The nirtogen contents of Ni-Fe, Ni-Cr and Ni-Fe-Cr weld metals deposited in nitrogen or air were systematically determined. Some of them were compared with the solubility of nitrogen measured in an equilibrium state at 1600°C. The main results obtained are summarized as follows: 1 The nitrogen content of Ni-Fe alloy weld metals increases continuously with the iron content of electrode wires. More nitrogen is absorbed in an air atmosphere than in a nitrogen atmosphere. 2 The nitrogen content of Ni-Cr alloy weld metals increases with the chromium content of electrode wires. Less nitrogen is absorbed in an air atmosphere than in a nitrogen atmosphere. 3 The nitrogen content of Ni-Fe-Cr weld metals is influenced greatly by the chromium content of electrode wires. 4 The nitrogen contents of Ni-Fe-Cr weld metals were shown with contour lines of iso-nitrogen content in a ternary diagram.
As a 0.05-0.08% C cast steel is inferior in toughness but superior in strength to a 0.01 % C cast steel which was reported in the previous report, the effects of alloying elements on the toughness and mechanical properties of the 0.05-0.08% C caset steel were investigated. Then the toughnesses of cast steels were summarized and compared with those of remelted casts of mild and high strength steel plates and electrode wires and also with those of their weld metals by CO2-O2 arc welding. Consequently the results obtained were discussed in comparison with the results of weld metals by other researchers. They are summarized as follows. 1) The toughness of the 0.05-0.08% C cast steel was improved by suitable additions of aluminium and nickel. The addition of chromium had a detrimental effect on the toughness of the 0.05-0.08% C cast steel, but it seemsto be effective to improve the toughness of the cast steel, if the carbon content of the cast steel is under 0.05%. The addition of molybdenum was not effective to improve the toughness of the 0.05-0.08% C cast steel. 2) Especially the transition temperature of the 0.08% C cast steel containing 0.002% Al was -40°C and lower than that of the 0.01 % C Mn-Si cast steel. 3) The tensile strength of the 0.05-0.08% C cast steel was scarcely influenced by additions of these alloying elements. Its value was about 55 kg/cm2. 4) The impact vlaues of the 0.44% Ni-added and 0.002% Al-added 0.08% C cast steel were much higher than those of remelted casts of mild and high strength steee plates and electrode wires and their weld metals. 5) These experimental results with cast steels are in good coincidence with those of weld metals.
For the prupose of examining the causes of lamellar tearing occurrence in multirun fillet welds, we have carried out various experiments, such as restraint cracking test for measuring various reaction stresses through the plate thickness, measurement of cracking time and hydrogen charged test. The test results are summarized as follows: (1) Critical reaction stress for lamellar tearing decreased with the increase of diffusible hydrogen contents in weld meta.l (2) Lamellar tearing occurred at temperature below 100°C. (3) The delayed fracture phenomenon of lamellar tearing could be reproduced from hydrogen charged test. (4) From (1) (2) (3), lamellar tearing is considered a cold crack due to hydrogen embrittlement. (5) The relation among diffusible hydrogen, restraint and materials associated with lamellar tearing were shown in Fig. 14.
Some creep rupture properties at 600 and 700°C of type AISI 304 and 316 austenitic stainless steels, 30 mm in thickness, are discussed by comparing the test results between both welded specimens and observing the repture region of welded joints macro-and microscopically. The results are as follows: (1) A difference in the creep rupture strength of welded specimens between the type 304 and the type 316 steels is hardly observed at 600°C In the case of test temperature 700°C, however, the creep rupture strength of weleded specimen of type 316 steel may tend to be lower than that of type 304 steel, as the rupture time becomes longer. (2) A crack, leading to a creep rupture, propagates preferentially in the region having fine carbides scattered in the austenite matrix adjacent to delta ferrite. Consequently, it has become clear that the creep rupture strength of welded joints of austenitic stainless steels is affected by the metallurgical change at high temperature in a long period, in the vicinity of the interface between the delta ferrite and the austenite in the weld metal.