Patent ID: 7481896
Filing Date: 2009-01-27
Classification: C21D

Abstract:
1. In a power transmission shaft of plain carbon steel or low alloy steel, the improvement comprising heat treating the shaft by a heat treatment regime comprising the steps of: a) a first carboaustempering at a temperature where austenite is formed; b) a first quenching to a temperature at which bainite and martensite form, and holding at that temperature to cause formation of bainite and martensite; c) a second carboaustempering at a temperature where austenite is formed; d) a second quenching to a temperature at which bainite and martensite form and holding at that temperature to cause a carbon rich case formed in at least one of said first or said second carboaustemperings to transform to a microstructure comprising bainite and martensite, and to cause the interior of the shaft to form a microstructure primarily of bainite; and e) tempering the shaft.