Research on QPQ rare earth nitriding process on properties of Q235 carbon steel

The effect of quench–polish–quench (QPQ) nitriding temperature and rare earth yttrium (Y) content on the microstructure and properties of Q235 steel was investigated. The nitriding layer is divided into an oxide layer (Li2Fe3O4 and Fe3O4), a compound layer (Fe3N), a diffusion layer, the addition of Y effectively increased the steel performance after nitriding, but too much rare earth yttrium will inhibit the nitriding effect. The thickness of nitriding layer of Q235 carbon steel increased and then decreased with the increasing of rare earth Y content, and the thickest nitride layer was obtained using 2%Y at 580°C. The best hardness and corrosion resistance was obtained using 2% Y at 565°C.