Enhancement of mechanical properties of low carbon steel based on heat treatment and thermo-mechanical processing routes

Document Type : Research Paper


School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran.


Thermal treatments and thermo-mechanical processing routes were applied on a conventional structural steel (st37 steel: 0.12C-1.11Mn-0.16Si) for improvement of tensile properties and enhancement of work-hardening behavior. Full annealing resulted in a sheet with coarse ferrite grains and pearlite colonies arranged alternatively in distinct bands, which showed high ductility, low strength, and the presence of the yield point elongation at the beginning of the plastic flow. The cold-rolled sheet, however, showed poor ductility but much higher strength level. The dual phase (DP) sheet, resulted from intercritical annealing in the austenite plus ferrite region, showed a remarkable strength-ductility balance. The latter was related to the excellent work-hardening behavior as a result of the glide and interaction of the quench-induced unpinned dislocations. A bimodal-sized ferritic structure with the appearance of a poor strain hardening regime after experiencing a high yield stress was obtained from the subcritically annealed cold-rolled DP microstructure. The ultrafine-grained sheet was processed by applying the abovementioned route on a martensitic microstructure, which resulted in low ductility but high strength at ambient temperature. These results demonstrated the ability to control the properties of conventional steels by simple thermal and thermo-mechanical treatments.

Low carbon steel, Grain refinement, Mechanical properties, Strain hardening rate


  1. Valiev RZ, Estrin Y, Horita Z, Langdon TG, Zechetbauer MJ, Zhu YT. Producing bulk ultrafine-grained materials by severe plastic deformation. JOM. 2006;58(4):33-9.
  2. Kawasaki M, Langdon TG. Principles of superplasticity in ultrafine-grained materials. Journal of Materials Science. 2007;42(5):1782-96.
  3. Suryanarayana C. Mechanical alloying and milling. Progress in Materials Science. 2001;46(1-2):1-184.
  4. Song R, Ponge D, Raabe D, Speer JG, Matlock DK. Overview of processing, microstructure and mechanical properties of ultrafine grained bcc steels. Materials Science and Engineering: A. 2006;441(1-2):1-17.
  5. Kim HJ, Kim YH, Morris JJW. Thermal Mechanisms of Grain and Packet Refinement in a Lath Martensitic Steel. ISIJ International. 1998;38(11):1277-85.
  6. Ueji R, Tsuji N, Minamino Y, Koizumi Y. Ultragrain refinement of plain low carbon steel by cold-rolling and annealing of martensite. Acta Materialia. 2002;50(16):4177-89.
  7. Najafi M, Mirzadeh H, Alibeyki M. Toward unraveling the mechanisms responsible for the formation of ultrafine grained microstructure during tempering of cold rolled martensite. Materials Science and Engineering: A. 2016;670:252-5.
  8. Lan HF, Liu WJ, Liu XH. Ultrafine Ferrite Grains Produced by Tempering Cold-rolled Martensite in Low Carbon and Microalloyed Steels. ISIJ International. 2007;47(11):1652-7.
  9. Azizi-Alizamini H, Militzer M, Poole WJ. Formation of Ultrafine Grained Dual Phase Steels through Rapid Heating. ISIJ International. 2011;51(6):958-64.
  10. Nouroozi M, Mirzadeh H, Zamani M. Effect of microstructural refinement and intercritical annealing time on mechanical properties of high-formability dual phase steel. Materials Science and Engineering: A. 2018;736:22-6.
  11. Papa Rao M, Subramanya Sarma V, Sankaran S. Processing of Bimodal Grain-Sized Ultrafine-Grained Dual Phase Microalloyed V-Nb Steel with 1370 MPa Strength and 16 pct Uniform Elongation Through Warm Rolling and Intercritical Annealing. Metallurgical and Materials Transactions A. 2014;45(12):5313-7.
  12. Wang Y, Chen M, Zhou F, Ma E. High tensile ductility in a nanostructured metal. Nature. 2002;419(6910):912-5.