HP Steel Research Articles

Role of Nb in modifying the microstructure of heat-resistant cast HP steel

Heat-resistant cast stainless steels have widespread uses in the petrochemical industry in pyrolysis and reformer furnaces; 25%Cr-20% Ni or 25% CR-33% NI high-carbon steels, designated HK and HP types, respectively, have traditionally been used, but requirements for higher productivity have raised the demand for improved performance. In the more recently developed steels, the Cr carbides normally present are replaced by carbides of Nb or Ti, or both, and the resulting alloys are termed modified HK or modified HP steels. The additions of Nb or Ti provide improved structural stability at high temperature in that their carbides are more stable than the normal secondary carbide precipitates of Cr, thus contributing to restraint of dislocation movement. Perhaps more important still is the eutectic modification caused by Nb additions that could restrict grain boundary sliding. This article reports on an investigation into the role of Nb in modifying the microstructure of HP steel in the as-cast and artificially aged conditions, for a series of alloys utilizing different levels of Nb.

高温時効に伴うHK40及びHP遠心鋳造管の共晶炭化物の形態変化

高温時効に伴うHK40及びHP遠心鋳造管の共晶炭化物の形態変化

モアレ用耐熱格子の溶接継手高温変形挙動観察への応用

Application of the thermostable moiré grating has been investigated for measuring the strain distribution of the welded joint deformed in high temperature. The thermostable moiré grating, produced by electrochemical technique, could be successfully reproduced to the welded joint in HP (0.5C-25Cr-35Ni) steel and to the dissimilar-metal joint, 1 1/4 Cr- 1/2 Mo steel to HK40 steel. The grating was stable even at a temperature of 900°C in HP steel welded joint and 510°C in dissimilar-metal joint under creep condition. Thermal expansion and the macroscopic creep deformation was measured by moiré method and local creep deformation was by fine grating method. From these strain measurement, the characteristic of the creep deformation and the creep crack initiation was discussed.