Effects of chemical composition of base metals (especially, C, O and Cr) on occurrence of vertical and horizontal cracks were investigated in deep penetration EBW in the flat position. Fifteen types of commercial steel plates and eight types of deposited weld metals, which contained various amounts of C, O and Cr, were used in this stydy. Penetration depths ranging from 50 to 80 mm were mostly used. It was concluded that, (1) Vertical cracks were likely to occur at 0.2 m/min welding speed when chemical composition of base metals was in the range of (C)≤0.25 %, (O)≤220 ppm and (%C)×(%O)≤2×10-3. (2) In case of welding of low C and high O base metals, the Cr content suppressed occurrence of vertical cracks. (3) Turbulence of welding phenomena caused by CO gas emission from the molten pool was attributed to be a main reason of vertical crack formation. (4) When abase metal, of which chemical composition was in the range of (C)<0.2 % and (O)<60 ppm, was welded at 0.5 m/min welding speed, occurrence ratio of vertical cracks increased with increase of the Cr content. This fact suggested another formation mechanism for vertical cracks. (5) In welding of killed steel, number of horizontal cracks increased with increase of the C content above 0.2 %. This tendency can be explained from the Fe-C phase diagram that decrease of maximum solid solubility of S and P is mainly responsible for the cracking.
Recrystallization behaviour of commercial pure aluminium may be affected by the morphology of substructures. In this study, commercial pure Al of 10 mm thick plate was prepared. That was machined to the plates of various thickness, then these were full annealed at 600°C for 30 min. All plates were made equal to 2 mm thick plates by three kind of treatments, these were cold-rolling, cold-rolling and 200°C×30 min. annealing (in this report, quasi stabilized treatment=Q.S.T.) and hotrolling. Each treatment induced another type of substructure, i.e. tangled dislocations, statically recovered structure, and dynamically recovered structure. Recrystallization behaviour of these three types of substructure-induced specimens was studied by isothermal heat treatments at various temperatures. And, softened width and recrystallized grain diameter at the electron beam weld heat affected zone of substructure-induced plates were compared. Test plates were 100 mm×100 mm square plates of 2 mm thickness. Obtained results were as follows; (1)Annealing at 200°C for 30 min. after cold-rolling gave smaller recrystallized grain diameter and hieher recrvstallization temperature than cold-rolled test specimens. (2)The higher the hot-roing temperaturc, the higher the recrystallization tempcrature became, but slight change of recrystallized grain diaameter was observcd. (3)While hardness of substructure-induced test speciren was below 30, hot-rolled test specimens had higher recrystallization temperature and smaller grain diameter than cold-rolled with or without Q.S.T.specimens. (4)Softened width and grain diameter of electron beam weld heat affected zone of cold-rolled plates were larger than these of cold-rolled with Q.S.T.or hot-rolled plates.
As a research of the essential characteristics of welding fumes, variations of elemental percentages in fumes have been studied as functions of respective percentages in the coverings, using various grades of commerical covered electrodes and some test electrodes. Together with observation of welding arc by means of high-speed camera, fume generating phenomena and mechanisms have been considered. In general, the content of an element in fume is linearly increased with increasing content in covering. The higher the vapor pressure, the larger the regression coefficient. In the cases of iron-oxide and alkaline, the correlation between contents in fume and in covering is much different according to the type of covering, lime or non-lime. Iron-oxide occupies almost 50 % in fumes from non-lime covering, while it is always lower than 25 % in fumes from lime covering. Alkaline content is much higher in lime fumes than non-lime even if they have the same content in covering. Intermediate covering of a test electrode produces fumes with intermediate characteristics in terms of iron-oxide and alkaline. Calcium is a major cause of the lime type behavior, and it is more effective when more calcium fluoride is contained. The arc of non-lime electrode generates from molten metal at the tip of the electrode, while that of lime electrode comes through the molten slag which covers the hanging drop at the tip. Therefore, the former fume composition is regulated by the molten metal composition, and the latter by the molten slag. Thus the mechanism of the difference between lime and non-lime can be explained.
The TLP (Transient Liquid Phase) weldability of nickel-base heat-resistant alloys (Hastelloy X, Inconel X-750 and Udimet 500) have been studied by microscopy, electron-probe-microanalysis, tensile tests and stress-rupture tests of the joints. The major cause to restrict the TLP weldability was the formation during welding of a continuous array of stable Ti, Al and/or Nb compounds at the joint interface, which produce a weak plane joint grain boundary. In order to prevent this phenomenon, it was found important for interlayer alloys to melt moderately the base metal surface at the joint interface. For this purpose it was indicated that such interlayer alloys as including both boron and silicon which lower the melting point of the interlayer were more effective for TLP welding.
Microstructure in weld-heat affected zone of high strength steel was investigated mainly from the viewpoint of martensite-austenite (M-A) constituent. Main results obtained were as follows. (1) Microstructure could be easily classified by scanning electron microscopy if suitable etching technique was used. (2) Main structure changed from martensite through BIII type bainite+BI III type bainite (mixed structure of BI and B III type) to BI type bainite, with increasing of cooling time. (3) Morphology of M-A constituent in BI type bainite changed from elongated shape to massive shape with increasing of cooling time. When cooling time increased further, the decomposed structure of ferrite and carbide appeared. Therefore, the amount of M-A constituent decreased when cooling time was very long. (4) M-A constituent was formed from the austenite in which carbon had been condensed up to 0.5-0.8% on cooling to about 400°C. (5) M-A constituent consisted of lath martensite, twin martensite and retained austenite.
A new test (the so called BNP test) has been proposed to evaluate the susceptibility of coarse grained HAZ to hot straining embrittlement by the authors. In this paper, to confirm the competence of the BNP test, the correlation between the degree of embrittlement in BNP test and that in PBC (pre-compression bending COD) test proposed by Satoh et al. has been investigated. The tests have been made on the coarse grained HAZ in HT 80 and SM 50 steels as a function of welding heat input. Results can be summarized as follows. (1) Transition temperatures (Trs) by BNP test shows a good correlation with Trs by PBC. (2) The increment of the transition temperature (ΔTrs) by hot straining embrittlement in BNP test shows good correlation with ΔTrs in PBC test. (3) Since the PBC test holds a close correlation with the Wells-Kihara wide plate test, an analogous situation may be expected for the BNP test.
This paper deals with the effect of welding conditions on changes of root gap during welding in case of butt weld joints without restraint like strong backs and tack welds ahead of the heat source. The calculations of changes of root gap during welding are carried out under various conditions of heat input and plate width by means of two dimensional finite element method supported by experimental results. The main conclusions obtained in this report are summarized as follows: (1) Root gap at heat source (Displacement at heat source (uH)) opens as the heat source moves. (2) Displacement at heat source (uH) is determined by heat input per unit plate thickness and unit weld length (q/vh), molten pool length lead from the mechanical point of view (lM) and plate width (W). (3) Displacement at heat source (uH) is approximately expressed by the following equation. uH=A(l/lm)m where m is determined by lM and W, and A is determined by q/vh, lM and W.
The root cracking in the root-pass welds was studied in the Report 1. It may be too conservative to employ the critical preheating temperature obtained from root-pass cracking tests for the necessary preheating temperature. In this study, the critical preheating temperatures for preventing cracking in the root-pass welds and multi-run welds have been compared for steels including mild steel, pressure vessel steel and high strength steel. The cracks investigated in these cracking tests include root crack, toe crack and under-head crack. The findings in this study are as follows: 1) The cad cracking susceptibility of carbon manganese steels and low alloy steels with carbon more than 0.16 % may be better evaluated by Ceq(WES) than PCM. For steels with carbon less than 0.16 %, PCM may be a proper parameter rather than Ceq. 2) The critical preheating temperature for preventing root cracking in multi-run welds is less than that for root-pass welds by 50 to 75°C, mainly because of a decrease in hydrogen accumulation at the root by a post heating effect of subsequent passes. 3) The critical preheating temperature for preventing toe and under-bead cracking in restrained multi-run butt weldments is lower than that for multi-run root cracking, especially in a lower Ceq range. 4) It may be practical to select the preheating and inter-pass temperature based on the toe cracking prevention preheating temperature rather than that for root cracking in root-pass welds.
The relation of the notch toughness of weld heat affected zone of 13Cr cast steel with 2 to 6 % of nickel added for the improvement of weldability and weld heat cycle was examined by means of a weld heat cycle simulating method and the following results were obtained: (1) The impact value (2uE0) was the highest in 2Ni when peak temperature in heat cycle was less than Ac, point and the lowest in 6Ni. Between Act and Ac3 points in 2Ni and 4Ni impact value drop was great but slight in 6Ni. (2) Temper embrittlement was not recognized in the region of 600 to 650°C as seen in low Ni-13Cr cast steel. (3) In 2Ni and 4Ni, the influence of temperature of a weld before commencement of postheating was large and when less than the vicinity of Mf point, the impact value would be remarkably improved due to postheating (more than 600°C). However, the value was little changed in 6Ni.
The effects of grain size, reduction and heat input on recrystallization in weld-heat affected zone of cold rolled commercial-purity aluminum were examined quantitatively using the method proposed by the authors previously. That is, the relation between grain size or reduction and the value of constants in recrystallization equation was obtained. Then, the effects of grain size, reduction and heat input on recrystallization width of weld-heat affected zone were obtained by combining recrystallization equation and heat conduction equation.