Effect of Various Elements on the Properties of 2lCr -4Ni Valve Steel

Abstract

To investigate the influence of C, Si, Ni, M n and N₂ on the properties of “21Cr-4Ni” valve steel, which was beginning to be used for automotive ind h ustry nowadays, the authors measured ardness change, mechanical properties at room and elevated temperature, rapture strength, magnetic permeability, oxidation resista nce in the air at elevated temperature, corrosion resistance to liquid PbO and 40% boiling HNO ₃ solution, hardness change in nitriding byNH₃ gas and carbo-nitriding by NaCN-BaCl₂ salt.
The results obtained were as follows:
(1) The as-quenched and the as-tempered hardness, the tensile and the yield strength at room temperature were increased with C contents, but the impact strength at room and elevated temperature were decreased with C contents. The corrosion resistance to liquid PbO was enhanced with C contents.
2) When Si content was (less than 0. 5%, the tensile and the rupture strength at elevated temperatures were most excellent, and the corrosion resistance to liquid PbO and 40% boiling HNO₃ solution were strong also. As Si content was increased more than 0. 5%, the corrosion resistance to liquid PbO and boiling 40% HNO₃ solution were decreased, but the oxidation resistance in the air at elevated temperatures was enhanced with Si addition.
3) The impact strength at room temperature was increased with (Ni addition, and the oxidation resistance in the air at elevated temperatures was enhanced by Ni addition.
4) The tensile strength and the yield strength at room temperature (were slightly increased with Mn contents, but the impact strength at elevated temperature was decreased by Mn addition.
5) This alloy steel was capable of nitriding by NH₃ gas, and carbo-nitriding by NaCNby BaCl₂ salt.