Microstructure and mechanical properties of the start bending point for X90 bend

Abstract

The effect of the hot induction bending process on the microstructure and mechanical properties of the start bending point for high-strength bends was investigated. Acicular ferrite (AF) is found to be absent in the microstructure of the start bending point. After whole heating process, the microstructure is composed of lath bainite (LB) and quasi-polygonal ferrite (QPF), with an impact absorbed energy of 202 J cm−2 and a strength is very similar to that of the baseline pipe. After local heating process, the impact absorbed energy is 103 J cm−2, which is lower than that of the baseline pipe. For thick-walled high-strength pipeline steel, the whole heating process is determined to be the optimum heat treatment for guaranteeing excellent strength and toughness combination.