Stainless Steel Standard Parts-Influence of Alloy Elements on Steel

Influence on heat treatment

① Influence on austenitizing during heating: Heat treatment of alloy steel can appropriately increase the heating temperature and extend the holding time.

Alloy cementite and alloy carbide in alloy steel have high stability and are not easy to dissolve into austenite; The diffusion of alloying elements after dissolving into austenite is very slow, so the austenitizing speed of alloy steel is slower than that of carbon steel. In order to accelerate the austenitizing, it is required to heat the alloy steel (manganese steel outside) to a higher temperature and keep the temperature for a long time. Stainless steel standard parts manufacturers say that all alloying elements except Mn have the effect of hindering austenite grain growth, especially the alloy carbides composed of strong carbides such as Ti and V have high stability and remain on austenite grain boundaries, which significantly hinders austenite grain growth. Therefore, the austenite grain is generally finer than that of carbon steel.

② Influence on the change of undercooled austenite: Alloy steel has better hardenability, which can reduce quenching cooling rate and quenching deformation. But the remaining austenite increased.

Except Co, all alloying elements dissolved in austenite increase the stability of undercooled austenite, shift the C curve to the right, reduce the critical cooling rate of martensite and improve the hardenability. This enables alloy steel to be quenched into martensite arrangement with a small cooling rate, which can reduce quenching deformation. Therefore, important parts with large size, complex shape or high precision need to be made of alloy steel. Except for Co and Al, most alloying elements reduce the Ms point, which makes the residual austenite of alloy steel after quenching more than that of carbon steel, which will adversely affect the quenching quality of parts.

③ Influence on tempering change: Alloy steel has good tempering resistance, better cooperation in strength and tolerance after tempering, and some steels can produce "secondary hardening".

Martensite of alloy steel is not easy to differentiate when tempered, and its softening resistance is strong, that is, it improves the tempering resistance of steel and has better tolerance and cooperation after tempering. Alloying elements can improve the bainite differentiation temperature. For steel containing more strong carbides such as Cr, Mo, W and V, when it is tempered at 500 ~ 600℃, alloy carbides are directly separated from martensite. These carbides are fine and dispersed, which makes the hardness of steel not decrease, but increase. This phenomenon is called "secondary hardening". However, some alloy steels should be prevented from "temper brittleness".