From the viewpoint of the prevention from being cracked by welding, it is greatly significant to adopt a post heating process in order to bring down the hardness of the hardened part in the welding heat-affected zone. Though there may be various kinds of post heating process, it seems the easiest to make use of gas flames. It was, however, not easy to heat exactly the part containing weld metal and heat-affected zone below the Al transformation point or above the As transformation point or at any other desired temperature. But "A process for local heating at constant maximum temperature with gas flames", which was published before by one of the authors, has made it quite easy. In this work, the outline of this post heating process was described first, and secondly the result of the experiment in which post heating of welded Dart of high tensile steel was done by using the equipment for this process was clearly shown. The experiment has confirmed that the hardened part in the welding heat-affected zone was surely softened by this process. Besides it was clarified that the hydrogen removal before immersion of welded part in glycerin was increased remarkably, if post heating is done just after completion of welding. But it goes without saying that the degrees of softening and hydrogen removal differ with the height of the maximum temperature and the proceeding rate of heating torch.
Transient temperature rise is calculated by using the newly derived formula n=eLR∝F0(δ) which is reported in Reference (2). Temperature curves of many points near arc starting and stopping points are drawn and comparison between them and those of quasistationary state is described and discussed. Fig. 1 and 2 show the calculated temperature curves of points which are illustrated in Fig. 3. The graphic way of drawing of these curves is shown in Fig. 19, 20 In these figures, the temperature rise as well as time elapsed are expressed in dimensionless quantities, temperature rise "n" is defined in equ. (1) and time elapsed vt=L is defined in equ. (3) and is illustrated in Fig. 4. In Fig. I and 2, curves (1) show the temperature curves of quasistationary state of the given points and (2) show the half values of (1). Curve (2) is very convenient for the consideration of the transient temperature. Fig. 10 and 11 illustrate the general characteristics of the transient temperature curves compared with (1) and (2). Fig. 5 and 6 show the maximum temperature, Fig. 7 shows the equithermal lines of maximum temperature and Fig. 18 shows it by experiment.
In previous report, we described the fundamental mechanism of penetration in electroslag welding considering the current and temperature distribution in slag pool. In this paper, the influence of some welding conditions (i.e. welding voltage, welding current, slag depth, root gap etc.) on the penetration of base metal is described using a certain flux. The experimental results are shown in Fig. 1-16. We see in Fig. 1 that the penetration decreases as the welding current is increased over a certain value under a constant terminal voltage. The decrease of penetration in spite of the increase of input power is worth notice, and the reason is given as follows. Fig. 7 illustrates the relation between the penetration and the wire tip position in molten slag pool. We know the penetration is affected by the mode of slag convection which is induced by the pinch effect of current flowing out from the wire tip. We see a poor penetration when wire tip is too near not to touch the molten metal pool, because the hot slag convection does not reach the side wall of base metal. When the wire feed speed is increased, the welding current as well as the steeping length of wire into the pool increases naturally under a constant voltage, and takes the mode of Fig. 7 (c). For given current, we see the increase of penetration for the increa of welding voltage as shown in Fig. 3. Increase of input power may be one reasen, but the change of wire tip position from Fig. 3 (a) to (b) or (c) is presumed as the main powerful reason. Effects of slag depth as well as root gap on the penetration shown in Fig. 11-14 can be understood in the same way.
It is well known that carbon in steel increases its strength but decreases its ductility and toughness. Recent welding technology required to get higher strength and toughness of larger weld metal. It is not always easy to realize these objects The purpose of this research is to know systematically the effects of elements of simultabeouly on the strength and toughness of weld metal. Especially the strength and toughness of extremely low carbon weld metal arenvestigated in order to find a proper electrode steel wire, which gives higher toughness and enough strength. Small tasted specimens were used for experiment instead of submerged arc weld metal. The results obtained as follows: 1. Extremely low carbon cast steel containing 0.01% C, 0.35% Si and 1.5% Mn gave excellent toughness and the same strength as mild steel. 2. 0.04% C cast steel gave the lowest transition temperature, compared as the lower and higher carbon cast steels. 3. The toughness of cast steel decreased steeply over 0.08% C or 2% Mn content.
A basic study on the dissolution of solid cobalt into molten copper was undertaken to obtain a fundamental knowledge in cobalt brazing. Cylinders were immersed in molten copper and then rotated under dynamic conditions of peripheral velocities from 19.0 to 61.5 cm/sec in the temperature range 1190°1340°C, the exposure time being from 45 sec to 120 sec. Rapid dissolvingof cobalt into molten copper occurred and the apperarnce of an etched surface after dissolution was observed. The rate of dissolution increased with an increase in temperature and rotational speed. A modified first-order kinetic equation was used to determine the dissolution-rate constants. These varied from 0.55 to 1.61 × 10-2 cm/sec depending on the temperature and the rotational speed, and were increased in proportion to 0.64-0.74 power of peripheral velocity. The activation energy for dissolution of solid cobalt into molten copper was estimated to be about 10.0 Kcal/mole. For a diffusion-controlled dissolution process, activation energy for dissolution is contributed to by the sum of activation energy for diffusion and some fraction of activation energy for viscosity. The dissolution rate of solid cobalt into molten copper is mixed-controlled.
The behaviour of grains and its boundaries in HAZ, accompanied with grain-coarsening and under stress conditions which are caused by solidification of weld metal or by welding heat, is related to hot cracking and embrittlement of HAZ. Moreover, grain-boundary migration plays an important role in hot working, creep and high temperature fatigue. In this paper, the behaviour of austenite grains and its boundaries of high strength steel during tensile deformation at high temperature around 1300°C was studied with microscope. The main conclusions obtained in this study are as follows: (1) Wide fluctuation of load was observed in load-elongation curves during hot tensile deformation. It was verified that its phenomenon is caused by dynamic recrystallization. The higher rate of deformation at high temperature around 1300°C and the lower rate at somewhat, lower temperature less than, 1100°C, the more easily dynamic recrystallization tends to occur. (2) The higherr rate of deformation at 1300°C, the higher grain-boundary migration rate and the faster it was saturated. (3) Migration of grain-boundary triple point is caused by mechnical sliding at boundary and atomicdiffusion. Consequently the triple point migrates alternately and zigzag. (4) Dynamic recrystallized grains were observed. Its nuclei occured preferentially and accidentally at the place near boundary within a grain.