Creep tests under internal-pressure on circumferentially EB-welded cylinders made of Hastelloy X were carried out for the investigation of structural behaviors of welded components in elevated temperature environment. Penetration cracks were not observed at base metal zone but at weld metal zone. EB welded zone of the cylinder showed the comparable creep ductility as compared with the non-welded cylinder. The creep rupture strength of EB-welded cylinders was lower than that of non-welded cylinders, but superior to TIG-welded cylinders. The rupture time ratio of EB-welded cylinders to non-welded cylinders was smaller than the ratio of EB weld metal to base metal obtained from uni-aixal tests. The decrease in rupture strength under internal pressure is considered due to the difference in creep rates between EB weld metal and base metal.
Electron beam welding has much advantage of thick material such as high quality, low distortion and short welding time by one side small pass welding. But one side deep penetration characteristics happen to make welding defects porosity in center of weld materials. For this porosity repair welding is sometimes difficult because of narrow melting width so that porosity free welding is required. In this report beam oscillation technique was investigated to avoid porosity in thick steel plate (up to 100 mm). Parameters of beam oscilaltion consist of frequency, amplitude and oscillation pattern. Welding was carried out to thick steel plates in horizontal position and one side welding. The results can be summarized as follows; 1) Low welding speed was effective to eliminate porosity. 2) Optimum conditions of beam oscillation studied were from 500 to 2000 Hz in frequency, from 0.5 to 2.0 mm in amplitude and sine, cycle or ellipse in oscillation pattern. 3) Bead width was increased by excess amplitude to parpendicular direction to welding direction so that solidification crack occured along centerline of weld metal. 4) Beam oscillation was avilable to eliminate porosity but under optimum oscillation condition bead shape of reverse side was irregularly underfilled. 5) For thick steel plate the range of optimum welding condition to eliminate porosity by beam oscillation technique was small and beam oscillation parallel to welding direction was effective to eliminate porosity.
A rectangular wave shape AC TIG power source with transistorized switching has been developed. It is possible to adjust wave shapes of the ratio of the time at negative current (tsp) and at positive current (tRP) from 1 to 9, by using this power source. Effects of tSP/tRP ratio on wled quality in TIG welding of thin aluminum plates were investigated quantatively. The results are as follows. 1) Stability of arc increases with increase of the tSP/tRP ratio. 2) Electrode consumption and number of blow holes decrease with increase of the ratio.
In the previous paper, stress distribution analyses of single-spot welded joint and multi-spot welded joints arranged in perpendicular to load direction were carried out, under prediction that fatigue strength of spot welded joints corresponds with stress distribution on line including nugget front where fatigue crack may generate. In this paper, fatigue tests of single-spot welded joint with various specimen widths and/or lap lengths and of multi-spot welded joints with various spot spaces and/or lap lengths were carried out. And, these experimental results were compared with the numerical results obtained from stress distribution analysis of single-and multi-spot welded joints in the previous paper. Main conclusions obtained in this investigation are as follows: (1) The effects of specimen width and lap length on fatigue strength of single-spot welded joint become clear. (2) The effects of spot space and lap length on fatigue strength of multi-spot welded joints become clear. (3) It is experimentally, proved that the effect of spot space on fatigue strength of multi-spot welded joint is equivalent to the effect of specimen width of the same length on fatigue strength of singlespot welded joint. (4) Moreover, it is found that at fatigue life of 2 × 106 cycles dependency of fatigue strength on specimen width or spot space and lap length obtained in these experiments correspond very well with that obtained from stress distribution analysis, although at fatigue life of 1 × 105 cycles do not so. Consequently, fundamental design data according to which prediction of fatigue strength of multi-spotwelded joints is possible without fatigue test of multi-spot welded joints from fatigue test results of single-spot welded joint with the same nugget diameter with nugget diameter of multi-spot welded joints, is obtained.
One side automatic welding by MIG+2SAW process on butt joint cut by oxygen plasma arc was studied in order to improve the sound weld metal and the welding efficiency. (1) The nitrogen and oxygen are concentrated in the plate edge cut by air plasma arc. The oxygen is concentrated but the nitrogen is not concentrated in it cut by oxygen plasma arc. One side & one run welding on butt joint cut by air plasma arc is apt to occur the blowhole; while the welding on it cut by oxygen plasma is superior to that by air plasma for the blowhole. (2) High current MIG+2SAW process is superior to 2SAW for the susceptibility of hot cracking when one side & one run welding is applied on butt joint because a bead geometry is good and the heat input is dispersed between MIG and 2SAW torches. This MIG+2SAW process can prevent a burnthrough and give a good reverse side bead and a good mechanical property to weld metal as well. (3) Oxygen plasma arc can improve the cutting speed compared with air plasma arc. High current MIG+2SAW process increases the traveling speed about 1.5 times than 2SAW. As a result the combination of oxygen plasma arc cutting and MIG+2SAW process improves the efficiency of one side automatic welding.
Fatigue crack propagation rate in weld metal or H.A.Z. does not always increase monotonously under conditions of constant alternating and maximum stress. In this report, the effect of the hard region on the fatigue crack propagation rate was investigated. Fatigue tests were performed on specimens containing the hard region under load controlled four point bending and edge crack tension. When a fatigue crack was remote from the soft-hard boundary, its propagation rate was increased monotonously. The crack comming near the boundary, the hard region was found to reduce the increrrlent of its propagation rate restricting the plastic zone. Fatigue crack propagation rate had a relationship with the cyclic crack opening displacement. The distance from the soft-hard boundary to the point where the increment of propagation rate was beginning to be reduced was related to the cyclic crack opening displacement at that point.
An investigation was carried out on the effects of impurity contents and cooling time from 800°C to 500°C of weld thermal cycle on stress relief cracking susceptibility in 2 1/4 Cr-1 Mo steel synthesized HAZ. In this study, critical displacement to crack initiation (Δl'/c) and critical stress to crack initiation (σSR) obtained by constant loading test on heating in stress relief thermal cycle was adopted as a parameter to evaluate the stress relief cracking susceptibility. The results are summerised as follows; 1) Δl'/c decreased with increasing of X=(10P+5Sb+4Sn+As)/100. 2) σSR at 600°C on heating decreased with increasing of X. 3) Δl'/c increased when the cooling time from 800°C to 500°C becomes shorter than 10 sec. and longer than 60 sec. In the former conditions austenite grain is refined and in the latter conditions upper bainite structure is formed.
The purpose of this study is to make clear the mechanism of weld cracking in 24Cr-24Ni-1.5Nb Febase heat resisting alloy and to prevent metallurgically weld cracking in this alloy. In this report, the feature of weld cracking in this alloy was clarified at first. The effect of alloying elements on the sensitivity of weld cracking was also examined. The main results obtained in this study are as follows; 1) The weld cracking in this alloy initiated at grain boundary in HAZ. 2) The morphology of crack surface was very smooth and plate-like or lameller eutectic phases (NbC eutectic) and granular eutectic phases (Cr carbide eutectic) were observed on the crack surface. 3) It became clear that weld cracking in this alloy was liquation cracking. 4) C and Si increased the sensitivity of weld cracking and Nb and Mn decreased the one in this alloy in the range of this experiment. It was recognized that there might be good relationship between the sensitivity of weld cracking and Nb/C (atomic % ratio) in this alloy. 5) It could be presumed that Cr carbide eutectic increased the sensitivity of weld cracking in this alloy.
It is considered that precipitation of γ' in welds plays a predominant role in properties of welds. So the effect of wlding and heat treatment conditions on precipitation of γ' in liquid phase diffusion weld was investigated. Liquid phase diffusion welding was carried out by using insert metal, following by subsequent heat treatment in order to promote homogenization in composition. Nickel-base superalloys used are TM-49 and MarM-247. The following results were obtained. 1. Only intragranular γ' forms in welds. Eutectic γ' which is in base metal does not form in weld. 2. Volume and particle size of γ' in welds made with insert metal that Al, Ti and Hf are added to are close to that in base metal. 3. Volume and particle size of γ' in welds made with insert metal that Al, Ti and Hf are excluded from increase to that in base metal with the rise of temperature and time of diffusion treatment.
Effects of microstructures, prior austenite grain size, soluble Ti, soluble N and insoluble Ti on the notch toughness of the synthetic weld heat affected zone have been investigated using mild steels with a microalloyelement Ti. The results obtained are as follows: (1) The austenite grains are refined by increase of Ti and N contents. Especially, the grain refinement occurs remarkably in specimens with less than 0.0060 wt% N. (2) The microstructures are changed by Ti and N contents and when Ti and N contents are optimum the finest ferrite-pearlite structures are obtained. (3) The notch toughness strongly depends on the quantities of a soluble N and Ti even if the microstructures are the most favorable. (4) Optimum Ti content to improve the notch toughness is given by following Eq. Optimum Ti=-1070N3+1.09N+ 0.0137 (wt%). (5) The summation of soluble Ti and soluble N should be considered as a important factor affecting the notch toughness.