A atudy is made on structural features and mechanical properties, especially on notch toughness of duplicated weld heat-affected zone and multi-quenched steel similar to refined weld heat-affected zone for Si-Mn and Si-Mn-Cr-V steels by induction heating and tempering in furnace, based on the results of notch toughness surveys of welded joint for quenched and tempered steel. Refined microstructure in weld heat-affected zone is produced by rapid heating and cooling thermal cycles above Ac1 temperature, whose maximum heating temperature are presumed to be lower in later ones. Shift of Ac1 and Ac3 transformation temperature was little observed, as compared with that of slower rate of heating, however, tranformation products in cooling were much influenced by heating temperature of thermal cycles, being martensitic in higher heating temperature, whereas rather ferritic in lower temperature. Hardness in duplicated weld heat-affected zone initially heated to 1350°C was lower after subjecting to the thermal cycles of lower heating temperature. Carbide grains in those steels were rather globular than ordinarily quenched and tempered steels. Subjecting to singly quenched thermal cycle, steels had the best notch toughness, when heated to just above Ac3 temperature followed by tempering, and toughness of singly quenched steel was improved further by repeated heating between Ac3-Ac1 temperature range followed by tempering. Microstructure of those steels consists of extreamly refined ferrite and globular carbides in both Si-Mn and Si-Mn-Cr-V steels, thus suggesting superior impact properties of those steels and special heat treatment for such steels. Generally steels have the poor impact properties, when repeatedly heated between Ac3-Ac1 temperature, however, tempering treatment gives the favourable effect on the impact properties.
Behaviour of failure in fillet welded joints at low temperature has been seldom inspected, and the fillet welded joint of anti-corrosive steel including a comparatively high P content is thought to be under the condition that brittle fracture is apt to be caused at low temperature. The behaviour of failure in various fillet welded joints at various temperatures is, therefore, investigated in connection with the investigation of resistance to weathering, weldability, workability etc. of arc welded joints. In the temperature range -120°C-120°C, fracture characteristics of various fillet welded joints under tension are classified in Table 4. The fracture of fillet is classified into two types, i.e. ductile fracture and brittle fracture ; and fracture transition temperatures are obtained rather distinctly. In the case of front fillet weld, the angle of ductile fracture is between 15°and 30°, and on the other hand, that of brittle fracture is almost invariably over 45°, increasing with decreasing temperature and reaching 70°-80° at about -110°C. In the case of side fillet weld, shear fracture does not occur at the throat section which is minimum section under -60°C, and brittle fracture occurs at the end of fillet in the base metal. The above-mentioned behaviour is thought to be attributable to the fact that the fracture stress of side fillet weld is mostly a shearing stress ; therefore, as at such a low temperature the material becomes very brittle and slip deformation is restrained, the shear strength of fillet exceeds the cohesive strength of base metal remarkably. The strength of double T fillet welded joint rapidly decreases under -80°C. This behaviour is thought to be caused by the fact that at such a low temperature, the material becomes very brittle, slip deformation being restrained, and stress concentration rapidly increases. If general condition of ductile fracture and brittle fracture due to combined stresses is assumed as follows : R=τ/σ><t/N, the ratio of shear strength to cohesive strength (t/N) will be about 1-1.6, and very larger than the ratio of shear strength to tensile strength (t/n), at -60°C-20°C.
In this report, author has studied for welding condition and mechanical properties of weld joint by newly developed self preheating thermit welding on the basis of the first report stating the research for thermit mixture. The results are as follows ; 1) The effect of refining time on soundness of thermit steel is evident, and this tells that an appropriate refining time gives a good notch toughness and elongation ratio to thermit-steel. For 22 mφ reinforcing bar, 3 to 5 seconds refining time seems to be fitting. 2) 30% thermit steel accomplished the purpose of preheating. If less than 30 % is used, the preheating tends to be insufficient and necessary joint strength is not secured. 3) Welding gap chiefly depends on the relation between cross section of bar and sprue. A good result is obtained when welding gap is 15-35% of minor axis of oval sprue. 4) Tensile strength of weld joint is stronger than reinforcing bar. 5) In other mechanical properties, joint strength by this thermit process compares favorably with that of other processes. Therefore, the thermit welding by self preheating type can be easily and satisfactorily applied to field welding for reinforcing bar.
In the previous report the outhors described a device, specially designed, for the wettability test and the values of the surface tension of the Pb-Sn alloys, which were measured with the device. The present report describes the results of experimental measurement of the wettability, i.e. the interfacial tension, contact angle, work of adhesion and wetting index, for the Ag-Cu alloys and also for the commercial braze (Ag-Cu-Zn alloy). It contains the following. 1) Measurement of the densities of the Ag-Cu alloys at elevated temperatures. The density of metals and alloys at elevated temperatures has not so far been measured. To calculate the surface tension, it is necessary to determine the density, so the latter was measured for the Ag-Cu alloys at 900-1000°C, appling the above device. 2) Measurement of the surface tension at elevated temperatures. The values of surface tension of the Ag-Cu alloys measured at 1150°C and the melting point plus 100°C are given Fig. 5. The results for the commercial braze are in Fig. 7 3) Determination of the wettability. The contact angles of the Ag-Cu alloys for the stainless steel (SUS 27) plate were measured. From the measured values and the interfacial tension, the works of adhesion and the wetting indexes were calculated (Fig. 6). These vlues calculated for the commercial braze are given in Fig. 8.