Second phases in steel.
The present and future relationship between the metallurgical development of new steels and the determination of second-phase compounds in these steels is emphasized on the basis of recent developments in the quantitative determination of these phases. Results of the application of DTA-EGA methods are presented as an example of this analytical approach, and the method used to measure the amounts of gases evolved from the reactions of second-phase compounds with O(2) is described in detail. The DTA-EGA method has also revealed phases that had not been found earlier in steels. Smaller amounts of second-phase compounds can be more accurately determined by this method than by any other procedure. Examples are cited for the reaction of O(2), H(2), steam, and NH(3) with second-phase compounds in the isolated residue, and the use of these reactions for the determination of second phases is discussed. A disadvantage of the DTA-EGA method is that it is dependent on the quantitative chemical separation of the second phase from the matrix steel by one of several methods. The relative merits of isolating second-phase compounds by electrochemical dissolution, by dissolution in halogen and alcohols or aliphatic esters, and by use of dilute acids are discussed in terms of their effect on the DTA-EGA determination.
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