Microstructural Effects of AISI 4130 Steel on Hydrogen Assisted Fatigue Crack Propagation

• Main Authors: Tau,Lin, 陶霖
• Other Authors: Chan,S.L.I;Shin,C.S.
• Format: Others
• Language: en_US
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/20031903768876510369

博士 === 國立臺灣大學 === 材料科學(工程)研究所 === 84 === The main objective of this research has been to carry out a systematic study on the influences of various microstructures of a popular structural steel, AISI 4130 steel, on hydrogen-enhanced fatigue crack propagation. Some important effects have been discussed in this work, including those of microstructure, strength, hydrogen permeation, tempering temperature for tempered martensitic structures, and isothermal treating temperature for bainitic structures. In this work, some conclusions could be outlined: (1) For ferrite/pearlitic structures, the distribution of ferrite/pearlite along the path of hydrogen penetration affected hydrogen diffusivity deeply. Then the results of hydrogen diffusivity can be applied to explain the hydrogen-assisted fatigue crack propagation behavior of the banded and random ferrite/ pearlite structures successfully. (2) The variation of hydrogen-assisted fatigue crack growth rates of specimens sampled from different orientations for banded ferrite/ pearlitic structure was very significant, slight for random in the random ferrite/pearlitic structure. (3) A similar hydrogen-enhanced fatigue crack growth behavior and a transgranular fracture mode were found in bainitic structures, though they have different tensile strength and hydrogen permeation rate. (4) The hydrogen-assisted fatigue crack propagation rate of tempered martensitic structures increased as yield strength increased. In higher strength tempered martensites, an irregular fracture mode, in which the intergranular crack propagated easily near surface of specimen, was found. (5) The microstructural effect was the dominant factor on the hydrogen-assisted fatigue crack growth behavior. Alternatively, the strength effects could not been featured systematically.