High-strength low-alloy (HSLA) steels are primarily used in the segment of vehicle production. They are characterized by an advantageous combination of mechanical properties, such as high yield strength, tensile strength and ductility. In the production of steel structures, it is possible to use elements with smaller cross-sections. This reduces weight, fuel consumption and emissions. In this case, we can talk about the so-called "green material". An important technology in the production of such lightweight structures is welding. Fusion welding methods significantly heat the base material in the weld area, in the so-called heat-affected zone. High-strength steels are sensitive to short-term exposure to high temperatures. The so-called softening effect occurs, which is localized in a narrow metallurgical area of the welded joint. One of the options for monitoring these structural changes due to welding is dilatometric tests. With their help, we can determine the transformation temperatures of austenite decomposition by controlled heating and cooling. Also the resulting microstructure and hardness of the steel for a given cooling rate. The aim of the paper is to determine, based on the analysis of dilatometry results, a welding in-situ CCT diagram that takes into account real temperature cycles during welding and the cooling rate in the form of the parameter t8/5. The control temperature cycles were designed according to the measured real welding cycles and cycles determined by simulation. The cooling rate was determined by the parameter t8/5 in the range of 2.2 s to 24.0 s. The results show that at the used cooling rates, the resulting microstructure is formed by bainite and martensite. This corresponds to a hardness in the range of 262 HV10 to 346 HV 10 for S960MC steel.
Harvanec et al. (Thu,) studied this question.