Microalloyed steel with good resistance to hydrogen for the cold-forming of machine parts having high properties

Abstract

The steel according to the invention is characterized in that, in order to keep its weight content of molybdenum below 0.45%, its chemical composition, besides the iron and the inevitable residual impurities that result from the smelting of the steel, corresponds to the following analysis, given as percentages by weight: 0.3≦C %≦0.5 0.20≦Mo %<0.45 0.4≦Mn %≦1.0 0.4≦Cr %≦2.0 0.04≦Ni %≦0.8 0.02≦Nb %≦0.045 0.03≦V %≦0.30 0.02≦Ti %≦0.05, with Ti>3.5 N 0.003≦B %≦0.005% S %≦0.015 P %≦0.015, and optionally 0.05≦Si %≦0.20; Al %≦0.05 and N %≦0.015. By cold forming a hot-rolled wire rod resulting from continuous casting, it is possible to obtain, after heat treatment, “ready-to-use” coined parts, such as cap screws for example for the automotive industry, that offer a tensile strength from 1200 to more than 1500 MPa while having a good hydrogen embrittlement resistance, and this with a specially controlled “raw material” production cost.