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Research Papers

# Modeling of Strain-Stress Relationship for Carbon Steel Deformed at Temperature Exceeding Hot Rolling Range

[+] Author and Article Information
Marcin Hojny

AGH-University of Science and Technology, Mickiewicza 30, 30-059 Kraków, Poland

Miroslaw Glowacki

AGH-University of Science and Technology, Mickiewicza 30, 30-059 Kraków, Polandmhojny@metal.agh.edu.pl

J. Eng. Mater. Technol 133(2), 021008 (Mar 04, 2011) (7 pages) doi:10.1115/1.4003106 History: Received January 05, 2010; Revised September 21, 2010; Published March 04, 2011; Online March 04, 2011

## Abstract

The subject of the presented paper is the modeling of strain-stress relationship, which is the main mechanical property characteristic of the behavior of steel subjected to plastic deformation. The major challenge of the research is the temperature of the deformation, which significantly exceeds the hot rolling temperature range. This paper presents the results of work leading to the development of a rheological model describing the phenomena accompanying the deformation of 18G2A grade steel at temperature $1420°C$ and higher. Such temperature is a characteristic of the central parts of steel strands subjected to latest, very high temperature rolling technologies such as integrated rolling and casting processes. Rheological models have crucial influence on the results of the computer simulation of the mentioned processes. The methodology of yield stress curves development requires high accuracy systems of tension and compression test simulation. Hence, the proposed testing procedure is related to dedicated hybrid finite element method system with variable density, which was developed by the authors. The experimental work has been done using the Gleeble® 3800 thermomechanical simulator in the Institute for Ferrous Metallurgy in Gliwice, Poland. The testing machine allows the physical deformation of samples while solidification of their central part is still in progress. The essential goal of the simulation was the computer reconstruction of both temperature changes and strain evolution inside a specimen subjected to simultaneous deformation and solidification. In order to verify the predictive ability of the developed rheological model, a number of compression tests using Gleeble® 3800 simulator have been done, as well. The comparison between the numerical and the experimental results is also a part of the presented paper.

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## Figures

Figure 1

Main features of the dedicated FEM system

Figure 2

Scheme of samples used for the experiments. TC1–TC2—thermocouples

Figure 3

The scheme of computer aided methodology of the development of strain-stress curves with the help of the dedicated FEM system

Figure 4

The standard Gleeble® equipment allowing examination of the NDT

Figure 5

Rough flow stress curve for 1400°C and tool velocity of 100 mm/s (Gleeble® thermomechanical simulator)

Figure 6

Flow stress curves at several temperature levels after smoothing. Temperature range: 1200–1400°C. Tool velocity: 100 mm/s.

Figure 7

Calculated yield stress functions at several temperature levels from the range of 1200–1400°C. Tool velocity: 100 mm/s.

Figure 8

Four selected stages of deformation process at temperature 1425°C with tool velocity of 100 mm/s. Experiment status: success.

Figure 9

The example view of samples deformed at 1450°C and 1460°C with tool velocities of 20 mm/s and 1 mm/s, respectively. Experiment status: failure.

Figure 10

Example strain versus stress curves at temperature of 1425°C and higher for tool velocities of 1 mm/s, 20 mm/s, and 100 mm/s

Figure 11

Example comparison between measured and calculated loads at temperature of 1425°C and tool velocity of 100 mm/s

Figure 12

Initial temperature distribution (just before the deformation) in the 1/4 of cross section of the sample deformed at 1425°C

Figure 13

Strain distribution in the 1/4 of cross section of the sample deformed at 1425°C with tool velocity of 100 mm/s

Figure 14

Effective stress distribution in the 1/4 of cross section of the sample deformed at 1425°C with tool velocity of 100 mm/s (view of the central part of the sample)

Figure 15

Mean stress distribution in the 1/4 of cross section of the sample deformed at 1425°C with tool velocity of 100 mm/s (view of the central part of the sample)

Figure 16

Final shapes of the samples after deformation at 1425°C, 1450°C, and 1460°C and with tool velocity of 100 mm/s

Figure 17

The comparison between measured and calculated lengths of zone, which was not subjected to the deformation—experiments at temperature of 1425°C with tool velocities of 1 mm/s, 20 mm/s, and 100 mm/s

Figure 18

The comparison between the maximum measured and the calculated radii of the sample—experiments at temperature of 1425°C with tool velocities of 1 mm/s, 20 mm/s, and 100 mm/s

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