Different Heat Treatment Process Of 35crmo Steel Stress Corrosion Susceptibility Studies

The main aim of this thesis is to improve the microstructure of materials and the grain size through the heat treatment process of high-strength low alloy 35CrMo steel which is common component of oil equipments and downhole tools. An experiment is conducted in the paper to study the influence of the grain size and the microstructure of materials on the stress corrosion cracking susceptibility of 35CrMo, through dynamic electrochemical charging in different current density, slow strain rate tension technique (SSRT) and modern microscopic analysis method. In recent decades, the extensive explorations of acidic oil and gas field or high H2S oil and gas field increased the possibility of stress corrosion cracking in oil equipment or down hole tools. Therefore, the research on 35CrMo steel'cracking caused by the stress corrosion or lag cracking is extremely significant for the safety of oilfield development process.The results show:The susceptibility of 35CrMo steel resistance stress corrosion lag cracking reduced with the increase of dynamic electrochemical charging current density 35CrMo steel grain size could be refined into 10.8μm and the grain grade was 10.0-10.5 at completely quenching and sub-temperature quenching and high temperature tempering process. Meanwhile, under the dynamic hydrogen charging and the dynamic electrochemical charging current density was 150mA/cm2 and 200mA/cm2,35CrMo steel is a very plastic and the fracture strength was 570MPa.580MPa, the elongation rate was 15.5%,15.0%, and reduction area of crosssection was 38.96%,33.27%. Fine and uniform tempering sorbite and undissolved ferrite micro structure will be derived from 35CrMo steel through sub-quenching temperature and high tempering tempering process. Under that condition, it will not only enchance the comprehensive mechanical performance of 35CrMo steel, but also increase the hydrogen traps'relative amount and enhance its uniformity, through which enhance the sussceptibility of 35CrMo steel resistance stress corrosion cracking. The susceptibility of 35CrMo steel resistance stress corrosion lag cracking was enhanced with the increasing refinement of grain size. Therefore, it can be seen that grain refinement is an effective way to enhance the susceptibility of 35CrMo steel resistance stress corrosion lag cracking.