Journal of Minerals and Materials Characterization and Engineering, 2014, 2, 428-469 Published Online September 2014 in SciRes. http://www.scirp.org/journal/jmmce http://dx.doi.org/10.4236/jmmce.2014.25047 How to cite this paper: Halfa, H. (2014) Recent Trends in Producing Ultrafine Grained Steels. Journal of Minerals and Mate- rials Characterization and Engineering, 2, 428-469. http://dx.doi.org/10.4236/jmmce.2014.25047 Recent Trends in Producing Ultrafine Grained Steels Hossam Halfa Steel Technology Department, Central Metallurgical Research and Development Institute (CMRDI), Helwan, Egypt Email: hossamhalfa@cmrdi.sci.eg , hossamhalfa@gmail.com Received 3 May 2014; revised 23 June 2014; accepted 3 July 2014 Copyright © 2014 by author and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract Ultrafine grained steels with grain sizes below about 1 µm offer the prospect of high strength and high toughness with traditional steel compositions. These materials are currently the subject of extensive research efforts worldwide. Alloy design is one of the first considered issues, while de- signing new steel with targeted mechanical properties. However, the alloying content of steel does not fully determine the mechanical properties, but manufacturing procedure, hot rolling and cooling parameters, heat treatment parameters etc. are also of vital importance. For instance, same steel with different processing conditions can exhibit rather large variations in properties. To be precise, chemical composition with the processing parameters determines the microstruc- ture, which in turn determines the properties of the steel. Steel is defined as an iron alloy con- taining C, Mn and Si that are generally used as alloying elements in steel. Micro-alloying elements such as Nb, Ti V, and B, are considered to be effective, causing strengthening as well as micro- structural refinement in small quantities below 0.1 wt% (therefore these are called micro-alloy elements) and are quite generally used in ultrafine grain steel. Substitution alloying elements, such as Mo, Ni, Cr and Cu are alloyed to suppress phase transformation temperatures, i.e. for reaching certain level of strengthening, since the strength of steel structures strongly depends on the phase transformation temperature. Accordingly, the alloy design of ultrafine grains steels with different structures generally relies on: i) carbon levels, ii) sufficient alloying to obtain the desired transformation temperature and iii) micro-alloying technology in conjunction with Thermo Me- chanical Controlled Processes (TMCP). Also, both advanced thermo-mechanical processes and se- vere plastic deformation strategies are used to produce ultrafine grained steels. Both approaches are suited to produce submicron grain structures with attractive mechanical properties. This overview describes the various techniques to fabricate ultrafine grained steels. Keywords Ultrafine, Thermomechanical, Severe Plastic Deformation, Structure