High hardenability q550d high-strength medium plate and processing method thereof

Abstract

The application discloses a high hardenability Q550D high-strength medium plate and a production method thereof, and relates to the technical field of medium plate processing. The element composition of the Q550D medium plate is adjusted, and a preparation process is used, so that the prepared medium plate has very high strength and hardenability, and meanwhile, production energy consumption is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plate processing, and particularly relates to a high hardenability Q550D high-strength plate and a processing method thereof. BACKGROUND

[0002] At present, the thickness of the Q550D plate is relatively thick, generally being 20mm-40mm. The Q550D plate with a thickness less than 20mm is prone to deformation, and has poor hardenability.

[0003] Therefore, it is a research focus to prepare the Q550D plate with high hardenability and low thickness and to meet the market demand. SUMMARY

[0004] In view of the defects of the prior art, the application provides a high hardenability Q550D high-strength plate and a processing method thereof.

[0005] The application is implemented by the following technical scheme:

[0006] The high hardenability Q550D high-strength plate comprises the following components in percentage by mass:

[0007] C: 0.10-0.15%, Si: 0.10-0.20%, Mn: 1.50-1.60%, Cr: 0.25-0.35%, Al: 0.020-0.035%, Nb: 0.025-0.040%, V: 0.035-0.055%, Ti: 0.010-0.020%, Mo: 0.050-0.070%, B: 0.001-0.0025%, N: 50-70ppm, P≤0.010%, S≤0.005%, H≤2.0ppm, O≤30ppm, and the balance of Fe and inevitable impurities.

[0008] The processing method of the high hardenability Q550D high-strength plate comprises the following steps:

[0009] (1) Steel smelting

[0010] The top and bottom combined blowing converter is adopted for smelting, the blowing gun position adopts a low-high-low mode in the smelting process, and the blowing is performed to the blowing end point; the argon mode is adopted for the converter bottom blowing, the flow is 230m 3 / h, the C content in the molten steel is 0.03-0.06wt% when the converter smelting is finished, the tapping temperature is 1600-1660℃, and the final slag basicity is controlled within the range of 3.2-4.1; the aluminum block, ferrosilicon, low-carbon manganese iron and low-chromium deoxidizing alloy are added when the converter tapping is to 1 / 3; after the tapping, the bottom argon blowing process of the ladle is adopted to stir the molten steel, and the molten steel surface is kept in a slight motion state; the nitrogen content in the molten steel after the converter is less than or equal to 40ppm;

[0011] (2) Refining

[0012] The molten steel is subjected to RH vacuum refining treatment, specifically, slagging agent, lime, foaming agent are added into the molten steel, and calcium carbide / aluminum block is used for deoxidation, after 15 minutes of treatment, boron, molybdenum iron, and chromium iron are added, the N content in the molten steel during the refining process is 30-50 ppm, H≤1.5 ppm, and O≤20 ppm;

[0013] (3) Slab continuous casting

[0014] The refined molten steel is cast, and a constant casting speed is maintained during the casting process, an outer arc chamfer crystallizer is used, the casting speed ranges from 0.85 m / min to 1.2 m / min; the dynamic heavy pressing increases the pressing amount of the two-phase region and the solid phase region, and the pressing amount of the solid phase region is 1.5-5 mm; the slab center segregation is ensured to be not greater than 1 level, and a slab with a thickness of 400 mm is obtained;

[0015] (4) Slab sectional heating

[0016] The slab is subjected to sectional heating by using a double-heat accumulation walking beam furnace; wherein the first heating section temperature is 950-1050℃, the second heating section temperature is 1030-1150℃, the third heating section temperature is 1250-1280℃, the fourth heating section temperature is 1200-1230℃, the heating time is controlled according to 9-10 min / cm, the slab time in the furnace is more than 4h, the soaking time is more than 50min, and the discharge temperature is 1100±20℃;

[0017] (5) Rolling

[0018] The iron oxide scale on the surface of the slab after sectional heating is removed, and then the slab is subjected to rough rolling;

[0019] The iron oxide scale on the surface of the slab after rough rolling is removed, and then the slab is cooled and subjected to finish rolling, to obtain a steel plate with a thickness of 12-50 mm;

[0020] Among them, the multi-directional nozzle descaling technology is used to remove the iron oxide scale on the surface of the slab, specifically, the opposite 15° water descaling is used, and the descaling pressure is 22 MPa, which can effectively avoid the problem of incomplete descaling

[0021] (6) Cooling

[0022] The steel plate after finish rolling is subjected to rapid cooling, and the cooling speed is 40-60℃ / s, to ensure that the steel plate generates upper bainite structure; wherein the fourth generation UFC ultra-fast cooling technology is used to cool the rolled steel plate, the temperature of the steel plate at the beginning of cooling is between 760-790℃, and the rapid cooling of the application can ensure that the steel plate generates bainite structure;

[0023] (7) Online tempering

[0024] After the cooled steel plate is straightened, an online slow cooling process is used instead of tempering. The slow cooling starts at 250-300℃ and lasts for 12 hours. During the process, a flattening device presses 20 tons of weight on the steel plate to prevent warping during stress release.

[0025] Preferably, the initial rolling temperature of the roughing mill in step (5) is 1080±20℃, the final rolling temperature is 800℃~950℃, and the total number of passes is 6. The reduction rate of the first three passes is 15%~20%, and the reduction rate of the last three passes is adjusted according to the thickness of the intermediate billet and the equipment conditions.

[0026] Preferably, the finishing rolling temperature in step (5) is 850-900℃, the total number of passes is 6, the reduction rate of the first 2 passes is 12%-15% (the reduction rate of the last 4 passes is adjusted according to the thickness of the intermediate billet and the equipment conditions), and the final rolling temperature is 790-810℃.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The processing technology of this invention can reduce the incidence of outer arc cracks in Q550D medium and thick plates;

[0029] This invention effectively improves production efficiency while reducing the grain size difference between the surface and the center of the thick plate.

[0030] This invention reduces production costs and energy consumption. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments.

[0032] Example 1

[0033] A high-hardenability Q550D high-strength medium-thick plate comprises the following components by mass percentage:

[0034] C: 0.15%, Si: 0.20%, Mn: 1.50%, Cr: 0.25%, Al: 0.020%, Nb: 0.025%, V: 0.035%, Ti: 0.010%, Mo: 0.050%, B: 0.001%, N: 60ppm, P≤0.010%, S≤0.005%, H≤2.0ppm, O≤30ppm, balance Fe and unavoidable impurities.

[0035] The processing method for high-hardenability Q550D high-strength medium-thick plate of the present invention includes the following steps:

[0036] (1) Steel smelting

[0037] Adopting top and bottom combined blowing converter smelting, adopting low-high-low mode for blowing gun position in smelting process, blowing to blowing end point, adopting argon mode for converter bottom blowing, flow is 230m 3 / h, C content in molten steel is 0.05wt% when converter smelting ends, tapping temperature is 1650 DEG C, and final slag basicity is controlled at 4.0; aluminum block, ferrosilicon, low-carbon ferromanganese and low-chromium deoxidizing alloy are added when converter tapping is to 1 / 3, after tapping, adopting bottom argon blowing process of ladle, molten steel is stirred, and the molten steel surface is kept in a slight motion state; nitrogen content in molten steel after converter is ≤40ppm;

[0038] (2) Refining

[0039] The molten steel is treated by RH vacuum refining, specifically, slagging agent, lime, foaming agent and calcium carbide / aluminum block are added to the molten steel for deoxidation, after 15 minutes of treatment, boron, molybdenum iron and chromium iron are added, N content in the molten steel during refining is 40ppm, H≤1.5ppm, and O≤20ppm;

[0040] (3) Slab continuous casting

[0041] The molten steel after refining is cast, and the constant casting speed is maintained during the casting process, the outer arc chamfer crystallizer is used, and the casting speed range is 1.0m / min; the dynamic heavy pressing is increased to increase the pressing amount of the two-phase region and the solid phase region, and the pressing amount of the solid phase region is 2.8mm; the slab center segregation is ensured to be not greater than 1 level, and the slab with a thickness of 400mm is obtained;

[0042] (4) Slab sectional heating

[0043] The slab is subjected to sectional heating by using a double-heat accumulation walking beam furnace; wherein the first heating section temperature is 1000 DEG C, the second heating section temperature is 1100 DEG C, the third heating section temperature is 1250 DEG C, the fourth heating section temperature is 1200 DEG C, the heating time is controlled according to 10min / cm, the slab is in the furnace for more than 4h, the soaking time is more than 50min, and the out-of-furnace temperature is 1100±20 DEG C;

[0044] (5) Rolling

[0045] The iron oxide skin on the surface of the slab after sectional heating is removed, and then the slab is subjected to rough rolling;

[0046] The iron oxide skin on the surface of the slab after rough rolling is removed, and then the slab is cooled and subjected to finish rolling, to obtain a steel plate with a thickness of 35mm;

[0047] The slab surface oxidation iron is removed by using the multi-directional nozzle descaling technology, specifically, the opposite 15 DEG water descaling is used, and the descaling pressure is 22MPa, so that the problem of incomplete descaling can be effectively avoided.

[0048] (6) Cooling

[0049] The finished steel plate is rapidly cooled at a rate of 50°C / s to ensure the formation of upper bainite structure. The present invention uses fourth-generation UFC ultra-fast cooling technology to cool the rolled steel plate. The temperature of the steel plate is 780°C at the beginning of cooling. The rapid cooling using the present invention can ensure the formation of bainite structure in the steel plate.

[0050] (7) Online tempering

[0051] After the cooled steel plate is straightened, an online slow cooling process is used instead of tempering. The slow cooling starts at 250℃ and lasts for 12 hours. During the process, a flattening device presses 20 tons of weight on the steel plate to prevent warping during stress release.

[0052] In step (5), the initial rolling temperature of the roughing mill is 1080±20℃, the final rolling temperature of the roughing mill is 900℃, and the total number of passes is 6. The reduction rate of the first three passes is 20%, and the reduction rate of the last three passes is adjusted according to the thickness of the intermediate billet and the equipment conditions.

[0053] In step (5), the initial rolling temperature is 850°C, the total number of passes is 6, the reduction rate of the first 2 passes is 15% (the reduction rate of the last 4 passes is adjusted according to the thickness of the intermediate billet and the equipment conditions), and the final rolling temperature is 790°C.

[0054] Example 2

[0055] A high-hardenability Q550D high-strength medium-thick plate comprises the following components by mass percentage:

[0056] C: 0.15%, Si: 0.10%, Mn: 1.60%, Cr: 0.35%, Al: 0.035%, Nb: 0.040%, V: 0.055%, Ti: 0.020%, Mo: 0.070%, B: 0.002%, N: 60ppm, P≤0.010%, S≤0.005%, H≤2.0ppm, O≤30ppm, balance Fe and unavoidable impurities.

[0057] The processing method for high-hardenability Q550D high-strength medium-thick plate of the present invention includes the following steps:

[0058] (1) Steel smelting

[0059] The smelting process employs a top-and-bottom combined blowing converter. During the smelting process, the blowing lance position adopts a low-high-low mode, and blowing continues until the blowing endpoint. The bottom blowing of the converter uses argon mode with a flow rate of 230 m³ / h. 3 / h, the content of C in the molten steel at the end of the converter smelting is 0.06wt%, the tapping temperature is 1660 DEG C, the final slag basicity is controlled at 4.0; the aluminum block, ferrosilicon, low-carbon manganese iron and low-chromium deoxidizing alloy are added at 1 / 3 of the converter tapping; after tapping, the bottom argon blowing process of the ladle is adopted to stir the molten steel and keep the molten steel surface in a slight motion state; the nitrogen content in the molten steel after the converter is ≤40ppm;

[0060] (2) Refining

[0061] The molten steel is subjected to RH vacuum refining treatment, specifically, a slagging agent, lime, a foaming agent and calcium carbide / aluminum block are added to the molten steel for deoxidization, 15 minutes after the treatment, boron, molybdenum iron and chromium iron are added, the N content in the molten steel during the refining process is 40ppm, H≤1.5ppm, O≤20ppm;

[0062] (3) Slab continuous casting

[0063] The molten steel after refining is cast, and at the same time, the constant casting speed is maintained during the casting process, the outer arc chamfer crystallizer is adopted, the casting speed range is 1.2m / min; the dynamic heavy pressing is increased to increase the pressing amount of the two-phase region and the solid phase region, and the pressing amount of the solid phase region is 5mm; the slab center segregation is ensured to be not greater than 1 level, and the slab with a thickness of 400mm is obtained;

[0064] (4) Slab sectional heating

[0065] The double-accumulation heat step-by-step heating furnace is adopted to heat the slab in sections; wherein the first heating section temperature is 1050 DEG C, the second heating section temperature is 1150 DEG C, the third heating section temperature is 1280 DEG C, the fourth heating section temperature is 1200 DEG C, the heating time is controlled according to 10min / cm, the slab time in the furnace is more than 4h, the soaking time is more than 50min, and the discharge temperature is 1100±20 DEG C;

[0066] (5) Rolling

[0067] The iron oxide skin on the surface of the slab after sectional heating is removed, and then the slab is roughed;

[0068] The iron oxide skin on the surface of the roughed steel billet is removed and then cooled to be finished, and the steel plate with a thickness of 50mm is obtained;

[0069] Wherein the multi-directional nozzle descaling technology is adopted to remove the iron oxide on the surface of the slab, specifically, the opposite 15 DEG water descaling is adopted, and the descaling pressure is 22MPa, which can effectively avoid the problem of incomplete descaling

[0070] (6) Cooling

[0071] The steel plate after finish rolling is rapidly cooled with a cooling speed of 60℃ / s to ensure the formation of upper bainite structure; wherein the fourth generation UFC ultra-fast cooling technology is used to cool the rolled steel plate, and the temperature of the steel plate at the beginning of cooling is 790℃, and the rapid cooling of the application can ensure the formation of bainite structure;

[0072] (7) Online tempering

[0073] The cooled steel plate is straightened and then tempered by using an online slow cooling process, wherein the slow cooling starting temperature is 300℃, the slow cooling time is 12h, and a weight of 20t is pressed on the steel plate by a flattening device during the process to prevent the steel plate from being cupped during stress release.

[0074] The rough rolling opening temperature in step (5) is 1080±20℃, the rough rolling final rolling temperature is 800℃, and the total pass is 6 passes, wherein the first three passes are 15%, and the last three passes are adjusted according to the intermediate blank thickness and equipment conditions.

[0075] The finish rolling opening temperature in step (5) is 900℃, the total pass is 6, the first two passes are 12%, the last four passes are adjusted according to the intermediate blank thickness and equipment conditions, and the final rolling temperature is 810℃.

[0076] It should be noted that the above enumeration is only a few specific embodiments of the present application, and obviously the present application is not limited to the above embodiments, but can also have other variations. All variations directly derived or indirectly derived by those skilled in the art from the disclosure of the present application should be considered as the protection scope of the present application.

Claims

1. A high hardenability Q550D high-strength medium plate, characterized in that, Comprise the following quality percentage of ingredients: C: 0.10~0.15%, Si: 0.10~0.20%, Mn: 1.50~1.60%, Cr: 0.25~0.35%, Al: 0.020~0.035%, Nb: 0.025~0.040%, V: 0.035~0.055%, Ti: 0.010~0.020%, Mo: 0.050~0.070%, B: 0.001~0.0025%, N: 50~70ppm, P≤0.010%, S≤0.005%, H≤2.0ppm, O≤30ppm, the balance of Fe and inevitable impurities; The processing method of the high hardenability Q550D high-strength medium plate comprises the following steps: (1) molten steel smelting The top and bottom combined blowing converter is used for smelting, the blowing gun position is in low-high-low mode during smelting, the blowing is carried out to the end, the argon mode is used for the bottom blowing of the converter, the flow is 230 m 3 / h, the content of C in the molten steel is 0.03-0.06wt% when the converter smelting is finished, the tapping temperature is 1600-1660℃, the final slag basicity is controlled in the range of 3.2-4.1; the aluminum block, ferrosilicon, low-carbon ferromanganese and low-chromium deoxidizing alloy are added when the converter tapping is to 1 / 3, the argon bottom blowing process is adopted for the ladle after the tapping, the molten steel is stirred and the molten steel surface is kept in a slight moving state; the nitrogen content in the molten steel after the converter is ≤40ppm; (2) refining The molten steel is subjected to RH vacuum refining treatment, and the specific method is to add slagging agent, lime and foaming agent to the molten steel and adopt calcium carbide / aluminum block deoxidation, then add boron, molybdenum iron and chromium iron after 15 minutes of treatment, the N content in the molten steel is 30-50ppm, H≤1.5ppm, and O≤20ppm during the refining process; (3) slab continuous casting The refined molten steel is cast, and the casting process is kept constant speed at the same time, an outer arc chamfer crystallizer is adopted, the casting speed ranges from 0.85m / min to 1.2m / min; the dynamic heavy pressing increases the pressing amount of the two-phase region and the solid phase region, and the pressing amount of the solid phase region is 1.5-5mm; the center segregation of the slab is ensured to be not more than 1 level, and a slab with a thickness of 400mm is obtained; (4) slab sectional heating The slab is subjected to sectional heating by adopting a double-heat accumulation walking beam furnace; wherein, the first heating section temperature is 950-1050℃, the second heating section temperature is 1030-1150℃, the third heating section temperature is 1250-1280℃, the fourth heating section temperature is 1200-1230℃, the heating time is controlled according to 9-10min / cm, the slab time in the furnace is more than 4h, the soaking time is more than 50min, and the out-of-furnace temperature is 1100±20℃; (5) rolling The iron oxide scale on the surface of the slab after sectional heating is removed, and then the slab is subjected to rough rolling; The iron oxide scale on the surface of the steel billet after rough rolling is removed, and then the steel billet is cooled and subjected to finish rolling to obtain a steel plate with a thickness of 12-50mm; (6) cooling The steel plate after finish rolling is subjected to rapid cooling at a cooling speed of 40-60℃ / s to ensure that the steel plate generates upper bainite structure; (7) online tempering The steel plate after cooling is straightened and then subjected to online slow cooling treatment, wherein the slow cooling starting temperature is 250~300℃, and the slow cooling time is 12h.

2. The high hardenability Q550D high-strength medium plate according to claim 1, characterized in that, The rough rolling opening temperature in step (5) is 1080±20℃, and the rough rolling final rolling temperature is 800℃~950℃, and the total pass is 6 passes, wherein the first three passes are 15%~20% in reduction rate.

3. The high hardenability Q550D high-strength medium plate according to claim 1, characterized in that, The finish rolling opening temperature in step (5) is 850~900℃, the total pass is 6, the first 2 passes are 12%~15% in reduction rate, and the final rolling temperature is 790~810℃.