On the Relation between Graphitization and Cooling Conditions of Partially Arc Melted Cast Iron

Effect of cooling conditions on the graphitization of partially arc melted cast irons were investigated. As test specimens, the cast iron containing ab. 3.3 per cent carbon and 1.5 per cent silicon were used. For the cast iron specimen melted in the central position in TIG arc, various heat-treatments were carried out and annealed at 750℃?850℃. The following results were obtained. (1) When the arc melting time was increased, tempered graphites became larger, because of the slow cooling rate of the treated specimens. (2) When the specimens were quenched into oil or water after the arc melting, the tempered graphite sizes were almost the same regardless of the time of arc melting. (3) When the cooling rate from molten metal to room temperature increased, a fine tempered graphite was obtained, especially by a rapid cooling from ab. 850℃. A heat-treatment to stabilize the structure before the graphitizing treatment made it difficult to obtain a fine tempered graphite. The results of the present study indicate that in the practical welding of cast iron, pre- and post-heat treatments make the graphitization difficult with the rise of the temperature, because of the decrease of the cooling rate on the weld part

Welding of Cast Iron and Nodular Graphite Cast Steel. I : Properties of the Heat Affected Zone of Cast Iron

Metallographic studies have been made on the structure and properties of the weld heat-affected zone in cast iron by the single-bead tests. The thickness of the ledeburitic layer varies with the melting point of the electrodes. In the martensitic layer, "white" and "dark" martensite were observed by using different electrodes and various welding conditions. It was determined from the isothermal transformation diagrams that these two types of martensite correspond respectively to fast and slow cooling below the M_s point, the critical cooling rate being about 1℃/sec. The amount of retained austenite was about 17 to 27 per cent, showing no appreciable difference between the electrodes. It was pointed out from the calculation that the diffusion of nickel from the deposited metal to the heat-affected zone was negligibly small

Effect of Preheat and Annealing on the Arc Welding of Cast Iron

Effects of preheat and annealing on the structures and the properties of deposited metal, and the white iron layer in the heat-affected zone of cast iron welds were investigated with the single bead method by using commerical mild steel and Ni 55 electrode. Bead-cracks by mild steel electrode were markedly decreased at preheat temperatures higher than 400℃. Microstructures also varied at this temperature, namely bainite was observed in the heat-affected zone, and the deposited metal was changed from martensite to white iron. With increasing preheat temperature, penetration of deposited metal was increased, consequently carbon content of the deposited metal was increased. Bead-cracks were decreased with decreasing welding currents. When preheat temperature was low, the hardness of weldment was increased by 300℃ annealing in both cases of mild steel and Ni 55 electrode, because of the increase of retained austenite and the precipitations of carbide

Welding by Single Bead Test, and Rapid Heating and Cooling Structures of 13% Chromium Stainless Steel

The metallographic studies have been performed on the structures of weld metal and heat-affected zone of 13% chromium martensitic stainless steel. The heat-affected zone was obtained by single bead welding, in which a single bead 10～12cm long was put on 13% chromium stainless steel plate 200×75×20mm^3. The isothermal austenitization diagrams (T-T-A diagram. Time-Temperature-Austenitization diagram) were determined for two specimens differently preheat-treated. The specimen was heated in a salt bath, followed by rapid quenching in water, and then T-T-A diagram was obtained from changes in hardness (Hv) and in matrix structure

Welding of Cast Iron and Nodular Graphite Cast Steel. II : Arc-Welding of Nodular Graphite Cast Steel

The arc-welding of nodular graphite cast steel containing 1.2～1.5 per cent carbon and 1.8～2.8 per cent silicon was studied by the single-bead test and the tensile test with butt-welded specimens. The microstructures of weld metal and of heat-affected zone were examined by the single-bead tests by using cast iron and pure iron electrodes under the various preheats or post-weld annealings. The most remarkable difference of the microstructure from that of cast iron was the lack of ledeburitic layer in the heat-affected zone. The tensile test with butt-welded specimens was carried out by using E7016, D4316 (E6016), Ni-55 and cast iron electrodes. With post-weld annealing at 850℃, E7016 and D4316 could be applied with tolerable success. Ni-55 was also applicable even without annealing. The distribution of hardness and the microstructure were examined with the butt-welded specimens

Behaviours of the Precipitates of 17-4 PH Stainless Steel by the Arc Welding Heat

Behaviours of the precipitates and hardness in the heat-affected zone of 17-4 PH stainless steel were investigated. The heat-affected zone was obtained by single bead welding using a TIG arc method, in which a single bead 10 cm in length was placed on the 17-4 PH stainless steel plate of 20×50×200 mm^3. To analyze the precipitates and the hardness distribution in heat-affected zone, the specimen, 15 mm in length and 5 mm in diameter, was rapidly heated and cooled by the reproducing weld thermal cycle apparatus using a high-frequency induction heating. The hardness of the specimen subjected to the thermal cycle by the reproducing weld thermal cycle apparatus was compared with the hardness in the heat-affected zone subjected to the weld thermal cycle under TIG arc welding. The results may be surmmarized as follows : (1) In the heat-affected zone of 17-4 PH stainless steel solution treated, the maximum hardness was obtained at about 600℃, and this temperature was about 100℃ higher than that of ordinary precipitation treatment. The higher the precipitation temperature, the lower became the maximum hardness with increasing precipitation time. (2) In the base metals subjected to the reproducing weld thermal cycle at a peak temperature of 650℃ prior to the precipitation treatment, there appeared some parts which were not hardened by the precipitation treatment. The softening temperature by the weld thermal cycles in the heat-affected zone of the base metal subjected to the precipitation treatment ranged from 650°to 900℃, and the solid solutioning was fully accomplished at a temperature above 900℃