Development of steels for high-strength bolts with excellent delayed fracture resistance

摘要

The properties of the newly developed steel (SKDS4) were investigated and it was concluded that:KNDS4 had much better delayed fracture resistance than conventional AISI 4140 in water. The addition of Ti, V, Mo, and Ni to KNDS4 was effective in increasing critical hydrogen content. In addition, Ti, Ni, and Mo increased KNDS4's corrosion resistance. For KNDS4, the amount of hydrogen absorbed under the same hydrogen charging conditions was less than that for AISI 4140. The diffusible hydrogen content in KNDS4 was also less. In addition, the delayed fracture properties of KNDS4 were improved by grain size refinement and the introduction of hydrogen trapping sites through the precipitation of fine Mo-Ti-V type complex carbides (less than 50 nm), resulting in increased critical hydrogen content.