20th International Forgemasters Meeting - IFM 2017

Recently, we have developed an advanced skin pass mill back up roll (SPM BUR) which is one of the most essential elements in the manufacture of flat products of metals. In this paper, the alloy design concept and the excellent properties of the developed SPM BUR was introduced. In order to optimize chemical composition and manufacturing process, the following procedures were adopted. First, the experimental specimens with different alloy elements were chosen as 5 candidate materials in total. Secondly, the high temperature compression, the dilatation tests and hardness, impact tests with respect to the different heat treatment condition were carried out to find the optimized condition for the manufacturing processes such as forging, normalizing, quenching and tempering. Thirdly, the disc to disc tests for the wear resistance of the candidate materials were carried out under the conditions of 1,470MPa test stress and emulsion lubricant of 3% mineral oil emulsion type and the wear resistance was discussed by correlation between the disc surface morphologies and the microstructures of the candidate materials. With increasing the alloying element, the candidate material deteriorates became slower under the condition of lubrication. The experimental results were used to find new material for prolonging the service life of the SPM BUR. Fourthly, the hardened surface parts would be obtained by induction hardening heat treatment were simulated using heat transfer coefficient and with continuous cooling behavior of the material. The simulation results were beneficial for the prediction of the effective hardened depth from the roll surface under the effective cooling system. Finally, the optimized alloy design based on the experimental data and simulation results, but also the cutting-edge process technologies, e. g. induction hardening, were applied for the manufacture of the forged SPM BUR. The developed SPM BUR was mounted in the POSCO roll manufacture and proved to have superior performance compared to the previous SPM BUR in the term of the surface machining rate in operation