A microstructural and low-cycle fatigue investigation of weld-repaired heat-resistant cast steels

The multi-pass weld-repair of heat-resistant cast steels is carried out using an automated shielded metal arc welding (SMAW) process, with various filler materials and pre-heating at 400 °C. Specimens weld-repaired with a filler material more resistant than the heat-resistant cast steel (over-matching) generally crack within the base metal following the tenth filling pass, whereas specimens buttered with a soft alloy prior to welding remain free of cracks. The high temperature strain-controlled fatigue lifetime of material weld-repaired without buttering is lower than that of bulk initial material. This is due to an increase of the stress amplitude as a result of the so-called over-matching. In the case of material welded following a prior buttering, the fatigue lifetime is reduced because of the stress tri-axiality generated in the thin soft layer which prevents its plastic flow. As a consequence, it is concluded that even though buttering prevents cracking efficiently during welding, it is not acceptable as far as fatigue performance, especially lifetime, is concerned.