Masatoshi Aramaki

Improvement of die life with surface texture control and solid lubricant

Abstract The methodology of controlling the surface texture of dies by means of Hybrid-shot peening was examined for the improvement of the die life cycle applied to high strength steel sheets. Hybrid-shot is double-shot peening, where the first treatment is performed using large particles, and the second one is performed with finer shot particles. The specimens of tool steels for dies treated by Hybrid-shot showed a high resistance against galling which was evaluated by the galling generation load of the draw bead test by using an oil lubricant, compared with the single shot specimens. This result suggested that the surface texture influenced the galling property. For a quantitative analysis of surface texture of die material, Fast Fourier Transformation (FFT) was used. Findings revealed that the ratio of the spectrum amplitude between high and low frequencies calculated by FFT corresponded to the galling generation load of draw bead tests. On the other hand, the conventional index of surface roughness, Rz, had no relationship to the galling generation load. Furthermore, the effect of solid lubricant, that is, the powder produced by scallop shell, on the galling property was studied. The addition of fine scallop shell powder in the oil lubricant increased the galling generation load.

Effects of Nitriding-Quenching and Carburizing-Quenching on Wear Properties of Industrial Pure Iron

Abstract The wear properties of industrial pure iron treated by nitriding-quenching and carburizing-quenching were investigated. Both the nitrogen martensite and carbon martensite produced by each treatment exhibited the same high degree of wear resistance. The results of sliding tests showed that the nano-indentation hardness near the surfaces of both samples had increased. The surface hardening of the nitrogen martensite was more noticeable than that of the carbon martensite. EBSD analysis revealed that plastic strain had been induced on a relatively large scale (around 20 μm) after sliding in the case of the nitrogen martensite. It was found that the high wear resistance of the nitrogen martensite led to strain hardening through the effect of the load applied in the sliding test.

FEM analysis of friction for pressing dies controlled by shot treatment

Abstract The finite element method (FEM) analysis of elastic-plastic deformation was applied to examine the effect of surface texture controlling of dies by means of hybrid-shot (double shot by two different kinds of particles) treatment on the galling property applied to high tensile strength steel sheets. The FEM analysis results showed that the apparent friction coefficient, which was calculated from pressing load and the drawing force, increased with each increase in the pressing load. The experimental results from the drawing tests with lubricant oil showed that the friction coefficient of the die after hybrid-shot treatment decreased slightly with the increase of the pressing load. On the other hand, the friction coefficient of the die without shot treatment, (i.e. nearly flat surface), slightly increased with the increase of the pressing load due to the digging effect. These findings reveal that the effect of surface texture of dies was caused not only by the elastic-plastic deformation but also by the oil lubrication condition. The FEM analysis was therefore performed by taking into account the digging effect as well as the micro-oil pool effect. The experimental result in the case of hybrid-shot dies corresponds well to the FEM result by adopting the virtual oil model where the oil segment was defined as an elastic solid body.

The effect of Si on the precipitates for Nb bearing high purity ferritic stainless steel

The effect of Si on the precipitation of the Laves phase in high purity 17Cr–0.5Nb ferritic stainless steel was investigated. Precipitation was observed using a scanning electron microscope and transmission electron microscope. Quantitative analysis of the amount of precipitates as Laves phase was performed. The precipitation rate of the Laves phase and the equilibrium amount of precipitates of the Laves phase increased with the amount of Si. A Si peak was detected in the Laves phase in 0.5Si steel by energy dispersive X-ray spectrometer analysis. It was revealed that precipitation of the Laves phase was promoted and the chemical composition of the Laves phase was changed by the addition of Si.

Effect of Microstructure on Formation of Ductile Fracture Surface in Steel Plate

In recent years, high strength steel plates for building and pipelines have been required to improve ductile fracture properties, assuming ground deformation in earthquake-prone region. The ductile fracture is performed by the result from coalescence of micro-voids followed by the nucleation and growth [1]. Fractured surface morphology reflects the void coalescence process, so it is important to consider the relationship between the fracture surface morphology and the micro-voids formation beneath the fractured surface to consider the ductile fracture properties. The voids nucleate sites are mainly particles such as inclusions or precipitates, and grain boundries. These voids grow and coalesce according to three modes. The first mode is directly coalescence of voids followed by growth [2]. The second one is the coalescence of voids caused by shear deformation followed by internal necking between voids [3]. The third one is the coalescence of voids caused by micro-voids nucleation in shear band between two larger voids [4]. It is expected that these modes influence local elongation property which is one of the indices for ductile fracture property through the formation of fractured surface. In this study, local deformation energy which is measured by load-displacement curve in tensile test is examined by focusing the voids nucleation, growth and coalescence, for high tensile strength plates of TS480-830MPa which is controlled by the microstructure through the cooling rate of heat treatment. The deformation energy is useful to consider the ductile fracture property of steel plates which have a different tensile strength.

Effects of co-addition of titanium and boron on microstructure of superplastic Cr–Mo steels

AbstractThe effects of titanium and boron on the microstructure of a low alloyed Cr–Mo steel with 0·6 wt-%C have been investigated by comparison with a steel containing only titanium and a steel free from both titanium and boron. Each of the steels was subjected to thermomechanical treatment and annealed at 700°C, resulting in small grains of size a few micrometres. The steel containing both titanium and boron possessed the smallest ferrite grains and M3C carbides of the three examined. This is attributed to a fine dispersion of borides (TiB2 ) and borocarbides (Ti(C,B)) of size 10 nm in the ferrite matrix through the pinning effect. At the grain boundaries small carbide particles were present which were effective in inhibiting grain boundary migration. The extremely fine borides and/or borocarbides were useful in suppressing intragranular deformation of ferrite grains due to precipitation hardening. This may have assisted in promoting grain boundary sliding, resulting in superior superplastic elongation.