Cold-resistant tool steel and method for producing the same

Abstract

The application relates to a cold-resistant tool steel and a production method thereof, and the chemical components of the steel are as follows in percentage by weight: C 0.30%-0.60%, Si<=0.5%, Mn 0.4%-1.5%, Cr 0.5%-2.0%, Mo 0.5%-2.0%, Ni 0.5%-1.5%, V 0.05%-0.5%, Al 0.02%-0.5%, N 0.003%-0.005%, Ca 0.0005%-0.005%, Si is not zero, impurity elements B<=0.0008%, P<=0.020%, S<=0.010%, and the balance is Fe and inevitable impurities. The tool steel produced by the application has the hardness of more than 55HRC, the yield strength of more than 600MPa, the impact energy of more than 30J, the surface oxidation depth of not more than 20mu, excellent wear resistance and impact toughness in a low-temperature environment, and the service life is obviously improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of tool steel production, and relates to a cold-resistant tool steel and a production method thereof. BACKGROUND

[0002] With the development of mechanization of various tool processing manufacturing industry, agriculture and garden animal husbandry, winter operation is more and more, and the demand for tools suitable for low-temperature environment and steel suitable for processing such tools is also more and more. The ordinary tool steel generally has high carbon content, great brittleness, poor toughness and plasticity, and is easy to crack in low-temperature environment, and has short service life. It is urgent to develop tool steel suitable for low-temperature environment below-40℃. On the other hand, the surface quality of steel directly affects the production process of the processed tool, and the steel with high surface quality can reduce the polishing amount, improve the processing and manufacturing productivity, reduce the production cost, and resist impact.

[0003] A low-temperature-resistant copper pipe and a preparation method thereof, application number 201310715230.1, the chemical composition of which has a mass percentage of C 0.05-0.15, Si 0.1-0.3, Ni 2.2-2.8, Cr 1.5-2.0, Mn 0.8-1.2, Al 0.3-0.6, Mo 0.2-0.4, Nb 0.1-0.2, Ti 0.05-0.15, Nd 0.03-0.05, Er 0.02-0.04, N 0.004-0.008, V 0.002-0.005, S≤0.01, P≤0.02, and the balance is Fe. It has good low-temperature impact toughness and can be used in extremely low-temperature areas below-196℃ for a long time, but the steel has low carbon content, low strength and hardness, and poor wear resistance, and is not suitable for tool steel.

[0004] A high-strength low-temperature-resistant steel and a production method thereof, application number 201510720341.0, discloses that C 0.05-0.2%, Si 0.1-0.26%, Mn 0.60-8.00%, Cr 0.4-0.8%, Mo 0.12-0.28%, Cu≤0.03%, Al 0.02-0.06%, Ti 0.010-0.018%, P≤0.012%, S≤0.005%, N 0.004-0.01%, O≤0.0012%, H≤0.00012%, Ca 0.001-0.005%, Sb 0.0001-0.0005%, Sn≤0.001%, As≤0.005%, B≤0.0010%, V≤0.08%, and Nb≤0.03%. The low-temperature impact power is significant, the impact power value at-20℃ is 260-350J, and the impact power value at-40℃ is 240-300J. However, the carbon content is low, the strength and hardness are low, the wear resistance is poor, and it is not suitable for tool steel.

[0005] A D6A hot-rolled wide strip steel for bimetal saw blade back material and a production method thereof, application number 201710014769.2, the chemical composition of which has a mass percentage of C 0.45-0.55, Si 0.05-0.30, Mn 0.6-1.0, P≤0.025, S≤0.010, Cr 0.9-1.20, V 0.08-0.15, Ni 0.50-0.70, Mo 0.90-1.20, Al 0.05-0.15, N 0.007-0.015, and the balance of Fe. The specification of the hot-rolled wide strip steel is (3.0-8.0)×(960-1500)mm. The steel is smelted in a 210t converter, refined in a ladle furnace and a vacuum furnace, and cast in a slab continuous casting machine. The slab is hot charged and hot sent. The entry temperature of the slab into the heating furnace is greater than 400℃, and the slab heating temperature is greater than or equal to 1200℃. The final hot-rolling temperature is 860-920℃. The rolled strip steel is cooled by layer cooling and sparse cooling, and the coiling temperature is 650-720℃. The hot-rolled steel coil is slowly cooled in a slow cooling pit or a slow cooling cover. The cross section of the D6A hot-rolled wide strip steel is (3.0-8.0)×(960-1500)mm. The thickness fluctuation of the strip steel is within ±0.08mm, the convexity is 45-55μm, the hardness difference in the same coil is within 6RHC, the grain size is fine (≤5μm), and is uniform. The microstructure of the strip steel is a mixed structure of ferrite + degenerated pearlite + granular bainite. From the surface layer to the center, the grain size is extremely fine and very uniform, and the average grain size is below 5μm. The invention has no means to control surface oxidation and decarburization, and the surface quality is poor. The low-temperature toughness and plasticity are poor, and the invention is not suitable for use in low-temperature environments. After converter smelting, the steel needs to be refined in an LF and treated by RH vacuum, which is double-furnace smelting, high cost, and low efficiency.

[0006] A cold-rolled strip steel for bimetal saw blade back material and a manufacturing method thereof, application number 201811343856.3, the hot-rolled steel coil is softened and annealed, pickled, spheroidized in a full-hydrogen hood furnace, cold-rolled by a single-stand reversible cold rolling mill, polished by a sand cloth polishing unit, annealed in a full-hydrogen hood furnace, and leveled to obtain a finished product. The invention is based on a general steel production device, solves the problems of surface decarburization and surface layer grain boundary oxidation, and the sponge iron obtained by annealing reduction is difficult to be pickled and has poor flatness control, and realizes high-quality and low-cost production. The average ferrite grain size of the cold-rolled strip steel for bimetal saw blade back material is 4-4.5μm, the cementite size is below 0.3μm, the spheroidization rate is above 95%, the average hardness is 256-280HV, there is no semi-decarburized layer and no grain boundary oxidation layer, and the width direction flatness is not more than 0.5% of the width. The invention has many annealing times, high cost, poor low-temperature toughness and plasticity, and is not suitable for use in low-temperature environments.

[0007] The steel grades and production methods mentioned in the above prior art all have certain defects and are not suitable for processing tools for low-temperature environment work. SUMMARY

[0008] The application provides a cold-resistant tool steel and a production method thereof. The tool steel produced by the application has a hardness of above 55HRC, a yield strength of above 600MPa, an impact energy of above 30J, and a surface intergranular oxidation depth of not more than 20μm after heat treatment in a low-temperature environment of-40℃, and has excellent wear resistance and impact toughness in a low-temperature environment, and the service life is obviously improved.

[0009] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0010] A cold-resistant tool steel, the chemical components in the steel are as follows in terms of percentage by weight: C 0.30%-0.60%, Si≤0.5%, Mn 0.4%-1.5%, Cr 0.5%-2.0%, Mo 0.5%-2.0%, Ni 0.5%-1.5%, V 0.05%-0.5%, Al 0.02%-0.5%, N 0.003%-0.005%, Ca 0.0005%-0.005%, Si is not zero, impurity elements B≤0.0008%, P≤0.020%, S≤0.010%, and the balance is Fe and inevitable impurities. Among them, 100≤C / N≤150.

[0011] The following will explain the mechanism of action of each alloy component of the structural steel of the application in detail, wherein the percentage symbol % represents percentage by weight:

[0012] C is the main solid solution strengthening element in the steel, and sufficient C and N in the application can inhibit surface decarburization and intergranular oxidation. If the content of C is lower than 0.38%, it is difficult to guarantee the strength and hardness of the steel plate. On the other hand, if the content of C is higher than 0.60%, the strength is too high, which deteriorates the toughness and plasticity of the steel, affects the yield strength ratio, and is not good for forming. Therefore, the content of C should be controlled in the range of 0.30%-0.60%.

[0013] Mn is a relatively cheap deoxidizer and desulfurizer, and is a necessary element for ensuring the strength and toughness of the steel. Manganese and iron can form a solid solution to improve the hardness and strength, and have relatively small influence on plasticity. Mn combines with S to form MnS, avoiding the formation of FeS at the grain boundary to cause hot cracking and affect the hot forming property of the tool steel. Meanwhile, Mn is also a good deoxidizer and increases the hardenability. If the content of Mn in the steel is low, it cannot meet the requirement of high strength and hardness, and if the content of Mn is too high, the segregation is serious, which affects the welding performance and forming property, and increases the production cost. Therefore, considering the cost and performance requirements and other factors, the content of Mn should be controlled in the range of 0.4%-1.5%.

[0014] Si is one of the common elements in steel, used as a reducing agent and deoxidizer in the steelmaking process, Si is a ferrite forming element, a non-carbide forming element, Si solid solution in ferrite improves hardenability and temper resistance, improves strength and hardness, improves wear resistance, significantly improves elastic limit, yield strength and yield ratio, and improves fatigue strength, prolongs the service life of steel. Si content more than 0.5% will promote the surface decarburization of tool steel, form loose oxide layer and intergranular oxidation and other micro crack defects, seriously affect the fatigue performance. Si≤0.5%.

[0015] Mo refines the grain of steel, improves the hardenability and thermal strength, and maintains sufficient strength and creep resistance at high temperature. In tool steel, it can improve the red hardness and inhibit the temper brittleness of alloy steel. Molybdenum is a medium-strong carbide-forming element. Mo 0.5-2.0%.

[0016] Cr is a medium-strong carbide-forming element. After adding Cr in the present application, the formed carbide reduces the carbon concentration in pearlite, reduces the microsegregation of carbon and other elements at the end of the dendrite, thereby inhibiting the microsegregation of finished steel plate, improving the spheroidization rate of pearlite, and improving the toughness and plasticity at low temperature. Cr also significantly improves strength, hardness and wear resistance, improves the oxidation resistance and corrosion resistance of steel, increases the A3 and A1 temperatures, moves the GS line to the upper left, slows down the A decomposition, and improves the hardenability; oxidation resistance improves surface quality, improves temper stability, high hardness, and improves wear resistance. Cr and C\N in the present application work together to improve corrosion resistance and high-temperature oxidation resistance, and improve surface quality. Cr 0.5-2.0%.

[0017] V improves hardenability at high temperature; forms VC, a high-melting-point, high-hardness, high-dispersion carbide, and significantly improves wear resistance; refines the grain, improves the yield ratio, and improves the temper stability; reduces the decarburization sensitivity, inhibits intergranular oxidation, and improves the surface quality.

[0018] V 0.05%-0.5%.

[0019] Ni can improve the strength of steel while maintaining good plasticity and toughness. Nickel has high corrosion resistance to acid and alkali, and has rust prevention and heat resistance at high temperature. Ni expands the γ phase zone, Ni does not form carbide but enters austenite to form infinite solid solution, and the maximum solubility in α iron is about 10%, which can be solid solution strengthened and improve the hardenability. In the present application, Ni and Mo, V work together to inhibit the formation of large lamellar pearlite, and the pearlite group is uniform and small, with a maximum diameter of not more than 20 μm, obtaining hard and fine pearlite, and the pearlite lamellar spacing is ≤0.3 μm. The ferrite grain is refined, the plasticity and toughness of the steel are improved under the condition of the same strength, especially the low temperature toughness. Ni 0.5%-1.5%.

[0020] N It is generally considered that N is a harmful element, the lower the N in the steel, the better. This is because, when the steel has a supersaturated nitrogen, placed for a long period of time or subsequently heated or annealed at 200-300 °C, the nitrogen in the steel will precipitate in the form of nitrides, it is generally believed that the generated nitrides are non-metallic inclusions, which affect the toughness and plasticity of the steel, and reduce the effect of alloying elements. The present application adopts a component design containing N, during smelting and continuous casting, by passing through the crystallizer near the continuous casting shell, N with a content of 0.003% or more is introduced to make it dissolve into the A body on the surface of the casting blank, reduce carbon diffusion, inhibit decarburization and intergranular oxidation on the surface of the casting blank, thereby improving the surface quality of the steel plate. On the other hand, the present application utilizes the strong A body forming effect of N to generate a large amount of γ phase, reduce the tendency of grain coarsening, significantly hinder the coarsening of A grains, refine the grains, and improve the low temperature toughness and welding performance of the steel. The present application limits 100≤C / N≤150, so as to ensure the effect of N on inhibiting decarburization and intergranular oxidation on the surface of the casting blank and refining the grains, thereby improving the low temperature toughness and plasticity of the steel.

[0021] P and S are both unavoidable harmful impurities in steel, their presence can seriously deteriorate the toughness of the steel, so measures should be taken to reduce the P and S content in the steel as much as possible. The present application limits the maximum P content to 0.020%, and the maximum S content to 0.010%. S exists in the form of CaS and CaAlS in steel, reducing the tendency to form MnS which is poor in hot brittleness, and the RH vacuum treatment time is not less than 20 minutes, promoting the floating of CaS, CaAlS and the like, reducing inclusions, and improving low temperature toughness. P: ≤0.025%, S: ≤0.010%.

[0022] B as an element to improve hardenability can significantly improve the hardenability of the steel plate. However, boron is too active, and it is difficult to control during smelting. If the boron content is high in high N steel, a large amount of BN compounds are formed, the austenite recrystallization is delayed, the austenitizing temperature of the steel is increased, and the boron embrittlement phenomenon occurs, causing the casting blank to crack. Therefore, the high N steel of the present application controls the boron content in the molten steel to be less than 0.0008%.

[0023] Al is used as a deoxidizing and nitrogen fixing agent during steelmaking, refines the grains, inhibits the aging of the steel, improves the toughness of the steel at low temperature, and can particularly reduce the brittle transition temperature of the steel; Al is a non-carbide forming element, which can improve the oxidation resistance of the steel, inhibit surface oxidation and decarburization, and improve the surface quality. Al 0.02%-0.5%.

[0024] As a micro-alloying element, Ca can refine grain, partially desulfurize, improve corrosion resistance, wear resistance, high temperature and low temperature performance of the steel, and increase impact toughness, fatigue strength, plasticity and welding performance of the steel; and increase cold heading property, shock resistance, hardness and contact endurance strength of the steel. Tool steel has high carbon, poor fluidity of molten steel, and inclusions are not easy to float. The present application adds Ca to change composition, quantity and form of non-metallic inclusions, accelerate molten steel flow, promote inclusions to float sufficiently, and improve steel purity. In the finished steel, various non-metallic inclusions are not more than 1.5 grade, and the steel surface finish is improved, anisotropy of the structure is eliminated, low temperature toughness is improved, and service life is prolonged. Ca 0.0005% to 0.005%.

[0025] A production method of cold-resistant tool steel, comprising:

[0026] 1) Smelting process: the steel plate of the present application is made by converter smelting, LF furnace refining, RH vacuum treatment, and rolling of cast slabs with thickness of 170 to 250 mm; the molten steel before tapping of the converter is 0.3%≤C≤0.50%; LF furnace refining is adopted, and the sulfur content after refining is ≤0.010%; RH vacuum treatment is performed for more than 20 minutes; electromagnetic stirring is used in the light press-down and crystallizer during continuous casting, the electromagnetic stirring current is 300 to 700 A, the frequency is 2.2 to 2.9 Hz, N is added to adjust the N content of the molten steel, the dynamic water volume of the crystallizer cooling water is 80 to 160 L / min, a special crystallizer protective slag is used for casting, the molten steel liquid level of the crystallizer is 750 to 850 mm, the superheat is 20 to 30℃; the continuous casting speed is 0.8 to 1.4 m / min, the secondary cooling water volume is 0.15 to 0.35 L / kg, the surface temperature deviation of the cast slab is not more than 10℃, the equiaxed crystal rate is more than 50%, and the columnar crystal end alloy liquid state micro-segregation is controlled;

[0027] 2) Cast slab treatment process: the cast slab is hot sent and hot charged, and the temperature of the cast slab before entering the walking beam furnace is more than 500℃; a weak reducing atmosphere is used in the furnace, and the total time in the furnace is 3 to 4 hours;

[0028] 3) Rolling process: high-pressure water is used for descaling before rough and finish rolling, the high-pressure water pressure is not less than 30 MPa to ensure the surface quality of the steel plate; the reduction rate of each pass of rough rolling is 15% to 35%, and the temperature is 1000 to 1250℃; the temperature difference of the whole length of the steel strip in each pass of rolling is ≤30℃; the reduction rate of each pass of finish rolling is ≤30%, and the rolling temperature is 800 to 1100℃; the temperature difference of the whole length of the steel strip in each pass of rolling is ≤20℃;

[0029] 4) cooling process: the steel plate enters the layer cooling after the finishing mill, uniformly cools, the cooling speed is 10-50℃ / s, is coiled after cooling to 500-700℃, slowly cools to below 200℃ at 3-10℃ / h; fine flake pearlite+ spheroidized pearlite mixed structure is obtained, the pearlite group diameter is ≤40μm, the pearlite flake interval is ≤0.3μm, and the spheroidized proportion is not less than 20%.

[0030] 5) heat treatment process: the steel strip does not carry out annealing treatment, directly opens flat, cuts, and processes various cutting tools and tool workpieces.

[0031] After the workpiece is processed, the workpiece is heated to 760-880℃ and oil quenched, and tempered at 300-400℃, to obtain fine martensite structure, the maximum length of the lath bundle is 20μm, and the maximum M-A island is 3μm.

[0032] The present application adopts converter smelting, LF furnace refining, and RH vacuum treatment; the molten steel before tapping is 0.3%≤C≤0.50%, to ensure that the carbon content in the billet after continuous casting of the refined steel is uniform and has no macrosegregation; after LF furnace refining, the sulfur content is ≤0.010%, Ca is added, the composition, quantity and form of non-metallic inclusions are changed, the RH vacuum treatment time is not less than 20 minutes, CaS, CaAlS and the like are promoted to float, inclusions are reduced, the steel purity is improved, the various non-metallic inclusions in the finished steel are not more than 1.0 level, the steel surface finish is improved, the anisotropy of the structure is eliminated, and the low-temperature toughness is improved; the continuous casting adopts light press-down and mold electromagnetic stirring, the electromagnetic stirring current is 300A-700A, the frequency is 2.2-2.9Hz, nitrogen is simultaneously passed, the N content of the molten steel is adjusted, the N is dissolved in the A body on the surface of the billet, the carbon diffusion is reduced, the decarburization and intergranular oxidation on the surface of the billet are inhibited, the steel plate surface quality is improved, and the low-temperature toughness of the steel is improved. Since the present application adopts high N composition design, to avoid the boron brittleness produced by N and B, the B in the molten steel of the converter is controlled to be ≤0.0008%.

[0033] The mold dynamic water quantity is 80-160L / min, special mold powder is used for pouring, the mold liquid level is 750-850mm, the superheat is 20-30℃, the inclusions and segregation are controlled, the continuous casting speed is 0.8-1.4m / min, the secondary cooling water quantity is 0.15-0.35L / kg, the billet surface temperature deviation is ensured to be not more than 10℃, the billet cooling speed is uniform, the structure is uniform, the strength difference of the same coil after rolling is ≤50MPa, the hardness difference of the same coil is ≤5HRB, the equiaxed crystal rate is more than 50%, and the columnar crystal end alloy liquid state microsegregation is controlled.

[0034] The billet is hot sent and hot charged, a step-by-step heating furnace is used for heating, the billet temperature is required to be above 500℃ before entering the heating furnace, and the billet surface temperature difference is reduced. The heating furnace uses weak reducing atmosphere, the billet surface quality is ensured, and oxidation decarburization is avoided.

[0035] Before rough and finish rolling, high pressure water is used to remove scale, the pressure of high pressure water is not less than 30MPa, and the surface quality of the steel plate is ensured. The reduction of each pass of rough rolling is 15% to 35%, and the temperature is 1000 to 1250℃, so that the temperature difference of the whole length of the steel strip in each pass is ensured to be less than or equal to 30℃, and the structure and performance are uniform. The reduction of each pass of finish rolling is less than or equal to 30%, and the rolling temperature is 800 to 1100℃, so that the temperature difference of the whole length of the steel strip in each pass is ensured to be less than or equal to 20℃, and the structure and performance are uniform, the tensile strength difference of the same roll is less than or equal to 50MPa, and the hardness difference of the same roll is less than or equal to 5HRB.

[0036] After the steel plate is discharged from the finish rolling mill, the steel plate is cooled by layer cooling, and the cooling speed is 10 to 50℃ / S, and the steel plate is coiled after being cooled to 500 to 700℃, and the steel plate is slowly cooled to below 200℃ at a cooling speed of 3 to 10℃ / h, so that a mixed structure of fine lamellar pearlite and spheroidized pearlite is obtained, the pearlite colony diameter is less than or equal to 40μm, the pearlite lamellar spacing is less than or equal to 0.3μm, and the spheroidization ratio is not less than 20%, the hot-rolled plate has excellent formability, the steel strip does not need to be annealed before being processed, and the steel strip is directly flattened and cut, and various blades and tools are processed. The finished product is heated to 760 to 880℃ and oil quenched, and tempered at 300 to 400℃, so that a fine martensite structure is obtained, the maximum length of the lath bundle is 20μm, the maximum M-A island is 3μm, the hardness at-40℃ is more than 55HRC, the yield strength is more than 600MPa, the impact energy is more than 30J, the wear resistance and impact toughness in a low-temperature environment are excellent, and the service life is obviously improved.

[0037] Compared with the prior art, the beneficial effects of the present application are:

[0038] The steel plate produced according to the above chemical composition and process is alloyed with Cr, Mo, Ni, V and N, and the process parameters such as the heating of the casting blank, the descaling pressure of rough and finish rolling, the rolling temperature, the reduction, the cooling speed and the coiling temperature are controlled, so that a mixed structure of fine lamellar pearlite and spheroidized pearlite is obtained, the pearlite colony diameter is less than or equal to 40μm, the pearlite lamellar spacing is less than or equal to 0.3μm, and the spheroidization ratio is not less than 20%, the surface of the steel plate is smooth, the intergranular oxidation depth of the surface is not more than 20μm, the tensile strength difference of the same roll is less than or equal to 50MPa, and the hardness difference of the same roll is less than or equal to 5HRB; after heat treatment, a fine martensite structure is obtained, the maximum length of the lath bundle is 20μm, the maximum M-A island is 3μm, the hardness at-40℃ is more than 55HRC, the yield strength is more than 600MPa, and the impact energy is more than 30J, the wear resistance and impact toughness in a low-temperature environment are excellent, and the service life is obviously improved. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is the metallographic structure diagram of the hot-rolled plate of the present application.

[0040] Figure 2 is the metallographic structure diagram of the workpiece after heat treatment of the tool steel of the present application. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the present application more clear, the specific embodiments of the present application are further described below in combination with examples. The following examples are used to specifically describe the present application, which are only general description of the present application and do not limit the present application.

[0042] The chemical component design of the steel in the embodiments of the present application is shown in Table 1, the production process of the embodiments is shown in Table 2, and the performance of the steel plate and the heat-treated workpiece in the embodiments is shown in Table 3.

[0043] Table 1 Chemical component and smelting process, %

[0044] Number C Si Mn P S Ni Cr V Mo Al Ca B C / N 1 0.38 0.22 0.58 0.012 0.003 0.85 0.52 0.15 0.62 0.025 0.0015 0.0004 100.68 2 0.49 0.14 1.12 0.015 0.002 0.53 0.65 0.25 0.55 0.042 0.0028 0.0001 102.45 3 0.39 0.27 0.41 0.008 0.004 0.62 1.73 0.28 1.21 0.027 0.0042 0.0002 110.00 4 0.32 0.15 0.65 0.006 0.006 0.51 0.95 0.33 0.95 0.16 0.0015 0.0005 104.35 5 0.55 0.24 0.83 0.016 0.014 0.65 0.85 0.15 0.87 0.43 0.0036 0.0003 144.00 6 0.48 0.25 0.75 0.011 0.003 0.72 0.64 0.11 0.68 0.38 0.0048 0.0007 102.13 7 0.59 0.06 0.88 0.013 0.008 0.65 0.55 0.08 0.52 0.08 0.0016 0.0004 120.77 8 0.47 0.15 1.18 0.014 0.01 0.55 0.83 0.27 0.83 0.07 0.00068 0.0003 130.56 9 0.34 0.35 0.89 0.019 0.007 1.17 0.65 0.43 0.63 0.24 0.0033 0.0001 111.89 10 0.45 0.26 1.21 0.01 0.01 0.83 1.85 0.12 1.32 0.18 0.0029 0.0002 127.83 11 0.6 0.49 0.66 0.008 0.002 1.25 1.97 0.46 1.97 0.056 0.0045 0.0002 127.14 12 0.48 0.06 1.32 0.012 0.005 1.42 0.85 0.05 0.85 0.039 0.0008 0 114.29 13 0.53 0.18 1.08 0.016 0.003 0.96 0.95 0.15 0.78 0.041 0.0027 0.0004 131.38 14 0.5 0.17 0.98 0.04 0.004 0.76 1.15 0.44 1.15 0.14 0.0025 0.0003 138.89 15 0.52 0.03 0.55 0.005 0.006 0.88 1.36 0.31 1.33 0.29 0.0009 0.0005 109.00 Comparative Example 0.53 0.25 0.6 0.012 0.008 0 0 0 0 0 0 0 -

[0045] Table 2 Production process of hot-rolled strip steel (I)

[0046]

[0047]

[0048] Table 2 Production process of hot-rolled strip steel (II)

[0049]

[0050] Table 3 Performance of steel plate and workpiece after heat treatment

[0051]

[0052]

Claims

1. A cold-resistant tool steel, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C 0.34%~0.60%, Si≤0.5%, Mn 0.4%~1.5%, Cr 0.5%~2.0%, Mo 0.5%~2.0%, Ni 0.5%~1.5%, V 0.05%~0.5%, Al 0.056%~0.5%, N 0.003%~0.005%, Ca 0.0005%~0.005%, Si is not zero, impurity elements B≤0.0008%, P≤0.020%, S≤0.010%, and the balance is Fe and unavoidable impurities; And it satisfies 100≤C / N≤150; The method for producing the cold-resistant tool steel includes: 1) Smelting process: Converter smelting, LF electric furnace refining, and RH vacuum treatment are adopted; the molten steel before tapping from the converter has a carbon content of 0.3% ≤ C ≤ 0.50%; after refining, the sulfur content is ≤ 0.010%, Ca is added, and RH vacuum treatment is carried out for more than 20 minutes; the casting superheat is 20~30℃; the continuous casting speed is 0.8~1.4m / min, and the secondary cooling water flow rate is 0.15~0.35L / kg; 2) Billet processing: The billet is hot-delivered and hot-charged, and the temperature of the billet before entering the heating furnace is above 500℃; the total time in the furnace is 3 to 4 hours. 3) Rolling process: Rough rolling: 15% to 35% reduction per pass, temperature 1000 to 1250℃, temperature difference between each pass of the steel strip ≤30℃; Finish rolling: ≤30% reduction per pass, rolling temperature 800 to 1100℃, temperature difference between each pass of the steel strip ≤20℃. 4) Cooling process: Layer cooling rate is 21-50℃ / s, cool to 500-585℃ and then roll up, and slowly cool to below 200℃ at a cooling rate of 3-10℃ / h.

2. A method for producing cold-resistant tool steel as described in claim 1, characterized in that, include: 1) Smelting process: Converter smelting, LF electric furnace refining, and RH vacuum treatment are adopted; Before tapping from the converter, the molten steel should have a carbon content of 0.3% ≤ C ≤ 0.50%; after refining, the sulfur content should be ≤ 0.010%, then Ca should be added, followed by RH vacuum treatment for at least 20 minutes; the casting superheat should be 20–30℃; the continuous casting speed should be 0.8–1.4 m / min, and the secondary cooling water flow rate should be 0.15–0.35 L / kg. 2) Billet processing: The billet is hot-delivered and hot-charged, and the temperature of the billet before entering the heating furnace is above 500℃; the total time in the furnace is 3 to 4 hours. 3) Rolling process: Rough rolling: 15% to 35% reduction per pass, temperature 1000 to 1250℃, temperature difference between each pass of the steel strip ≤30℃; Finish rolling: ≤30% reduction per pass, rolling temperature 800 to 1100℃, temperature difference between each pass of the steel strip ≤20℃. 4) Cooling process: Layer cooling rate is 21-50℃ / s, cool to 500-585℃ and then roll up, and slowly cool to below 200℃ at a cooling rate of 3-10℃ / h.

3. The method for producing a cold-resistant tool steel according to claim 2, characterized in that, The thickness of the cast billet is 170-250 mm.

4. The method for producing a cold-resistant tool steel according to claim 2, characterized in that, The continuous casting process employs light pressure reduction and electromagnetic stirring in the crystallizer. The electromagnetic stirring current is 300A to 700A, and the frequency is 2.2 to 2.9Hz. At the same time, nitrogen is added to adjust the nitrogen content of the molten steel. The dynamic flow rate of cooling water in the crystallizer is 80 to 160L / min, and the molten steel level in the crystallizer is 750 to 850mm.

5. The method for producing a cold-resistant tool steel according to claim 2, characterized in that, High-pressure water descaling is performed before both roughing and finishing rolling, with a pressure of not less than 30 MPa.

6. The method for producing a cold-resistant tool steel according to claim 2, characterized in that, Step 4 above yields a mixed structure of lamellar pearlite and spheroidized pearlite, with pearlite cluster diameter ≤ 40 μm and pearlite lamellar spacing ≤ 0.3 μm.

7. A heat treatment process for cold-resistant tool steel workpieces, characterized in that, The cold-resistant tool steel workpiece is processed using the cold-resistant tool steel described in claim 1. The heat treatment process of the cold-resistant tool steel workpiece is oil quenching at 760-870℃ and tempering at 300-400℃.

8. The heat treatment process for cold-resistant tool steel workpieces according to claim 7, characterized in that, The cold-resistant tool steel workpiece after heat treatment has a martensitic structure with lath bundles up to 20 μm in length and MA islands up to 3 μm in size.

9. The heat treatment process for cold-resistant tool steel workpieces according to claim 7, characterized in that, After heat treatment, cold-resistant tool steel workpieces have a hardness of over 55 HRC, a yield strength of over 600 MPa, and an impact energy of over 30 J at -40℃.

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