Definition - What does Hot Shortness mean?
Hot shortness is a tendency for some alloys to separate along grain boundaries when stressed or deformed at temperatures near the melting point. In metallurgy, it is brittleness, usually of steel or wrought iron, when the metal is hot, due to a high sulfur content.
The term is used for the character of steel, which becomes brittle at hot working temperatures above 0.6 Tm (recrystallization temperature, where strain hardening is removed). Hot shortness hinders hot-working operations.
Corrosionpedia explains Hot Shortness
Hot shortness is a condition of metal at excessively high working temperatures characterized by low mechanical strength and a tendency for the metal to crack rather than deform. Hot shortness is caused by a low-melting constituent, often present only in minute amounts, that is segregated at grain boundaries. The presence of iron sulfide causes problems in hot working, and this phenomenon is called hot shortness.
Hot shortness is reduced by the addition of manganese, which combines with the sulfur to form manganese sulfide. As manganese sulfide has a higher melting point than iron sulfide, which would form if manganese were not present. The weak spots at the grain boundaries are greatly reduced during hot working.
Sulfur causes hot shortness in steel unless sufficient manganese is added. Sulfur has a greater affinity for manganese than iron and forms manganese sulfide, which has a melting point above the hot rolling temperature of steel, which eliminates hot shortness. Hot shortness means that the steel literally breaks apart during hot rolling, resulting in a scrapped product.
If aluminum is hot short, it means that it has a tendency to crack when it reaches a certain temperature range. That is why when tack welds aluminum without using filler metal, it cracks. Another area where hot shortness is a problem is when welding from an edge.
Hot shortness of welds can result from contamination by sulfur, lead, phosphorus, cadmium, zinc, tin, silver, boron, bismuth, or any other low-melting-point element, which forms intergranular films and causes severe liquid-metal embrittlement at elevated temperatures. During weld pool solidification, impurities like sulfur get cooler at a lower temperature than surrounding weld, hence due to solidification of sulfur, cracking occurs.