Materials Science and Engineering A283 (2000) 136 – 143 Mechanical properities of an HSLA bainitic steel subjected to controlled rolling with accelerated cooling P.C.M. Rodrigues a , E.V. Pereloma b, *, D.B. Santos c a Department of Mechanical Engineering, FUNREI, Sa ˜o Joa ˜o del Rei, MG, Brazil b Department of Materials Engineering, Monash Uniersity, Clayton, VIC 3800, Australia c Department of Metallurgical and Materials Engineering, UFMG, Belo Horizonte, MG, Brazil Received 6 September 1999; received in revised form 6 December 1999 Abstract Controlled rolling followed by accelerated cooling was utilised in laboratory simulations to study the microstructure and mechanical properties of an HSLA low carbon bainitic steel. The effects of processing parameters, such as cooling start temperature and cooling rates, on the final microstructure and mechanical properties were studied. Optical microscopy and transmission electron microscopy were used to evaluate the complex microstructures consisting of polygonal ferrite, pearlite, bainite and martensite/retained austenite constituent. The use of the multiple regression analysis allowed establishment of the relationships between mechanical properties and accelerated cooling variables: cooling rates and cooling start temperatures. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Bainitic steel; Controlled rolling; Accelerated cooling; Mechanical properties; Microstructural characterisation www.elsevier.com/locate/msea 1. Introduction HSLA low carbon steels with multiphase microstruc- ture have been extensively studied in the last two decades [1 – 4]. These steels have high tensile strength, good toughness and weldability. This combination of properties has led to their application in the automotive industry, in manufacturing of large diameter pipes for gas and oil transportation in the areas of low tempera- ture and as plates for naval ships construction. Multiphase microstructures consisting of polygonal ferrite, pearlite, bainite and martensite can be produced in a great variety of HSLA low carbon steels as a result of an appropriate combination of chemical composi- tion, thermomechanical processing and accelerated cooling conditions. The choice of optimum parameters for accelerated cooling, such as accelerated cooling start and finish temperatures and cooling rate, also depends on the chemical composition of the steel and the ther- momechanical processing (TMP) employed [5,6]. Accelerated cooling after controlled rolling produces a refined final microstructure and favours the formation of low transformation temperature products, like bainite and martensite – austenite (MA) constituent [7,8]. The majority of works has been directed towards the study of microstructural evolution during acceler- ated cooling [4,9]. However, only a limited amount of research was carried out on the effect of accelerated cooling variables on the mechanical properties of steels [1,10]. The objective of the present work was to study the influence of cooling rate and accelerating cooling start temperature on the mechanical properties (Vickers mi- crohardness, yield strength, tensile strength and total elongation) of a HSLA low carbon bainitic steel and to establish the correlation between them. 2. Experimental procedure The chemical composition of the steel investigated is given in Table 1. This steel contains 21 ppm of B and is microalloyed with Nb, Ti, V and Ni. The presence of B and high Mn content increases hardenability of steel, * Corresonding author. Tel.: +61-3-99054916; fax: +61-3- 99054940. 0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0921-5093(99)00795-9