Hot shortness
Cracking during hot working or welding caused by low-melting iron-sulfide films at grain boundaries. The material ruptures easily at red-heat temperatures under load.
Hot shortness occurs when sulfur in steel combines with iron to form iron sulfide. This stuff melts at red heat and settles as a thin film on the grain boundaries. If you then bend or weld the material, it simply breaks away at these points, even though the steel otherwise looks good. The problem mainly occurs with sulfur-containing steel when it enters the critical temperature range during welding or hot forming. Make sure your base material and also the filler metal have a low sulfur content. If you are unsure whether the material is suitable for this, ask rather or use a steel that is approved for welding.