Microstructure, Texture, Grain Boundary Characteristics and Mechanical Properties of a Cold Rolled and Annealed Martensitic Steel

Abstract

The microstructural and textural evolution and changes in Grain Boundary Character Distribution (GBCD) during annealing of a prior cold worked (30 %, 50 % and 80 %) Fe-C martensitic steel have been studied, and correlated with mechanical properties. It has been demonstrated that ultrafine grains in the range 50-250 nm can be obtained by choosing appropriate amounts of cold rolling and annealing. Increasing the annealing temperature in all the three materials produces the expected results, namely decrement of strength with a concomitant increase in ductility. Although reasonably sharp g-fibres were obtained in most of the cases, the very low r-bar values (Ͻ1.0) make the steels unsuitable for deep drawing purposes. It has been suggested that grain boundary engineering may lead to better strength-ductility combinations in this steel for enhanced range of applications.KEY WORDS: texture; cold rolling; annealing; mechanical properties; Grain Boundary Character Distribution; martensite. rolling mill with a roll diameter of 250 mm. The rolling was performed at a roll peripheral speed of 27.5 m · min Ϫ1 with machine oil as lubricant. The cold rolling could be successfully done without any edge cracking. Specimens of 15 mm in width and 100 mm in length were cut from the cold rolled sheets along the rolling direction (RD) for subsequent annealing and mechanical testing. The annealing of the cold rolled specimens was carried out at different temperatures ranging from 200-700°C, for 30 min with an interval of 100°C. From the annealed samples tensile specimens were prepared in accordance with ASTM E8M-04 standard and were subsequently polished. Tensile tests of polished samples were carried out at room temperature in Instron 4 210 machine with a constant cross-head speed of 0.5 mm · min Ϫ1. The bulk hardness values (H v ) were calculated from the average of seven separate measurements taken at randomly selected points by using a load of 5 kg for 15 s. A detailed microstructural characterization was performed using Field Emission Gun Scanning Electron Microscope (FEG-SEM) and Transmission Electron Microscope (TEM). Specimens after etching with 2 % Nital, were observed along the cross section in a FEG-SEM operated at 15 kV. Thin foil TEM study was conducted in a PHILIPS CM200 TEM operated at 100 kV. Thin foils were prepared by twin jet electro polishing using a solution of 10 % HClO 4 ϩ90 % CH 3 COOH. Global texture measurements were carried out on the half thicknesses of the 30 %, 50 % and 80 % cold rolled as well as annealed (at 500°C and 700°C) samples using X-ray Diffraction (XRD) method in a PANalytical MRD machine. The (110), (200), (112) and (222) pole figures were determined, from which the Orientation Distribution Functions (ODFs) were calculated using the method of Bunge. 11)The grain boundary characterization was carried out in FEG-SEM operated at 20 kV equipped with an OIM/EBSD attachment. Samples after polishing with colloidal silica, were put in the sample holder of the SEM/EBSD equipment. Using a step size of 1....

Microstructure and modelling of shear forming

“…This type of processing and heat treatment has been proved to affect greatly the microstructure of martensitic steels. Ghosh et al [69] analysed the microstructural changes of a low carbon martensitic steel (0.17 wt% C) after cold rolling and annealing. They found that high thickness reduction cold rolling (50% and 80% thickness reduction) plus annealing at 700 ˚C resulted in the partial recrystallisation of martensite forming…”

“…Figure 45: Micrographs of low carbon martensitic steel after: a) No processing (Initial microstructure), b) 30% reduction cold rolling, c) 50% reduction cold rolling and d) 80% reduction coldrolling [69]. …”

Formation and Evolution Mechanism of the Inclusions of Al2O3·SiO2·CaO and Al2O3·SiO2·CaO·MgO in Seamless Steel Tube Steel

“…In recent years, some investigations on the formation of the inclusions in steel were carried out with thermodynamic analysis. [5][6][7][8][9][10][11] For example, Wang et al [7] investigated the effect of oxide component content on the low melting point zone in the Al 2 O 3 •SiO 2 •CaO•MgO system using FactSage software. It was found that the low melting point zone becomes wide with the increase in CaO content within the range of 0-30 mass% and the decrease in SiO 2 content within the range of 5-25 mass%.…”

Characteristics of the Cold-Rolling Texture in a Multi-Layered Material Composed of SUS301 and SUS420J2 Steels

“…Deformation and annealing texture development in steels have been studied in details. [5][6][7][8][9][10] In cold-rolled SUS301 steel, it was found that the main texture component was characterized by f110gh112i Brass, f110gh001i Goss and f112gh111i Copper components. 6) In ferritic stainless steels and martensitic steels, -fiber and -fiber were observed to be the dominant texture components.…”

“…6) In ferritic stainless steels and martensitic steels, -fiber and -fiber were observed to be the dominant texture components. [8][9][10] Although the mechanical properties of multi-layered materials have been extensively studied, 1) few reports have been addressed on the texture development of the structural multi-layered materials during cold-rolling and subsequent annealing. It is considered that the different mechanical properties of the components in composites will obviously affect the stress and strain states during rolling and further influence the crystallographic texture development in the component steels.…”