| 摘要 |
PURPOSE: A method for estimating hot brittleness of BI-S free cutting steel is provided to recognize the propagation path of micro cracks around a fraction, thereby obtaining a reference temperature of the hot brittleness to be applied to the billet rolling. CONSTITUTION: In a method for estimating hot brittleness of BI-S free cutting steel, the BI-S free cutting steel consists of C 0.05-0.15wt%, Mn 0.5-2.0wt%, S 0.15-0.40wt%, P 0.01-0.10wt%, O 0.003-0.020wt%, Bi 0.03-0.30wt%, Si 0.01wt% or less, Al 0.009wt% or less, residual Fe and inevitable impurities. A reduction rate of fracture depth of the BI-S free cutting steel is measured by the high temperature tension test, and the reference temperature of the hot brittleness is estimated at a temperature when the fracture depth reduction rate becomes 57-67%.
|
