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. Also, the chemical composition of the steel plate satisfies 1Ti/N6 and (Ca+REM+Zr)/Al0.11, where the effective S content in steel=S-0.8Ca-0.34REM-0.35Zr. and the effective S content in steel: 0.0006-0.005%; finely dispersed inclusions may be formed, and the amount of composite inclusion CaO+Al.sub.2O.sub.3+MnS+TiN in the steel plate is at a proportion of 12%. With respect to welding in which the thickness of the steel plate is 50-70 mm, the tensile strength of a base material is 510 MPa. and welding input energy is 200-400 kJ/cm, the average Charpy impact work of a welding heat-affected area of the steel plate at 40 C. is 100 J or more, and 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, wherein the thickness of the steel plate is 50-70 mm, the tensile strength of a 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 a 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, and wherein the steel plate consists essentially of a chemical composition in mass percentage: C: 0.05-0.08%, Si: 0.10-0.30%, Mn: 1.2-1.6%, P0.02%, S: 0.002-0.008%, B: 0.0005-0.005%, Ni: 0.20-0.40%, Cu: 0.15%-0.3%, Ti: 0.005-0.03%, Al: 0.003-0.03%, Ca: 0.001-0.005%, REM0.01%, Zr0.01%, N: 0.001-0.006%, and the balance of Fe and other inevitable impurities; wherein the chemical composition satisfies the following relationship:
1Ti/N6 and (Ca+REM+Zr)/Al0.11; an effective S content in steel=S-0.8Ca-0.34REM-0.35Zr which is in a range of 0.0006-0.005%; and the proportion of composite inclusion CaO+Al.sub.2O.sub.3+MnS+TiN in the steel plate is 12% or more.

2. A thick steel plate for high heat input welding and having great heat-affected area toughness, wherein the thickness of the steel plate is 50-70 mm, the tensile strength of a 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 a 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, and wherein the steel plate consists essentially of a chemical composition in mass percentage: C: 0.05-0.08%, Si: 0.10-0.30%, Mn: 1.2-1.6%, P0.02%, S: 0.002-0.008%, B: 0.0005-0.005%, Ni: 0.20-0.40%, Cu: 0.15%-0.3%, Ti: 0.005-0.03%, Al: 0.003-0.03%, Ca: 0.001-0.005%, REM0.01%, Zr 0.01%, N: 0.001-0.006%, Nb: 0.03% or Cr0.2%, and the balance of Fe and other inevitable impurities; wherein the chemical composition satisfies the following relationship: 1Ti/N6 and (Ca+REM+Zr)/Al0.11; an effective S content in steel=S-0.8Ca-0.34REM-0.35Zr which is in a range of 0.0006-0.005%; and the proportion of composite inclusion CaO+Al.sub.2O.sub.3+MnS+TiN in the steel plate is 12% or more.

3. 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, refining and continuous casting comprising smelting, refining, continuous casting metal to obtain a slab for the thick steel plate having a chemical composition in mass percentage: C: 0.05-0.08%, Si: 0.10-0.30%, Mn: 1.2-1.6%, P: 0.02%, S: 0.002-0.008%, B. 0.0005-0.005%, Ni: 0.20-0.40-6, Cu: 0.15-0.3%, Ti: 0.005-0.03%, Al: 0.003-0.03%, Ca: 0.001-0.005%, REM 0.01%, Zr0.01%, N: 0.001-0.006%, and the balance of Fe and other inevitable impurities; wherein the chemical composition satisfies the following relationship: 1Ti/N6, (Ca+REM+Zr)/Al0.11; an effective S content in steel=S-0.8Ca-0.34REM-0.35Zr, which is in a range of 0.0006-0.005%; and the amount of composite inclusion CaO+Al.sub.2O.sub.3+MnS+TiN in the steel plate is controlled at a proportion of 12% of total inclusions; 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 rolling temperature is less than 930 C., and cumulative reduction rate is greater than 30%; and 3) cooling comprising performing water cooling at a cooling rate of 2 to 30 C./s to a final cooling temperature of 300 to 550 C.; and wherein the thickness of the steel plate is 50-70 mm, the tensile strength of a 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 a 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.

4. The method of manufacturing a thick steel plate for high heat input welding and having great heat-affected area toughness according to claim 3, wherein the thick steel plate further comprises at least one element of Nb or Cr, the amount of Nb is 0.03 mass % or less, and the amount of Cr is 0.2 mass % or less.

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 and (Ca+REM+Zr)/Al ratio 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) 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, water cooling is performed at a cooling rate of 3 to 10 C./s to a final cooling temperature of 300 to 550 C.

(4) 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.

(5) Aging impact test specimens are taken from the 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 of the 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 (Ca+REM+Zr)/Al0.11, and the effective S content in steel: 0.0006-0.005%; and the amount of composite inclusion CaO+Al.sub.2O.sub.3+MnS+TiN in the steel plate is at a proportion of 12%.

(7) In Comparative Examples 1 and 2, the Al content is greater than 0.03%, the (Ca+REM+Zr)/Al ratio is less than 0.11, the effective S content of Comparative Example 1 is less than 0.0006%, and the effective S content of Comparative Example 2 is greater than 0.005%. In addition, the amount of composite inclusion CaO+Al.sub.2O.sub.3+MnS+TiN of Comparative Example 1 is at a proportion of less than 12%.

(8) Table 2 shows the tensile properties, impact toughness, aging impact 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 in the mechanical properties of the base material between 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 material510 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. The values of Examples 1 to 5 are 108, 125, 115, 120, and 170 (J), respectively, and the values of Comparative Examples 1 and 2 are 11, 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.

(10) 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 2 is too high, the aging impact performance of the plate thickness is significantly reduced.

(11) The present application adopts appropriate ingredient design. By controlling appropriately Ti/N ratio and (Ca+REM+Zr)/Al ratio in steel, the effective S content in steel, and the amount at a proportion of composite inclusion CaO+Al.sub.2O.sub.3+MnS+TiN in the steel plate, during solidification and phase change, 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 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 shipbuilding, construction, offshore platforms, bridges, pressure vessels and petroleum, natural gas pipelines and so on to improve the high heat input welding performance of thick steel plates.

(12) TABLE-US-00001 TABLE 1 No. C Si Mn P S Al Ti Ca REM Zr N Example 1 0.079 0.14 1.21 0.019 0.0020 0.017 0.0300 0.0018 0 0 0.0060 Example 2 0.075 0.11 1.55 0.006 0.0051 0.030 0.0050 0.0010 0 0.01 0.0049 Example 3 0.070 0.30 1.54 0.012 0.0072 0.022 0.0150 0.0050 0.005 0 0.0044 Example 4 0.066 0.20 1.59 0.007 0.0080 0.003 0.0098 0.0020 0.010 0 0.0028 Example 5 0.051 0.22 1.52 0.017 0.0070 0.015 0.0065 0.0025 0 0 0.0011 Comparative 0.074 0.19 1.47 0.009 0.0011 0.035 0.0130 0.0030 0 0 0.0023 Example 1 Comparative 0.061 0.26 1.55 0.008 0.0098 0.045 0.0120 0.0020 0.005 0.002 0.0046 Example 2 (Ca + REM + Effective No. B Ni Cu Nb Cr Ti/N Zr)/Al S content Example 1 0.0036 0.34 0.18 0.016 0.14 3.00 0.11 0.0006 Example 2 0.0022 0.21 0.23 0.006 0.19 1.02 0.31 0.0008 Example 3 0.0042 0.39 0.15 0 0 3.41 0.27 0.0015 Example 4 0.0005 0.27 0.29 0.015 0 3.50 0.94 0.0030 Example 5 0.0050 0.33 0.26 0.030 0.13 5.91 0.12 0.0050 Comparative 0.0025 0.36 0.17 0.016 0.14 5.65 0.06 0.0013 Example 1 Comparative 0.0015 0.27 0.20 0.014 0.10 2.61 0.07 0.0075 Example 2

(13) 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 the average the amount at aging impact a proportion work (J) of (%) of HAZ toughness hot 1/2 plate composite welding thickness rolling thickness at inclusion CaO + input of the steel and Rp0.2 Rm A .sub.vE.sub.40 40 C., 5% Al.sub.2O.sub.3 + MnS + energy .sub.vE.sub.40 No. plate (mm) cooling (Mpa) (Mpa) (%) (J) strain TiN (KJ/cm) (J) Example 1 68 TMCP 433 548 26 270 180 12.0 406 108 Example 2 60 TMCP 442 565 27 293 175 17.2 430 125 Example 3 50 TMCP 436 560 26 280 217 22.5 245 115 Example 4 70 TMCP 432 550 25 320 235 35.7 450 120 Example 5 68 TMCP 410 525 27 310 212 41.3 405 170 Comparative 70 TMCP 430 550 25 305 202 5.1 410 11 Example 1 Comparafive 68 TMCP 442 558 27 285 12 48.2 385 17 Example 2