Secondary carbide precipitation
Secondary carbide precipitation is the process where fine carbide crystals precipitate from the supersaturated solid solution during tempering. This leads to secondary hardening of the steel.
Physikalisch-chemischer Wirkmechanismus
While welding, an excess of carbon forms in the supersaturated solid solution, which is precipitated as a carbide (e.g. Fe₃C). This process happens through cooling and balancing the carbon content.
Metallurgical Relevance & Welding Risks
Secondary hardening increases the strength and toughness of the steel, improving its mechanical properties. However, cooling too quickly can cause the carbide to be fine and hard to dissolve, leading to cracks and hardness problems in the weld pool.
Werkstattpraxis & Handlungsanweisungen
To make the most of secondary hardening, control the cooling step. Too fast cooling (e.g. by high cooling water flow) can lead to fine carbide and hardness problems. Recommended cooling times vary by steel type, but generally should be between 10 and 30 seconds.