Fracture toughness of aisi M2 high-speed steel and corresponding matrix tool steel
- PDF / 3,425,771 Bytes
- 11 Pages / 594 x 774 pts Page_size
- 98 Downloads / 258 Views
I.
INTRODUCTION
THE application
of fracture toughness testing or fracture mechanics to high-speed and related steels is relatively recent, and the volume of literature is modest. H2 Study of fracture toughness of tool steels has lagged behind that for other families of steels, most probably because practical importance of the fracture property of the steels has not been established. Fracture toughness of tool steels deserves metallurgical attention because fracture is one of the most common failure modes of tool materials, and because of the uniqueness of the steels' chemical compositions, microstructures, and mechanical properties. Two steels were investigated in this study of fracture toughness, AISI M2 high-speed steel (6 pct W-5 pct Mo-4 pct Cr-2 pct V-0.8 pct C-bal. Fe) and a tool steel with a composition 2 pet W-2.75 pct Mo-4.5 pct Cr-1 pct V-0.5 pet C-bal. Fe. The latter steel is commercially known as VASCO-MA, and for convenience will be called MA. The MA steel derives its composition from the matrix (defined as the total microstructure of a high-speed steel less primary carbides) of the AISI M2 when austenitized according to industrial practice. Such steel is often called a "matrix" steel because of the origin of its composition. The combination of a high-speed steel and its corresponding matrix steel has been chosen in this study because comparison of properties of two such different but closely related steels was expected to yield valuable metallurgical information. The objective of this research program was to determine the relationship between fracture toughness, microstructure, CHONGMIN KIM, formerly with Climax Molybdenum Company of Michigan, Ann Arbor, MI, is now Senior Research Engineer with the Metallurgy Department, General Motors Research Laboratories, Warren, MI 48090. A. RICHARD JOHNSON is Staff Metallurgist with Climax Molybdenum Company of Michigan, Ann Arbor, MI 48106. WILLIAM F. HOSFORD is Professor, Materials and Metallurgical Engineering Department, University of Michigan, Ann Arbor, MI 48109. Manuscript submitted December 15, 1980. METALLURGICAL TRANSACTIONS A
and hardness resulting from hardening and tempering heat treatments. In the present work the austenitizing temperature was varied from well below normal practice to well above it, and the steels were studied in both as-hardened and hardened-and-tempered conditions. The heat treatments produced microstructures with considerable differences in grain size, retained austenite content, and hardness, facilitating study of the effect of such factors on fracture toughness. The effect of grain size on the fracture toughness was further investigated by comparing steel samples coarsened by double-hardening with samples having a normal finegrained microstructure. An experimental study of the effect of tempering temperature was included because of the interest in finding whether the tempering temperature p e r se has any influence on fracture toughness at a fixed level of tempered hardness.
II.
EXPERIMENTAL PROCEDURE
A . Materials and H
Data Loading...
