Refinement of Ferrite Grain Size near the Ultrafine Range by Multipass, Thermomechanical Compression

  • PDF / 2,238,074 Bytes
  • 15 Pages / 593.972 x 792 pts Page_size
  • 75 Downloads / 173 Views

DOWNLOAD

REPORT


hermomechanical controlled processing (TMCP) aimed at continuous refinement in the ferrite (a) grain size has been a topic of extensive research.[1–4] It was established that the use of fine austenite grain sizes (c-DAVG between 14 and 20 lm) and the application of large strain (e > 0.5) between Ae3 and Ar3 temperatures [in the range of 923 K to 1123 K (650 C to 850 C)] at a high strain rate (_e > 0.1/s), followed by rapid cooling (cooling rate (CR) > 30 K/s) of the samples, can develop homogeneous distribution of ultrafine ferrite (UFF) grains through dynamicstrain-induced austenite (c) fi ferrite (a) transformation (DSIT).[3–6] The c fi a transformation start temperatures under equilibrium cooling (Ae3) and under actual cooling (Ar3) are usually separated by a narrow temperature range [~50 K to 100 K (~50 C to 100 C)], which depends on the CR employed during transformation.[1–6] In an industrial rolling mill, however, application of the S. PATRA, Master’s Student, and D. CHAKRABARTI, Assistant Professor, are with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology (I.I.T.), Kharagpur, West Bengal, 721 302, India. Contact e-mail: [email protected] S. NEOGY, Scientist, is with the Materials Science Division, Bhabha Atomic Research Centre (BARC), 400 085, Mumbai, India. VINOD KUMAR, Assistant General Manager, is with the R & D Centre for Iron and Steel, RDCIS, SAIL, Ranchi, 834 002, India. A. HALDAR, Head, is with the Products Research Group, Research and Development, Tata Steel, Jamshedpur, 831 007, India. Manuscript submitted June 13, 2011. Article published online September 1, 2012 4296—VOLUME 43A, NOVEMBER 2012

aforementioned deformation conditions are difficult due to the requirement of excessive rolling load, precise temperature control, and water-cooling capability.[3–10] Industrial plate rolling is carried out in multiple light passes (less than 30 pct reduction per pass), which are separated by a short interpass time (5 to 30 seconds).[1–3] Hence, for the industrial processing of UFF grained plate, the question arises of how to divide the entire deformation into a multipass schedule, restricting the deformation in each step within the feasible limit. Although some of the earlier studies[5–10] developed UFF grain structures through multipass rolling of thin strips (~2-mm thickness), that practice has hardly risen to the level of regular (industrial) production. The present study, therefore, investigates the effect of thermomechanical processing parameters such as (1) soaking temperature; (2) distribution of strain among the roughing, intermediate, and finishing passes; (3) interpass time; and (4) CR on the grain refinement in microalloyed steel. In order to set a guideline for the development of UFF structure in an industrial scale, the influence of the aforementioned parameters on the metallurgical events responsible for the c and a grain refinement, such as (1) static-recrystallization (SRX) and dynamic-recrystallization (DRX) of c, (2) static-transformation (ST) an

Data Loading...