The effect of chromium on antimony and nickel grain boundary segregation in iron
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The Effect of Chromium on Antimony and Nickel Grain Boundary Segregation in Iron C.L. BRIANT Grain boundary segregation in multicomponent alloys can be a very complex process. An element added to the alloy may or may not segregate. The added element may also enhance segregation of other elements present in the alloy, decrease segregation of other elements either through site competition or precipitation, or have no effect on the segregation at all. It is thought that segregation of an element increases as its activity in the alloy increases. If one considers all of the compositiondependent terms that are part of an expression for the activity of an element in a multicomponent alloy, it is not surprising that all of the possibilities listed above can be observed. Since numerical expressions for these composition-dependent terms are often unknown, it is also difficult to predict segregation in these materials. Therefore, we must still rely on experiments to establish the basic facts. In recent years, a significant amount of research has been aimed at examining segregation in binary, ternary, and quaternary alloys. The goal of this work has been to establish for these simple alloys a description of segregation that can then be used at least to rationalize segregation results in alloys that contain many elements. Almost all of this work has been done on iron-based materials. One clear result established by these studies is that nickel additions increase the segregation of antimony in iron. I~ 7] Early work on antimony segregation in steel suggested that chromium might also increase antimony segregation, although it was felt that this effect would be much smaller than the effect of nickel. [2] This idea would be consistent with the fact that in contrast to nickel, chromium has little effect of the activity of antimony in iron. [8] However, the effect of chromium on antimony segregation had never been examined in highC.L. BRIANT, Staff Scientist, is with the Research and Development Center, General Electric Company, P.O. Box 8, Schenectady, NY 12301. Manuscript submitted March 8, 1989. 2170-- VOLUME 20A, OCTOBER 1989
purity iron-based alloys. This communication reports a study of the effect of chromium on antimony and nickel segregation in iron. Four alloys were used for this study. Their compositions are listed in Table I. All alloys contained 0.06 wt pct antimony and 3.5 wt pct nickel. This base Fe-Ni-Sb alloy has been investigated in several studies. 16'71 The alloys contained chromium ranging between 0.1 and 3 wt pct. Strips of each material were cut from the ingot and homogenized at 1200 ~ for 48 hours and water-quenched. They were then cold-rolled to a thickness of 0.127 cm. Pieces of this rolled strip were annealed at 675 ~ for 200 hours, furnace-cooled to 560 ~ held at this temperature for 500 hours, and water-quenched. The heat treatments at 675 ~ and 560 ~ were carried out with the samples in flowing wet hydrogen to decarburize them. It has been shown in previous studies that this heat treatment allows equilib
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