Effect of interstitial impurities, especially for nitrogen, on impact properties of submerged arc welded metal was investigated using a new technique through which only nitrogen content was varied. The results are summarized as follows. 1. Snoek's internal friction peak intensity of weld metal shows lower value than as normalized mild steel which comes mainly from existence of texture and short mean ferrite path. Solute nitrogen content (A wt%) is thought to be calculated as A(wt%)=7.0×Q-1_max where Q-1_max is Snocek's peak height. 2. Internal friction curves of weld metal are separted into four single relaxation peaks, C, Nl, N3 and N4, which are thought to be carbon Snoek's peak, nitrogen Snoek's peak and N-Mn interaction peaks respectively, and deform shaped relaxationpeak, X-peak. 3. Ductility of weld metal decreases gradually as total nitrogen content increases but at low nitrogen content level this ductility dependence on nitrogen shows reverse tendency. 4. Ducitility of weld metal decreases as solute nitrogen content increases and for HT-60 specimen which varies almost proportionally. 5. The main role of nitrogen on impact properties of weld metal is thought to be that solute nitrogen and secondary solute nitrogen which interact with other impurity lattice atoms rasise frictional force of dislocation to decrease ductility of weld metal.
Although there are many data on the mechanical properties and toughness of weld metals of various kinds of coated electrode, only a few of reports will be found on the effect of types of coated electrode on the fatigue strength of welded joint, e.g. it is well known that the weld metal by low-hydrogen lime type electrode has better toughness than those by other type electrodes, but a low-hydrogen lime type electrode gives more rough and irregular bead form in comparison with other type electrodes. Therefore, it is not always clear, which type of electrode will give more beneficial welded joint in relation to its fatigue strength. This point was experimentally studied by this report. The obtained results are as follows: 1) In the case of the same electrode, the fatigue strength of the vertical welded joint with reinforcement is 2-6 kg/mm2 lower than that of the flat welded joint. 2) The welded joint with reinforcement by low-hydrogen type electrode gives the higher fatigue strength of welded joint in comparison with other type electrodes. 3) Titania type electrode gives the lowest fatigue strength of welded joint of all.
The characteristics of brittle fracture and fatigue failure in the body which has several cracks and defects being close to each other, are different from those in the body having single crack due to the interaction. For the plate containing parallel cracks of equal length, it is reported recently that not only the brittle fracture stress but also the critical COD are larger than those for the plate containing single crack and increase with decrease of distance of parallel cracks. Accordingly, the COD concept is not simply applicable to that case. In this report, deformation behaviors such as stress, strain, plastic zone size ahead of crack tip and COD in the plate containing two parallel equal length cracks under uniaxial tension are investigated by the elastic-plastic analysis based on the finite element method and the experiment. Main results obtained are as follows: COD of parallel cracks under same load decrease with decrease of distance of cracks. When COD is constant, magnitudes and distributions of stress ay and strain sy in tensile direction around crack tip are much the same regardless of distance of cracks and yet distributions of σx differ with distance of cracks. Moreover, it is shown that the parameter with respect to the brittle fracture initiation may possibly exist which is dependent on triaxiality of stress around crack tip.
The effect of Mo on transformation behaviour in synthetic weld heat-affected zone of steel was investigated using simplified steels made of pure metals and graphite. Mo element displaced the SH-CCT diagram for ferrite and pearlite transformation regions to a longer time, and extended Zwischenstufengefüge (Zw) transformation region to a longer time. Each critical cooling time Cf', Cp' and Ce' increased with Mo content. Morphologies of ferrite, pearlite and Zw were strongly influenced by Mo. In the region of longer cooling time (cooling time from A3 to 500°C; above 60 sec), the growth of massive ferrite and ferrite sawteeth were controlled by the addition of Mo, and fine colony pearlite formed between both ferrite sideplates or both rodlike ferrites precipitated more easily than lamellar or degenerate pearlite. In the case of middle and shorter cooling time (cooling time; under 60 see), ferrite sideplate and rodlike ferrite or needlelike ferrite were more liable to develop than massive ferrite and ferrite sawteeth, and fine colony pearlite formed more easily than other pearlite. Zw accompanied with fine carbide precipitated easily in this region of cooling time. Mo element rasied the hardenability curves in synthetic weld heat-affected zone of steels. It seemed that the hardness is influenced considerably by the morphological change of, ferrite. The effect of Mo on the hardness of martensite was a little.
In this study, diffusion phenomenon of carbon and dissolution phenomenon of graphite in spheroidal graphite cast steel were researched in the case of both time and temperature varying simultaneously such as weld thermal cycles. Experimental results obtained in this study are as follows; (1) Diffusion phenomenon of carbon from graphite particle to matrix in the austenitic temperature range during weld thermal cycles can be explained phenomenologically by equation (4) in the initial stage of diffusion phenomenon. (2) The critical dissolution curve of graphite in the austenitic temperature range during weld thermal cycles obtained by equation (8) shifts slightly to the left from the critical dissolution curve determined experimentally.
The final purpose of this study is to clarify corrosion fatigue behaviour of steel plates and welded joints. In this report, the effect of alloyed elements on corrosion fatigue of steel plate was described. Results obtained are as follows: 1) In air, fatigue strength of low carbon steel alloyed by phosphor was increased than that of low carbon Si-Mn steel, but no effect of titanium, copper and chromium alloying was observed on the fatigue strength. 2) The effect of alloyed elements on the increment of corrosion fatigue strength in 3% NaCl aq. solution was observed not at all. Conversely, corrosion fatigue strength of titanium-alloyed low carbon steel was very low value. 3) Fatigues trength in air increased with the increment of the tensile strength of steel plates, but corrosion fatigue strength was not varied in spite of increment of the tensile strength. 4) Corrosion fatigue test in 3% NaCl aq. solution showed no endurance limit.
Parallel gap resistance welding of Ag plated 0.18 mm diameter oxygen free copper wires to three types of patterns (solder plated, Au plated, Au+Ni plated) of printed circuit boards (P/B) was investigated. Formation of weld fillets, metallurgical microstructures and mechanical properties of the welds were examined and some analysis of weld mechanism was made. The results are summarized as follows. A. Welding to the solder plated P/B, 1) Weld strength is held by Cu-Ag-Sn alloying phase in the pressure weld area of the wire and the pattern under the electrode indentation. And the solder fillet does not contribute to weld strength. 2) Linear relation is recognized between weld strength and the maximum pressure weld width. B. Welding to the Au and Au+Ni plated P/B, 3) When the weld fillet is small, weld strength is held by the pressure weld area as is in the case of the solder plated P/B. When large fillets are formed, weld strength is held by them. 4) Au plating has the role as the brazing agent. 5) Ni plating is effective for prevention or decrease of thermal damages to the pattern and the substrate.
Dealing with cold cracking of welded joints, it is rather convenient to devide the type of joint into two; butt and fillet welded. For butt joint, many good research works have been done and detail in-formation of the joint during welding has been provided. On the other hand, concerning cold cracks of fillet weld, many experimental researchs have been performed. With slight changes in the restraint for thermal deformation, various types of cracking have been observed, for example, at the toe and root, and under bead on the web side, and at the toe, heel and root on the flange side, etc., since local stress strain history may differ to a great extent. In this paper, a series of theoretical analysis of elastic-plastic behavior of fillet weld of the first bead was performed under various restraining conditions for steel of 50 kg/mm2 by the finite element method developed by one of the authors. Based on the results of the theoretical analysis, the following information was obtained. (1) When the restraint for uniform contraction of web is low, possible weld cracks many occur at the toe, root, and heel on the flange side, on the other hand, when this restraint becomes higher, the crack initiation is considered to move on the web side, such as at the root, toe, of the weld of the web. When the restraint is extremely strong, crack initiates at the root on the web side and propagates to the toe on the flange side. (2) When the restraint for rotation is low, the type of cracking is just similar to the previous case where the restraint for uniform contraction is low. When this restraint becomes severer and constrains free contraction along the flange, crack may be observed at the toe on the flange. (3) When fillet weld is laid on both sides of T-connection, crack is liable to occur in the first fillet weld, since the restraint stresses of the second weld are superimposed on the residual stresses produced by the first one. And cracks may be located at the root on the web and the toe on the flange.
Researching the variation of the maximum arc length in coated welding quantitatively, some empirical equations were introduced. In addition, critical wind velocity was defined which made a welding arc unable to be sparked as the extreme windy condition of obstructing the arc strike and characteristics of it was made clear experimentally. Results of the experiments are summarized as follows: (1) The relation between the maximum arc length(L) and the wind velocity(V) varies with a hyperbolic perbolic curve and within less than 1 m/s of wind velocity, the experimental curve is out of the hyperbola of the equation. Examples of the equation are shown below in case of lime-titania type electrode. L=23V-0.508 at 120Amp.of D.C L=31V-0.435 at 200Amp.of D.C. (2) The relation between the maximum arc length and covered flux thickness varies with a parabolic curve in t/r variables and reducing the value of t to zero, the experimental curve is out of the parabola of the equation. Examples of the equation are shown below in case of 120Amp. of D.C. L=22.71(t/r)0.174 at 0 m/s of wind velocity. L=6.3l (t/r)0.226 at 8 m/s of wind velocity. (3) The variation of reduction ratio of the maximum arc length[L(v)/L(o)] against the wind velocity describes a hyperbolic curve. Here L(v) shows the maximum arc length under blowing and L(o) under no blowing. In a bare electrode or coated one in high current region, it agrees with the hyperbola but in low current region it is off the hyperbola locally. (4) The variation of L(v)/L(o) against the covered flux thickness describes approximately a parabolic curve. The distribution has two limit lines. The upper line shaped by the values in high current maintains the parabolic curve independently of the wind but the lower line shaped in low current changes with the wind. (5) Critical wind velocity may be 30 m/s in ordinary condition of coated electrode. The velocity is proved to be raised by increasing the welding current, the flux thickness and decreasing the gap of electrodes. In a constant gap, the velocity depends upon the set angle of electrode and the angle of 1/4π is more effective than of 1/2π.