The effects of Al, Nb and C on the formation of white constituents were examined first. And on the basis of the results (Fig. 2), the methods of improving the hot crack sensitivity of Inconel 713C were inquired into. The effects of valid elements to improve the hot crack sensitivity of Inconel 713C on the mechanical properties of Inconel 713C were investigated. The conclusions obtained in this study are as follows; (1) The formation of white constituents is arrested with an increasing C content or with decreasing Al and Nb contents. Fig. 2 shows critical formation cruves of white constituents. (2) The hot crack sensitivity of Inconel 713C can be improved by increasing the C content or decreasing the Al content. (3) The hot crack sensitivity of Inconel 713C can be estimated by Fig. 2 on the basis of Al, Nb and C contents in Inconel 713C. (4) The creep rupture strength at 816°C of Inconel 713C lowers when decreasing the Al content from 6.1 % (nominal composition of Al in Inconel 713C) to 4.7%. (5) The effect of C on the creep rupture strength and high temperature tensile strength of Inconel 713C is not recognized, C content being varied from 0.12% to 0.4%. (6) The elongation and reduction of area of high carbon Inconel 713C are poor. From a view-point of ductility, it is desirable to lower the C content in Inconel 713C. Finally, adding 0.2-0.3%C to Inconel 713C is effective to improve the hot crack sensitivity of Inconel 713C without lowering mechanical properties.
The welding of austenitic manganese steel to high carbon steel has been thought to be very difficult due to the difference of their metallurgical properties and others. The authors paid special attention to the procdeure to join them by manual arc welding after buttering the groove face of carbon steel. Various fundamental experiments were performed to select proper electrodes for buttering and joining, and welding conditions, though mention here is given mainly of the buttering electrode selection tests- 1) Hardness test and microscopic inspection of weld metal, 2) Angle-expanding type cracking test of weld metal and, 3) Impact test of weld zone. Based on the results obtained, austenitic manganese steel rail and carbon steel rail (high carbon steel) were welded together, and the welded rails were subjected to bending test, drop-weight test and so forth. The results show that considerably reliable welds are obtained if they are welded together by the following methods: 1) Austenitic manganese steel which has good weldability and no casting defects is used. 2) The welding groove is finished to V or X and arc welding process is executed in flat position. 3) The vicinity of the groove of carbon steel is preheated to 300-400°C, then two layers with 25Cr-2ONi or 25Cr-12Ni type electrodes or one more layer with 16Mn-16Cr type electrodes are buttered over the groove face. 4) The manganese steel rail and the buttered carbon steel rail are welded together with 16Mn-16Cr electrodes. Craters are peened after each pass followed by forcible cooling of the weld zone. 5) The impurities contained such as phosphorus should be as low as possible in the electrodes and the electrodes should give weld metals of very low crack susceptibility. 6) The postheating which is usually adopted for the welding of high carbon steel is not performed. The final object of this study is to establish the prodceure to weld austenitic manganes steel crossing to carbon steel rail and the welds are now under field test.
In this study, the effects of nitrogen an/or oxygen added to shielding gas on the weldability of aluminum alloys were investigated. Test materials were welded by manual and machine MIG welding equipments under various welding conditions. Weldability was evaluated by various properties of welds, such as appearance, shape and depth of penetration, porosities, structures, mechanical properties and others. The results were as follows: (1) Addition of nitrogen to argon gas was apt to form brown scales on bead surface of aluminum and its alloys, particularly of Al-Mg alloys, but the bead shape was scarcely disturbed by the addition of up to 10% nitrogen. It increased the depth of penetration and improved the tensile strength with refined structures of weld metal. Furthermore, it reduced the porosities in commercially pure aluminum welds, though it was not always effective for reducing them in aluminum alloys, particularly in alloys containing magnesium considerably. (2) Addition of oxygen to argon gas was apt to cause the puckering phenomenon, but that of up to 5% oxygen gave a comparatively excellent bead shape with no puckering. It increased the depth of penetration and produced the welds with few porosities in both aluminum and its alloys. (3) Simultaneous addition of nitrogen and oxygen to argon gas disturbed the bead shape with remarkable scales. It tended to form inclusions in welds, while it increased considerably the depth of penetration and occasionally decreased the porosities. (4) Consequently, it was considered that addition of nitrogen gas up to 10% or that of oxygen gas up to 5% was effective in practical applications, but simultaneous addition of them was not desirable.
Systematic research has been made on a high power CW CO2 gas laser to clarify its characteristics as a heat source, which include the characteristics of the laser beam focussing, interaction between laser beam and materials, distribution of temperature in laser heating and the characteristics of heat processing such as welding, cutting and drilling. This paper discusses the results of the analysis on the characteristics of the beam focussing of the CO2 gas laser. The size and shape of the focussed laser beam are measured expediently using film and the locations of the focal points and focal lines are determined. The method for measuring the actual energy distribution at focal point and focal line is developed. Conclusions obtained are summarized as follows; 1) As an optical system to focus the high power CO2 gas laser beam, a concave reflecting mirror is recommendable rather than a lens. 2) The astigmatism is inevitable in this optical system due to off axial incident beam. It becomes, however, negligible when incident angle θ<6°. When θ<6°, energy density distribution at focal point may be approximated by Gaussian curve and the diameter of the focussed laser beam at the e-1 power point is about 0.5mm, which is approximately four times the diffraction limit. This provides an energy density of 5.6×104 Watts/cm2 at the center of the spot for 100 Watts incident beam. 3) The diameter of the laser beam measured agrees with the diameter calculated from measured beam divergence, 1.8 milliradians, and given focal length. 4) Focussed laser beam can be deformed easily by means of the astigmatism which increases gradually with an increasing θ when θ>6°.
A study has been made of the properties of explosively bonded interface between aluminum and dissimilar metals such as copper and mild-steel. Tests were carried out on the effect of heat-cycle on the structures and mechanical properties of bonds in order to clarify the applicability to the transition pieces. In the explosive bonding of Al-Cu, alloying layers were considerably formed in the interface, and their constitution was θ (CuAl2) phase mainly. By heat-cycle, the growth of another alloying layers which seemed to be γ2(Cu9Al4) phase was observed between Cu-matrix and θ(CuAl2) phase. Alloying layers observed in explosively bonded Al-Fe seemed to be composed of the eutectic of α(Al) and θ(FeAl3) phase. By heat-cycle, θ(FeAl3) phase grew to exist by itself for the most part. However, there was some possibility of existing of another intermetallic compounds such as η(Fe2Al5). The shear strength of the explosive bonds in Al-Cu and Al-Fe lowered with raise of temperatures of heat-cycles and there was observed a change in their fracture mode. This resulted from the influence of the formation or growth of intermetallic compounds by heat-cycle. But by heat-cycle of 3 pass welds the growth of an alloying layer was not so often observed as that by 550°C×3 min. From this result, there can be confirmed the applicability of these bonded materials to transition piece. However, it was necessary to pay full attention to selection of explosive conditions, since the cracks and voids which seemed to reduce the properties of explosive bonds were observed in the alloying layer of bonds.
Underbead cracking was investigated in relation to the progress of isothermal transformation in the heat-affected zone of two high tensile strength steels. C.C.T. diagram for one of the two steels was determined using specimens austenitized in hydrogen and in vacuum. Delayed cracking tests were carried out using specimens, into which hydrogen was charged in austenitic and martensitic states. Main results obtained are summarized as follows: 1. Underbead cracking is closely related with the progress of isothermal transformation in the welding heat-affected zone. 2. Holding time for the prevention of underbead cracking is shortest in the intermediate transformation range. 3. Below the Ms point, longer holding time is required to prevent underbead cracking with a lowering of temperature. 4. Hydrogen dissolved in steel does not play any significant role in the transformation. 5. From delayed cracking tests on two series of high tensile strength steel specimens containing the same amount of hydrogen charged in austenitic and martensitic states, incubation period for cracking in the former series was found to be about ten times longer than in the latter.