Weldability of HLE steels requires great rigour (Part 1: thermomechanical steels)

Abstract

Steels with elasticity limits between 650 and 680 MPa include thermomechanical steels and quenched and tempered steels. Thermomechanical steels have excellent weldability, but, nevertheless, require fillers with low diffusible H₂ levels, and a rigorous control over the welding operations, due to the molten zone. Quenched and tempered steels require almost automatic recourse to preheating, and frequently post-heating, but at moderate temperatures. The heterogeneity of the commercial range of base metals available, and the poverty of the range of filler materials with very high elasticity limits, are crucial problems. The risk of cold cracking in the molten zone is very high and, sadly, less well understood than that of cold cracking in the HAZ. Given that the maintenance of good mechanical characteristics requires limiting the T _r 800–500, the weldability range is very narrow. The welding of these steels is not intrinsically complex, but requires considerable rigour.