In order to significantly improve the overall performance and service life of alloy spring steel, it is not enough to improve the smelting process. It is also necessary to continuously seek for beneficial alloying elements, develop new production processes and new steel grades to meet the ever-increasing requirements.
3.1 Multiple alloying of spring steel
The alloying elements used in standard alloy spring steel are not extensive enough, and the alloy series are relatively simple, failing to make full use of the effect of multiple alloying. The latest development trend of spring steel alloying is to make full use of the composite alloying effect of alloying elements to expand the use range of alloying elements, especially the use of trace alloying elements that have not been used before, and the use of multiple (even seven yuan or more) alloy series In order to improve the hardenability of spring steel, reduce the tendency of decarburization, and improve the comprehensive performance of spring steel.
For steel grades that are sensitive to decarburization, adding a small amount of chromium, vanadium, niobium, and molybdenum to the steel grade can improve the decarburization sensitivity of steel and reduce the decarburization of spring steel. Adding trace amounts of boron, vanadium, molybdenum, nickel, and chromium can improve The elasticity of spring steel.
India’s Ved.Parkash study shows that adding chromium to silico-manganese spring steel can improve the hardenability and yield strength of spring steel (adding 0.5% Cr increases by 15%), and the decarburization layer is significantly reduced. When smelting 60Si2Mn spring steel, Nanchang Iron and Steel Plant increased the residual chromium content in the steel to 0.35% to 0.85%, and found that the mechanical properties of the flat steel produced by it reached the level of 55SiMnVB. A trace amount of boron can prolong the incubation period of the phase transformation of spring steel, reduce the critical quenching speed, thereby improving the hardenability of the steel, and its optimum content is 0.0005% to 0.003%. According to relevant literature reports: steel contains 0.0015%-0.003% B, which can replace 1.0%-1.25% Ni, 0.1%-0.25% Mo, 0.30%-0.35% Cr, 0.2%-0.7% Mn, 0.1% V, 1.6 %Si, 0.00l%B can be equivalent to 1.33%Ni+0.31%Cr+0.04%Mo. Vanadium and niobium can refine grains and improve the quality of steel; molybdenum and nickel can improve the plasticity and surface finish of steel .
3.2 Rare earth treatment of spring steel
Since the main inclusions of electric furnace steel with low sulfur content are Al2O3 and aluminosilicate, if rare earth is added to the steel, the number of inclusions in the steel can be reduced, and the formation of fatigue cracks can be reduced. Rare earth can also affect the steel. The effect of microalloying, thereby improving the fatigue life of spring steel.
3.3 Development of new steel grades
Various countries have conducted a lot of research on the development of spring steel grades. Foreign countries have focused on improving the design stress of spring steel, and correspondingly proposed some steel grades with higher stress. For example, due to the high elasticity resistance of Si-Mn series alloy spring steel, a Si-Cr series alloy steel 54SiCr6 steel was added when Germany revised the spring steel standard in 1988; another example is the Si-Cr series alloy steel of SUP12 in Japan. . The United States developed chromium-free spring steel due to insufficient chromium resources. U.K. Tinsley Bridge Company adopted the “UZ Metallurgical” technology to develop low-alloy spring steel 0.4C-Mn(Cr)-B, hereinafter referred to as “test steel”, which was compared with the leaf spring produced by conventional spring steel 525H60. The test steel did indeed perform well. It has excellent surface core fatigue crack expansion ability, and the elastic strength and tensile strength are higher than that of conventional spring steel . US Patent 5009843 also introduces a low-carbon spring steel with excellent fatigue resistance and elasticity resistance: C 0.35%-0.55%, Si 1.80%-3.00%, Mn 0.50%-1.50%, Ni 0.50%-3 .00%, Cr 0.10%-1.50%, Al 0.01%-10.05%, N 0.010%-10.025%.
The development of spring steel in my country should be studied from the following aspects: ① Based on 60Si2Mn steel, study the best composition and application of 60Si2MnB steel, 60Si2Mn skimming steel and 60Si2MnCr steel; ② the introduction of some foreign advanced steel grades; ③ due to low carbon horses Stenite spring steel is easy to smelt in a converter, and has low cost, low decarburization tendency, and good hot workability. It should focus on research, development and application. In recent years, my country’s low-carbon martensitic spring steel is based on 28MnSiB steel. By increasing the content of silicon and carbon in the steel, 33MnSiB steel, 33MnSiB steel and 35MnSiB steel have been developed to improve the strength and elasticity of spring steel.