Mn-Cr バネ鋼の恒温変態による機械的性質

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For purpose of making clear the relation between the microstructure and the mechanical properties, firstly the isothermal transformation diagram of the Mn-Cr spring steel were determined, and mechanical properties were also determined with the specimens austenitized at 850℃ and isothermally transformed at each temperature, ranging between 300℃ (above Ms point) and 650℃. This diagram presented a doubly curved shape on account of a carbide-forming element such as chromium, and the pearlite transformation was sluggish as compared with the bainite transformation, so it led to be suitable for a hardenability. It was found that the content of the transformed martensite, quenched into an oil bath at 200℃, was less than that into a metal bath on account of the stabilization of austenite. The extraction replica method was the most available for making clear the carbide character, showing that the shapes of carbides in the bainite differed from those in the pearlite, and that the carbide became finer with decrease of transformation temperature in a bainite range. Most of the mechanical properties showed the irregular behavior in the upper bainite range. The mechanical properties were also plotted against Rockwell hardness and it was found that the tensile strength and endurance limit were proportional to the hardness, while the yield strength was out of proportion on account of the lower yield-tensile ratio in the pearlite range. The reduction of area showed a striking drop in the upper bainite range, but was increased gradually with decrease of transformation temperature. It was concluded that the reduction of area was depending mainly on the structure obtained at each temperature. As to the impact value, no remarkable change was observed.
社団法人日本鉄鋼協会の論文
1961-06-01

Mn-Cr バネ鋼の恒温変態による機械的性質

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