Isao Okane

Fatigue crack growth rate of brazed joint.

It is well known that fatigue crack propergates accompanying a small scale yielding at the crack tip. In filler metal between base metals of brazed joint, fatigue crack growth rate depends possively on the degree of restraint of crack tip plastic deformation by base metals, because the width of crack tip plastic deformation zone is nearly the same with the width of joint gap and crack tip plastic deformation can be restrained by base metals.The theoretical discussions on correlation of crack tip plastic deformation and base metals revealed;1) The degree of restraint of crack tip plastic deformation by base metals depends on yield strength of filler metal in joint gap, stress intencity factor and joint gap.2) Under shear stress, crack tip deformation is restrained when joint gap is smaller than a certain scale, and fatigue life of joint becomes longer.3) Under tensile stress, base metals do not restrain a crack tip plastic deformation, and fatigue crack growth rate depends on stress concentration factor range which becomes greater with the width of joint gap.Some experiments on fatigue crack propergation rate in copper filler metal of steel butt joint showed good agreement with the theoretical assumptions.

High Temperature Properties of Brazed Joint with Filler Metal Containing Palladium

The creep rupture test at 600°C of brazed joint of AISI 316 type austenitic stainless steel has been examined. The brazed joint was made with 21 Pd-48Ni-31 Mn filler metal under the heating conditions of 1, 180°C×2 min and cooling rate of 130°C/min in 5×10-4 Torr atomosphere.From the test results, it is clear that the brazed joint used is difficult to apply in practice, because of the very scattered values of its rupture strength. This unstable test results are cused by microcracks in the dendrites occured at solidification of filler metal. Accordingly, an improvement of the brazed joint may expected by controlling the growth of dendrites. In this study, this control is carried out with the addition of a little titanium to the filler alloy used, for the prevention of the growth of dendrites in brazed metal.

Study on Press-sintering of Sprayed Coating

The press-sintering process of the sprayed coating to improve the denseness and the bonding of the deposited coating has been developed. This new process is superior to the conventional fusing process in which the structural change and the thermal strain of the substrate take place during the treatment. Then, the press-sintering process is applied to a Nickel base self-fluxing alloy coating deposited by oxy-acetylene flame spraying process. Some properties of the press-sintered coating are also investigated.In conclusion, it is clear that the coating, sintered under suitable pressing, has almost the same denseness and bonding as the fused coating, and a higher wear resistance than the fused one.

A study on Rupture properties of Large Welded Specimens of HT70 Steel for Nuclear Pressure Vessels (Report 1)

In the foregoing reports, comparison in creep rupture strength between large and small size welded specimens, discussion on the mechanism of creep rupture and the influence of heat treatment after welding were made. In this report, the difference in rupture configuration between large and small size welded specimens, and welding methods viewed from creep rupture configuration are discussed.The large size welded specimens are ruptured at the heataffected zone of base metal (HAZ) near the bond, while the small size welded specimens are ruptured at HAZ near the base metal. The plate thickness of the steel used is 30 mm, and the welded joints are made by multi-layer welding. Therefore, it may be considered that the properties at welded joint of specimens of both sizes are different. It is clear from the foregoing report that creep strength may be proportionate to the absorbed energy to rupture in a high temperature tensile test. Therefore, tensile tests at 450°C on synthetic HAZ specimens, with respect to the coarse grain part near bond and the fine grain part near base metal in HAZ of small size welded specimens, are carried out to measure the absorbed energy. The value of absorbed energy in fine grain part is less than that in coarse grain part. Consequently, it may be considered that small size welded specimens are ruptured at fine grain part of HAZ near base metal, while large size welded specimens are ruptured at coarse grain part of HAZ near bond.The creep rupture configurations of large size specimens are discussed in various ways. As a result, it is believed to be desirable for improving the creep rupture strength of welded joint to make the pentration of the final bead as shallow as possible.