Sulphide and Its Effect on Solidification Cracking in Weld Metal of Steel (Report 2) Theoretical Investigations on Change in Liquid Composition among Cells or Cellular Dendrites and Law of Its Coincidence in Fe-S-X Ternary Alloys

• Published in: JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 42; no. 10; pp. 996 - 1006
• Main Authors: Senda, Tomio, Matsuda, Fukuhisa, Nakagawa, Hiroji
• Format: Journal Article
• Language: Japanese
• Published: JAPAN WELDING SOCIETY 25.10.1973
• ISSN: 0021-4787; 1883-7204
• DOI: 10.2207/qjjws1943.42.996

Theoretical Investigation is discussed on the change in liquid composition among growing cells or cellular dendrites in Fe-S-X ternary alloy, where X is the third element. Main conclusions obtained are as follows: 1) Under the condition that the liquid among the growing cells or cellular dendrites is completely mixed and the diffusion in solid is negligible, the liquid composition in Fe-S-X ternary phase diagram follows the “changing curve in composition” given by: Cls={CSI/CXX(1-kS)/(1-kX)}CIX(1-kS)/(1-kX) where Cls and Clx are the concentrations of S and X in liquid respectively, CsI and CxI are these initial concentrations, and ks and kx are these equilibrium distribution coefficients. 2) The law of coincidence for the change in liquid compositions in alloys of various compositions is given by: CXI(1-kS)/(1-kX)/CsI=constant Alloys whose compositions satisfy this equation undergo the same change in liquid composition, and therefore sulphides formed have same composition. 3) In the case of Fe-rich Fe-S-O alloy, the changing curve in composition, until the liquid composition reaches the miscibility gap in Fe-S-O diagram, is given by: Cl/S=(CsI/CoI)Clo where ClO and Cor are the concentration in liquid and initial concentration of O respectively. 4) The law of coincidence in Fe-rich Fe-S-O alloys is given by: Cor/Csr=constant 5) In the case of Fe-rich Fe-S-Mn alloy, the changing curve in composition, untill the liquid composition reaches the eutectic curve crystallizing (Mn, Fe)S in Fe-S-Mn diagram, is given by: in the region of δ solidification Cls=(CSI/CMI3) ClM3 in the region of γ solidification ClS=(CsI/CMI5)ClM5 where ClM and CmI, are the concentration in liquid and initial concentration of Mn respectively. 6) The law of coincidence in Fe-rich Fe-S-Mn alloys is given by: in the region of δ solidification CMId3/CsI=constant in the region of γ solidification CMI5/CsI=constant 7) In the case of welding the complete mixing of liquid and the negligible effect of diffusion in solid on the solute distribution in liquid are approximately estimated. Therefore it is considered that the changing curve in composition and the law of coincidence can be applied to the weld solidification.