The Secondary Hardening of Tungsten Steels

AbstractThe tempering characteristics of a steel with 2 at.−%W 1.1 at.−%C in the range 500–700°C have been studied and structural changes related to the secondary-hardening phenomenon. The sequence of carbides found both at grain boundaries and in the matrix has been established,and detailed structural observations have been made on the nucleation of W2C and M6C. The ageing behaviour is contrasted with that of a comparable molybdenum steel in which the carbide reactions occur more rapidly. Trace additions of Nb Ti and Ta improve the basic strengthening reaction by providing a fine secondary carbide dispersion which also inhibits the coarsening of the dislocation network. The main carbide dispersion is also refined.