Role of ε martensite in tensile properties and hydrogen degradation of high-Mn steels

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 533; pp. 87 - 95
• Main Authors: YOUNG SOO CHUN, JI SOO KIM, PARK, Kyung-Tae, LEE, Young-Kook, CHONG SOO LEE
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 30.01.2012
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Degradation; Elasticity. Plasticity; Exact sciences and technology; Fracture mechanics; Fractures; Martensite; Martensitic transformations; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microstructure; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Stainless steels; Tensile properties; Trapping; Epsilon martensite; TRIP; Slip; Transition metal; Tensile property; Manganese steels; TWIP; Transformation induced plasticity; Dislocation; Grain boundary; Crack propagation; Twinning induced plasticity; High Mn steels; Austenitic steel; Austenite; Martensitic transformation; Hydrogen charging; Microstructure; Martensite; Hydrogen embrittlement; Crack initiation; Strain rate
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.11.039

Effects of epsilon martensite on tensile properties and hydrogen degradation behaviors of a high Mn steel were investigated. For this purpose, a Fe-15Mn-2Cr-0.6C steel containing various amount of epsilon martensite was prepared and tensile tested at room temperature. Microstructures were examined by electron back scattered diffraction and transmission electron microscopy. Then, a series of electrochemical hydrogen pre-charging, slow strain rate tests, and thermal desorption spectrometry (TDS) analyses was conducted to examine the hydrogen degradation behaviors. Deformation of the steel without epsilon martensite (i.e. fully austenitic) was dominated by slip and mechanical twinning, but that of the steel containing epsilon martensite was mainly attributed to transformation induced plasticity in association with strain induced martensitic transformation during deformation, resulting in higher work hardening rate. However, tensile strength and elongation on the steel containing epsilon martensite were lower than those of the fully austenitic steel, since cracks were prone to be initiated and propagated at the region of epsilon martensite which is harder than austenite. Furthermore, it was found that epsilon martensite provided many diffusible hydrogen trapping sites. Consequently, the notch fracture stress of the steel containing epsilon martensite decreased significantly as the diffusible hydrogen content increased. The activation energy for hydrogen detrapping from its trapping sites was also calculated by means of the TDS analyses, -22kJ/mol for the gamma / epsilon interfaces, and -37kJ/mol for dislocations/ gamma grain boundaries.