A soft-vacuum electron beam welder, welding pressure of which could be arbitrarily varied in the range from hard vacuum (10-4 Torr) to soft vacuum (1 Torr), was made experimentally. With this equipment, experiments with respect to shape of fusion zone in soft vacuum and influences of environment gas on weld bead were carried out using such metals as AISI 304 stainless steel, 2S-aluminum, 75S-, 52S- and Z5A-aluminum alloys, copper, brass, titanium and ziroconium. In case of small working distance, weld penetration depth begins to decrease at an air pressure of 10-2-10-1 Torr to a smaller value at 1 Torr by 15-35 per cent of that in hard vacuum. This rate of decrease does not depend on welding speed, but on kind of material. On the other hand the bead width hardly varies with an increasing environment gas pressure. There are two effects of environment gas on weld bead, that is, ability to suppress change of chemical composition resulting from evaporation of volatile elements and gas contamination effect on weld especially in reactive metals. The latter effect can be prevented by using argon as environment gas.
The authors have investigated the effect of C, Cr and B addition on the gas contents and the formation of blowholes in deposited metals by non shielded arc welding process with flux cored wire. Moreover, in this paper, they have theoretically discussed the phenomena of blowhole formation in the deposited metals of multicomponent system from a standpoint of chemical metallurgy. The results of this investigation are summarized as follows: (1) The contents of oxygen and nitrogen in the deposited metal are decreased by the increase of C and B therein, but increased by the increase of Cr. (2) The total volume of blowholes in deposited metal decreases with the increase of Cr and B, while the effect of C addition on the occurrence of blowholes is not so clear. (3) In explaining the mechanism of blowhole formation, it is easier to explain it by means of the product of activity of C and oxygen, ac⋅ao and activity of nitrogen, aN than by means of the contents of oxygen and nitrogen. The blowhole formation in defosited metals which are fully deoxydized through B is more affected by aN than ac ac⋅ao (4) The critical values of ac⋅ao and aN for the blowhole formation are obtained as ac⋅ao≅2×10-3 and aN≅4×10-2.
A series of study was carried out to realize automatic welding of austenitic manganese steel rail which had been conventionally performed by manual arc welding process. Using austenitic manganese steel as base metal, 16 Mn-16 Cr wire as electrode, and mainly CO2, A and N2 singly or mixed as shielding gas, build up welding was performed. Further, with the welding conditions varied, single bead welding was made. The mechanical properties. chemical composition and microstructure of weld metal were investigated on these welds. For any shielding gas used, the mechanical properties of deposited metal are satisfactory. Impact value is particularly good in the case of A-N2 gas;This is presumably partly due to relatively small contents of non-metallic inclusions. Among the welding defects, hardly any crack occurs, but blow holes are observed more often in N2-CO2 gas and in A-O2 gas containing considerable quantities of O2. As for the chemical composition of deposited metal, with an increased CO2 or O2 content of shielding gas the consumption of manganese in welding increases and as the result the manganese content of deposited metal decreases (transfer efficiency of manganese is about 80% for single use of CO2 gas). The decrease of chromium content is small but it shows the same tendency as manganese content. Nickel content hardly depends on the composition of shielding gas. Meanwhile, if the N2 content of shielding gas is large, the N content of deposited metal also grows large (0.49% for 20% CO2-80% N2). The deposition efficiency is high when the shielding gas is rich in A; and it is low when the gas is rich in CO2, N2 and O2. Under high arc voltage and under low welding current, the weld metal surface is liable to develop blow holes (pits), accompanied by a drop in the deposition efficiency and an increase in spattering, if the shielding gas is rich in CO2. In this case the manganese content of weld metal is lower than in others. If the welding is performed in appropriate shielding gas under appropriate welding conditions, use of 16 Mn-16 Cr welding wire will assure weld metal having high mechanical properties and almost free from any welding defects.
For purposes in evaluating the elastic and plastic behaviors of weld zones, tensile tests and alternating plane bending tests beyond the elastic range were carried out on the transverse-weld specimens of a 80 kg/mm2 class heat-treated high-strength steel, and the individual stress-strain curves for the weld metal, heat-affected zone and base metal were observed in detail. The strain was measured with electric-resistance strain gauge of 1 mm gauge-length sticked on each zone. Also, these curves were compared with those examined on the quenched or and tempered specimens of the base metal. The tests revealed the following: The over-heated zone, which exhibited high hardness and low ductility, began to yield gradually at considerably small stress as against the abrupt yielding of the base metal, the 0.02% offset elastic limit of the zone being about half of the yield point of the base metal. This low elastic limit again resulted in oilquenched specimens, whose microstructures were similar to that of the over-heated zone in the weld. In the cyclic bending each stress-strain hysteresis loop for the weld metal, softened zone and base metal widened with decrease in elastic limit as cycling continued, while the loop for the over-heated zone became rather narrow due to strain hardening in similar way for the quench-hardened base metal.
Using a new apparatus which can restrict the expansion and contraction of a synthetic specimen at an arbitrary temperature during thermal cycles, the hot cracking tendency of weld HAZ was examined on three high strength steels. The main results are summarized as follows: (1) In a test steel Z(HY-130 class), hot cracks occurred in the condition that a synthetic specimen was heated to above 1, 350°C and was restrained within the temperature range of 1, 350 to 1, 380°C. (2) Hot cracks were found in grain boundaries extremely coarsened by weld thermal cycles, which showed mostly white, relatively broad networks, so-called "heavy boundaries". (3) By an electon-probe microanalysis, an enrichment with many elements was observed such as Ni, Cr, Si and P, and Mn and S locally on heavy boundaries.
It has been impossible to predict proper welding procedures using the results of small restraint cracking tests, since the relationship between small specimens and actual welded structures has not been clear on account of their cooling rate and the intensity of restraint. In the present investigation are reproduced various intensities of restraint on small specimens, so that the effect of the restraint may be clarified. Introducing the weldment cracking parameter, Pw, a method is established to predict the adequate welding procedures for a given chemical composition of steel used, the amount of diffusible hydrogen in weld metal and the intensity of restraint of the weldments. Although the cooling processes are different depending on the size of structures, preheating method and the ambient temperature, even for the same preheating temperature, generalized welding procedures can be given by using the criterion of critical cooling time interval from 300°C to 100°C. The relationship between Pw and critical cooling time interval from 300°C to 100°C indicates the proper welding procedure which assures sound weldments without any cracks. For a given value of Pw, it is only necessary to preheat the structure in such a way that the cooling time lies above the limiting line.