Thick steel plate for high heat input welding and having great heat-affected area toughness and manufacturing method therefor

Abstract

A thick steel plate for high heat input welding and having great heat-affected area toughness and a manufacturing method therefor, comprising the steps of smelting, casting, rolling, and cooling. Chemical composition is properly controlled for the steel plate and satisfies 1Ti/N6 and Mg/Ti>0.017, where effective S content in steel=S1.3 Mg0.8 Ca0.34 REM0.35 Zr, and effective S content in steel: 0.0003-0.003%; finely dispersed inclusions may be formed in the steel plate, and the amount of composite inclusion MgO+Ti.sub.2O.sub.3+MnS in the steel plate is controlled at a proportion greater than or equal to 5%. The tensile strength of a base material so acquired is 510 MPa, insofar as welding input energy is 200-400 kJ/cm, the average Charpy impact work of the steel plate at 40 C. is 100 J or more, at the same time, the average Charpy aging impact work of the base material of thickness at 40 C. is 46 J or more.

Claims

1. A thick steel plate for high heat input welding and having great heat-affected area toughness, comprising a chemical composition in mass percentage: C: 0.05-0.09%, Si: 0.10-0.30%, Mn: 1.2-1.6%, P0.02%, S: 0.0015-0.007%, Ni: 0.2-0.4%, Ti: 0.005-0.03%, Mg: 0.005-0.004%, N: 0.001-0.006%, Al: 0.004-0.036%, Ca0.0032%, REM: 0.005%, Zr0.003%, Cr: 0.06-0.2%, and a balance of Fe and other inevitable impurities; wherein the chemical composition satisfies the following relationship:
1Ti/N6,Mg/Ti0.017; the effective S content in steel=S1.3Mg0.8Ca0.34REM0.35Zr; the effective S content in steel: 0.0003-0.003%; the amount of composite inclusion MgO+Ti.sub.2O.sub.3+MnS in the steel plate, calculated based on areal density, is at a proportion of 5%.

2. The thick steel plate for high heat input welding and having great heat-affected area toughness according to claim 1, wherein the thick steel plate further comprises element of Nb, and the amount of Nb is 0.03 wt % or less.

3. The thick steel plate for high heat input welding and having great heat-affected area toughness according to claim 1, wherein the tensile strength of the base material of the thick steel plate is 510 MPa, and when welding input energy is 200-400 kJ/cm, the average Charpy impact work of the welding heat-affected area of the steel plate at 40 C. is 100 J or more, and the average Charpy aging impact work of the base material of plate thickness at 40 C. is 46 J or more.

4. A method of manufacturing a thick steel plate for high heat input welding and having great heat-affected area toughness, wherein the method comprises the following steps: 1) smelting and casting comprising smelting, refining, continuous casting metal to obtain a slab for a steel plate having a chemical composition in weight percentage: C: 0.05-0.09%, Si: 0.10-0.30%, Mn: 1.2-1.6%, P0.02%, S: 0.0015-0.007%, Ni: 0.2-0.4%, Ti 0.005-0.03%, Mg: 0.0005-0.004%, N: 0.001-0.006%, Al: 0.004-0.036%, Ca0.0032%, REM0.005%, Zr0.003%, Cr: 0.06-0.2%, and a balance of Fe and other inevitable impurities; and, the chemical composition satisfying the following relationship:
1Ti/N6,Mg/Ti0.017; the effective S content in steel=S1.3Mg0.8Ca0.34REM0.35Zr; the effective S content in steel: 0.0003-0.003%; the amount of composite inclusion MgO+Ti.sub.2O.sub.3+MnS in the steel plate, calculated based on areal density, is controlled at a proportion 5%; 2) rolling comprising heating the slab to 1050-1250 C., wherein initial rolling temperature is higher than 930 C., cumulative reduction rate is greater than 30%, and wherein finish roiling temperature is less than 930 C., and cumulative reduction rate is greater than 30%; 3) cooling comprising cooling the surface temperature of the steel plate from 750 C. or more to 500 C. or less at a cooling rate of 2-20 C./s.

5. The method of manufacturing a thick steel plate for high heat input welding and having great heat-affected area toughness according to claim 4, wherein the thick steel plate further comprises element Nb, and the amount of Nb is 0.03 wt % or less.

6. The method of manufacturing a thick steel plate for high heat input welding and having great heat-affected area toughness according to claim 4, wherein the tensile strength of the base material of the steel plate is 510 MPa, the average Charpy impact work of the welding heat-affected area of the steel plate at 40 C. is 100 J or more under the condition that welding input energy is 200-400 kJ/cm, and the average Charpy aging impact work of the base material of plate thickness at 40 C. is 46 J or more.

7. The thick steel plate for high heat input welding and having great heat-affected area toughness according to claim 2, wherein the tensile strength of the base material of the thick steel plate is 510 MPa, and when welding input energy is 200-400 kJ/cm, the average Charpy impact work of the welding heat-affected area of the steel plate at 40 C. is 100 J or more, and the average Charpy aging impact work of the base material of plate thickness at 40 C. is 46 J or more.

8. The method of manufacturing a thick steel plate for high heat input welding and having great heat-affected area toughness according to claim 5, wherein the tensile strength of the base material of the steel plate is 510 MPa, the average Charpy impact work of the welding heat-affected area of the steel plate at 40 C. is 100 J or more under the condition that welding input energy is 200-400 kl/cm, and the average Charpy aging impact work of the base material of plate thickness at 40 C. is 46 J or more.

Description

DETAILED DESCRIPTION

(1) Hereinafter the technical solution of the present invention will be further explained with reference to examples.

(2) Table 1 shows the chemical composition, Ti/N ratio, Mg/Ti ratio and the effective S content of Examples and Comparative Examples of the present invention. Table 2 shows the mechanical properties of base material, inclusion properties, and impact toughness of welding heat-affected area of Examples and Comparative Examples of the present invention.

(3) In the present invention, in order to ensure the suitable strength and toughness of base material, the slab is obtained through smelting, refining and continuous casting, and then the slab is heated to 1050 C. to 1250 C., the initial rolling temperature is 1000 to 1150 C., the cumulative reduction rate is 50%; and the finishing temperature is 700 to 850 C., the cumulative reduction rate is 53% to 67%%; after the finish rolling, the surface temperature of the steel plate is cooled from 750 C. or more to 500 C. or less at a cooling rate of 4-8 C./s.

(4) Aging impact test specimens are taken from the base material of plate thickness, then Charpy impact tests of three samples are performed at 5% strain and 40 C., The data of aging impact test sample is the average value of the three measurement results.

(5) Electro-pneumatic vertical welding is used to perform one pass welding for steel plates having different thickness at 200 to 400 kJ/cm of welding input energy. Impact specimens are taken from the fusion line of plate thickness, and then are introduced into a V-notch for impact toughness testing. Charpy impact tests of three samples are performed at 40 C. The data of the impact toughness of the welding heat-affected area is the average value of three measurement results.

(6) It can be seen from Tables 1 and 2 that, in the Examples, the composition is controlled according to the chemical composition range determined by the present invention, and satisfies 1Ti/N6 and Mg/Ti0.017. Furthermore, the effective S content in steel is controlled to be 0.0003-0.003%; and the amount of composite inclusion MgO+Ti.sub.2O.sub.3+MnS in the steel plate at a proportion is controlled to be 5%.

(7) In Comparative Examples 12, the Mg contents in the steel both are less than 0.0005%, and both don't meet the requirements of Mg/Ti0.017 and effective S content in the steel of 0.0003 to 0.003%. At the same time, the proportion of composite inclusion MgO+Ti.sub.2O.sub.3+MnS in the steel plate of Comparative Example 2 does not meet the requirement of 5% or more. In addition, in Comparative Example 1, the Ti/N ratio does not satisfy the requirements of the present invention.

(8) Table 2 shows the tensile properties, impact toughness, aging impact performance of the base material and impact toughness of the welding heat-affected area in the examples and comparative examples. Yield strength, tensile strength, and section shrinkage of the base material are the average value of two test data. Aging impact and Charpy impact work of welding heat-affected area at 40 C. of the base material are the average value of three test data.

(9) From the data in the table, it can be seen that there is no obvious difference between the tensile and impact properties of the base material of the Examples and the Comparative Examples, which both can satisfy the requirement that the manufactured steel plate has a thickness of 50-70 mm and a tensile strength of base material 510 MPa. Charpy impact work of the welding heat-affected area at 40 C. is tested under the conditions of a welding input energy of 200 to 400 kJ/cm. And the values of Examples 1 to 6 are 130, 160, 230, 180, 182 and 105 (J), respectively, which all are greater than 100 J. The values of Comparative Examples 1 and 2 are 22, 17 (J). The impact toughness of the welding heat-affected area of Examples is greatly improved and can satisfy requirements of the high heat input welding of 200 to 400 kJ/cm. In addition, in all Examples, the average Charpy aging impact work of the base material of plate thickness at 40 C. is 46 J or more. Since the effective S content of Comparative Example 1 exceeds the upper limit of 0.003%, the aging impact performance of the plate thickness is significantly reduced.

(10) The present application adopts appropriate ingredient design. By controlling appropriately Ti/N ratio and Mg/Ti ratio in steel, the effective S content in steel, and the amount at a proportion of composite inclusion MgO+Ti.sub.2O.sub.3+MnS in the steel plate, during the solidification and phase chase, the growth of intracrystalline acicular ferrite on the surface of these inclusions is promoted, or the growth of Austenite grains during high heat input welding is suppressed, and the high heat input welding performance of the thick steel plate is improved. The thickness of the steel plate produced in present invention is 50-70 mm, the tensile strength of a base material is 510 MPa, the high heat input welding performance of the welding heat-affected area is .sub.vE.sub.40100 J under the condition that welding input energy is 200-400 kJ/cm, and at the same time, the average Charpy aging impact work of the base material of plate thickness at 40 C. is 46 J or more. The present invention can be used in the manufacturing process of thick steel plates for ships, buildings and marine structures and so on to improve the high heal input welding performance of thick steel plates.

(11) TABLE-US-00001 TABLE 1 Unit: mass No. C Si Mn P S Al Ti Mg Ca REM Zr N Example 1 0.089 0.30 1.20 0.008 0.0033 0.004 0.0066 0.0015 0.005 0 0 0.0011 Example 2 0.050 0.22 1.55 0.010 0.0062 0.050 0.0051 0.0040 0 0 0 0.0025 Example 3 0.071 0.28 1.32 0.007 0.0051 0.007 0.0130 0.0020 0 0.005 0 0.0046 Example 4 0.007 0.21 1.39 0.017 0.0070 0.016 0.0110 0.0005 0.0032 0 0.0022 0.0028 Example 5 0.078 0.15 1.48 0.013 0.0015 0.030 0.0300 0.0005 0.0003 0 0 0.0052 Example 6 0.075 0.10 1.31 0.019 0.0059 0.018 0.0065 0.0018 0 0 0.003 0.006 Comparative 0.077 0.21 1.36 0.008 0.0060 0.028 0.017 0.0002 0.002 0 0 0.002 Example 1 Comparative 0.064 0.19 1.48 0.007 0.0010 0.035 0.010 0 0.0015 0.005 0.002 0.0048 Example 2 Effective No. Ni Nb Cr Ti/N Mg/Ti S Content Example 1 0.32 0.010 0.20 6.00 0.227 0.009 Example 2 0.39 0.015 0.17 2.04 0.784 0.0010 Example 3 0.20 0.030 0.006 2.83 0.154 0.0008 Example 4 0.25 0.018 0.09 3.95 0.045 0.0030 Example 5 0.3 0.004 0.18 2.77 0.017 0.0003 Example 6 0.28 0.006 0 1.08 0.277 0.0025 Comparative 0.31 0.019 0.06 8.50 0.012 0.0041 Example 1 Comparative 0.37 0.022 0.13 2.08 0.000 0.0026 Example 2

(12) TABLE-US-00002 TABLE 2 The mechanical properties of the base material, inclusion properties, and impact toughness of the welding heat-affected area of Examples and Comparative Examples The mechanical properties of the base material Inclusion thick- the average the amount at a HAZ ness Charpy aging proportion (%) toughness of impact work of composite welding the hot (J) of inclusion input steel rolling plate thickness MgO + energy plate and Rp0.2 Rm A .sub.vE.sub.40 at 40 C., Ti.sub.2O.sub.3 + (KJ/ .sub.vE.sub.40 No. (mm) cooling (Mpa) (Mpa) (%) (J) 5% strain MnS cm) (J) Example 1 60 TMCP 442 565 27 293 220 10 355 130 Example 2 70 TMCP 472 590 25 342 215 30 390 160 Example 3 68 TMCP 422 525 27 330 190 18 396 230 Example 4 50 TMCP 433 560 28 315 245 5 205 130 Example 5 70 TMCP 426 530 25 263 220 6 406 182 Example 6 68 TMCP 434 547 24 276 210 13 408 105 Comparative 68 TMCP 440 560 26 286 15 36 386 22 Example 1 Comparative 50 TMCP 430 550 25 310 220 0 230 17 Example 2