Production method of carburized gear steel
By first heating up and then cooling down the casting billet, the grain size and hardness of carburized gear steel are controlled, and the problem of processing difficulties caused by increasing the hardness of steel in the prior art is solved, and the process is achieved without adding heat treatment steps and effective control in the case of controlled rolling and cooling equipment.
Patent Information
- Application Number
- CN202411674433.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-21
- Publication Date
- 2025-02-21
AI Technical Summary
When the heating temperature of the existing carburized gear steel production methods increases, the hardness of the steel also increases, resulting in difficulty in subsequent processing, and annealing or normalizing processes are required to reduce hardness, increasing production costs and cycles.
By first heating up the casting billet and then cooling down in the heating furnace, the grain size and hardness of the carburized gear steel are controlled to ensure that without using controlled rolling and cooling equipment, the grain size and hardness are guaranteed. .
It is realized that without adding heat treatment processes and controlled rolling and cooling equipment, the steel is not mixed and the hardness is within the appropriate range, and the production cost and cycle are reduced.
Smart Images
Figure CN119491088A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of metallurgical technology, and in particular to a method for producing carburized gear steel. Background Art
[0002] In order to meet the requirements of high hardness on the gear surface and high toughness in the core, gear steel usually uses low carbon steel with a C content of 0.15% to 0.25%, which is convenient for subsequent surface carburizing or nitriding treatment. The current carburized gear steel in China mainly adopts Cr series, Mn-Cr series, Cr-Mn-Ti series, Cr-Mo series, Cr-Ni-Mo series, etc. Regardless of the series of carburized gear steel, in order to control the performance of subsequent parts, the steel is required to be carburized without mixed crystals.
[0003] In the current production method of carburized gear steel, as the heating temperature increases, the hardness of the steel after rolling will also increase. The higher hardness affects the subsequent processing of the steel. In order to reduce the hardness, annealing or normalizing processes need to be added. Annealing and normalizing and other heat treatment processes increase production costs and production cycles. Summary of the invention
[0004] The purpose of the present invention is to provide a method for producing carburized gear steel in order to overcome the defects of the prior art.
[0005] The present invention solves the technical problem by adopting the following technical solutions.
[0006] The present invention provides a method for producing carburized gear steel, which comprises: controlling the grain size and hardness of a carburized gear steel product by first heating and then cooling a cast billet in a heating furnace.
[0007] The present invention has the following beneficial effects:
[0008] The present invention provides a method for producing carburized gear steel, which comprises: controlling the grain size and hardness of the finished carburized gear steel by first heating and then cooling the ingot in a heating furnace. The ingot is first heated to a high temperature to fully dissolve elements such as Al, Ti, Nb, and V to prevent the occurrence of mixed crystal phenomenon when the round steel is tested for austenite grain size, and then the temperature is lowered and rolled to ensure that the hardness of the round steel meets the requirements, thereby ensuring both the grain size and the hardness without using controlled rolling and controlled cooling equipment. BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.
[0010] Figure 1 This is the metallographic diagram of the carburized gear steel obtained in Example 1;
[0011] Figure 2 This is the metallographic image of the carburized gear steel obtained in Comparative Example 1. DETAILED DESCRIPTION
[0012] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.
[0013] A method for producing carburized gear steel provided in an embodiment of the present invention is described in detail below.
[0014] An embodiment of the present invention provides a method for producing carburized gear steel, which includes: controlling the grain size and hardness of a carburized gear steel product by first heating and then cooling a cast billet in a heating furnace.
[0015] At present, carburized gear steel usually forms second phase particles such as AlN, Ti(C, N), Nb(C, N), V(C, N) to pin the grain boundaries, inhibit the growth of austenite grains, and prevent mixed crystals by adding elements such as Al, Ti, Nb, V, etc. In order to give full play to the anti-mixed crystal effect of elements such as Al, Ti, Nb, V, etc., it is usually necessary to heat the ingot to a temperature above 1180°C so that elements such as Al, Ti, Nb, V, etc. are fully dissolved into the austenite phase, so that enough uniform and fine second phase particles can be formed to pin the grain boundaries during the subsequent rolling and cooling process. However, as the heating temperature increases, the hardness of the steel after rolling will also increase. The higher hardness affects the subsequent processing of the steel. For this reason, it is necessary to increase post-rolling annealing or normalizing to reduce the hardness of the material, or use a controlled rolling and controlled cooling process to control the hardness of the steel during the rolling process. For example: When the heating temperature of the ingot is 1200℃ during the production of φ30mm 20CrMnTiHH round steel, no mixed crystal phenomenon is found after carburizing the round steel at 930℃ for 6h, but the hardness of the round steel is 245HBW, which exceeds the customer's requirement of 179-219HBW for round steel hardness. The round steel needs to add annealing or normalizing process to reduce the hardness. However, heat treatment processes such as annealing and normalizing increase production costs and production cycles, and controlled rolling and controlled cooling can only be used in production lines with controlled rolling and controlled cooling functions, which are not ideal solutions. How to ensure that the steel is not mixed and has a more suitable hardness without adding heat treatment processes and controlled rolling and controlled cooling equipment has become a problem that needs to be solved urgently.
[0016] In view of the above problems, the grain size and hardness control requirements are achieved by controlling the temperature and time of each section of the casting in the heating furnace. The specific process is as follows:
[0017] The heating furnace is divided into 4 sections from the beginning to the end for control, namely the preheating section, the first heating section, the second heating section, and the soaking section. The temperature of the preheating section is controlled below the austenitizing temperature and is slowly heated for a long time to reduce the internal stress of the billet and prevent stress cracking during the heating process of the billet. The temperature of the first heating section is controlled to be above the austenitizing temperature for a period of time to austenitize the billet structure. The temperature of the second heating section is controlled to be above 1180℃, and stays for a corresponding long time according to the size of the billet, so that the Al, Ti, Nb, V and other elements in the steel are fully dissolved into the austenite phase, so that enough uniform and fine second phase particles can be formed to pin the grain boundaries during the subsequent rolling and cooling process. The temperature of the soaking section is then reduced to a corresponding temperature range below 1150℃ according to the relationship between the heating temperature and hardness of the corresponding steel grade, so that the hardness of the steel after rolling is within the required range. Since the control temperature in each stage is the furnace temperature, in order to prevent the temperature of the steel billet in the soaking section from not being reduced to the set temperature range, resulting in the hardness not meeting the requirements, the corresponding compensation time is set according to the temperature difference between the soaking section and the second heating section to ensure that the temperature of the casting billet is reduced to the corresponding temperature. In this way, the casting billet is first heated to a high temperature to fully dissolve elements such as Al, Ti, Nb, and V to prevent the occurrence of mixed crystals when the round steel is tested for austenite grain size, and then the temperature is lowered and rolled to ensure that the hardness of the round steel meets the requirements. Both the grain size and the hardness are guaranteed without using controlled rolling and controlled cooling equipment.
[0018] In some optional embodiments, the following steps are included: the ingot is heated in a heating furnace in sequence through a preheating section, a first heating section, a second heating section and a soaking section, wherein: the heating temperature of the ingot in the second heating section in the heating furnace is controlled to be ≥ the heating temperature of the soaking section, and a corresponding compensation time is set according to the temperature difference between the soaking section and the second heating section, so as to achieve grain size and hardness control of the carburized gear steel product.
[0019] In some optional embodiments, the temperature of the preheating section is controlled to be ≤700°C.
[0020] In some optional implementations, the preheating period is controlled to be ≥ 60 min.
[0021] In some optional embodiments, the temperature of a heating section is controlled at 750-1150°C.
[0022] In some optional embodiments, the heating period is controlled to be ≥30 min.
[0023] In some optional embodiments, the temperature of the second heating stage is controlled at 1180-1260°C.
[0024] In some optional embodiments, the second heating period time t is controlled 二加 ≥0.2*W, where: t二加 is the residence time in the second heating section, in min, and W is the width of the ingot, in mm.
[0025] In some optional embodiments, the temperature of the soaking section is controlled at 1050-1150°C.
[0026] In some optional embodiments, the soaking time t 均热 ≥0.1*W+0.2*ΔT, where: t 均热 is the residence time in the soaking section, in min, W is the width of the ingot, in mm, ΔT is the temperature difference between the set temperature of the second heating section and the set temperature of the soaking section, in ℃.
[0027] As can be seen from the above, the embodiment of the present invention provides a method for producing carburized gear steel, which realizes the grain size and hardness control requirements by controlling the temperature and time of each section of the ingot in the heating furnace. Specifically, the heating furnace is divided into 4 sections from the beginning to the end for control, namely, the preheating section, the first heating section, the second heating section, and the soaking section. Among them: the temperature of the preheating section is controlled below the austenitizing temperature and is slowly heated for a long time to reduce the internal stress of the ingot and prevent stress cracking during the heating process of the ingot. The temperature of the first heating section is controlled to be above the austenitizing temperature for a period of time to austenitize the ingot structure. Based on the use requirements of the heating furnace equipment, the temperature of the second heating section cannot exceed 1260°C (the equipment requires the heating temperature to be controlled at 1000-1260°C). A large number of tests have proved that in order to prevent mixed crystals, the maximum temperature of the second heating section needs to be ≥1180°C, and in order to control the hardness of the material, the temperature of the soaking section is reduced to below 1150°C and above 1050°C according to the relationship between the heating temperature and hardness of the corresponding steel type, so that the hardness of the steel after rolling can be within the required range. The purpose of setting the second heating period is to ensure that the overall temperature of the billet can reach the target value, and that the elements such as Al, Ti, Nb, and V are fully dissolved, so as to avoid the situation where the surface temperature of the billet reaches the target value but the internal temperature does not reach the target value or the elements such as Al, Ti, Nb, and V are not fully dissolved, resulting in the appearance of mixed crystals inside during detection. The purpose of setting the soaking period is to ensure that the overall temperature can be reduced to the target value, so as to avoid the situation where the surface temperature of the billet reaches the target value but the internal temperature does not reach the target value due to the short time.
[0028] The present invention will be further described below in conjunction with the embodiments.
[0029] A method for producing carburized gear steel, wherein the heating furnace is divided into four sections for control from the beginning to the end, namely, a preheating section, a first heating section, a second heating section, and a soaking section. Among them:
[0030] 1. Preheating section: The temperature of the preheating section is controlled to ≤700℃ and the time is ≥60min.
[0031] 2. Heating section 1: The temperature of heating section 1 is controlled at 750-1150℃, and the time is ≥30min.
[0032] 3. Second heating section: According to the grain size requirements of steel, the temperature of the second heating section is controlled at 1180-1260℃. The time of the second heating section is adjusted according to the size of the ingot. 二加 ≥0.2*W, where: t 二加 is the residence time in the second heating stage (in min), and W is the width of the casting (in mm).
[0033] 4. Soaking section: According to the steel hardness requirements, the temperature of the soaking section is controlled within the corresponding range of 1050-1150℃. The soaking time is adjusted according to the size of the ingot and the temperature difference between the second heating section and the soaking section. 均热 ≥0.1*W+0.2*ΔT, where: t 均热 is the residence time in the soaking section (unit: min), W is the width of the ingot (unit: mm), and ΔT is the temperature difference between the set temperature of the second heating section and the set temperature of the soaking section (unit: °C).
[0034] 5. Ingot rolling: After the ingot is taken out of the furnace, it is rolled according to the normal rolling process.
[0035] Example 1
[0036] Use 280mm square billet to roll φ30mm 20CrMnTiHH round steel (hardness requirement 179-219HBW)
[0037] 1. Preheating section: The temperature of the preheating section is controlled at 650℃ and the time is 65min.
[0038] 2. Heating section 1: The temperature of heating section 1 is controlled at 1009℃ for 30min.
[0039] 3. Second heating section: According to the grain size requirements of steel, the temperature of the second heating section is controlled at 1200℃, and the time of the second heating section is 60min.
[0040] 4. Soaking section: According to the hardness requirements of the steel, the temperature of the soaking section is controlled at 1130℃ and the soaking time is 50 minutes.
[0041] 5. Billet rolling: After the billet is taken out of the furnace, it is rolled according to the normal rolling process. The round steel is tested for austenite grain size by simulated carburizing method, and no mixed crystals are found. The hardness of the round steel is 208HBW.
[0042] Example 2
[0043] Use 280mm square billet to roll φ45mm 20MnCr5HH round steel (hardness requirement ≤229HBW)
[0044] 1. Preheating section: The temperature of the preheating section is controlled at 680℃ and the time is 80min.
[0045] 2. Heating section 1: The temperature of heating section 1 is controlled at 1020℃ for 45min.
[0046] 3. Second heating section: According to the grain size requirements of steel, the temperature of the second heating section is controlled at 1230℃, and the time of the second heating section is 80min.
[0047] 4. Soaking section: According to the hardness requirements of the steel, the temperature of the soaking section is controlled at 1100℃ and the soaking time is 70 minutes.
[0048] 5. Billet rolling: After the billet is taken out of the furnace, it is rolled according to the normal rolling process. The round steel is tested for austenite grain size by simulated carburizing method, and no mixed crystals are found. The hardness of the round steel is 189HBW.
[0049] Example 3
[0050] Use 200mm square billet to roll φ28mm 22CrMoHH round steel (hardness requirement ≤229HBW)
[0051] 1. Preheating section: The temperature of the preheating section is controlled at 630℃ and the time is 75min.
[0052] 2. Heating section 1: The temperature of heating section 1 is controlled at 950℃ for 60min.
[0053] 3. Second heating section: According to the grain size requirements of steel, the temperature of the second heating section is controlled at 1210℃, and the time of the second heating section is 50min.
[0054] 4. Soaking section: According to the hardness requirements of the steel, the temperature of the soaking section is controlled at 1080℃ and the soaking time is 65 minutes.
[0055] 5. Billet rolling: After the billet is taken out of the furnace, it is rolled according to the normal rolling process. The round steel is tested for austenite grain size by simulated carburizing method, and no mixed crystals are found. The hardness of the round steel is 196HBW.
[0056] Comparative Examples 1-4
[0057] 20CrMnTiHH round steel with φ30mm is rolled from 280mm square billet
[0058] The steps are similar to those in Example 1, except that the temperature and time control of the second heating section and the soaking section and the test results are shown in the following table (according to the national standard GB / T231.1-2018 Metal Material Brinell Hardness Test Part 1: Hardness value obtained by testing the test party):
[0059]
[0060] Combining the above table with Figure 1-Figure 2 It can be seen that, by adopting the solution provided in Example 1 of the present invention, no mixed crystals appear in the prepared product, and the hardness is within the required range, while by adopting the solution provided in Comparative Examples 1-4, mixed crystals (such as Figure 2 As shown, some differences have mixed crystals), or the hardness exceeds the requirements. For example, the temperature of the second heating section of comparative example 1 is lower than 1180°C, and mixed crystals appear in the round steel; the temperature of the soaking section of comparative example 2 is higher than 1150°C, and the hardness of the round steel exceeds the upper limit required; the time of the second heating section of comparative example 3 is lower than the time required for calculation by the formula, and mixed crystals appear in the round steel; the time of the soaking section of comparative example 4 is lower than the time required for calculation by the formula, and the hardness of the round steel exceeds the upper limit required. The round steels prepared by the solutions provided in the comparative examples cannot meet the use requirements.
[0061] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.
Claims
1. A method for producing carburized gear steel, characterized in that: It includes: The grain size and hardness of the carburized gear steel product can be controlled by first heating up the ingot and then cooling it down in the heating furnace.
2. The production method according to claim 1, characterized in that The following steps are involved: The ingot is heated in the heating furnace in sequence through four sections: preheating section, first heating section, second heating section and soaking section. The heating temperature of the ingot in the second heating section in the heating furnace is controlled to be ≥ the heating temperature of the soaking section, and the corresponding compensation time is set according to the temperature difference between the soaking section and the second heating section to achieve grain size and hardness control of the carburized gear steel product.
3. The production method according to claim 2, characterized in that: Control the preheating section temperature ≤700℃.
4. The production method according to claim 2, characterized in that: Control the preheating time ≥60min.
5. The production method according to claim 2, characterized in that: The temperature of a heating section is controlled at 750-1150°C.
6. The production method according to claim 2, characterized in that: Control the heating period to ≥30min.
7. The production method according to claim 2, characterized in that: Control the temperature of the second heating section at 1180-1260℃.
8. The production method according to claim 2, characterized in that: Control the second heating period time t 二加 ≥0.2*W, where: t 二加 is the residence time in the second heating section, in min, and W is the width of the ingot, in mm.
9. The production method according to claim 2, characterized in that: Control the temperature of the soaking section at 1050-1150℃.
10. The production method according to claim 2, characterized in that: Control the soaking time t 均热 ≥0.1*W+0.2*ΔT, where: t 均热 is the residence time in the soaking section, in min, W is the width of the ingot, in mm, ΔT is the temperature difference between the set temperature of the second heating section and the set temperature of the soaking section, in ℃.