Parameter Identification for Thermo-Mechanical Constitutive Modeling to Describe Process-Induced Residual Stresses and Phase Transformations in Low-Carbon Steels

Muhammed Zubair Shahul Hameed,Ewald Werner,Stefan Rappl,Tobias Robl,Christian Krempaszky,Thomas Obermayer,Kai Osterminski,Christoph Hubertus Wölfle

doi:10.3390/app11020550

Muhammed Zubair Shahul Hameed, Ewald Werner + Show 6 more

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https://doi.org/10.3390/app11020550

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Journal: Applied Sciences	Publication Date: Jan 8, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: Technical University of Munich

Abstract

Reinforcing steel bars (rebars) are widely manufactured using the Tempcore™ process. Several studies have been conducted analyzing the effect of the heat treatment route on the strength and corrosion resistance of rebars, but knowledge of its effects on the residual stresses of the finished product are largely lacking. This paper presents experimental investigations to identify the material parameters necessary to simulate the Tempcore™ process using thermo-elasto-plastic constitutive modeling in order to study the generation of residual stresses during the manufacturing process. Mechanical parameters such as yield strength at elevated temperatures and elastic constants were determined experimentally. A continuous cooling transformation diagram needed to model the phase transformations was also identified and is presented here. Residual stress distributions in the surface region of the rebar were characterized using X-ray diffraction. Further characterizations of microstructure, chemical composition, and hardness were carried out. The constitutive modeling approach for the numerical simulation is briefly described for which the experimentally determined parameters are required as input.

Highlights

This paper presents experimental investigations to identify the material parameters necessary to simulate the TempcoreTM process using thermo-elasto-plastic constitutive modeling in order to study the generation of residual stresses during the manufacturing process
TempcoreTM is the trademark for the heat treatment route that was developed in the 1970s by CRM Group and has since been widely used for the manufacturing of reinforcing steel bars [1,2]
The longitudinal cross-section was further used to investigate any difference in microstructure on either sides of the transverse ribs that might have arisen due to the water being sprayed from one direction only inside the quenching chamber of the manufacturing unit

Summary

Introduction

TempcoreTM is the trademark for the heat treatment route that was developed in the 1970s by CRM Group and has since been widely used for the manufacturing of reinforcing steel bars (rebars) [1,2]. It is a quench and self-tempering thermo-mechanical process wherein the hot rolled rebars come out of the last hot-rolling mill at a temperature above Ac3 at which the rebars are still in their austenitic state and are rapidly quenched with water sprayed onto their surface at high volumetric flow rate. This composite nature of the rebar with an outer hard layer and a ductile inner core is achieved with a relatively simple heat treatment process that produces high-strength rebars that are bendable and weldable without the need for micro-alloying with V or Nb [1,2,3]

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