Interesting facts about Chromium in steel

Cr renders steels oil and air-hardenable. By reduction of the critical rate of cooling necessary for martensite formation, it increases hardenability, thus improving its susceptibility to hardening and tempering. Notch toughness is reduced however, but ductility suffers only very slightly. Weldability decreases in pure chromium steels with increasing Cr content. The tensile strength of the steel increases by 80-100 MPa per 1% Cr. Cr is a carbide former. Its carbides increase the edge-holding quality and wear resistance. High temperature strength and high-pressure hydrogenation properties are promoted by chromium. Whilst increasing Cr contents improve scaling resistance, a minimum content of about 13% chromium is necessary for corrosion resistance of steels; this must be dissolved in the matrix. The element restricts the γ-phase and thus extends the ferrite range. It does however stabilize the austenite in austenitic Cr-Mn and Cr-Ni steels. Thermal and electrical conductivity are reduced. Thermal expansion is reduced (alloys for glass sealing). With simultaneously increased carbon content, Cr contents up to 3% increase remanence and coercive field intensity.