Strength and toughness of T42 high-speed steel

Abstract

Hardness and compressive strength, Young's modulus, bend strength, and fracture toughness were measured in wrought and commercially sintered T42 high-speed steel. After identical heat treatments, no significant differences were found between wrought and sintered materials in hardness (800–1010 HV50), Young's modulus (∼220 GN m⁻²), or fracture toughness (9−18 MN m^−3/2). The four-point bend strengths in the wrought material were slightly higher in specimens cut longitudinal to the working direction than in transverse specimens (1·3–2·4 GN m⁻²), and both were markedly superior in strength to the sintered material (1·0–1·2 GN m⁻²). For three-point bend tests with laboratory-sintered material, the stresses for brittle fracture were in the range 1·9–3·0 GN m⁻², a level comparable to the wrought specimens. Wrought material contained carbide stringers with a scattering of large Me carbides, whereas in the sintered material pores and incomplete bonding could be detected, albeit infrequently. Fracture initiation in wrought material was mainly from large carbides or groups of carbides, while in sintered specimens initiation was mainly from pores, which were generally smaller in the laboratory-sintered than in the commercially sintered material. There was reasonable agreement between the sizes of these flaws and those estimated by critical flaw analysis. None of the wrought specimens, and only a few of the sintered specimens, showed evidence of microcracking, the cracks detected occurring at small pores or regions of poor bonding; the large carbides in wrought T42 and the larger pores in sintered T42 were already at the critical size for failure initiation, so no microcracking occurred.