The Importance of Vacuum and Remelting Practices in a Modern Specialty Steel Plant. Part II: The Production of Different Specialty Steels

Abstract

The various groups of specialty steels require different melting techniques, treatments, pouring methods, and remelting processes. Depending on their composition and application, quality and cost are significant factors governing the decision for a specific procedure. For example, the two-stage technique—UHP electric furnace or BOF-vacuum plant—is successful in the production of anti-friction bearing steel, in that it reduces the oxide content and produces a more consistent product. In the production of alloyed engineering steels, as used by the automotive industry, excellent results are obtained with this same two-step method. This method reduces melting times with gains in purity and closer control of alloying content and grain size. For special requirements such as aircraft engines, the steel is vacuum-melted and vacuum-remelted. Precision forgings require degassing treatments and with unusual specifications for purity and freedom from segregation vacuum-arc or electro-slag remelting. Special purity tool steels are initially melted in the arc furnace or oxygen converter and then treated under vacuum. Widespread use is made of the possible variations in the two-stage arrangement, “melting furnace-vacuum plant”, in the production of stainless steels. As opposed to the traditional methods of producing this type of steel, appropriate combinations result in significant cost and quality advantages. High purity stainless steels, particularly in the form of flat shapes, are commonly VAR- or ESR-remelted. However, the most pronounced effects in melting, vacuum treatment, and remelting are found in the field of high-temperature materials.