Development of High-Strength Bulk Ultrafine-Grained Low Carbon Steel Produced by Equal-Channel Angular Pressing
- PDF / 5,849,926 Bytes
- 18 Pages / 593.972 x 792 pts Page_size
- 71 Downloads / 218 Views
N
LOW carbon steel (LCS) is one of the major structural materials with moderate strength and good ductility. However, it can be strengthened by grain refinement to the submicrometer range without loss in ductility.[1] Equal-channel angular pressing (ECAP) has become a popular technique in effecting such grain refinement,[2–8] since it has a few advantages over other severe plastic deformation techniques.[9–11] The authors’ group has reported results of ECAP of interstitial-free (IF) steel describing the microstructural refinement, evolution of high-angle boundaries, strengthening, and hardening achieved when subjected to εvm of 24.[12] It is, in general, realized that there is an upper equivalent
RAJ BAHADUR SINGH, N.K. MUKHOPADHYAY, G.V.S. SASTRY, and R. MANNA are with the Department of Metallurgical Engineering, Indian Institute Technology, Banaras Hindu University, Varanasi 221005, India. Contact e-mail: [email protected] Manuscript submitted January 7, 2017. METALLURGICAL AND MATERIALS TRANSACTIONS A
strain limit for a specific material and conditions of ECAP beyond which the material fails. Huang et al. have also refined IF steel to the grain size of 210 nm by the accumulative roll bonding process at εvm = 4.8.[13] After ECAP of IF steel for an equivalent strain of 12, the domain size reduces to 41 nm.[14] The amount of imposed strain plays an important role in modifying the microstructure and subsequently influencing the mechanical properties.[15–18] IF steel is also deformed through high-pressure torsion up to an equivalent strain of 15 by which grain size is reduced to 580 nm.[19] IF steel is also strained by the semicontinuous ECAP process up to an equivalent strain of 4.8. Grains are refined to 0.55 µm, and high-angle grain boundary (HAGB) fraction is increased to 90 pct. Ultimate tensile strength (UTS) is increased to 710 MPa, and total elongation reaches 12 pct.[20] The present investigation aims at understanding the mechanism operative in the steel in the presence of interstitial solutes. ECAP of LCS can partially dissolve the pearlitic Fe3C in ferrite matrix at an equivalent strain of 4.[24,25] The strength of the ultrafine-grained LCS increases by 3 to 5 times that of the unprocessed
Fig. 1—(a) ECAP die assembly with workpiece; (b) equal-channel angular pressed workpiece with reference directions, X, Y, and Z or ED, TD, and ND, respectively; (c) orientation and location of tensile sample and location of other samples; and (d) location and orientation of other samples for OM, hardness measurement, transmission electron microscopy, EBSD, scanning electron microscopy, and XRD.
one.[4,6–8,22,24,26–28] The enhancement is attributed to reduced grain size, increase in dislocation density, partial dissolution of cementite, and increase in misorientation angle.[3,4,6,24,27–31] However, the ductility of the material decreases significantly with increasing imposed strain.[7,8,30] Until now, the microstructural development and strengthening behavior of LCSs have been reported under ECAP conditions up to an equiv
Data Loading...
