This paper discribes micro deformation of filler metal at brazed butt joint under pure, shear load. We measured static torsional deformation of butt joint of two types of carbon steel and pure iron brazed with pure copper. Filler metal at brazed joint proved to have a certain yield stress which was not simply related to the joint clearance and the strength of base metal. The experimental results have good agreement with the theoretical presumptions.
In the process of fabrication of large size penstock, thick plate is used and cold bending and welding are applied. The resulting residual stresses should exhibit complex three dimensional distribution. These residual stresses should influence brittle fracture and fatigue strength. Therefore, it is worthwhile to measure these residual stresses as accurate as possible. The authors presented the new measuring principle based on the theory of inherent strains and developed several measuring methods for three dimensional residual stresses, which were very accurate, judging from the theory of elasticity, although some approximate methods such as Rosenthal-Norton Method have been used so far. In this paper, the authors develop a new measuring method of residual stresses due to cold bending. For actual measurement, a large size model of penstock of 80 kgt/mm2 class high tensile strength steel plate is fabricated. Residual stresses due to cold bending are measured in the shell plate. Welding residual stresses at the longitudinal and circumferential weld joints are measured by the method which the authors presented before. It is observed that the maximum residual stress is about 50 kgf/mm2 to 60 kgf/mm2 which is less than the yield stress of the material.
The effects of V on creep rupture properties and high temperature mechanical properties of 308 stainless steel weld metals for use of the welded joint of pipe and vessel in the fast breader reactor are investigated and the results obtained are sumarized as follows. 1) Tensile strength and rupture elongation of 308V weld metal almost coinside with those for SUS304 stainless steel in the temperature region between 500°C and 600°C. 2) Under certain circumstances the creep rupture strength and creep rupture elongation of 308V weld metal are higher in comparison with those for SUS304 stainless steel. 3) High temperature tensile properties of 308V weld metal are almost same as those for 308 weld metal, on the other hand creep rupture strength and creep rupture elongation of 308V weld metal are higher as compared with those for 308 weld metal. 4) Superior creep rupture properties of 308V weld metal as compared with those for 308 weld metal are caused by the following factors. i) V contents in the austenite matrix of 308V weld metals are three and a half times to five times as mutch as that of 308 weld metal. ii) Fine precipitates containing V are formed in the austenite matrix of 308V weld metal in the course of creep rupture test. These fine precipitates are difficult to remelt in the long time creep rupture test. V-less fine precipitates formed in 308 weld metal remelt in austenite in the creep process easily. iii) When multiplied dislocations locked by fine precipitates, recoverly and recrystallization are delayed in the creep process and high dislocation density is kept on the steady state creep process. Creep strength is strengthened progressed as discribed above. iv) In proportion as fine precipitates remelt in the austenite, the precipitates in the S ferrite gradually increase in quantity and in size, and the brittleness of the a ferrite is progressed.
ransmission electron microscopic observation revealed the dislocation structure of various ferrites in mild steel and high strength steel weld metals. On the basis of these results the toughness of these steel weld metals was discussed. The main results were in the following. (1) Dislocation density in ferrite of these weld metals increased with cooling rate of 10 to 1000°C/sec at solidification. The Dislocation densities ranged over 5.0×109 to 1.5×1010/cm2 for mild steel weld metal and 1.0×1010 to 3.0×1010/cm2 for high strength steel weld metal. (2) Significant decrease of dislocation densities of as-deposited weld metals was observed after the following weld pass. (3) Brittle-ductile transition temperature of these steel weld metals depended on not only the ferrite size but also the dislocation structure in ferrites.
By means of eccentrically covered electrode of ilmenite type and cellulose type coating which has a definite outer diameter and various eccentricities relating to the core wire of a given diameter, the fusion penetration phenomena of stringer bead made on base metal plate in the flat position welding and fire cracker welding were investigated. Furthermore up-slope welding in the flat position were investigated under variously inclined base plate. The results obtained are summarized as follows: (1) Flat position welding; a) The shape of penetration becomes Central Penetration Type when the coating thickness is thinner at front side of the electrode travelling and comparatively low arc voltage in the flat position. (2) Fire cracker welding; a) When the thicker coating thickness are facing to the base plate, the arc is blown up so that the sound weld can't be made easily. When to some extent the arc is directed to the base plate the appearance of weld bead becomes smoother. (3) Up-slope welding; a) The most favourable inclination of the base plate for practical use occurs at θ = γ, θ being the angle of arc jet, γ the inclination angle of base plate. b) The base plate of large inclination may be successfully welded with electrode of large eccentricity, even when a satisfactory welding can't be achieved by electrode of small eccentricity.
Fatigue tests were performed on corner welded joints to investigate the effective factors such as jointing method and leg length of weld. The material used was a structural carbon steel (S35C, 32 mm in thickness). Three type of corner welded joints were chosen as follows, fully lap (type B), half lap (type A) and non lap (type C) corner fillet joints with various leg length. Fatigue tests were carried out under completely reversed plane bending stress at frequency of 1650 cpm. The results were confirmed by FEM stress analysis. The following conclusions are obtained. (1) The welded joint of type C shows the highest fatigue strength under cyclic bending stress and the next is type A. (2) The above results are mainly affected by leg length of welds. (3) It was found from the FEM stress analysis that the optimum leg length of these corner welded joint was about 80 percent of plate thickness.
CO2 arc spot welding is a simple welding process which has been commonly used in the manufacture of rolling stock. However the relationships between welding parameters and weld dimensions have not been evaluated statistically. In this study, welds were made by changing welding parameters (welding current, arc voltage, arc time and upper plate thickness) and relationships between welding parameters and weld dimensions (button dia., penetration depth, nugget dia. and shear tensile force of weld joint) were statistically determined. The suitability of the experimental equations thus established is discussed and it has been made clear that these equations could be used to estimate the weld dimensions (button dia., penetration depth, nugget dia. and shear tensile force of weld joint) from the welding parameters.
In this study, the effect of tensile prestrain and hammer peening, which give locally deformation and prestrain at weld toe, on fatigue strength was investigated, using mild steel (SS 41) welded joint with reinforcement. The following experimental results were obtained; 1) The fatigue strength of welded joint was increased with increase of tensile prestrain. 2) Hardness of weld toe was increased with increase of tensile prestrain. 3) The tensile residual stress on the surface of welded joint was remarkably decreased by 0.15 or 0.20 % tensile prestrain compared with as-welded joint. Moreover, tensile prestrain over 1.0 % converted the residual stress from tension into compression. 4) The fatigue strength improvement of welded joint by tensile prestrain was attributed to increase of hardness and compressive residual stress. 5) The fatigue strength of welded joint-by proper hammer peening was improved about 50 % compared with as-welded joint. This improvement was caused by mainly form effect of weld toe and additionally work hardening.