Mechanism of degradation of stabilized corrosion‐resistant steel during the welding cycle

The purpose of this paper is to clarify the destabilisation mechanism that occurs with two types of ferritic corrosion‐resistant steel during the welding cycle.

A series of experimental weld joints was made to verify the actual response of non‐stabilised corrosion‐resistant steel, and of the same steel that had been stabilised by added titanium. The character and extent of the ensuing structural changes were analysed. The essential characteristics of degradation in the heat‐affected zone are evaluated using optical and scanning electron microscopy; individual phases are identified by means of EDX microanalysis. The underlying mechanism for the loss of stability is induced experimentally in several stages; depending on the thermal doping level and interaction with the environment during the welding process, phases of various types are precipitated. These phases subsequently are studied in connection with the original microstructural characteristics of the steel and the induced grain boundary decohesion of the surface layer. The scope and character of the damage are analysed and the results verified by analysing the actual operating damage to the weldment.

A degradation mechanism of stabilised corrosion‐resistant steel 1.4510 is induced that is associated with destabilisation of titanium phases. The importance is demonstrated of ensuring that a protective atmosphere is maintained during welding, and various phase changes in the surface layers are identified that can delimit the use of appropriate post‐weld passivation procedures.

Identification of the mechanism underlying the damage to the surface layer in welded stabilised ferritic steel will find application in development of welding technology, specifically in designing a technology process and subsequent surface treatment.

The results bring new knowledge of material response of steel 1.4510 under specific material processing conditions; a destabilisation mechanism related to precipitation of several titanium‐containing phases is identified. The result enables the fatigue limit of the welded material as a function of the welding technology employed, which offers increased service life under specific application conditions.