The effects of stress at elevated tremperatures on age hardening in quenched low carbon rimmed steel after keeping at 620...700°C for 10...60 min were investigated. The results obtained are as follows: (1) Quench aging is promoted by the stress at elevated temperatures. The higher the heating temperature the larger the effects become. And the effects also become larger as the heating time is larger or the stress is larger. (2) It is recognized that the tendency to brittleness in the specimens stressed at elevated temperatures is evidently larger than that in the unstressed specimens.
Metallurgical and mechanical properties have been investigated concerning a dissimilar joint, 2 1/4Cr-1 Mo steel (ASTMF22) to austenitic stainless steel (AISI316), and a carbon steel (SM41A) joint produced by "Insert-type" electron beam welding technique. The conclusions can be summarized as follows: 1) In the restraint cracking test of a dissimilar joint using a Lehigh restraint cracking test specimen, crater cracking is observed at every crater irrespective of insert metal width and its material, that is, 25Cr-12Ni austenitic stainless steel and Inconel 600 but not any other cracking. 2) Microstructure of weld metal of a dissimilar joint is martensitic and austenitic respectively with introduction of 0.4 mm-wide 25Cr-12Ni austenitc stainless steel insert metal and Inconel 600 insert metal. Carburized and decarbruized bands are respecitvely observed in weld metal and HAZ adjacent to 2 1/4 Cr-1 Mo steel base metal due to post-weld heat treatment with introduction of 25Cr-12Ni austenitic stainless steel insert metal. This decarburized and coarse grain zone tends gradually to increase with an increase of insert metal width. This trouble hardly occurs with introduction of Inconel 600 insert metal. Weld metal of carbon steel joint forms ferritic and pearlitic structure after post-weld heat treatment. 3) Hardness of weld metal zone of a dissimilar joint shows high value, that is, Hv 450 and Hv 320 approximately in as-welded condition and even in heat-treated condition respectively with introduction of 0.4 mm-wide 25Cr-12Ni austenitic stainless steel. When 0.8 mm and 1.2 mm-wide 25Cr-12Ni austenitic stainless steel and Inconel 600 insert metal are introduced, hardness of weld metal zone is around Hv 200. Weld metal zone of carbon steel joint is softened up to Hv210 approximately by post-weld heat treatment. 4) By means of XMA area analysis along weld center and XMA line scanning across the welds at transverse cross-section, it has been proved that weld metal of a dissimilar joint fluctuates a little in Cr and Mn content with introduction of 25Cr-12Ni austentic stainless steel and in Ni, Cr and Fe content with introduction of Inconel 600 insert metal respectively. However, it may be safely said that fluctuation of concentration distribution of elements is not so remarkable as expected. Fluctuation of element of carbon steel joint is hardly recognized in weld metal zone in any case. Estimation formula is herein proposed on element distribution in weld metal zone produced by "Insert-type" electron beam welding technique. 5) Tensile, bending and impact properties of the welds are satisfactory in any case. 6) It might be condisered that there is hardly any appreciable difference in creep rupture strength resulting from insert metal width and its material at 550°C and 600°C. It should also be added that creep rupture strength at 550°C nearly approaches that of 2 1/4Cr-1Mo steel joint derived from ASTM Data irrespective of insert metal width and its material. In addition, there is hardly any effect of decarburized and coarse grain zone on creep rupture properties and feature of fracture if rupture time is shorter than 2000h at 550°C and 1000h at 600°C respectively.
In this study, the reliability of solid state bonded joints of TD nickel was examined by tensile tests at high temperatures and fractography. The main results obtained are summarized as follows: (1) The joint efficiencies of solid state bonded joints made by one-step bonding method were about 100%. And the joint efficiencies were superior to those of the fusion welded joints. But, the reduction of area in such joints was inferior to that in the base metal. (2) The joint efficiencies of solid state bonded joints made by two-step bonding method were 100% and the reduction of area in such joints was 80-100% of that in the base metal.
The relation between a grain boundary and a mottling appearing on a radiograph of austenitic stainless steel weldments and castings was investigated. 1. Some evidences that seem to suggest a close relation between a grain boundary and a mottling were obtained. 2. The mottled appearance is related to the δ ferrite content in the weldment. However, a disappearance of the δ ferrite caused by a solution treatment has little effect, if any, on the mottled appearance. The result suggests that there is no relation between the δ ferrite itself and the mottled appearance. The results obtained in this investigation seem to suggest that grain boundary is important concerning the mechanism of the mottled appearance.
The effect of Mn on transformation behaviour in synthetic weld heat-affected zone of steel was investigated using simplified steels made of pure metals and graphite. Mn element displaced the SH-CCT diagram for each transformation region to a longer time and to a lower reaction temperature. Each critical cooling time Cf', Cp' or Cc' obtained from the SH-CCT diagram for welding increased with Mn content. Especially, the effects of Mn above 1 % on each critical coloing time were remarkable. Morphologies of ferrite, pearlite and Zw (Zwischenstufengefüge) were strongly influenced by Mn. When Mn content increased, the morphology of ferrite formation was more liable to develop sideplate and rodlike or needlelike ferrite than massive ferrite. Pearlite morphology was affected by Mn. The fine colony pearlite formed between both ferrite sideplates or both rodlike ferrites precipitated more easily than lamellar or degenerate pcarlite. Zw precipitated easily in the region of longer cooling time (cooling time from A3 or Ac3 to 500°C; above 60 see). In this case, Zw seemed to have the morphology in which austenite between both ferrite sideplates or both thick rodelike ferrites decomposed to ferrite and a relative large cementite. Martensite transformation was promoted by Mn content in steel. The effect of Mn on the hardness of martensite was a little, while Mn element (above 0.5 %) raised the hardenability curves obtained from the diagram that expresses the relation between cooling time and hardness in synthetic weld heat-affected zone of steel. It seems that the volumes of Zw and martensite increase with Mn content.
In this paper, a newly developed narrow-gap one-side arc welding process is introduced. This process is a CO2-O2 or CO2 arc welding with insertion of a specially designed coated rod and with backing flux. The advantages of the new process are; high welding efficiency, excellent reverse side bead appearance, less weld metal, low cost of welding operation and so on. This paper describes the principle of the process, welding materials used, welding details, properties of weld metal and welded joints, welding efficiency, economy of the process and examples of application of this process to the shop welding of steel structures of building.
Effects of sulphur, nickel, carbon, manganese and phosphorus on weld solidification crack susceptibility of various commercial and tentative high tensile steels (tensile strength: 50-100 kg/mm2 class) have been investigated using the Longi-Varestraint test. Main conclusions obtained are as follows: 1) Sulphur, even at 0.005% level, remarkably increases the solidification crack susceptibility. 2) Nickel and carbon promote the detrimental effect of sulphur (and phosphorus). 3) Even in the steel containing nickel and/or crabon, the high crack susceptibility induced by sulphur can be lowered by increasing the manganese content. And the manganese content required agrees with the value deduced theoretically in the previous paper. This is given by the condition that Mn5S is larger than 310-560. 4) Phosphorus also remarkably increases the crack susceptibility in the steel containing nickel (and carbon).
Previous reports showed that sulfur-segregation and hot cracking sensitivity of steel weld metalmight increase remarkably through the peritectic reaction of the Fe-C or Fe-Ni phase diagram using as-cast steel specimens. This significant sulfur-segregation in solidification grain boundary through the peritectic reaction may not only increase the hot cracking sensitivity but also decrease the toughness of steel weld metal. Then, the effect of the Fe-C peritectic reaction on the toughness of as-solidified steel was investigated using as-cast specimens with various carbon contents. It was experimentally confirmed that the toughness of as-solidified steel with more than 0.1% of carbon content deteriorated remarkably because of the significant sulfur-segregation through the Fe-C peritectic reaction. It is concluded from the facts described above that the carbon content should be controlled to less than 0.1% with lower sulfur content to assure enough toughness of steel weld metal.
Various types of cold cracks, such as a toe, an underbead, a heel, and a root crack, are found in the fillet welds of 50 kg/mm2 grade high tensile strength steel. Many studies have been performed on each particular type of crack, giving useful information on the nature and mechanism of the cracking. This investigation was planned, firstly, to analyze the stress distribution by simple linear model, secondly, to develop a new cracking test which could produce each type of crack under the restraint quantitatively evaluated and finally, to use the test to obtain basic information on each crack, especially the correlation between the crack type and intensity, of restraint. Main results obtained are as follows. (1) The linear model used in this analysis provides a good approximation for the relative steress distributions in the fillet weldment. (2) In the small intensity of restraint, stress in HAZ of flange and its toe is larger than other parts of welds, and in large intensity of restraint, large stress concentrates at the root of the weld metal and the toe of web. (3) In the one pass fillet welding, toe crack in HAZ of web occurs not by angular displacement but by restraining vertical displacement of the plates. (4) The CRP (Controlled Restraint Fillet) test developed in this investigation can readily produce all types of the cold cracks in fillet welds. (5) The surface cracks appear at the web toe in the large intensity of restraint, and at the flange toe in the small intensity of restraint. (6) As regards the sectional cracks, the toe crack at the web occurs under the largest intensity of restraint and the heel crack under the smallest one. The root or underbead crack occurs the intermediate wide region between the above-mentioned two extremeities. (7) With the increase in the intensity of restraint, the cracking ratio of weld metal root cracks increases and that of the heel cracks decreases. (8) The cracking strongly depends on the intensity of restraint and also on the dimensions of the test piece even under the same intensity of restraint. (9) The toe and the underbead cracks are both the hydrogen induced cracks, but differ in the macroscopic appearance due to the different stress field induced by the condition of restraint. (10) Results of the analysis by the linear model are in good accordance with those of the CRF cracking test.
The impact properties at the bond of weld joints for 80 kg/mm2 class high tensile strength steels were investigated in relation to the austenite grain size, ferrite lath size and shape of carbide. Fracture mode at 0°C with increasing heat input changed cleavage type from dimple partten and fracture continuation was found to pass through a region of the relative rough ferrite lath, which was situated at about 50-250μm from fusion line. With increasing heat input, the region of the relative rough ferrite lath was widly, austenite grain size at near by bond also grew up and the transition temperature raised. The toughness at near by bond depended on austenite grain size in only rapid cooling rate, but in lower cooling rate and in size of 60-200μm austenite grain, its toughness did not show clearly to depend on austenite grain size. Therefore, based on the observation of fracture surface and microstructure by two-stage replica method, the unit facet and ferrite lath size were defined. The unit facet and ferrite lath size showed a good correlation to the transition temperature. These results suggested that the bond brittelness depend on the morpology of structure, namely, the ferrite lath size and/or the distance of individual carbide precipitated lath boundary and in lath.