Calculation of liquidus temperature of low and high alloyed iron base melts from their chemical composition by means of the equivalence factors

Liquidus temperature of a steel is calculated from its chemical composition according to the so far proposed procedures by simply summing up the iron melting point lowering effects of all in the steel contained elements Xi, as they are given by approximating the iron liquidus curves with the straight lines in the corresponding binary Fe‐Xi systems. The intensification of the iron melting point lowering effect with the increasing concentration of each element contained in the steel has not been at all or only partly taken into account in this approach. This is the reason why the calculated steel liquidus temperatures are not accurate enough. In the here proposed new calculation procedure the iron melting point lowering effect of an alloying element Xi is first translated into an equivalent effect of carbon in the Fe‐C system by converting the concentration of Xi into an equivalent concentration of carbon taken as a reference element. The carbon equivalent iron melting point lowering effect of all elements contained in the steel including carbon is then evaluated by summing up the calculated equivalent carbon concentrations of all elements together with carbon into a fictitious total equivalent carbon concentration. A so calculated total equivalent carbon concentration has made it possible to determine with a good accuracy the steel liquidus temperature along the stable δ/α or γ liquidus lines in the Fe‐C system. The success of a melting point calculation is strongly dependent on the accuracy of the equivalence factor equations for each alloying element. They are derived by relating the iron liquidus line in the binary Fe‐Xi system to that in the Fe‐C phase diagram. Die bisherigen Gleichungen für die Berechnung der Liquidustemperatur aus der Zusammensetzung der Stähle sind unbefriedigend, da die Addition der schmelzpunkterniedrigenden Wirkung der einzelnen Legierungselemente nicht der Tatsache Rechnung trägt, daß sich diese Wirkung mit steigenden Gehalten der einzelnen Legierungselemente und der andern, gleichfalls vorhandenen, verstärkt. Daher überträgt das vorgeschlagene neue Berechnungsverfahren die schmelzpunkterniedrigende Wirkung der einzelnen Legierungselemente auf die äquivalent wirkenden Konzentration des Bezugselementes Kohlenstoff im System Fe‐C, addiert die errechneten Konzentrationen zur fiktiven, äquivalenten Gesamtkonzentration und berechnet damit die Liquidustemperatur der Stahllegierung mit den Gleichungen für die δ/α‐ bzw. γ ‐Liquiduslinie