Influence of Si and Ni on surface hot-shortness of Cu-Sn containing steel heated in water vapor containing atmosphere

This paper describes the influence of Si and Ni on surface hot-shortness of 0.3%Cu-0.04%Sn containing steel heated in water vapor containing atmosphere, where the atmosphere was changed in a manner of x%H2O-1%O-2-bal.N-2 (x=0, 10, 20, 30). Surface hot-shortness was assessed by measuring the surface cracking depth occurring in the 1100degreesC hot-deformed specimens after 1250degreesC heating in the water vapor atmosphere. The microstructure at the scale/steel interface was closely observed and the effect of the mass gain on surface cracking depth was investigated. For lower than 0.01% Si steel, the surface cracking depth increased largely with the mass gain, while an addition of 0.1% Si seems to suppress the surface cracking, especially at increased mass gains and the change with the mass gain was small. Steels with 0.14%Ni-Si<0.01% and 0.14%Ni-0.02%Si contained showed unexpectedly a marked surface cracking even in as low as 0.6 kg/m(2) mass gain of 0%H2O-1%O-2-bal.N-2 and the surface cracking decreased considerably with an increase in the mass gain. Si and Ni were found to be favorable alloying elements for suppression of the surface hot-shortness at increased mass gains in water vapor containing atmosphere. The mechanism of the suppression was discussed in terms of the unevenness of scale/steel interface and occlusion of Cu-Sn-Ni or Cu-Sn enriched liquid alloy into the scale.