Effect of nitrogen partial pressures in the welding atmospheres of several gas mixtures on the nitrogen content of aluminum weld metals was systematically studied. The important conclusions are as follows; 1. Aluminum weld metals absorb a large quantity of nitrogen in the welding atmospheres containing nitrogen. 2. The nitrogen contents of weld metals increase with increasing arc voltage and decrease with increasing welding current. 3. Anomalous nitrogen absorption by weld metal is observed at low atmospheric pressures. 4. The existence of an oxidizing gas in arc atmospheres does not contribute to the enhancement of nitrogen absorption by aluminum weld metals.
A bead-on-plate welding was done on each specimen of aluminum single crystals (purity: 99.93%, size: lt×20×200) with TIG arc or electron-beam. Optical and X-ray diffractive investigations were made on.the structures and crystallographic properties of subgrains which had been developed in the weld metal. The conclusions obtained are as follows; (1) Subgrains are observed in the weld metal and they tend to grow in the direction of ‹100›. (2) Crystals in the weld metal do not always grow in the direction normal to the weld isotherm. (3) Mean widths of subgrains tend to decrease when the growth rate increases. (4) Mean valuess of misorientations between subgrains decrease when the welding speed increases. (5) Mean dislocation. densities in subgrains which were calculated from'the values of the misorientations and the widths of subgrains were almost the same as the results which had been reported by T.S. Noggle and J.S. Koehler in the case of the melt-grown specimens of 99.99% aluminum.
AISI 405 stainless steel and its clad steel are widely used in chemical apparatus, such as oil refiners, heat exchangers and so on. Several cracks are often found in the weldment with the same chemical composition electrode (D41ONb) after welding or annealing. Investigations on phenomena of these cracking and their prevention were carried out. Conclusions are as follows. 1) Delayed cracking with very long incubation period occurs in 405 stainless steel weldment; this was never experienced in the structural steel weldment. 2) These cracks are prevented by preheating and adoption of MIG welding. Reducing the hydrogen content of deposited metal is most necessary to preverrt these cracks. 3) Cracking occurs in high Cr content weldment such as Mr, 17Cr, and even in almost ferrite structure. These phenomena are very different from those in structural steel.
17-4 PH stainless steel transforms to martensite during cooling from the solution-treatment temperature and is strengthened by precipitation in the low carbon martensite matrix. But there has been very little information given to date on the nature of the precipitates in this steel. We made a study on the precipitates by transmission electron microscopy and electron diffraction technique. The results obtained are summarized as follows: (1) The precipitate is fcc copper rich phase with a lattice parameter of 3.595-3.600 A. (2)On prolonged aging, the precipitate grows into a rod with its longitudinal direction parallel to ‹111› martensite matnx. The precipitate-martensite matrix orientation relationship is similar to the Kurdjurnov-Sachs relationship, i.e. (111)ppt//(110)matrix ppt//matrix.
The authors have investigated the penetration mechanism of base metal and the polarity effect in electroslag welding. The paper discusses the penetration mechanism of base metal considering the electric conductivity of molten slag, the temperature and current distribution in slag pool under the welding conditions shown in Table 1. In general, the metal is deeply penetrated only at the lower part of slag pool as is shown in Fig. 1. The temperature distribution of slag pool is shown in Fig. 2. The temperature at the bottom of slag pool is considerably high, i.e., about 1700-2000°C. On the other hand, it is low, i.e., about 1400-1500°C at the upper part. The relation between the electric conductivity and the temperature of molten slag is shown in Fig. 3, where one notices that the electric conductivity remarkably increases as the temperature rises above 1400°C. The temperature distribution of slag pool (Fig. 2) and the characteristic of electric conductivity (Fig. 3) lead one to the presumption that the most part of welding current concentrates on the bottom of slag pool. This was experimentally verified as shown in Fig. 4. The current distribution shown in Fig. 5 causes a difference of electromagnetic pressure between the wire end and the bottom of slag pool, and consequently it generates the convection of molten slag. (Fig. 5) The lower part of base metal, therefore, is effectively melted. When direct current is used, the polarity effect on the penetration of base metal is as follows; In straight polarity (wire cathode), the metal is penetrated not only at the lower part but also at the upper part of slag pool. In this case, the melting speed of wire is less than that in reverse polarity (wire anode). As to the melting speed of wire in R.P. and S.P., a model experiment was conducted as shown in Fig. 9 and it was found that the melting speed of R.P. was greater than that of S.P. It was experimentally proved that the potential difference at anode side was higher than that at cathode side as shown in Fig. 12.