IMPROVING THE LIFE OF CONTINUOUS CASTING ROLLS THROUGH SUBMERGED ARC CLADDING WITH NITROGEN-ALLOYED MARTENSITIC STAINLESS STEEL

摘要

Continuous casting rolls are subjected to extreme temperature fluctuations and harsh environmental conditions during service. High slab contact pressures, high surface temperatures, adhesive or abrasive wear by slag or oxides and thermal fatigue all contribute towards deterioration of the roll surface. Rolls may also suffer surface degradation as a result of corrosion. The slab is cooled using water spray, often containing hydrofluoric acid as product of the reaction between water and the mould flux powder used to keep the molten metal from adhering to the copper mould plate. This results in an aggressive low pH environment that may promote pitting or crevice corrosion and stress corrosion cracking failures. In order to prolong the life of continuous casting rolls in service, the rolls are surfaced using martensitic stainless steel weld cladding. After surfacing, the roll may be given a post-weld heat treatment to temper the martensite to the required hardness level, or to relieve thermally-induced stresses. This investigation examined the submerged arc cladding of continuous casting rolls using nitrogen-alloyed martensitic stainless steel, and focused on the effect of the weld thermal cycle and post-weld heat treatment on carbide precipitation in the clad layer. The precipitation of chromium-rich carbides during welding or post-weld heat treatment may lead to weld decay due to chromium depletion, rendering the roll surface susceptible to pit nucleation and crack initiation.