Papers by Keyword: Automotive Steel

Abstract: The development of ultra-high-strength automotive steel sheets for lightweight automobiles is still an effective strategy from the material point of view. In the case of cold-rolled steels for BIW(Body In White), it has been a long time since steel with 980MPa of UTS or higher were commercialized, and the use of 1.2GPa and 1.5GPa of cold-rolled steels is also increasing. However, in the case of hot-rolled steel for chassis, the increase in strength is not as fast as that of cold-rolled steel, because chassis parts are the lower structure of a vehicle and are very sensitive to durability.

Abstract: With the objective of partial and total replacement of nickel by nitrogen in austenitic exhausted valve steel X45CrNiW18-9, a program of work with series of experimental heats was designed. Experimental heats were carried out in 10 Kg. induction furnace under nitrogen pressure. The chemical composition of produced stainless steels was determined. The produced automotive steel grades were forged. The nitrogen contents were determined. The produced forged stainless steels were subjected to solution treatment at 1050 °C for 1 hour, followed by water cooling. Isothermal oxidation test is used to detect the behavior of new grades at different temperatures in air for solution treated stainless steels. The mass gain was measured for samples exposed to air at temperatures (500 °C, 600 °C, 700 °C, 800°C) for different time intervals, up to 1000 hrs. The oxide layer thickness for two selected steels was investigated by using optical microscope. XRD was used to detect types of oxides which are formed during oxidation process at 800 °C for 1000 hrs for represented investigated exhausted valve steels. Scanning Electron Microscope was used to make scan steels surface, after heating at 500 °C and 800 °C for l000hr. The mechanism of the oxidation of developed steels was investigated. It was found controlled by diffusion mechanism and the kinetic of oxidation process is parabolic. Oxidation rate of the investigated stainless steels for times, up to 8 h and between 200 andl000 h, at all investigated temperatures (500 °C - 800 °C), is parabolic and the oxidation is diffusion controlled. While in the time region 10 to 200 h, it obeys combined mechanisms. Partial replacement of nickel, by nitrogen, improves the oxidation resistance in air at temperature range 500°C - 800°C.

Abstract: With excellent mechanical properties and low density, Fe-Mn-Al-C steel would be the first choice for automotive lightweight design in future. In this paper, microstructural evolution, mechanical properties and strain hardening behavior of Fe-18Mn-9.5Al-0.65C steel before and after solution treatment were investigated. The experimental steel had (α+γ) duplex phase structure, density of 6.82g/cm³ and high product of strength and ductility. After hot rolling, the steel showed microstructural morphology of austenite matrix and banded ferrite, tensile strength of over 1000MPa and elongation of 25%. During solution treatment, the tensile strength, as well as the yielding strength, decreased with the increase of solution temperature, while the elongation increased first and then decreased sharply for excessively coarsening of grains. After solution treated at 1000°C for 1h, the elongation reached 44%, and product of strength and ductility was 34GPa·%, which was 36% higher than that of the hot-rolled steel. Excellent comprehensive properties are attributed to the multiple-stage strain hardening behavior during tensile deformation, as well as the crush and separation of banded ferrite to form a uniform structure during solution treatment.

Abstract: In this Paper an original 800MPa cold rolled dual phase steel with low carbon and high silicon as well as some amount of Mn had been investigated in lab. The study shows that the microstructures of the steel mainly consist of ferrite, along with martensite with the content of 20%~25% which distributes homogenously on the ferrite grain boundary. The grain size of the ferrite is homogenous and with the grade of 13-14. The characteristics of the microstructure results in the excellent mechanical properties of the steel with Rp0.2=485~515MPa,tensile strength Rm=795~805MPa,total elongation A80mm=18%~19.5%,and n=0.135-0.145.

Abstract: Results of uni-axial tensile loading of three automotive steels at different strain rates (0.0011–3200s-1) are reported here. Quasi-static tensile tests were performed under the strain rate of 1.1×10-3 s-1 using an electromechanical universal testing machine, whereas dynamic tests were carried out under the strain rate in the range of 1100 to 3200 s-1 using a Split Hopkinson Tensile Bar apparatus. Based on the experimental results, the material parameters of widely used Johnson–Cook model which described the strain rate and temperature-dependent of mechanical behaviour were determined. The experiments show that strain-rate hardening is superior to thermal softening: yield stresses, tensile strength, deformation, and energy dissipation increase with the strain rate from quasi-static tests to dynamic tests. The Johnson–Cook model can describe the behaviour of these steels and provides the opportunity to study the material and structural response.