Rheological Model for Simulation of Hot rolling of New Generation Steel Strips for Automotive Applications

Abstract

The main objective of this paper is the development of a rheological model for automotive steels for the conditions of hot strip rolling and implementation of this model in a finite element program is. Three types of steels were investigated, IF, dual phase and TRIP steel. Plastometric tests were performed on a Gleeble 3800 simulator for the temperature range 850-1200 oC and strain rates 3-150 S·1. Inverse analysis was applied to eliminate the influence of disturbances occurring in the plastometric tests and to determine the real flow stress of the material. The coefficients in the flow stress equation were evaluated and this equation was implemented in the FEM code as the constitutive law. The model was validated by comparison of measured and calculated loads in the compression tests and by strip rolling experiments conducted in the laboratory mill. Validation confirmed a good predictive capability of the rheological model. ExperimentsThe axisymmetrical compression tests were conducted on the Gleeble 3800 simulator at the Institute for Ferrous Metallurgy in Gliwice, Poland. Three steels with the chemical composition given in Table 1 were investigated. The axisymmetrical samples measuring <j>10x12 mm were deformed at temperatures 950°C, 1050°C, 1150°C and 1200°C and at constant strain rates of 3 S·I, 12 s', 50 S-I and 150 S-I at each temperature. These are the conditions which cover the whole range of parameters in the hot strip rolling.

Effect of Finishing Hot‐Working Temperature on Microstructure of Thermomechanically Processed Mn–Al Multiphase Steels

“…A clear peak of ϵ p followed by decreasing the flow stress can only be observed for the specimens compressed at 1150°C and strain rate of 0.1 s −1 (Figure ). The strain values required for DRX are relatively high when compared to other TRIP steels . The same concerns the values of flow stresses, which approaches 300 MPa for the specimens deformed at 850 °C with a strain rate of 10 s −1 (Figure ).…”

“…Thermomechanical processing models of C‐Mn and HSLA steels are well developed and documented in literature. Presently, the focus is placed on modeling of thermomechanical treatment of different AHSS grades (DP, TRIP, CP, QP – Quenching and Partitioning), in which a final multiphase microstructure is substantially dependent on decomposition of austenite during run‐out table cooling and coiling . The efficient modeling of phase transformation from pancaked austenite still represents a challenge mainly due to a complex character of the bainitic transformation …”

Perceptive Review of Ferrous Micro/Macro Material Models for Thermo-Mechanical Processing Applications

“…Equations describing the flow stress were further improved to obtain better description of softening and saturation in a wide range of temperatures and strain rates. The equation proposed by Sellars and Tegart and presented also in ref., is based on the DRX parameters. This equation gives realistic description of the flow stress in hot forming.…”

Computer-aided design work for hot stamping process by the example of a magnesium alloy product

“…możliwości wprowadzania usztywnień konstrukcji poprzez zaginanie oraz przetłaczanie blach, z jednoczesnym utrzymaniem niewielkiej wagi całej konstrukcji. Coraz częściej stosuje się stale o podwyższonej wytrzymałości (advanced high strength steels -AHSS), dzięki czemu moż-na zmniejszać grubość poszczególnych elementów, redukując masę wyrobu [2,3]. W przypadku elementów stalowych proces tłoczenia realizowany jest w głównej mierze na zimno; nie dotyczy to jednak stali martenzytycznych o bardzo wysokiej wytrzymałości, które są formowane w podwyższonych temperaturach [4,5].…”