Time variation and final residual deformation of rectangular plate when heat is delivered at one edge χ=0 at t=0, elasticity being assumed to be constant for T<Ts and becomes to zero for T>Ts. By substituting the input heat as initial average temperature rise Tavo of the whole plate, the deformation is treated in dimensionless form as function of Ts/Tavo, though Ts is assumed as 700°C for convenience. Fig.8 shows the time variation of deformation defined in equ. (1), (10), (11).Fig.14 shows the relation between the residual deformation and input heat.
The fracture toughness in a low alloy welded steel has been examined with particular reference to HAZ microstructures. It is shown that a wide variety of structure in the HAZ adjacent to fusion boundary through thickness is produced by virtue of the different thermal histories experienced by each part in a multi-pass welded low alloy steel. The HAZ microstructures can be classified into seven distinct kinds (named A, B, C, D, E, F and G) according to the microscopic constituent and grain size. Fracture toughness dependence on the HAZ microstructures is demonstrated by instrumented Charpy dynamic Kd and static COD test on small specimens taken from the full thickness welded plate. The slit tip is carefully located in the HAZ adjacent to fusion boundary. The results make it clear that static COD test is more available for assessing fracture toughness dependence on the HAZ microstructures than instrumented Charpy impact test. The martensitic-bainitic HAZ microstructures (A, B and C) which are localized in the vicinity of the weld toe fusion boundary impair most significantly of all the HAZ microstructures. Furthermore, the emphasis must be placed upon the fact that martensitic-bainitic HAZ microstructure G tempered at relative high temperature during following welding process has excellent toughness, although .the microstructure G seems to be similar to the microstructure of weld toe HAZ.
In a previous paper, we have shown the effect of welding conditions on welding deformations in bead-on-plate test. In the present report, we deal with the effect of welding conditions on welding deformations in multipass welded butt joint. The results obtained in this report are summarized as follows: (1) Welding deformations in multipass welded butt joint are derived by the use of conventional formulae of welding deformations in bead-on-plate test. (2) Effect of welding process on welding deformations in multipass welded butt joint depends on specific deposited heat. (3) Welding deformations in multipass welded butt joint are decided from total number of beads N, which is functions of thickness, heat input, bevel angle, density of wire and specific deposited heat.
A new method of resistance butt welding without the end preparation of workpieces is developed. The influence of welding current and initial platen velocity on the process of the weld formation are discussed and the mechanical and metallurgical properties of the welded joints are experimentally investigated. In conclusion, the welded joints with good quality can be easily obtained under certain welding conditions by new resistance butt welding process and in this welding process, the abutting surface of the workpieces is fused by intensitve Joule's heating due to high current density and high contact resistance constructed by the flashing of 1-2 cycles, and the oxide at the interface of the welded joint can easily disperse into the molten metal layer in the weld.
Occurrence of reheat cracking is promoted by presence of elements which show a precipitation hardening phenomenon. It might be natural to consider the secondary hardening phenomenon, during stress relief heat treatment, is a factor controlling the tendency of the cracking behaviours. In this report, investigations have shown that one of the materials, which were used to examine the phenomenon, namely Nb-Mo type 80 kg/mm2 class steel—precipitation hardening steel—, showed very low susceptibility to the cracking comparing to T-1 type steel. Therefore it is neccessary to reconsider if there are relations or no relations between cracking susceptibility and secondary hardening phenomenon. In this study, these phenomena were examined measuring the hardness and strength at high temperature of HAZ and the conclusions obtained were as follows;- (1) There is no relationship between the second precipitation hardening and the susceptibility of the cracking and also it can be said that high hardness value of HAZ at high temperature does not correspond to high susceptibility of the cracking. (2) It can be said that when the strength of HAZ at high temperature is high, the susceptibility of the cracking is low and when the strength is low, susceptibility is high. Therefore the strength of HAZ at high temperature, where the appearance of fractured surface has the typical grain boundary fractured one, plays very important role, in another expression, boundary strength of HAZ at high temperature is one of the main factor influencing the cracking.
Roughness of the surface to be welded is one of the important factors affecting the weld characteristics on the diffusion welding. The purpose of this study is to investigate the influences of the surface roughness upon the welding process and the weldability of diffusion welds, using copper bars treated by various surface polishings. The following results were obtained. 1. Size and shape of void on welded interface depend upon roughness and shape of welded surface. The rougher surface promotes the decrease in size of void and the increase in the number of void. 2. The welding process may be considered in terms of the four stages. A clearly defined demarcation between stages does not exist, and the stages overlap. the first stage: the growth of the welded area depends upon the plastic deformation. the second stage: the growth of the welded area depends upon the creep deformation. the third stage: the shrinkage and the elimination of voids on the weld interface occur due to the mechanism of sintering. the fourth stage: all voids shrink, and the original weld interface disappears or migrates. 3. The second stage of the welding process is due to welding pressure, temperature and time. And the finer surface roughness is, the shorter this stage is. 4. The third stage is closely related to surface roughness. The shrinkage of voids in diffusion welding is similar to one in sintering, and begins to be promoted when the radius of void decreases to 2μ. 5. Welding pressure is effective to promote the third stage.