Hydrogen-Assisted Crack Growth in the Heat-Affected Zone of X80 Steels during in Situ Hydrogen Charging.

Qu Qu,Feng Feng,Du Du,Bi Bi,An An,Zheng Zheng,Yang Yang

doi:10.3390/ma12162575

Abstract

Herein, the hydrogen embrittlement of a heat-affected zone (HAZ) was examined using slow strain rate tension in situ hydrogen charging. The influence of hydrogen on the crack path of the HAZ sample surfaces was determined using electron back scatter diffraction analysis. The hydrogen embrittlement susceptibility of the base metal and the HAZ samples increased with increasing current density. The HAZ samples have lower resistance to hydrogen embrittlement than the base metal samples in the same current density. Brittle circumferential cracks located at the HAZ sample surfaces were perpendicular to the loading direction, and the crack propagation path indicated that five or more cracks may join together to form a longer crack. The fracture morphologies were found to be a mixture of intergranular and transgranular fractures. Hydrogen blisters were observed on the HAZ sample surfaces after conducting tensile tests at a current density of 40 mA/cm2, leading to a fracture in the elastic deformation stage.

Highlights

From the viewpoint of having low oil and gas resources and rich coal resources in China, the Chinese government has chosen to develop the coal gas industry
Zhang et al analyzed the effects of the heat-affected zone (HAZ) microstructure on the hydrogen permeation of X80 steels, and the results showed that the coarse-grained granular bainite and bainite ferrite in the HAZ increased the hydrogen diffusivity [32]
The X80 steel used is a dual-phase steel, wherein the base metal is comprised of polygonal ferrite (PF) with fine grains and granular bainite (GB), which is comprised of fine lath ferrite and some island constituents [40]

Summary

Introduction

From the viewpoint of having low oil and gas resources and rich coal resources in China, the Chinese government has chosen to develop the coal gas industry. Hydrogen atoms enter the steels in the cathodic-protected process or from coal gas [2,3,4,5,6], leading to a degradation in the mechanical properties of steel such as tensile strength, fracture toughness, and acceleration of the fatigue crack-growth rates [5,7,8,9]. This process is known as hydrogen embrittlement (HE), a topic that requires more attention. Hydrogen diffuses to the tip of the cracks, leading to the acceleration of crack

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