Gas-Inclusions in Mild Steel Arc Welds (1st. Report) Relation between gas-inclusions in weld metal and mechanical properties By N. Nagai, H. Shioya, K. Yano, K. Kunii, Y. Kawakami, T. Okauchi Abstract As regards the essential investigation of gas-inclusion in mild-steel weld deposits, a few informations have been published. However even at present the constituents, combined state and behaviour of gas-inclusion have many ambiguous points yet to be clarified. In order to determine the contents of oxide inclusion in weld metal, the authors after studying the various experimental results, adopted two analytical methods i. e., vacuum fusion method and Fitterer's residual method, which give a comparatively good stability of analytical value. On the other hand the hydrogen in weld metal was analysed by vacuum extraction method at high temperature (800 Ž), and the nitrogen was analysed by distillation method in addition to vacuum fusion method. In 1st report, they have been able to make clear some relations between these gas-inclusions and mechanical properties of weld metal. (A) In case of absence of hydrogen 1) The hyrogen in weld metal was removed by normalizing and annealing at 950 Ž. 2) Owing partly to difference in quantities of the alloy elements in weld metal, it was impossible to clarify the relation between gas-inclusion and the hardness, yield point and tensile strength of all-weld metal. 3) The relation between gas-inclusion and percentage of elongation or reduction in area of allweld metal had no appreciable tendency. 4) The lowering rate of impact value by "anneal-brittleness" (as named by Mr. Kikuchi) was nearly proportional to the difference between the oxygen obtained by vacuum fusion method and that by Fitterer's residual method. That is, it was found that the more the contents of the oxygen indeterminable by Fitterer's residual method increase, the higher the lowering rate by anneal-brittleness" becomes. (B) In case of presence of hydrogen (as welded) 1) When the fractured tensile specimen showed a severe occurrence of "fisheyes" in an arc weld ; percentage of elongation and reduction in area of all-weld metal decreased. 2) Contrary to expectation, the relation between the occurring rate of "fisheyes" and contents of hydrogen obtained by vacuum extraction method at high temperature (800 Ž) had no appreciable tendency.
Table 1 Comparisons of Oxygen Obtained by Vacuum Fusion and by Residue Analysis Table 2 Comparisons of Oxygen Obtained by Vacuum Fusion and by Residue Analysis 31
Table 3 Presumption of Compounds from Residues of Fitterer Residue Analysis Table 4 Examination of Reliability about Analytical Value of Oxide-Inclusion 32
Fig. 1 Specimen and sampling A. c Microscope specimen (A.C.) a M. " " (F.C.) a' }Analytical sample for vacuum fusion method H. A. Hardness " (A.C.) H. F." " (F. C.)b b'} " for alcoholic iodine method T. A. Tension "(A.C.)T. F. " " (F.C.)c c'} " for Fitterer.residual method I. A. Impact " (A.C.) s s'} " for common chemical analysis I. F. " " (F.C.) e }" for electrical analysis method (Gakushin method) Fig. 2 Cooling curves of heat treatments
Table 6 Chemical Composition of Deposits Table 7 Results of Analytical Test of Oxide Inclusion
Fig. 3 Results of hardness test (Vicker's hardness) Fig. 4 Vicker's hardness specimen and the location of points Fig. 5 Determination of broken position of all-weld-metal tensile specimen Table 3 Mechanical Properties of All-Weld-Metal 36
Table 9 Results of Charpy Impact Test Table 10 Difference of O2-contents Obtained by Vacuum Fusion Method and by Fitterer Residual Method 37
Fig. 6 Relations between differences of O2 contents obtained by vacuum fusion method and by Fitterer residual method and dropping rate of Charpy impact value Fig. 7 Relations between O0, N2 contents in weld metal and Charpy impact value of deposited metal 38 Fig. 8 Relation between oxygen,(v.f.m.- F.R.M.) and total H2
Table 11 Total Hydrogen in Welds Table 12 Relation between 02 and H2 Contents in Deposited Metal and Formation of "Fisheyes" ~... detected œ... suddenly detected... sometimes detected Z... none
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