A dipping test that a water cooled copper plate was continuously dipped at 14 mm/s was performed in order to investigate solidifying shell growth in initial solidification. Anomalous rough surfaces and uneven shell growth were exhibited for an ultra-low carbon steel (0.005 mass% C) and a hypo-peritectic carbon steel (0.116 mass% C), while for a low carbon steel (0.044 mass% C) and a hyper-peritectic carbon steel (0.304 mass% C), flat surfaces were formed. The carbon content dependence of the anomalous uneven shell growth can be explained by stress caused by solidification shrinkage and = transformation occurring from a fraction solid 0.7, where shell begins to have strength, to 1.0, complete solidification state. Besides the analysis shows that decrease of the cooling rate can reduce the stress in the shell generated during the initial solidification.

Refractory tubes such as a shrouding nozzle and a submerged entry nozzle are employed for molten steel transferring from a ladle to a tundish, and a tundish to a mold, respectively, to prevent molten steel from being oxidized. When the cross-sectional area in the molten steel flow channel is suddenly contracted and subsequently enlarged, a negative pressure is generated at the area. Thereby air is permeated into the molten steel flow through the refractory tube and oxidizes the molten steel.The permeability of a submerged entry nozzle was predicted from measurement of the gas permeated through the refractory tube by a dipping test. Using the predicted permeability and the pressure analysis in fluid flow, we calculated the oxidation rate by the permeated air during molten steel transferring. As a result, the concentration decrease rate of aluminum in molten steel is estimated 0.35 ppm per hour and this oxidation formed by the permeated air does not attribute to alumina build-up in the submerged entry nozzle.

A series of experiments have been carried out using an upsetting-extrusion-type tribometer to investigate the effect of the surface preprocessing of a workpiece on the friction behavior of dry in-place type lubricant coating. Experiments were carried out in the transition range of seizure for tool surface reduced peak height. Experiments using a typical conversion lubricant coating and dry in-place type lubricant coated on seven types of preprocessed surface showed that the tribo-performance of the dry in-place type lubricant coated on an acid-pickled and shot-blasted surface is insufficient. However, the dry in-place type lubricant coated on a shot-blasted surface in two stages using microscopic particles or phosphates as thin films gives excellent antiseizure performance and keeps the frictional shear factor low up to a tool surface reduced peak height Rpk of 0.07µm, the critical Rpk for the conversion lubricant coating is 0.05µm. The observation of a forged surface showed that the excellent performance of dry in-place type lubricant coated on a shot-blasted surface in two stages is due to its combined surface texture.

A series of experiments has been carried out using an upsetting-extrusion type tribometer to investigate the effect of tool surface roughness on the friction behavior of lubricant coating. Experiments using a typical conversion lubricant coating and three types of alternative lubricant coating showed that the reduced peak height Rpk is a more appropriate parameter than the maximum height of the profile, Rz, to express the effect of tool surface roughness on seizure generation in cold forging. When Rpk is larger than the critical Rpk, the generation of seizure becomes more striking for the alternative lubricant coating than for the typical conversion coating. In this experiment, the critical Rpk changes with the type of lubricant coating and is in the range of 0.045-0.056 µm. When no seizure occurs, frictional shear factor hardly varies with the type of lubricant coating and surface expansion ratio.

A new extrusion process with bulge deformation type tribotest has been developed to investigate the frictional behavior of lubricant coatings on the surface of steel wire in cold forging. In the tribotest, the friction behavior in forward extrusion processing can be evaluated sensitively by adding bulge deformation. The sensitivity to the frictional shear factor was optimized by changing the land part shape and angle of the taper of the die entrance. The frictional shear factor of the lubricant coating can be obtained by plotting the measured forging load or the shape of the billet after forging on the calibration curve obtained by the finite element method. A series of experiments were carried out using two types of bonderized coating and a dry in-place lubricant coating. It was revealed that the variation in the frictional shear factor at processing temperatures from 20 to 200℃ is less for the dry in-place lubricant coating than for the bonderized coating.