Vacuum carburizing method for ultrahigh alloy stainless gear bearing steel

Abstract

The invention discloses a vacuum carburizing method of ultrahigh alloy stainless gear bearing steel, which belongs to the field of metal heat treatment, and comprises the following steps: S1, alloy element solid solution: putting the ultrahigh alloy stainless gear bearing steel into a vacuum carburizing furnace, heating to 1100-1120 DEG C along with the furnace under the protection of nitrogen, preserving heat for a period of time, and carrying out solid solution treatment; s2, cooling and carburizing are conducted, specifically, after solution treatment, alloy elements are fully dissolved in austenite, then the furnace temperature is reduced to 950-980 DEG C, and then a carburizing mode is started; s3, components of the carburizing medium are adjusted, specifically, a conventional pure acetylene carburizing medium is adjusted into nitrogen-acetylene mixed gas, the content of acetylene in the carburizing medium is diluted, and the ratio of nitrogen to acetylene in the mixed gas is larger than or equal to 5; s4, weak saturation carburizing is conducted, specifically, nitrogen-acetylene mixed gas with the flow being 1250-1500 L / h is continuously introduced into the furnace for weak saturation carburizing; and S5, final diffusion: after the weak saturation carburization is finished, pure nitrogen is introduced for final diffusion, the carbon concentration is diffused to be within the technical requirement range, and the weak saturation carburization time / final diffusion time is larger than or equal to 1.5. According to the method, the phenomena that carbide is thick and large and the surface is cracked after the ultra-high alloy stainless gear bearing steel is carburized are thoroughly solved, and the problem that the carburizing speed is seriously influenced due to the fact that the diffusion time of a traditional supersaturation carburizing method is extremely long and austenite is extremely carbon-poor is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal heat treatment, and specifically relates to a vacuum carburizing method for ultra-high alloy stainless gear bearing steel. Background Art

[0002] With the rapid development of China's aviation industry, the performance requirements for aviation engine gears and their bearings have become increasingly stringent. After carburizing and quenching heat treatment of parts, while maintaining a certain core toughness, it is still required to have good core strength, surface wear resistance and hot corrosion resistance. The development of aviation gear bearing materials has also gone through three generations. Among them, 15Cr14Co12Mo5Ni and CSS-42L are the most typical aviation third-generation gear steels at present and are ideal materials for manufacturing aviation gears and bearings. However, due to the extremely high alloy content in this material, containing a large amount of strong carbide-forming elements such as Cr and Mo, it belongs to easy-to-saturate carburizing steel. Using the traditional supersaturated flow pulse vacuum carburizing process is extremely easy to cause phenomena such as coarse carbides and surface cracking, forming strip-shaped needle-like carbides and network carbides similar to Widmanstätten structure. The metallographic structure is shown in Figure 2 At present, in the industry, only by infinitely extending the diffusion time after strong carburizing can the phenomena of coarse carbides and surface cracking be reduced. The strong diffusion ratio is reduced to less than 1:120. This method still belongs to the supersaturated flow pulse carburizing method, not only with unsatisfactory effects, but also extremely slow carburizing speed and extremely low production efficiency. After 40 hours of carburizing, the effective hardened layer depth is only about 1.2 mm. Therefore, it is urgent to study a vacuum carburizing method for ultra-high alloy stainless gear bearing steel to completely solve the problems of coarse carbides, surface cracking and extremely low production efficiency after carburizing. Summary of the Invention

[0003] The purpose of the present invention is to provide a vacuum carburizing method for ultra-high alloy stainless gear bearing steel, which solves the problems of coarse carbides, surface cracking and extremely low production efficiency existing in the prior art after carburizing and quenching of ultra-high alloy stainless gear bearing steel.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A vacuum carburizing method for ultra-high alloy stainless gear bearing steel includes the following steps:

[0006] Step S1, alloy element solution: Put the ultra-high alloy stainless gear bearing steel into a vacuum carburizing furnace, and heat it up to 1100°C - 1120°C with the furnace under nitrogen protection and hold for a period of time for solution treatment;

[0007] Step S2, cooling carburizing: After solution treatment, the alloy elements are fully dissolved in austenite, and then the furnace temperature is lowered to 950°C - 980°C and then the carburizing mode is started;

[0008] Step S3, adjustment of carburizing medium composition: Adjust the conventional pure acetylene carburizing medium to a nitrogen-acetylene mixed gas to dilute the content of acetylene in the carburizing medium, and the nitrogen / acetylene of the mixed gas ≥ 5;

[0009] Step S4, weak saturation carburizing: Continuously introduce a nitrogen-acetylene mixed gas with a flow rate of 1250 - 1500 L / h into the furnace for weak saturation carburizing;

[0010] Step S5, final diffusion: After the weak saturation carburizing is completed, change to pure nitrogen for final diffusion to diffuse the carbon concentration within the technical requirements, and the weak saturation carburizing time / final diffusion time ≥ 1.5.

[0011] Advantages of the present invention:

[0012] By subjecting the alloying elements of the ultra-high alloy stainless gear bearing steel to solution treatment before carburizing, the present invention enables the alloying elements to be fully dissolved in austenite, avoiding the direct contact between strong carbide-forming elements such as Cr and Mo and C atoms to form coarse carbides. At the same time, most of the C atoms in the furnace atmosphere are adsorbed and dissolved in austenite. By adjusting the composition ratio of the carburizing medium, the traditional supersaturated carburizing method is evolved into a weak saturation carburizing method, so that during the entire carburizing process, the C content in the furnace atmosphere is only enough to maintain the lower limit of the solubility limit of austenite in the ultra-high alloy stainless gear bearing steel; thereby maximizing the restriction of the formation of alloy carbides such as Cr and Mo, avoiding the phenomena of coarse carbides and surface cracking after carburizing of the ultra-high alloy stainless gear bearing steel, and also solving the problem that due to the extremely long diffusion time of the traditional supersaturated carburizing method, the austenite is extremely carbon-depleted in the later stage of diffusion, seriously affecting the carburizing speed. Brief description of the drawings

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0014] Figure 1 It is a flowchart of a vacuum carburizing method for an ultra-high alloy stainless gear bearing steel of the present invention;

[0015] Figure 2 It is the metallographic structure and surface cracks of the 15Cr14Co12Mo5Ni material tested by the traditional supersaturated flow pulse vacuum carburizing method;

[0016] Figure 3 It is a process curve graph of the weak saturation carburizing process of the 15Cr14Co12Mo5Ni material;

[0017] Figure 4 It is the quenching + cold treatment + tempering process curve diagram of 15Cr14Co12Mo5Ni material;

[0018] Figure 5 It is the metallographic structure of 15Cr14Co12Mo5Ni material tested by the weak saturation vacuum carburizing method. Specific implementation mode

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0020] An embodiment of the vacuum carburizing method for ultra-high alloy stainless gear bearing steel:

[0021] Step S1, material selection: Select 15Cr14Co12Mo5Ni material, the technical requirement is that the effective hardened layer depth is 1.1 - 1.3 mm, the boundary hardness of the effective hardened layer is 613 HV, the surface hardness requirement is ≥ 63 HRC, and the metallographic structure is evaluated according to the 4.4 rating chart standard of HB5492, and the requirement is 1 - 4 grades;

[0022] Step S2, alloy element solution: Make the selected material into a specimen, put it into a vacuum carburizing furnace, and under the protection of nitrogen, heat it up to 1100 °C with the furnace and keep it warm for 180 min for solution treatment. See specifically Figure 3 ;

[0023] Step S3, temperature reduction carburizing: After reducing the furnace temperature to 950 °C, start to introduce the carburizing medium nitrogen-acetylene mixed gas, nitrogen / acetylene = 5;

[0024] Step S4, weak saturation carburizing: Continuously introduce the nitrogen-acetylene mixed gas with a flow rate of 1250 L / h into the furnace, and the weak saturation carburizing holding time is 240 min. See specifically Figure 3 ;

[0025] Step S5, final diffusion: After the weak saturation carburizing is completed, change to pure nitrogen for final diffusion, the final diffusion holding time is 120 min, and then enter the cooling chamber for slow cooling. See specifically Figure 3 。

[0026] Step S6, high-temperature tempering: After carburizing and slow cooling according to the above steps, then perform high-temperature tempering at 700 °C for 300 min.

[0027] Step S7, quenching + tempering: After high-temperature tempering, reheating is carried out for quenching at 1050°C → cryogenic treatment at -75°C → aging at 510°C → cryogenic treatment at -80°C → aging at 500°C. See specifically Figure 4 . After testing, the effective hardened layer depth is 1.25 mm, the surface hardness is 65.2 HRC, the carbide is grade 2, and there are no cracks on the surface. See specifically Figure 5 .

[0028] The materials applicable to the present invention are mainly low-carbon ultra-high alloy stainless gear bearing steels, and the applicable products are mainly aircraft engine gears and bearings that require carburization. By using the method of solution treatment followed by weak saturation carburization of the present invention, the problems of coarse carbides, surface cracking, and extremely low production efficiency after carburization can be completely solved. The carburization speed of this method is more than 4 times faster than that of the traditional supersaturated flow pulse vacuum carburization method.

[0029] The above content is only an example and explanation of the concept of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, as long as they do not deviate from the concept of the invention or exceed the scope defined by this claims, they should all fall within the protection scope of the present invention.

Claims

1. A vacuum carburizing method for a superalloy stainless gear bearing steel, characterized in that, It includes the following steps: Step S1, solution of alloying elements: Put the ultra-high alloy stainless gear bearing steel into a vacuum carburizing furnace, and heat it up to 1100°C - 1120°C with the furnace under nitrogen protection and hold for a period of time for solution treatment; Step S2, temperature reduction and carburizing: After the solution treatment, the alloying elements are fully dissolved in austenite, and then the furnace temperature is reduced to 950°C - 980°C and the carburizing mode is started; Step S3, adjustment of carburizing medium composition: Adjust the conventional pure acetylene carburizing medium to a nitrogen-acetylene mixed gas to dilute the content of acetylene in the carburizing medium, and the nitrogen / acetylene of the mixed gas ≥ 5; Step S4, weak saturation carburizing: Continuously introduce a nitrogen-acetylene mixed gas with a flow rate of 1250 - 1500 L / h into the furnace for weak saturation carburizing; Step S5, final diffusion: After the weak saturation carburizing is completed, change to pure nitrogen for final diffusion to diffuse the carbon concentration within the technical requirements, and the weak saturation carburizing time / final diffusion time ≥ 1.5.

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