Microstructural-Mechanical Property Relationships in High Strength Cast Steels.

摘要

The influence of different types of chill materials placed under the entire bottom surface of 20in. x 20in. x 5-1/2in. thick AISI 4335type cast steel plates on the rate of removal of heat from the solidifying casting was determined. The effects that these chills exerted on the metallographic structure and mechanical properties after quenching and tempering to high strength were determined. The results obtained with these chilled 20in. x 20in. x 5-1/2in. plates were compared to bottom chilled 60in. x 48in. x 4to 6in. thick plates cast by two cooperating commercial foundries. It was determined that the rate of heat transfer into a bottom chill increases somewhat during the pour to a relatively high value but then decreases sharply to a constant value of about 75plus or minus 5Btu/hr-FtF about 3minutes after the pour for all chill materials tested. This decrease in heat transfer occurs because of a gap formation at the casting-chill interface. Water cooled copper was the most effective chill material because of its higher heat diffusivity. The secondary dendrite arm spacing in the steel castings are refined by the steeper thermal gradients accompanying the faster rate of heat removed. (Author)