Influence of alloying elements on Continuous Cooling Transformation (CCT) diagram

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Table of contents

Literature review
I.1 Dual Phase steel microstructure formation
I.1.1 Austenite formation during intercritical annealing
I.1.2 Transformation of austenite after intercritical annealing
I.1.3 Changes in ferrite phase during intercritical annealing and cooling
I.1.4 Dual Phase steel microstructure
I.2 Martensite structure
I.2.1 Martensitic transformation
I.2.2 Martensite morphology
I.3 The effect of the alloying elements
I.3.1 Influence of alloying elements on Continuous Cooling Transformation (CCT) diagram
I.3.2 The role of different alloying elements
I.3.3 The effects of alloying elements on austenitising
I.3.4 The effects of alloying elements on ferrite formation
I.3.5 The effects of alloying elements on martensite formation
I.3.6 Segregations in Ingots and Castings
I.4 Tempering
I.4.1 Tempering of ferrous martensites
I.4.2 Stages of tempering
I.4.3 Tempering reactions in DP steels
I.5 The DP steel deformation behaviour
I.5.1 Mechanical behaviour
I.5.2 Continuous yielding behaviour
I.5.3 Tensile strength
I.5.4 Ductility
I.6 The damage mechanisms in DP steel during the ductile fracture process
I.6.1 Void nucleation
I.6.2 Void growth
I.6.3 Void coalescence
I.7 Microscopic fracture appearance in DP steel
I.8 Damage resistance of DP steel through Hole Expansion (HE)
Microstructures and mechanical properties
II.A Microstructure formation
II.A.1 Chemical composition and initial microstructures
II.A.2 Continuous Cooling Transformation (CCT) diagram for studied DP steel
II.A.3 Determination of intercritical region temperatures
II.A.4 Heat treatments
II.A.4.1 Thermal treatment cycles
II.A.4.2 Direct quenching
II.A.4.3 Rapid cooling and quenching heat treatment
II.A.5 Summary
II.B Mechanical properties
II.B.1 As-quenched material
II.B.1.1 Stress-strain curves
II.B.1.2 Mechanical properties evolution
II.B.2 Tempered material
II.B.2.1 Stress-strain curves
I.B.2.2 Mechanical properties evolution with tempering
II.B.3 Summary
Fine characterisation of the microstructure
III.1 Autotempering study
III.2 As-quenched microstructure study
III.3 Evolution of microstructure with tempering
III.4 Macrosegregation analysis
III.5 Summary
Carbon distribution analysis by NanoSIMS
IV.1 Introduction
IV.2 Experimental results and discussion
IV.2.1 Investigation of the as-quenched state
IV.2.2 Investigation of carbon distribution after tempering
IV.3 Understanding the carbon distribution
IV.4 Summary
Damage resistance through hole expansion
V.1 Damage resistance of the as-quenched material
V.2 Hole Expansion evolution with tempering temperature
V.3 HE-ferrite fraction correlations evolution with tempering temperature
V.4 Mechanical properties: correlation between HE and UTS
V.5 Summary
Damage mechanisms
VI.1 Fractography analysis of tensile test specimens
VI.2 Formation of microstructural damage during tensile testing
VI.2.1 Study of the as-quenched samples
VI.2.2 Study of the tempered samples
VI.3 Damage behaviour evolution with tempering
VI.4 Summary
Modeling of DP steel damage behaviour
VII.1 Application of the existing model
VII.2 Extension to include internal martensite damage
VII.3 Summary
Appendix 1: Experimental procedure
A1.1 Dilatometry
A1.2 Heat treatments
A1.3 Microstructure characterization
A1.3.1 Light microscopy
A1.3.2 Quantitative analysis
A1.3.3 Scanning electron microscopy
A1.3.4 Electron probe microanalysis
A1.3.5 NanoSIMS analysis
A1.3.6 Transmission electron microscopy (TEM)
A1.4 Mechanical characterization
A1.4.1 Tensile properties
A1.4.2 Charpy pendulum impact test
A1.4.3 Limiting Hole Expansion ratio, HE
A1.5 Fractography
A1. 6 Void analysis
Appendix 2: Charpy impact test
Appendix 3 : Résumé élargi de la thèse en français
A3.I Etude bibliographique
A3.I.1 La microstructure des aciers Dual-Phase (DP)
A3.I.2 La martensite
A3.I.3 Revenu de la martensite
A3.I.4 Revenu dans les aciers DP
A3.I.5 Comportement mécanique des aciers Dual Phase
A3.I.6 Absence de palier élastique dans les aciers Dual-Phases
A3.I.7 L’endommagement lors de la rupture ductile
References