This paper deals with the effect of welding conditions on separating forces produced in restraints like strong backs or tack welds during butt welding. The calculations have been carried out on variations of separating forces during welding under various conditions of heat input, plate length and restraint or tack weld pitch, using the finite element method explained previously. It is assumed that the rigidity of restraints and tack welds is infinite. The main conclusions obtained in the study are summarized as follows: The larger the effective molten pool length on the mechanical point of view (lM) is, the larger is the difference of separating forces between restraints and tack welds. The result depends on the type of restraint: in case of restraint like strong back, the restraint acts as a restraint after heat source passed through it, but in case of tack weld, the tack weld melts and cannot act as a restraint after heat source passed through it. The maximum separating force produced in an end restraint or an end tack weld ((Fy/h)emax) can be characterized as follows. (Fy/h)emax in the end tack weld is smaller than in the end restraint under the following conditions: lp=1200mm 416≤lM≤1663 (mm) 6000≤q/υh≤24000 (cal/cm2) where lp is a restraint or tack weld pitch, lM is an effective molten pool length on the mechanical point of view and q/υh is heat input per unit thickness and unit weld length. (Fy/h)emax increases as the heat input (q/υh) increases under consta-nt lM and decreases as the effective molten pool length (lM) increases under constant q/υh. Effect of plate length (L) on (Fy/h)emax depends on the welding conditions (q/υh, lM) and plate length (L). A restraint pitch has larger effects on (Fy/h)emax than a tack weld pitch. These results can be applied to tow electrodes submerged arc welding under the conditions that distance between leading electrode and trailing electrode (lLT) is small compared to lM.
Effects of welding speed, micro-alloy element and amount of C on the weld solidification structures have been investigated using TIG welds of mild steels and carbon steels (0.36 wt% C) with a micro-alloy element, such as Ti, Nb and Zr. The results obtained are as follows. (1) The weld solidification structures are changed by welding speed, that is, axial crystal is developed at slow welding speed, stray crystal and columnar crystal at moderate and equiaxed dendrite at high. (2) The weld solidification structures are also changed by addition of the micro-alloy element. For specimens with the micro-alloy element, axial crystal is not obtserved and equiaxed dendrite is developed at lower welding speed in comparison with specimens without the micro-alloy element. (3) The formation of equiaxed dendrite is influenced by kind and amount of the micro-alloy element and G/R (G: temperature gradient, R: growth rate). When TiN and TiC etc., these disregistries are small, exist in molten pool, heterogeneous nucleation occurs easily and the ratio of equiaxed dendrite zone to the bead width becomes larger.
In this study, the effect of phosphorous on the crack initiation stress at grain boundary at 600°C was researched using reheat crack sensitive HT80 and A387-12 steels, and insensitive A533B-C1.1 steel. From the experimental results, it was concluded that phosphorous atoms segregated to grain boundaries in these steels during heating up to 600°C and as the results, the cohesive strengthen of grain boundaries were decreased in proportion to segregated content of phosphorous at grain boundaries.
Mechanical properties of austenitic stainless steel friction welded joint have been studied in connection with the amount of non-metallic inclusion, namely sulfur content, in base metal. In this experiment, the effect of sulfur content of base metal on tensile strength, elongation, reduction of area, and Charpy absorbed energy of friction welded joint was investigated by changing the amount of sulfur in the region. of 0.014%-0.204%. The results obtained are summarized as follows. 1) Ratios of the effect of sulfur content on each of the mechanical properties of friction welded joint and those of base metal are 5:1 in elongation, 3:1 in reduction of area, , and 1:1 in Charpy absorbed energy. 2) Ductility and notch toughness of friction welded joint decrease with the increase in sulfur content of base metal. However, the effect of friction welding on the ductility of joint is slight, if the sulfur content is less than 0.025%. 3) Elongation of base metal is closely related to reduction of area and Charpy absorbed energy of friction welded joint. Therefore, it can be considered that the elongation of base metal is one of the indices to the friction weldability of that material.
Two of the authors have already proposed the general principles for measurement of residual stresses. In this paper, the authors develop a new measuring theory of three dimensional residual stresses in a long welded joint by using the theory of inherent strains, which is based on one of these principles. First of all, the characteristic of the distribution of its inherent strains induced in a long welded joint is clarified. This characteristic makes the measuring theory simple. According to this resulting theory, three dimensional inherent strains can be divided into the components of inherent strains contained in a sliced thin vertical cross section (T-specimen) to the weld line and longitudinal inherent strains contained in sliced thin plates (Li-specimens) parallel to the direction of the weld line. Then, the measurement of three dimensional welding residual stresses in a very thick plate has become practically possible. When residual stress distributions are uniform along the weld line, the theory should provide the exact measured ones. By this developed theory, the distributions of residual stresses in an electroslag welded joint are measured for the first time. And the estimated residual stresses show a fairly good coincidence with the directly observed stresses on its surfaces. It can be concluded that the present theory is reliable and practically applicable to measure such complex triaxial residual stresses.
The effect of retained austenite on notch toughness in HAZ of 9% nickel steel welds had been discussed in author's previous paper. In this paper, the above correlation and factors affecting on the formation of retained austenite during weld process were investigated in more detail by using the simulation technique. The obtained result indicated a noticeable effect of a peak temperature, in particular near 620°C being closer to Acc1 temperature (about 630°C), of secondary thermal cycle, after primary thermal cycle 850 to 1350°C, on the amount of retained austenite, and however, there was a lesser effect of another factors, such as heating and cooling rates etc. on it. In the other hand, since the formation of globular austenite occured rapidly and abundantly during heating process in welding, as comparing the ordinary heat treatment, there was a variation in the amount of the retained austenite in very short time if holding at the peak temperature of tempering cycle. It was found that there was a fairly good correlation between the amount of retained austenite and toughness. When the grains, however, were remarkably coarsened by the primary thermal cycle similar to that near weld bond, the toughness was no longer improved regardless of the amount of retained austenite, unless the secondary thermal cycle being above 800°C. This secondary cycle resulted in the grain refinement and the formation of the enriched zone of alloying elements, where the stable austenite precipitated in 3rd thermal cycle, mainly, at prior austenite grain boundaries.
Vibration and radiated sound during CO2 arc welding have been measured in order to analyze the behavior of the molten pool. The results indicate that the welding vibration such as the low frequency motion of the molten pool can be measured with accuracy by a piezo-electric accelerometer of sensitivity of 100 mV/G class, and that the welding vibration has a good competence as the information singal to exhibit the behavior of the molten pool.
With the view of developing the welding device for full automatic control of the horizontal narrow gap welding, we have applied the BIP (Binary Image Processor) system and its algorithm to the automatic measurement of the groove width, the automatic detection of the welding start and stop position and the weld line tracking. The groove width and the welding start and stop position can be measured with the accuracy of approximately 0.2 (mm), by applying the BIP system, the TV-camera, micro-computer system and the specific algorithm. The information for the weld line tracking can also be obtained, by using. the BIP system, the TV-camera, micro-computer system and the PMD (Position Measurement Device) system.