Temperature variation of any point of thick mother plate due to the linear moving heat source is calculated from the newly derived fundamental equation reported in literature (1). Temperature curves are compared with those due to the instantaneously delivered line heat source. Fig. 12 shows the temperature curves near bead ends and we see the differences of temperatures of starting and stopping sides compared with that of infinite velocity.
The correlation between V Charpy test and COD test is investigated for the structural steel with strength range from mild steel to HT80 including their weld zone. The results are summerized as follows: (1) The transition temperature T*i of δc is defined as the temperature at which δc=δi=0.16 mm. Temperature shift ΔT* between T*i and vTs is expressed as a function of yield strength at the room temperature and the plate thickness by the following relation. ΔT*=vTs-T*i =120-σY0-5(√t-√20) (1) where ΔT*, T*i:(°C) vTs:V Charpy 50% crystallinity transition temperature (°C) σYo:yield stress at R.T. (kg/mm2) t:plate thickness (mm) (2) The relation between δc(T) and vE(T+ΔT*) is obtained for the vE transition range. δc(T)=0.02vE(T+ΔT*) (2) where δc(T):δc at T=T (mm) vE(T+ΔT*):vE at T=T+ΔT* (kg-m) For the upper shelf range of vE, δc can be estimated from Eq. (2) by using vE* value instead of VE. Where vE* is defined by the following relation. vE*=vE*0 exp (-T0/T) (3) Ev*0 and T0 are material constants, which are determined empirically from the assumption that temperature dependence of vE in the transition range is of Arrhenius type, i.e., vE* is an extrapolated value of Eq. (3) to the upper shelf temperature of T.
The initiation and propagation characteristics of the lamellar tearing are studied by the AE technique. MIG welding process in a chamber charged with argon is used to eliminate the noises started from the self-crushing of slag. From the results of the small type through thickness restraint, cracking test, three mechanisms to the occurrence of lamellar tearing are proposed which correspond with the metallurgical factors, such as chemical analysis and non-metallic inclusions, of the rolled plate. As the conventional type of the lamellar, tear, the cracking is originated by the decohesion of the non-metallic inclusions from the matrix and extended to fibrous fractures right after completing the weld deposition prior to the individual element of the crack linking up intermittently. This intermittent behavior reveals to be lasted for several hours, and the propagation of the crack is of the typical hydrogen induced cracking. For the steel which has sufficiently poor through thickness ductility, the lamellar tear can be initiated and propagated by only shear-mode. For the steel which has high susceptibility to hydrogen embrittlement, the lamellar tear is apt to follow the root or toe cracks in the pattern of parallel to the surface of the plate.
The attempts was conducted to develop the testing procedure which provided a quantitative assessment of lamellar tearing susceptibility on the basis of its occurrence mechanism. Several lamellar tearing tests, in which the constant strain test proposed by authers was included, were carried out on different types of Al-killed steels, and the physical meanings of their criteria were discussed. Using the constant strain test, the critical strain levels which need to the decohesion cracking and hydrogen-induced one from non-metallic inclusions are determined respectively, and the causes of lamellar tearing will be able to be clearified for individual plate. The value of reduction of area in a through-thickness tensile test will be considered to have comparatively good correlation with the cracking from MnS inclusions, whereas the value will not correlate with the lamellar tearing when it is induced from oxide inclusions at the sub-surface of plate. The difference between the susceptibility to root crack in a roll direction and that in a through-thickness direction was apt to increase with the rise of the lamellar tearing susceptibility. Microanalyses by EPMA showed that the inclusions playing a significant role for the cracking were found to be sulfide for Al-killed steels with more than 0.01 %S, alumina for those with less than the level.
In diffusion welding, the insert metal is generally used in order to attain intimate contact at lower temperature and pressure. Ion plating process, in which deposition and cleaning advance are expected at the same time, is effectively applied as method to insert metals between welding interface. The purpose of this study is to investigate the influence of ion plating condition on growth of coating film and the weldability of ion plated iron, copper and aluminum. Then the insert metal is silver. The following results were obtained. 1) The adherence of the silver coating to the substrate is excellent and this film is clean. Therefore ion plating is superior in the weldability to other mtehods, such as chemical deposition, vacuum deposition and foil, as method to apply the insert metal. 2) In diffussion welding while ion plating, the lower Ar pressure is, the higher discharge voltage and discharge input are, the better the weldability is. Proper thickness of the insert metal is 5-10μ. 3) Surface which dose not face to the evaporation source is coated too, and the weldability of this side is similar to other side. 4) Ratio of deposition and throwing power does not depend on substrate material, discharge voltage and current, but on gas pressure, rate of evaporation and distance between electrodes.
As a basic research of diffusion welding, a diffusion process of interlayer metal near the bonded interface and the mechanical properties of the bonded specimens were investigated. Experiments were made in the several combinations of base metals and interlayer metals which had either a continuous solid solubility or a limited solubility. A summary of the results obtained were as follows; 1. Weldability, such as tensile strength and reduction of area, of copper bonded by inserting a gold foil being a continuous solid solubility for copper were superior to those which was bonded directly without any interlayer metals and those which was bonded by inserting a silver foil having a limited solubility for copper. 2. For the improvement of the weldability in diffusion welding, it is desirable to use interlayer metals which diffuse to a greater extent into base metals. 3. Apparent diffusion coefficients of interlayer metals into base metals were estimated by neglecting the dependence on concentration. As the results, at a relatively low temperature range the apparent diffusivities obtained were much larger than impurity diffusion coefficients for the attribution to boundary diffusion, but at a high temperatuer range the apparent diffusion coefficients approach to the impurity diffusion coefficients.