Welding of advanced high-strength steels

Resistance spot welding is commonly applied in the production of steel car structures. The article presents processes during the welding of high-strength steel sheets with protective coatings (including recently introduced protective-coated advanced steels with an organic layer). Special attention was given to tests investigating the welding of advanced high-strength TRIP-type steels. These steels, when welded with a simple one-pulse welding programme, are characterised by very high hardness in the welding area, and as a result, undergo a rupture in the trans-crystallisation plane during peel testing. In order to improve the plasticity of a joint, it proved appropriate to apply a two-pulse welding technology while joining such steels. It was ascertained that the use of an appropriately adjusted second current pulse would make it possible to obtain lower metal hardness in a weld nugget. During peel testing, joints welded with the second heating current pulse are destroyed by the complete peeling of a weld nugget.