056] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, V, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0057] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1680 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1610 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1585 C. until the oxygen content in the molten steel reaches 20 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth, V into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 7 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 8 in Table 1; raising the temperature of the molten steel to 1590 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1150 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1065 C. and the precision rolling temperature at 1025 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 965 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 9

[0058] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, V, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0059] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1675 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1605 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1575 C. until the oxygen content in the molten steel reaches 20 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth, V into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 7 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 9 in Table 1; raising the temperature of the molten steel to 1580 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1105 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1045 C. and the precision rolling temperature at 1005 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 945 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Embodiment 10

[0060] The present embodiment provides a steel rebar, comprising the following elements: C, Si, Mn, P, S, Cr, Mo, Sn, Rare Earth element, V, Ti, Fe and unavoidable impurities, wherein, the weight percentages of the ingredients are as shown in Table 1, the mechanical properties are as shown in Table 2, and the corrosion resistance performance is as shown in Table 3.

[0061] The present embodiment also provides a production method of steel rebar comprising the following steps:

S1: performing preliminary desulfurization of molten iron by using a KR method to control the sulfur content at no more than 0.01%. Because sulfur element as an impurity element would reduce mechanical properties and corrosion resistance performance of steel and normally cannot be removed in a convertor, therefore, in order to reduce the sulfur content in steel, preliminary desulfurization treatment needs to be performed in molten iron. Before performing desulfurization, the blast furnace slag needs to be removed in order to increase the desulfurization efficiency. A mixture of lime powder and fluorite mixed at a mass ratio of 9:1 is adopted as the desulfurization agent. After still standing of the desulfurated molten iron, the desulfurization residue is removed to prevent it from entering the convertor and causing convertor resulfurization. Thereby, the sulfur content in the steel is ensured to be controlled at less than 0.01%.
S2: performing smelting in a convertor, by feeding the molten iron processed by Step S1 together with steel scrap and/or pig iron into a convertor to be smelted, thus obtaining steel with a carbon content less than 0.05% and a phosphorus content less than 0.01% for steel tapping. The convertor is a top and bottom combined blown converter.
S3: performing steel tapping with a steel tapping temperature of 1685 C. During the steel tapping process, alloying elements of Si and Mn are added for deoxygenation, and carbon powder and slag former are also added. During the operation process of steel tapping, a protective gas is blown into the molten steel for stirring the molten steel at a pressure of 0.5 MPa. The fluidity of the molten steel is utilized to make the deoxygenation of the added Si and Mn elements more thoroughly and to facilitate the removal of inclusions by floating. The carbon powder and slag former are added to increase the carbon content of steel and to produce reduced slag, so as to prepare for the subsequent refining procedure outside the convertor.
S4: performing refining outside the convertor, by adding Cr element and meanwhile performing decarburization by blowing oxygen at 1620 C. in an RH vacuum refining furnace, so that C element is partially removed by the decarburization process, thereby controlling the contents of Cr and C elements within the required range; performing deoxygenation with an LF furnace at 1585 C. until the oxygen content in the molten steel reaches 20 ppm, and adding the required alloying elements of Mn, Mo, Sn, Rare Earth, V, Ti into the steel after deoxygenation, wherein, while the added alloying elements may be a pure metallic element, normally they are added in the form of iron alloy; and then adding calcium-ferrum alloy to perform denaturation treatment on the inclusions, performing soft stirring by blowing inert gas for 7 min to make the ingredients and temperature of the steel uniformly distributed and to facilitate the removal of inclusions by floating, so that the contents of the ingredients are controlled within the ranges as shown in data of Embodiment 10 in Table 1; raising the temperature of the molten steel to 1595 C. during a later period of processing with the LF furnace, in order to ensure smooth operation of continuous casting, and then adding a cover agent which usually is carbonized rice husk.
S5: continuous casting, by casting the molten steel under protective casting with a continuous casting machine to produce small square billets of 150 mm150 mm.
S6: performing rolling, by heating the continuous casting slab to 1195 C. in a heating furnace, performing rough rolling, moderate rolling and precision rolling by using a continuous rod and wire rolling machine with the start rolling temperature at 1095 C. and the precision rolling temperature at 1045 C., without passing water cooling after precision rolling, and placing the rolled steel after precision rolling onto a cooling bed for air cooling until room temperature, thereby producing a finished product of steel rebar as shown in Table 1, wherein, the temperature when the rolled steel is initially placed onto the cooling bed is 955 C. By means of the technique of controlled rolling and controlled cooling, the microstructure of bainite plus ferrite is finally obtained.

Experimental Example

[0062] In order to prove the technical effects of the present invention, the following experiments are performed on the steel rebar produced by Embodiment 1-10 and comparison examples 1-3:

1. Experimental Methods

[0063] 1.1 mechanical property tests: performed according to GB1499.2-2007, steel used in reinforced concrete, Part II: hot-rolled ribbed rebar. The yield strength (R.sub.0.2), tensile strength (R.sub.m), and after-fracture elongation percentage (A) are tested.
1.2 corrosion resistance performance tests:
1.2.1 cyclic immersion corrosion test: performed according to corrosion test methods of steel rebar in a chloride ion environment, a draft for consultation proposed by Steel Industry Association of China and drafted by institutes of Iron and Steel Research Institute and Metallurgical Industry Information Standardization Research Institute.
The test sample is a cylinder of 13 mm50 mm;
The test solution is a solution of sodium chloride with an initial concentration of (0.340.009)mol.Math.L.sup.1 (an initial mass percentage of 2.0%0.05%). And the specific test conditions are as follows:

Temperature: 45 C.2 C.

Humidity: 70%10% RH

[0064] PH value of solution: 6.5-7.2
Test time: 360 h
Each cyclic period: 60 min5 min, with an immersion time of 12 min2 min
Highest temperature of test sample surface after baking: 70 C.10 C.
1.2.2 salt spray corrosion test: performed according to GBT10125-1997, corrosion tests in an artificial atmosphere, salt spray test.
The test sample is a test plate of 3 mm15 mm40 mm;
The test solution is a solution of sodium chloride with a concentration of (505)g.Math.L.sup.1 (a mass percentage of 5.0%0.5%). And the specific test conditions are as follows:

Temperature: 35 C.2 C.

[0065] PH value of solution: 6.5-7.2
Test time: 360 h

2. Experimental Results

[0066] Table 2 shows the effects about mechanical properties of Embodiment 1-10 and comparison examples 1-3. Table 3 shows the effects about corrosion resistance performance of Embodiment 1-10 and comparison examples 1-3.

TABLE-US-00002 TABLE 2 Effects about mechanical properties R.sub.0.2/MPa R.sub.m/MPa A/% R.sub.m/R.sub.0.2 A.sub.gt/% Embodiment 1 432 627 24.5 1.45 11.8 Embodiment 2 408 613 25.3 1.50 12.6 Embodiment 3 482 696 24.5 1.44 11.1 Embodiment 4 561 728 18.9 1.30 10.8 Embodiment 5 611 793 19.6 1.29 10.5 Embodiment 6 554 755 20.8 1.36 10.3 Embodiment 7 524 716 21.2 1.37 10.7 Embodiment 8 523 743 25.0 1.42 11.3 Embodiment 9 536 729 21.0 1.36 10.7 Embodiment 10 621 795 18.0 1.28 9.5 Comparison 435 632 22.0 1.45 12.0 Example 1 Comparison 486 586 13.4 1.21 6.2 Example 2 Comparison 477 687 24.8 1.44 11.0 Example 3

TABLE-US-00003 TABLE 3 Effects about corrosion resistance performance cyclic immersion test salt spray test Increase of Increase of Corrosion Relative corrosion resis- Corrosion Relative corrosion resis- rate corrosion tance performance rate corrosion tance performance (g/m.sup.2 .Math. h) rate (%) (g/m.sup.2 .Math. h) rate (%) Embodiment 1 0.415 0.127 690 0.411 0.130 666 Embodiment 2 0.191 0.058 1616 0.205 0.065 1437 Embodiment 3 0.419 0.128 682 0.432 0.137 629 Embodiment 4 0.356 0.109 821 0.367 0.117 758 Embodiment 5 0.441 0.135 643 0.445 0.141 608 Embodiment 6 0.349 0.106 839 0.360 0.114 775 Embodiment 7 0.386 0.118 749 0.395 0.125 697 Embodiment 8 0.272 0.083 1105 0.288 0.091 994 Embodiment 9 0.370 0.113 786 0.381 0.121 727 Embodiment 10 0.433 0.132 657 0.435 0.138 624 Comparison 3.278 1 3.150 1 Example 1 Comparison 0.365 0.111 798 0.377 0.120 736 Example 2 Comparison 0.456 0.151 561 0.463 0.160 526 Example 3 (The relative corrosion rates in Table 3 are all compared with Comparison Example 1, by setting the relative corrosion rate of Comparison Example 1 to be 1.000)

[0067] As known from Table 3, in Embodiment 1-10, because Cr, Sn, Mo, Rare Earth elements are added, the corrosion resistance performance of steel rebar is increased by more than 600% compared with Comparison Example 1. As can be seen from the corrosion resistance performance data of Comparison Example 3, the increment of the corrosion resistance performance of steel rebar which does not contain Sn element is not as great as that of steel rebar which contains Sn element. By comparing Embodiment 1, 2, 3 and Comparison Example 2, it can be concluded that, when the Sn content is within the range of 0.02-0.04%, along with the increase of the Sn content, the corrosion resistance performance of steel rebar increases, but its yield strength and tensile strength decrease. And when the Sn content surpasses 0.04%, the corrosion resistance performance of steel rebar presents no more notable increment, but the mechanical properties are adversely affected, especially the after-fracture elongation percentage and the maximum stress total elongation percentage decrease significantly, while the ratio of tensile strength to yield strength also considerably decreases. In Embodiments 4-10, V and/or Ti elements are added into steel rebar, and it can be seen from Table 2, the adding of V and/or Ti elements improves the yield strength and tensile strength of steel rebar, and at the same time, the after-fracture elongation percentage is greater than 18%, the ratio of tensile strength to yield strength is greater than 1.25, and the maximum stress total elongation percentage is greater than 9%, thereby endowing the steel product with good anti-knock performance.

[0068] In the steel rebar of the present invention, by reasonably designing the ingredients and accurately controlling the element ingredients and temperature during the smelting process, in combination with the technique of controlled rolling and controlled cooling, the steel rebar is made to obtain a microstructure of bainite plus ferrite (with the ferrite accounting for a percentage of 50%-70%) as shown in FIG. 1, thereby endowing the steel rebar with excellent comprehensive mechanical properties as well as excellent corrosion resistance performance which is increased by more than 6 times compared to ordinary steel rebar, so that the service life requirement of reinforced concrete structures in oceanographic engineering can be fulfilled.

[0069] Apparently, the aforementioned embodiments are merely examples illustrated for clearly describing the present invention, rather than limiting the implementation ways thereof. For those skilled in the art, various changes and modifications in other different forms can be made on the basis of the aforementioned description. It is unnecessary and impossible to exhaustively list all the implementation ways herein. However, any obvious changes or modifications derived from the aforementioned description are intended to be embraced within the protection scope of the present invention.