Fracture Mechanics Characteristics of Cast Roll Materials for Steel Hot Rolling

Abstract

  In hot rolling, rolls generally wear out under normal operations. However mechanical or thermal cracks generate and propagate, when accidents occur during the rolling operation. Therefore, fracture toughness and crack propagation characteristics were investigated using COD and CT test specimens for the typical materials of hot rolling rolls, such as alloy cast steel (CS), adamite (AD), Ni-hard cast iron (IC), high chromium cast iron (HCR) and multi-component white cast iron (HSS). Fracture toughness decreases as eutectic carbides crystallized. The Paris-Erdogan relation, da/dN=C (ΔK_I)^m holds between the rate of crack propagation (da/dN) and the range of stress intensity factor (ΔK_I), and the relation between the constants C and m is expressed by C ＝ 1.88 × 10^-5/10.6^m. The constant m has a large value over 2 mass% C where the carbides exist, and the higher the hardness, the larger is constant m. Crack growth is faster in the order of CS, AD, HCR, IC and HSS.