A tool steel and a method for producing the same

Abstract

The application relates to a tool steel and a preparation method thereof, and the chemical composition of the tool steel comprises C, Si, Mn, P, S, Cr, Mo, Ni, V, RE and Fe; wherein the content of C is 0.25-0.35% in mass fraction, the content of Si is 0.20-0.50% in mass fraction, the content of Mn is 0.90-1.10% in mass fraction, the content of P is <=0.020% in mass fraction, the content of S is <=0.010% in mass fraction, the content of Cr is 3.00-4.20% in mass fraction, the content of Mo is 0.50-1.40% in mass fraction, the content of Ni is 0.50-0.90% in mass fraction, the content of V is 0.30-0.50% in mass fraction, and the content of RE is 0.001-0.010% in mass fraction; the metallographic structure of the tool steel comprises martensite, bainite and residual austenite. The application realizes a good match between high strength and high plasticity, thereby improving the mechanical properties of the tool steel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel preparation, in particular to a tool steel and a preparation method thereof. BACKGROUND

[0002] Alloy tool steel is a kind of steel grade based on carbon tool steel with the addition of alloy elements such as chromium, molybdenum, tungsten and vanadium to improve hardenability, toughness, wear resistance and heat resistance, and is widely used.

[0003] However, in recent years, with the upgrading of user requirements, the requirements for alloy tool steel are getting higher and higher. With the increase of hardness and strength, the steel is prone to break during pickling, and annealing must be performed before pickling to achieve material softening, which is a relatively complex process. SUMMARY

[0004] The present application provides a tool steel and a preparation method thereof to solve the technical problem of how to improve the mechanical properties of the tool steel.

[0005] In a first aspect, the present application provides a tool steel, the chemical composition of the tool steel comprising:

[0006] C, Si, Mn, P, S, Cr, Mo, Ni, V, RE and Fe; wherein, in terms of mass fraction,

[0007] The content of C is 0.25% to 0.35%, the content of Si is 0.20% to 0.50%, the content of Mn is 0.90% to 1.10%, the content of P is ≤0.020%, the content of S is ≤0.010%, the content of Cr is 3.00% to 4.20%, the content of Mo is 0.50% to 1.40%, the content of Ni is 0.50% to 0.90%, the content of V is 0.30% to 0.50%, and the content of RE is 0.001% to 0.010%.

[0008] The metallographic structure of the tool steel comprises martensite, bainite and residual austenite.

[0009] Optionally, the content of C is 0.28% to 0.34%, the content of Si is 0.20% to 0.40%, the content of Mn is 0.90% to 1.10%, the content of P is ≤0.015%, the content of S is ≤0.005%, the content of Cr is 3.50% to 4.20%, the content of Mo is 1.00% to 1.40%, the content of Ni is 0.50% to 0.80%, the content of V is 0.30% to 0.40%, and the content of RE is 0.002% to 0.010%.

[0010] Optionally, the RE comprises at least one of La and Ce.

[0011] Optionally, the volume fraction of the residual austenite is ≤10%.

[0012] Optionally, the tool steel satisfies the following mechanical properties: yield strength ≥1000MPa, tensile strength ≥1700MPa, hardness 450HV-600HV, and elongation ≥15%.

[0013] In a second aspect, the application provides a preparation method of the tool steel of the first aspect, and the method comprises:

[0014] heating the slab, and then rolling to obtain a hot-rolled plate;

[0015] coiling the hot-rolled plate, controlling the coiling temperature, and then cooling under a set cooling rate to obtain the tool steel.

[0016] Optionally, the coiling temperature is 550-750℃.

[0017] Optionally, the set cooling rate is ≤0.5℃ / s.

[0018] Optionally, the heating temperature is 1150-1300℃.

[0019] Optionally, the final rolling temperature of the rolling is 800-950℃.

[0020] The above technical solution provided by the embodiments of the application has the following advantages compared with the prior art:

[0021] The content of C is 0.25% to 0.35% and the content of Mn is 0.90% to 1.10%, which can increase the stability of residual austenite, ensure the plasticity and toughness of the tool steel; the content of Si is 0.20% to 0.50%, which can improve the elastic limit, yield point and tensile strength of the tool steel; the content of Cr is 3.50% to 4.20%, which can improve the wear resistance, high temperature strength and hardenability of the tool steel; the content of P is ≤0.020% and the content of S is ≤0.010%, which can reduce the generation of sulfide inclusions; the content of Mo is 0.50% to 1.40%, which can improve the hardenability of the tool steel; the content of Ni is 0.50% to 0.90%, which can improve the strength and plasticity of the tool steel at the same time, and the brittle temperature is very low; the content of V is 0.30% to 0.50%, which can increase the elastic limit of the steel, and increase the high temperature durable strength and creep resistance of the steel at the same time; the content of RE is 0.001% to 0.010%, which can reduce the segregation of C and other elements to the grain boundary, purify the molten steel, improve the nature, form and distribution of inclusions, and improve the hardness and impact toughness of the tool steel; through the synergistic effect of the above alloying elements, the microstructure grains of the tool steel can be refined, so as to improve the tensile strength and hardness of the tool steel; the dispersed residual austenite is introduced into the martensite and bainite hard phase microstructure, which can improve the plasticity and toughness of the tool steel, realize the good matching of high strength and high plasticity, and improve the mechanical properties of the tool steel. BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings incorporated into the specification and forming a part thereof illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0024] Figure 1 A metallographic structure diagram of a tool steel according to some embodiments of the present application;

[0025] Figure 2 An EBSD diagram of 4% residual austenite content in a metallographic structure of a tool steel according to some embodiments of the present application;

[0026] Figure 3 A flowchart of a preparation method of a tool steel according to some embodiments of the present application. DETAILED DESCRIPTION

[0027] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0028] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values in the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers in the described range, such as 1, 2, 3, 4, 5 and 6, which applies to any range. In addition, whenever a numerical range is indicated in the present application, it refers to any cited number (fraction or integer) in the indicated range.

[0029] In the present application, in addition, in the description of the specification of the present application, the terms “include”, “contain” and the like mean “include but not limited to”. In the present application, “at least one” means one or more, and “multiple” means two or more. “At least one”, “at least one of the following” or the like means any combination of the items, including any combination of single item or multiple items. For example, “at least one of a, b or c”, or “at least one of a, b and c” can mean a, b, c, a-b (i.e. a and b), a-c, b-c or a-b-c, wherein a, b and c can be single or multiple.

[0030] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0031] In a first aspect, the present application provides a tool steel, the chemical composition of the tool steel comprising:

[0032] C, Si, Mn, P, S, Cr, Mo, Ni, V, RE and Fe; wherein, in terms of mass fraction,

[0033] The content of C is 0.25%-0.35%, the content of Si is 0.20%-0.50%, the content of Mn is 0.90%-1.10%, the content of P is ≤0.020%, the content of S is ≤0.010%, the content of Cr is 3.00%-4.20%, the content of Mo is 0.50%-1.40%, the content of Ni is 0.50%-0.90%, the content of V is 0.30%-0.50%, and the content of RE is 0.001%-0.010%;

[0034] The metallographic structure of the tool steel comprises martensite, bainite and residual austenite.

[0035] In some embodiments, the content of C is 0.28%-0.34%, the content of Si is 0.20%-0.40%, the content of Mn is 0.90%-1.10%, the content of P is ≤0.015%, the content of S is ≤0.005%, the content of Cr is 3.50%-4.20%, the content of Mo is 1.00%-1.40%, the content of Ni is 0.50%-0.80%, the content of V is 0.30%-0.40%, and the content of RE is 0.002%-0.010%.

[0036] In the embodiments of the present application, the grain size of the tool steel can be refined through the synergistic effect of alloying of alloying elements, so as to improve the tensile strength and hardness of the tool steel; the plasticity and toughness of the tool steel can be improved through introduction of dispersed residual austenite in the martensite and bainite hard phase structure, so as to realize good matching of high strength and high plasticity, thereby improving the mechanical properties of the tool steel

[0037] C and Mn as elements to stabilize austenite can increase the stability of residual austenite, ensure its stability to room temperature, and also be beneficial to increase the content of residual austenite. When the content of Mn is too high, serious manganese segregation can form brittle banded structure. Lower C content, combined with appropriate Mn content, ensures the plasticity and toughness of the steel. The role of Si is to increase the elastic limit, yield point and tensile strength of the steel, and too high silicon content makes the steel decarburization tendency obvious, resulting in the generation of surface micro-cracks. P has a strong solid solution strengthening effect to increase the strength of the steel, but P is an element with strong segregation tendency, and usually also causes the co-segregation of sulfur and manganese, which is not conducive to the uniformity of the product organization. S is easy to form manganese sulfide inclusions with manganese, and the more the number and the larger the size of the sulfides, the more unfavorable to the fatigue performance. Cr has a beneficial effect on the wear resistance, high temperature strength and hardenability of the steel, and can effectively improve the high temperature strength of the steel within the above numerical range; when the chromium addition amount is too high, although the tensile strength increases, the elongation will decrease significantly, and carbide precipitation will also occur, resulting in cracking. Mo can improve the hardenability of the steel, and at the same time inhibit the decrease of plasticity and toughness due to too high chromium content, and improve the thermal strength of the steel, but the increase of molybdenum content will bring a substantial increase in cost. Ni can increase the strength and plasticity of the steel at the same time, and its embrittlement temperature is extremely low. V cooperates with Mn and Cr in the steel to increase the elastic limit of the steel, and at the same time increases the high temperature endurance strength and creep resistance of the steel. Appropriate amount of rare earth element RE can reduce the segregation of carbon and other elements to grain boundaries, purify the steel liquid, improve the nature, form and distribution of inclusions, and also can improve the hardness, impact toughness and other properties of the steel. For example, the content of C can be 0.25%, 0.28%, 0.30%, 0.33%, 0.355, etc., the content of Si can be 0.20, 0.30, 0.40, 0.50, etc., the content of Mn can be 0.90%, 1.0%, 1.10%, etc., the content of P can be 0.02%, 0.015%, 0.018%, etc., the content of Cr can be 3.0%, 3.5%, 4.0%, 4.2%, etc., the content of Mo can be 0.5%, 0.7%, 0.9%, 1.1%, 1.4%, etc., the content of Ni can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, etc., the content of V can be 0.30%, 0.35%, 0.4%, 0.45%, 0.5%, etc., and the content of RE can be 0.001%, 0.003%, 0.005%, 0.008%, 0.01%, etc.

[0038] In some embodiments, the RE includes at least one of La and Ce.

[0039] In the embodiments of the present application, the RE can be La, Ce, or a mixture of La and Ce.

[0040] In some embodiments, the volume fraction of the residual austenite is ≤10%.

[0041] In the embodiments of the present application, the residual austenite is introduced into the hard phase martensite structure, which can improve the elongation of the material, and the effect mainly depends on the volume fraction and stability of the residual austenite; the austenite is a soft phase, and too high volume fraction will cause the decrease of the strength and hardness of the material. For example, the volume fraction of the residual austenite can be 10%, 9%, 8%, 7%, etc. Figure 1 A metallographic structure diagram of a tool steel according to some embodiments of the present application; Figure 2 An EBSD diagram of 4% residual austenite content in the metallographic structure of a tool steel according to some embodiments of the present application; see Figures 1-2 .

[0042] In some embodiments, the tool steel satisfies the following mechanical properties: yield strength ≥1000 MPa, tensile strength ≥1700 MPa, hardness 450HV-600HV, and elongation ≥15%.

[0043] In the embodiments of the present application, the tool steel has excellent mechanical properties: yield strength ≥1000 MPa, tensile strength ≥1700 MPa, hardness 450HV-600HV, and elongation ≥15%.

[0044] In a second aspect, the present application provides a preparation method of the tool steel of the first aspect, Figure 3 A flowchart of a preparation method of a tool steel according to some embodiments of the present application; see Figure 3 , the method comprising:

[0045] S1, heating the slab and then rolling to obtain a hot-rolled plate;

[0046] In some embodiments, the heating temperature is 1150-1300°C.

[0047] In the embodiments of the present application, the heating temperature is limited, the composition of the slab is uniformly distributed, and the high-temperature deformation resistance of the steel is reduced, which prepares for the subsequent rolling process and reduces the rolling load. For example, the heating temperature can be 1150°C, 1160°C, 1170°C, 1180°C, 1190°C, 1200°C, 1220°C, 1240°C, 1260°C, 1280°C, etc. The heating time in the furnace can be ≥180 min, which can fully austenitize the slab and further homogenize the composition.

[0048] In some embodiments, the finish rolling temperature of the rolling is 800-950°C.

[0049] In the embodiments of the present application, the rolling includes rough rolling and finish rolling, and the finish rolling temperature of the rolling is also the finish rolling temperature of the finish rolling. The finish rolling temperature is limited to refine the austenite grains and reduce the rolling load. For example, the finish rolling temperature can be 800 DEG C, 830 DEG C, 850 DEG C, 880 DEG C, 900 DEG C, 930 DEG C, 950 DEG C, etc.

[0050] S2, the hot-rolled plate is coiled, and the coiling temperature is controlled, and then the coiling temperature is cooled at a set cooling rate to obtain the tool steel.

[0051] In some embodiments, the coiling temperature is 550 DEG C to 750 DEG C.

[0052] In some embodiments, the set cooling rate is ≤0.5 DEG C / s.

[0053] In the embodiments of the present application, the coiling temperature and the cooling rate after coiling are limited to obtain the expected mechanical properties, while avoiding surface cracks caused by excessive residual stress. For example, the coiling temperature can be 550 DEG C, 580 DEG C, 600 DEG C, 630 DEG C, 650 DEG C, 680 DEG C, 700 DEG C, 720 DEG C, 750 DEG C, etc. The set cooling rate can be 0.5 DEG C / s, 0.4 DEG C / s, 0.3 DEG C / s, 0.2 DEG C / s, etc.

[0054] The preparation method of the tool steel includes the following steps: pretreating molten iron, smelting to obtain molten steel, continuous casting to obtain a slab, heating the slab, rough rolling and finish rolling to obtain a hot-rolled plate, cooling the hot-rolled plate, and coiling to obtain the tool steel.

[0055] The preparation method of the tool steel is based on the tool steel described above. The specific chemical composition of the tool steel can refer to the embodiments described above. Since the preparation method of the tool steel adopts part or all of the technical solutions of the embodiments described above, it at least has all the beneficial effects brought by the technical solutions of the embodiments described above, which will not be repeated here.

[0056] In summary, by adding alloying elements such as Cr, Mo, Ni, and V in the steel, the wear resistance, strength, and hardenability are improved. By controlling the alloy composition and production parameters, the tool steel prepared can be directly pickled without annealing, thereby solving the problem of broken strips of high-strength alloy tool steel directly pickled without annealing.

[0057] The present application is further described in conjunction with the following specific examples. It should be understood that these examples are only intended to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods in the following examples, if not otherwise specified, are generally determined according to the national standards. If there is no corresponding national standard, the general international standards, the conventional conditions, or the conditions suggested by the manufacturers are used.

[0058] Example 1

[0059] A tool steel, the chemical composition of which includes, in mass fraction: C: 0.35%, Si: 0.38%, Mn: 0.90%, P: 0.010%, S: 0.001%, Cr: 3.80%, Mo: 0.50%, Ni: 0.60%, V: 0.35%, La+Ce: 0.0048%, and the rest is Fe and inevitable impurities.

[0060] A method for preparing a tool steel, comprising: hot metal pretreatment, converter smelting, refining, continuous casting, and hot rolling. The hot rolling is performed at a furnace time of 210 min and a heating temperature of 1250℃. The finish rolling temperature of the finish rolling is 880℃, the coiling temperature is 700℃, and the cooling rate after coiling is 0.1℃ / s.

[0061] The metallographic structure of the tool steel is: martensite, bainite, and 4% residual austenite.

[0062] The mechanical properties are: yield strength 1040 MPa, tensile strength 1750 MPa, hardness 524 HV, and elongation 15%.

[0063] Example 2

[0064] A tool steel, the chemical composition of which includes, in mass fraction: C: 0.31%, Si: 0.50%, Mn: 1.00%, P: 0.010%, S: 0.0005%, Cr: 4.20%, Mo: 1.40%, Ni: 0.60%, V: 0.35%, La+Ce: 0.0020%, and the rest is Fe and inevitable impurities.

[0065] A method for preparing a tool steel, comprising: hot metal pretreatment, converter smelting, refining, continuous casting, and hot rolling. The hot rolling is performed at a furnace time of 210 min and a heating temperature of 1250℃. The finish rolling temperature of the finish rolling is 880℃, the coiling temperature is 700℃, and the cooling rate after coiling is 0.005℃ / s.

[0066] The metallographic structure of the tool steel is: martensite, bainite, and 8% residual austenite.

[0067] The mechanical properties are: yield strength 1150 MPa, tensile strength 1900 MPa, hardness 597 HV, and elongation 17%.

[0068] Example 3

[0069] A tool steel, the chemical composition of which comprises, in mass fraction: C: 0.25%, Si: 0.28%, Mn: 1.00%, P: 0.015%, S: 0.0005%, Cr: 3.00%, Mo: 1.15%, Ni: 0.90%, V: 0.35%, La+Ce: 0.009%, the balance being Fe and inevitable impurities.

[0070] A tool steel preparation method, comprising: hot metal pretreatment, converter smelting, refining, continuous casting, hot rolling. The hot rolling in-furnace time is 190 min, the heating temperature is 1260℃. The finish rolling temperature of finish rolling is 900℃, the coiling temperature is 650℃, and the cooling rate after coiling is 0.005℃ / s.

[0071] The metallographic structure of the tool steel is: martensite, bainite and 1% residual austenite;

[0072] The mechanical properties are: yield strength 1100MPa, tensile strength 1800MPa, hardness 464HV, and elongation 16.4%.

[0073] Comparative Example 1

[0074] A tool steel, the chemical composition of which comprises, in mass fraction: C: 0.33%, Si: 0.24%, Mn: 0.76%, P: 0.008%, S: 0.001%, Cr: 3.57%, Mo: 2.23%, Ni: 0.85%, V: 0.37%, the balance being Fe and inevitable impurities.

[0075] A tool steel preparation method, comprising: hot metal pretreatment, converter smelting, refining, continuous casting, hot rolling. The hot rolling in-furnace time is 210 min, the heating temperature is 1250℃. The finish rolling temperature of finish rolling is 880℃, the coiling temperature is 700℃, and the cooling rate after coiling is 0.1℃ / s.

[0076] The metallographic structure of the tool steel is: ferrite and pearlite.

[0077] The mechanical properties are: yield strength 1182MPa, tensile strength 1517MPa, hardness 52.0HRC, and elongation 7.5%.

[0078] Comparative Example 2

[0079] A tool steel, the chemical composition of which comprises, in mass fraction: C: 0.32%, Si: 0.35%, Mn: 0.65%, P: 0.009%, S: 0.003%, Cr: 3.09%, Mo: 2.02%, Ni: 0.32%, V: 0.36%, the balance being Fe and inevitable impurities.

[0080] A tool steel preparation method, comprising: hot metal pretreatment, converter smelting, refining, continuous casting, hot rolling. Wherein the hot rolling furnace time is 210 min, the heating temperature is 1250℃. The finish rolling temperature of finish rolling is 880℃, the coiling temperature is 700℃, and the cooling rate after coiling is 0.1℃ / s.

[0081] The metallographic structure of the tool steel is tempered sorbite.

[0082] The mechanical properties are: yield strength 1191MPa, tensile strength 1585MPa, hardness 50.1HRC, and elongation 12.4%.

[0083] In conclusion, the tool steel provided by the application has high strength and high plasticity, so that direct pickling without annealing can be realized, and the defects of high-strength alloy tool steel direct pickling without annealing are avoided. The chemical composition of the tool steel provided by Comparative Examples 1-2 is not within the scope of the embodiments of the application, and the strength and plasticity are low.

[0084] The above only describes the specific embodiments of the application, so that those skilled in the art can understand or implement the application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A tool steel characterized by, The tool steel comprises the following chemical components: C, Si, Mn, P, S, Cr, Mo, Ni, V, RE and Fe, wherein the mass fractions of the components are as follows: The content of C is 0.25%-0.35%, the content of Si is 0.20%-0.50%, the content of Mn is 0.90%-1.10%, the content of P is ≤0.020%, the content of S is ≤0.010%, the content of Cr is 3.00%-4.20%, the content of Mo is 0.50%-1.40%, the content of Ni is 0.50%-0.90%, the content of V is 0.30%-0.50%, and the content of RE is 0.001%-0.010%. The metallographic structure of the tool steel comprises martensite, bainite and residual austenite, and the volume fraction of the residual austenite is ≤10%. The tool steel satisfies the following mechanical properties: the yield strength is ≥1000MPa, the tensile strength is ≥1700MPa, the hardness is 450HV-600HV, and the elongation is ≥15%.

2. Tool steel according to claim 1, characterized in that The content of C is 0.28%-0.34%, the content of Si is 0.20%-0.40%, the content of Mn is 0.90%-1.10%, the content of P is ≤0.015%, the content of S is ≤0.005%, the content of Cr is 3.50%-4.20%, the content of Mo is 1.00%-1.40%, the content of Ni is 0.50%-0.80%, the content of V is 0.30%-0.40%, and the content of RE is 0.002%-0.010%.

3. The tool steel of claim 1, wherein, The RE comprises at least one of La and Ce.

4. A method of producing the tool steel according to any one of claims 1 to 3, characterized by, The method comprises the following steps: heating a slab, and then rolling the slab to obtain a hot-rolled plate; coiling the hot-rolled plate, controlling the coiling temperature, and then cooling the hot-rolled plate at a set cooling rate to obtain the tool steel.

5. The method of claim 4, wherein, The coiling temperature is 550°C-750°C.

6. The method of claim 4, wherein, The set cooling rate is ≤0.5°C / s.

7. The method of claim 4, wherein, The heating temperature is 1150°C-1300°C.

8. The method of claim 4, wherein, The finishing temperature of the rolling is 800°C-950°C.

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