STEEL AND PROCESS FOR PRODUCTION, AND A METHOD OF PROCESSING THE STEEL

Abstract

A steel, particularly as steel sheet, having the following composition: 0.02-0.1% by weight of carbon; 0.01-0.1% by weight of silicon; 0.60-2.00% by weight of manganese; >0 and 0.01% by weight of aluminum; 0.01-0.30% by weight of copper; 0.01-0.60% by weight of nickel; 0.01-0.30% by weight of chromium; 0.005-0.050% by weight of niobium; 0.005-0.050% by weight of titanium; 0.0005-0.0050% by weight of sulfur; 0.001-0.005% by weight of calcium; 0.0050% by weight of oxygen; 0.010% by weight of nitrogen; 0.02% by weight of phosphorus; 0-0.0050% by weight of magnesium; 0-0.0060% by weight of Vanadium; 0-0.15% by weight of molybdenum; and balance: iron and production-related impurities, and a process for production and a method of processing the steel.

Claims

1. A steel, comprising: 0.02-0.1% by weight of carbon; 0.01-0.1% by weight of silicon; 0.60-2.00% by weight of manganese; >0 and 0.01% by weight of aluminum; 0.01-0.30% by weight of copper; 0.01-0.60% by weight of nickel; 0.01-0.30% by weight of chromium; 0.005-0.050% by weight of niobium; 0.005-0.050% by weight of titanium; 0.0005-0.0050% by weight of sulfur; 0.0010-0.0050% by weight of calcium; 0.0050% by weight of oxygen; 0.010% by weight of nitrogen; 0.02% by weight of phosphorus; 0-0.0050% by weight of magnesium; 0-0.0060% by weight of vanadium; 0-0.15% by weight of molybdenum; and balance: iron and production-related impurities.

2. The steel according to claim 1, comprising at least one of the following: <0.05% by weight of carbon; 1.00-1.70% by weight of manganese; 0.1% by weight of copper; 0.4% by weight of nickel; 0.10% by weight of chromium; >0.001% by weight of oxygen; 0.001-0.0040% by weight of sulfur.

3. The steel according to claim 2, comprising 0.2% by weight of nickel.

4. The steel according to claim 1, comprising a bainitic microstructure.

5. The steel according to claim 4, comprising a fine-grain bainitic microstructure.

6. The steel according to claim 1, comprising an average grain size of <15 m.

7. The steel according to claim 6, comprising an average grain size of <14 m.

8. The steel according to claim 1, comprising a proportion of high-angle grain boundaries of >50%.

9. The steel according to claim 8, comprising a proportion of high-angle grain boundaries of >60%.

10. The steel according to claim 1, comprising nonmetallic inclusions.

11. The steel according to claim 10, comprising complex agglomerates that have a matrix of a CaTiOs compound, and Al.sub.2O.sub.3, MgO and MnS constituents intercalated therein.

12. The steel according to claim 10, wherein a ratio of density of particles of nonmetallic inclusions in a size range from 0.5 to 2 m to a density of particles of nonmetallic inclusions in a size range from 2 to 5 m is less than 5.

13. The steel according to claim 12, wherein the density ratio is less than 3.

14. The steel according to claim 1, wherein the steel is a cast steel.

15. The steel according to claim 14, wherein the steel is a cast and rolled semifinished product.

16. The steel according to claim 15, wherein the steel is a slab or a sheet.

17. The steel according to claim 1, wherein the steel, after treatment by physical welding simulation of a coarse grain zone with an energy input of 3.5 kJ/mm to 30 KJ/mm, has a notch impact energy of at least 75 J, where the notch impact energy is ascertained by a Charpy notch impact bending test at 40 C. or at 20 C. according to standard DIN EN ISO 148-1:2017.

18. The steel according to claim 17, wherein the treatment by physical welding simulation of the coarse grain zone is with an energy input of >7 KJ/mm.

19. The steel according to claim 18, wherein the treatment by physical welding simulation of the coarse grain zone is with an energy input of >15 KJ/mm.

20. The steel according to claim 18, wherein the steel has a notch impact energy of at least 100 J.

21. The steel according to claim 20, wherein the steel has a notch impact energy of at least 130 J.

22. The steel according to claim 17, wherein the notch impact energy is ascertained by the Charpy notch impact bending test at 40 C. for a welding simulation with just a single cycle and at 20 C. for a welding simulation with two cycles.

23. The steel according to claim 1, wherein the steel, after processing by welding in a region affected by heat of welding or with an energy input of 3.5 KJ/mm to 30 KJ/mm has a notch impact energy of at least 75 J, where the notch impact energy is ascertained at a fusion line of a weld seam formed by the welding by the Charpy notch impact bending test at 40 C., according to standard DIN EN ISO 148-1:2017.

24. The steel according to claim 23, wherein the steel is processed with an energy input of >7 KJ/mm.

25. The steel according to claim 24, wherein the steel is processed with an energy input of >15 KJ/mm.

26. The steel according to claim 25, wherein the steel has a notch impact energy of at least 100 J.

27. The steel according to claim 26, wherein the steel has a notch impact energy of at least 130 J.

28. A process for producing steel, comprising the step of forming the steel with the following composition: 0.02-0.1% by weight of carbon; 0.01-0.1% by weight of silicon; 0.60-2.00% by weight of manganese; >0 and 0.01% by weight of aluminum; 0.01-0.30% by weight of copper; 0.01-0.60% by weight of nickel; 0.01-0.30% by weight of chromium; 0.005-0.050% by weight of niobium; 0.005-0.050% by weight of titanium; 0.0005-0.0050% by weight of sulfur; 0.0010-0.0050% by weight of calcium; 0.0005-0.0050% by weight of oxygen; 0.010% by weight of nitrogen; 0.02% by weight of phosphorus; 0-0.0050% by weight of magnesium; 0-0.0060% by weight of vanadium; 0-0.15% by weight of molybdenum; and balance: iron and production-related impurities.

29. The process according to claim 28, including casting the steel by continuous casting to form a semifinished product.

30. The process according to claim 29, including casting the steel by continuous casting to form a slab.

31. The process according to claim 29, including heating the semifinished product to a temperature between 110 and 1250 C.

32. The process according to claim 31, including heating the semifinished product to a temperature between 1150 and 1200 C.

33. The process according to claim 29, including thermomechanically rolling the semifinished product in at least two rolling phases, where a degree of forming after a first phase is >0.20.

34. The process according to claim 29, including welding the semifinished product with an energy input of 3.5 KJ/mm to 30 KJ/mm.

35. The process according to claim 34, including welding the semifinished product with an energy input of >7 KJ/mm.

36. The process according to claim 35, including welding the semifinished product with an energy input of >15 KJ/mm.

Description

EXAMPLES

[0094] The invention is elucidated in detail hereinafter by working examples and the appended tables.

[0095] Table 1 shows the composition of inventive steels A, B, C and D. Steels E, F and G have a conventional composition and serve as reference. The compositions are reported in % by weight.

[0096] Table 2 gives the rolling parameters with which the steels have been produced.

[0097] Mechanical properties of the sheets produced, namely results from tensile tests, hardness measurements, notch impact bending tests and for fracture mechanics (Crack Tip Opening Displacement, CTOD) are shown in table 3.

[0098] In order to test the steels, deposit welts have been conducted on steel sheets having a thickness of 80 mm. A submerged arc welding machine with which the real welds (deposit welts and multipass welds) have been conducted is composed of several components: a UniWeld welding unit with Subarc-5 controller as submerged-arc twin-head welding system with the power sources 1 OERLIKON TRE1004 AC and 1 SAF Starmatic 1000DC. The welds were performed with the OE SD3 electrode and the OP 121TT powder (both from LincolnElectric).

[0099] Table 4 shows results from a Charpy notch impact test according to DIN EN ISO 148-1, done as a standard test by pendulum impact instrument for determination of notch impact energy.

[0100] The notch impact test was conducted on a sheet metal surface at a fusion line of a weld seam of a deposit weld, in each case at 40 C. at different energy inputs that are stated in kJ/mm.

[0101] The energy input has been determined by means of the above formula 1. In the case of submerged arc welding, for example, the thermal efficiency is k=1.

[0102] For the sheets made from melt A, produced according to rolled plate 2, and for those made from melt E, produced according to rolled plate 9, several single-pass deposit welds have been undertaken with the different energy inputs given in table 4. Three measurements have been undertaken, the respective individual values from which are reported, and the average of the respective individual values is given.

[0103] The results show that the notch impact energies of the welded sheet that has been formed from the inventive melt A are much higher than those for the sheet made from reference melt E. The differences in the notch impact energies between the sheet made from the inventive steel compared to those made from the reference steel increase with rising energy input in the welding operation.

[0104] Table 5 shows results from notch impact bending tests on sheets with real multipass welds having an energy input of 5 kJ/mm along a weld seam formed in the multipass welding operations in the middle of the sheet at 80 C. Notch impact bending tests have been conducted on a sheet that has been produced from inventive melt A according to the rolled plate 2 and on a sheet of reference melt G that has been produced according to the rolled plate 10. The notch impact energies which for the sheet that has been produced from the inventive steel are much higher than those for the sheet made from the reference steel.

[0105] Table 5 also shows results of notch impact bending tests on sheets with real multipass welds having an energy input of 7 kJ/mm along a weld seam formed in the multipass welding operations in the middle of the sheet at 80 C. Notch impact bending tests have been conducted on a sheet that has been produced from inventive melt B according to the rolled plate 5 and on a sheet of reference melt F that has been produced according to the rolled plate 10. In the case of an energy input of 7 kJ/mm too, it is found that the notch impact energies which for the sheet that has been produced from the inventive steel are much higher than those for the sheet made from the reference steel.

[0106] Further notch impact energies were determined by a physical welding simulation of the coarse grain zone elucidated hereinafter.

[0107] In order to perform the Charpy notch impact test according to standard DIN EN ISO 148-1 on a material treated by a physical welding simulation, first of all, a sample blank having a length of at least 55 mm in the transverse direction of the sheet and a cross-sectional area of 10 mm10 mm (rolling directionnormal direction) was taken from the layer of 1/4 sheet thickness of the material under examination. The welding simulations were effected with a Gleeble 3800 hot forming simulator and the QuickSim 2 software (version 2.5.8011.33152). For preparation, in the case of these notch impact blanks (normal sample without notch), a thermocouple pair was mounted by point welding methods on a lateral face at a distance of 27.5 mm from the end face. The samples thus prepared were inserted into the hot forming simulator and clamped with minimal stress between the copper dies provided for the purpose, and centered at the position of the thermocouple. During the experiment, the flow of current necessary for resistance heating was provided through these dies, and closed-loop control was exerted via the welded-on thermocouples.

[0108] The temperature regime corresponding to the respective welding process was determined by the abovementioned integrated calculation method according to Hannerz (formula 4).

[0109] The input parameters chosen for T.sub.max=1350 C. (second cycle 775 C. or 750 C.) were T.sub.0=100 C. and ta/s=40 s, 60 s, 200 s, 300 s or 500 s (then correspondingly proportionally if the second cycle is at T.sub.max <800 C.). Closed-loop control upon cooling was effected at least down to a temperature of 350 C. After the welding simulation, the thermocouples were removed, a 2 mm-deep V-shaped notch was introduced at that point, and the length of the samples was shortened if necessary to 55 mm.

[0110] Finally, the weld-simulated samples were tested as standard by means of the pendulum tester to ascertain the notch impact energy.

[0111] The values given below for the energy inputs are based on a treatment by physical welding simulation of the coarse grain zone by conversion of the desired energy input to a 18/5 time using the formulae 2 and 3 shown above.

[0112] The preheating temperature T.sub.V is appropriately assumed to be 200 C., and a welding factor of 0.9 (F.sub.1 and F.sub.2) for the simulation of a multipass weld. The sheet thickness d envisaged was 80 mm.

[0113] Tables 6 and 7 give results of notch impact bending tests on various sheets that have been produced from melts A to G and according to various ones of the rolled plates 1 to 11 and have been treated as elucidated above for welding simulation.

[0114] Table 6 shows the notch impact bending test results [0115] with a 18/5 time of 500 s, corresponding to an energy input of 35 kJ/mm, for a cycle at 1350 C., [0116] with a 18/5 time of 300 s, corresponding to an energy input of 27 KJ/mm, for a cycle at 1350 C., [0117] with a 18/5 time of 200 s, corresponding to an energy input of 22 KJ/mm, both for one cycle at 1350 C. and for two cycles, with the first cycle conducted at 1350 C. and the second cycle at 775 C.

[0118] Table 7 shows the notch impact bending test results [0119] with a 18/5 time of 60 s, corresponding to an energy input of 7 KJ/mm, both for one cycle at 1350 C. and for two cycles, with the first cycle conducted at 1350 C. and the second cycle at 750 C., and [0120] with a 18/5 time of 40 s, corresponding to an energy input of 5 KJ/mm, both for one cycle at 1350 C. and for two cycles, with the first cycle conducted at 1350 C. and the second cycle at 775 C.

[0121] For the sheets that have been produced from the inventive steels, considerably greater notch impact energies are found for all energy inputs, both for one and for two cycles and for the averages from the tests.

[0122] Results of microstructure analyses are shown in table 8. The proportion of large-angle grain boundaries of the sheets made from the inventive steels, apart from the sheet made from melt C according to rolled plate 6, is lower than in the case of the sheets made from the reference steels, but >50% for all sheets. Moreover, the particle density of particles having a diameter of 0.5 m-2 m for the sheets made from the inventive steels is smaller than in the case of those made from the reference steels, and the particle density of particles having a diameter of 2 m-5 m in the case of the sheets made from the inventive steels is greater than in the case of those made from the reference steels. Accordingly, the ratio of the particle densities of particles having a diameter of 0.5 m-2.0 m to those having a diameter of 2 m-5 m for the sheets made from the inventive steels is smaller than for those made from the reference steels. These results show that, in the case of the sheets made from the inventive steel, because of the agglomerates, the number of nonmetallic inclusions in the size range of 0.5 to 2 m that are formed from the Al.sub.2O.sub.3, MgO and MnS constituents and not incorporated into the agglomerates formed from the CaTiO.sub.3 compound is reduced.

TABLE-US-00001 TABLE 1 C Si Mn P S N Al Cu Mo Ni Cr V Nb Ti Ca O Mg A 0.046 0.056 1.46 0.009 0.0015 0.0020 0.002 0.03 0.01 0.07 0.04 0.001 0.018 0.008 0.0021 0.0017 B 0.050 0.034 1.48 0.010 0.0017 0.0024 0.001 0.03 0.01 0.05 0.03 0.002 0.017 0.009 0.0020 0.0024 0.0002 C 0.053 0.029 1.46 0.011 0.0019 0.0032 0.001 0.02 0.04 0.03 0.001 0.015 0.006 0.0014 0.0012 D 0.047 0.068 1.46 0.010 0.0008 0.0022 0.002 0.03 0.01 0.05 0.03 0.019 0.010 0.0020 0.0018 E 0.059 0.356 1.45 0.012 0.0006 0.0036 0.032 0.03 0.01 0.04 0.03 0.001 0.016 0.002 0.0017 0.0002 F 0.063 0.354 1.34 0.012 0.0012 0.0053 0.034 0.02 0.01 0.02 0.03 0.001 0.014 0.003 0.0020 0.0004 0.0011 G 0.056 0.414 1.59 0.013 0.0010 0.0044 0.033 0.27 0.02 0.52 0.23 0.001 0.001 0.008 0.0028 0.0004

TABLE-US-00002 TABLE 2 Dimensions in mm Temperatures in C. Number of Finish Slab Interphase Rolling Cooling Rolled rolling Exit Interphase phase End temper- start end temper- Cooling speed in Melt plate phases thickness thickness thickness thickness Length Width ature ature end C./s A 1 3 490 215 145 80 13994 2199 1161 876 786 RT A 2 3 490 215 145 80 13898 2199 1166 853 794 418 3.55 B 3 3 490 215 145 80 16612 2199 1180 871 788 453 3.36 B 4 3 490 215 145 80 16587 2199 1191 873 787 441 3.44 B 5 2 490 145 80 16625 2199 1203 791 423 3.38 B 6 2 490 145 80 16312 2199 1177 788 419 3.43 C 7 2 490 145 80 14216 2199 1219 786 430 3.52 D 8 2 490 145 80 14130 2199 1192 767 409 3.45 E 9 3 340 193 136 90 11187 3092 1146 866 797 506 3.07 F 10 2 390 157 80 24514 2205 1126 775 496 2.66 G 11 3 290 175 122 65 12055 2215 1083 804 769 463 6.73 indicates data missing or illegible when filed

TABLE-US-00003 TABLE 3 Notch impact bending test Quarter of sheet CTOD Indiv. Indiv. Indiv. Indiv. Indiv. Indiv. Hardness value 1 value 2 value 3 value 1 value 2 value 3 Rolled Transverse tensile test HV10 50 C. 50 C. 50 C. 60 C. 60 C. 60 C. Melt plate Rp0.2 Rm A5 Averages long. long. long. transv. transv. transv. A 1 390 484 29.2 156.7 348 349 350 2.98 2.92 A 2 385 471 31.0 150.8 366 367 369 2.88 2.64 B 3 384 471 30.8 163.8 309 327 329 0.77 0.57 0.85 B 4 388 472 28.6 168.3 356 362 364 0.90 0.91 1.06 B 5 392 476 28.3 160.0 308 323 325 0.90 0.42 0.91 B 6 391 475 28.8 165.5 356 360 375 0.97 1.02 0.99 C 7 394 468 33.8 149.3 309 321 323 0.71 0.71 0.71 D 8 393 476 32.9 148.3 347 353 353 1.06 0.58 0.47 E 9 408 499 27.1 308 324 324 F 10 383 490 32.9 168.3 293 295 306 1.08 2.07 1.62 G 11 428 524 31.3

TABLE-US-00004 TABLE 4 1-pass deposit weld 1-pass deposit weld 16 kJ/mm 12 kJ/mm Notch impact bending test Notch impact bending test Sheet surface - Melt line Sheet surface - Melt line Indiv. value 1 Indiv. value 2 Indiv. value 3 Average Indiv. value 1 Indiv. value 2 Indiv. value 3 Average Rolled 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. plate transv. transv. transv. transv. transv. transv. transv. transv. A 2 203 132 179 171.3 174 161 181 172.0 E 9 50 51 53 51.3 58 51 169 92.7 1-pass deposit weld 1-pass deposit weld 8 kJ/mm 4 kJ/mm Notch impact bending test Notch impact bending test Sheet surface - Melt line Sheet surface - Melt line Indiv. value 1 Indiv. value 2 Indiv. value 3 Average Indiv. value 1 Indiv. value 2 Indiv. value 3 Average 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. transv. transv. transv. transv. transv. transv. transv. transv. A 172 204 69 148.3 218 44 158 140.0 E 78 69 76 74.3 80 52 116 82.7 indicates data missing or illegible when filed

TABLE-US-00005 TABLE 5 Real multipass weld Real multipass weld 7 kJ/mm 5 kJ/mm Notch impact bending test Notch impact bending test Middle of sheet - Melt line Middle of sheet - Melt line Indiv. Indiv. Indiv. Indiv. Indiv. Indiv. value 1 value 2 value 3 Average value 1 value 2 value 3 Average Rolled 80 C. 80 C. 80 C. 80 C. 80 C. 80 C. 80 C. 80 C. Melt plate transv transv. transv. transv. transv transv. transv. transv. A 2 135 197 178 170.0 B 5 188 214 191 197.7 F 10 16 17 8 13.7 G 11 132 16 70 72.7

TABLE-US-00006 TABLE 6 Gleeble: 1 cycle (1350 C.) Gleeble: 1 cycle (1350 C.) t8/5 = 500 s --> 35 kJ/mm t8/5 = 300 s --> 27 kJ/mm Notch impact bending test Notch impact bending test Quarter of sheet - CG-HAZ simulation Quarter of sheet - CG-HAZ simulation Indiv. value 1 Indiv. value 2 Indiv. value 3 Average Indiv. value 1 Indiv. value 2 Indiv. value 3 Average Rolled 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. 40 C. Melt plate transv. transv. transv. transv. transv. transv. transv. transv. A 1 A 2 B 3 B 4 B 5 22 23 16 20.3 12 266 23 100.3 B 6 C 7 9 17 9 11.7 D 8 10 19 14 14.3 8 182 245 145.0 E 9 F 10 G 11 Gleeble: 1 cycle (1350 C.) Gleeble: 2 cycles (1350 C., 775 C.) t8/5 = 200 s --> 22 kJ/mm t8/5 = 200 s --> 22 kJ/mm Notch impact bending test Notch impact bending test Quarter of sheet - CG-HAZ simulation Quarter of sheet - ICRCG-HAZ simulation Indiv. value 1 Indiv. value 2 Indiv. value 3 Average Indiv. value 1 Indiv. value 2 Indiv. value 3 Average Rolled 40 C. 40 C. 40 C. 40 C. 20 C. 20 C. 20 C. 20 C. Melt plate transv. transv. transv. transv. transv. transv. transv. transv. A 1 239 242 259 246.7 243 220 215 226.0 A 2 275 245 230 250.0 367 322 367 352.0 B 3 223 9 237 156.3 269 9 7 95.0 B 4 11 256 231 166.0 B 5 15 254 232 167.0 242 279 8 176.3 B 6 300 12 8 106.7 7 23 363 131.0 C 7 207 13 29 83.0 239 288 208 245.0 D 8 20 244 262 175.3 307 219 258 261.3 E 9 26 16 7 16.3 75 121 136 110.7 F 10 7 8 192 69.0 13 180 105 99.3 G 11 12 10 16 12.7 19 23 21 21.0

TABLE-US-00007 TABLE 7 Gleeble: 1 cycle (1350 C.) Gleeble: 2 cycles (1350 C., 750 C.) t8/5 = 60 s --> 7 kJ/mm t8/5 = 60 s --> 7 kJ/mm Notch impact bending test Notch impact bending test Quarter of sheet - CG-HAZ simulation Quarter of sheet - ICRCG-HAZ simulation Indiv. Indiv. Indiv. Indiv. Indiv. Indiv. value 1 value 2 value 3 Average value 1 value 2 value 3 Average Rolled 40 C. 40 C. 40 C. 40 C. 20 C. 20 C. 20 C. 20 C. Melt plate transv. transv. transv. transv. transv. transv. transv. transv. A 1 A 2 B 5 276 328 9 204.3 343 366 364 357.7 E 9 F 10 22 15 20 19.0 301 18 14 111.0 G 11 65 71 175 103.7 Gleeble: 1 cycle (1350 C.) Gleeble: 2 cycles (1350 C., 775 C.) t8/5 = 40 s --> 5 kJ/mm t8/5 = 40 s --> 5 kJ/mm Notch impact bending test Notch impact bending test Quarter of sheet - CG-HAZ simulation Quarter of sheet - ICRCG-HAZ simulation Indiv. Indiv. Indiv. Indiv. Indiv. Indiv. value 1 value 2 value 3 Average value 1 value 2 value 3 Average Rolled 40 C. 40 C. 40 C. 40 C. 20 C. 20 C. 20 C. 20 C. Melt plate transv. transv. transv. transv. transv. transv. transv. transv. A 1 327 317 329 324.3 A 2 313 313 312 312.7 273 263 366 300.7 B 5 E 9 37 57 27 40.3 240 18 33 97.0 F 10 G 11

TABLE-US-00008 TABLE 8 Ratio of particle Average grain High-angle Particle Particle densities Grain size size in m grain boundaries density mm.sup.1 density mm.sup.1 0.5 m < d 2.0 m Rolled class 5 area fraction proportion in % 0.5 m < d 2.0 m 2.0 m < d 5.0 m divided by Melt plate Light microscope EBSD EBSD AsB + EDX AsB + EDX 2.0 m < d 5.0 m A 1 10.5 13.52 54.2 22.1 23.0 0.96 A 2 10.5 12.83 65.0 26.6 14.5 1.83 B 3 10.5 12.60 66.2 37.5 20.6 1.82 B 4 11 12.61 63.7 40.6 19.1 2.13 B 5 10.5 12.98 66.5 22.3 17.7 1.26 B 6 11 13.25 65.5 36.9 20.3 1.82 C 7 9 12.79 77.2 22.4 20.3 1.10 D 8 9.5 11.98 66.2 20.6 17.9 1.15 E 9 11 17.70 69.1 70.2 4.8 14.63 F 10 10.5 12.46 81.0 62.8 7.6 8.26 G 11 10.5 9.13 74.2 121.4 6.7 18.12