Abstract
The goal of this work is to propose a general mechanism for hydrogen induced crack initiation in steels based on a microstructural study of multiple steel grades. Four types of steels with strongly varying microstructures are studied for this purpose, i.e. ultra low carbon (ULC) steel, TRIP (transformation induced plasticity) steel, Fe-C-Ti generic alloy, and pressure vessel steel. A strong dependency of the initiation of hydrogen induced cracks on the microstructural features in the materials is observed. By use of SEM-EBSD characterization, initiation is found to always occur at the hard secondary phase particles in the materials.
Highlights
E xperimental electrochemical charging of steels with hydrogen mimics, on the one hand, well hydrogen generation and entry in the material from sources such as corrosion or applications such as arc welding [1]
Small amounts of hydrogen in a metal in combination with external or residual stresses can lead to hydrogen embrittlement (HE) or hydrogen assisted cracking (HAC), which results in subcritical failure of the materials [2, 3, 4]
Hydrogen induced internal cracking and blistering can occur in metals subjected to high fugacity hydrogen environments, such as high pressure hydrogen gas environments or under extreme cathodic charging conditions, even without the application of an external load or residual stress, though such stresses can contribute to hydrogen induced cracking (HIC) [5, 6]
Summary
E xperimental electrochemical charging of steels with hydrogen mimics, on the one hand, well hydrogen generation and entry in the material from sources such as corrosion or applications such as arc welding [1]. Intensive electrochemical charging can induce both surface and internal damage in a material [5]. Hydrogen induced internal cracking and blistering can occur in metals subjected to high fugacity hydrogen environments, such as high pressure hydrogen gas environments or under extreme cathodic charging conditions, even without the application of an external load or residual stress, though such stresses can contribute to HIC [5, 6]. HIC occurs when the hydrogen concentration in the steel matrix exceeds a threshold hydrogen concentration. The internal pressure theory [14, 15, 16] explains the phenomenon of HIC in high fugacity hydrogen environments. The theory states that HIC results from the formation of high pressure hydrogen gas bubbles in internal voids and microcracks.
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