Generally there are 5 sorts of internal defects of weld, namely blow-hole, slag-inclusion, lack of fusion, incomplete penetration and crack; but under existing circumstances, it is difficult to classify these defects by ultrasonic echo-pulse testing. For the purpose of studying to classify welded defects by ultrasonic spectrum analysis, at the outset, we attempted to distinguish crack from the other defects. We searched for each associated ultrasonic spectrum connected with NDI-STB-A2-4 mmφ hole, NDI-STB-Al (I.I.W. type)-1.5 mmΦ hole, incomplete penetration, crack and fractured surface by calculation and ultrasonic spectrum analyser. As the associated ultrasonic spectrum of crack has great roughness as compared with those of the other defects, crack can be distinguished from the other defects by associated ultrasonic spectrum.
Bending result of 405 stainless steel weldment is remarkably affected by chemical composition of welded materials, especially Al content, as described in previous report. Various Al content specimens are used in this experiment, and their bending test results, mechanical properties of bond are studied. Effects of Veining structure, hydrogen content of weld metal are also researched. Results are as follows: 1) Bending properties of 405 stainless weldment are remarkably affected by Al content of welded materials. 2) Welded joint of 405 stainless steel which contains more Al and less C is poor in bending properties, and low temperature post heat treatment is necessary for improving the bending properties. 3) Veining structure and hydrogen in weld metal have no effect on bending properties.
Heat-affected zone cracking due to stress relief heat treatment has been investigated on a wide variety of ferritic steels. This investigation was undertaken to prove the relationship between this type of cracking and the metallurgical and mechanical properties. 1) It is necessary for cracking to occur that the structure is in quenched state and coarse grained before stress relieving, i.e. this cracking may not occur in an overaged structure or in a fine grain structure. 2) When this cracking occurs during stress-relieving, it is always accompanied by the formation of fine intragranular precipitates, leading to enhanced stress concentration at the three grain junction. 3) The stress-relief cracking susceptibility of a steel can be described by ΔG=[Cr]+3.3[Mo]+8.1[V]-2 such that when ΔG is positive the steel is susceptible. 4) The macroscopic behavior is in a good agreement with and confirmed by the microscopic observations.
In this report, the presumption of crack initiation temperature was attempted first. The hot ductility behaviors during cooling process of weld thermal cycle in hot crack sensitive Inconel 713C and insensitive Inconel 713C were investigated. The causes of hot crackings in Inconel 713C were clarified in conformity to the experimental results with crack initiation temperature and hot ductility behaviors, and general consideration with the relation between hot crack sensitivity and hot ductility behavior during cooling process of weld thermal cycle or local melting phenomenon in an alloy. The conclusions obtained in this study are as follows; 1) It is presumed that weld crackings in the heat affected zone of Inconel 713C initiates at the temperature more than 1200°C at least. 2) Nil-ductility temperature ranges of the alloy containing white constituents (Heat V-3) and the alloys containing no white constituents (Heat V-11, V-32, V-34) are about 100°C and 10-30°C respectively. The extensive nil-ductility temperature range of Heat V-3 is due to low melting point white constituents. 3) Hot crack sensitive Inconel 713C contains white constituents and its nil-cuctility temperature range is wide. The main cause of hot crackings in the heat affected zone of Inconel 713C is white constituents considering the fact that low melting point white constituents is the dominant cause to spread nil-ductility temperature range.
This study was carried out directly to detect the constituent of gas in blowholes of weld metal by a microscopic micro-analysing and a mass spectrometer. Aluminum and its alloy, mild steel, high strength steel and austenitic stainless steel were used as base metals. And a bead - on - plate was deposited by the gas shielded metal arc welding under various shielding gases for each base metal. The diameter of a collected gas bubble from blowholes was measured by the microscope under a thin glass in absorbent step by step. The composition of the gas bubble was determined by calculation from the difference of diameters of the bubble before and after an absorbent solution. The quantity of hydrogen was determined from the loss of explosion by a special explosion pipet. The remainder gas after the microscopic micro-analysing was determined by the mass spectrometer (JMS-OISG). According to the results of analysis for aluminum deposit metal, a blowhole consists of the following gases; hydrogen about 75-85%, oxygen and argon several % and nitrogen 10-20%. In aluminum alloy deposit metal, oxygen could not be measured. Carbon dioxide, hydrogen sulphide, carbon monoxide and metahne were not recognized in both cases. Blowhole in mild steel deposit metal is full of carbon monoxide, hydrogen and nitrogen. Under the carbon dioxide shielding gas with a wire of insufficient deoxydation elements or carbon dioxide shielding gas with excess oxygen, blowholes consist mainly of carbon monoxide over 55% and nitrogen. Blowholes which were formed in a bead on rusted steel or on greased steel contained mainly 40-60% of hydrogen and 30-40% of carbon monoxide. In austenitic stainless steel deposit metal, the gas in blowhole is also carbon monoxide, hydrogen, nitrogen and argon in the case of argon and argon-nitrogen shielding.
Flashing phenomena in flash welding of mild steel are studied by oscillogram using comparatively small size test pieces. The secondary no load voltage of welding transformer is adjusted in a range of 5-30 V. See Fig. 1. Secondary current of transformer is directly measured by using co-axial cylindrical shunt shown in Fig. 2. For simplicity of experiment, a straight cam is used and the platen velocity is adjusted to 1.75-28 mm/sec under the experimental condition. In the early stage of flashing, alternation of two distinct periods is observed, one being the period of alternation of short circuit and arcing and the other being the no current period. See Fig. 8. The above mentioned alternation of successive short circuit and arcing is the special character when steel is used in air, the cause being CO gas produced in molten metal in arcing period. See Fig. 11-13. The volume expansion of molten metal due to CO gas results in a short circuit and the contraction of CO gas results in the breaking of the short circuit. It is observed the short circuit is apt to occur more frequently when the instantaneous current becomes close to zero. The reason can be of course explained by the decreasing of repulsive arc force which acts on the molten metal. For secondary no load voltage of 5 V, arc decays quickly, while for no load voltage larger than 15 V, arc is sustained for a long time and results in great heating of the test piece. For no load voltage of 5 V, frequent short circuit and arc of small current occur as shown in Fig. 15, because the molten metal is not flashed off as in the case of large heat input and results in the short gap for a given platen velocity. The circuit constant L/R affects also the arcing mode. For small values of L/R, arc energy is naturally small and frequent short circuits are observed as shown in Figs. 16 and 18. It must be noticed that the duration of a short circuit becomes very short, because the high current density of the contact point heats up the contact point and makes early breaking of the contact.
Studies on the bead formation have been carried out in the case of two electrodes submerged arc tandem method. It has been made clear that two arcs have their own functions in bead formation; that is, the lead-arc has the function of "Digging the base-metal" and the trial one that of "Regulating the bead appearance." Taking these functions into consideration, the possibility of high speed welding has been examined with five kinds of tandem methods. As the result of it, it is found out that the deflection of the trail arc chiefly influences the bead appearance, and that the bead appearance is beautiful even in the high speed range if only the trail arc is deflected in the welding direction. When an alternating current is used, the phase angle between two arc-currents is very important, and when a direct current is used, attention must be paid to the earth position; that is, start side or end side. It means that the bead appearance is governed by the interaction between the magnetic fields of the arcs and the current through the base metal.