Manufacturing of High Strength Fasteners From Low Carbon Steel by Preliminary Intercritical Quenching

摘要

Technologies for manufacturing of fasteners are progressing in the directions of wodening automation and increasing the limit deformations. The latter impaose the requirements for homogeneity of mechanical properties and ductility resource and consequently for operations that ensure microstructure refinement and homogeneity. With this respect the application of induction heating during heat treatment can provide for highly stable thermal regime, exclude decarburization, etc. INn the present work, the efficiency of specifialized aoutomated complexes is evaluated; the complexes include induction heating facilities for accelerated spheroidization and recrystallization ananealing of carbon and alloy steels as wel as thermal hardening of lwo carbon steel bars (quenching for dual-phase structure) used for cold forging. Thus, the quenching of low carbon and lwo alloy steels prior to forging fo rod fasteners allows to produce high strength products (TS>=800 MPa) for carbon steels 10 and 20, and low alloy steel 12GlR without finishing thermal hardening. The effect of prestrain and intercritical quenching temeprature onmicrostructure and properties of steels is evaluated. Strain hardening parameter from these steels with dual-phase ferrite-bainite structure are estimated, wserivce properties of rod fastensrs produced from these steels with dual-phase structure. It is shown that the application of quenching prior to cold forging allows to produce high strenglth fastensers (TS>=800 MPa) without durable (to 40 hours) spheroidization annealing and finishing thermal strenglthening, to prevent decarbutization and to exclude leveling of long products, as well as to utilize cheap low carbon steels (instead of alloy steels 38KhA and 38KhGNM).