Process for producing mechanical part from case-hardened or nitrided case-hardened steel and steel for producing such part

摘要

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