Thermomechanical Processing of High-Strength Low-Alloy Steels - 1st Edition - ISBN: 9780408110341, 9781483164052

Thermomechanical Processing of High-Strength Low-Alloy Steels

1st Edition

Authors: Imao Tamura Hiroshi Sekine Tomo Tanaka
eBook ISBN: 9781483164052
Imprint: Butterworth-Heinemann
Published Date: 17th March 1988
Page Count: 256
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Thermomechanical Processing of High-Strength Low-Alloy Steels considers some advanced techniques and metallurgical bases for controlled-rolling.

This book contains 12 chapters. In Chapter 1, the purpose of thermomechanical processing and historical survey is described, while in Chapter 2, the kinetics of phase transformations and refinement of grain size in steels are elaborated. The techniques and metallurgical bases for controlled-rolling in the recrystallization, non-recrystallization, and (? + y) regions are reviewed in Chapters 3 to 5. Chapters 6 and 7 discuss the deformation resistance during hot-rolling and restoration processes. The phase transformations during cooling following hot-rolling are mentioned in Chapter 8, followed by a summarization of the effects of alloying elements in Chapter 9. Chapters 10 and 11 deal with the mechanical properties of controlled-rolled steel and prediction and control of microstructure and properties by thermomechanical processes. The problems faced and possibilities for future developments are stated in the last chapter.

This publication is recommended for physicists, metallurgists, and researchers concerned with controlled-rolling, including non-specialists who have some knowledge of metallurgy.

Table of Contents

1 Introduction

1.1 What is Thermomechanical Processing?

1.2 Historical Survey

1.2.1 Controlled Low-Temperature Hot-Rolling Of Ships' Plates

1.2.2 Controlled-Rolling of Low-Carbon Niobium-Containing Steels

1.2.3 Outline of Controlled-Rolling

1.2.4 Further Developments of Controlled-Rolling

1.2.5 Accelerated Cooling in Plate-Rolling Mills


2 Austenite to Ferrite Transformation and Refinement of a Grain Size

2.1 γ→α Phase Transformation

2.1.1 Classification of Phase Transformation

2.1.2 Effect of Alloying Elements on γ→α Transformation

2.1.3 Precipitation of Alloy Carbide from α

2.2 Transformation Kinetics

2.2.1 Transformation Kinetics of γ (Isothermal)

2.2.2 Continuous Cooling Transformation Kinetics of γ

2.3 α Grain Size Transformed from γ

2.3.1 Major Purpose of Controlled-Rolling

2.3.2 Expression for α Grain Size (Isothermal)

2.3.3 Estimation of α Grain Size Formed by Continuous Cooling Transformation

2.4 Deformation Behaviour of Steels at Elevated Temperatures

2.4.1 Restoration During Hot-Deformation

2.4.2 Static Restoration During Holding Right After Hot-Deformation

2.4.3 Effect of Alloying Elements on the Retardation of Recrystallization

2.4.4 Texture Due to Hot-Deformation

2.5 α Grain Refinement by the Work-Hardening of Austenite

2.5.1 α Nucleation in Deformed γ (Isothermal)

2.5.2 Growth of α in Deformed γ (Isothermal)

2.5.3 α Grain Size Formed from Deformed γ (Isothermal)

2.6 α Grain Refinement by Accelerated Cooling

2.7 Summary


3 Deformation of Austenite in the Recrystallization Region

3.1 Metallurgical Changes During and After Constant-Rate Hot-Deformation

3.2 Dynamic and Metadynamic Recrystallization by Rolling Hot-Deformations

3.3 Temperature-Reduction-Recrystallization

3.4 Controlled-Rolling for Refinement of Recrystallized γ Grains

3.5 Effects of Alloying Elements on Recrystallization Behaviour

3.5.1 Recrystallization Kinetics

3.5.2 Recrystallized Grain Size


4 Deformation of Austenite in the Nonrecrystallization Region

4.1 Retardation of Recrystallization of γ

4.2 Formation and Role of Deformation Bands

4.3 Strain-Induced and/or Strain-Enhanced Transformation


5 Deformation in the (Austenite Plus Ferrite) Two-Phase Region

5.1 Deformation Behaviour in the (γ+α) Two-Phase Region

5.2 Anisotropy and Texture

5.3 Separation

5.4 Elimination of Separation


6 Deformation Resistance at Elevated Temperatures

6.1 Strain Hardening and Restoration

6.2 Metallurgical Factors Affecting Hot-Strength

6.3 Hot-Deformation Resistance Formulae


7 Softening Behaviour Immediately After Rolling and Strain Accumulation

7.1 Softening Behaviour Immediately After Hot-Rolling

7.2 Factors Affecting Softening

7.3 Introduction of Strain Accumulation into Deformation and Resistance Formulae

7.4 Computer Simulation for Predicting Mill Load


8 Transformation Behaviours of Austenite After Thermomechanical Treatment

8.1 Transformation from Recrystallized γ

8.2 Transformation from Nonrecrystallized γ


9 Alloying Elements and Impurities

9.1 Microalloying Elements

9.1.1 Solubility Products

9.1.2 Retardation of γ Recrystallization

9.1.3 Grain Refinement and Precipitation Hardening

9.2 Substitutional Alloying Elements

9.3 Impurity Elements


10 Properties of Controlled-Rolled Steels

10.1 Strengthening and Toughening Mechanisms

10.1.1 Interpretation of Mechanical Properties

10.2 Mechanical Properties

10.2.1 High-Tensile Steel with a Tensile Strength Of 50kgf/mm2 (Ht-50 Steel)

10.2.2 Line-Pipe Steels

10.2.3 Acicular a Steel

10.2.4 As-Hot-Rolled Dual-Phase Steel

10.3 Weldability

10.3.1 Susceptibility to Weld Cracking

10.3.2 Toughness at the Heat-Affected Zone


11 Prediction and Control of Microstructural Change and Mechanical Properties in Hot-Rolling

11.1 A Model to Predict Recrystallized γ Grain Size During Hot-Rolling

11.1.1 Dynamic Recrystallization

11.1.2 Static Recrystallization

11.1.3 Statically Recrystallized Grain Size

11.1.4 Grain Growth

11.1.5 Static Recovery

11.1.6 Effective γ Grain Boundary Area for the Formation of a Grains

11.2 Prediction of γ Grain Size in Multipass Rolling

11.3 Strain-Induced Precipitation of Niobium Carbonitrides

11.4 Strain Accumulation in the Low-Temperature γ Region

11.5 Deformation in the (γ+α) Two-Phase Region

11.6 Relation Between Microstructure and Strength and Toughness


12 Further Developments in Thermomechanical Processing

12.1 Controlled-Cooling After Controlled-Rolling

12.1.1 Effects of Cooling Variables on Mechanical Properties

12.1.2 Transformed Microstructure and Strengthening Mechanism

12.2 Hot-Charge Rolling and Hot-Direct Rolling


13 Conclusion



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About the Author

Imao Tamura

Hiroshi Sekine

Tomo Tanaka

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