Temperability of Mn-Cr Spring Steel

Abstract

The temperability of the Mn-Cr spring steel, namely the behaviors of the carbide and the mechanical properties going through a process of tempering are studied in this report, and the results obtained are as follows:
(1) In the case when the tempering parameter T (C+log t) is introduced, the hardness is decreased linearly with tempering parameter up to 500°C.
(2) From measurement of X-ray line broadening, it is suggested that the hardness is dependent upon the lattice strain of ferrite.
(3) By the tempering above 500°C, the alloy elements such as Cr and Mn concentrate into the carbide phase; and there is a remarkable fall in the hardness that is caused by the removal of the alloy elements from the matrix ferrite. So, it is possible to conclude that the factors affecting on the hardness are the crystal strain of a matrix ferrite and- also the content of alloy elements in the ferrite.
(4) The shapes of the carbide formed during tempering does not affect the hardness, but the ductility and the fatigue strength.
(5) The yield-tensile ratio takes a low value in the presence of an excessive lattice strain of ferrite; and, with rising of the tempering temperature, this value is increased gradually as a result of disappearance of strain.
However, it tends to be decreased by growth of carbide particles with further rising of tempering temperature. Consequently, it takes the maximum value at a temperature of 450-500°C.