A high carbon chromium roller workpiece and its multi-stage heat treatment preparation process

Abstract

The present invention relates to the technical field of heat treatment of high-carbon chromium materials, and more specifically to a high-carbon chromium roller workpiece and a multi-stage heat treatment process for preparing the workpiece. The workpiece is produced by this process. The process comprises loading a plurality of high-carbon chromium roller workpieces into a heating furnace in a staggered arrangement; performing a first heat treatment on the high-carbon chromium roller workpieces; performing a second heat treatment on the high-carbon chromium roller workpieces; performing a third heat treatment on the high-carbon chromium roller workpieces; performing a salt bath quenching treatment on the high-carbon chromium roller workpieces; performing a water quenching treatment on the high-carbon chromium roller workpieces; and performing post-processing on the high-carbon chromium roller workpieces to obtain the target high-carbon chromium roller workpiece. The present invention can improve the core hardness of the high-carbon chromium roller workpiece and reduce the degree of hardness gradient attenuation and the retained austenite content.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of high-carbon chromium materials, in particular to a high-carbon chromium roller workpiece and a multi-stage heat treatment preparation process thereof. Background Art

[0002] The main bearing of a shield machine is a key core component of the machine. It is a large bearing that operates at low speeds and under heavy loads, capable of simultaneously withstanding large combined loads such as axial loads, radial loads, and overturning moments. Because shield machine main bearings primarily operate under harsh conditions such as high impact, high loads, and large offset loads, high requirements are placed on the main bearing rollers' load-bearing capacity and dimensional stability during service. Therefore, the industry demands that main bearing rollers exhibit high surface hardness, high core hardness, a gentle hardness gradient decay, and low retained austenite content. However, the traditional martensitic quenching heat treatment process is prone to the following deficiencies: For example, when using the traditional martensitic quenching heat treatment process on main bearing rollers with a size of φ70*(80-120)mm, problems such as low core hardness (less than 50HRC), significant hardness gradient decay (gradient difference greater than 15HRC), and retained austenite content greater than 15% are common.

[0003] In summary, it is necessary to develop a high-carbon chromium roller workpiece and its multi-stage heat treatment preparation process to solve the problems of low core hardness, significant hardness gradient attenuation and high retained austenite content in the traditional martensitic quenching heat treatment process. Summary of the Invention

[0004] The present invention aims to provide a high carbon chromium roller workpiece and a multi-stage heat treatment preparation process thereof. The specific technical solution is as follows:

[0005] In a first aspect, the present invention provides a multi-stage heat treatment process for preparing a high carbon chromium roller workpiece, comprising:

[0006] Step S1, loading a plurality of high carbon chromium roller workpieces into a heating furnace in a staggered arrangement;

[0007] Step S2, performing a first heat treatment on the high carbon chromium roller workpiece; the first heat treatment comprises controlling the heating furnace to heat to a temperature of A at a first heating rate. c1 , the holding time is t1; among them, A c1 The temperature at which the structure of the high carbon chromium roller workpiece begins to transform into austenite;

[0008] Step S3, performing a second heat treatment on the high carbon chromium roller workpiece; the second heat treatment comprises controlling the heating furnace to heat to a temperature of A at a second heating rate. c1 +30~A c1 +50℃, holding time is t2;

[0009] Step S4, performing a third heat treatment on the high carbon chromium roller workpiece; the third heat treatment comprises controlling the heating furnace to heat to a temperature of A at a third heating rate. c1 +60~A c1 +80℃, holding time is t3;

[0010] Step S5, performing salt bath quenching treatment on the high carbon chromium roller workpiece; wherein the salt bath quenching temperature is M s -20~M s -10℃, salt bath quenching time is t4; M s The temperature at which the high carbon chromium roller begins to produce martensite structure in the workpiece;

[0011] Step S6, performing water quenching treatment on the high carbon chromium roller workpiece; the water quenching temperature is 0-5°C, and the water quenching time is t5;

[0012] Step S7: performing post-processing on the high carbon chromium roller workpiece to obtain a target high carbon chromium roller workpiece.

[0013] Optionally, the first heating rate used in step S2 is 90-110° C. / h, and the insulation time t1 used is 25-35 min.

[0014] Optionally, the second heating rate used in step S3 is 55-65° C. / h, and the insulation time t2 used is 8-12 min.

[0015] Optionally, the third heating rate adopted in step S4 is 77-83° C. / h, and the insulation time t3 adopted is 8-12 min.

[0016] Optionally, the salt bath quenching time t4 used in step S5 is 30~60min; the transfer time of transferring the high carbon chromium roller workpiece from the heating furnace to the salt bath is less than 20s; the salt bath quenching treatment also includes a first stirring treatment; wherein the stirring speed is 1000~1500r / min.

[0017] Optionally, the water content of the salt bath used in step S5 is W1=k·D+z·H; wherein W1 is the water content of the salt bath, D is the diameter of the high carbon chromium roller workpiece, H is the height of the high carbon chromium roller workpiece, k is 0.005~0.02, and z is 0.002~0.02.

[0018] Optionally, the water quenching time t5 used in step S6 is 15~25min; the transfer time of transferring the high carbon chromium roller workpiece from the salt bath to water is less than 20s; the water quenching treatment also includes a second stirring treatment; wherein the stirring speed is 1000~1500r / min.

[0019] Optionally, in step S7, the post-processing includes sequentially performing a cleaning process and a tempering process on the high carbon chromium roller workpiece;

[0020] The tempering temperature used in the tempering treatment is 160-200° C., and the tempering time is 12-14 hours.

[0021] In a second aspect, the present invention provides a high carbon chromium roller workpiece, which is prepared by the multi-stage heat treatment preparation process of the high carbon chromium roller workpiece.

[0022] Optionally, the high carbon chromium roller workpiece includes a GCr15SiMn high carbon chromium roller workpiece.

[0023] The application of the technical solution of the present invention has at least the following beneficial effects:

[0024] The present invention provides a high-carbon chromium roller workpiece and a multi-stage heat treatment preparation process thereof. In step S1, a plurality of high-carbon chromium roller workpieces are loaded into a heating furnace in a staggered arrangement, so as to facilitate subsequent uniform heating of each high-carbon chromium roller workpiece; a first heat treatment in step S2, a second heat treatment in step S3, and a third heat treatment in step S4 are adopted to implement multi-stage heating treatment of the high-carbon chromium roller workpiece. By strictly controlling the heating rate, heating temperature, and holding time, the carbides and alloy elements in the high-carbon chromium roller workpiece material can be significantly dissolved into the matrix, which is beneficial to improving the core hardness of the high-carbon chromium roller workpiece during the salt bath quenching treatment in step S5 and the water quenching treatment in step S6, and reducing the degree of hardness gradient attenuation. and residual austenite content; specifically, the use of salt bath quenching treatment is beneficial to the cooling rate of the high carbon chromium roller workpiece surface exceeding the critical speed of martensite transformation, and at the same time will not quench the surface of the high carbon chromium roller workpiece; the use of water quenching treatment is to increase the cooling rate of the core of the high carbon chromium roller workpiece, reduce the production of troostite in its core, and increase the hardness of the workpiece core; while improving the hardness of the workpiece core, the gradient attenuation degree of the workpiece core hardness and the workpiece surface hardness can be reduced; the use of multi-stage heating treatment can significantly dissolve the carbides and alloy elements in the high carbon chromium roller workpiece material into the matrix, improve the hardenability of the high carbon chromium roller workpiece material, improve the hardness of the workpiece core, and help reduce the residual austenite content.

[0025] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0027] Figure 1This is a schematic structural diagram of a plurality of high-carbon chromium roller workpieces arranged in a staggered manner in Example 1 of the present invention;

[0028] Figure 2 Schematic diagram of the multi-stage heat treatment process for preparing a carbon-chromium roller workpiece in Example 1 of the present invention;

[0029] Figure 3 This is a metallographic diagram of the core structure of the high carbon chromium roller workpiece prepared in Example 1 of the present invention;

[0030] Figure 4 This is a metallographic diagram of the core structure of the high carbon chromium roller workpiece prepared in Comparative Example 1 of the present invention;

[0031] Among them, 1. High carbon chromium roller workpiece. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention. Example 1:

[0033] A multi-stage heat treatment preparation process for a high carbon chromium roller workpiece, comprising:

[0034] Step S1: Arrange multiple high-carbon chromium roller workpieces 1 (the high-carbon chromium material is selected from GCr15SiMn high-carbon chromium material that complies with the national standard GB / T18254-2016 high-carbon chromium bearing steel. The size of the high-carbon chromium roller workpiece 1 can be selected in the range of φ70*(70-120) mm. In this embodiment 1, the size of the high-carbon chromium roller workpiece 1 is φ70*120 mm) in a staggered arrangement (i.e., with gaps, see Figure 1 ) into the heating furnace;

[0035] Step S2, see Figure 2 , performing a first heat treatment on the high carbon chromium roller workpiece 1; the first heat treatment comprises controlling the heating furnace to heat to a temperature of A at a first heating rate of 100°C / h c1 , the holding time is t1=30min; among them, A c1 A is the temperature at which the structure of the high carbon chromium roller workpiece 1 begins to transform into austenite. c1 The value range is 750±10℃. In this embodiment 1, A c1 The specific value is 750℃;

[0036] Step S3, performing a second heat treatment on the high carbon chromium roller workpiece 1; the second heat treatment comprises controlling the heating furnace to heat the workpiece at a second heating rate of 60°C / h to a temperature of A c1 +40℃, holding time is t2=10min;

[0037] Step S4, performing a third heat treatment on the high carbon chromium roller workpiece 1; the third heat treatment comprises controlling the heating furnace to heat the high carbon chromium roller workpiece 1 at a third heating rate of 80°C / h to a temperature of A. c1 +70℃, holding time is t3=10min;

[0038] Step S5, performing salt bath quenching treatment on the high carbon chromium roller workpiece 1; wherein the salt bath quenching temperature is M s -15℃, salt bath quenching time is t4; M s M is the temperature at which the high carbon chromium roller workpiece 1 begins to generate martensite structure. s The value range is 170±5℃. In this embodiment 1, M s The specific value is 172℃; M s =441.04-360.4X γc +11.79ln(d γ ), where d γ is the austenite grain size, which ranges from 12.6±5μm. In this embodiment 1, d γ The specific value is 13μm; X γc is the molar fraction of carbon atoms in austenite, and its value range is 0.8-0.85. In this embodiment 1, X γc The specific value is 0.83;

[0039] Step S6, performing water quenching treatment on the high carbon chromium roller workpiece 1; the water quenching temperature is 0° C., and the water quenching time is t5;

[0040] Step S7: post-processing the high carbon chromium roller workpiece 1 to obtain a target high carbon chromium roller workpiece 1.

[0041] The salt bath quenching time t4 used in step S5 is 10 minutes; the transfer time of transferring the high carbon chromium roller workpiece 1 from the heating furnace to the salt bath is less than 20 seconds; the salt bath quenching treatment also includes a first stirring treatment; wherein the stirring speed is 1250 r / min.

[0042] The salt bath water content used in step S5 is W1 = k·D + z·H, where W1 is the salt bath water content, D is the diameter of the high-carbon chromium roller workpiece 1, H is the height of the high-carbon chromium roller workpiece 1, k is 0.012, and z is 0.01. Limiting the salt bath water content ensures that the cooling rate of the high-carbon chromium roller workpiece 1 surface exceeds the critical martensitic transformation speed while preventing quenching cracks on the high-carbon chromium roller workpiece 1 surface.

[0043] The water quenching time t5 used in step S6 is 20 minutes; the transfer time of transferring the high carbon chromium roller workpiece 1 from the salt bath to the water is less than 20 seconds; the water quenching treatment also includes a second stirring treatment; wherein the stirring speed is 1250 r / min.

[0044] In step S7, the post-processing includes sequentially performing cleaning and tempering on the high carbon chromium roller workpiece 1;

[0045] The tempering temperature used in the tempering treatment is 180° C. and the tempering time is 14 h. Example 2:

[0046] The same as in Example 1 is that the tempering time is 12 h.

[0047] Comparative Example 1:

[0048] The high carbon chromium roller workpiece 1 is prepared by a conventional martensitic quenching heat treatment process. Specifically, the high carbon chromium roller workpiece 1 of the same material and size as in Example 1 is loaded into a heating furnace in a staggered arrangement; the heating furnace is controlled to heat at a heating rate of 100°C / h to a temperature of A. c1 +70℃, holding time is 60min; the high carbon chromium roller workpiece 1 is subjected to salt bath quenching treatment, and the salt bath quenching treatment used is different from that in Example 1 in that the quenching time is 45min; the high carbon chromium roller workpiece 1 is air-cooled, and after cooling to room temperature, it is cleaned in the same way as in Example 1; the high carbon chromium roller workpiece 1 is cryogenically treated with liquid nitrogen, the treatment temperature is -80℃, and the treatment time is 2h; after the temperature of the high carbon chromium roller workpiece 1 returns to room temperature, it is tempered at 180℃ for 12h.

[0049] Comparative Example 2:

[0050] Different from Comparative Example 1, the cryogenic treatment was cancelled.

[0051] Comparative Example 3:

[0052] The difference from Example 2 is that the water quenching treatment is replaced by air cooling treatment, that is, the high carbon chromium roller workpiece 1 is subjected to air cooling treatment, and then the post-treatment similar to that of Example 2 is performed after cooling to room temperature.

[0053] The high carbon chromium roller workpieces 1 prepared in Examples 1-2 and Comparative Examples 1-3 and samples of the high carbon chromium roller workpieces 1 provided by a domestic bearing factory were subjected to performance tests, respectively. The performance test results are shown in Table 1.

[0054] Table 1 Performance test results

[0055]

[0056] As shown in Table 1, compared to Comparative Examples 2-3 and a high-carbon chromium roller workpiece sample provided by a domestic bearing manufacturer, the present invention's combination of multi-stage heating treatment, two-stage quenching treatment, and appropriate tempering time in Examples 1-2 significantly improves the core hardness of the prepared high-carbon chromium roller workpiece 1, while maintaining essentially unchanged surface hardness, and significantly reduces the degree of hardness gradient decay and retained austenite content. Compared to Comparative Example 1, the present invention's combination of multi-stage heating treatment, two-stage quenching treatment, and appropriate tempering time in Example 1 significantly improves the core hardness of the prepared high-carbon chromium roller workpiece 1, while maintaining essentially unchanged surface hardness, and significantly reduces the degree of hardness gradient decay.

[0057] Depend on Figure 3-Figure 4 It can be seen that compared with Comparative Example 1, the high carbon chromium roller workpiece prepared in Example 1 has a fine structure, good uniformity, and a significantly reduced troostite content, which is beneficial to improving the core hardness of the workpiece and reducing the gradient attenuation degree of the core hardness and the surface hardness of the workpiece.

[0058] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A multi-stage heat treatment process for preparing a high carbon chromium roller workpiece, characterized in that: include: Step S1, loading a plurality of high-carbon chromium roller workpieces into a heating furnace in a staggered arrangement; wherein the material of the high-carbon chromium roller workpiece is selected from GCr15SiMn high-carbon chromium material that complies with the national standard GB / T18254-2016 high-carbon chromium bearing steel, and the size range of the high-carbon chromium roller workpiece is φ70*(70-120) mm; Step S2, performing a first heat treatment on the high carbon chromium roller workpiece; the first heat treatment comprises controlling the heating furnace to heat to a temperature of A at a first heating rate. c1 , the holding time is t1; among them, A c1 The temperature at which the structure of the high carbon chromium roller workpiece begins to transform into austenite; the first heating rate is 90-110°C / h, and the holding time t1 is 25-35 minutes; Step S3, performing a second heat treatment on the high carbon chromium roller workpiece; the second heat treatment comprises controlling the heating furnace to heat to a temperature of A at a second heating rate. c1 +30~A c1 +50℃, holding time is t2; the second heating rate is 55-65℃ / h, the holding time t2 is 8-12min; Step S4, performing a third heat treatment on the high carbon chromium roller workpiece; the third heat treatment comprises controlling the heating furnace to heat to a temperature of A at a third heating rate. c1 +60~A c1 +80℃, holding time is t3; the third heating rate is 77-83℃ / h, and the holding time t3 is 8-12min; Step S5, performing salt bath quenching treatment on the high carbon chromium roller workpiece; wherein the salt bath quenching temperature is M s -20~M s -10℃, salt bath quenching time is t4; M s The temperature at which the structure in the high carbon chromium roller workpiece begins to generate martensite structure; the salt bath quenching time t4 is 30 to 60 minutes; the water content of the salt bath used is W1 = k·D + z·H; wherein W1 is the water content of the salt bath, D is the diameter of the high carbon chromium roller workpiece, H is the height of the high carbon chromium roller workpiece, k is 0.005 to 0.02, and z is 0.002 to 0.02; Step S6, water quenching the high carbon chromium roller workpiece; the water quenching temperature is 0-5°C, the water quenching time is t5; the water quenching time t5 is 15-25 minutes; Step S7: performing post-processing on the high carbon chromium roller workpiece to obtain a target high carbon chromium roller workpiece.

2. The multi-stage heat treatment preparation process for high carbon chromium roller workpiece according to claim 1, characterized in that: The transfer time of transferring the high carbon chromium roller workpiece from the heating furnace to the salt bath is less than 20 seconds; the salt bath quenching treatment also includes a first stirring treatment; wherein the stirring speed is 1000-1500 r / min.

3. The multi-stage heat treatment process for preparing a high carbon chromium roller workpiece according to claim 1, characterized in that: The transfer time of transferring the high carbon chromium roller workpiece from the salt bath to the water is less than 20 seconds; the water quenching treatment also includes a second stirring treatment; wherein the stirring speed is 1000-1500 r / min.

4. The multi-stage heat treatment process for preparing a high carbon chromium roller workpiece according to claim 1, characterized in that: In step S7, the post-processing includes sequentially performing a cleaning process and a tempering process on the high carbon chromium roller workpiece; The tempering temperature used in the tempering treatment is 160-200° C., and the tempering time is 12-14 hours.

5. A high carbon chromium roller workpiece, characterized in that: The high carbon chromium roller workpiece is prepared by the multi-stage heat treatment preparation process according to any one of claims 1 to 4.

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