Compression characteristics of 6Cr21Mn10MoVNbN heat resistant valve alloy at elevated temperatures

Abstract

6Cr21Mn10MoVNbN is a new type of alloy used for heavy duty engines. Thermal simulation, metallography, X-ray diffraction and theoretical analysis have been used to study the deformation behaviour of the alloy at elevated temperatures. By introducing an internal variable parameter, a constitutive equation has been suggested for the dynamic calculation of the stress/strain curve for this alloy based on the Zerrilli–Armstrong equation used for fcc materials. The data calculated using the equation developed agree fairly well with the experimental data. The microstructure of the alloy is found to depend greatly on temperature and strain rate. When the alloy is deformed at 850°C, Cr₂₃C₆ precipitates from the matrix. The lower the strain rate, the more Cr₂₃C₆ precipitated from the matrix. At the same time, the amount of Cr₂₃C₆ decreases with increasing temperature. Between 850 and 1050°C, the amount of NbN in the alloy increases with increasing temperature and reaches a peak at 1050°C. NbN begins to decrease when the temperature gets to 1150°C. At this temperature, carbides and nitrides in the alloy, especially those distributed on the grain boundaries, begin to be dissolved into the matrix in great deal. The microcracks propagate easily along the grain boundaries of the alloy.