中炭素鋼の高温延性と窒化アルミの形態 : 鋼中の窒化アルミの研究 II

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The effect of aluminum nitride (AlN) precipitates on the high-temperature ductility of medium-carbon steel was investigated. Small tensile test pieces (Fig. 1) were made from the steels containing different amounts of aluminum and nitrogen (Table 1 and 2), and were drawn at 500∿1000℃. At first, tensile test pieces were made from the 50kg ingots as cast and were drawn without preheat-treatment. 1) The high-temperature ductility of medium-carbon steels as cast was decreased extremely by the addition of aluminum (Fig. 2 and 3). The steel containing about 0.05% acid-soluble aluminum had the lowest ductility, which was reduced from half to one-fourth of the ductility of the steel containing no aluminum. This phenomenon seemed to be on account that the small AlN particles precipitated dispersedly and pearlite obstruct to deform uniformly, and consepuently the rupture proceeded along the line of AlN particles precipitated at the grain-boundary of austenite. 2) The steels containing more than 0.05% acid-soluble aluminum had higher ductility (Fig. 2 and 3). This phenomenon seemed to be due to the fact that the more the aluminum content, the higher the precipitation temperature of AlN became, and consequently the large AlN particles precipitated at wider intervals. Next, the effect of AlN precipitates on the high temperature ductility during cooling after the solution-treatment of AlN precipitates was investigated. The tensile test pieces as cast were heated for 30mn at 1350℃ in order to dissolve AlN precipitates. Some of them were cooled slowly (cooling rate 150℃/h) and some rapidly from 1350℃ to 1000∿500℃, and then drawn. 3) The ductility in austenite (above 800℃) during slow-cooling from 1350℃ did not decrease by the addition of aluminum (Fig. 6). This phenomenon seemed to be due to the fact that the AlN particles precipitated during slow-cooling from 1350℃ are large and at wide intervals. 4) The ductility in ferrite and pearlite (below 700℃) during slow-cooling from 1350℃ decreased by the addition of aluminum (Fig. 6). This phenomenon seemed to be due to the fact that the rupture started from the line of AlN particles precipitated at the center of ferrite-net and proceeds along it. 5) The steel containing about 0.05% acid-soluble aluminum had the lowest ductility below 700℃ and the steels containing more than 0.05% acid-soluble aluminum had higher ductility (Fig. 6). This phenomenon seemed to be due to the fact that the more the aluminum content, the higher the precipitation temperature of AlN becomes and the cylindrical AlN particles precipitated at wider intervals, and consequently the brittle rupture became difficult to occur. 6) The ductility during rapid-cooling from 1350℃ was decreased by the addition of aluminum. This phenomenon seemed to be dependent on the fact for the line of small AlN particles precipitated along the austenite grain-boundary during cooling. Next, with the tensile test pieces made from the forged steel, the effect of AlN precipitates on the high-temperature ductility during cooling after solution-treatment was investigated. 7) The ductility during cooling of the forged steels was also influenced by the addition of aluminum like the ductility of the steels as cast. Finally, the mechanism of panel cracking found in medium-carbon steel ingot was considered. 8) Presumably there was a relation between the phenomenon that the panel cracking of medium-carbon steel ingot was increased by the addition of aluminum and the experiment resulted in that the ductility at high temperature was decreased by the addition of aluminum.
1962-05-01

中炭素鋼の高温延性と窒化アルミの形態 : 鋼中の窒化アルミの研究 II

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