Takeo Tamura

Decomposition Behavior of Tungsten Carbide in Cemented Carbide Machined by EDM

Cemented carbides are composed of tungsten carbide and cobalt as a binder. Tungsten carbide (WC) can be decomposed into tungsten and carbon at about 620 in air, and the carbon that separates from WC reacts with oxygen to form carbon dioxide gas. In this study, these phenomena are applied to the electrical discharge machining (EDM) of cemented carbides in deionized water. First, using deionized water as the dielectric working fluid, it is ensured that dissolved oxygen exists in the liquid. Secondly, as EDM is a removal method based on melting and evaporation, the workpiece temperature around the sparking area exceeds the melting point of the material. Therefore, cemented carbides are machined by EDM in deionized water. As a result, it was found that the debris obtained during EDM is composed of tungsten (W) and tungsten oxide (WO3). Moreover, the carbon that separates from WC reacts with the dissolved oxygen in the gap between the electrode and the workpiece to form carbon dioxide gas. Thus, in the EDM of cemented carbides in deionized water, the removal mechanism based on the decomposition of tungsten carbide is in effect as well as that based on melting and evaporation.

Contributory Factors to Accurate Prediction of Rate of Stress Corrosion Cracking in Boiling Water Reactor Under Unexpected Condition During Operation: Part 3—The Effect of High Loading Rate on SCC Growth Behaviour

The goal of the study is to reveal the effect of high loading rate on the stable SCC growth behaviour of nuclear-grade stainless steel, SUS316L. To this end, the Split-Hopkinson pressure bar (SHPB) experiments on SUS316L were performed first to establish the dynamic tensile stress-strain response at strain rates up to 700s−1 . The analyses of dynamic stress intensity factors for wedge loading experiments on modified compact tension specimens during SCC test were then performed by the finite element method. The outline of the wedge loading experiments by the use of the Split-Hopkinson pressure bar is briefly mentioned in this paper as well.Copyright

Heat treatment of welds by pulsed YAG laser. Study of micro‐repair welding by pulsed YAG laser (Report 2)

To establish a fundamental technology for micro-repair welding of SKD11 alloy tool steel rotary cutters by pulsed YAG laser using SUJ2 high-carbon chromium bearing steel filler metal, the previous report in this series describes an investigation of the effect of the pulse number on the weld metal hardness and the bending strength of welds. It is well known that, when laser repair welding is performed with SUJ2 filler metal during this process, the hardness of the weld metal is lower than that of the SKD11 cutter base metal and that parts repair-welded by YAG laser are unable to assure normal rotary cutter functions. This paper examines a pulsed YAG laser heat treatment method and fundamental heat treatment conditions necessary to improve the weld metal hardness reduced by laser repair welding to a value of around HV680 as the normal base metal hardness of SKD11 alloy tool steel rotary cutters.

Effect of laser pulse shot number on hardness and strength of the welded zone study on micro repair welding by pulsed YAG laser (Report 1)

In recent years, as a substitute for reciprocating type cutters, rotary type cutters which are capable of high speed manufacture of blanks of paper and plastic materials etc. have been extensively employed in the manufacture of blanks for medical pads etc. including food and drink cartons. Rotary cutters, used for the continuous manufacture of blanks, are employed mainly for the production of paper receptacles consumed in a large volume, such as milk packs and coffee cups; however, during the manufacture of blank products, cutters sometimes become unusable following blade tip end fracture caused by the entanglement of foreign matter. Conventionally, repair welding of micro fracture zones of rotary cutters is carried out by a method of trial and error relying upon experience and intuition by means of TIG welding; however, weld defects, such as undercut and cracking occur frequently.