Effect of small amounts of Ni on liquid-Cu embrittlement in hot-rolled mild steel after high-temperature oxidation

The effects of additions of as little as 0.02%Ni to mild steel on the morph ology of the scale-steel interface and surface cracking were studied during high-temperature oxidation and subsequent hot-ductility tests of 0.5%Cu-be aring steel. Liquid-Cu embrittlement occurs in a steel containing 0.5%Cu-0. 001%Ni because of concentrated liquid-Cu layer at the scale-steel interface over the temperature range of 1100-1300 degrees C. The addition of as litt le as 0.023%Ni to 0.50%Cu-containing steel recovers the ductility in the ox idation temperature range of 1250-1300 degrees C. This is because liquid-Cu particles are occluded into the scale. Thus, the amount of enriched Cu per unit surface area decreases at the scale-steel interface. It is suggested that liquid-Cu particle occlusion, which has nor yet been elucidated, resul ts from heterogeneous enrichment of Ni and heterogeneous oxidation at the s cale-steel interface.