Holding Time Influence on the Hot Ductility Behavior of a Continuously Cast Low Alloy Steel

Marina Gontijo,Sergiu Ilie,Jakob Six,Christian Hoflehner,Christof Sommitsch

doi:10.3390/met11010064

Marina Gontijo, Sergiu Ilie + Show 3 more

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https://doi.org/10.3390/met11010064

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Journal: Metals	Publication Date: Dec 30, 2020
Citations: 4	License type: CC BY 4.0

Affiliation: Graz University of Technology, Voestalpine (Austria)

Abstract

Cracking during the continuous casting process is undesirable and continuous work is being carried out to find further improvements and understand the mechanisms that lead to failure. Investigations on the hot ductility behavior of a continuously cast low alloyed steel using different holding times before straining were done in the present work. Samples were heated to melting temperature in a vacuum atmosphere and then cooled to one of the three test temperatures chosen: 750, 850, and 900 °C. When the desired temperature was reached, the sample was isothermally held for either 10, 90, 300, or 3600 s before the tensile test started, with a strain rate of 10−3 s−1. The reduction of area was measured, SEM images of the fractured surfaces were taken plus LOM images for the analysis of the microstructure. The results show that there was no significant change in the ductility at any of the temperatures until 300 s, with a change in behavior at 3600 s. This was further confirmed with the images and precipitation kinetics simulations. The results are described and compared.

Highlights

During the continuous casting of steels, surface and internal cracks can be originated by the different thermal and mechanical stresses present [1,2,3,4]
Considering the errors related to each point until 300 s, which ranged between 1 and 10% depending on the test parameters, no great difference was seen in the reduction of area (RA) regarding the different holding times
For the plain low alloyed steel studied, where only AlN, MnS, and Fe3 C are expected to be formed, changing the holding time before the tensile test in the range of 10 and 300 s did not have a significant impact on the RA measurements, but the increase in this holding time to 3600 s brought changes, showing that this parameter can influence the hot ductility behavior of the steel

Summary

Introduction

During the continuous casting of steels, surface and internal cracks can be originated by the different thermal and mechanical stresses present [1,2,3,4]. The hot ductility of low alloyed steels usually presents its minimum in the temperature range of 700 ◦ C to 1000 ◦ C, which is the usual range of the bending and straightening operation in the continuous casting process and the most critical for the formation of cracks [2,5,7,8] This lower ductility is known to be caused by two main factors, the austenite–ferrite transformation, and the nucleation of precipitates, depending strongly on the alloying elements present [6,9,10,11]. In the context of the nucleation of precipitates, local hardening occurs, provoking stress concentration and promoting the initiation of cracks [4,12]

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