Solid carburizing process method for 20cr2ni4a carburizing steel
By grinding and polishing the surface of the 20Cr2Ni4A metallographic sample of carburized steel and using a specific combination of carburizing agents, along with an optimized heating and cooling process, the problems of thin carburized layer and unclear grain size were solved, and the depth and grain size of the carburized layer were effectively displayed.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANXI TAIGANG STAINLESS STEEL CO LTD
- Filing Date
- 2023-07-14
- Publication Date
- 2026-05-15
AI Technical Summary
In the existing technology, the carburizing effect of 20Cr2Ni4A carburizing steel is poor, the carburized layer cannot meet the standard requirement of more than 1mm, and the austenite grain size cannot be clearly displayed in the cementite network.
The metallographic sample surface was ground and polished. A carburizing agent consisting of 20% BaCO3, 5% CaCO3, and 75% charcoal was used. The furnace was heated to 800±10℃ and held for 2-3 hours, then heated to 930±10℃ and held for 6.5±0.5 hours. The temperature was then lowered to 800±10℃ at a rate of 50-60℃/hour, and finally cooled to room temperature in the furnace.
It achieved the standard requirement of a carburized layer of more than 1 mm, ensured the rating and judgment of austenite grain size, and improved the visibility of carburizing effect and grain size.
Smart Images
Figure CN116904914B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metal heat treatment technology, specifically relating to a solid carburizing process for austenitic grain size of carburized steel 20Cr2Ni4A. Background Technology
[0002] According to GB / T6394-2017, for carburized steel and carbon steel and alloy steel with carbon content ≤0.25%, the carburizing method is used to display the austenite grain size. It is required that after carburizing heat treatment, a carburized layer of more than 1 mm be obtained, and a cementite network be formed in the hypereutectoid region, so as to display the austenite grain morphology.
[0003] The solid carburizing process involves heating the furnace to 930±10℃ and holding for 6 hours, followed by furnace cooling to room temperature. During testing, it was found that this heat treatment method resulted in poor carburizing of 20Cr2Ni4A steel, with the carburized layer failing to meet the standard requirement of over 1mm. Furthermore, the cementite network precipitated at the grain boundaries did not clearly show the austenite grain size. Therefore, a new solid carburizing process needs to be developed. Summary of the Invention
[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a solid carburizing process for austenitic grain size of 20Cr2Ni4A carburized steel.
[0005] Specifically, the solid carburizing process method for the metallographic specimen of carburized steel 20Cr2Ni4A provided by the present invention includes:
[0006] (1) Treat the surface of the metallographic sample;
[0007] (2) Place the metallographic sample into a carburizing container containing carburizing agent;
[0008] (3) Place the carburizing container into the heating furnace and heat it. After heating the furnace to 800±10℃ and holding it for 2-3 hours, continue to heat it to 930±10℃ and hold it for 6.5±0.5 hours. Then, cool it down to 800±10℃ at a rate of 50~60℃ / h and finally cool it down to room temperature with the furnace.
[0009] In the solid carburizing process of the above-mentioned carburized steel 20Cr2Ni4A metallographic sample, in step (3), the temperature is raised to 800℃ and held for 2 hours, then raised to 940℃ and held for 6 hours, and then cooled to 800℃ at 50℃ / hour, and then cooled to room temperature in the furnace.
[0010] In the above-mentioned solid carburizing process method for the metallographic sample of carburized steel 20Cr2Ni4A, in step (1), the surface of the metallographic sample is subjected to metallographic grinding and polishing treatment.
[0011] The solid carburizing process of the above-mentioned carburized steel 20Cr2Ni4A metallographic specimen, by weight percentage, includes BaCO3: 20%-30%, CaCO3: 5%-10%, and charcoal: 60%-75%.
[0012] The solid carburizing process method for the above-mentioned carburized steel 20Cr2Ni4A metallographic specimen, by weight percentage, includes BaCO3: 20%, CaCO3: 5%, and charcoal: 75%.
[0013] The solid carburizing process method for the above-mentioned metallographic specimen of carburized steel 20Cr2Ni4A, wherein the carburizing container is made of heat-resistant stainless steel pipe 347H.
[0014] The solid carburizing process method for the above-mentioned metallographic specimen of carburized steel 20Cr2Ni4A, wherein the carburizing container includes an exhaust port.
[0015] In the above-mentioned solid carburizing process for metallographic specimens of carburized steel 20Cr2Ni4A, the distance between the metallographic specimen and the outer wall of the carburizing container, and between the metallographic specimens themselves, is >30mm.
[0016] The solid carburizing process for the above-mentioned metallographic specimen of carburized steel 20Cr2Ni4A, wherein the heating furnace is an SRX-8-13 box-type resistance furnace.
[0017] The technical solution of the present invention has the following beneficial effects:
[0018] This invention investigated the factors affecting solid carburizing effect through experiments, developed a solid carburizing process method for austenitic grain size of carburized steel 20Cr2Ni4A, met the requirements of grain size inspection standards, ensured the rating and determination of austenitic grain size of steel, and provided guidance for solid carburizing processes of other similar steel grades. Attached Figure Description
[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention.
[0020] Figure 1 The image shows the carburizing effect of carburizing agent A.
[0021] Figure 2 The image shows the carburizing effect of carburizing agent B.
[0022] Figure 3 The image shows the carburizing effect of carburizing agent C.
[0023] Figure 4 The image shows the carburizing effect of carburizing agent D.
[0024] Figure 5 The image shows the carburizing effect after the metallographic sample is treated by process 1.
[0025] Figure 6 The image shows the carburizing effect after the metallographic sample is treated in process 2.
[0026] Figure 7 The image shows the carburizing effect after the metallographic sample is treated in process 3.
[0027] Figure 8 The image shows the carburizing effect after the metallographic sample was treated in process 4.
[0028] Figure 9 The image shows the carburizing effect after the metallographic sample was treated in process 5.
[0029] Figure 10 The image shows the carburizing effect after the metallographic sample was treated in process 6.
[0030] Figure 11 The image shows the carburizing effect after the metallographic sample was treated in process 7.
[0031] Figure 12 The image shows the carburizing effect after the metallographic sample was treated in process 8.
[0032] Figure 13 The image shows the carburizing effect after carburizing an unpolished metallographic sample.
[0033] Figure 14 This image shows the carburizing effect after carburizing a polished metallographic sample. Detailed Implementation
[0034] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.
[0035] When a numerical range is disclosed in this invention, the range is considered continuous and includes the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Further, when the range refers to an integer, it includes every integer between the minimum and maximum values of the range. Moreover, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed in this invention should be understood to include any and all subranges to which they are incorporated.
[0036] Specifically, the solid carburizing process method for austenitic grain size of 20Cr2Ni4A carburized steel provided by the present invention includes:
[0037] (1) Grinding and polishing the surface of the metallographic sample;
[0038] (2) Place the metallographic sample into a carburizing container containing carburizing agent;
[0039] (3) Place the carburizing container into the heating furnace and heat it. After heating the furnace to 800±10℃ and holding it for 2-3 hours, continue to heat it to 930±10℃ and hold it for 6.5±0.5 hours. Then, cool it down to 800±10℃ at a rate of 50~60℃ / h and finally cool it down to room temperature with the furnace.
[0040] This invention, through research, has discovered that the heating rate has no effect on the carburized layer depth, and isothermal heating significantly improves the carburizing effect, while isothermal cooling has little impact on the carburized layer. The cooling rate is a crucial factor in determining the carburized layer depth; too slow a cooling rate leads to increased original grain size in the steel, while too rapid a cooling rate results in insufficient carburized layer depth. Insufficient holding time at high temperatures leads to poor carburizing, while excessive holding time causes austenite grain growth. Based on experimental results and work efficiency, this invention determines the optimal carburizing heat treatment process as follows: heat to 800℃ and hold for 2 hours, then heat to 940℃ and hold for 6 hours, followed by cooling at 50℃ / hour to 800℃, and finally cooling to room temperature in the furnace.
[0041] In this invention, the carburizing effect of the metallographic sample can be improved by grinding and polishing the surface of the sample.
[0042] In some preferred embodiments, the carburizing agent comprises, by weight percentage: BaCO3: 20%-30%, CaCO3: 5%-10%, and charcoal: 60%-75%. More preferably, the carburizing agent comprises: BaCO3: 20%, CaCO3: 5%, and charcoal: 75%.
[0043] To ensure the carburizing effect of metallographic specimens, the specimens need to be placed in a specially designed carburizing container with an vent. Extensive testing has verified that the vent should not be too large or too small, but rather between 0.3 and 0.5 mm, ensuring a good clearance fit. If the vent is too small, it can cause an explosion due to excessive pressure during heating; if the vent is too large, the carburizing process will fail.
[0044] Optionally, the carburizing container includes a cylinder and a cover. The cover is located above the cylinder. The cylinder is a cylindrical tube with an opening at the top, and the cover is a cylindrical tube with an opening at the bottom. A vent hole is provided on the cover, and a circular protrusion is provided in the upper middle part of the cover.
[0045] In order to prevent deformation, the carburizing container is made of heat-resistant stainless steel pipe 347H, since the carburizing container is in a high-temperature heating state for a long time.
[0046] Preferably, the distance between the sample and the outer wall of the carburizing container, and between samples, should be greater than 30 mm to ensure the carburizing effect.
[0047] Optionally, the heating furnace can be any type of heating furnace, preferably an SRX-8-13 box-type resistance furnace.
[0048] Example
[0049] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions.
[0050] 1. Selection of raw materials for carburizing agent
[0051] In order to select a carburizing agent with good effect, four carburizing agent formulations were selected for carburizing effect comparison test. The specific formulation composition is shown in Table 1.
[0052] Table 1. Composition of Carburizing Agent Formulation
[0053]
[0054] The sample surface was ground and then polished. The heating equipment was an SRX-8-13 box-type resistance furnace, and the standard carburizing heat treatment process was followed: the temperature was raised to 940℃ in the furnace, held for 6 hours, and then cooled in the furnace. Different carburizing agents listed in Table 1 were used for carburizing, and the carburizing effects are as follows. Figures 1-4 As shown, the carburized layer depths obtained by the four carburizing agents A, B, C, and D are 159 μm, respectively. Figure 1 ), 218μm ( Figure 2 ), 306μm ( Figure 3 ), 231μm ( Figure 4 None of the above methods could meet the standard requirement of a carburized layer of more than 1 mm. Meanwhile, the experimental results showed that the carburized layer obtained using a C (BaCO3: 20%, CaCO3: 5%, charcoal: 75%) carburizing agent was the largest and had the best carburizing effect. Therefore, this formula was selected as the raw material for the carburizing heat treatment process.
[0055] 2. Develop an experimental plan for the carburizing heat treatment process.
[0056] 1) In order to improve the carburizing effect, an isothermal stage is added during the heating or cooling process. After consulting relevant information, the Ac3 of carburizing steel 20Cr2Ni4A is 765℃, and the isothermal temperature is selected as 800℃.
[0057] 2) To obtain a carburized layer that meets the standard requirements, the heat treatment carburizing process was studied. The sample surface was ground and polished. The carburizing agent used was: BaCO3: 20%, CaCO3: 5%, charcoal: 75%. The carburizing process and the corresponding depth of the precipitated cementite network are shown in Table 2. The metallographic structure observation results are as follows: Figure 5-12 As shown.
[0058] Table 2. Carburizing heat treatment process and depth of cementite network precipitated in the carburized layer
[0059]
[0060] After carburizing using the eight processes listed in the table above, the treated samples were polished and etched. The results of the carburized layer observation are shown below. Figure 5-12 Combining Table 2 and Figure 5-12 The following conclusions can be drawn: (1) The heating rate has no effect on the depth of the carburized layer. (2) Isothermal heating during the heating process can significantly improve the carburizing effect, while isothermal heating during the cooling process has little effect on the carburized layer. (3) The cooling rate is one of the important factors in the depth of the carburized layer. A cooling rate that is too slow (<50℃ / hour) will cause the original grain size of the steel to grow, but a cooling rate that is too fast will result in insufficient depth of the carburized layer. (4) Based on the experimental results and work efficiency, process 7 in Table 2 can be concluded as the optimal carburizing heat treatment process, and the resulting carburized layer meets the standard requirements.
[0061] 3. The Influence of Carburized Sample Surface Condition on Carburizing Effect
[0062] Two types of metallographic samples, one polished by machining and the other by metallographic grinding and polishing, were subjected to carburizing heat treatment. The carburizing agent used was: BaCO3: 20%, CaCO3: 5%, and charcoal: 75%. The treatment process was as follows: the temperature was raised to 800 ℃ and held for 2 hours, then raised to 940 ℃ and held for 6 hours, then cooled to 800 ℃ at a rate of 50 ℃ / hour, and finally cooled to room temperature in the furnace. The treated samples were then polished and etched. The metallographic structure of the treated samples was observed as follows. Figure 13 and Figure 14 As shown in the figure, the metallographic polished sample exhibits better carburizing effect.
[0063] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are merely illustrative of the invention and should not be construed as limiting its scope. It should be noted that any variations and substitutions equivalent to these embodiments should be considered to be covered within the scope of the claims. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A solid carburizing process for a metallographic specimen of carburized steel 20Cr2Ni4A, characterized in that, include: (1) Treat the surface of the metallographic sample; (2) Place the metallographic sample into a carburizing container containing carburizing agent; The carburizing agent, by weight percentage, comprises BaCO3: 20%-30%, CaCO3: 5%-10%, and charcoal: 60%-75%. (3) Place the carburizing container into the heating furnace and heat it. After heating the furnace to 800℃ and holding it for 2 hours, continue to heat it to 930±10℃ and hold it for 6.5±0.5 hours. Then, cool it down to 800±10℃ at a rate of 50℃ / h and finally cool it down to room temperature with the furnace.
2. The solid carburizing process method for the metallographic specimen of carburized steel 20Cr2Ni4A according to claim 1, characterized in that, In step (3), the furnace is heated to 800 ℃ and held for 2 hours, then heated to 940 ℃ and held for 6 hours, then cooled to 800 ℃ at 50 ℃ / hour, and then cooled to room temperature with the furnace.
3. The solid carburizing process method for the metallographic specimen of carburized steel 20Cr2Ni4A according to claim 1, characterized in that, In step (1), the surface of the metallographic sample is subjected to metallographic grinding and polishing treatment.
4. The solid carburizing process method for the metallographic specimen of carburized steel 20Cr2Ni4A according to claim 1, characterized in that, The carburizing agent comprises, by weight percentage: BaCO3: 20%, CaCO3: 5%, and charcoal: 75%.
5. The solid carburizing process method for the metallographic specimen of carburized steel 20Cr2Ni4A according to claim 1, characterized in that, The carburizing container is made of heat-resistant stainless steel pipe 347H.
6. The solid carburizing process method for the metallographic specimen of carburized steel 20Cr2Ni4A according to claim 1, characterized in that, The carburizing vessel includes an exhaust port.
7. The solid carburizing process method for the metallographic specimen of carburized steel 20Cr2Ni4A according to claim 1, characterized in that, The distance between the metallographic specimen and the outer wall of the carburizing container, and between the metallographic specimens themselves, is greater than 30 mm.
8. The solid carburizing process method for the metallographic specimen of carburized steel 20Cr2Ni4A according to claim 1, characterized in that, The heating furnace is an SRX-8-13 box-type resistance furnace.