Quenched and tempered microstructure
A microstructure consisting of tempered martensite or bainite tailored by quenching and high-temperature tempering. It combines high yield strength with superior fracture toughness.
Quenched and tempered steel has a structure that gives it strength and toughness through hardening and tempering. During welding, the heat destroys this tempering in the heat-affected zone. Directly at the weld, the steel can harden again and become brittle, and right next to it a soft zone forms. The component loses strength there and there is a risk of cracking. So you must preheat the steel and keep an eye on the interpass temperature. After welding, stress relief annealing is necessary to temper the structure again and restore toughness. If that is not possible, use only low-hydrogen filler materials and keep the heat input as low as possible.