The effect of prior heat treatments on the structure and properties of warm-rolled AlSl 52100 steel
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INTRODUCTION
AISI 52100
is a 1 pct carbon, 1.5 pct chromium steel, widely used in bearing and tool applications because of good wear and rolling contact fatigue resistance. It is usually supplied in a spheroidize-annealed condition for fabricability. Post-fabrication heat treatment generally consists of partial austenitization at a temperature just below A~m followed by quenching and tempering to a hardness of Rockwell C 60-63. The as-quenched microstructure consists of residual, undissolved carbides in a martensitic matrix containing some retained austenite. It has been found ~'2 that refinement of the residual carbides and homogenization of their distribution result in improved roiling contact fatigue resistance. The effect of grain size refinement has not been evaluated in this steel, but work by Shur 3 on a 0.75 pct carbon steel indicates that grain refinement also leads to improved rolling contact fatigue resistance. In light of the importance of residual carbides, Stickels4 investigated post-fabrication heat treatments and demonstrated that carbide refinement could be attained by a twostep process. First, the steel was austenitized at a high temperature, 1040 ~ to dissolve all carbides and then isothermally transformed to produce either pearlite or bainite; second, the steel was conventionally austenitized, quenched, and tempered. The first step resulted in a fine carbide size which resulted in more rapid dissolution in the second step. The final structure was harder, more uniform in carbide distribution and contained more retained austenite. Grain size refinement was not noted. Grange s'6 examined the effects of similar heat treating cycles and multi-cycle rapid austenitizing treatments and demonstrated that such treatments could produce final microstructures consisting of submicron size carbides in a refined martensitic matrix. Granges also noted that prior treatments producing grain and 1". R. McNELLEY is Associate Professor of Mechanical Engineering, United States Naval Postgraduate School, Monterey, CA 93940. M.R. EDWARDS, Principal Lecturer, and A. DOIG, Senior Scientific Officer, are both with Metallurgy Branch, Royal Military College of Science, Shrivenham, Swindon, England. D.H. BOONE is Staff Scientist, Materials and Molecular Research Division, Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720. C. W. SCHULTZ, formerly Graduate Student, Department of Mechanical Engineering, United States Naval Postgraduate School, is currently with the Office of the Supervisor, Conversion and Repair, United States Navy, New Orleans, LA 70142. Manuscript submitted January 12, 1982. METALLURGICALTRANSACTIONSA
carbide refinement enhanced the response of the steel to subsequent rapid heat treatment for final hardening. Thermomechanical processing methods7 to produce a refined spheroidized condition provide an alternative approach to microstructural refinement for this steel. These methods are generally applicable to steels containing from 1 to 2.3 pct carbon and produce microstructures co
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