A method for improving the x32 hardness of bimetal band saw back material

Abstract

The application discloses a method for improving the hardness of a bimetallic band saw back material X32, and belongs to the technical field of metal processing. 23 The method is characterized by the following steps: step one, material selection, selecting an alloy steel X32 hot-rolled coil as raw material; step two, primary annealing, carrying out cover annealing on the material in step one, heating at a temperature of 810-850 DEG C, annealing for 10-25 h, and then continuously cooling at a cooling rate of greater than or equal to 14 DEG C / h to a temperature of less than or equal to 450 DEG C; and step three, primary cold rolling, placing the steel coil after the primary annealing in a single-stand rolling mill to perform primary cold rolling. The method effectively reduces the number density of carbides and the content of Cr and Mo elements in a cold-rolled product by optimizing the combination of annealing temperature, time and cooling mode, so that the bimetallic band saw blade has higher back material hardness and improved fatigue performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal processing, and particularly relates to a method for improving the X32 hardness of a double-metal band saw back material. BACKGROUND

[0002] The double-metal band saw blade plays an indispensable role in the mechanical processing industry, especially in the cutting of ferrous and non-ferrous metals, due to its excellent cutting efficiency, long service life, and wide applicability. It is worth mentioning that during the actual application of the double-metal band saw blade, the back material that bears the saw blade not only has to withstand the periodic changes in force caused by the tensioning of the saw blade, but also has to directly contact the metal material to be cut. This dual role makes the back material prone to fatigue and wear phenomena during long-term use. In view of this situation, the back material of the double-metal band saw must be made of a material with extremely high hardness and excellent wear resistance to ensure that the entire band saw blade can maintain stable performance and prolong its overall life under extreme working conditions.

[0003] The production of cold-rolled X32 steel strip takes hot-rolled X32 steel strip as the initial material. Through repeated precise cold rolling processes and related annealing treatments in multiple links, a complex microstructure coexisting with "deformed ferrite and carbides (mainly composed of M 23 C6)" is finally formed. Then, to prepare a mature double-metal band saw, the material needs to go through a series of meticulous processing steps. First, the tooth material is welded and connected, followed by an annealing process to ensure that the metal has good ductility and mechanical strength. Then, precise tooth cutting and bending operations are performed to give the band saw blade the appropriate tooth shape and bending degree. Next, the band saw blade must also undergo a strict heat treatment process, or after the tooth material is welded, the bending and heat treatment processes are directly performed to further improve its hardness and durability, so that the preparation of a high-quality double-metal band saw blade is completed. This comprehensive processing process ensures that the double-metal band saw can exhibit excellent cutting performance in subsequent actual applications, meeting the stringent requirements of industrial production for material cutting precision and efficiency.

[0004] Among them, when the heat treatment is implemented, the manufacturer adopts a standard "quenching-tempering" process flow. This process plays a crucial role in the production of cold-rolled X32 steel strip, because the specific content of alloy elements such as chromium (Cr) and molybdenum (Mo) in the carbide M 23 C6 and the number density exhibited will be changed through the M 23The dissolution kinetics of C6 carbide generates indirect interaction. The mutual influence at this level eventually significantly determines the hardness and wear resistance of the double-metal band saw back material. Only by strictly controlling the content and distribution of these alloying elements can the optimization of the quenching process be ensured and the desired physical properties of the double-metal band saw back material be achieved. Therefore, the quenching-tempering process is a key step that cannot be ignored and is directly related to whether the double-metal band saw back material can maintain its excellent and long-acting performance in the face of extreme working conditions of severe mechanical stress and wear.

[0005] However, in the above annealing process, the goal is generally to fully recrystallize ferrite and spheroidize carbide to facilitate subsequent cold rolling deformation, resulting in M 23 Excessive Cr and Mo element content and number density of C6 inhibit the effective improvement of the hardness and wear resistance of the double-metal band saw back material.

[0006] Therefore, a hardness improvement method for a double-metal band saw back material X32 is proposed to solve or alleviate the above problems. SUMMARY

[0007] The purpose of the present application is to solve the shortcomings in the prior art and propose a hardness improvement method for a double-metal band saw back material X32, which fully utilizes the effect of the bell-type annealing process on the dissolution and re-precipitation behavior of M 23 C6 to achieve the annealing purpose of ferrite equiaxialization and carbide spheroidization while reducing the M 23 C6 element content and number density of C6, thereby achieving the improvement of the hardness and wear resistance of the double-metal band saw back material X32 after the final quenching and tempering process.

[0008] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0009] A hardness improvement method for a double-metal band saw back material X32, comprising the following steps,

[0010] Step 1: material selection, selecting an alloy steel X32 hot-rolled coil as the raw material;

[0011] Step 2: primary annealing, bell-type annealing the material of step 1, heating temperature is 810-850℃, annealing time is 10-25h, and then cooling to below 450℃ at a cooling rate of ≥14℃ / h;

[0012] Step 3: primary cold rolling, placing the steel coil after primary annealing in a single-stand rolling mill for primary cold rolling, cumulative deformation is >50%;

[0013] Step four, secondary annealing, the once cold-rolled steel coil is subjected to batch annealing, the annealing temperature is 740-800℃, and the annealing time is 18-30h;

[0014] Step five, secondary cold rolling, the secondary annealed steel coil is placed on a single stand rolling mill for secondary cold rolling, and the cold-rolled product thickness is 0.95-1.68mm.

[0015] Through the above technical scheme, the process flow adopted by the present application selects the alloy steel X32 hot-rolled coil as the starting material for processing, and by accurately controlling the key variables of the first annealing treatment stage, i.e. temperature, duration and cooling rate, the effective reduction of the chromium (Cr) and molybdenum (Mo) element content and the number density of the carbon compound M 23 C6 in the final product of the cold-rolled X32 steel strip is successfully achieved. This strictly controlled heat treatment process not only stabilizes the microstructure characteristics of the material, but also lays a foundation for the optimization of the material performance.

[0016] Further, in the complex preparation process of the bimetallic band saw, especially in the quenching operation stage, it is observed that the M 23 C6 carbide can quickly re-dissolve into the austenite matrix. This key dissolution step, combined with the high carbon and alloy element content, provides the necessary conditions for the low-temperature completion of the martensitic phase change, thereby significantly enhancing the hardness and wear resistance of the bimetallic band saw back material. For cutting tool materials, the improvement of hardness and wear resistance is directly related to the extension of cutting performance and working life.

[0017] In summary, the performance improvement of the bimetallic band saw back material not only depends on the fine control of the heat treatment process mentioned earlier, but also depends on the strict adjustment and optimization of the internal microstructure of the material. Through this scientific method, the fine adjustment of the material microstructure and the precise control of the heat treatment process are combined, which is crucial for achieving superior comprehensive mechanical properties. This synergistic effect not only helps to improve the cutting capacity of the band saw and reduce production costs, but also helps to meet the growing demand for cutting efficiency and durability in the industry, bringing significant economic benefits and process efficiency.

[0018] Finally, this enhanced performance indicates that we have successfully developed a technology that can significantly extend the service life of the bimetallic band saw, while improving its reliability under high stress conditions. In this way, this technology improves the expectations of the performance and durability of the bimetallic band saw in the industrial field, especially in applications that require high strength and precise cutting, which reflects its vast application prospects and potential market value.

[0019] Preferably, the alloy steel X32 hot-rolled coil has the following components by mass percentage: C 0.30-0.35%, Si 0.25-0.35%, Mn 0.90-1.10%, Cr 3.9-4.0%, V 0.30-0.45%, Mo 1.1-1.3%, Ni 0.30-0.80%, P≤0.015%, S≤0.015%, the balance being Fe and unavoidable impurities, the mass percentage of the unavoidable impurities being not more than 0.04%.

[0020] Through the above technical solution, the method not only improves the production process of the specific cold-rolled X32 strip steel, but also goes deep into the raw material level, and the components contained in the alloy steel X32 hot-rolled coil are accurately adjusted, and a series of changes are made on the basis of the new optimization of the primary annealing process, so as to reduce the M 23 The concentration and number density of chromium (Cr) and molybdenum (Mo) elements contained in the C6 type carbide are ensured to be more fully and effectively utilized in the temperature setting, time and cooling mode during annealing, and through such process optimization, the inherent potential is maximized, and remarkable progress is made in further reducing the number density of carbides and the content of chromium and molybdenum elements in the cold-rolled product, and this series of changes finally have a good effect on the production of bimetal band saw blades, that is, higher back material hardness and significantly improved fatigue performance, and the overall performance and reliability of the product are significantly improved.

[0021] Preferably, the thickness of the alloy steel X32 hot-rolled coil is 3.4-3.8 mm.

[0022] Through the above technical solution, considering that the thickness of the alloy steel X32 hot-rolled coil in the initial state is obviously more than twice the thickness of the cold-rolled product, this feature sets the initial condition for the subsequent processing process, so that the alloy steel X32 hot-rolled coil still maintains sufficient thickness space after experiencing the first and second cold-rolling behaviors, and such margin provides the necessary tolerance for any deformation that may occur after the completion of the subsequent cold-rolling operation, and guarantees that there is no negative impact on the quality of the final product, therefore, this consecutive processing procedure ensures that the thickness of the obtained cold-rolled product at the end of the entire production process meets the specific demand standards specified in the consumer market and meets the expectations of different customers.

[0023] The present application has the following beneficial effects:

[0024] The present application introduces a hardness enhancement method for bimetallic band saw back material X32. This method inherits and utilizes the existing production technology framework of cold-rolled X32 strip steel, that is, through multiple precise cold rolling processes and precisely arranged annealing steps, a key innovation is implemented.

[0025] This improvement involves meticulous optimization of the traditional single annealing process, resulting in a more optimal state of M 23 The chromium (Cr) and molybdenum (Mo) element content and number density of C6 carbides reach a more optimal state. This adjustment successfully enhances the hardness and wear resistance of bimetallic band saw back material without changing the subsequent process arrangement, whether it is the combination of "tooth material welding-annealing-tooth cutting and bending-heat treatment" or the processing sequence of "tooth material welding-bending-heat treatment". The bimetallic band saw back material produced using this invention exhibits superior load resistance when facing continuous changes in tension, and its ability to resist fatigue wear during contact and interaction with cutting metal is also enhanced. This enhanced durability significantly improves the fatigue life of the bimetallic band saw back material during long-term operation, thereby improving cutting efficiency while saving users the frequency of replacing band saws and maintenance costs, achieving the dual benefits of high efficiency and economy. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Flowchart of the present application;

[0027] Figure 2 Flowchart of the production process of cold-rolled X32 strip steel in the prior art;

[0028] Figure 3 Comparison chart of Cr and Mo element content of M23C6 in the one-time annealing structure and cold-rolled finished product structure of the present embodiment and comparative example X32;

[0029] Figure 4 Equivalent diameter distribution chart of M23C6 in the cold-rolled X32 finished product structure of the present embodiment and comparative example. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments.

[0031] Embodiment:

[0032] A bimetallic band saw back material X32 hardness enhancement method, as Figure 1As shown, the alloy steel X32 hot-rolled coil with a thickness of 3.8 mm is placed in a batch annealing furnace, heated to 820°C for 12 hours, then continuously cooled to 200°C at a rate of 15°C / h, and then naturally cooled to room temperature; the alloy steel X32 strip after the first annealing treatment is placed on a single-stand rolling mill for first cold rolling treatment, rolled into a cold-rolled coil with a thickness of 1.5 mm, and the cumulative deformation is 60.5%; the alloy steel X32 coil after the first cold rolling is placed in a batch annealing furnace for second annealing at 750°C for 18 hours, then cooled to 700°C at a rate of 28°C / h for 4 hours, and finally cooled to room temperature at a rate of 30°C / s; the alloy steel X32 coil after the second annealing is continuously placed on a single-stand rolling mill for second cold rolling treatment, and a cold-rolled X32 finished steel coil with a thickness of 1.08 mm is obtained.

[0033] The composition of the alloy steel X32 hot-rolled coil used is as follows in terms of weight percentage: C 0.32%, Si 0.3%, Mn 1.0%, P 0.01%, S 0.004%, Cr 4.0%, Ni 0.75%, Mo 1.26%, V 0.35%, the balance being Fe and 0.02% unavoidable impurities.

[0034] Comparative Example:

[0035] The conventional cold rolling production process of the bimetallic band saw back material X32 is as follows, as shown in the flow chart of FIG. 1. Figure 2 As shown, the alloy steel X32 hot-rolled coil with a thickness of 3.8 mm is placed in a batch annealing furnace, heated to 820°C for 12 hours, then continuously cooled to 200°C at a rate of 15°C / h, and then naturally cooled to room temperature; the alloy steel X32 strip after the first annealing treatment is placed on a single-stand rolling mill for first cold rolling treatment, rolled into a cold-rolled coil with a thickness of 1.5 mm, and the cumulative deformation is 60.5%; the alloy steel X32 coil after the first cold rolling is placed in a batch annealing furnace for second annealing at 750°C for 18 hours, then cooled to 700°C at a rate of 28°C / h for 4 hours, and finally cooled to room temperature at a rate of 30°C / s; the alloy steel X32 coil after the second annealing is continuously placed on a single-stand rolling mill for second cold rolling treatment, and a cold-rolled X32 finished steel coil with a thickness of 1.08 mm is obtained.

[0036] The composition of the alloy steel X32 hot-rolled coil used is as follows in terms of weight percentage: C 0.32%, Si 0.3%, Mn 1.0%, P 0.01%, S 0.004%, Cr 4.0%, Ni 0.75%, Mo 1.26%, V 0.35%, the balance being Fe and 0.02% unavoidable impurities.

[0037] The Cr% and Mo% of M 23 C6 in the first annealing structure and the cold-rolled X32 finished structure of the example and the comparative examples are detected, and the following results are obtained. Figure 3It can be found that when the example is compared with the comparative example, it can be observed that during the one-time annealing process of the example, the microstructure features formed present obvious changes, specifically, the composition M 23 The relative content of chromium (Cr) and molybdenum (Mo) of C6 is significantly reduced. This initial content reduction lays the foundation for subsequent steps, meaning that during the subsequent one-time cold rolling, followed by a two-time annealing process, and a series of processes such as two-time cold rolling, the low content feature of the example in structure is maintained and consolidated. As a result, the example exhibits its robustness in terms of chromium (Cr) and molybdenum (Mo) content, and thus the material properties exhibited by the example remain at a low level throughout the entire processing cycle, which is very advantageous in terms of the performance stability of the final product.

[0038] The M 23 C6 equivalent diameter distribution of the example and the comparative example cold-rolled X32 finished product structure is compared, and after the SEM photos with a magnification of ×8000 are counted, it can be obtained that Figure 4 The M 23 C6 average equivalent diameter of the example and the comparative example is 0.46 μm and 0.578 μm respectively, and the number density is 0.975 μm -2 and 0.821 μm -2 respectively. As can be seen from Figure 3 , the relatively small M 23 C6 average equivalent diameter of the comparative example is caused by more number of M 23 C6 ≤0.12 μm.

[0039] Then, the hardness of the cold-rolled X32 finished product strip steel of the example and the comparative example is detected, and the following table Table 1 shows the content.

[0040] Hardness / HV 1 2 3 4 5 6 7 8 9 10 Average Example 299.7 289.3 291.2 287.4 288.6 311.7 304.6 298.4 292.3 288.6 295.2 Comparative Example 275.8 277.7 268.2 276.1 288.3 266.8 269.6 270.2 273.9 269.6 273.6

[0041] Table 1

[0042] In the actual example, by optimizing the heat treatment process, the hardness test of the finished product of the cold-rolled X32 strip steel shows that the hardness value is significantly improved compared with the control sample, specifically, the hardness value is increased by 21.6 HV, which is a direct manifestation of the optimization of material performance. In order to further verify the reliability and scientificity of this result, it is compared with the experimental data in Figure 3 , and it is found that they present a mutually confirming relationship.

[0043] Specifically, in Figure 3The data analysis shows that the average equivalent diameter of M23C6 phase in the material obtained by the embodiment is larger, and the number density is smaller. At the same time, the percentage content of chromium (Cr) and molybdenum (Mo) in these M23C6 phases is low, and these factors combined together imply that the remaining carbon (C), chromium (Cr) and molybdenum (Mo) content in the ferrite matrix is relatively high. And these remaining alloying elements are important contributors to hardness improvement, especially the increase of carbon content, which has a direct and important effect on improving the hardness of the material.

[0044] Through systematic analysis and comprehensive consideration of multiple influencing factors, the improvement of the hardness of the material obtained in the embodiment is actually due to the change of the behavior of M23C6 phase at the microscale caused by the optimization of the bell annealing process, which further affects the macro performance index. Such results not only provide us with a clear direction on how to improve the hardness of the cold-rolled X32 steel strip, but also reflect the profound influence of the microstructure on the overall performance of the material. By regulating the distribution and state of alloying elements at the microscale, the macro performance of the material can be effectively controlled, which has important guiding significance for material engineering and product development.

[0045] Therefore, according to the above content, the method selects hot-rolled X32 steel strip as the initial material, and improves the traditional process flow by precisely controlling the temperature, time and cooling mode of the first annealing. The process includes first annealing, first cold rolling, second annealing and second cold rolling operation. In addition, in the subsequent heat treatment step of the standard "tooth material welding-annealing-tooth cutting and bending-heat treatment" or "tooth material welding-bending-heat treatment", the method significantly improves the hardness and wear resistance of the bimetallic band saw back material X32. Through the implementation of this comprehensive method, the performance of the product can be significantly improved.

[0046] According to the principle of the above advantages, the technology adopts a bell annealing process to precisely control the dissolution and re-precipitation process of M 23 C6 carbide phase, and realizes the optimization of the internal organizational structure of the material. While ensuring the annealing goal of equiaxial ferrite grains and carbide spheroidization, the content of chromium (Cr) and molybdenum (Mo) elements and their number density in M 23 C6 phase are effectively reduced, which is beneficial to the improvement of the hardness of the material. 23The rapid dissolution of C6 carbide phase in the final quenching heating stage lays the foundation, and the low temperature martensite transformation that occurs thereafter significantly improves the hardness and wear resistance of the bimetallic band saw back material X32. The hardness improvement method of the bimetallic band saw back material X32 disclosed in the present application aims to reduce the fatigue wear that may occur during the contact between the back material and the cut metal by enhancing the hardness and wear resistance, thereby significantly improving the service life and reliability of the bimetallic band saw in actual application. Through this method, the working efficiency and durability of the bimetallic band saw are comprehensively enhanced, making it more suitable for high-efficiency and long-period cutting tasks.

[0047] More specifically, in the prior art, taking the steel strip for a bimetallic band saw back material and its preparation method and a cold rolling and annealing process for avoiding alloy saw blade steel X32 mixed crystal defects and its application with application numbers CN201810845315.4 and CN202110479376.5 as examples, in the "one annealing" process, the heating, isothermal (750℃) and cooling processes are all located in the "ferrite + carbide (mainly M 23 C6)” phase region, M 23 C6 nucleates and grows and coarsens at the high-density lath interfaces in the hot-rolled bainite, while Cr and Mo are constantly partitioned from the matrix to M 23 C6 during this process.

[0048] In the one annealing process in the present application, M 23 C6 also nucleates at the high-density lath interfaces in the hot-rolled bainite, but during heating to 810-850℃ and isothermal for 10-25h, the matrix changes from ferrite to austenite, and thermodynamics drives a large amount of M 23 C6 to dissolve into the matrix; partial re-precipitation occurs during subsequent cooling, but the potential nucleation site density is significantly reduced compared to the hot-rolled bainite lath interfaces, and Cr and Mo partitioning from the matrix to M 23 C6 only occurs after M 23 C6 re-precipitates, and the partitioning time is shortened. Therefore, under the "one annealing" process conditions described in the present patent, the Cr and Mo element content and number density of M 23 C6 in the cold-rolled X32 steel strip finished product are reduced.

[0049] Therefore, it is sufficient to illustrate that the present application implements the optimization combination of key process parameters such as annealing temperature, time and cooling method through a carefully designed experimental scheme. The core of this strategy is to accurately control the influence of the heat treatment process on the cold-rolled product, and the goal is to significantly reduce the number density of carbides in the material and reduce the content of chromium (Cr) and molybdenum (Mo) elements. In the production of bimetallic band saw blades, through such an optimized heat treatment process, it ensures that the back material can obtain higher hardness, which is crucial to improve the ability of bimetallic band saw blades to resist repeated stress fatigue deformation during use.

[0050] Considering the influence of various process parameters on the performance of the material, the present application not only focuses on the improvement of hardness, but also targets the specific application scenario, i.e. the cyclic load that the bimetallic band saw blade bears during cutting operation, thereby improving the fatigue performance of the back material of the band saw blade. Such improvement is extremely beneficial to improve the overall efficiency of the band saw and reduce maintenance costs, because the band saw back material with higher hardness and better fatigue performance can better cooperate with the band saw blade part, ensure the cutting performance during long-term operation, reduce the risk of accidental wear or breakage, and thereby prolong the service life of the band saw.

[0051] In summary, the technical solution of the present application provides an efficient way to improve the performance of cold-rolled products, which can positively affect the key performance indicators of bimetallic band saw blades, especially in terms of hardness improvement and fatigue performance enhancement. Through the implementation of this innovative method, the application range of bimetallic band saw blades can be further expanded to meet more stringent industrial cutting requirements and gain an advantage in fierce market competition.

[0052] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can make equivalent replacements or changes to the technical solutions and inventive concepts of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for improving the hardness of X32 backing material in a bimetallic band saw, comprising the following steps: Step 1, material selection: select alloy steel X32 hot-rolled coil as raw material; Step 2, one-time annealing: the material from Step 1 is annealed in a bell-type manner, with a heating temperature of 810-850℃ and an annealing time of 10-25h, and then cooled to below 450℃ by a continuous cooling rate of ≥14℃ / h. Step 3, cold rolling: The steel coil after one annealing is placed on a single-stand rolling mill for one cold rolling, with a cumulative deformation of >50%; Step 4, secondary annealing: The steel coil after primary cold rolling is subjected to annealing in a bell-type annealing process at a temperature of 740–800℃ for 18–30 hours. Step 5, secondary cold rolling: The steel coil after secondary annealing is placed on a single-stand rolling mill for secondary cold rolling. The thickness of the cold-rolled finished product is 0.95 to 1.68 mm.

2. The method for improving the hardness of X32 bimetallic band saw backing material according to claim 1, characterized in that, The composition of the alloy steel X32 hot-rolled coil, by mass percentage, is: C 0.30-0.35%, Si 0.25-0.35%, Mn 0.90-1.10%, Cr 3.9-4.0%, V 0.30-0.45%, Mo 1.1-1.3%, Ni 0.30-0.80%, P≤0.015%, S≤0.015%, with the balance being Fe and unavoidable impurities, the unavoidable impurities comprising no more than 0.04% by mass.

3. The method for improving the hardness of X32 bimetallic band saw backing material according to claim 1, characterized in that, The thickness of the alloy steel X32 hot-rolled coil is 3.4 to 3.8 mm.

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