The concept that the toughness of low and medium strength steels is well defined by the two parameters δ_i (COD at fibrous crack initiation) and T_i (fibrous-cleavage transition temperature in fracture initiation) has been applied to the toughness evaluation of welded joint. Tests were made on the coarse-grained region of the heat-affected zone (HAZ) of SM50C by using 3 point bend specimens in the tem-perature range from -196°C to room temperature.
Although δ_i of HAZ specimen takes almost the same value as that of base metal, T_i's of HAZ specimens show high temperatures than those of the base metal by 60°-70°C, for both fatigue-precracked and 0.1R mechanical-notched specimens. The value of the stretched zone depth (SZD) measured on the fracture surface shows the value of COD at fracture initiation regardless of the material (base metal or HAZ) and fracture mode (fibrous or cleavage). Therefore, the toughness of a welded joint could be evaluated by SZD instead of COD.

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Fatigue test was performed on a base metal and weld metals of 5052-O aluminum alloy having each solidification structure of columnar crystals, feathery crystals and equixaed dendrites. Investigations have been made on the relation between the weld solidification structures and fatigue characteristics.
The fatigue strengths of the weld metals were less than the strength of the base metal. In the weld metals the strength of equixaed dendrites was the highest. In the base metal, columnar crystals and equiaxed dendrites, anisotropy of the fatigue strength was not observed. In feathery crystals, however, the anisotropy was observed. The crack propagation rates in the weld metals were less than the rate in the base metal. In the weld metals the rate was the lowest in equiaxed dendrites and the highest in columnar crystals. In the feathery crystals the rate was almost the same as that in columnar crystals when the growth direction of feathery crystals was parallel to the direction of propagation of fatigue cracks. When the growth direction of feathery crystals was normal to the direction of propagation of fatigue cracks, however, the rate decreased to that in equiaxed dendrites. Besides, it was made clear from the obser-vation of the feature of fatigue crack propagation that the cracks propagated very easily along twin planes of feathery crystals.

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Weld decay in SUS 304 is a well-known phenomenon. The cause is said to be M₂₃C₆ precipitated in HAZ during welding. Many investigations have been carried out concerning the precipitation behaviour of M₂₃C₆ in SUS 304. However, few investigations about one during thermal cycles have been conducted. Consequently, the precipitation behaviour of M₂₃C₆ in HAZ of SUS 304 is not yet made so clear as that during the isothermal heat treatment.
In this report, in order to make clear the precipitation behaviour of M₂₃C₆ in HAZ of SUS 304, the method called "additivity rule", predicting the phenomenon during thermal cycle from one during the isothermal heat treatment was applied and its validity was considered.
The results obtained in this report are as follows;
1) The deterioration of corrosion resistance of SUS 304 not only in weld decayed region but in the region located between that and the weld metal in HAZ is caused by the precipitation of M₂₃C₆.
2) The beginning time for the precipitation of M₂₃C₆ during thermal cycles can be calculated from the precipitation curves of M₂₃C₆ during the isothermal heat treatment by applying the "additivity rule".
3) The region where M₂₃C₆ precipitates in HAZ during welding can be also predicted by applying the "additivity rule".

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It is reported that reheat crackings in steels initiate at stress concentrated regions like a toe of weld. If materials have excellent deformabilities at such stress concentrated regions, no reheat crackings occur. Consequently, the deformability at the stress concentrated region can be used as one of parameters to

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Structure and mechanical properties of heat resistant superalloy Inoc. 713C joint bonded by TLP (transient liquid phase) method being a new diffusion bonding process have been investigated fundamen-tally. Bonding was carried out by using insert metal (Ni-15Cr-3.5B) in a vacuum induction furnace, following by subsequent post heat treatment in order to promote homogenization in compositions. The following results were obtained.
1. With increasing the bonding temperature and time, the structure at the bonded interface was improved and became similar to that of the base metal. On the other hand, when bonding was achieved in relatively low pressure, grain coarsening occurred near the bonded interface, on the contrary, the bonded interface made in the high pressure seemed to remain' as grain boundary.
2. In bonding for about an hour, the constitution of the bonded interface considerably resembled that of the base metal.
3. Solidification time of insert metal estimated from diffusion state of boron was approximately agreed with the result of structure observation.
4. By selecting the suitable bonding conditions, tensile strength was easily equivalent to the base metal and also fairly good results about the creep strength were obtained though scattering somewhat.

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This paper describes an experimental study on the tensile characteristics of welded polypropylene at low temperature. The results of some measurements on the mechanical properties, fracture surfaces and X-ray diffraction patterns are reported and discussed.
This study intends to clarify the low temperature characteristics of welded part comparing, with those of

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From the viewpoint of soothing the bond embrittlement of large heat input welding such as electrogas arc and electroslag welding, design of chemical compositions of steel was carried out. Lowering the Si-content and B-addition were found to be very effective in order to improve the notch toughness of the weld bond, and low Si-Cu-Ni-Mo-V-B steel was adopted for 60 kg/mm² tensile strength steel plate (quenched and tempered). The steel plate manufactured by a 250 ton converter following the aimed chemical com-positions showed very excellent notch toughness at the weld bond even in large heat input welding more than 100 KJ/cm.

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