STEEL FOR ALLOY STRUCTURE AND MANUFACTURING METHOD THEREFOR

Abstract

Disclosed is a steel for an alloy structure, the chemical elements of the steel being, in percentage by mass: 0.35-0.45% of C, 0.27-0.35% of Si, 0.6-0.8% of Mn, 0.015-0.05% of Al, 0.06-0.1% of V, 0.2-1.0% of Zr, 0.001-0.005% of Mg, 0.025% or less of P, 0.015% or less of S, 0.005% or less of N, 0.001% or less of 0, the balance being Fe and other inevitable impurities. In addition, also disclosed is a manufacturing method for the steel for an alloy structure, the method comprising steps of: (1) smelting, refining, and casting; (2) blooming and cogging; (3) secondary hot rolling to form a product; and (4) heat treatment including quenching and tempering. The steel for an alloy structure is designed by adding trace alloy elements, the steel for an alloy structure is further strengthened and toughened, and the manufacturing cost is low.

Claims

1. A steel for an alloy structure, comprising the following chemical elements in percentage by mass: 0.35-0.45% of C, 0.27-0.35% of Si, 0.6-0.8% of Mn, 0.015-0.05% of Al, 0.06-0.1% of V, 0.2-1.0% of Zr, 0.001-0.005% of Mg, 0.025% or less of P, 0.015% or less of S, 0.005% or less of N, 0.001% or less of O, the balance being Fe and other inevitable impurities.

2. The steel for the alloy structure according to claim 1, further comprising at least one selected from the following chemical elements: Ce, Hf, La, Re, Sc, and Y, wherein the total addition amount of these elements is 1% or less.

3. The steel for the alloy structure according to claim 1, wherein the content by mass percentage of chemical elements satisfies at least one of the following: 0.08-0.1% of V; 0.3-0.7% Zr; and 0.001-0.003% of Mg.

4. The steel for the alloy structure according to claim 1, wherein a ratio of the content by mass of chemical elements further satisfies at least one of the following: Zr/N=40˜200; Zr/V=2˜16.7; and Zr/C=0.4˜2.8.

5. The steel for the alloy structure according to claim 1, wherein a ratio of the content by mass of chemical elements further satisfies at least one of the following: Mg/O=0.5˜3; and Mg/S=0.6˜5.0.

6. The steel for the alloy structure according to claim 1, wherein a microstructure of the steel for the alloy structure is ferrite+pearlite, and the steel for the alloy structure contains ZrC, ZrN, MgO, and MgS particles.

7. The steel for the alloy structure according to claim 6, wherein the sum of the number of the ZrC and ZrN particles is 3-15 pieces/mm.sup.2.

8. The steel for the alloy structure according to claim 6, wherein the sum of the number of the MgO and MgS particles is 5-20 pieces/mm.sup.2.

9. The steel for the alloy structure according to claim 6, wherein the ZrC, ZrN, MgO, and MgS particles have a diameter of 0.2-7 μm.

10. The steel for the alloy structure according to claim 1, wherein the steel for alloy structure has a yield strength of 755 MPa or more, a tensile strength of 900 MPa or more, an elongation percentage of 12% or more, and an impact toughness of 100 J or more.

11. A manufacturing method for the steel for the alloy structure according to claim 1, comprising steps of: (1) smelting, refining, and casting; (2) blooming and cogging; (3) secondary hot rolling to form a product; and (4) heat treatment comprising quenching and tempering.

12. The manufacturing method according to claim 11, wherein a heating temperature is 1,150-1,250° C. in the step of blooming and cogging; and a heating temperature is 1,150-1,250° C. in the step of secondary hot rolling to form the product.

13. The manufacturing method according to claim 11, wherein in the step of heat treatment, a heating temperature is controlled within a range of 855-890° C. during quenching, and a cooling speed is controlled within a range of 50-90° C./s during quenching; and a heating temperature is controlled within a range of 645-670° C. during tempering, and a cooling speed is controlled within a range of 50-90° C./s during tempering.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0058] A steel for an alloy structure and a manufacturing method therefor, which are provided by the present invention, will be further explained and illustrated below in combination with specific embodiments, but the explanation and illustration do not constitute improper limitation to the technical solution of the present invention.

Embodiments 1-6 and Comparative Examples 1-3

[0059] A steel for an alloy structure, which is provided by Embodiment 1-6, is prepared by adopting the following steps:

[0060] (1) carrying out smelting by an electric furnace, LF refining, and casting.

[0061] (2) blooming and cogging: the heating temperature is 1,150-1,250° C.

[0062] (3) carrying out secondary hot rolling to form a product: the heating temperature is 1,150-1,250° C.

[0063] (4) heat treatment including quenching and tempering, wherein a heating temperature is controlled within a range of 855-890° C. during quenching, a cooling speed is controlled within a range of 50-90° C./s during quenching, and a cooling agent adopts mineral oil; and a heating temperature is controlled within a range of 645-670° C. during tempering, a cooling speed is controlled within a range of 50-90° C./s during tempering, and a cooling agent adopts mineral oil or water.

[0064] It should be noted that in some other embodiments, refining may also adopt RH refining, and in the final stage of VD (or RH) refining, a small amount of ferrozirconium-iron and a small amount of magnesium aluminum alloy may be sequentially added, soft stirring with argon blowing is carried out after the mass percentage of each chemical element in the steel meets a range defined by the invention, and an argon flow rate is controlled within a range of 5-8L/min.

[0065] In some preferred embodiments, in the step (1), casting may adopt bloom continuous casting, and a casting speed is controlled within a range of 0.45-0.65m/min; mould fluxes are adopted, mould electromagnetic stirring is adopted, the current is 500A, the frequency is 2.5-3.5 Hz, and a proportion of equiaxed grains of a continuously cast bloom is 20% or more.

[0066] In some preferred embodiments, in the step (2), a blank may be preprocessed before blooming and cogging and for example, may be subjected to surface finishing and polishing to remove visible surface defects so as to ensure high surface quality.

[0067] Comparative examples 1-3 are obtained by adopting ingredients and a manufacturing process in the prior art.

[0068] Table 1 lists the mass percentage of each chemical element of the steel for the alloy structure in Embodiments 1-6 and an existing steel for an alloy structure in comparative examples 1-3.

TABLE-US-00001 TABLE 1 (wt %, the balance of Fe and other inevitable impurities) Number C Si Mn V P S N Al Zr O Mg Ce La Zr/ N Zr/C Zr/V Mg/S Mg/O Embod- 0.40 0.35 0.8 0.1 0.015 0.015 0.005 0.05 0.3 0.001 0.004 0.1 —  60 0.75  3 0.27 4 iment 1 Embod- 0.44 0.27 0.6 0.06 0.025 0.008 0.003 0.02 0.20 0.0008 0.002 — 0.2  67 0.45  3.3 0.25 2.5 iment 2 Embod- 0.43 0.32 0.7 0.08 0.016 0.008 0.004 0.04 1.0 0.0010 0.005 — — 250 2.33 12.5 0.625 5.0 iment 3 Embod- 0.35 0.29 0.5 0.06 0.018 0.005 0.002 0.015 0.88 0.0010 0.003 — — 440 2.5 14.7 0.6 3.0 iment 4 Embod- 0.42 0.34 0.6 0.09 0.013 0.007 0.003 0.03 0.73 0.0007 0.005 — — 243.3333 1.74  8.1 0.71 7.14 iment 5 Embod- 0.43 0.28 0.5 0.07 0.007 0.005 0.004 0.035 0.58 0.0009 0.001 — — 145 1.35  8.3 0.2 1.11 iment 6 Comp- 0.40 0.28 0.004 0.015 0.005 0.018 — 0.0008 — 0 0  0 0  0 0 0 arative example 1 Comp- 0.41 0.35 0.016 0.012 0.004 0.04 — 0.0007 — 0 0  0 0  0 0 0 arative example 2 Comp- 0.42 0.32 0.7 0.025 0.005 0.004 0.035 — 0.0009 — 0 0  0 0  0 0 0 arative example 3

[0069] Table 2 lists conditions of microstructures in the obtained steel for the alloy structure in Embodiments 1-6 and microstructures in the obtained existing steel for the alloy structure in Comparative examples 1-3.

TABLE-US-00002 TABLE 2 Sum of Number of Sum of Number of Diameter of ZrC, ZrC and ZrN MgO and MgS ZrN, MgO and particles particles MgS particles Number Microstructure (pieces/mm.sup.2) (pieces/mm.sup.2) (μm) Embodiment 1 ferrite and pearlite 3 20 0.2-5 Embodiment 2 ferrite and pearlite 12 5 0.2-6 Embodiment 3 ferrite and pearlite 15 12 0.2-7 Embodiment 4 ferrite and pearlite 5 8 0.2-4 Embodiment 5 ferrite and pearlite 8 16 0.2-7 Embodiment 6 ferrite and pearlite 10 10 0.2-5 Comparative ferrite and pearlite 0 0 — example 1 Comparative ferrite and pearlite 0 0 — example 2 Comparative ferrite and pearlite 0 0 — example 3

[0070] Table 3 lists specific process parameters of the steel for the alloy structure in

[0071] Embodiments 1-6 and the existing steel for the alloy structure in Comparative examples 1-3.

TABLE-US-00003 TABLE 3 Step (3) Step (2) Heating Heating temperature temperature during Step (4) during secondary Heating Heating Cooling blooming hot rolling temperature Cooling temperature speed and to form a during speed during during during cogging product quenching quenching tempering tempering Number (° C.) (° C.) (° C.) (° C./s) (° C.) (° C./S) Embodiment 1 1150 1250 855 50 645 82 Embodiment 2 1180 1220 890 85 670 50 Embodiment 3 1220 1180 860 66 650 90 Embodiment 4 1250 1150 870 90 660 78 Embodiment 5 1190 1180 865 78 655 66 Embodiment 6 1230 1200 855 83 645 88 Comparative 1250 1250 850 40 640 35 example 1 Comparative 1230 1210 860 35 650 45 example 2 Comparative 1200 1230 870 45 655 40 example 3

[0072] In order to verify the implementation effect of the invention and meanwhile, prove the excellent effects of the invention with respect to the prior art, the steel for the alloy structure in Embodiments 1-6 and the existing steel for the alloy structure in comparative examples 1-3 are subjected to mechanical testing. A steel with a thickness of 25mm is adopted for testing.

[0073] According to the present invention, a tensile test (test on the yield strength R.sub.el, the tensile strength R.sub.m, and the elongation percentage) adopts a zwick/roell Z330 tensile testing machine to carry out testing, and the testing standard adopts the national standard GB/T 228.1-2010, wherein tests on the yield strength R.sub.el, the tensile strength R.sub.m and the elongation percentage are respectively carried out according to standards defined by 3.10.1, 3.10.2 and 3.6.1 in this standard.

[0074] The impact toughness is tested by a Zwick/Roell PSW 750 impact testing machine, the testing standard adopts the national standard GB/T 229-2007, and the value of the impact toughness is obtained by testing the energy absorbed by the steel for the alloy structure in a charpy impact test.

[0075] A statistics and testing method of the number of the ZrC and ZrN particles, the number of the MgO and MgS particles, and the diameters of the grains of ZrC, ZrN, MgO and MgS particles is carried out by a scanning electron microscope (SEM) matched with an Oxford energy disperse spectroscopy oxford X-max 20, wherein a model of the scanning electron microscope is a Zeiss scanning electron microscope EVO 18, and a testing standard adopts the standard GB/T30834-2014.

[0076] Table 4 lists testing results of the embodiments and comparative examples.

TABLE-US-00004 TABLE 4 Yield Tensile Strength Strength Elongation Impact R.sub.el R.sub.m Percentage Toughness Number (MPa) (MPa) (%) (J) Embodiment 1 755 900 12 123 Embodiment 2 765 905 13 125 Embodiment 3 763 910 12 108 Embodiment 4 770 908 14 137 Embodiment 5 767 912 13 117 Embodiment 6 758 907 12 100 Comparative 735 885 10 78 example 1 Comparative 730 890 11 85 example 2 Comparative 732 893 10 73 example 3

[0077] It can be seen in combination with Table 2 and Table 4 that according to the steel for the alloy structure in the embodiments of the invention, the microstructure is ferrite+pearlite, the steel contains the grains of ZrC, ZrN, MgO and MgS particles, and these particles take effects of refining and stabilizing austenite crystal grains and are beneficial for improving the mechanical properties of the material, and thus, compared with the existing steel for the alloy structure in comparative examples 1-3 in the prior art, the steel for the alloy structure in the embodiments of the invention shows better mechanical properties, and for the steel for the alloy structure in the embodiments, the yield strength is 755 MPa or more, the tensile strength is 900 MPa or more, the elongation percentage is 12% or more, and the impact toughness is 100 J or more.

[0078] To sum up, according to the present invention, the steel for the alloy structure is designed by adding trace alloy elements; by adding the proper amount of Zr and Mg, controlling the low content of total oxygen, and utilizing the characteristics of the added trace alloy elements, the steel for the alloy structure is further strengthened and toughened, so that the steel for the alloy structure has high strength and low material cost.

[0079] In addition, by the manufacturing method provided by the present invention, the steel for the alloy structure, which is ultrahigh in mechanical property, good in impact toughness, and low in manufacturing cost, can be obtained.

[0080] It should be noted that the prior art part in the scope of protection of the present invention is not limited to the embodiments given out by the application documents, and all the prior art, without conflict with the solution of the present invention, including, but are not limited to, the prior patent literatures, the prior publications, the prior public use and the like, shall fall within the scope of the protection of the present invention.

[0081] In addition, the combination modes of all the technical characteristics in the invention are not limited to the combination modes recorded in claims of the invention or the combination modes recorded in the specific embodiments, and all the technical characteristics recorded in the invention can be freely combined or integrated in any mode, unless there are conflicts therebetween.

[0082] It also should be noted that the embodiments listed above are merely specific embodiments of the present invention. It is obvious that the present invention is not limited to the embodiments above, and similar changes or modifications made therewith could be directly obtained from the contents disclosed by the present invention or very easily thought of by those skilled in the art, and all shall fall within the scope of protection of the present invention.