On Carbides in Tungsten High Speed Steels.

Study on carbides in commercial special steels by electrolytic isolation-VII

Abstract

The carbides isolated electrolytically from two kinds of high speed steels-18-4-1 and 11-4-2-were studied by chemical analysis and X-ray examination. The results obtained are as follows.
(1) The carbides in the annealed structure of these high speed steels are composed of M₆C, M₂₃C₆ and a little amount of MC, as reported by many investigators.
(2) By austenitizing treatment, M₂₃C₆ completely dissolves into matrix, but most part of M₆C remains as undissolved carbides. By the same treatment, MC in 18-4-1 steel is dissolved completely, but in the case of 11-4-2 steel, a part of it remaias.
(3) The chemical composition of the matrix of these steels quenched from 1250°C are very similar as follows:
(4) On tempering above 400°C, cementite appears first, and then W₂C, MC and M₇C₃ transitionally precipitate, and finaly M₆C and M₂₃C₆ are formed.
(5) The tungsten concentration in precipitated carbides increases gradually with the rise of tempering temperature. But the vanadium concentration in precipitated carbides reaches to a maximum percentage, and then dicreases with the rise of tempering temperature: This may result from the fact that the rate of carbide formation of tungsten is slower than that of vanadium, and so the previously formed vanadium carbides are diluted by the later formed tungsten carbides.