High-thermal-conductivity hot stamping die steel and heat treatment method thereof

Abstract

The invention discloses hot stamping die steel with high thermal conductivity. The hot stamping die steel comprises the following components: 0.30-0.35% of C; 0.03 to 0.15% of Si; mn: 0.05 to 0.20%; 0.10% to 0.30% of Cr; 3.00% to 3.30% of Mo; 1.10% to 1.30% of W; 2.00% to 2.30% of Ni; 0.70% to 0.90% of Co; 0.15% to 0.20% of Cu; 0.001% to 0.002% of Ce; la: 0.0005% to 0.001%; and the balance of Fe and impurities. According to the method, V is not used, meanwhile, the content of alloy elements such as Si and Cr is greatly reduced, the heat conductivity of steel is improved, the content of elements such as Mo, Ni, Cu, W, Co, La and Ce is improved, the purpose of age hardening is achieved, a special age hardening heat treatment process (namely a solid solution and age hardening mode) is combined, the hardness of the produced hot stamping die steel reaches 47-49 HRC, and the hardness of the produced hot stamping die steel is greatly improved. And the high-temperature strength, the high-temperature wear resistance and the high-temperature thermal fatigue performance of the material are greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of die steel and heat treatment thereof, in particular to a high thermal conductivity hot stamping die steel and a heat treatment method thereof, which are used for manufacturing a high-strength steel plate hot stamping die. Background Art

[0002] With the increasing energy crisis and environmental problems, automobile lightweighting has become an inevitable path for the sustainable development of the world's automobile industry. High-strength steel plates are widely used in high-strength vehicle bodies to simultaneously achieve lightweighting and improve collision safety. High-temperature high-strength steel plates are stamped and quenched in the mold, and the mold must have high thermal conductivity, thermal strength, wear resistance, and high-temperature fatigue resistance.

[0003] The thermal conductivity of H13 steel used in the early stage was 29W / (m·K) at 400℃, and its thermal fatigue performance was poor. Later, ASSAB reduced silicon and increased molybdenum to launch 8418 die steel (DIEVAR steel), which has higher impact toughness and thermal fatigue performance. However, the thermal conductivity of 8418 die steel is only 30.5W / (m·K) at 400℃, which cannot meet the harsh conditions of hot stamping of ultra-thick plate high-strength steel. It is urgent to develop die materials that can meet the needs of hot stamping.

[0004] In addition, hot stamping die steel is generally heat treated by quenching and hardening. In order to improve the hardness and strength of the steel and meet the use requirements, alloy elements such as Si, Cr, and V are added to improve the hardenability of the steel. However, these elements will greatly reduce the thermal conductivity of the material, making the material's high-temperature strength, high-temperature wear resistance, and high-temperature thermal fatigue performance unsatisfactory.

[0005] Comparative analysis of the present invention and the prior art:

[0006] By entering the keywords of the present invention to search Chinese and foreign patents, it is found that the patent publication numbers of hot stamping die steel and its manufacturing method related to this patent are:

[0007] (1) The invention patent with Chinese patent publication number CN 108774712 A discloses an ultra-high thermal conductivity hot stamping die steel and a manufacturing method thereof. The mass percentage of each alloy element of the steel is: C 0.40-0.50%; Si≤0.30%; Cr≤0.30%; Mn 0.80-1.5%; Ni 0.80-1.50%; Mo 1.30-2.0%; V 1.30-2.0%; trace B; balance Fe. The contents of Si, Cr and V in the main components are higher than those of the present invention, and the heat treatment adopts high temperature quenching and multiple high temperature tempering.

[0008] (2) The invention patent with Chinese patent publication number CN 109023113 B discloses a method for preparing a variable strength hot stamping die material. The mass percentage of each alloy element of the steel is: C 0.40-0.55%, Si≤0.50%, Mn 0.94-1.50%, Cr 2.50-2.93%, Mo 2.43-3.00%, V 0.50-0.80%, P≤0.010%, S≤0.001%, Fe balance, and the mass ratio of Mn, Mo and Cr is 1-1.2:2.0-2.1:3.0-3.2. The contents of Si, Cr and V in the main components are higher than those of the present invention, and the heat treatment adopted is quenching and tempering heat treatment.

[0009] The present invention reduces Si and Cr, eliminates V, increases Mo, Ni, Cu, W, Co, La and Ce, and adopts a low-energy consumption heat treatment process of aging hardening to manufacture high thermal conductivity hot stamping die steel, so that the thermal conductivity of the high thermal conductivity hot stamping die steel at 400°C is increased by nearly 30% compared with 8418 die steel. At the same time, the heat treatment process is simplified, the complicated heat treatment process of 8418 including cumbersome ultra-fine treatment, vacuum quenching and multiple high-temperature tempering is avoided, and the energy consumption of heat treatment is reduced. Summary of the invention

[0010] The object of the present invention is to provide a high thermal conductivity hot stamping die steel and a heat treatment method thereof, wherein V is not used, and at the same time, the content of alloy elements such as Si and Cr is greatly reduced to improve the thermal conductivity of the steel, and the content of elements such as Mo, Ni, Cu, W, Co, La, and Ce is increased to achieve the purpose of aging hardening. Combined with a special aging hardening heat treatment process (i.e., a solid solution plus aging hardening method), the hardness of the produced hot stamping die steel reaches 47 to 49 HRC, which meets the application requirements of the steel, and greatly improves the high temperature strength, high temperature wear resistance and high temperature thermal fatigue performance of the material.

[0011] To achieve the above-mentioned purpose, the present invention provides a technical solution: a high thermal conductivity hot stamping die steel, whose alloy composition includes the following elements, calculated by element weight percentage: C: 0.30-0.35%; Si: 0.03-0.15%; Mn: 0.05-0.20%; Cr: 0.10-0.30%; Mo: 3.00-3.30%; W: 1.10-1.30%; Ni: 2.00-2.30%; Co: 0.70-0.90%; Cu: 0.15-0.20%; Ce: 0.001-0.002%; La: 0.0005-0.001%; ​​the rest is Fe and impurities.

[0012] More preferably, the impurities are S, P, N, O, and H.

[0013] More preferably, the alloy further comprises 0.15-0.2% copper, 0.001-0.002% cerium, and 0.0005-0.001% lanthanum.

[0014] The present invention also provides a heat treatment method for high thermal conductivity hot stamping die steel, comprising the following steps:

[0015] 1) Forging the die steel according to the weight percentage of the elements in the high thermal conductivity hot stamping die steel, performing a solution water cooling treatment at 1030-1050° C. after forging, and then tempering at 500-530° C. for 2-3 hours, adjusting the hardness to 30-35 HRC, and then performing rough machining of the die;

[0016] 2) After rough machining of the mold, age harden at 580-620℃ for 9-12h and adjust the hardness to 47-49HRC for use.

[0017] Further preferably, the rough processing of the mold is sawing and machining into the mold.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Generally, hot stamping die steel is heat treated by quenching hardening. In order to improve the hardness and strength of the steel and meet the use requirements, alloy elements such as Si, Cr, and V are added to improve the hardenability of the steel. However, these elements will greatly reduce the thermal conductivity of the material. To solve this contradiction, the present invention does not use V (V is used in existing hot stamping die steels), and at the same time greatly reduces the content of alloy elements such as Si and Cr to improve the thermal conductivity of the steel, and increases the content of elements such as Mo, Ni, Cu, W, Co, La, and Ce to achieve the purpose of aging hardening. Combined with a special aging hardening heat treatment process (i.e., solid solution plus aging hardening), the hardness of the produced hot stamping die steel reaches 47-49HRC, which meets the application requirements of the steel.

[0020] 2. The high thermal conductivity hot stamping die steel of the present invention reduces the content of Si, Cr, Mn, and V, and increases Co (Co is not used in existing hot stamping die steels). This can reduce the hardenability of the steel, reduce the content of martensite structure generated in the steel during the heat treatment process, and improve the high temperature creep resistance of the steel.

[0021] 3. The high thermal conductivity hot stamping die of the present invention increases the content of elements such as Mo, Ni, Cu, W, La, and Ce. After high-temperature solid solution, these elements can improve the MC type and M type when kept at 530-620°C. 2The C alloy carbide dispersion precipitation hardening effect can reach a hardness of 43 to 50 HRC, so as to achieve the purpose of replacing quenching hardening (the present invention adopts the method of solid solution plus aging hardening instead of quenching hardening), and greatly improves the high temperature strength, high temperature wear resistance and high temperature thermal fatigue performance of the material.

[0022] 4. The heat treatment method for high thermal conductivity hot stamping die steel of the present invention is achieved by solution treatment plus aging hardening, avoiding the complex heat treatment process of ultrafine treatment, vacuum quenching, and three high-temperature tempering required by the heat treatment process of 8418 die steel, shortening the heat treatment time by more than half and saving energy consumption.

[0023] 5. The thermal conductivity of the present invention is about 30% higher than that of 8418 die steel under the condition of 48HRC hardness, which meets the cooling capacity requirements of thick plate hot stamping dies.

[0024] 6. The present invention shortens the cooling time of the high-temperature and high-strength steel plate in the mold, speeds up the production rhythm, and thus saves production costs.

[0025] 7. The high thermal conductivity hot stamping die steel obtained by combining the high thermal conductivity hot stamping die steel and the heat treatment method of the present invention has excellent high temperature thermal conductivity, high temperature wear resistance, thermal stability, and high temperature thermal fatigue performance.

[0026] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a test comparison chart of thermal conductivity of the high thermal conductivity hot stamping die steel of the present invention and 8418 die steel at different temperatures when the hardness is 48HRC. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] Example 1

[0031] The present embodiment provides a high thermal conductivity hot stamping die steel, comprising the following components in parts by weight: C: 0.30-0.35%; Si: 0.03-0.15%; Mn: 0.05-0.20%; Cr: 0.10-0.30%; Mo: 3.00-3.30%; W: 1.10-1.30%; Ni: 2.00-2.30%; Co: 0.70-0.90%; Cu: 0.15-0.20%; Ce: 0.001-0.002%; La: 0.0005-0.001%; ​​the rest is Fe and impurities.

[0032] The high thermal conductivity hot stamping die steel of the present invention does not use V (V is used in existing hot stamping die steels), and at the same time greatly reduces the content of alloy elements such as Si and Cr to improve the thermal conductivity of the steel, and increases the content of elements such as Mo, Ni, Cu, W, Co, La, Ce, etc. to achieve the purpose of aging hardening. Combined with a special aging hardening heat treatment process (i.e., a solid solution plus aging hardening method), the hardness of the produced hot stamping die steel reaches 47-49HRC, which meets the application requirements of the steel.

[0033] Example 2

[0034] The present embodiment differs from the first embodiment in that the impurities are S, P, N, O, and H.

[0035] Example 3

[0036] The present embodiment differs from the embodiment 1 in that it further comprises 0.15-0.2% copper, 0.001-0.002% cerium, and 0.0005-0.001% lanthanum.

[0037] In this embodiment, the addition of cerium and lanthanum elements can prevent grain coarsening. Ni, W, Mo, and Co are all effective elements for comprehensively improving wear resistance, high-temperature thermal strength, and thermal conductivity.

[0038] Example 4

[0039] A heat treatment method for high thermal conductivity hot stamping die steel comprises the following steps:

[0040] 1) Forging the die steel according to the weight percentage of the elements in the high thermal conductivity hot stamping die steel in Examples 1 to 3, performing a solution water cooling treatment at 1030-1050° C. after forging, and then tempering at 500-530° C. for 2-3 hours, adjusting the hardness to 30-35 HRC, and then performing rough machining of the die;

[0041] 2) After rough machining of the mold, age harden at 580-620℃ for 9-12h and adjust the hardness to 47-49HRC for use.

[0042] The heat treatment method for high thermal conductivity hot stamping die steel of the present invention is achieved by solution treatment plus aging hardening, avoiding the complex heat treatment process of ultrafine treatment, vacuum quenching, and three high-temperature tempering required by the 8418 die steel heat treatment process, shortening the heat treatment time by more than half, saving energy consumption, and greatly improving the high-temperature strength, high-temperature wear resistance and high-temperature thermal fatigue performance of the material.

[0043] Example 5

[0044] A high thermal conductivity hot stamping die steel, comprising the following components in parts by weight:

[0045] C: 0.33%; Si: 0.06%; Mn: 0.09%; Cr: 0.24%; Mo: 3.11%; W: 1.13%; Ni: 2.12%; Co: 0.78%; Cu: 0.19%; Ce: 0.0013%; La: 0.0007%; the rest is iron and impurities.

[0046] The heat treatment method of the high thermal conductivity hot stamping die steel adopts the following steps:

[0047] 1) Forging the die steel according to the weight percentage of the elements in the above-mentioned high thermal conductivity hot stamping die steel, after forging, the die steel is subjected to a solution treatment at 1030-1040°C for 2h and water cooling treatment, followed by tempering at 510-520°C for 3h, adjusting the hardness to 30-34HRC, and then rough machining of the die;

[0048] 2) After rough machining of the mold, age harden at 590-600℃ for 10 hours and adjust the hardness to 48-49HRC for use.

[0049] The performance test experimental data is as follows:

[0050] The performance tests of the high thermal conductivity hot stamping die steel obtained in this embodiment and the 8418 die steel at different temperatures with a hardness of 48HRC were compared, and the results are as follows:

[0051] (1) Hardness after aging hardening: 48HRC;

[0052] (2) The impact energy of the unnotched 7*10*55 specimen is greater than 220 J;

[0053] (3) Comparison of thermal conductivity test data is shown in Table 2 and Figure 1 .

[0054] Table 1 Comparison of the composition of the present invention and 8418

[0055]

[0056] From the above comparison, it can be seen that the present invention reduces the content of Si, Cr, and Mn, has no V, and increases Co, which can reduce the hardenability of steel, reduce the content of martensite structure generated in the steel during heat treatment, and improve the high-temperature creep resistance of steel.

[0057] Table 2 Comparison of thermal conductivity between the present invention and 8418

[0058] Steel Grade 200℃ 400℃ 500℃ 700℃ 8418 30.3 30.5 30.3 25.7 The present invention 42.4 39.6 36.6 28.5

[0059] By comparison, it can be seen that the thermal conductivity of the present invention is improved by about 30% compared with 8418 die steel under the condition of 48HRC hardness, which meets the cooling capacity requirements of thick plate hot stamping dies.

[0060] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0061] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high thermal conductivity hot stamping die steel, characterized in that: The alloy composition includes the following elements, calculated by element weight percentage: C: 0.30-0.35%; Si: 0.03-0.15%; Mn: 0.05-0.20%; Cr: 0.10-0.30%; Mo: 3.00-3.30%; W: 1.10-1.30%; Ni: 2.00-2.30%; Co: 0.70-0.90%; Cu: 0.15-0.20%; Ce: 0.001-0.002%; La: 0.0005-0.001%; ​​the rest is Fe and impurities.

2. The high thermal conductivity hot stamping die steel according to claim 1, characterized in that: The impurities are S, P, N, O, and H.

3. The high thermal conductivity hot stamping die steel according to claim 1, characterized in that: It also includes 0.15-0.2% copper, 0.001-0.002% cerium, and 0.0005-0.001% lanthanum.

4. A heat treatment method for high thermal conductivity hot stamping die steel, characterized in that: The following steps are involved: 1) Forging the die steel according to the weight percentage of the elements in the high thermal conductivity hot stamping die steel as claimed in any one of claims 1 to 3, performing a solution water cooling treatment at 1030-1050° C. after forging, and then tempering at 500-530° C. for 2-3 hours, adjusting the hardness to 30-35HRC, and then performing rough machining of the die; 2) After rough machining of the mold, age harden at 580-620℃ for 9-12h and adjust the hardness to 47-49HRC for use.

5. The heat treatment method for high thermal conductivity hot stamping die steel according to claim 4, characterized in that: The rough processing of the mold is sawing and machining into the mold.

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