Application of New Estimating Method of Fracture Toughness by Use of Equation of σ_m=ψKS_lcS_mf^1/2 to High Speed Steel

Abstract

We investigated whether our new estimating method of fracture toughness (K_IC) by use of equation of σ_m-ψK_IC S_mf^1/2 (σ_m; three point bending fracture strength, ψ, a material factor, S_mf; total macroscopic area of bending fracture surface of all fragments for one test piece) is applicable to high speed steel (HSS) having K_IC and σ_m values higher than those of WC-l0mass%Co hardmetal. It was found that a linear relation was observed between σ_m and S_mf^1/2 for three kinds of HSS specimens (SKH12, SKH51 and SKH55, according to JIS G4403), respectively, and that the values (K^E_IC) of fracture toughness (about 21, 20 and 18MPam^1/2, respectively) estimated from the slopes of the regression lines between σ_m and S_mf^1/2 coincided well with the values (K^M_IC) of fracture toughness measured with SEPB method. Therefore, it was concluded that this new estimating method of K_IC is also applicable to HSS.