Evaluation of homogeneous compression flow curves using square cross-sectioned specimens
- PDF / 317,058 Bytes
- 3 Pages / 598.28 x 778.28 pts Page_size
- 41 Downloads / 126 Views
cation by replacing it at regular intervals are inappropriate for test results at higher strains. The suggested methodm which encompasses both these diverse approaches for determining HCFC has not been fully exploited. The present investigation seeks to verify the applicability of this approach for obtaining HCFC using square cross-sectioned (SCS) specimens. The suggested approach for obtaining HCFC by Ray and Mallikt~l is based on the upper bound solution to the problem of uniform compression of a solid cylinder between fiat dies, given by Avitzur. tT~In this solution, the applied stress (P) is related to the material flow stress (o') as
P/cr = 1 + C(d/h)
[1]
where C is a constant relating the shear stress at the specimen-platen interface to the material flow stress. In the earlier work, m the constancy of C for a particular strain level has been verified for cylindrical specimens. Applicability of Eq. [1] to evaluate HCFC using SCS specimens thus first requires an examination of the dependence of C on the s/h ratio of a material, where s is the average length of the sides of the square cross section and h is the height of the sample. Second, an assessment K.K. RAY, Associate Professor, and A. GHOSH, Research Scholar, are with the Department of Metallurgical Engineering, Indian Institute of Technology, Kharagpur 721302, India. K.V.S.J. RAO, formerly Undergraduate Student, Department of Metallurgical Engineering, Indian Institute of Technology, is Graduate Engineer, Essar Steels Ltd., Hazira, Gujrat, India. Manuscript submitted August 9, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS A
of the compatibility of the flow curves obtained by using cylindrical and SCS specimens is a natural requisite. In order to examine the applicability of the proposed method for SCS specimens, compression tests were carried out on a structural steel having the nominal composition C-0.40, Mn-0.90, S-0.012, P-0.032, Si-0.3, Ni-0.56, Cr-0.55, Mo-0.2, A1-0.02, Fe-balance (all in weight percent). The as-received material was soaked at 1123 K for 30 minutes, oil quenched, and tempered at 873 K for 60 minutes in a salt bath before preparing the test specimens. The average prior austenitic grain size of the steel was found to be 20.6 /zm, and the heattreated specimens revealed tempered martensitic structure. The Vickers hardness of the heat-treated material (tested by a LECO* hardness tester using 1 kgf load for *LECO is a trademark of Leco Corporation, St. Joseph, MI.
15 seconds dwell time) was found to be 302 kg/mm 2. Compression tests were carried out on two types of specimen geometries having d/h and s/h ratios of approximately 1, 1.5, and 2, the cylindrical and the SCS specimens possessing diameter and side-length of approximately 7 mm and 6.2 mm, respectively. The sides of the SCS specimens were selected as to keep the total cross-sectional area for both types of specimens approximately equal. The tests were carried out on a 20,000 kgf capacity universal testing machine at room temperature (-305 K) at an average crosshead speed of
Data Loading...
