Kwang Suk Son

Assessment of Hot Ductility Behavior of 16Mn-0.5C Steel

This work assesses the hot ductility behavior of high manganese steel under hot working conditions. Reduction of area (RA) behavior of 16 Mn-0.5 C steel was investigated to consider it for production in a slab and subsequent hot rolling process. All specimens were machined from the as-cast slab. A hot ductility test was accomplished by a cast simulator through a temperature range of 650 °C-1200 °C with 50 °C intervals. The obtained RA values ranged between 30% and 60%, with a maximum at 850°C, and this is far from the general RA behavior of low carbon steel. This result could be attributed to the fact that the specimen is fully austenitic through all test temperatures, and that there is no ferrite at the low temperature end and reduced dynamic recrystallization at the high temperature end. Microstructural evaluation of the fractured specimen revealed that the deformation was concentrated at the grain boundary, and there was little matrix deformation. These results suggest that the grain boundary sliding is the basic cause of the fracture and low values of hot ductility in high manganese steel. †(Received Match 11, 2013)

Effect of low-cycle fatigue on the hot ductility of plain carbon steel

In a continuous casting steelmaking operation, the surface of a slab is under a condition that can be characterized as high-temperature, low-cycle fatigue in which the tensile and compressive stress is repeatedly developed. For this reason, for the evaluation of the hot ductility of a slab, considering the fatigue deformation is more feasible before a tensile or compressive test. In this study, the effects of low-cycle fatigue on the hot ductility of steels with a carbon content of 0.06–0.8 wt.% are investigated at various temperatures. For a carbon content of 0.06%, there were no significant differences between the RA values from a simple tensile test and those from a tensile test after fatigue deformation. The tendency of ductility deterioration with fatigue deformation is evident in 0.1 %C steel, and is due to the deformation-induced ferrite film that forms around the prior austenite grain. Conversely, high carbon steel containing 0.8 %C did not show a recovery of hot ductility in a low temperature region, and the specimen on which the tensile was measured after fatigue showed a higher hot ductility in the low temperature region, which is thought to result from the pearlite refinement effects. As the results obtained in this work showed noticeable differences in the hot ductility of carbon steel through the test conditions, it is suggested that for more accurate data, fatigue deformation be adopted in which the temperature range in an unbending operation is determined in the steelmaking factory.

Microstructural Control of Al-Sn Alloy with Addition of Cu and Si

The effect of various alloying elements and melt treatment on the microstructural control of AlSn metallic bearing alloy was investigated. The thickness of tin film crystallized around primary aluminum decreased with the addition of 5% Cu in Al-Sn alloy, with tin particles being reduced in size by intervening the Ostwald ripening. With the addition of Si in Al-10%Sn alloy, the tin particles were crystallized with eutectic silicon, resulting in uniform distribution of tin particles. With the addition of Cu and Si in Al-Sn alloy, both the tensile strength and yield strength increased, with the increasing rate of yield strength being less than that of tensile strength. Although the Al-10%Sn-7%Si alloy has similar tensile strength compared with Al-10%Sn-5%Cu, the former showed superior abrasion resistance, resulting from preventing the tin particles from movement to the abrasion surface. (Received November 30, 2009)