Heat treatment method of hobbing cutter ring and hobbing cutter ring

Abstract

The invention provides a heat treatment method of a hobbing cutter ring and the hobbing cutter ring, and relates to the technical field of high-speed steel hobbing cutter ring casting.The heat treatment method comprises the following steps that an as-cast cutter ring is subjected to embedding treatment, so that the as-cast cutter ring can isolate oxygen in the normalizing heat treatment process; and carrying out normalizing heat treatment on the embedded as-cast cutter ring to obtain the hob cutter ring. The embedded as-cast cutter ring is isolated from oxygen, and during normalizing heat treatment, on one hand, the surface of the cutter ring can be prevented from being oxidized at high temperature, and the stability, high strength and high hardness of the surface structure of the hob cutter ring are ensured; and on the other hand, heat treatment in a vacuum furnace is not needed, discharging cooling can be achieved, and the cooling speed is high, so that the content of martensite in the hobbing cutter ring is guaranteed, meanwhile, carbide coarsening can be restrained, and therefore the high hardness and impact toughness of the hobbing cutter ring are guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of high-speed steel hob cutter ring casting, and particularly relates to a heat treatment method for a hob cutter ring and the hob cutter ring. Background Art

[0002] The cutter ring is an important part of the shield machine cutter. Its main function is to break rocks by rotating and squeezing them. In extremely hard rocks or highly abrasive formations, the cutter ring faces huge challenges. It not only requires extremely high hardness and wear resistance, but also requires sufficient toughness and fracture resistance. Therefore, high-speed steel is usually used to make the cutter ring.

[0003] At present, the main heat treatment method for the cutter ring of the hob is to place the cutter ring in a muffle furnace for normalizing heat treatment. However, high-speed steel is highly sensitive to oxygen at high temperatures, so the surface of the cutter ring is easily oxidized, resulting in a decrease in the surface precision of the cutter ring after heat treatment (for example, a thicker oxide layer is formed on the surface). It will also cause the surface components of the cutter ring to burn, resulting in a loose surface of the cutter ring, and a decrease in the strength and hardness of the surface of the cutter ring. In order to solve the problem of easy oxidation of the cutter ring surface, the relevant technology proposes to place the cutter ring in a vacuum heat treatment furnace for normalizing heat treatment. The vacuum heat treatment furnace can isolate oxygen and avoid oxidation of the cutter ring surface. However, during cooling, in order to protect the precision parts in the furnace, the furnace door cannot be opened directly, that is, it can only be cooled with the furnace. Due to the slow cooling speed with the furnace, the martensite content in the final cutter ring is low, and the carbide and grain size are large, which leads to the hardness, strength and impact toughness of the high-speed steel hob cutter ring. Reduced.

[0004] In view of this, it is necessary to provide a heat treatment method for a hob cutter ring to solve the problem that the cutter ring is prone to surface oxidation during normalizing heat treatment in a muffle furnace. Summary of the invention

[0005] Therefore, the present invention provides a heat treatment method for a hob cutter ring and a hob cutter ring, which can solve the technical problem in the prior art that the hob cutter ring is prone to surface oxidation during normalizing heat treatment in a muffle furnace.

[0006] In order to solve the above problems, the present invention provides a heat treatment method for a hob cutter ring, comprising the following steps:

[0007] The cast cutter ring is embedded so that the cast cutter ring can be isolated from oxygen during the normalizing heat treatment process; then the embedded cast cutter ring is subjected to normalizing heat treatment to obtain the hob cutter ring.

[0008] Further, the step of embedding the as-cast knife ring includes:

[0009] The as-cast cutter ring is placed in a ceramic container; wherein the ceramic container is filled with embedding powder, and the as-cast cutter ring is embedded in the embedding powder.

[0010] Furthermore, the embedding powder is graphite powder;

[0011] Preferably, the particle size of the graphite powder is 4.0 to 10.0 μm;

[0012] Preferably, the density of the graphite powder is 2.5-3.0 g / cm 3 ;

[0013] Preferably, the flowability of the graphite powder is 30 to 50 s / g.

[0014] Furthermore, in the step of normalizing heat treatment:

[0015] T = 1000 + 100 × k / m; wherein T is the normalizing temperature, in ° C; k is the thickness of the embedding powder embedded outside the as-cast cutter ring, in cm; m is the thickness of the as-cast cutter ring, in cm; and / or

[0016] t=120+100×k / m; where t is the holding time, in min; k is the thickness of the embedding powder embedded outside the as-cast knife ring, in cm; m is the thickness of the as-cast knife ring, in cm;

[0017] Preferably, 0cm<m≤50cm, 0<k / m≤1.

[0018] Furthermore, in the normalizing heat treatment step: the heating rate is 2 to 5°C / min; and / or

[0019] The normalizing heat treatment is carried out in a muffle furnace.

[0020] Furthermore, after the normalizing heat treatment step, the process further includes the following steps:

[0021] After coming out of the furnace, the graphite powder on the surface of the hob cutter ring is removed and then air-cooled to room temperature.

[0022] Furthermore, before the step of embedding the as-cast cutter ring, the method further includes: surface cleaning and degreasing the as-cast cutter ring.

[0023] Furthermore, in terms of mass percentage, the cast knife ring includes: C: 3.3-3.7wt%, Si: 5.3-5.7wt%, Al: 0.4-0.8wt%, B: 0.1-0.3wt%, V: 8.5-9.0wt%, Nb: 0.4-0.8wt%, Mo: 2.3-2.7wt%, N: 0.06-0.09wt%, La+Ce: 0.2-0.5wt%, and the balance is Fe.

[0024] On the other hand, the present invention provides a hob cutter ring, wherein the grain size of the hob cutter ring is 2.5 to 4 μm; the microstructure of the hob cutter ring includes a martensite matrix, austenite and carbide;

[0025] Among them, the volume fraction of the martensite matrix is ​​40-50%; the volume fraction of the austenite is 10-15%; the carbides are dispersed in the martensite matrix, and the carbides include VC and M7C3; the volume fraction of VC is 25-30%, and the size of VC is 4-8μm; the volume fraction of M7C3 is 13-17%, and the size of M7C3 is 10-15μm.

[0026] Furthermore, the hob cutter ring is obtained by subjecting the cast cutter ring to heat treatment and fine machining; wherein the heat treatment adopts any of the heat treatment methods described above.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] 1. The present invention provides a method for heat treatment of a hob cutter ring, wherein the cast cutter ring is embedded and then subjected to normalizing heat treatment to obtain the hob cutter ring; based on the method of the present application, the embedded cast cutter ring is isolated from oxygen, and during the normalizing heat treatment, on the one hand, oxidation of the cutter ring surface at high temperatures can be avoided, thereby ensuring the stability of the hob cutter ring surface structure, as well as high strength and high hardness; on the other hand, there is no need to perform heat treatment in a vacuum furnace, and the cutter ring can be cooled after being taken out of the furnace, with a high cooling rate, thereby ensuring the martensite content in the hob cutter ring, and at the same time inhibiting the coarsening of carbides, thereby ensuring the high hardness and impact toughness of the hob cutter ring.

[0029] 2. Furthermore, the present invention uses graphite powder to embed the cast cutter ring. Since the graphite powder has a moderate density, does not react with the cast cutter ring, and has excellent thermal conductivity, it can better isolate oxygen and ensure heat transfer during the heat treatment process to ensure sufficient heat treatment; further, the particle size of the graphite powder is set to 4.0-10.0 μm to avoid graphite powder agglomeration while ensuring that oxygen remains in the graphite powder; the fluidity of the graphite powder is set to 30-50 s / g to ensure that the graphite powder can embed the cast cutter ring of complex shape.

[0030] 3. On the other hand, the present invention provides a hob cutter ring, which is obtained by the above-mentioned heat treatment method and has a grain size of 2.5 to 4 μm; the microstructure of the hob cutter ring includes a martensite matrix, austenite and carbides; wherein the volume fraction of the martensite matrix is ​​40 to 50%; the volume fraction of the austenite is 10 to 15%; the carbides are dispersed in the martensite matrix, which include VC and M7C3, the volume fraction of VC is 25 to 30%, and the size of VC is 4 to 8 μm; the volume fraction of M7C3 is 13 to 17%, and the size of M7C3 is 10 to 15 μm; the high content of martensite ensures the surface hardness and impact toughness of the hob cutter ring, the fine and dispersed carbides can play the role of second phase strengthening to further improve the hardness and strength of the hob cutter ring, and the grain refinement can simultaneously improve the toughness of the alloy through the fine grain strengthening effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0032] Figure 1 Schematic diagram of the heat treatment method of the present invention;

[0033] Figure 2 This is a microstructure morphology of the hob cutter ring prepared in Example 2;

[0034] Figure 3 This is a comparison chart of the impact toughness and compressive strength of the hob cutter rings prepared in Comparative Example 1 and Example 1;

[0035] Figure 4 This is a comparison chart of the impact toughness and compressive strength of the hob cutter rings prepared in Comparative Example 2 and Example 1;

[0036] Figure 5 A comparison chart of the compressive strength and impact toughness of the hob cutter rings prepared in Example 3 and Example 1;

[0037] Figure 6 This is a microstructure morphology of the hob cutter ring prepared in Example 4;

[0038] Figure 7 A comparison diagram of the EBSD morphology and relative content of phase structures of the hob cutter ring prepared in Example 4 and Example 1;

[0039] Figure 8 This is a comparison diagram of the distribution of carbides in the hob cutter rings prepared in Comparative Example 3 and Example 1;

[0040] Fig. 9 This is a comparison chart of the compressive strength and impact toughness of the hob cutter ring prepared in Comparative Example 3 and Example 1. DETAILED DESCRIPTION

[0041] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0042] The present invention provides a heat treatment method for a hob cutter ring, comprising the following steps:

[0043] Graphite powder is loaded into a ceramic container, the cast cutter ring is placed in the ceramic container, and then graphite powder is loaded into the ceramic container to cover the cast cutter ring, ensuring that the cast cutter ring is buried in the embedding powder, that is, the embedding of the cast cutter ring is completed, and the cast cutter ring is isolated from oxygen; then the lid of the ceramic container is covered, and the ceramic container containing the graphite powder and the cast cutter ring is placed in a muffle furnace, and the muffle furnace is heated to the normalizing temperature at a heating rate of 2 to 5°C / min to start the normalizing heat treatment; after being taken out of the furnace, a metal brush is used to remove the graphite powder attached to the surface of the cutter ring, and then it is air-cooled to room temperature to obtain a hob cutter ring.

[0044] The particle size of graphite powder is 4.0-10.0 μm; the density of graphite powder is 2.5-3.0 g / cm 3 ; The fluidity of graphite powder is 30-50s / g. As an excellent thermal conductive and heat insulating material, graphite can effectively control the temperature distribution during heat treatment (i.e., evenly distribute the heat during heating), reduce the adverse effects of thermal stress on the cutter ring, and the chemical stability of graphite also ensures the purity of the cutter ring during heat treatment; when the particle size of graphite powder is too large, the pores between the powders are large, and a certain amount of oxygen is retained in the graphite powder, which is easy to cause the cutter ring embedded in graphite to oxidize at high temperature; when the particle size of graphite powder is too small, the surface area is larger, and more surface energy is exposed to the outside. These surface energies will cause the graphite powder to aggregate into agglomerates, which is not conducive to fully wrapping the cast cutter ring; when the density of graphite powder does not meet the above range, it is easy to float or sink and aggregate in the ceramic container, resulting in poor oxygen isolation effect; when the fluidity of graphite powder does not meet the above range, the graphite fluidity is poor, and the graphite powder cannot fully embed the cutter ring of complex shape, resulting in high temperature oxidation. Removing the graphite powder attached to the surface after leaving the furnace can further increase the cooling rate.

[0045] In some embodiments, in the normalizing heat treatment: T=1000+100×k / m; wherein T is the normalizing temperature, in degrees Celsius; k is the thickness of the graphite powder embedded outside the as-cast cutter ring, in cm; m is the thickness of the as-cast cutter ring, in cm; t=120+100×k / m; wherein t is the holding time, in min; k is the thickness of the graphite powder embedded outside the as-cast cutter ring, in cm; m is the thickness of the as-cast cutter ring, in cm; preferably, 0cm<m≤50cm, 0<k / m≤1. After the as-cast cutter ring is embedded with graphite powder, the graphite powder will increase the heat insulation effect of the heat treatment component (as-cast cutter ring). Therefore, the normalizing temperature and holding time are adjusted according to the thickness of the graphite powder embedded outside the as-cast cutter ring and the thickness of the as-cast cutter ring itself to ensure that the as-cast cutter ring is fully normalized. However, if the normalizing temperature is too high and the holding time is too long, the structure will become coarse, including carbides and martensite matrix.

[0046] Among them, the thickness k of the graphite powder embedded outside the cast knife ring is the average thickness calculated by the thickness of the graphite powder on the top of the cast knife ring in the ceramic container, the thickness of the graphite powder on the bottom of the cast knife ring, and the thickness of the graphite powder on both sides of the cast knife ring; among them, the thickness of the graphite powder on the top of the cast knife ring refers to the thickness of the graphite powder above the upper surface of the cast knife ring, which can be measured by a ruler; the thickness of the graphite powder on the bottom of the cast knife ring refers to the thickness of the graphite powder below the lower surface of the cast knife ring, which can be measured by a ruler; the thickness of the graphite powder on both sides of the cast knife ring is calculated by the size of the ceramic container and the diameter of the cast knife ring; for irregularly shaped cast knife rings, the thickness m of the cast knife ring is its average thickness.

[0047] Based on the above method, the cast cutter ring after embedding is isolated from oxygen. During the normalizing heat treatment, on the one hand, oxidation of the cutter ring surface at high temperature can be avoided, thereby ensuring the stability of the surface structure of the hob cutter ring, as well as high strength and hardness; on the other hand, there is no need to perform heat treatment in a vacuum furnace, and the cutter ring can be cooled after being taken out of the furnace at a high cooling rate, thereby ensuring the martensite content in the hob cutter ring and inhibiting the coarsening of carbides, thereby ensuring the high hardness and impact toughness of the hob cutter ring.

[0048] Among them, the driving force for the formation of martensite is mainly determined by the cooling rate and the temperature of the supercooled austenite. The cooling rate of supercooled austenite must be greater than the critical cooling rate to prevent it from transforming into pearlite or bainite; when the cooling rate is low, the supercooled austenite cannot quickly reduce its temperature, resulting in an increase in the driving force for other phase changes, thereby inhibiting the formation of martensite. In addition, the cooling rate determines the crystallization behavior of the material. When the cooling rate is slow, the supercooled austenite (i.e., austenite that has not undergone phase change) has more time to crystallize, thereby forming larger grains in the solid structure after cooling; while a higher cooling rate can make the austenite solidify quickly, forming smaller grains. The high content of martensite ensures the surface hardness and impact toughness of the hob cutter ring, and the finely dispersed carbides can play the role of second phase strengthening to further improve the hardness and strength of the hob cutter ring. Grain refinement can simultaneously improve the toughness of the alloy through fine grain strengthening.

[0049] Before embedding the as-cast knife ring, the process also includes: surface cleaning and degreasing of the as-cast knife ring to ensure the purity of the material surface.

[0050] In some embodiments, the cast knife ring includes, by mass percentage: C: 3.3-3.7wt%, Si: 5.3-5.7wt%, Al: 0.4-0.8wt%, B: 0.1-0.3wt%, V: 8.5-9.0wt%, Nb: 0.4-0.8wt%, Mo: 2.3-2.7wt%, N: 0.06-0.09wt%, La+Ce: 0.2-0.5wt%, and the balance is Fe.

[0051] On the other hand, the present invention provides a hob cutter ring, the grain size of the hob cutter ring is 2.5-4 μm; the microstructure of the hob cutter ring includes a martensite matrix, austenite and carbide;

[0052] Among them, the volume fraction of the martensite matrix is ​​40-50%; the volume fraction of austenite is 10-15%; carbides are dispersed in the martensite matrix, and carbides include VC and M7C3; the volume fraction of VC is 25-30%, and the size of VC is 4-8μm; the volume fraction of M7C3 is 13-17%, and the size of M7C3 is 10-15μm. Among them, M7C3 includes Cr7C3 and Fe7C3. The finely dispersed carbides can play the role of second phase strengthening to further improve the hardness and strength of the knife ring, and grain refinement can simultaneously improve the toughness of the knife ring through fine grain strengthening.

[0053] Furthermore, the hob cutter ring is obtained by subjecting the cast cutter ring to heat treatment and fine machining; wherein the heat treatment adopts any of the above-mentioned heat treatment methods.

[0054] The cast cutter ring in the present invention is obtained by smelting raw materials according to the components to obtain an alloy ingot, which is then cast twice to form a hob cutter ring, and then subjected to rough machining; the hob cutter ring after heat treatment according to the above method is cleaned, stress-relief annealed and other fine processing to further improve the performance and service life of the hob cutter ring.

[0055] The present invention is further described below with reference to specific embodiments and comparative examples.

[0056] Example 1

[0057] This embodiment provides a method for heat treatment of a hob cutter ring. The heat treatment process is as follows: Figure 1 As shown, the specific steps include:

[0058] Graphite powder is loaded into a ceramic container, the cast cutter ring is placed in the ceramic container, and then graphite powder is loaded into the ceramic container to cover the cast cutter ring, thus completing the embedding of the cast cutter ring and isolating the cast cutter ring from oxygen; then the lid of the ceramic container is closed, and the ceramic container containing the graphite powder and the cast cutter ring is placed in a muffle furnace, and the muffle furnace is heated to the normalizing temperature at a heating rate of 3°C / min to start the normalizing heat treatment; after being taken out of the furnace, a metal brush is used to remove the graphite powder attached to the surface of the cutter ring, and then the cutter ring is air-cooled to room temperature to obtain a hob cutter ring.

[0059] The cast knife ring includes, by mass percentage, C: 3.5wt%, Si: 5.5wt%, Al: 0.6wt%, B: 0.2wt%, V: 8.7wt%, Nb: 0.6wt%, Mo: 2.5wt%, N: 0.07wt%, La+Ce: 0.4wt%, and the balance is Fe; the particle size of the graphite powder is 6μm; the density of the graphite powder is 2.7g / cm 3 ; The fluidity of graphite powder is 40s / g; the thickness of graphite powder embedded outside the cast knife ring is 10cm; the thickness of the cast knife ring is 20cm; the normalizing temperature is 1050℃; the holding time is 170min.

[0060] Example 2

[0061] This embodiment provides a heat treatment method for a hob cutter ring, which specifically includes the following steps:

[0062] Graphite powder is loaded into a ceramic container, the cast cutter ring is placed in the ceramic container, and then graphite powder is loaded into the ceramic container to cover the cast cutter ring, thus completing the embedding of the cast cutter ring and isolating the cast cutter ring from oxygen; then the lid of the ceramic container is closed, and the ceramic container containing the graphite powder and the cast cutter ring is placed in a muffle furnace, and the muffle furnace is heated to the normalizing temperature at a heating rate of 2.5°C / min to start the normalizing heat treatment; after being taken out of the furnace, a metal brush is used to remove the graphite powder attached to the surface of the cutter ring, and then the cutter ring is air-cooled to room temperature to obtain a hob cutter ring.

[0063] The cast knife ring includes, by mass percentage, C: 3.4wt%, Si: 5.6wt%, Al: 0.7wt%, B: 0.15wt%, V: 8.6wt%, Nb: 0.5wt%, Mo: 2.4wt%, N: 0.08wt%, La+Ce: 0.3wt%, and the balance is Fe; the particle size of the graphite powder is 5μm; the density of the graphite powder is 2.6g / cm 3 ; The fluidity of graphite powder is 35s / g; the thickness of graphite powder embedded outside the cast knife ring is 12cm; the thickness of the cast knife ring is 30cm; the normalizing temperature is 1040℃; the holding time is 160min.

[0064] The microstructure of the hob cutter ring obtained in this embodiment is as follows: Figure 2 As shown in the figure, it can be seen that there is no significant oxidation behavior on the surface of the hob cutter ring, and the surface is composed of martensite, austenite and carbide. Among them, the carbides are finely dispersed, the size of M7C3 eutectic carbides is about 10-15μm, and the size of VC is 4-8μm. It is beneficial to improve the impact toughness and strength of the cutter ring.

[0065] Comparative Example 1

[0066] This comparative example provides a heat treatment method for a hob cutter ring, which specifically includes the following steps:

[0067] The as-cast cutter ring is placed in a muffle furnace, and the temperature of the muffle furnace is increased to the normalizing temperature at a heating rate of 3°C / min to start the normalizing heat treatment; after being taken out of the furnace, it is air-cooled to room temperature to obtain a hob cutter ring.

[0068] Among them, in terms of mass percentage, the cast knife ring includes: C: 3.5wt%, Si: 5.5wt%, Al: 0.6wt%, B: 0.2wt%, V: 8.7wt%, Nb: 0.6wt%, Mo: 2.5wt%, N: 0.07wt%, La+Ce: 0.4wt%, and the balance is Fe; the normalizing temperature is 1050°C; and the holding time is 160min.

[0069] The impact toughness and compressive strength of the hob cutter ring prepared in this comparative example and in Example 1 are compared. Figure 3 As shown, it can be seen that the impact toughness and compressive strength of the hob cutter ring of this comparative example are significantly lower than those of Example 1. This is because the heat treatment method of this comparative example does not use graphite embedded cast cutter ring, but directly heat treats the cutter ring, causing more serious burn damage on the cutter ring surface and less martensite and carbide content, which leads to a decrease in the hardness and compressive strength of the cutter ring surface.

[0070] Comparative Example 2

[0071] This comparative example provides a heat treatment method for a hob cutter ring, which specifically includes the following steps:

[0072] Graphite powder is loaded into a ceramic container, the cast cutter ring is placed in the ceramic container, and then graphite powder is loaded into the ceramic container to cover the cast cutter ring, thus completing the embedding of the cast cutter ring and isolating the cast cutter ring from oxygen; then the lid of the ceramic container is closed, and the ceramic container containing the graphite powder and the cast cutter ring is placed in a muffle furnace, and the muffle furnace is heated to the normalizing temperature at a heating rate of 3°C / min to start the normalizing heat treatment; after being taken out of the furnace, a metal brush is used to remove the graphite powder attached to the surface of the cutter ring, and then the cutter ring is air-cooled to room temperature to obtain a hob cutter ring.

[0073] The cast knife ring includes, by mass percentage, C: 3.5wt%, Si: 5.5wt%, Al: 0.6wt%, B: 0.2wt%, V: 8.7wt%, Nb: 0.6wt%, Mo: 2.5wt%, N: 0.07wt%, La+Ce: 0.4wt%, and the balance is Fe; the particle size of the graphite powder is 6μm; the density of the graphite powder is 2.7g / cm 3 ; The fluidity of graphite powder is 40s / g; the thickness of graphite powder embedded outside the cast knife ring is 10cm; the thickness of the cast knife ring is 20cm; the normalizing temperature is 1020℃; the holding time is 170min.

[0074] The impact toughness and compressive strength of the hob cutter ring prepared in this comparative example and in Example 1 are compared. Figure 4 As shown, it can be seen that the impact toughness and compressive strength of the hob cutter ring of this comparative example are significantly lower than those of Example 1. This is because the normalizing temperature of this comparative example is lower than the temperature calculated according to T=1000+100×k / m, resulting in the cutter ring not reaching the complete austenitization temperature after graphite embedding, and the microstructure grains are coarse, which reduces its impact toughness and compressive strength.

[0075] Embodiments 1 and 2 are preferred embodiments that adopt the essential features and preferred technical features of the present invention, and the following embodiments are embodiments that adopt the essential features and non-preferred technical features.

[0076] Example 3

[0077] This embodiment provides a heat treatment method for a hob cutter ring, which specifically includes the following steps:

[0078] Graphite powder is loaded into a ceramic container, the cast cutter ring is placed in the ceramic container, and then graphite powder is loaded into the ceramic container to cover the cast cutter ring, thus completing the embedding of the cast cutter ring and isolating the cast cutter ring from oxygen; then the lid of the ceramic container is closed, and the ceramic container containing the graphite powder and the cast cutter ring is placed in a muffle furnace, and the muffle furnace is heated to the normalizing temperature at a heating rate of 3°C / min to start the normalizing heat treatment; after being taken out of the furnace, a metal brush is used to remove the graphite powder attached to the surface of the cutter ring, and then the cutter ring is air-cooled to room temperature to obtain a hob cutter ring.

[0079] The cast knife ring includes, by mass percentage, C: 3.5wt%, Si: 5.5wt%, Al: 0.6wt%, B: 0.2wt%, V: 8.7wt%, Nb: 0.6wt%, Mo: 2.5wt%, N: 0.07wt%, La+Ce: 0.4wt%, and the balance is Fe; the particle size of the graphite powder is 6μm; the density of the graphite powder is 2.7g / cm 3 ; The fluidity of graphite powder is 40s / g; the thickness of graphite powder embedded outside the cast knife ring is 10cm; the thickness of the cast knife ring is 20cm; the normalizing temperature is 1020℃; the holding time is 150min.

[0080] Comparison of the impact toughness and compressive strength of the hob cutter rings prepared in this embodiment and in Example 1 Figure 5 As shown, it can be seen that the impact toughness and compressive strength of the hob cutter ring of this embodiment are significantly lower than those of embodiment 1. This is because the insulation time of this embodiment is less than the time calculated according to t=120+100×k / m, resulting in the cutter ring not reaching the complete austenitizing temperature after being embedded in graphite, and the grain size of the cutter ring is coarse (about 6.5-8μm), which reduces its impact toughness and compressive strength.

[0081] Example 4

[0082] This embodiment provides a heat treatment method for a hob cutter ring, which specifically includes the following steps:

[0083] Graphite powder is loaded into a ceramic container, the cast cutter ring is placed in the ceramic container, and then graphite powder is loaded into the ceramic container to cover the cast cutter ring, that is, the cast cutter ring is embedded and the cast cutter ring is isolated from oxygen; then the lid of the ceramic container is closed, and the ceramic container containing the graphite powder and the cast cutter ring is placed in a muffle furnace, and the muffle furnace is heated to the normalizing temperature at a heating rate of 3°C / min to start the normalizing heat treatment; after being taken out of the furnace, the component (cutter ring) is removed from the graphite powder, and then air-cooled to room temperature to obtain a hob cutter ring.

[0084] The cast knife ring includes, by mass percentage, C: 3.5wt%, Si: 5.5wt%, Al: 0.6wt%, B: 0.2wt%, V: 8.7wt%, Nb: 0.6wt%, Mo: 2.5wt%, N: 0.07wt%, La+Ce: 0.4wt%, and the balance is Fe; the particle size of the graphite powder is 6μm; the density of the graphite powder is 2.7g / cm 3 ; The fluidity of graphite powder is 40s / g; the thickness of graphite powder embedded outside the cast knife ring is 10cm; the thickness of the cast knife ring is 20cm; the normalizing temperature is 1020℃; the holding time is 170min.

[0085] The organizational morphology of the hob cutter ring prepared in this embodiment is as follows Figure 6 As shown, it can be seen that the size of the carbides is relatively large. This is because the graphite powder attached to the surface of the knife ring is not removed after the embodiment is fired, resulting in a slightly higher cooling rate, which accelerates the diffusion of elements such as C, V, and Cr, and promotes the growth of carbides; the coarse carbides reduce the driving force for martensite formation, resulting in a lower martensite content in the knife ring, resulting in a significant decrease in its surface hardness and impact toughness; the specific comparison of the martensite content in this embodiment and Example 1 is as follows: Figure 7 As shown, it can be seen that the volume fraction of martensite decreases from 43.9% in Example 1 to 29.3%.

[0086] Comparative Example 3

[0087] This comparative example provides a heat treatment method for a hob cutter ring, which specifically includes the following steps:

[0088] Graphite powder is loaded into a ceramic container, the cast cutter ring is placed in the ceramic container, and then graphite powder is loaded into the ceramic container to cover the cast cutter ring, thus completing the embedding of the cast cutter ring and isolating the cast cutter ring from oxygen; then the lid of the ceramic container is closed, and the ceramic container containing the graphite powder and the cast cutter ring is placed in a muffle furnace, and the muffle furnace is heated to the normalizing temperature at a heating rate of 3°C / min to start the normalizing heat treatment; after being taken out of the furnace, a metal brush is used to remove the graphite powder attached to the surface of the cutter ring, and then the cutter ring is air-cooled to room temperature to obtain a hob cutter ring.

[0089] The cast knife ring includes, by mass percentage, C: 3.5wt%, Si: 5.5wt%, Al: 0.6wt%, B: 0.2wt%, V: 8.7wt%, Nb: 0.6wt%, Mo: 2.5wt%, N: 0.07wt%, La+Ce: 0.4wt%, and the balance is Fe; the particle size of the graphite powder is 6μm; the density of the graphite powder is 2.7g / cm 3; The fluidity of graphite powder is 40s / g; the thickness of graphite powder embedded outside the cast knife ring is 10cm; the thickness of the cast knife ring is 20cm; the normalizing temperature is 1100℃; the holding time is 170min.

[0090] The normalizing temperature of this comparative example exceeds the temperature calculated according to the formula T = 1000 + 100 × k / m, which makes the carbides such as VC and M7C3 coarse, such as Figure 8 As shown in the figure, the toughness of the final cutter ring decreases, as shown in the figure. Fig. 9 shown.

[0091] It is easy for those skilled in the art to understand that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention. These improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A method for heat treatment of a hob cutter ring, characterized in that: The following steps are involved: The cast cutter ring is embedded so that the cast cutter ring can be isolated from oxygen during the normalizing heat treatment process; then the embedded cast cutter ring is subjected to normalizing heat treatment to obtain the hob cutter ring.

2. The heat treatment method of the hob cutter ring according to claim 1, characterized in that: The steps of embedding the cast knife ring include: The as-cast cutter ring is placed in a ceramic container; wherein the ceramic container is filled with embedding powder, and the as-cast cutter ring is embedded in the embedding powder.

3. The heat treatment method for a hob cutter ring according to claim 2 is characterized in that: The embedding powder is graphite powder; Preferably, the particle size of the graphite powder is 4.0 to 10.0 μm; Preferably, the density of the graphite powder is 2.5-3.0 g / cm 3 ; Preferably, the flowability of the graphite powder is 30 to 50 s / g.

4. The heat treatment method of the hob cutter ring according to claim 2, characterized in that: In the step of normalizing heat treatment: T = 1000 + 100 × k / m; wherein T is the normalizing temperature, in ° C; k is the thickness of the embedding powder embedded outside the as-cast cutter ring, in cm; m is the thickness of the as-cast cutter ring, in cm; and / or t=120+100×k / m; where t is the holding time, in min; k is the thickness of the embedding powder embedded outside the as-cast knife ring, in cm; m is the thickness of the as-cast knife ring, in cm; Preferably, 0cm<m≤50cm, 0<k / m≤1.

5. The heat treatment method of a hob cutter ring according to claim 1, characterized in that: In the normalizing heat treatment step: the heating rate is 2-5°C / min; and / or The normalizing heat treatment is carried out in a muffle furnace.

6. The heat treatment method of a hob cutter ring according to claim 1, characterized in that: After the normalizing heat treatment step, the furnace is also taken out of the furnace and cooled: After coming out of the furnace, the graphite powder on the surface of the hob cutter ring is removed and then air-cooled to room temperature.

7. The heat treatment method of a hob cutter ring according to claim 1, characterized in that: Before the step of embedding the as-cast cutter ring, the method further includes: surface cleaning and degreasing the as-cast cutter ring.

8. The heat treatment method of a hob cutter ring according to claim 1, characterized in that: In terms of mass percentage, the cast knife ring includes: C: 3.3-3.7wt%, Si: 5.3-5.7wt%, Al: 0.4-0.8wt%, B: 0.1-0.3wt%, V: 8.5-9.0wt%, Nb: 0.4-0.8wt%, Mo: 2.3-2.7wt%, N: 0.06-0.09wt%, La+Ce: 0.2-0.5wt%, and the balance is Fe.

9. A hob cutter ring, characterized in that: The grain size of the hob cutter ring is 2.5-4 μm; the microstructure of the hob cutter ring includes a martensite matrix, austenite and carbide; Among them, the volume fraction of the martensite matrix is ​​40-50%; the volume fraction of the austenite is 10-15%; the carbides are dispersed in the martensite matrix, and the carbides include VC and M7C3; the volume fraction of VC is 25-30%, and the size of VC is 4-8μm; the volume fraction of M7C3 is 13-17%, and the size of M7C3 is 10-15μm.

10. The hob cutter ring according to claim 9, characterized in that: The hob cutter ring is obtained by subjecting a cast cutter ring to heat treatment and fine machining; wherein the heat treatment adopts the heat treatment method described in any one of claims 1 to 8.

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