Effect of martensite-austenite (MA) distribution on mechanical properties of inter-critical Reheated Coarse Grain heat affected zone in X80 linepipe steel

Inter-Critically Reheated CGHAZ of Ultra-High-Strength Martensitic Steel with Different Cooling Rates

“…In addition, previous research has shown that the toughness of the HAZ is mainly affected by the MA and grain boundaries [ 28 , 29 ]. The stress concentration points such as the MA/ferrite interface can easily become the priority positions for the initiation of microcracks [ 15 ]. According to the Griffith theory, the premise of crack nucleation is that the elastic strain energy released is higher than the surface energy of the crack [ 30 , 31 ].…”

“…In terms of the ICR CGHAZ, the cooling rate can strongly affect the evolution of MA and grain boundaries in ultra-low carbon steel [ 13 , 14 ]. Huda et al [ 15 ] revealed that the size of MA was finer and the distribution of MA was more benign in 10 °C/s than 2 °C/s in the ICR CGHAZ of X80 pipeline steel, which increased impact toughness. Qi et al [ 5 ] found that the cooling rate during the second thermal cycle can influence the formation of necklace-type MA along PAGBs.…”

Simultaneously Improving Mechanical Properties and Stress Corrosion Cracking Resistance of High-Strength Low-Alloy Steel via Finish Rolling within Non-recrystallization Temperature

“…Although the YS and UTS of R2 are close to that of R3, its elongation is considerably lower than that of R3 probably due to the presence of massive M/A constituents in R2. Extensive studies have demonstrated that massive M/A constituents in steel are prone to trigger crack initiation due to local stress concentration between M/A and matrix and are detrimental to ductility and toughness [62][63][64][65][66][67][68]. However, M/A constituents are not always harmful and sometimes they could be favorable for mechanical properties, if they are fine in size and are homogeneously distributed [69][70][71].…”

“…Firstly, the M/A constituents could generate local stress concentration under applied stress due to deformation incompatibility with the matrix [71,82]. Many literature works have demonstrated that massive M/A constituents were prone to trigger crack initiation because of local stress concentration [63][64][65][66][67][68]. Meanwhile, the massive M/A constituents could result in micro-galvanic corrosion between M/A constituents and matrix due to Volta potential variation [34,87].…”

“…13 Cross-sectional morphologies of the fractures of R1 a, R2 b and R3 c, d in simulated marine atmosphere. The images in red boxes are magnified ones in white boxes [65,67,93], larger size of M/A constituents with sharp corner would cause higher local stress concentration [62,66,67,94]. Moreover, the micro-galvanic corrosion effect of larger M/A consistent could be more prominent due to their larger cathode area based on the galvanic corrosion theory [87,95].…”