CN102011055B - Hard bainite bearing manufacturing method - Google Patents

Abstract

The invention relates to a method for manufacturing a hard bainite bearing. Pure low carbon low alloy steel is adopted, oxygen and hydrogen contents are 5ppm and less than 0.5ppm respectively, phosphor and sulphur contents are less than 0.005wt% respectively, and carbon content is 0.15-0.22wt%, and aluminium content is 1.0-1.2wt%; and the manufacturing process comprises: raw materials is subject to plastic hot working, and then mechanical cold working is carried out, thus obtaining a bearing; carburization is carried out on the surface of the bearing; and then normalizing, austenitizing, quenching, cold treatment, tempering and other heat treatments are carried out on the bearing. The center part of the product manufactured by the method is in a low carbon tempered martensite structure, and the surface is a long-life bearing in a high carbon hard bainite structure. The bearing provided by the invention has stable dimensions when in use. Under the condition of high stress, the service life of the bear provided by the invention is improved by more than twice compared with a GCr15 steel bearing which is widely applied at present.

Description

Hard bainite bearing manufacturing method

TECHNICAL FIELD This invention relates to the heat treatment method of a steel material.

BACKGROUND OF THE INVENTION As we all know, bearings are key basic parts in mechanical equipment. They must have excellent wear resistance and high contact fatigue resistance. The quality of bearings is directly related to the service life of the entire equipment. The quality of the bearing depends largely on the bearing material and its heat treatment process. At present, commonly used bearing steels include chromium bearing steel, chromium-free bearing steel, stainless bearing steel, high temperature bearing steel and carburized bearing steel. Among them, the typical steel grade of chromium bearing steel is GCr15, which is a widely used bearing steel for the manufacture of small and medium-sized bearings and some large bearings. GCr9SiMn and GCr15SiMn have higher manganese and silicon content, which improves hardenability, and GCr15SiMn can be used to manufacture some large and extra large bearings. Quenching and low-temperature tempering are commonly used heat treatments for chromium bearing steel. When producing precision bearings and measuring tools with chromium bearing steel, internal stress and residual austenite cannot be completely eliminated due to low-temperature tempering, and the workpiece will be deformed during long-term storage or use. . In order to avoid this from happening, more complex heat treatment is required. Chromium-free bearing steel is a multi-alloy bearing steel developed later, which often contains alloying elements such as silicon, manganese, molybdenum, and vanadium, such as GSiV, GMnMoV, and GSiMnMoV. Due to the joint action of alloying elements, the hardenability of this type of steel is high. After quenching, the parts can get relatively uniform high hardness, wear resistance, contact fatigue resistance and toughness, and the tendency of quenching deformation is small, and the tempering stability is good. However, there are also problems such as high sensitivity to decarburization, high annealing hardness, and inferior corrosion resistance to chromium bearing steel. Stainless bearing steel is developed to adapt to the development of industries such as chemistry, petroleum, and shipbuilding. Bearings working in various corrosive environments must have high corrosion resistance. Generally, bearing steel with chromium content is not competent. Therefore, high-carbon and high-chromium stainless bearing steel has been developed. Chromium is the main alloying element of this type of steel, such as 9Cr18, 9Cr18Mo and so on. Its shortcoming is that the scope of application is limited. Bearings in aero-engines, aerospace vehicles, gas turbines and other devices work under high-temperature, high-speed and high-load conditions, and their working temperature is above 300°C. The working temperature of aluminum low-alloy bearing steel can only be below 250 ° C. If the temperature rises again, it will cause a sharp drop in hardness and fail. Therefore, for bearings working at higher temperatures, bearing steels with sufficiently high high-temperature hardness, high-temperature wear resistance, high-temperature contact fatigue strength and high oxidation resistance should be used. At present, there are two types of high-temperature bearing steel: high-speed steel bearing steel (such as W18Cr4V) and high-chromium martensitic stainless steel (such as Cr14Mo4V). Its disadvantage is that the price is relatively high. Carburized bearing steel is mainly used to make large (outer diameter greater than 250mm) or extra-large (outer diameter greater than 450mm) bearings on large rolling mills, generators and mining machinery. These bearings are large in size, work under extremely high contact stress, and are frequently subjected to impact and wear. Therefore, in addition to the requirements for general bearings, large bearings also require sufficient toughness and high compression resistance in the core. Strength and hardness, so low-carbon alloy carburizing steel is used to manufacture. After carburizing and quenching and low-temperature tempering, the surface layer is hard and wear-resistant, and the core maintains high strength and toughness. At the same time, the surface is in a state of compressive stress, which is beneficial to improving fatigue life. Commonly used carburized bearing steels are G20CrMo, G20CrNiMo, G20CrNi 2Mo, G20Cr2Ni4 and G20Cr2Mn2Mo. Its disadvantage is that the price is relatively high.

SUMMARY OF THE INVENTION The object of the present invention is to provide a method for manufacturing hard bainite bearings with simple heat treatment, low decarburization sensitivity, moderate annealing hardness, corrosion resistance and low price. The invention mainly uses a carburizing treatment method and a special heat treatment method to process the bearing with a certain chemical composition into a high-performance bearing with a hard bainite structure on the surface and a low-carbon tempered martensite in the center.

Hard bainite is a high carbon content carbide-free bainite ferrite structure, which is obtained by austempering at a temperature slightly higher than the Ms point of the material to obtain a bainite with a very small substructure size and no carbides organize. It has the hardness of quenched martensite structure and the toughness of quenched and tempered structure.

Technical scheme of the present invention is:

1. Raw material of the bearing: pure 20CrAl steel prepared by vacuum smelting and vacuum consumable electroslag technology. The chemical composition of the 20CrAl is: carbon content is 0.15-0.22wt%, aluminum content is 1.0-1.2wt%, chromium content is 1.2-2.0wt%, phosphorus and sulfur content are less than 0.005wt% respectively; oxygen and hydrogen content are respectively below 5ppm and 0.5ppm, and the rest is iron. For bearings with larger size and higher hardenability requirements, elements such as Ni, Mo or W can be added to 20CrAl composition steel, and the corresponding steel is 20CrMoAl or 20CrWAl or 20CrNiMoAl or 20CrNiWAl steel, and the molybdenum content is <0.5wt %, nickel content <0.5wt%, tungsten content <1.0wt%.

2. Use conventional forging or rolling to carry out plastic heat processing on raw materials.

3. Machining bearings: The above-mentioned plastic heat-processed materials are mechanically cold-processed into bearings.

4. Carburizing the bearing surface: heating the bearing to 920-950°C and carburizing for 200-300 minutes. After carburizing, the carbon content of the bearing surface is 0.9-1.2wt%, and the carburizing layer depth is 1.0-1.5mm.

5. Heat treatment of bearings:

a. Heat the above-mentioned bearing to 900-930°C for 60-120 minutes, and perform normalizing treatment to eliminate the reticular carbide;

b. Heat the above-mentioned bearing to 860-880°C for 60-120 minutes, perform austenitization treatment, and then carry out austenitizing treatment at 200-300°C for 30-200 minutes;

c. Air-cool the above-mentioned bearing to room temperature, and keep it at -100--50°C for 30-90 minutes for cold treatment;

d. Heat the above-mentioned bearing to 150-250°C and keep it warm for 60-120 minutes for tempering treatment.

Compared with the prior art, the method of the present invention has the following advantages: on the one hand, the product of the present invention ensures the hardenability of the bearing, so that the core can obtain a martensitic structure after quenching; on the other hand, it ensures that the surface layer of the bearing is easy to A bainite structure is obtained, and the bainite should be carbide-free bainite. This is beneficial to improve the rolling contact fatigue resistance of the bearing. The structure state of the bearing parent material is a tempered martensite structure, which maintains the conventional mechanical properties such as tension and impact of the tempered martensite structure. The rolling contact fatigue life of the bearing with hard bainite structure on the surface layer of the invention is more than three times that of the traditional GCr15 steel bearing. The friction and wear performance of this hard bainite structure is tested by a friction and wear testing machine, and it is found that its friction and wear performance is more than three times that of the traditional GCr15 steel. In other words: obtain high-performance bearings with tempered martensite in the center and ultra-fine bainite structure on the surface. Such bearings are dimensionally stable during use, and their service life is longer than that of widely used bearings under high stress conditions. The fatigue life of traditional GCr15 steel bearings is increased by more than 2 times.

Detailed ways

Example 1

The pure 20CrAl steel prepared by vacuum smelting and vacuum consumable electroslag technology has the following chemical composition by weight: carbon content is 0.15%, aluminum content is 1.08%, chromium content is 1.26%, phosphorus content is 0.0009%, sulfur content It is 0.003%, the oxygen content is 4ppm, the hydrogen content is 0.4ppm, and the rest is iron. The above-mentioned raw materials are subjected to forging plastic heat processing, and the above-mentioned plastic heat processed materials are subjected to mechanical cold processing to form bearings. The above-mentioned bearing was heated to 945° C. for 300 minutes and carburized. After carburizing, the carbon content on the surface of the bearing was 1.2 wt %, and the carburized layer depth was 1.4 mm. After air cooling, heat the above-mentioned bearings to 930°C for 115 minutes for normalizing treatment; then heat to 880°C for 110 minutes, then place them in nitrate salt at a temperature of 290°C for 100 minutes; air-cool the above-mentioned bearings to room temperature, and then place Keep the temperature at -95°C for 90 minutes; finally heat the above bearing to 240°C for 60 minutes. The surface hardness of the obtained product of the present invention is HRC63, and the core hardness is HRC43. This bearing is used in a port coal transportation system, and its service life is more than 80% higher than that of ordinary GCr15 steel bearings.

Example 2

The pure 20CrMoAl steel prepared by vacuum smelting and vacuum consumable electroslag technology has the following chemical composition by weight: carbon content 0.19%, aluminum content 1.0%, chromium content 1.85%, molybdenum content 0.45%, phosphorus content It is 0.003%, the sulfur content is 0.002%, the oxygen content is 4.5ppm, the hydrogen content is 0.3ppm, and the rest is iron. The above-mentioned raw materials are subjected to rolling plastic heat processing, and the above-mentioned plastic heat processed materials are subjected to mechanical cold processing to form bearings. The above-mentioned bearing was heated to 935° C. for 200 minutes and carburized. After carburizing, the carbon content on the surface of the bearing was 1.05 wt %, and the carburized layer depth was 1.2 mm. After air cooling, heat the above-mentioned bearing to 920°C for 80 minutes for normalizing treatment; then heat it to 870°C for 80 minutes, and then keep it for 180 minutes in a fluid particle cooling bed at 220°C; air-cool the above-mentioned bearing to room temperature, and then place Keep the temperature at -70°C for 60 minutes; finally heat the above-mentioned bearing to 200°C for 80 minutes. The surface hardness of the obtained product of the present invention is HRC64, and the hardness of the core is HRC47. The heavy-duty bearing of coal mining machinery manufactured by the present invention has a service life that is more than double that of ordinary GCr15 steel bearings.

Example 3

Pure 20CrNiWAl steel prepared by vacuum smelting and vacuum self-consumption electroslag technology, the weight percentage of its chemical composition is: carbon content 0.18%, aluminum content 1.18%, chromium content 1.55%, tungsten content 0.79%, nickel The iron content is 0.41%, the phosphorus content is 0.005%, the sulfur content is 0.0013%, the oxygen content is 4ppm, the hydrogen content is 0.3ppm, and the rest is iron. The above-mentioned raw materials are subjected to forging plastic heat processing, and the above-mentioned plastic heat processed materials are subjected to mechanical cold processing to form bearings. The above-mentioned bearing was heated to 925° C. for 220 minutes and carburized. After carburizing, the carbon content on the surface of the bearing was 0.92 wt %, and the carburized layer depth was 1.1 mm. After air cooling, heat the above bearing to 910°C for 65 minutes for normalizing treatment; then heat it to 860°C for 65 minutes, then place it in nitrate salt at 230°C for 40 minutes; air cool the above bearing to room temperature, and then place Keep the temperature at -80°C for 40 minutes; finally heat the above-mentioned bearing to 160°C for 70 minutes. The surface hardness of the obtained product of the present invention is HRC62, and the core hardness is HRC43. The service life of the large-size bearing manufactured by the present invention is more than 1 times that of ordinary GCr15 steel bearings.

Claims (2)

1. A method for manufacturing a hard bainite bearing, characterized in that: (1) Pure 20CrAl steel prepared by vacuum smelting and vacuum consumable electroslag technology, the weight percentage of its chemical composition is: carbon content is 0.15-0.22%, aluminum content is 1.0-1.2%, chromium content is 1.2-2.0% , the phosphorus and sulfur contents are less than 0.005%, the oxygen and hydrogen contents are respectively below 5ppm and 0.5ppm, and the rest is iron; (2) Plastic heat processing of raw materials by conventional forging or rolling; (3) Carrying out mechanical cold processing of the above-mentioned plastic heat processed material into a bearing; (4) Heating the above-mentioned bearing to 920-950°C, carburizing for 200-300 minutes, the carbon content of the bearing surface after carburizing is 0.9-1.2wt%, and the carburizing layer depth is 1.0-1.5mm; (5) Heat treatment of bearings: a. Heat the above-mentioned bearing to 900-930°C for 60-120 minutes, and perform normalizing treatment; b. Heat the above-mentioned bearing to 860-880°C for 60-120 minutes, perform austenitization treatment, and then heat it at 200-300°C for 30-200 minutes to perform austempering treatment; c. Air-cool the above-mentioned bearing to room temperature, and keep it at -100~-50°C for 30~90 minutes; d. Heat the above-mentioned bearing to 150-250°C and keep it warm for 60-120 minutes for tempering treatment. 2. The method for manufacturing hard bainite bearings according to claim 1, characterized in that: Ni, Mo or W elements are added to the 20CrAl composition steel, and the molybdenum content is <0.5wt%, the nickel content is <0.5wt%, and the tungsten Content<1.0wt%.