A new method is described for measuring the eccentricity and the bending in nonferrous electrode by making use of the electromagnetic type instrument widely used to measure the eccentricity of steel core electrode and already reported in our previous paper (cf. J. Japan Welding Society 19, 203 (1950)) The principle is to transform the changes in coating thickness and in core bending into the displacement of the iron plate attached to the instrument. By this method, the bending can be measured with great accuracy, but as for the eccentricity, errors frequently enter in its measurement owing to the effect of electrode bending. So we improved the measuring method to lessen the effect and succeeded in selecting electrodes of small eccentricity (less than 3%). We also measured the core bending by this method, finding out that the cause of eccentricity was sometimes attributable to the core bending. Advantages of this method are as follows: 1) We can use the electro-magnetic type instrument. 2) Operation is easier than the high frequency method presented in one of our papers (cf. Bul. Electrotech. Lab. 15, 144 (1951)). 3) Measurement is done without stripping off electrode coating.
The purpose of peening in welding practice are as follows : 1) Relief of residual stress due to welding 2) Decrease of distorsion and aegle change in welding 3) Prevention of crack after welding But the effect on the notch sensitivity of welded joint might be undesirable, then we tried to carry out this experiment. From the butt-joint of the welded plate, peened under various conditions, modified Kahn's test piece was produced, and the notch sensitivity test was carried out. The transition temperature of peened weld metal was very low, compared with that of mother metal, so the effect of peening to the weld metal was negligible.
It must be recommended in our country where nickel is now in short supply, to use high chromium stainlees steel as a substitute of chromium-nickel stainless steel. High Cr stainless steels studied here contains 20-24 pet Cr, 2-3 pet Ni, 0.08 pet C and are so called ferritic stainless steels and not hardened significantly by heat treatmet. However, because these steels are susceptible to several types of embrittlement, their welding characteristics should be understood. The oxyacetylene welding process is not recommended for joining these stainless steels, because of considerable grain growth and carbon pick up. Metal arc welding is the process most wideey used, and the amount of heating at the joint is usually substantially less than with the oxyacetylene process. Argon-shielded tungsten-arc welding is, well suited for these steels. Satisfactory results are obtained by welding the ferritic stainless steels with electrodes having composition identical to those of the parent metals, but post annealing treatments are essential. Austenitie chromium-nickel electrodes can be used satisfactorily because the austenitic weld metal is not susceptible to the high-temperature embritteement. On the other hand, ferrite grain size increases when heated above approximately 1050°C. This feature is the factor which exerts the greatest influence on the properties of a weld joint. Such commercial alloys as these can contain austenite at high temperature. A mixed structure of ferrite and austenite at high temperature can be retained, if cooled fairly rapidly. This austenite may transform into martensite. This will make the heat-affected zone relatively brittle. Sigma-phase precipitation was not found in welded joint. 475°C brittleness can occur in the welded joint, so it must be avoided to cool slowly through this temperature. Lack of ductility in the as welded condition may be due to phenomena associated with the solution of carbides at temperature above 1, 200°C.
Notched bead bend specimen of Lehigh type was used to evaluate the influence of welding on the notch sensitivity of structural mild steels. The test pieces werc arc welded manually and compared with the unwelded base plates. Some of them were cooled to -10°C and them welded to examine the effects of different welding temperatures. The ductility transition temperatures (Tra or Tφ) were determined by measuring Ghe.bend angle at maximum load (aM) or the lateral contraction below notch (φBN) respectively, and the fracture transition temperature (Trs) was decided by the fracture appearance. Tests results revealed that Tra and Tφ were seriously raised after arc welding except one killed steel, accompanied by great reductions of aM and φBN. So a considerable danger of susceptibility to crack growth may be said to be present in heat affected zones. On the other hand, TrS was hardly influenced by welding;namely, it was indicated that the transition temperature of welded joint might not rise particularly when a crack, initiated in the heat-affected zone, plopagated into the base plate The increase of hardness was also slight in specimens welded at -10°C, and their transition temperatures were exactly the same as those welded at room temperature. At the same time, it was proved that there existed satisfactory correlations between transition temperatures of steels determined by various test methods, if they were classified in to the fracture and ductility transition temperature and compared between each group. For example, Trs correlated well to the transition temperature determined by the fracture appearance in the Kahn tear test, and Tra also did so to 15 ft-1bs. transition temperature measured by the V-notched Charpy test.
Continued from the preceding paper, the mild steel rectangular plates, which had a weld bead along one edge as shown in Fig.1, were local-heated by a gas flame. The residual stresses at the Point 1 and 4 in both directions parallel to and perpendicular to the welded edge were measured by the X-ray diffraction method before and after local heating. The stress near the weld was reduced to a small value by local heating similarly in the preceding paper, and the one around the heated zone was repressed to a relatively small tension. Simultaneously, the lengthes of aa, bb and cc were measured. And these dimensions were found to be dilated by local heating. These findings enabled the author to clarify the mechanism of stressrelieving by local heating qualitatively.