STEEL BOARD FOR POLAR MARINE ENGINEERING AND PREPARATION METHOD THEREFOR

Abstract

A steel board for polar marine engineering and a preparation method therefor. According to weight percentage, the components of the steel board are: C: 0.06-0.09%, Si: 0.20-0.35%, Mn: 1.48-1.63%, Nb: 0.020%-0.035%, Ti: 0.010%-0.020%, V: 0.020%-0.035%, Ni: 0.08%-0.17%, Als: 0.015%-0.040%, P: ≤0.013% and S: ≤0.005%. The preparation method for the steel board comprises: pre-refining, refining and casting to obtain a cast billet, and the slowly cooling down same. The slowly cooled billet is heated and then rolled out to obtain the steel board; and the steel board is cooled down and ready. The steel has an excellent comprehensive performance in terms of having high strength and low temperature resistance, being easy to weld and corrosion proof, and the steel has good low-temperature aging impact toughness.

Claims

1. A steel board for polar marine engineering, components of the steel board in terms of mass percentage comprising: C: 0.06-0.09%, Si: 0.20-0.35%, Mn: 1.48-1.63%, Nb: 0.020%-0.035%, Ti: 0.010%-0.020%, V: 0.020%-0.035%, Ni, 0.08%-0.17%, Als: 0.015%-0.040%, P: ≤0.013%, S: ≤0.005%, N: 50.006%, B: 50.005%, the rest are Fe and unavoidable impurities; and CEV≤0.39%, Pcm≤0.20%, wherein
CEV=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15,
Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V %10+5B≤0.20%.

2. The steel board for polar marine engineering according to claim 1, wherein the components of the steel board in terms of mass percentage are: C: 0.06-0.075%, Si: 0.20-0.28%, Mn: 1.48-1.58%, Nb: 0.020%-0.035%, Ti: 0.013%-0.018%, V: 0.030%-0.045%, Ni: 0.08%-0.12%, Als: 0.025%-0.040%, P: ≤0.013%, S: ≤0.005%, the rest are Fe and unavoidable impurities.

3. The steel board for polar marine engineering according to claim 1, wherein, based on a weight of the steel board, a mass percentage content of each component of the unavoidable impurities is: H≤0.0002%, O≤0.003%, As≤0.007%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010% and Ca≤0.005%.

4. A method for preparing the steel board for polar marine engineering according to claim 1, comprising: primary refining of molten steel and scrap to obtain a primary molten steel, then refining the primary molten steel casting to obtain a cast billet, then slowly cooling the cast billet; heating the cast billet after the slow cooling to obtain a hot cast billet; rolling the hot cast billet to obtain the steel board; and cooling the steel board to obtain the steel board for polar marine engineering.

5. The method for preparing the steel board for polar marine engineering according to claim 4, wherein, the primary refining is carried out under top-bottom combined blowing converter conditions, the molten steel is desulfurized using KR pretreatment, with the molten steel containing ≤0.015 wt. % sulfur after desulfurization.

6. The method for preparing the steel board for polar marine engineering according to claim 4, wherein the refining is LF+RH refining.

7. The method for preparing the steel board for polar marine engineering according to claim 4, wherein during the casting, the whole process is protected casting, a liquidus temperature is 1515-1525° C., superheat is required to be not more than 17° C., a light press down technique is used at a solidification end of the cast billet in a sector section, and the cast billet is slowly cooled in a pit and stack for not less than 60 hours.

8. The method for preparing the steel board for polar marine engineering according to claim 4, wherein during the heating, the heating rate is greater than 10 mins/cm and a uniform heat time is not less than 40 mins: after heating of the cast billet, the hot cast billet is subjected to high pressure water phosphorus removal.

9. The method of preparing the steel board for polar marine engineering according to claim 4, wherein the rolling includes a two-stage controlled rolling of roughing rolling and finishing rolling, the roughing rolling being a recrystallization zone rolling and the finishing rolling being an unrecrystallized zone rolling.

10. The method for preparing the steel board for polar marine engineering according to claim 4, wherein the cooling includes air cooling when a thickness of the steel board is 6-14 mm.

11. The steel board for polar marine engineering according to claim 1, wherein the components of the steel board in terms of mass percentage are: C: 0.06-0.075%, Si: 0.20-0.28%, Mn: 1.48-1.58%, Nb: 0.020%-0.035%, Ti: 0.013%-0.018%, V: 0.030%-0.045%, Ni: 0.08%-0.12%, Als: 0.025%-0.040%, P: ≤0.013%, S≤0.005%, the rest are Fe and unavoidable impurities; a mass percentage content of V and Ni in the components of the steel board satisfy the following relationship formula:
0.211C+0.041Mn+0.738Nb+1.19Ti≤V+Ni≤0.318C+0.065Mn+0.943Nb+1.867 Ti.

12. The method for preparing the steel board for polar marine engineering according to claim 4, wherein, the primary refining is carried out under top-bottom combined blowing converter conditions; prior to the primary refining, the molten steel is desulfurized using KR pretreatment, with the molten steel containing ≤0.015 wt. % sulfur after desulfurization, the scrap/(molten steel+scrap)≤8 wt. %, and nickel plate is added with the scrap, the primary refining is carried out using a double slag process, with a final slag alkalinity of a second slag-making smelting controlled at R=3.0-4.0, with a single catch carbon, with slag material added 3-4 mins before an end of the primary refining: ferro-manganese aluminum is added in a forepart of a steel tapping phase to deoxidation, and manganese metal, ferro-niobium, ferro-vanadium and ferrosilicon alloy are added when the primary molten steel is out to one-fourth steel tapping to three quarters of a time to add finished.

13. The method for preparing the steel board for polar marine engineering according to claim 4, wherein the refining is LF+RH refining, and includes bottom-blowing argon adopted in the whole process for stirring, aluminum particles, calcium carbide are used for deoxidation, a top slag before leaving a station is yellow-white slag or white slag, the yellow-white slag or the white slag holding time is not less than 10 mins, a titanium line is fed at the end of the refining, a final slag alkalinity amount is controlled above 2.5, during the LF refining, a composition is fine-tuned using metallic manganese, ferrosilicon, ferro-niobium and ferro-vanadium alloys, and in the RH refining, a degassing time is not less than 5 mins and a calcium-aluminum line is fed for calcification, soft blowing is carried out before leaving the station, and the soft blowing time is not less than 12 mins.

14. The method of preparing the steel board for polar marine engineering according to claim 4, wherein the rolling includes a two-stage controlled rolling of roughing rolling and finishing rolling, the roughing rolling being a recrystallization zone rolling and the finishing rolling being an unrecrystallized zone rolling, and an opening rolling temperature of the finishing rolling is 860 to 960° C. and a final rolling temperature of the finishing rolling is 820-840° C.

15. The method for preparing the steel board for polar marine engineering according to claim 4, wherein the cooling includes air cooling when a thickness of the steel board is 6-14 mm, and when the thickness of the steel board is 14-40 mm, the cooling is ACC water cooling with an inlet water temperature of 770-780° C. and an outlet water temperature of 600-650° C., after water cooling, the steel board is straightened.

16. The method for preparing steel board for polar marine engineering according to claim 5, wherein during the heating, the heating rate is greater than 10 mins/cm and a uniform heat time is not less than 40 mins; after heating of the cast billet, the hot cast billet is subjected to high pressure water phosphorus removal.

17. The method of preparing steel board for polar marine engineering according to claim 5, wherein the rolling includes a two-stage controlled rolling of roughing rolling and finishing rolling, the roughing rolling being a recrystallization zone rolling and the finishing rolling being an unrecrystallized zone rolling.

18. The method for preparing steel board for polar marine engineering according to claim 5, wherein the cooling includes air cooling w % ben a thickness of the steel board is 6-14 mm.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] In order to highlight the purpose, technical solutions and advantages of the present disclosure, the present disclosure is further described below in connection with embodiments, examples of which are expressed by way of explanation of the present disclosure rather than limiting the present disclosure. The technical solutions of the present disclosure are not limited to the specific embodiments enumerated below, but also include any combination between the specific embodiments.

[0045] Any of the features disclosed in this specification, unless specifically recited, can be replaced by other equivalent or alternative features having a similar purpose. Unless specifically recited, each feature is only one example of a series of equivalent or similar features.

(1) smelting: the molten steel in the converter is desulfurized using KR pretreatment, and using top-bottom combined blowing converter smelting, and then LF+RH refining, the whole process to do a good job of composition, purity and gas content control, continuous casting process using the whole protection casting; casting billet should be off-line stacking or into the slow cooling pit for slow cooling, slow cooling time of not less than 60 hours.

[0046] Wherein, the raw materials into the furnace must meet the technical requirements of the converter process, the blast furnace molten molten steel is desulfurized by KR pretreatment, the sulfur content of the incomings molten molten steel is ≤0.015%, the desulfurization is completed by picking up the slag on the surface of the molten molten steel, the loading quantity is strictly controlled, the loading quantity error 2 tons. Nickel plate added with scrap, the amount of scrap added shall not exceed 8% of the total loading.

[0047] The use of double slag process smelting, the final slag alkalinity control in R=3.0-4.0, the use of a single catch carbon, slag material in the end before 3 mins added. Block slag out of steel, eliminsate a large number of under slag, put the steel time is not less than 3 mins; using ferromanganese aluminum 3.5 kg/t steel deoxidation, steel tapping to a quarter of the time, add manganese metal, ferro-niobium, ferro-vanadium, ferrosilicon alloy in batches, steel tapping to three-quarters of the time added.

[0048] in the LF refining process, the bottom-blowing argon is adopted in the whole process for stirring, the aluminum particles, calcium carbide are used for the slag adjustment, deoxidation, the entire smelting process shall not be bare steel, to prevent secondary oxidation of steel. Out of the station before the top slag must be yellow-white slag or white slag, yellow-white slag or white slag holding time is not less than 10 mins, because titanium is very easy to oxidation, so titanium line is fed at the end of refining, the final slag alkalinity as much as possible to control above 2.5. The use of manganese metal, ferrosilicon, ferro-niobium, ferro-vanadium, nickel plate and other alloys for composition fine-tuning to ensure that the composition meets the internal control, LF refining time of not less than 45 mins.

[0049] RH refining process requires avoiding chemical temperature rise, controlling the purity of the steel and gas content, ensuring that the pure degassing time is not less than 5 mins. feeding calcium-aluminum line for calcification treatment, improving the morphology of inclusions and effectively removing inclusions. soft blowing is carried out before leaving the station, and the soft blowing time shall not be less than 12 mins. preferably, the vacuum degree is 25-65 Pa (e.g. 35 Pa, 40 Pa, 45 Pa, 50 Pa, 55 Pa, etc.).

[0050] Through the above steps, It is possible to obtain a target molten steel having a composition consisting of C: 0.06-0.09%, Si: 0.20-0.35%, Mn: 1.48-1.63%, Nb: 0.020%-0.035%, Ti: 0.010%-0.020%, V: 0.020%-0.035%, Ni: 0.08%-0.17%, Al: 0.015%-0.040%, the rest being Fe and unavoidable impurities. However, the present disclosure is not limited to this, but it is also possible to obtain steel in the above composition range by other means or process.

[0051] In the continuous casting process of the present disclosure, the whole process is protected casting, the liquidus temperature is calculated as 1515° C. according to the middle limit of the intermediate specification composition, the superheat is required to be not more than 17° C. (e.g. 14, 15, 16° C.), the light press down technique is used at the solidification end of the fan section billet, the billet is pitted and stacked for slow cooling for not less than 60 hours to fully reduce the tissue stress and thermal stress generated by the billet during cooling. The pulling speed of 175 mm billet section thickness is controlled as 1.25-1.35 m/mins, 200 mm billet section thickness is controlled as 1.3-1.4 m/mins, 250 mm billet section thickness is controlled as 1.1-1.3 m/mins, 300 mm billet section thickness is controlled as 0.8-0.9 m/mins.

[0052] 2) Heating:

[0053] Add the continuous casting billet to the heating furnace for heating, and the casting billet loading method is cold loading.

[0054] Wherein, in order to prevent the heating process of alloy elements in the grain boundary bias aggregation caused by micro-cracking of the cast billet, the disclosure uses the cold loading method to feed the slab into the heating furnace, the heating rate required ≥10 mins/cm calculation, to ensure that the billet burn evenly burn through. The uniform heating time is not less than 40 mins, and the temperature difference at each point of the billet is not more than 15° C., and the billet is de-phosphorized with high-pressure water after leaving the heating furnace.

[0055] 3) Rolling:

[0056] The rolling is a two-stage controlled rolling of roughing rolling and finishing rolling, the roughing rolling being a recrystallization zone rolling; an opening rolling temperature of the roughing rolling is preferred to 1185-1200° C., a final rolling temperature of the roughing rolling is preferred to 1160-1190° C.; in order to prevent excessive grain growth, the finishing rolling being an unrecrystallized zone rolling, an opening rolling temperature of the finishing rolling is controlled in 860-960° C., a final rolling temperature of the finishing rolling is controlled in 820-840° C.

[0057] 4) Cooling:

[0058] Thickness less than 14 mm steel board using air-cooling process, the steel board which thickness greater than 14 mm being ACC water cooling after rolling, an inlet water temperature of 770-780° C., and an outlet water temperature of 600-650° C., after water cooling, the steel board is straightened. Finished thickness ≥25 mm steel board water cooling as soon as possible after the pit cooling or stacking slow cooling, slow cooling time of not less than 48 hours.

[0059] The chemical composition of each embodiment of the present disclosure is shown in Table 1; the smelting process parameters of each embodiment of the present disclosure are shown in Table 2; the rolling process parameters of each embodiment of the present disclosure are shown in Table 3; the mechanical properties of each embodiment of the present disclosure are tested according to GB/T 228 and GB/T 2289, as shown in Table 4 and Table 5.

TABLE-US-00001 TABLE 1 Chemical composition of steels of examples 1-3 of the present disclosure (wt %, the rest is Fe). Thickness C Si Mn P S Ni Nb V Ti Als N B PCM CEV 15 mm 0.071 0.23 1.53 0.01 0.001 0.09 0.032 0.023 0.016 0.03 0.0042 0.0003 0.17 0.37 25 mm 0.065 0.24 1.5 0.01 0.003 0.09 0.021 0.021 0.017 0.038 0.0034 0.0002 0.15 0.33 40 mm 0.07 0.25 1.51 0.01 0.005 0.1 0.022 0.022 0.015 0.038 0.0037 0.0004 0.16 0.34

[0060] Note: CEV=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15≤0.39% Pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B≤0.20% V+Ni meets 0.211C+0.041Mn+0.738Nb+1.19Ti≤V+Ni≤0.318C+0.065Mn+0.943Nb+1.867Ti

TABLE-US-00002 TABLE 2 Smelting process parameters of the steel of examples 1-3 of the present disclosure LF soft RH RH soft RH Liquid blowing vacuum blowing pure Mid pack Pulling phase line Superheat time/ degree/ time/ degassing temperature/ speed/m/ temperature/ degree/ Specification Example mins Pa mins time/mins ° C. mins ° C. ° C. 15 mm 1 5 50 12 23 1535 1.1 1520 16 25 mm 2 5 60 12 14 1530 1.2 1520 16 40 mm 3 5 30 12 5 1538 1.1 1521 15

TABLE-US-00003 TABLE 3 Rolling and cooling process parameters of the steel of examples 1-3 of the present disclosure Opening Opening rolling Final rolling rolling Final rolling Inlet Outlet Steel temperature of temperature of temperature of temperature of water water output the roughing the roughing the finishing the finishing temper- temper- Specification Example temperature rolling rolling rolling rolling ature ature 15 mm 1 1198 1187 1132 868 829 780 607 25 mm 2 1195 1186 1131 866 827 778 615 40 mm 3 1191 1170 1118 863 827 779 636

TABLE-US-00004 TABLE 4 Mechanical properties of steels of examples 1-3 of the present disclosure −40° C. transverse impact work/J Elongation Impact Upper yield strength/ Tensile strength/ after break/ Impact Impact Impact work Specification MPa MPa % work 1 work 2 work 3 average 15 mm 468 580 23 311 297 326 311 25 mm 556 615 23.5 296 300 288 295 40 mm 499 590 23 286 296 288 290

[0061] The steel board with age impact properties were aged for 1 hour at 5%, 250° C. for aging conditions. The impact properties of the aged steel board are shown in Table 5.

TABLE-US-00005 TABLE 5 Aging Impact of Steel of examples 1-3 of the present disclosure −40° C. longitudinal impact work/J Impact Impact Impact Impact work Specification work 1 work 2 work 3 average 15 mm 279 283 289 283 25 mm 295 285 283 289 40 mm 295 299 285 293

[0062] In summary, the steel board for polar marine engineering of the present disclosure has excellent comprehensive performance of high strength, low temperature resistance, easy welding, fatigue resistance, etc., good low temperature aging impact toughness, thickness direction performance uniformity and batch-to-batch performance stability, and Z-directional performance (i.e., section shrinkage in thickness direction when tensile) are greater than 40%; and relatively low cost, simple process and easy operation. The high-strength low-temperature resistant marine engineering steel of the present disclosure is suitable for application in extremely cold climate and high comprehensive performance requirements.

[0063] The process parameters of the present disclosure (such as temperature, time, etc.) interval upper and lower limit taking values as well as interval values can realize the present method, and the examples of implementation are not listed here.

[0064] Anything not described in detail in the present disclosure can be adopted from the conventional technical knowledge in the field.

[0065] Finally, it should be noted that the above embodiments are used only to illustrate the technical solutions of the present disclosure and not to limit them. Although the disclosure is described in detail with reference to the embodiments, a person of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solution of the disclosure does not depart from the spirit and scope of the technical solution of the disclosure, which should be covered by the scope of the claims of the disclosure.