The role of alloy elements in dense bearing rolling bearing steel.
1. The role of silicon element in GCr15 bearing steel
It is conducive to the formation of ferrite structure with body centered cubic structure, without forming carbides in steel. It is located on the left side of iron in the periodic table and mainly solidly soluble in iron. It has little effect on the diffusion coefficient of carbon in austenite and has little effect on the formation rate of austenite. It can increase the A1 point and relatively slow down the formation rate of austenite. When there is a slight obstruction or no effect on the grain size of austenite during heating, it can delay the pearlite phase transformation and cause the C curve to shift to the right, causing the nose on the C curve to move towards the high-temperature area, reducing the Ms point, improving the stability of undercooled austenite, thereby reducing the critical cooling rate for quenching and improving the hardenability of the steel. It can significantly slow down the decomposition of martensite at lower temperatures, but it does not slow down the decomposition of martensite during tempering at 400-500 ℃, significantly hindering the aggregation of carbides, hindering the elimination of various distortions in steel during tempering, and generally delaying the quenching of steel α The process of phase recovery, recrystallization, and carbide aggregation suppresses the decrease in hardness and strength of the steel, and enhances the tempering stability of the steel. Can be improved α The recrystallization temperature of the phase can significantly enhance the tempering brittleness of the steel, alter the microstructure of each phase of the steel, and increase the number of pearlite. The main purpose is to increase the hardenability of steel. After high-temperature tempering, all quenched parts can obtain high and uniform comprehensive mechanical properties, especially high yield strength ratio, significantly strengthening ferrite, and even improving the toughness of steel within a certain range.
2. The Role of Chromium in GCr15 Bearing Steel
Sealable γ When the content of elements in the phase zone reaches a certain amount, γ The phase zone is closed, even if the γ The area shrinks into a very small range, beyond which the alloy occurs γ reach α Phase transformation is beneficial for the formation of ferrite structure with body centered cubic structure. Carbides can be formed in steel, which are transitional transition group elements located on the left side of iron in the periodic table, which can reduce the carbon content at the eutectoid point of steel and reduce the carbon content at the γ The maximum solid solubility in can be achieved by adding a large amount of γ The phase zone disappears and all ferrite structures are obtained. It is a strengthening element that reduces the diffusion coefficient of carbon in austenite, thus greatly delaying the transformation process from pearlite to austenite. In steel, the special carbides formed are not easily soluble, which slows down the formation rate of austenite and can increase the A1 point, relatively slowing down the formation rate of austenite. Significantly α The recrystallization temperature of the phase is pushed towards high temperature, causing obvious tempering brittleness in the steel, strongly preventing the further development of martensite decomposition, which can change the microstructure of each phase of the steel and increase the number of pearlite. By increasing the hardenability of steel, all quenched parts can achieve high and uniform comprehensive mechanical properties after high-temperature tempering, especially high yield strength ratio, significantly strengthening ferrite, and even improving the toughness of steel within a certain range. If special carbides that are difficult to dissolve are formed, if the holding time is insufficient during heating, austenite with extremely uneven composition will be obtained. It has a moderate hindrance effect on the grain size of austenite during heating, which can delay the pearlite phase transformation, reduce the Ms point, improve the stability of undercooled austenite, thereby reducing the critical cooling rate of quenching and improving the hardenability of steel. Significantly hinders the aggregation of carbides, hinders the elimination of various distortions in steel during tempering, and generally delays the quenching of steel α The process of phase recovery, recrystallization, and carbide aggregation inhibits the decrease in hardness and strength of the steel, and enhances the role of manganese in 5.3 GCr15 bearing steel
Openable γ If a certain number of phase zones are reached, they can be completely suppressed α The emergence of phase zones, replaced by γ Therefore, if the r region is quenched to room temperature, it is easy to obtain austenite. Can be improved α The recrystallization temperature of the phases causes obvious tempering brittleness in the steel, which can change the microstructure of each phase of the steel and increase the number of pearlite. Carbides can be formed in steel, which are transitional transition group elements located on the left side of iron in the periodic table. They can reduce A3 and A1, and after a large amount of addition, they can even lower A3 to below room temperature. Therefore, the steel still has austenite structure at room temperature, which can change the working transformation temperature and lower the A1 point. Relatively speaking, reducing the A1 point increases the degree of superheat, which increases the formation rate of austenite, refines pearlite, and is conducive to austenite formation, The austenite grain size during heating is helpful. It can delay the pearlite phase transformation, reduce the Ms point, improve the stability of undercooled austenite, thereby reducing the critical cooling rate for quenching and improving the hardenability of the steel. In order to increase the hardenability of steel, all quenched parts can obtain high and uniform comprehensive mechanical properties after high-temperature tempering, especially high yield strength ratio, significantly strengthening ferrite, and improving the toughness of steel within a certain range.
