The characteristics of crack initiation were examined by Kinzel test about the heat affected zone of SM41 and SM58 steels. The hardnesses of HAZ(Hv) were changed in series by controlling the welding conditions. The notch sharpness (ρ) and depth (t) were also changed. The experiments were carried out to determine the load for micro-crack initiation (Pci) in the temperature ranges of cleavage and fibrous fracturing. Then, the critical value of crack initiating load (Pci) was defined as well as the critical temperature for crack initiation (Trci). At the same time, the max. load (Pmax) and general yielding load (PGY) were measured. The results obtained were summarized as follows. (1) The correlation between Pci, Pmax and PGY was clarified with Kinzel specimens having various notch shapes and hardnesses of heat affected zone. It was known also that the first micro-crack initiated would be of shear type, even in the temperature range of apparent cleavage fracturing above Trci. (2) The relations between Trci, Pci and t/ρ were indicated quantitatively. The correlations between Trci, Pci and Hv were also determined.
In previous report, various properties of weld metals with 16 Mn-16 Cr welding wire were investigated, which were deposited automatically by gas shielded arc welding process. The automatic welding being characterized by large heat input, the weld heat-affected zone (HAZ) extends over a wide area and, in the case of austenitic manganese steel, the embrittlement of weld HAZ is likely to aggravate on account of carbide precipitation. The following experiments, in this study, were made to reveal the deterioration of toughness as a part of the study on gas shielded arc welding. The thermal cycles in various parts of the weld were measured in single bead welding of austenitic manganese steel plates and continuous automatic welding (electrogas welding) of austenitic manganese steel rails. Based on the data obtained 15 simple thermal cycles (5 peak temperatures ×3 thermal cycle speeds) were selected, which were similar to those produced in actual weld. Austenitic manganese steel specimens were subjected to the above thermal cycles reproduced by synthetic thermal cycle apparatus, and to impact test as well as microscopic inspection. Deterioration of toughness in synthetic HAZ takes place around 650°C of peak temperature and it becomes heavy at low speed of thermal cycle. In that case, precipitations of carbides appear at intercrystalline boundaries. At over 1300°C of peak temperature, the toughness of synthetic HAZ decreases remarkably regardless of the speed of thermal cycle; this is due to the presence of intercrystalline cracks or cavities caused through heating. The toughness of synthetic HAZ at 650°C of peak temperature tends to be somewhat low when the impact test temperature is low (-40-20°C). Finally the decrease of toughness in weld HAZ was discussed from the standpoint of carbide-preciptation temperature-range in thermal cycles measured. Mention was also made of high temperature cracks observed.
A micro-cavity in a polycrystalline metal plays a role of barrier to the migration of grain boundaries. It is presumed from previous investigations that a number of micro-cavities remain along the weld interface of solid phase welds and impede the migration of grain boundaries at high temperature. The solid phase welds in pure copper were made in 5 minutes at 400°C with about 30% deformation in thickness in high vacuum. Post-heat treatments were carried out on such welds at temperatures in the range 900-1060°C in high vacuum. The result was examined metallurgically and it was concluded that a migration of fixed grain boundaries on the weld interface occurred across the weld interface when a shrinkage or elimination of micro-cavities on the weld interface was accomplished by the volume diffusion of atoms from the grain boundaries to the micro-cavities during post-heat treatment. From this point of view the metallurgical mechanism in solid phase welding was considered.
In this report, authors have discussed the spreading phenomenon of solders on the Fe plate, Cu plate and BsP3 plate. The results obtained from this investigation are as follows. (1) The spread area of Sn-Pb solder on Cu and BsP3 plates is more increased by using ZnCl2+SnCl2. This is owing to make Cu-Sn alloy layer on above plates contacted with flux by adding SnCl2. On the other hand the spread area of Sn-Pb solder on the Fe plate is decreased by adding SnCl2 in ZnCl2. (2) The spread area of tested solders on above plates is increased by using ZnCl2+NH4 Cl flux. It seems that increases of spread area is caused by HCl from heat dissolution of NH4Cl. And increases of spread area is not affected greatly by reducing action of interfacial tension between solders and fluxes. (For example, value of interfacial tension between molten Sn and molten ZnCl2+NaCl+NH4Cl flux is nearly equal to molten Sn/ZnCl2 interfacial tension value, nevertheless value of spread area of solder with ZnCl2+NaCl+NH4Cl is larger than ZnCl2 flux.) (3) The spread area of 50% Sn-50% Pb solder is reduced by adding small quantity of Sb. (4) The flux turns into active by adding NH4Cl in various fluxes, but addition of KCl, NaCl and KCINaCl have little effect.
In this paper, it is tried to clarify the behaviour of the fatigue crack propagation in the, central slitted specimens with finite width of structural steels, mild steel, 60 kg/mm2 high strength steel (HT 60) and 80 kg/mm2 high strength steel (HT 80), under pulsating tension. As a result of the fatigue test, the following facts were repealed: 1) As shown in Fig. 2, S-N curves of mild steel and high strength steels (both of HT 60 and HT 80 are almost same) cross each other at the stress level of about 12 kg/mm2, and high strength steels are more advantageous than mild steel in the range of higher stress level but are not at lower stress level. 2) The difference of fatigue strength of the central slitted specimen with finite width is dependent on the fatigue crack propagation process. In mild steel, the incubation phenomenon is very remarkable, as shown in Fig. 7, and it has effect on its fatigue life. 3) "Fourth power law" proposed by Paris et al. can be applied to the behaviour of the fatigue crack propagation in the central slitted specimen with finite width of high strength steels (Figs. 8 & 9). However, it can not be applied to that of mild steel because of a remarkable incubation phenomenon (Fig. 10). 4) The plastic behaviour near the crack tip is related to the fatigue crack propagation. The plastic zone size and the deformation of the crack tip are small in high strength steels as shown in Photo. 2 and the fracture mode would be subjected to maximum tensile component in stress field at crack tip. However, they are very large in mild steel (Photo. 3), and the mode would be related not only to maximum principal stress at the crack tip but also to other stress components, slip deformation, work hardening, etc.
Effects of the nitrogen partial pressures in the welding atmospheres of several gas mixtures and welding conditions on the nitrogen content and porosity of titanium weld metals were systematically studied. The important conclusions obtained are as follows; 1. Titanium weld metals absorb large amounts of nitrogen in arc welding in atmospheres with rich nitrogen. 2. The nitrogen content of titanium weld metals decrease with an increasing welding current as in other metals. 3. The existence of an oxidizing gas in arc atmospheres does not contribute to the enhancement of nitrogen absorption into titanium weld metals. 4. Nitrogen absorbed causes porosity of welds.