| 摘要 |
PURPOSE:To remarkably reduce the cost of manufacture of a gearbox made of spheroidal graphite cast iron and to make the gearbox small in size and light in weight by austempering a stock under specified conditions optionally after rough working and by working it to regular dimensions. CONSTITUTION:When a gearbox made of spheroidal graphite cast iron is manufactured, a stock is austempered by heating, holding at 830-900 deg.C for 0.5-3hr, rapid cooling to 200-400 deg.C and holding for >=0.5hr optionally after rough working. A bainite-austenite mixed structure is formed as the matrix structure by the austempering. The stock is then worked to regular dimensions.
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