① Increase the hardenability of steel. Hardenability refers to the depth of the martensite layer from the surface when steel is quenched, and is the main parameter for achieving good comprehensive performance. Except for Co, almost all alloying elements such as Mn, Mo, Cr, Ni, Si and C, N, B can improve the hardenability of steel, among which Mn, Mo, Cr, B have the strongest effect, followed by Ni, Si, and Cu. Strong carbide-forming elements such as V, Ti, Nb, etc. can only increase the hardenability of steel when dissolved in austenite.
② Affect the tempering process of steel. Since alloying elements can hinder the diffusion of various atoms in steel during tempering, compared with carbon steel at the same temperature, they generally play a role in delaying the decomposition of martensite and the aggregation and growth of carbides, thereby improving the tempering stability of steel, that is, improving the steel's resistance to tempering softening. The effects of V, W, Ti, Cr, Mo, and Si are more significant, while the effects of Al, Mn, and Ni are not obvious. Steels containing high levels of carbide-forming elements such as V, W, and Mo, when tempered at 500 to 600°C, will precipitate fine and dispersed special carbide particles such as VC[kg2]MoC, WC, etc., replacing part of the coarser alloy cementite, so that the strength of the steel no longer decreases but increases, that is, secondary hardening occurs (see tempering). Mo has a preventive or weakening effect on the temper brittleness of steel.
③ Affects the strengthening and toughening of steel. Ni strengthens ferrite by solid solution strengthening; carbide-forming elements such as Mo, V, and Nb increase the yield strength of steel by both dispersion hardening and solid solution strengthening; carbon has the most significant strengthening effect. In addition, the addition of these alloying elements generally refines austenite grains and increases the strengthening effect of grain boundaries. The factors affecting the toughness of steel are relatively complex. Ni improves the toughness of steel; Mn easily coarsens austenite grains and is sensitive to temper brittleness; reducing the content of P and S and improving the purity of steel play an important role in improving the toughness of steel (see strengthening of metals).
alloy seamless cold drawn tube
