In this report, an idea as to estimating the degree of variation of the lattice-bond strength due to hydrogen which exits in metals was proposed. And so, for some transition metals, a quantitative calculation of the rate of lattice-decohesion was done with success, by taking the behavior of d-orbital electrons in consideration and by adopting Engel-Brewer theory, which is attempt to correlate the existing crystal structures with electron configurations.
This paper describes the relation between the characteristic value "As" at high temperature and properties of joint, where "As" is the ratio of the projected area of the indentation to the load. The following results were obtained after investigation on joints of Cu, Ti, Ni, Fe, Al (pure metal) and SUS 304 stainless steel. 1. Deformation at high temperature depends on diffusion. "As" is proportionate to diffusion coefficient and is formulated by temperature and time. 2. When the growth of the welded area does not depend on the shrinkage due to the mechanism of sintering, but mainly on the creep deformation, the properties of joint are determined by the following parameters. (a) Real welded area Ar=As⋅WL(mm2) (b) Joint Efficiency Ej=C2⋅C3Ar/A×100=C2⋅C3⋅As⋅WL/A×100(%) (c) Welding deformation As⋅WL/A≤0.2 ; Dw=O(%) As⋅WL/A>0.2 ; Dw=C4(As⋅WL/A-0.2)×100 (%) WL : welding load (kg) A : apparent welded area (mm2) C2 : constant that is related to the quality of real welded part C3 : constant that is ralated to the distribution and the shape of void C4 : constant 3. The shrinkage and the elimination of voids on welded area due to the mechanism of sintering depend markedly on diffusion coefficient. 4. Welding process is closely related to diffusion coefficient. BCC metals, such as aFe and flTi, are larger on diffusion coefficient and superiorer on the weldability than FCC and HCP metals.
The effect of deformation on hydrogenn diffusion has been studied with an electro-chemical flux monitoring technique sensitive to 10-13 atomsH/cm2-s during tensile test and constant load rupture test. Tensile test and constant load test have carried out, over a range of aging time and strain rates, on notched specimens of steel, hydrogen charged and quenched. When specimen was allowed to stand at room temperature under removed stress after deformation, the amount of evolved hydrogen decreased with increasing plastic strain and diffusion coefficient of hydrogen at near by notched part decreased. The result is explained by suggesting that hydrogen is trapped in defects and dislocations in plastic enclave. During tensile test, with increasing plastic strain, the amount of evolved hydrogen from plastic enclave increased than from elastic range in specimen and increased with decreasing deformed velosity, as cross head speed. As aging time increases, evolved hydrogen from near by notch increased and N.T.S. decreased, with more increasing aging time, N.T.S. recovered from embrittlement and that hydrogen decreased. The results are explained by suggesting that hydrogen trapped mainly dislocations is trasported with dislocation to plastic enclave under slower C.H.S. and with more increasing aging time removed out from dislocation. However, under quick C.H.S., trapped hydrogen is broken away from dislocation. On the constant load rupture test, the amount of evolved hydrogen from plastic enclave near by notched part and crack tip increased remarkably right before hydrogen delayed cracking.
For TIG and MIG arc welding, shielding gases such as Ar, He and CO2 are widely used to protect the weld parts from the surrounding air. Up to now, the optical method known as the Schrieren method, gas chromatography and the thermistor technique have been used to observe the shielding gas flow pattern. However, these methods are limited to examining the static state no arcing condition. We have developed an experimental method to make the actual gas flow pattern during arcing visible using a laser light source, and have found that the shielding gas distribution around the arc changed remarkably with an increase in current, arc length, gas flow rate, etc. when compared with the no arcing state.
In the previous paper, multirun RRC (Rigid Restraint Cracking) test and Modified Cranfield test were carried out for evaluating the susceptibility of lamellar tearing of SM41 and HT50. As the result, the phenomena of lamellar tearing was deeply dependent on the distribution of non-metallic inclusion (mainly Mn-S of A-type inclusion) and the restraint condition of joint, with discussing the relation between the susceptibility of lamellar tearing in the both testing methods and through-thickness tensile properties of steels. In this report, for the application to an actual structure, it is examined to get a standard for selection of plate material in the point of view of the prevention of lamellar tearing by a H-type restraint cracking test with an interposed plate. Conclusions obtained are as follows. (1) Higher sulphur content and restraint intensity (K) increase crack susceptibility. Also, good correlation between the susceptibility of lamellar tearing and through-thickness properties, such as the reduction of area at Z-direction, the ratio of transverse shrinkage by Brodeau-type test, or Inclusion Shape Factor in microstructure. Therefore, these may be available as an acceptance criteria for lamellar tearing. (2) The changes of leg length and groove geometry influence to the critical value of crack initiation in the above tests. (3) As for the susceptibility for lamellar tearing, good correlation between crack sensitivity parameters in Modified Cranfield test and H-type restraint cracking test is obtained. So, the susceptibility of lamellar tearing may be evaluated with the parameter obtained by Modified Cranfield test, which is simple and effective in reproducible, by clarifying the above correlation. (4) The susceptibility of lamellar tearing at interposed structure, as an example of the application of an actual structure in shipbuilding, is determined by calculating the value of restraint intensity of joint. As a result, grade of steel plate adopted may be selected by the above mentioned criteria for the prevention of lamellar tearing.