Heat treatment method of high-hardness and high-toughness die steel

Abstract

The invention discloses a heat treatment method for high-hardness and high-toughness die steel. The heat treatment method comprises the following steps of spheroidizing annealing, stress relief tempering, quenching, cryogenic cooling, high-temperature tempering, detection and re-annealing. According to the method, the disadvantage of insufficient toughness and the situation that corner chipping and cracking are prone to occurring are solved through a heat treatment method, the toughness and abrasion resistance of steel can be brought into full play, excellent dimensional stability and coating performance are achieved, the overall service life of the fine blanking die can be greatly prolonged by 3-5 times compared with the service life of traditional CR12MO1V1, and the service life of the fine blanking die is prolonged by 3-5 times compared with that of traditional CR12MO1V1. And the service life is prolonged by more than one time compared with that of DC53.

Description

Technical Field

[0001] The invention relates to the technical field of die steel, and in particular to a heat treatment method for high-hardness and high-toughness die steel. Background Art

[0002] In conventional fine stamping die applications, since the material thickness of the stamped product is usually relatively thick, the die steel is required to have higher toughness and a hardness of at least HRC60 to achieve better wear resistance. Therefore, DC53 cold working die steel is widely used in the market, because DC53 materials can effectively solve the problem of insufficient toughness and easy corner collapse and cracking of D2 materials. Due to the comprehensive requirements of the automotive industry for safety factors and energy conservation and emission reduction, more and more high-strength steel plates are being put into use.

[0003] In the existing technology, the precision stamping of high-strength steel plates has increasingly become a bottleneck in the mold industry. DC53 materials have also gradually shown the disadvantage of insufficient toughness and are prone to chipping and cracking.

[0004] Therefore, how to provide a heat treatment method for high-hardness and high-toughness die steel to solve the problems existing in the prior art is of great significance to its application. Summary of the invention

[0005] In view of this, the purpose of this application is to provide a heat treatment method for high hardness and high toughness die steel to solve the problem.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A heat treatment method for high-hardness and high-toughness die steel comprises the following steps:

[0008] S1: Spheroidizing annealing, spheroidizing annealing includes the following steps:

[0009] S1.1: Heat the workpiece to 820-870℃ and keep it warm for 2-4 hours;

[0010] S1.2: Slowly cool down to 600℃ with the furnace, the cooling rate shall not exceed 15℃ per hour;

[0011] S1.3: Remove from the oven and air cool to room temperature;

[0012] S2: The annealed workpiece is subjected to stress relief tempering, and the stress relief tempering includes the following steps:

[0013] S2.1: Heat the workpiece to 500-550℃ and keep it warm for 4-8 hours;

[0014] S2.2: Remove from the oven and air cool to room temperature;

[0015] S3: Quenching the workpiece after stress relief tempering, the quenching includes the following steps:

[0016] S3.1: First stage preheating: heating rate 1℃~5℃ / min, heating to 550±10℃; keeping warm for 1-2 hours;

[0017] S3.2: Second stage preheating: heating rate 5℃~12℃ / min, heating to 850±10℃; keeping warm for 1-2 hours;

[0018] S3.3: The third stage of preheating: heating rate 5℃~12℃ / min, heating to 1000±10℃, keeping warm for 0.5-1 hour;

[0019] S3.4: Continue heating to 1100°C at a heating rate of 8°C to 15°C / min and keep warm for 1 hour;

[0020] S3.5: Rapid cooling in the first stage;

[0021] S3.6: Second stage rapid cooling;

[0022] S3.7: After being taken out of the furnace, the workpiece is placed in the air to cool to room temperature to complete the quenching.

[0023] S4: subjecting the quenched workpiece to deep cryogenic treatment;

[0024] S5: High temperature tempering, high temperature tempering includes the following steps:

[0025] S5.1: Temper the cryogenically treated mold in a vacuum furnace, atmosphere protection furnace or air furnace;

[0026] S5.2: At least three high temperature temperings before finishing and one stress relief tempering after finishing;

[0027] S5.3: The tempering temperature can be selected according to the hardness requirements;

[0028] S5.4: The stress relief tempering temperature after finishing shall not exceed 480 degrees;

[0029] S5.5: After tempering, furnace cooling or air cooling is adopted;

[0030] S5.6: The holding time for mold tempering and stress relief tempering is generally calculated as 1 hour per 25 mm thickness, and the minimum holding time is not less than 3 hours.

[0031] S6: Hardness test: Use a hardness tester to test the hardness of the mold steel;

[0032] S7: re-quenching;

[0033] If the mold hardness is too low and unqualified, re-quenching is required. The re-quenching process refers to S3. Annealing treatment is required before re-quenching. The annealing temperature refers to S1, and the cooling rate is not higher than 33°C per hour.

[0034] Preferably, step S4 comprises the following steps:

[0035] S4.1: Place the mold cooled to room temperature into a cryogenic furnace for cryogenic treatment:

[0036] S4.2: First stage precooling: cooling rate 1℃~3℃ / min, cooling to -40℃; keeping warm for 1-2 hours;

[0037] S4.3: Second stage precooling: cooling rate 1℃~3℃ / min, cooling to -80℃; keeping warm for 1-2 hours;

[0038] S4.4: The third stage of precooling: cooling rate 1℃~3℃ / min, cooling to below -150℃; keeping warm for 1-2 hours.

[0039] Preferably, S3.5: rapid cooling in the first stage, rapidly cooling to 550±10°C, with a cooling rate of ≥28°C / min;

[0040] S3.6: Second stage rapid cooling: Appropriately slow down the cooling speed to below 150°C, and the cooling rate is ≥10°C / min.

[0041] Preferably, in S5.3, at least one tempering temperature is ensured to be not less than 520°C, and the three tempering temperatures are all ensured to be not less than 500°C.

[0042] Preferably, the steel is cooled to room temperature after each tempering in S5.5.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. The present invention can give full play to the toughness and wear resistance of steel, and has excellent dimensional stability and coating performance.

[0045] 2. The present invention can greatly improve the overall life of the fine stamping die, which is 3-5 times longer than the traditional CR12MO1V1 and more than 1 times longer than the DC53.

[0046] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application so that it can be implemented in accordance with the contents of the specification, and to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following is a detailed description of the preferred embodiments of the present application in conjunction with the accompanying drawings as follows.

[0047] Based on the detailed description of the specific embodiments of the present application in combination with the accompanying drawings below, those skilled in the art will become more aware of the above and other objects, advantages and features of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can also be obtained based on these drawings without creative work. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0049] Figure 1 It is a process and temperature comparison diagram of the present invention. DETAILED DESCRIPTION

[0050] To make the purpose, technical scheme and advantages of the embodiment of the present application clearer, the technical scheme in the embodiment of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, rather than all of the embodiments. In the following description, specific details such as specific configuration and components are provided only to help fully understand the embodiments of the present application. Therefore, it should be clear to those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application. In addition, for clarity and brevity, the description of known functions and structures is omitted in the embodiment.

[0051] In addition, the present application may repeat reference numerals and / or letters in different examples. This repetition is for the purpose of simplicity and clarity, and does not in itself indicate the relationship between the various embodiments and / or settings discussed.

[0052] The term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist at the same time. The term " / and" in this article describes another type of association object relationship, indicating that there can be two relationships. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the previous and next associated objects are in an "or" relationship.

[0053] It should also be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusions.

[0054] See also Figure 1 The present invention provides a technical solution for a heat treatment method of a high-hardness and high-toughness die steel, comprising the following steps:

[0055] S1: Spheroidizing annealing, spheroidizing annealing includes the following steps:

[0056] S1.1: Heat the workpiece to 820-870℃ and keep it warm for 2-4 hours;

[0057] S1.2: Slowly cool down to 600℃ with the furnace, the cooling rate shall not exceed 15℃ per hour;

[0058] S1.3: Remove from the oven and air cool to room temperature;

[0059] S2: The annealed workpiece is subjected to stress relief tempering, and the stress relief tempering includes the following steps:

[0060] S2.1: Heat the workpiece to 500-550℃ and keep it warm for 4-8 hours;

[0061] S2.2: Remove from the oven and air cool to room temperature;

[0062] S3: Quenching the workpiece after stress relief tempering, the quenching includes the following steps:

[0063] S3.1: First stage preheating: heating rate 1℃~5℃ / min, heating to 550±10℃; keeping warm for 1-2 hours;

[0064] S3.2: Second stage preheating: heating rate 5℃~12℃ / min, heating to 850±10℃; keeping warm for 1-2 hours;

[0065] S3.3: The third stage of preheating: heating rate 5℃~12℃ / min, heating to 1000±10℃, keeping warm for 0.5-1 hour;

[0066] S3.4: Continue heating to 1100°C at a heating rate of 8°C to 15°C / min and keep warm for 1 hour;

[0067] S3.5: Rapid cooling in the first stage, quickly cooling to 550±10℃, with a cooling rate of ≥28℃ / min;

[0068] S3.6: Second stage rapid cooling: appropriately slow down the cooling speed to below 150℃, the cooling rate is ≥10℃ / minS3.7: After leaving the furnace, place the workpiece in the air to cool to room temperature to complete the quenching;

[0069] S4: subjecting the quenched workpiece to deep cryogenic treatment;

[0070] S4.1: Place the mold cooled to room temperature into a cryogenic furnace for cryogenic treatment:

[0071] S4.2: First stage precooling: cooling rate 1℃~3℃ / min, cooling to -40℃; keeping warm for 1-2 hours;

[0072] S4.3: Second stage precooling: cooling rate 1℃~3℃ / min, cooling to -80℃; keeping warm for 1-2 hours;

[0073] S4.4: The third stage of precooling: cooling rate 1℃~3℃ / min, cooling to below -150℃; keeping warm for 1-2 hours;

[0074] S5: High temperature tempering, high temperature tempering includes the following steps:

[0075] S5.1: Temper the cryogenically treated mold in a vacuum furnace, atmosphere protection furnace or air furnace;

[0076] S5.2: At least three high temperature temperings before finishing and one stress relief tempering after finishing;

[0077] S5.3: The tempering temperature can be selected according to the hardness requirements, and at least one tempering temperature is not less than 520℃, and three tempering temperatures are not less than 500℃;

[0078] S5.4: The stress relief tempering temperature after finishing shall not exceed 480 degrees;

[0079] S5.5: After tempering, furnace cooling or air cooling is used. After each tempering, the furnace cooling or air cooling is used. The furnace cooling or air cooling is used after each tempering.

[0080] S5.6: The holding time for mold tempering and stress relief tempering is generally calculated as 1 hour per 25 mm thickness, and the minimum holding time is not less than 3 hours.

[0081] S6: Hardness test: Use a hardness tester to test the hardness of the mold steel;

[0082] S7: re-quenching;

[0083] If the mold hardness is too low and unqualified, re-quenching is required. The re-quenching process refers to S3. Annealing treatment is required before re-quenching. The annealing temperature refers to S1, and the cooling rate is not higher than 33°C per hour.

[0084] Embodiment 1:

[0085] The mold steel used is DC53 type cold working mold steel.

[0086] S1: Spheroidizing annealing, to further refine the structure of the steel, spheroidizing annealing includes the following steps:

[0087] S1.1: Heat the workpiece to 850℃ and keep it warm for 2 hours;

[0088] S1.2: Slowly cool down to 600℃ with the furnace, the cooling rate shall not exceed 15℃ per hour;

[0089] S1.3: Remove from the oven and air cool to room temperature;

[0090] S2: The annealed workpiece is subjected to stress relief tempering to eliminate the mold processing stress. The stress relief tempering includes the following steps:

[0091] S2.1: Heat the workpiece to 500°C and keep it at this temperature for 4 hours;

[0092] S2.2: Remove from the oven and air cool to room temperature;

[0093] S3: Quenching the workpiece after stress relief tempering, the quenching includes the following steps:

[0094] S3.1: First stage preheating: heating rate 5℃ / min, heating to 550±10℃; keep warm for 1 hour;

[0095] S3.2: Second stage preheating: heating rate 12℃ / min, heating to 850±10℃; keep warm for 1 hour;

[0096] S3.3: The third stage of preheating: heating rate 12℃ / min, heating to 1000±10℃, keeping warm for 1 hour;

[0097] S3.4: Continue heating to 1100°C at a heating rate of 15°C / min and keep at this temperature for 1 hour;

[0098] S3.5: Rapid cooling in the first stage, quickly cooling to 550±10℃, with a cooling rate of ≥28℃ / min;

[0099] S3.6: Second stage rapid cooling: slow down the cooling speed appropriately to below 150℃, the cooling rate is ≥10℃ / minS

[0100] 3.7: After coming out of the furnace, place the workpiece in the air to cool to room temperature to complete the quenching;

[0101] S4: subjecting the quenched workpiece to deep cryogenic treatment;

[0102] S4.1: Place the mold cooled to room temperature into a cryogenic furnace for cryogenic treatment:

[0103] S4.2: First stage precooling: cooling rate 3℃ / min, cooling to -40℃; keeping warm for 2 hours;

[0104] S4.3: Second stage precooling: cooling rate 3℃ / min, cooling to -80℃; keeping warm for 2 hours;

[0105] S4.4: The third stage of precooling: cooling rate 3℃ / min, cooling to below -150℃; keeping warm for 2 hours;

[0106] S5: High temperature tempering, high temperature tempering includes the following steps:

[0107] S5.1: Temper the cryogenically treated mold in a vacuum furnace, atmosphere protection furnace or air furnace;

[0108] S5.2: At least three high temperature temperings before finishing and one stress relief tempering after finishing;

[0109] S5.3: The tempering temperature can be selected according to the hardness requirements, and at least one tempering temperature is not less than 520℃, and three tempering temperatures are not less than 500℃;

[0110] S5.4: The stress relief tempering temperature after finishing shall not exceed 480 degrees;

[0111] S5.5: After tempering, furnace cooling or air cooling is used. After each tempering, the furnace cooling or air cooling is used. The furnace cooling or air cooling is used after each tempering.

[0112] S5.6: The holding time for mold tempering and stress relief tempering is generally calculated as 1 hour per 25 mm thickness, and the minimum holding time is not less than 3 hours.

[0113] S6: Hardness test: Use a hardness tester to test the hardness of the mold steel;

[0114] S7: re-quenching;

[0115] If the mold hardness is too low and unqualified, re-quenching is required. The re-quenching process refers to S3. Annealing treatment is required before re-quenching. The annealing temperature refers to S1, and the cooling rate is not higher than 33°C per hour.

[0116] When used specifically, the workpiece is heated to 820-870°C and kept warm for 2-4 hours; slowly cooled to 600°C with the furnace, with a cooling rate of no more than 15°C per hour; taken out of the furnace and air-cooled to room temperature; the annealed workpiece is subjected to stress relief tempering, and the stress relief tempering includes the following steps: heating the workpiece to 500-550°C and keeping warm for 4-8 hours; taken out of the furnace and air-cooled to room temperature; first stage preheating: heating rate 1°C~5°C / min, heating to 550±10°C; keeping warm for 1-2 hours; second stage preheating: heating rate 5°C~12°C / min, heating to 850±10°C; keeping warm for 1-2 hours ; The third stage of preheating: heating rate 5℃~12℃ / min, heating to 1000±10℃, keeping warm for 0.5-1 hour; heating rate 8℃~15℃ / min to 1100℃, keeping warm for 1 hour; the first stage of rapid cooling, quickly cooling to 550±10℃, cooling rate ≥28℃ / min; the second stage of rapid cooling: appropriately slow down the speed to cool to below 150℃, cooling rate ≥10℃ / minS3.7: After taking out of the furnace, place the workpiece in the air to cool to room temperature to complete quenching; perform deep cryogenic treatment on the quenched workpiece; cool the mold to room temperature The mold is placed in a cryogenic furnace for cryogenic treatment: the first stage of precooling: cooling rate 1℃~3℃ / min, cooling to -40℃; keeping warm for 1-2 hours; the second stage of precooling: cooling rate 1℃~3℃ / min, cooling to -80℃; keeping warm for 1-2 hours; the third stage of precooling: cooling rate 1℃~3℃ / min, cooling to below -150℃; keeping warm for 1-2 hours; the mold after cryogenic treatment is placed in a vacuum furnace, atmosphere protection furnace or air furnace for tempering; at least three high-temperature temperings before finishing, and one stress relief tempering after finishing; the tempering temperature can be selected according to the hardness requirements, Ensure that at least one tempering temperature is not lower than 520℃, and three tempering temperatures are not lower than 500℃; the stress relief tempering temperature after fine machining shall not be higher than 480 degrees; furnace cooling or air cooling is adopted after tempering, and it shall be cooled to room temperature after each tempering. The insulation time of mold tempering and stress relief tempering is generally calculated as 1 hour for every 25mm thickness, and at least not less than 3 hours; use a hardness tester to test the hardness of mold steel; if the mold hardness is too low and unqualified, re-quench it. Refer to S3 for the re-quenching process. Annealing treatment is required before re-quenching. Refer to S1 for the annealing temperature, and the cooling rate is not higher than 33℃ per hour.

[0117] The above description is only the preferred embodiment of the present invention, which does not limit the protection scope of the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. Within the spirit and principle of the present invention, any change, modification, replacement, integration and parameter change of these embodiments by conventional substitution or capable of achieving the same function without departing from the principle and spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A heat treatment method for high hardness and high toughness die steel, characterized in that: The following steps are involved: S1: Spheroidizing annealing, spheroidizing annealing includes the following steps: S1.1: Heat the workpiece to 820-870℃ and keep it warm for 2-4 hours; S1.2: Slowly cool down to 600℃ with the furnace, the cooling rate shall not exceed 15℃ per hour; S1.3: Remove from the oven and air cool to room temperature; S2: The annealed workpiece is subjected to stress relief tempering, and the stress relief tempering includes the following steps: S2.1: Heat the workpiece to 500-550℃ and keep it warm for 4-8 hours; S2.2: Remove from the oven and air cool to room temperature; S3: Quenching the workpiece after stress relief tempering, the quenching includes the following steps: S3.1: First stage preheating: heating rate 1℃~5℃ / min, heating to 550±10℃; keeping warm for 1-2 hours; S3.2: Second stage preheating: heating rate 5℃~12℃ / min, heating to 850±10℃; keeping warm for 1-2 hours; S3.3: The third stage of preheating: heating rate 5℃~12℃ / min, heating to 1000±10℃, keeping warm for 0.5-1 hour; S3.4: Continue heating to 1100°C at a heating rate of 8°C to 15°C / min and keep warm for 1 hour; S3.5: First stage rapid cooling; S3.6: Second stage rapid cooling; S3.7: After being taken out of the furnace, the workpiece is placed in the air to cool to room temperature to complete the quenching. S4: subjecting the quenched workpiece to deep cryogenic treatment; S5: High temperature tempering, high temperature tempering includes the following steps: S5.1: Temper the cryogenically treated mold in a vacuum furnace, atmosphere protection furnace or air furnace; S5.2: At least three high temperature temperings before finishing and one stress relief tempering after finishing; S5.3: The tempering temperature can be selected according to the hardness requirements; S5.4: The stress relief tempering temperature after finishing shall not exceed 480 degrees; S5.5: After tempering, furnace cooling or air cooling is adopted; S5.6: The holding time for mold tempering and stress relief tempering is generally calculated as 1 hour per 25 mm thickness, and the minimum holding time is not less than 3 hours. S6: Hardness test: Use a hardness tester to test the hardness of the mold steel; S7: re-quenching; If the mold hardness is too low and unqualified, re-quenching is required. The re-quenching process refers to S3. Annealing treatment is required before re-quenching. The annealing temperature refers to S1, and the cooling rate is not higher than 33°C per hour.

2. A heat treatment method for high hardness and high toughness die steel as claimed in claim 1, characterized in that: The step S4 comprises the following steps: S4.1: Place the mold cooled to room temperature into a cryogenic furnace for cryogenic treatment: S4.2: First stage precooling: cooling rate 1℃~3℃ / min, cooling to -40℃; keeping warm for 1-2 hours; S4.3: Second stage precooling: cooling rate 1℃~3℃ / min, cooling to -80℃; keeping warm for 1-2 hours; S4.4: The third stage of precooling: cooling rate 1℃~3℃ / min, cooling to below -150℃; keeping warm for 1-2 hours.

3. A heat treatment method for high hardness and high toughness die steel as claimed in claim 2, characterized in that: S3.5: Rapid cooling in the first stage, rapidly cooling to 550±10°C, with a cooling rate of ≥28°C / min; S3.6: Second stage rapid cooling: appropriately slow down the cooling speed to below 150°C, the cooling rate is ≥10°C / min.

4. A heat treatment method for high hardness and high toughness die steel as claimed in claim 3, characterized in that: In S5.3, at least one tempering temperature is guaranteed to be not less than 520℃, and three tempering temperatures are guaranteed to be not less than 500℃.

5. A heat treatment method for high hardness and high toughness die steel as claimed in claim 4, characterized in that: After each tempering in S5.5, the product is cooled to room temperature.

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