A Quantified Study of the Resistance of Duplex Stainless Steels to HISC: Part 1 - Significance of the three-dimensional phase distributions and morphological properties on hydrogen transport

This paper is associated with a larger programme of research, studying the resistance to hydrogen-induced stress cracking (HISC) of a wrought and a hot isostatically-pressed (HIP) UNS S31803 duplex stainless steel (DSS), with respect to both the independent and interactive effects of the three key components of HISC: microstructure, stress/strain, and hydrogen. In the first part presented here, several material properties such as the three-dimensional (3D) microstructure, distribution and morphology/geometry of the two phases, i.e. ferrite and austenite, and their significance on hydrogen transport have been determined quantitatively, using X-ray computed tomography (CT) microstructural data analysis and modelling. This provided a foundation for the study to compare resistance to HISC initiation and propagation of the two DSSs with differing microstructures, using hydrogen permeation measurements, environmental fracture toughness testing of single-edge notched bend test specimens, in the Part 2 paper of this study [1].

Study on Production Process, Microstructure, Properties of 15MnNbR Pressure Vessel Steel

The production process, microstructure, and mechanical properties of 15MnNbR pressure vessel steel were studied by optical microscopy, universal tensile testing, and low-temperature impact toughness testing. It was found that the microstructure obtained after controlled rolling and cooling (known as thermo-mechanical control processing) consisted of ferrite and pearlite with non-uniform grain size. The banded microstructure was prominent, the strength was high, and the toughness was poor. After normalizing, the grain size was refined, both the microstructural uniformity and the banded microstructure were improved, and the strength and toughness of the steel were enhanced. After normalizing and water cooling, the grain was further refined, the microstructure was homogenized, the banded microstructure disappeared, and the strength and toughness of the test steel were improved simultaneously, resulting in excellent comprehensive mechanical properties.

Effect of Hydrogen in Mixed Gases on the Mechanical Properties of Steels—Theoretical Background and Review of Test Results

This review summarizes the thermodynamics of hydrogen (H2) in mixed gases of nitrogen (N2), methane (CH4) and natural gas, with a special focus on hydrogen fugacity. A compilation and interpretation of literature results for mechanical properties of steels as a function of hydrogen fugacity implies that test results obtained in gas mixtures and in pure hydrogen, both at the same fugacity, are equivalent. However, this needs to be verified experimentally. Among the test methods reviewed here, fatigue crack growth testing is the most sensitive method to measure hydrogen effects in pipeline steels followed by fracture toughness testing and tensile testing.

Elucidating the Effect of Step Cooling Heat Treatment on the Properties of 2.25 Cr–1.0 Mo Steel Welded with a Combination of GMAW Techniques Incorporating Metal-Cored Wires

The prospect of using metal-cored wires instead of solid wires during gas metal arc welding (GMAW) of 2.25 Cr–1.0 Mo steels embraces several challenges. The in-service requirements for the equipment made up of these steels are stringent. The major challenge faced by the manufacturers is temper embrittlement. In the current study, the temper embrittlement susceptibility of the welded joint was ascertained by subjecting it to step cooling heat treatment. A 25 mm thick 2.25 Cr–1.0 Mo weld joint was prepared using a combination of the regulated metal deposition (RMD) and GMAW processes incorporating metal-cored wires. After welding the plates were exposed to post-weld heat treatment followed by a rigorous step cooling heat treatment prescribed by API standards. The temper embrittlement susceptibility of the weld joint was ascertained by Bruscato X-factor as well as by formulating ductile-to-brittle transition temperature (DBTT) curves by carrying out the impact toughness testing at various temperatures. Detailed microscopy and hardness studies were also carried out. It was established from the study that the X-factor value for the welded joint was 15.4. The DBTT for the weld joint was found to occur at −37 °C which was well below 10 °C. Optical microscopy and scanning electron microscopy indicated the presence of carbides and the energy dispersive X-ray spectrometry studies indicated the presence of chromium and manganese-rich carbides along with the presence of sulfur near the grain boundaries. This study establishes a base for the usage of metal-cored wires particularly in high temperature and pressure application of Cr–Mo steels.