Microstructural Evolution of 31CrMoV9 Steel upon Controlled Gaseous Nitriding Treatment

Abstract

Abstract/KurzfassungThe evolution of the microstructure and the surface residual stress upon controlled gaseous nitriding of quenched and tempered 31CrMoV9 steel was investigated by varying the nitriding potential and the nitriding time at the nitriding temperature of 550 °C. A graded microstructure developed as a function of depth: a surface adjacent decarburized-nitrided zone, in which all tempering induced carbides had transformed to nitrides, under loss of the released carbon through the surface, is followed by a nitrided zone in which the carbon released from the carbide-to-nitride transformation had diffused to grain boundaries and precipitated there as (new) carbides. The extent of decarburization showed a strong dependence on whether or not an outer iron-nitride compound layer was present, as well as on the type of iron nitride present at the specimen surface. The surface residual stresses varied as a function of nitriding time and nitriding potential which has been discussed in terms of the rates of the carbide-to-nitride transformation, the decarburization and/or the carbide precipitation along the grain boundaries. n

Influences of Vanadium and Silicon on Case Hardness and Residual Stress of Nitrided Medium Carbon Steels

“…[29,30] However, alloys that contain elevated amounts of nitride forming elements such Cr, Mo, V, and Si often have magnitudes of compressive residual stress after nitriding between 600 and 1000 MPa. [30][31][32] Clearly, the content of nitride formers, and likely the precipitation of nitride phases during nitriding influence residual stress.…”

Comparison of Experimental Curves of Alloy Steels after Gas Nitriding

“…With the aim of improving the physical characteristics of iron materials, and more specifically of steels, various methods are used, and one of them is nitriding [1][2][3][4][5][6][7][8]. This process takes place in temperatures of over 500 0 C and in solid, liquid or gas environments [9].…”