Sulfide Stress Cracking Behavior of a Martensitic Steel Controlled by Tempering Temperature

Abstract

A medium-carbon Cr–Mo–V martensitic steel was thermally processed by quenching (Q) at 890 °C and tempering (T) at increasing temperatures from 650 °C to 720 °C and the effect of tempering temperature, Tt, on sulfide stress cracking (SSC) behaviors was estimated mainly via double cantilever beam (DCB) and electrochemical hydrogen permeation (EHP) tests and microstructure characterization. The results indicate that the threshold stress intensity factor for SSC, KISSC, increased with increasing Tt. The overall and local H concentration around the inclusions decreased with increasing Tt, due to reductions in the amounts of solute atoms, grain boundaries and dislocations, which effectively prevented SSC initiation. Also, increasing Tt caused an increased fraction of high-angle boundaries, which evidently lowered the SSC propagation rate by more frequently diverting the propagating direction and accordingly restricted SSC propagation. The overall SSC resistance of this Q&T–treated steel was therefore significantly enhanced.

Characteristic properties of the microstructure and microtexture of medium-carbon steel subjected to sulfide stress cracking

“…При этом в данной области также обнаружили участки с повышенным содержанием мартенсит/аустенитной составляющей неправильной формы. В области излома наблюдаются многочисленные вторичные микротрещины, поскольку мартенситная структура менее устойчива к СРН и требует дополнительного отпуска [21].…”

A Review of the Factors That Can Increase the Risk of Sulfide Stress Cracking in Thermomechanical Controlled Processed Pipeline Steels

“…Sun et al [ 19 ] proposed that the relationship between the size of grain boundaries and the density of hydrogen traps ( can be equated using (Equation ()) where: n is the number of grains counted per m 3 and and are the surface area and volume of a grain; the width of grain boundaries () such as PAG, packets, blocks, and laths can be assumed to be 10 times the distance between two atoms (); the ratio between the dislocation density () and was assumed to be 5:1 for the same N in the same microstructure. [ 19 ] In light of this, Bai et al [ 80 ] suggested that smaller grains would have less dislocation pile‐up when compared to larger grains, therefore reducing localized accumulation of hydrogen concentration at grain boundaries.…”

“…[16,17] The initiation and propagation of SSC at these PAG boundaries is not only affected by the size of PAGs or type of element that partitioned to these boundaries, but also the type of microstructure constituent that nucleates from these boundaries. [18][19][20][21] Hence, the following sections will highlight and discuss different microstructure constituents of interests within PAG in relevance to their contribution to SSC. This section will briefly review the types of microstructures of interest commonly found in low-carbon TMCP pipeline steels.…”

“…[74] This is because the hydrogen dissolution energy for the preferable octahedral sites in austenite is lower than the preferable tetrahedral site, leading to a higher hydrogen solubility in austenite than ferrite. [79] Sun et al [19] proposed that the relationship between the size of grain boundaries and the density of hydrogen traps (NÞ can be equated using (Equation ( 1))…”

“…where: n is the number of grains counted per m 3 and S G and V G are the surface area and volume of a grain; the width of grain boundaries (x GB ) such as PAG, packets, blocks, and laths can be assumed to be 10 times the distance between two atoms (x a ); the ratio between the dislocation density (ρ Dis ) and x a was assumed to be 5:1 for the same N in the same microstructure. [19] In light of this, Bai et al [80] suggested that smaller grains would have less dislocation pile-up when compared to larger grains, therefore reducing localized accumulation of hydrogen concentration at grain boundaries. Additionally, HE susceptibility is also dependent on the disorientation angle at grain boundaries.…”