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I.

INTRODUCTION

IN recent years, the development of steel alloys has been helped by research undertaken to relate steel composition and microstructure to mechanical properties. At the refining stage of alloy steelmaking, research on solution rates and solution mechanisms of solid additives in raw steel is also needed as an aid to efficient processing and control o f steel bath chemistry. While a significant body o f research on the subject o f alloy additives dissolution in steel has already been reported and summarized ~'2 for both low melting point (e.g., aluminum, ferromanganese) and high melting point (e.g., vanadium, molybdenum) additives, the work now presented for the iron/titanium system marks a novel departure. Titanium with a melting point o f 1660 °C, some 60 °C greater than steel processing temperatures, has a strong affinity for iron, with which it forms intermetallics. The system therefore represents an ideal extension to previous studies relating to the lower melting point exothermic silicon alloys l°'H and those relating to high melting point non-exothermic alloy/steel systems.1 As well as being of basic interest, titanium also has promising practical potential as an alloy additive for liquid steel. Some o f the effects of titanium in alloy steels are that it: (1) reduces martensitic hardness and hardenability in medium-chromium steels, (2) prevents formation o f austenite in high-chromium steels, and (3) prevents localized depletion of chromium in stainless steel over long periods of heating. No work on the subject of titanium dissolution in iron has been reported apart from that o f Shantarin and Shurygin,3 who studied dissolution rates o f Ti, Cr, Mo, and W in pure molten iron. They found that dissolution rates in pure iron increased in the order Mo-W-Cr-Ti. They provided no explanations, nor were the precise mechanisms considered or identified. STAVROS A. ARGYROPOULOS is N.S.E.R.C. Assistant Professor, Department of Metallurgical Engineering, McGill University, 3450 University Street, Montreal, Quebec, Canada H3A 2A7. RODERICK I.L. GUTHRIE, Professor, McGill University, is currently on sabbatical at University of Surrey, England. Manuscript submittedDecember 6 , 1982.

METALLURGICAL

TRANSACTIONS B

II.

EXPERIMENTAL PROCEDURES

Preliminary immersion tests of titanium cylinders in steel showed that a customary shell o fsteel 4 first froze around the cylinder following initial immersion. However, more strikingly, it was found that a 'premature' internal reaction between the encasing steel shell and the solid titanium took place. Figure 1 provides an idea o fthe extent of this reaction at the steel shell/titanium interface. Based on these preliminary findings, the first set o f experiments aimed at finding out when and how the exothermic reaction between steel and titanium started. Small composite cylindrical samples, 2.54 cm in diameter and 1.5 c m long, were therefore machined and pressed tightly together. The titanium used was designated as ASTM

Fig. 1--Cross-section of titanium cylinder (2.