Wrought steel part and method for manufacturing thereof

Abstract

A steel component for an automotive transmission system includes a core made of the following elements: 0.15%≦C≦0.25%; 1.0%≦Mn≦1.6%; 0.4%≦Si≦0.9%; 0.001%≦Al≦0.1%; 0.10%≦Mo≦0.5%; 1%≦Cr≦1.5%; O≦P≦0.09%; O≦S≦0.09% ; 0%≦N≦0.09%; 0≦Nb≦0.06%; 0%≦Ni≦1%; 0%≦V≦0.2%; 0%≦Ti≦0.1%; 0%≦Cu≦1%; 0%≦B≦0.008%; 0%≦Sn≦0.1%; 0%≦Ce≦0.1%; 0%≦Mg≦0.10%; 0%≦Zr≦0.10%; Remaining components Composed of iron and unavoidable impurities caused by processing, the microstructure of the core of the steel component comprises at least 90% martensite by area percentage, and optionally accumulates 1% to 10% of any one or more of retained austenite, pearlite, ferrite, and bainite, as well as precipitates of aluminum and / or niobium in the form of AlN and / or Nb(C,N), wherein the percentage of original austenite grains with a size of 3 to 5 is limited to a maximum of 10% of the total grains. Such a steel component comprises a martensite depletion layer with a depth of 1 mm or less on all its surfaces, such martensite depletion layer comprising 55% to 72% martensite, 10% to 40% retained austenite, and the remainder being any one or more of bainite, ferrite, or cementite.

Images