Carbon bearing steel structural improvements and performance improvements

With China's equipment manufacturing industry to develop high-quality and high precision, for the manufacture of ball bearings,Taper bearing and other steel sleeve is gaining attention. Along with the bearing industry sustained and rapid development, bearing steel market prospects. And, precision bearings and other basic mechanical casting industry has become a national "Twelve Five" period focus on the development of the industry. Therefore, it is necessary to intensify research on bearing steel, bearing steel to improve the quality.
        Recently, Russian scholars GSVodovozova and PAZhdanov et al studied the carbon bearing steel structure and mechanical properties, and through experiments with ShKh15 class bearing steel were compared and analyzed in hardness, homogeneity and grain size The conclusions of the actual production of carbon bearing steel provides a theoretical basis.
        Inhomogeneity into a "bottleneck"
        In general, the performance requirements of bearing steel is a high hardness, good flexibility and fatigue resistance properties, especially anti-contact fatigue failure resistance. For carbon steel, when the carbon content of 0.95% to 1.15% of the meet these requirements; while the carbon content is 0.10% to 0.20% of the carbon bearing steel is often necessary for carbonitriding process to meet the above requirements. Bearing steel anti-contact fatigue failure of performance, depending on the non-metallic inclusions in steel coarse particles accumulate, the heterogeneity carbide crystal size differences and other factors. The combined effect of these defects causing the bearing steel in the course of micro-stress concentration and premature embrittlement (peel, cut formation and cracking, etc.).
Widely used class of bearing steel ShKh15 displayed obvious drawback is that the structure is not homogeneous due. It is through the chemical composition analysis of a feature, i.e. carbon content (0.95% to 1.10%), due to the heterogeneity of carbon and carbide segregation resulting development. In order to avoid this situation is not homogeneous occurrence or improvement of this situation, by increasing the length of time necessary for the homogenization annealing.
By adding suitable alloying elements can be achieved using low carbon content steel required hardness level. As we all know, as bearing steel, you can use low-carbon and medium carbon chromium - nickel, chromium - manganese and chromium - silicon - manganese steel. These steels are no carbon eutectoid steel main drawback --- carbides not homogeneous.
        Taking into account the above factors, need to be developed to provide energy savings and prolong bearing life bearing steel production technology.
        Fine and uniform microstructure
        Recent research is innovative steel bearing steel, able to meet the more dense sheet components, and applications more economical material to improve quality, reduce production cycle and ShKh15 steel and has the same or better performance. Kawasaki Steel Corporation (Japan) and NTN (Japan) steel company has developed and put into a class of carbon bearing steel. Such carbon bearing steel, the carbon content is reduced to 0.75% ~ 0.80%, so that the steel in the casting stage to the eutectic composition in addition to the formation of carbides, and without using the diffusion annealing. In addition, to reduce the carbon content in the case of steel, technology is more conducive to punching and shearing.
In order to assess the chemical composition of the steel, microstructure and mechanical properties, Russian scholars under laboratory conditions for ordinary steel and bearing steel ShKh15 carbon bearing steel fracture resistance were different heats rolling experiments and other tests .
        Gas analysis showed that only the first 2 heats up the oxygen content of steel is found, but the overall oxygen content within the allowable range, the other heats the oxygen content of the steel in accordance with the technical standards GOST901 (no more than 0.0015%). Organization for the study of macro-and microstructure, from the experimental heats in selected specimens for microscopic observation. While preparing a diameter of 5 mm cylindrical tensile test specimen (according GOST1497-84); prepared with a V-shaped groove (under GOST9454 II) 10 mm × 10 × 55 mm specimen 毫米 for static bending test; take fatigue cracking crack maximum depth of 2 mm specimen fracture toughness test (according GOST9454 second category).
        The ultimate carbon bearing steel heat treatment using generally accepted ShKh15 class bearing steel specification: at 840 ℃ ~ 845 ℃ heat-curing, soaking 35 minutes to 40 minutes after the M2M-16 oil cooling, oil temperature at 30 ℃ ~ 60 ℃ , followed by tempering at 155 ℃ for 3.5 hours. According GOST9013 (61.5HRC ~ 62.5HRC), the final hardness after tempering of 62HRC. Hot-rolled low magnification by the state does not exist free ferrite pearlite sandwich structure, grain size of not less than seven (according GOST5639), no coarse carbide precipitation, low magnification even small, in favor of steel Further Finishing.
        To provide good cutting and preparation before hardening steel requires an intermediate heat treatment, ie 800 ℃ ~ 690 ℃ under Spheroidizing 17 hours, in the annealed condition, globular pearlite grain level 2, steel experimental heats low magnification meet GOST801 technical specifications. Longitudinal assessment of microscopic cross section microstructure banded structure. Hardened steel specimens from 850 ℃, and then cooled at 150 ℃ tempered for 1 hour, the microstructure of steel strip experimental structure is not more than 1 ~ 2, the values ​​for the hot-rolled GOST801 fully meet the technical specifications ShKh15 requirements. The same test sample used to evaluate the residual carbide steel network, confirm no more than 3, more uniform structure of the tested steel. Therefore, taking into carbide segregation index and the structure is not homogeneous, experimental steel meets all the technical specifications and standards significantly more than ShKh15 class bearing steel.
        Good mechanical properties
Evaluation of non-metallic inclusions and the experimental sample selection GOST1778-80 was prepared according to. Non-metallic inclusions are mainly carbides and oxides, there is almost no spherical inclusions ductility single mixed silicates, showing the size of 1.5, exists in the second second steel inside the furnace, and the oxide inclusions contaminated scrap. In hot conditions, laboratory heats of steel used carbonitriding process for micro-alloyed hardness of 35HRC ~ 38HRC. To achieve globular pearlite annealing using laboratory heats carbonitriding steel alloyed with a hardness of 195HB ~ 217HB, its value is slightly higher than the GOST801 technical specifications hardness 179HB ~ 207HB. In the new hardened state, the experimental steel hardness 65HRC ~ 67HRC.
        Tempering the quenched steel hardness of display, the experimental heats of steel at 160 ℃ tempering temperature did not decrease hardness of hardened steel, i.e. the level of 65HRC.
The hardened and tempered state mild steel mechanical experimental results showed that all cases are due to brittle fracture caused by the mechanism, breaking strength and yield stress values ​​are almost equal, they are 624 ~ 920N/mm2, elongation, and relevant area is reduced to near zero. Fracture toughness test sample size of 10 mm × 10 毫米 55 mm, and for centralized bending, sharp cut to open the sample advance and fatigue cracks. In the hardening and 150 ℃ ~ 180 ℃ tempering, the right use of V and Nb micro-alloyed specimens in the experiment. Status and data from the tissue showed that the experimental fracture toughness of steel (carbon bearing steel) and are similar ShKh15 steel, tempering temperature rise from 150 ℃ 180 ℃ without reducing the fracture toughness of steel.
        Through the experiment of steel chemical composition, microstructure and macroscopic tissue analysis, hardness, mechanical properties and fracture resistance of a comprehensive study concluded that a new experimental heats level of mechanical properties of bearing steel and bearing steel ShKh15 class rather, 64HRC ~ 65HRC hardness level than GOST801 technical specifications, experimental heats of steel and bearing steel ShKh15 class fracture toughness values ​​are similar. The use of V and Nb microalloyed steel bearing GOST801 technical specifications to meet the requirements of the experimental steel is more pure. Meanwhile, the low magnification carbide is not homogeneous low, there is no residual carbon grid. Therefore, the new micro-alloyed carbon bearing steel bearing steel has more class than ShKh15 good performance.

With China's equipment manufacturing industry to develop high-quality and high precision, for the manufacture of ball bearings, roller bearings and other steel sleeve is gaining attention. Along with the bearing industry sustained and rapid development, bearing steel market prospects. And, precision bearings and other basic mechanical casting industry has become a national "Twelve Five" period focus on the development of the industry. Therefore, it is necessary to intensify research on bearing steel, bearing steel to improve the quality.
        Recently, Russian scholars GSVodovozova and PAZhdanov et al studied the carbon bearing steel structure and mechanical properties, and through experiments with ShKh15 class bearing steel were compared and analyzed in hardness, homogeneity and grain size The conclusions of the actual production of carbon bearing steel provides a theoretical basis.
        Inhomogeneity into a "bottleneck"
        In general, the performance requirements of bearing steel is a high hardness, good flexibility and fatigue resistance properties, especially anti-contact fatigue failure resistance. For carbon steel, when the carbon content of 0.95% to 1.15% of the meet these requirements; while the carbon content is 0.10% to 0.20% of the carbon bearing steel is often necessary for carbonitriding process to meet the above requirements. Bearing steel anti-contact fatigue failure of performance, depending on the non-metallic inclusions in steel coarse particles accumulate, the heterogeneity carbide crystal size differences and other factors. The combined effect of these defects causing the bearing steel in the course of micro-stress concentration and premature embrittlement (peel, cut formation and cracking, etc.).
Widely used class of bearing steel ShKh15 displayed obvious drawback is that the structure is not homogeneous due. It is through the chemical composition analysis of a feature, i.e. carbon content (0.95% to 1.10%), due to the heterogeneity of carbon and carbide segregation resulting development. In order to avoid this situation is not homogeneous occurrence or improvement of this situation, by increasing the length of time necessary for the homogenization annealing.
By adding suitable alloying elements can be achieved using low carbon content steel required hardness level. As we all know, as bearing steel, you can use low-carbon and medium carbon chromium - nickel, chromium - manganese and chromium - silicon - manganese steel. These steels are no carbon eutectoid steel main drawback --- carbides not homogeneous.
        Taking into account the above factors, need to be developed to provide energy savings and prolong bearing life bearing steel production technology.
        Fine and uniform microstructure
        Recent research is innovative steel bearing steel, able to meet the more dense sheet components, and applications more economical material to improve quality, reduce production cycle and ShKh15 steel and has the same or better performance. Kawasaki Steel Corporation (Japan) and NTN (Japan) steel company has developed and put into a class of carbon bearing steel. Such carbon bearing steel, the carbon content is reduced to 0.75% ~ 0.80%, so that the steel in the casting stage to the eutectic composition in addition to the formation of carbides, and without using the diffusion annealing. In addition, to reduce the carbon content in the case of steel, technology is more conducive to punching and shearing.
In order to assess the chemical composition of the steel, microstructure and mechanical properties, Russian scholars under laboratory conditions for ordinary steel and bearing steel ShKh15 carbon bearing steel fracture resistance were different heats rolling experiments and other tests .
        Gas analysis showed that only the first 2 heats up the oxygen content of steel is found, but the overall oxygen content within the allowable range, the other heats the oxygen content of the steel in accordance with the technical standards GOST901 (no more than 0.0015%). Organization for the study of macro-and microstructure, from the experimental heats in selected specimens for microscopic observation. While preparing a diameter of 5 mm cylindrical tensile test specimen (according GOST1497-84); prepared with a V-shaped groove (under GOST9454 II) 10 mm × 10 × 55 mm specimen 毫米 for static bending test; take fatigue cracking crack maximum depth of 2 mm specimen fracture toughness test (according GOST9454 second category).
        The ultimate carbon bearing steel heat treatment using generally accepted ShKh15 class bearing steel specification: at 840 ℃ ~ 845 ℃ heat-curing, soaking 35 minutes to 40 minutes after the M2M-16 oil cooling, oil temperature at 30 ℃ ~ 60 ℃ , followed by tempering at 155 ℃ for 3.5 hours. According GOST9013 (61.5HRC ~ 62.5HRC), the final hardness after tempering of 62HRC. Hot-rolled low magnification by the state does not exist free ferrite pearlite sandwich structure, grain size of not less than seven (according GOST5639), no coarse carbide precipitation, low magnification even small, in favor of steel Further Finishing.
        To provide good cutting and preparation before hardening steel requires an intermediate heat treatment, ie 800 ℃ ~ 690 ℃ under Spheroidizing 17 hours, in the annealed condition, globular pearlite grain level 2, steel experimental heats low magnification meet GOST801 technical specifications. Longitudinal assessment of microscopic cross section microstructure banded structure. Hardened steel specimens from 850 ℃, and then cooled at 150 ℃ tempered for 1 hour, the microstructure of steel strip experimental structure is not more than 1 ~ 2, the values ​​for the hot-rolled GOST801 fully meet the technical specifications ShKh15 requirements. The same test sample used to evaluate the residual carbide steel network, confirm no more than 3, more uniform structure of the tested steel. Therefore, taking into carbide segregation index and the structure is not homogeneous, experimental steel meets all the technical specifications and standards significantly more than ShKh15 class bearing steel.
        Good mechanical properties
Evaluation of non-metallic inclusions and the experimental sample selection GOST1778-80 was prepared according to. Non-metallic inclusions are mainly carbides and oxides, there is almost no spherical inclusions ductility single mixed silicates, showing the size of 1.5, exists in the second second steel inside the furnace, and the oxide inclusions contaminated scrap. In hot conditions, laboratory heats of steel used carbonitriding process for micro-alloyed hardness of 35HRC ~ 38HRC. To achieve globular pearlite annealing using laboratory heats carbonitriding steel alloyed with a hardness of 195HB ~ 217HB, its value is slightly higher than the GOST801 technical specifications hardness 179HB ~ 207HB. In the new hardened state, the experimental steel hardness 65HRC ~ 67HRC.
        Tempering the quenched steel hardness of display, the experimental heats of steel at 160 ℃ tempering temperature did not decrease hardness of hardened steel, i.e. the level of 65HRC.
The hardened and tempered state mild steel mechanical experimental results showed that all cases are due to brittle fracture caused by the mechanism, breaking strength and yield stress values ​​are almost equal, they are 624 ~ 920N/mm2, elongation, and relevant area is reduced to near zero. Fracture toughness test sample size of 10 mm × 10 毫米 55 mm, and for centralized bending, sharp cut to open the sample advance and fatigue cracks. In the hardening and 150 ℃ ~ 180 ℃ tempering, the right use of V and Nb micro-alloyed specimens in the experiment. Status and data from the tissue showed that the experimental fracture toughness of steel (carbon bearing steel) and are similar ShKh15 steel, tempering temperature rise from 150 ℃ 180 ℃ without reducing the fracture toughness of steel.
        Through the experiment of steel chemical composition, microstructure and macroscopic tissue analysis, hardness, mechanical properties and fracture resistance of a comprehensive study concluded that a new experimental heats level of mechanical properties of bearing steel and bearing steel ShKh15 class rather, 64HRC ~ 65HRC hardness level than GOST801 technical specifications, experimental heats of steel and bearing steel ShKh15 class fracture toughness values ​​are similar. The use of V and Nb microalloyed steel bearing GOST801 technical specifications to meet the requirements of the experimental steel is more pure. Meanwhile, the low magnification carbide is not homogeneous low, there is no residual carbon grid. Therefore, the new micro-alloyed carbon Roller bearing steel tapered bearing steel has more class than ShKh15 good performance.