Low-temperature secondary hardening tempering method for gradient-deformed high-carbon martensitic stainless steel
Technical Field
The invention relates to the technical field of hot working process and heat treatment process of high-carbon martensitic stainless steel, in particular to a process for obtaining carbide reinforced high-carbon martensitic stainless steel, which is suitable for the production process of the carbide reinforced high-carbon martensitic stainless steel.
Background
The high-carbon martensitic stainless steel is widely applied to manufacturing bearings, valve cores of hydraulic systems, cutters and scissors and the like. The difference of the performance of the high-carbon martensitic stainless steel used by the products at home and abroad mainly comes from the control level of carbide. Taking a high-grade kitchen knife as an example, the nano-scale carbide in the foreign high-grade kitchen knife is distributed on the martensite matrix in a fine, uniform and dispersed manner. However, the domestic steel for the knife and the scissors does not basically contain nano-scale carbide, so that the hardness and the wear resistance of the knife are difficult to further improve, and the sharpness of the knife is further influenced. Due to the restriction of the domestic high-carbon martensitic stainless steel structure and the control level of carbide, the domestic market of high-grade kitchen knives is almost monopolized by foreign well-known brands.
Although the Chinese knife and scissors enterprises develop high-quality steel grades such as 8Cr13MoV for knife and scissors in recent years, the domestic knife and scissors have a plurality of defects in carbide control. The secondary carbide in the foreign similar cutting steel is dispersed and distributed on the martensite matrix, while the main type of the secondary carbide in the domestic high-quality cutting is M23C6The quenching steel has low hardness, large quantity, uneven size and distribution (the size is 0.2-2 mu m), is difficult to control to be fine and even in the quenching process, and does not contain MX type nano-scale carbide. This organization can result in a cutting edge M during the machining and service process23C6The type secondary carbides are exfoliated to leave pits in situ, reducing the toughness (breakout) of the cutting edge, and meanwhile, the exfoliated carbides also become high-hardness abrasive particles to further abrade the matrix.
The traditional secondary hardening is that when carbide forming elements such as Ti, Mo, Nb, V and W are added into steel, a remarkable hardening effect appears in quenched steel within the temperature range of 500-600 ℃, and the secondary hardening is called as secondary hardening. The process control factor is that the diffusion of solid solution elements is replaced, the solid solution elements can be effectively carried out at a higher temperature range, and martensite is rapidly decomposed at a high temperature, so that the hardness and the wear resistance of the cutter are remarkably reduced, and therefore, the martensitic stainless steel for the cutter is generally tempered at a low temperature for 1-3 hours. In the conventional processing cutter, only partial removal of internal stress occurs at the lower tempering temperature, and nano-scale carbide cannot be effectively precipitated.
Through a special heat treatment process, the dispersed alloy cementite can be precipitated from the high-carbon microalloy steel with lower alloy content during low-temperature tempering, so that low-temperature secondary hardening is realized. And the high-carbon martensitic stainless steel cutter cannot precipitate cementite or alloy cementite under the condition of low-temperature tempering due to the high chromium content, so that the high-carbon martensitic stainless steel cutter is difficult to be strengthened by the cementite. Meanwhile, micro alloy elements Mo, V and the like are often added into the high-carbon martensitic stainless steel, and in the prior art, the micro alloy elements are enriched in large-size M23C6The secondary carbide is dissolved in the matrix, and does not precipitate the microalloy elementThe strengthening effect may also compromise the service performance and service life of the tool. Therefore, it is important to find a low-temperature tempering secondary hardening process suitable for the high-carbon martensitic stainless steel for the cutter.
Disclosure of Invention
In order to solve the problems, the invention provides a low-temperature tempering method with secondary hardening effect for gradient-deformed high-carbon martensitic stainless steel, which is characterized in that after a cutter blank is subjected to solution treatment, gradient austenite deformation treatment is carried out, the cutter blank is forged to a finished cutter shape, a large number of dislocations are introduced at a cutter edge while the crystal grains at the edge part are obviously refined, and the low-temperature tempering method is adopted to promote the dispersion precipitation of nano-scale carbide, so that the hardness, the corrosion resistance, the sharpness and the service life of the cutter are improved.
The invention is suitable for processing the high-carbon martensitic stainless steel containing micro-alloy elements, and the steel comprises the following components in percentage by weight: c: 0.6-1.0, Mn is less than or equal to 0.8, Si is less than or equal to 1, Cr: 12-18 parts of high-carbon martensitic stainless steel, wherein Mo is less than or equal to 1, V is less than or equal to 1, Nb is less than or equal to 0.5, N is less than or equal to 0.2, S is less than or equal to 0.03, P is less than or equal to 0.05, and the balance is Fe.
Further, the method comprises:
s1: cutting a cutter blank by adopting a cold-rolled plate with the thickness of 2-3 mm, and carrying out solution treatment on the cutter blank;
s2: carrying out 4-7 times of gradient austenite deformation treatment on the cutter blank, wherein the austenitizing temperature is 1030-1070 ℃, the austenitizing heat preservation time is 5-10 min, the deformation temperature is 500-800 ℃, the thickness of the cutting edge is reduced to 1-1.5 mm from 2-3 mm, and then air cooling to room temperature;
s3: and (3) tempering the tool blank at a low temperature of 210-230 ℃ for 10-20 hours.
Further, in step S1, after the cutter blank is carved, the surface of the cutter blank is coated with a high temperature oxidation resistant coating to prevent the cutter blank from being oxidized seriously in the solid solution process.
Further, in the step S1, the solid solution treatment process includes heating the cutter blank to 1100-1130 ℃, keeping the temperature for 5-15 min, discharging the cutter blank out of the furnace, and cooling the cutter blank to room temperature.
Further, in step S1, straightening is performed during discharging and air cooling of the cutter blank, so as to improve the flatness of the cutter, the yield and the efficiency of the subsequent grinding process.
Further, in step S2, the gradient austenite deformation processing specifically includes: carrying out gradient austenite deformation treatment on the cutter blank subjected to solid solution, wherein the austenitizing temperature is 1030-1070 ℃, the austenitizing heat preservation time is 5-10 min, and M is ensured23C6Partial dissolution of type secondary carbides; the deformation temperature is 500-800 ℃, the deformation is carried out for 4-7 times, a large amount of dislocation is generated in the tissue of the cutter, the thickness of the cutting edge is reduced to 1-1.5 mm from 2-3 mm, the shape of the cutter blank is close to that of a finished cutter, the grinding efficiency is greatly improved, and the grinding cost is reduced; and then air-cooling to room temperature, after gradient austenite deformation treatment, the deformation of the blade is the largest, the hardness and the wear resistance are the highest, the cutting capability of the cutter is obviously improved, the deformation of other parts is small, the hardness is low, the toughness is good, and the performance distribution of the gradient is favorable for improving the service performance of the cutter.
Further, in step S2, the tool blank after the gradient deformation is straightened again in the air cooling process, so as to further improve the straightness of the tool, and further improve the yield and the efficiency of the subsequent grinding process.
Further, in step S3, the blank is tempered at a low temperature of 210 to 230 ℃ for 10 to 20 hours.
Further, in step S3, in order to ensure precipitation strengthening of carbides, the tempering time is set to the upper limit at the low tempering temperature and the tempering time is set to the lower limit at the high tempering temperature. In order to ensure the sufficient precipitation of carbide, the low tempering temperature requires sufficient tempering time, namely, the temperature is kept for 20 hours at 210 ℃, and the time is properly shortened at the high tempering temperature, namely, the temperature is kept for 10 hours at 230 ℃.
The invention has the following beneficial effects:
1) the grain size at the blade is obviously refined through gradient austenite deformation treatment, and the strength, toughness and sharpness of the cutter are improved;
2) significantly refines the large size M in the cutter tissue23C6Type secondary carbides, which make more alloying elements dissolve in the matrix structure in solutionOn one hand, the toughness and the corrosion resistance of the cutter are improved, and on the other hand, enough microalloy elements are provided for the precipitation of nano-scale carbide;
3) the high-carbon martensitic stainless steel is promoted to generate a low-temperature tempering secondary hardening effect through gradient austenite transformation treatment, a large amount of MX-type carbonitride with the size of about 10nm is obtained, the strength and the hardness of the cutter are improved without losing toughness, and finally the sharpness of the cutter is obviously improved;
4) compared with the traditional quenching and tempering process, the method needs less cutter blank raw materials, greatly improves the grinding efficiency, reduces the grinding cost and facilitates the recovery of excess materials.
Drawings
FIG. 1 is a diagram of the low temperature secondary hardening tempering process of the present invention;
FIG. 2(a) is a schematic view of a knife texture produced by a conventional tempering process in an embodiment of the present invention, 5000;
FIG. 2(b) is a 5000x view of the structure of a cutting tool produced by a low-temperature secondary hardening tempering process according to an embodiment of the present invention;
FIG. 2(c) is a structural diagram of a knife tool produced by a low-temperature secondary hardening tempering process in the embodiment of the present invention, 20000 x;
FIG. 3 shows nano-scale carbides precipitated from a cutting tool produced by a low-temperature secondary hardening tempering process according to an embodiment of the present invention;
FIG. 4 is a calculation of the contribution of carbides of different sizes and volume fractions to strength;
FIG. 5 shows the effect of deformation and non-deformation at different tempering temperatures on the low temperature secondary hardening effect in the examples of the present invention;
g is subjected to gradient austenite deformation, and Z is not subjected to gradient austenite deformation;
FIG. 6 is a graph showing the effect of deformation and non-deformation on tool sharpness at different tempering temperatures in an embodiment of the present invention;
wherein G is after gradient austenite deformation, Z is not after gradient austenite deformation, ICC is initial sharpness, TCC is sharpness tolerance.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
On the contrary, the invention is intended to cover alternatives, modifications, equivalents and alternatives which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, certain specific details are set forth in order to provide a better understanding of the present invention. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details.
The invention is further described with reference to the following figures and specific examples, which are not intended to be limiting.
As shown in fig. 1, the present embodiment provides a low-temperature secondary hardening tempering method for gradient-deformed high-carbon martensitic stainless steel, which includes performing a gradient austenite deformation treatment after a tool blank is subjected to a solution treatment, forging the tool blank to a finished tool shape, refining the grains at the edge portion, introducing a large number of dislocations at the edge, and promoting the dispersion and precipitation of nano-scale carbides by using a low-temperature tempering method, thereby improving the hardness and sharpness of the tool.
Examples
After 8Cr13MoV martensitic stainless steel which is subjected to electroslag remelting, hot rolling, spheroidizing annealing, cold rolling and annealing is processed into a cutter blank with the thickness of 2.5mm, the specific method comprises the following steps:
(1) heating the cutter blank to 1100 ℃, preserving the heat for 10min, discharging the cutter blank out of the furnace, and cooling the cutter blank to room temperature.
(2) And (3) carrying out gradient austenite deformation treatment on the cutter blank subjected to solid solution, wherein the deformation temperature is 600 ℃, so that the thickness of the cutter blade is reduced from 2.5mm to 1.3mm, and then air-cooling to room temperature.
(3) And (3) tempering the cutter blank subjected to the gradient austenite deformation treatment at a low temperature of 220 ℃ for 15 hours.
(4) Meanwhile, a control group which is not subjected to gradient austenite deformation treatment, different tempering temperatures and different tempering times is set to compare the improvement effect of the process on the structure and the performance of the cutter.
FIG. 2(a) is a knife texture map (5000x) produced by the conventional process, FIG. 2(b) is a knife texture map (5000x) produced by the process of the present invention, and FIG. 2(c) is a knife texture map (20000x) produced by the process of the present invention, it can be seen that a large amount of large size M exists in the knife texture produced by the conventional process23C6Type II secondary carbides, and in the tool structure produced by the process of the present invention, M23C6The size of the type secondary carbide is obviously reduced, and a large amount of nano-scale carbides which are dispersed and distributed appear. FIG. 3 shows the nano-scale carbide precipitated from the cutting tool produced by the low-temperature secondary hardening tempering process in the embodiment of the present invention, and it can be seen that the nano-scale carbide precipitated during the low-temperature tempering process is mainly (V, Ti, Nb) (C, N) and has a size of about 10 nm. M in high-carbon martensitic stainless steel23C6The size of the type secondary carbide is larger, generally 100nm, while the size of the MX-type carbonitride precipitated in the low-temperature tempering process is smaller, about 10nm, and FIG. 4 is a calculation result of the contribution of carbides with different sizes and volume fractions to the strength, and it can be seen that the contribution of the carbonitride with small size to the strength is far larger than that of the M with large size23C6A type carbide. FIG. 5 is a graph showing the effect of deformation and non-deformation at different tempering temperatures on the low temperature secondary hardening effect, wherein G is after gradient austenite deformation and Z is without gradient austenite deformation. As can be seen from fig. 5, the proper increase of the tempering temperature (from 200 ℃ to 220 ℃) can significantly accelerate the secondary hardening of the blade without damaging the secondary hardening effect, and the further increase of the tempering temperature can aggravate the softening at the initial stage of tempering, and the secondary hardening effect is obviously weakened; the quenching hardness of the cutter after the gradient austenite deformation is higher than that of a common cutter, the gradient deformation can inhibit tempering softening and improve the tempering secondary hardening effect, but the secondary hardening peak position is not influenced. FIG. 6 is a graph of the effect of deformation and non-deformation on tool sharpness for different tempering temperatures, where G is after gradient austenite deformation, Z is no gradient austenite deformation, ICC is initial sharpness, and TCC is sharpness tolerance. As can be seen from FIG. 6, the initial sharpness and sharpness of the tool are changed in gradientThe durability is obviously higher than that of a cutter which is not subjected to gradient deformation; the time required for tempering secondary hardening can be obviously reduced and the sharpness of the tool can be improved by properly increasing the tempering temperature (from 200 ℃ to 220 ℃), and the sharpness of the undeformed tool is damaged by further increasing the tempering temperature, and the gradient deformed tool is less influenced.
The above-described embodiment is only one of the preferred embodiments of the present invention, and general changes and substitutions by those skilled in the art within the technical scope of the present invention are included in the protection scope of the present invention.