Papers by Keyword: Interstitial Free Steel

Abstract: Nanomechanical testing using depth sensing indentation (DSI) provides a straightforward solution for quantitatively characterizing each of phases in microstructure because it is very powerful technique for characterization of materials in small volumes. Measuring the local properties (indentation hardness H_IT, indentation modulus E_IT, indentation energy: total W_total, elastic W_elast, plastic W_plast) of each microstructure component separately in multiphase materials gives information that is valuable for the development of new materials and for modelling. The mechanical properties of materials measured by DSI are affected by the experimental procedure, by the measurement conditions and factors which result from the material characteristics and device construction. We have to determine the effect of individual factors on the measurement in order to reach the repeatability and to allow the comparing the mechanical properties of the material. The aim of this investigation is to determine the measurement factors that affect indentation hardness of individual microstructural components and global mechanical properties of thin steel sheets. We investigated the factors which result from the material characteristics (crystallographic orientation of grain, grain boundary and anisotropy), preparation of the sample surface (roughness of sample surface) and method of measurement (pile-up, ISE).

Abstract: Nanomechanical testing using depth sensing indentation (DSI) provides a straightforward solution for characterizing of mechanical properties (indentation hardness H_IT, Young’s modulus E_IT, indentation energy: total W_total, elastic W_elast, plastic W_plast) of homogeneous (bulk) materials. However, real materials such as multi-phase steels are a heterogeneous material on the microscopic scale (microstructure). We need to know the local mechanical properties of each phase separately in those materials for reasons development of new materials and for modeling. Mechanical properties of each phase separately in multiphase materials are difficult or even impossible to examine in bulk material ex situ.In this paper we describe the technique for measuring the mechanical properties of each phase separately in multiphase steel by two-dimensional mapping tool. This approach relies on large arrays of nanoindentations (known as grid indentation) and statistical analysis of the resulting data [1, 2]. The aim of this investigation is to optimize the parameters of the grid indentation for a given microstructure of steel sheets.

Abstract: Design structures made of aluminium alloy and steel are useful to meet the needs of automotive industry such as light weight and higher strength. An effective joining technique to join light weight metals such as aluminium alloys with steel is required. Friction stir spot welding (FSSW) is relatively a new solid state process and it is a derivative of Friction Stir Welding. It creates a spot, lap joint weld without bulk melting. The FSSW parameters such as tool rotational speed, plunge depth, and dwell time plays a major role in determining the strength of the joints and need to be optimized to get quality joints. In this investigation, a central composite rotatable design with three factors and five levels was chosen to minimize the number of experimental conditions. Response surface methodology (RSM) was applied to optimize the FSSW parameters to attain maximum lap shear strength of the spot weld.

Abstract: Strain rate is a significant external factor and its influence on material behaviour in forming process is a function of its internal structure. In this contribution the influence of loading on the deformation IF steel is investigated using rotate hammer. To study the influence of rate deformation from 8.33 x 10^-3 s^-1 to 4000 s ^-1 to changes in the fracture of steel sheet used for bodywork components in cars. Experiments were performed on samples taken from interstitial free (IF) grade strips produced by cold rolling and hot dip galvanizing. Material strength properties were compared based on measured values, and changes to fracture surface character were observed.

Abstract: In order to analyze the mechanical behaviour of ultra-low carbon steel in warm rolling, the flow stress and pyroplastric behaviour were investigated on the Gleeble-3500 with the deformation temperatures in the warm range. The strain rates of 0.1, 1 and 10s^-1 were applied to the temperatures above. A series of stress-strain curves were obtained after the compression Gleeble tests with different parameters. The result indicates the flow stress increases with the decreasing deformation temperatures during the compression. And it increases with the increasing strain rate as well. The constitutive equation, which includes the deformation activation energy Q and the Kelvin temperature T, was developed by using the concept that proposed by C. M. Sellars and W.J. M. Tegart. These equation results can be verified by the results of Gleeble compression test. It indicates the average error is reasonable and acceptable for predicting the flow stress and pyroplastic deformation behaviour of ultra-low carbon steel in warm temperature range. The achieved constitutive equation provides theoretical fundaments for designing the warm rolling process of ultra-low carbon steel. The experimental data also can be used as material property parameters for the establishment of finite element (FE) model.

Abstract: Ferrite rolling of interstitial free steel strip in the temperature range 650-850°C can effectively reduce furnace costs and scale formation as a result of lower strip reheating temperatures. Different lubrication conditions of lubricating oil, solid lubricant and dry condition were used during ferrite rolling tests of thin interstitial free steel strip on a 2-high Hille 100 experimental rolling mill. Different rolling speed, rolling temperature and reductions were applied to the rolling process. The rolling force and roll roughness were affected by the lubrication conditions and rolling parameters. Solid lubricant indicated an improved performance in terms of the roll roughness, as well as the oxidation property of the strip surface during ferrite rolling.

Abstract: The present study highlights the approach to multiscale analysis of the grain refinement during thermomechanical processing of microalloyed steels. HSLA steels for pipe-line use are introduced in which strain-induced precipitation and strain-induced transformations are controlled to produce ultra-fine grained microstructures. Multiscale modeling combining Digital Material Representation and Crystal Plasticity enables to gain a better fundamental understanding of mechanical response and microstructure evolution of precipitation strengthened austenite and ferrite of three microalloyed steel grades. The opportunities for the development of new thermomechanical processing schedules, focused on the grain refinement, are enhanced and the proposed models identifications procedure on the basis of the torsion tests at various forming conditions are presented and discussed. In the pipe-line grade steels, the combination of microalloying elements, accelerated cooling and transformation temperature, has led to much higher grain refinements and increased amount of bainitic ferrite microstructures than in the standard thermomechanical processing. Sensitivity analysis of studied microalloyed steel grades in the light of the discussed problems using microstructural analysis of obtained microstructures was also performed. Finally, the main challenges related to the multiscale modeling of proposed ideas are addressed.

Abstract: Effect of phosphorus content on the mechanical properties and microstructure of IF steel sheets was investigated. Average grain size and recrystallization texture were measured by electron backscatter diffraction (EBSD). The results showed that the higher P resulted in higher tensile strength and lowered the elongation and r-value. The average grain size increased with decreasing P content. The //ND (γ-fiber) pole intensity had a lowest value for IF steel with the highest P content which in turn deteriorate r-value. The element P played an important role in recrystallization process which affected the mechanical properties and microstructure of IF steels.

Abstract: Cold rolling and salt bath annealing simulation were conducted to study the evolution of microstructure and textures of a commercially produced Titanium stabilized interstitial free steel by means of optical microscopy and X-ray texture measurement. The results show that all of the as cold-rolled specimens are completely recrystallized after annealing. As the cold-rolling reduction increases, the recystallized ferrite grains are refined, The intensities of the stable {114} and {223} components remain strong after recrystallization. The orientation intensity of the {111} and {111} also increases accordingly. As the cold-rolling reduction increases to 90%, the intensity of {111} tend to be higher than that of {111}.

Abstract: Effect of annealing time on the microstructure and texture of IF steel sheets was investigated. Average grain size, grain boundary character and recrystallization texture were measured by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) in order to clarify the effect of annealing time on microstructure of recrystallization process. The average grain size increased with increasing annealing time. With rising annealing time, the number of low angle boundary (0～15o) decreased due to the mergence of grain with sub-boundary. The //ND (-fiber) pole intensity had a highest value annealed at 60s. The annealing time played an important role in recrystallization process which affected the mechanical properties and microstructure of IF steels.