Influence of Partitioning Process on the Microstructure and Mechanical Properties of High Deformability Oil-Gas Pipeline

Abstract

Multiphase structure of bainite and M/A constituent can be obtained for X80 oil-gas pipeline through a novel heat online partitioning (HOP) technology. The effects of partitioning temperature on the microstructure and mechanical properties of the experimental steels were researched by means of mechanical properties test, microscopic analysis, and X-ray diffraction. The results show that with the increase of the partitioning temperature, the strength of the experimental steel decreases and the ductility increases because of the increase of bainite lath width, the decrease of dislocation density, the increase of retained austenite content, and carbides coarsening. The decrease of the volume content and stability of retained austenite is the key factor, which leads to the increase of strength and the decrease of plasticity in a high range of partitioning temperature.

Ultrahigh strength ductile microalloyed steel with a very low yield ratio developed by quenching and partitioning heat treatment

“…Demand by the oil and gas transportation pipeline industry for steel with better mechanical properties, mainly strength and toughness, for more effective and efficient oil and gas transportation has led to the development of a series of pipeline steels. These mechanical properties of steels are derived from the manipulation of microstructure through composition optimization 4 , 5 , thermomechanical processing 6 , 7 and heat treatment 8 – 11 . Thermomechanical and/or heat treatment processing transforms the ferrite-pearlite banded microstructure into various phases and/or morphologies , including polygonal ferrite, quasi-polygonal ferrite, granular-bainitic ferrite, bainitic ferrite and acicular ferrite 2 , 12 .…”

“…Carbon enriched austenite stabilizes at room temperature and consequentially induce simultaneous improvement in the strength and ductility of the steel. This quenching and partitioning procedure was initially proposed and then widely used on medium carbon steel and was latter also applied to low carbon transformation induced plasticity steel 14 and pipeline steel 11 . In the present study, we used quenching and partitioning heat treatment on microalloyed low carbon pipeline grade steel API X65 in order to study the effect on microstructure and mechanical properties.…”