Yuichi Tanaka

Relationship Between Some Physico-Mechanical Properties and Numerical Indexes of Graphite Shape in Compacted-Vermicular Graphite Cast Irons

The main purpose of this paper is to present some data on the mechanical and physical properties of compacted-vermicular graphite cast iron and to give a reasonable interpretation to the characteristics by using numerical indexes indicating the shape of graphite flakes in the structure. After describing the preparation of the material and a new method for measuring thermal diffusivity of the iron, the influence of kind and amount of alloy added for treatment and of cooling rate upon the graphite shape is discussed by using the indexes of the structure. The thermal diffusivities and mechanical characteristics such as tensile strength and hardness are shown as functions of the indexes to clarify the relationship between them. Furthermore, the present indexes are compared with those proposed earlier to find which is most suitable for the cast iron treated in this work. Authors propose a definition of compacted-vermicular graphite cast iron, which is reasonable from the physico-mechanical point of view, and also show some typical mechanical properties and measures required to produce such cast iron with desirable features.

Influence of water embrittlement effect on mechanical properties of ADI

Water embrittlement in ADI has been studied experimentally for several loading conditions. The phenomenon has been explained on the basis of a hypothesis of hydrogen embrittlement. In addition to conventional tensile specimens, hole-edged CT specimens that can be used to measure the bending load were used. It was found that the latter were more susceptible to water embrittlement than the former, at the maximum tensile load. Some specimens were pre-strained in dry conditions before tensile testing in wet conditions. Specimens that had been pre-strained to values beyond the non-prestrained water rupture point exhibited very similar values in their rupture strain and rupture stress, regardless of the pre-strain value. A hydrogen embrittlement hypothesis is proposed to explain the experimental fact that the water embrittlement effect is observed for ADI but not in the case of a ferrite matrix.

Effect of Temperature on Plastic Buckling Strength of Shot Peened Pipe of Magnesium Alloys

This paper deals with the effect of temperature on plastic buckling strength of cylindrical pipe of some magnesium alloys subjected to shot peening process. Workpieces are three cylindrical pipes of AZ31, AZ61 and AZ80 magnesium alloys. The shape of pipe is 30mm in height, 16mm and 14mm in outer and inner diameters. The shot peening treatment was given on the surface of cylindrical pipe using an air-type peening machine. Plastic buckling strength test was performed under axial compression in a case of both ends with fixed condition, at several temperatures between 293K and 573K and at a crosshead speed of 1 mm/min using an Instron-type testing machine. From the experimental result, buckling stresses for all kinds of AZ31, AZ61 and AZ80 alloy pipe were strengthened after the shot peening treatment, but a few of differences for the increasing ratio. The buckling stress of the shot-peened pipe was kept higher than that of as received one up to the test temperature of 473K, however it tended to be around equal at 573K.

Influence of Hardening Hardness on Heat Crack Formation of Hot Working Die Steel for Aluminum Die Casting.

Thermal fatigue characteristics of die steel for hot working SKD 61 and improved SKD 61 were investigated. The cylindrical test bars with U-notch were directly immersed into Al-alloy melt kept at 923K, and then cooled quickly to water. The investigation led to the following conclusions : 1) The number of heat cracks of the improved SKD 61 was fewer than that of SKD 61. It was especially pronounced in the hardness of HRC 45 or more. 2) The heat crack length of SKD 61 and the improved SKD 61 became small as the hardness increased. The minimum value of heat crack length was obtained the specimen with HRC 50. The total length of heat cracks of the improved SKD 61 became about 1/4 that of SKD 61. The maximum length of it became about 2/5 of SKD 61. 3) The heat crack resistance of the improved SKD 61 is superior to the resistance of SKD 61, because the tensile strength of the improved SKD 61 is higher than that of SKD 61 over the whole testing temperature.