Temperature Dependence of Mechanical Properties for Advanced Line Pipe Steels With Bainitic Microstructures

There is currently significant interest in developing quantitative linkages between microstructures and mechanical properties (yield stress and ductile-brittle transition temperature) for the weld heat-affected zone of pipelines. In this study, two line pipe steels with carbon contents of 0.03 and 0.06 wt pct were subjected to idealized thermal treatments to create microstructures that are representative for the coarse grained heat-affected zone (CGHAZ) for submerged arc and gas metal arc welds. The microstructure was characterized by a combination of optical metallography and electron backscatter diffraction (EBSD) mapping. Tensile tests and Charpy impact tests were conducted over a range of temperatures between ambient and - 196 degrees C. Microstructure-property models were developed for the yield strength and cleavage stress as a function of temperature. The ductile-brittle transition temperature was rationalized in a classical approach where plastic yielding and cleavage fracture are competitive processes. The results present a quantitative framework to predict yield stress and the ductile-brittle transition temperature based on the characteristics of the microstructure.

Automated summary

There is a growing interest in establishing quantitative correlations between microstructures and mechanical properties (yield stress and ductile-brittle transition temperature) for the weld heat-affected zone of pipelines. In this study, two line pipe steels with different carbon contents were subjected to thermal treatments to create specific microstructures. The microstructure was characterized using optical metallography and electron backscatter diffraction mapping. Tensile and impact tests were conducted over a range of temperatures, and microstructure-property models were developed for yield strength and cleavage stress. These findings provide a framework for predicting mechanical properties based on microstructural characteristics.