Mechanism of work hardening in Hadfield manganese steel
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A U S T E N I T I C manganese steel, called Hadfield manganese steel after its inventor, Robert Hadfield, t is a tough, nonmagnetic, Fe-C-Mn alloy, useful for severe service combining abrasion and heavy impact. The ASTM Standard A-128-642 covering this steel allows composition ranges from 1.0 to 1.4 pct C and from 10 to 14 pet Mn. However, commercial alloys with manganese contents greater than 12 to 13 pct are seldom used because of cost. Moreover, work hardening in a 1.15 pct C alloy reaches a maximum at 13 pct Mn. 3 Hadfield steel is usually austenitized to dissolve carbides and to produce homogeneous austenite, which is preserved by water quenching from above 1000 ~ Typical mechanical properties are: 3 a) yield strength (0.2 pct offset), 379 MPa; b) ultimate tensile strength, 965 MPa; c) elongation in 50 mm, 50 pet; d) reduction of area, 40 pct; e) hardness, as quenched, 190 HB; f) hardness, at fracture, 500 HB; g) Charpy V-notch impact, 169 J at 22 ~ 7 J at - 196 ~ The unique feature of this tough, high-strength steel is the rapid work hardening, from a yield strength of 379 MPa to an ultimate tensile strength of 965 MPa. In gouging abrasion tests, the Hadfield steel performs better than wrought alloy steels, cast alloy steels, stainless steels, tool steels or high-chromium white irons. 4 These combinations of properties make it useful in such diverse applications as crawler treads for tractors, railroad frogs, grinding mill liners, crusher jaws and cones, impact hammers, dipper bucket teeth and nonmagnetic plates for electromagnets. Y. N. DASTUR and W. C. LESLIE are at the Department of Materials & Metallurgical Engineering,Universityof Michigan, Ann Arbor, MI 48109. Manuscript submitted August 11, 1980. METALLURGICALTRANSACTIONSA
Although this steel has been used for nearly a century since its development in 1882, the mechanism of rapid work hardening remains unclear. The purpose of this study was to determine the mechanism of rapid work hardening in Hadfield steel with the intent of solving one of the classical mysteries of physical metallurgy. PREVIOUS S T U D I E S A N D P R O P O S E D M E C H A N I S M S OF W O R K H A R D E N I N G IN H A D F I E L D STEEL It is commonly taught that the rapid work hardening in Hadfield steel arises from strain-induced transformation of y to ~ or c martensites: but it has been shown that the austenite of Hadfield's composition is stable during plastic strain, 6-8 even below - 1 9 6 ~176 Straininduced transformation occurs only because of decarburization or local segregation of manganese that leads to unstable austenite compositions. Some workers l~'12 attributed the rapid work hardening to fine mechanical twinning. However, their studies did not include measurements of rates of work hardening nor description of microstructures obtained at a variety of strain rates and temperatures. Lambakakhar and Paska113 observed no correlation between frequency of twins and hardness. Instead, they concluded that the hardness of Hadfield steel is more likely a function of the general
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