Shoji Kiguchi

Surface hardening of two cast irons by friction stir processing

The Friction Stir Processing (FSP) was applied to the surface hardening of cast irons. Flake graphite cast iron (FC300) and nodular graphite cast iron (FCD700) were used to investigate the validity of this method. The matrices of the FC300 and FC700 cast irons are pearlite. The rotary tool is a 25mm diameter cylindrical tool, and the travelling speed was varied between 50 and 150mm/min in order to control the heat input at the constant rotation speed of 900rpm. As a result, it has been clarified that a Vickers hardness of about 700HV is obtained for both cast irons. It is considered that a very fine martensite structure is formed because the FSP generates the heat very locally, and a very high cooling rate is constantly obtained. When a tool without an umbo (probe) is used, the domain in which graphite is crushed and striated is minimized. This leads to obtaining a much harder sample. The hardness change depends on the size of the martensite, which can be controlled by the process conditions, such as the tool traveling speed and the load. Based on these results, it was clarified that the FSP has many advantages for cast irons, such as a higher hardness and lower distortion. As a result, no post surface heat treatment and no post machining are required to obtain the required hardness, while these processes are generally required when using the traditional methods.

Effect of graphite morphology on decarburized cast iron

The decarburization of cast irons graphite has been studied as part of the process to make high-value-added cast iron. The aim is to develop new uses for cast irons. Once the graphite has been eliminated in a surface layer by high temperature oxidation in air, other materials conferring improved properties can be infiltrated into the resulting pores. The effects of holding time (3–48h), holding temperature (1023–1223K) and chemical composition (3.27–4.0%C, 2.0–4.0%Si) were investigated for each graphite morphology (flake graphite, compacted graphite, spheroidal graphite). As a result, it was found that the rate of formation of porosity (due to the decomposition of graphite) in cast iron obeyed the diffusion law. The rate of formation of porosity in flake graphite irons was faster than that for the other graphite morphologies, probably because flake graphite is continuous in the matrix, whereas spheroidal graphite exists as independent deposits. It has been found that the continuity of the graphite has a strong effect on the rate of formation of porosity.

Effects of tertiary elements on inter-graphite spacing of unidirectionally solidified Fe-C alloys

The effects of 0.004–0.108mass%S, 0.068–1.10 mass% Si, 0.047–0.177 mass% Ti, and 0.0350–0.078 mass% Zr on inter-graphite spacing λ of grey cast iron were investigated using a unidirectional solidif...

Effect of C Content on High Temperature Erosive Wear Characteristics of Fe-Based V Containing Multi-Component Cast Steel with Ni

Hot hardness and oxidation property of target material influences greatly on the erosion behavior at elevated temperature. The correlation between hot hardness and oxidation property of multi component white cast irons and its erosion resistance were investigated, and try to estimate the high temperature erosion behavior in the study. Nine kinds of multi component white cast iron and cast steel were used in this study. Specimen were machined into a flat plate with dimension of 50×50×10 mm. High temperature erosion test machine was used to investigate the erosive wear property of experimental materials at 1173K. Alumina grits (average diameter: 1.16 mm, hardness: 1250 HV1) which were used as impact particles were heated to 1073K and shoot on the heated specimen by hot air at the velocity of 100 m/s. The total particle loading was 2 kg. In order to clarify the correlation of hot hardness, oxidation property and the erosion resistance of specimens, hot hardness test was carried out specimens, to estimate erosion damage caused by solid particle. Hot hardness of specimens showed a value comparable to 200～250HV1. Result of erosion and oxidation tests, erosion rate and amount of oxidation of the specimen were suppressed by Ni addition. It suggested that the more amount of Ni contents, the lower the erosion rate and the less the amount of oxidation.

Mechanical Properties and Thermal Expansion Characteristics of Low Thermal Expansion Ductile Cast Iron with same Nickel Equivalent (NiE)

Low thermal expansion ductile cast iron is expected to become a new structural material with high dimensional stability against temperature change. We tried to develop a new low thermal expansion ductile cast iron by means of adding C and Si to Superinver alloy. In this study we prepared four kinds of ductile cast irons whose Co contents vary from 0% to 12 %, and investigated about the effects of Co content and solution-treatments on several main characteristics such as coefficient of thermal expansion and mechanical properties. The results obtained are as follows: With increase of Co content the amount of martensite increases but this martensite can be inverse-transformed to austenite totally or greatly by solution-treatment followed with water-quenching. In the case of Co content less than some 9 % the ability of relatively larger plastic deformation can be expected in inverse-transformed austenite.

Effect of C and Si on mechanical properties of austempered ductile iron

It is well known that ductile cast iron can be strengthened and toughened by austempering. The tensile strength and the fatigue strength of austempered ductile iron (ADI) are equal to those of forged steel. Previous studies have been aimed at establishing a suitable process to obtain both strength and toughness in ADI.1,2 These studies focused on the effect of alloying such as Mo, Ni, Mn, Cu, etc. and the austempering conditions such as temperature and holding time. In this study, a new type of ADI with higher toughness and higher elongation was developed as compared with conventional ADI. A new type of ADI with a low carbon content was achieved by reducing the initial carbon content, long annealing and ordinary austempering. The suitable silicon content was found to be 2.5% and effective alloying was 0.25% Mo and 0.7% Cu to obtain maximum impact energy and elongation.

Effects of Sulphur, Titanium and Zirconium on the Shape of Solid-Liquid Interface in Fe-C binary alloys

The effects of sulphur, titanium and zirconium on the shape of the eutectic solidification interface in Fe-C binary alloys were investigated by the quenching into ice water during unidirectional solidification. The oscillatory schematic model for graphite branching is proposed by considering the shape of the solidification interface and the protuberance length of the graphite flakes. The specimens contain 0.012, 0.108, 0.37 mass % S, 0.177 mass % Ti, and 0.078 mass % Zr, respectively. They are 80 g in weight, 18 mm in diameter, and 55 mm in length. The temperature gradient at the solid-liquid interface is about 2.5 K/mm.