PROCESS FOR PRODUCING PART FROM CASE-HARDENED OR NITRIDED CASE-HARDENED STEEL AND STEEL FOR PRODUCING SUCH PART

摘要

A novel carburising or carbonitriding steel has the composition (by wt.) 0.2-0.26% C, 0.05-0.5% Si, 1 to less than 1.6% Mn, 0.4-1.5% Cr, 0.08 to less than 0.27% Mo, 0 to less than 0.6% Ni, 0.003-0.06% Al, 0-0.3% Cu, 0-0.1% S, less than 0.03% P, optionally up to 0.02% Te, up to 0.04% Se, up to 0.07% Pb and up to 0.005% Ca, balance Fe and impurities. Also claimed is a process for manufacturing a mechanical steel part by subjecting a rough steel part to surface carburising or carbonitriding, the steel having (a) the composition (by wt.) 0.15-0.35% C, 0-0.6% Si, 0 to less than 5% Mn + Cr + Ni + Mo, 0-0.1% Al, 0 to less than 0.5% Cu, 0-0.15% S, less than 0.03% P, optionally up to 0.02% Te, up to 0.04% Se, up to 0.07% Pb and up to 0.005% Ca, balance Fe and impurities; (b) a Jominy curve in which J3 = 45-50 HRC, J11 = 39-47 HRC and J25 = 31-40 HRC; and (c) average values J3m, J11m, J15m and J25m of five Jominy tests such that MOD(J11m - J3m x 13 divided by 22 - J25m x 8 divided by 22) = 2.5 HRC and J3m - J15m = 9 HRC.