Secondary Hardening Mechanism
Secondary hardening: Fine special carbides form during tempering of high-alloy steels, leading to a temporary hardness increase.
Physicochemical Mechanism of Action
During secondary hardening, fine special carbides form from austenite in high-alloy steel. These carbides are formed by the diffusion of carbon and other alloying elements into the grain boundaries of the austenite. This process leads to a local increase in hardness in the material.
Metallurgical Relevance & Risks in Welding
Secondary hardening can lead to increased stress buildup and cracking, especially when the steel type is high-alloy. Too rapid cooling can intensify the hardness increase and impair the toughness of the material.
Workshop Practice & Action Instructions
To control secondary hardening, welding should be carried out at reduced temperatures. Use a long cooling time (t8/5 > 25 s) and avoid rapid cooling. This helps regulate the hardness of the material and avoid cracks.