A new ductile iron for mechanically and thermally strained rolls : Part 2: Material development varying Ni, Mo, Cr content using DoE
For manufacturing of steel wires, tubes, and profiles in hot rolling mills the toughest conditions occur in the front rolling stands where the mechanical load comes along with a constant change of hot rolling stock and cooling liquid. Conventional roll materials as pearlitic or acicular cast irons are not able to overcome these intense conditions because of their lack of ductility. A fine selection of alloying elements leads to a new material with a microstructure uniting bainite, austenite, and martensite inducing high hardness and strength, without lacking elongation. For this purpose, a full-factorial design of experiments was created consisting of three alloying elements in two concentrations each. The alloys were cast, heat-treated, and underwent extensive investigations on mechanical properties and microstructure. The results were analyzed and implemented in mathematical models whose combination and optimization led to the identification of the ideal alloy meeting the required strength, hardness, and elongation.