Effect of tempering temperature on the work-hardening rate of five HSLA steels
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I.
INTRODUCTION
THE literature
on the effect of tempering temperature on the strength and toughness of quenched and tempered plain carbon and alloy steels is extensive. There are, however, very few cases in which the work-hardening rate has been determined as a function of tempering temperature. 1'2 Fracture of metals occurs by a process of void nucleation, growth, and coalescence. Void coalescence is associated with flow localization 3 and such a process is observed in high strength steels. 4'5'6 Both void growth and mechanisms of flow localization and shear banding are favored by low work hardening rates. 58 Thus one may expect a close relationship among work-hardening rate, toughness, and microstructure (through dislocation interactions), and determinations of the work-hardening behavior may give a useful insight into the reasons for variations in toughness with tempering temperature. The present work was undertaken with the objective of determining whether compositions and processing aspects had a significant effect on the work-hardening rate variations in the tempering of steels. Five steels were chosen for consideration in this test program. The steels have a similar composition but exhibit some important differences. One has a significantly higher carbon content than the others, while three have molybdenum and vanadium concentrations that should promote secondary hardening. Furthermore, two of the steels are produced by special processes: one was calcium-silicide deoxidized and vacuum degassed and the other was electro-slag refined. The steels were solution treated, quenched, and then tempered at 50 ~ intervals in the range 200 ~ to 700 ~ The usual tempering curve was established with hardness measurements, and strength and work-hardening behavior were determined from the results of compression tests. Data of this type can then be compared with published summaries of strength and toughness data and microstructural changes during tempering for a wide range of quenched and tempered steels ~'2'9'1~to gain some insight into the possible reasons for toughness variations. P. L. WINTER and R. L. WOODWARD are with Australian Department of Defence, Materials Research Laboratories, P.O. Box 50, Ascot Vale, Victoria 3032, Australia. Manuscript submitted October 12, 1984.
METALLURGICAL TRANSACTIONS A
II.
EXPERIMENTAL
The steels selected were an alloy constructional steel, 4130, in the form of 6.35 mm thick plate, two forged cylindrical gun barrel steels, designated G / C S D and G/ESR according to the manufacturing process, and two armor steels, designated A/0.3 and A/0.5 according to the carbon content of the plates. The compositions of the steels are listed in Table I. The steels were selected to give a variation in tempering response and to have a variety of inclusion distributions, depending on the manufacturing process, at approximately the same strength level. The 4130 steel is a basic oxygen steel, containing some stringer inclusions, and because of a lack of vanadium and a low level of molybdenum the 4130
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