1 Overview

1.1 The Technology of Controlled Rolling and Controlled Cooling

1.2 R＆D Program of"Super Steels"and"New Generation Steel Materials"

1.3 The Formation of Ultra-fine Grains and Microstructural Refinement of Steels-Core Technique for the R＆D of New Generation Steel Materials

1.4 Theory and Technology on Ultra-fine Grains

1.4.1 The state change and microstructure refinement of austenite during hot deformation

1.4.2 Deformation induced ferrite transformation

1.4.2.1 Thermodynamic consideration of deformation induced ferrite transformation

1.4.2.2 DIFT phase transformation and characters of transformed products

1.4.3 Deformation induced precipitation and medium temperature phase transformation control

1.4.4 The influence of nanometer size precipitates on ultra fine grain steel

1.4.5 Ultragrain refinement of alloy structural steels and the way of increasing the resistance against delayed fracturing

1.4.6 The development of carbide-free bainite/martensite multiple phase steels

1.5 Several Key Technologies Concerning the Development of Ultra Fine Grain Steels

1.5.1 Steel cleanness

1.5.2 Refinement and homogenization of solidification structure

1.5.3 Brief introduction of welding technique and economy of ultra fine grain steels

References

2 Refinement of Austenitic Microstructure and Its Influence on γ→α Transformation

2.1 Thermomechanical Control Process and Refinement of Austenitic Microstructure

2.1.1 Rolling at the austenite-recrystallization temperature region(RARTR)

2.1.1.1 Metadynamic recrystallization

2.1.1.2 Static recrystallization

2.1.2 Rolling in austenite non-recrystallization temperature region

2.1.3 Rolling at the under-cooled austenite

2.1.4 Accelerated cooling and microstructural refinement

2.2 Influence of Austenitic Recrystallization on Subsequently Transformed Grain Size

2.2.1 Influence of recrystallized or deformed austenite on ferrite transformation

2.2.1.1 Influence of recrystallized austenite on ferrite transformation

2.2.1.2 Influence of partially recrystallized austenite on ferrite transformation

2.2.1.3 Influence of non-recrystallized austenite on ferrite transformation

2.2.2 Influence ofrecrystallization in the austenite on DIFT

References

3 Deformation Induced Ferrite Transformartion

3.1 Introduction

3.2 Experimental Confirmation and Study Method of DIFT

3.2.1 Microstructure observation on the quenched sample

3.2.2 Mechanical behavior measurement

3.2.3 Dilatometry measurement

3.2.4 In-situ X-ray diffraction

3.3 Thermodynamics of DIFT

3.3.1 Deformation stored energy

3.3.2 Transformation driving force

3.3.3 Ad3 versus deformation stored energy

3.4 Kinetics of DIFT

3.4.1 Microstructural evolution and nucleation sites

3.4.2 Transformation fraction versus strain

3.4.3 Ferrite grain number and grain size versus transformation fraction

3.4.4 Theoretical analysis

3.4.4.1 Ferrite nucleation rate and deformation stored energy

3.4.4.2 Ferrite grain growth and deformation stored energy

3.5 Mechanisms of DIFT

3.6 Factors Influencing DIFT

3.6.1 Deformation variables

3.6.1.1 Strain

3.6.1.2 Deformafion temperature

3.6.1.3 Strain rate

3.6.2 Chemicai compositions

3.6.2.1 Effect of carbon and manganese

3.6.2.2 Effect of niobium and vanadium

3.6.3 Prior austenite grain size

3.7 Applications of DIFT

3.7.1 Applications of DIFT in plain low carbon steel

3.7.1.1 Plain low carbon steel rebar

3.7.1.2 Plain low carbon steel strip

3.7.2 Applications of DIFT in microalloyed steel

3.7.2.1 Laboratory trial production of 700MPa grade ultrafine grained steel

3.7.2.2 Industrial production of high strength Cu-P-Cr-Ni weathering resistance steel

References

4 Microstructure Refinement of Steels by TSCR Technology

4.1 Microstructure Refinement Process and Austenite Recrystallization of Low Carbon Steels Produced by TSCR Technology

4.1.1 Contrast between TSCR technology and traditional technology

4.1.2 The refinement process of microstructure during CSP hot continuous rolling

4.1.2.1 Variation of the grain size in rolling direction

4.1.2.2 Variation of grain size in rolling plane

4.1.2.3 Comparison of microstructure in transverse,rolling and surface direction of ZJ330 rolling block workpiece for different passes

4.1.3 The relationship between texture and the austenite and the ferrite

4.1.3.1 Texture analysis by EBSD

4.1.3.2 Orientation analysis by EBSD

4.1.4 Austenite recrystallization of low carbon steel during continuous hot rolling process

4.1.4.1 Microstructure evolution model of austenite during hot continuous rolling for low carbon steel

4.1.4.2 Simulation of microstructure evolution for austenite during hot continuous rolling of low carbon steel

4.2 Microstructure and Properties of Low Carbon Steel Produced by Thin Slab Casting and Rolling(TSCR)

4.2.1 Comparison on microstructure and properties of low carbon hot strip with different thermal histories

4.2.1.1 Production comparison experiments of CSP and traditional technology in producing hot low carbon strip

4.2.1.2 Comparison and analysis of mechanical properties and microstructure of strips produced by two kinds of process

4.2.2 Analysis of structure property in low carbon hot strip produced by CSP and traditional process

4.2.2.1 Comparison of structure and property of low carbon hot strip produced by CSP and traditional process

4.2.2.2 Analysis of influencing factor on microstructure and properties of hot strip produced by CSP

4.2.2.3 Microstructure and properties of C-Mn strips with high strength produced by CSP process

4.3 Mechanism and Precipitation Characteristic of AlN in Low Carbon Steel Produced by Thin Slab Casting and Rolling Technology

4.3.1 AlN precipitation in low carbon steel of thin slab casting and rolling

4.3.1.1 Experirnent on precipitation of AlN during heating and rolling

4.3.1.2 Experiment analysis on precipitation of AlN in hot rolled strip by thin slab casting and rolling

4.3.2 Precipitation dynamics of AlN

4.3.2.1 Dynamics model of AlN precipitation

4.3.2.2 Dynamics condition of AlN and simulation result

4.3.3 Effect of fine AlN particles on structure and performance

4.3.3.1 Effect of AlN particles on the precipitation of austenite section

4.3.3.2 Effect of AlN precipitation during the phase transformation

4.4 Control on Soft Mechanism of Cold Rolling Thin Slab by Continuous Casting and Rolling

4.4.1 Requirements of cold-rolled sheet for deep drawing to the property of cold rolling billet and the control methods on soften steel

4.4.2 Mechanism of adding B micro-alloy into low-carbon steel on grain growth coursing and steel softening

4.4.2.1 Action of adding B micro-alloy into steel on the coursing of grain growth

4.4.2.2 Effects of adding B into steel on the precipitation in low carbon steel

4.4.3 Effects of the hot rolling and cooling technology on the softening of low carbon steel

4.4.3.1 The effects of finishing temperature on theperformance of SPHC

4.4.3.2 The effects of finishing reduction on the property of SPHC

4.4.3.3 The effects of coiling temperature on the property of SPHC

4.4.3.4 The effects of hot rolled lubrication on the property of SPHC

4.4.3.5 The effects of cooling methods on the property of SPHC

4.4.4 The effects of the control method of different softening technology on the formability of cold-rolled sheet 08Al

4.4.4.1 The composition and technology of hot rolled low carbon steel of CSP

4.4.4.2 The technologies of cold rolling and annealing

4.4.4.3 The effects of coiling temperature and total cold-rolled reduction on r-value of steel 08Al with and without B

4.4.4.4 The effects of coiling temperature and total cold-rolled reduction on the yield strength of08Al steel with and without B

4.4.4.5 The effects of coiling temperature and the total cold-rolled reduction on elongation percentage

4.4.4.6 Texture analysis of B free and B added steel

4.5 Precipitations in the CSP Low Carbon Steels

4.5.1 Introduction

4.5.2 Sulfide and oxide dispersive precipitates

4.5.2.1 Precipitates in slabs and rolling pieces of the low carbon steels

4.5.2.2 Sulfides in the low carbon steels with varying content of sulfur

4.5.2.3 Mechanism of the sulfide precipitation in the condition of CSP process

4.5.2.4 Effects of the sulfide and oxide on formation of other phases

4.5.2.5 Other nanometer precipitates in the steels

4.5.3 Carbides and carbonitrides in Ti containing steels

4.5.3.1 In general feature

4.5.3.2 Experimental investigation

Summary

References

5 Microstructure Fining Theory of Low-carbon Bainitic Steel

5.1 Social Needs for Low-carbon Bainitic Steel with a Grade of More than 600MPa

5.2 Strengthening Mechanism of Low(Ultra-low)Bainitic Steel

5.3 Primary Characteristics of Several Kinds of Low-carbon Bainitic Steels Developed in China

5.3.1 CCT curve characteristics of the steels

5.3.2 Recrystallization curve characteristics during hot-processing

5.3.2.1 C-Mn steel and Nb or B individually added steel

5.3.2.2 When alloying elements such as Nb,,B,Cu are combinedly added

5.3.3 PTT curve characteristics of the steel

5.4 Theoretical Thought for Furthering Fining the Intermediate-temperature Transformation Microstructures

5.4.1 Basic key points for intermediate temperature transformation microstructure fining

5.4.2 Theoretical background for proposing the relaxation-precipitation-controlling transformation(RPC)technology

5.4.3 Basic ideas of TMCP+RPC technology

5.5 Ultra-fining Process,Actual Fining Effect and Typical Microstructures

5.5.1 Selecting composition range of micro-alloying elements fully performing ultra-fining process effect

5.5.1.1 Principle of composition design

5.5.1.2 Starting points of composition selection

5.5.1.3 Strength evaluation

5.5.2 Typical process of relaxation-precipitation-controlling transformation(RPC)technology

5.5.3 Typical fining microstructures under RPC process and its comparison with other processes

5.5.4 Effects of RPC process and composition on microstructure and properties

5.5.4.1 Effect of relaxing time

5.5.4.2 Effects of final-rolling temperature

5.5.4.3 Effects of cooling rate on microstructure and properties

5.5.5 Strength,plasticity and toughness of the steel from industrial Trial Production of RPC process

5.6 Study on Fining Process Parameters of Intermediate-temperature Transformed Microstructure Through Thermo-mechanical Simulation

5.6.1 Microstructure evolution after deformation and relaxation under different temperatures

5.6.2 Quantitative statistics of bainitebundle size

5.7 Forming Mechanism of Typical Fining Microstructures

5.7.1 Two kinds of typical microstructure morphology in samples after RPC process

5.7.2 Formation and influence of substructure during relaxation

5.7.3 Induced precipitation in deformed austenite and Its effects(Yuan et al,2004;Yuan et al,2003)

5.7.4 Formation,Morphology of acicular ferrite and its effect on fining

5.7.4.1 Morphology characteristics of acicular ferrite

5.7.4.2 Effect of relaxation on formation of acicular ferrite

5.8 Study on the Variation of Microstructure and Properties of Fined Steels during Tempering and Its Cause Analysis

5.8.1 Hardness changes and their difference between the microstructure-fined steel and the quenched and tempered steel with the same compositions

5.8.2 Microstructure stability in tempering process

5.8.3 Effect of tempering temperature on mechanical properties of the steel

5.9 Concluding Note

References

6 Microstructure Refining and Strengthening of Martensitic Steel

Introduction

6.1 Challenges of High Strength Martensitic Steel

6.1.1 Delayed fracture

6.1.2 Fatigue failure

6.2 Microstructure Refinement in Toughening and Improving DF Property of Martensitic Steels

6.2.1 Technologies for martensitic microstructure refining

6.2.2 Effect of microstructure refinement on strength and toughness

6.2.3 Effect of microstructure refinement on DF resistance

6.2.3.1 Stress corrosion cracking

6.2.3.2 Sustained load tensile delayed fracture

6.2.3.3 Discussion of the dependence of DF resistance on grain size

6.3 Grain Boundary Strengthening in Improving DF Property of Martensitic Steels

6.3.1 Reducing segregation of impurities at grain boundaries

6.3.2 Controlling grain boundary carbide

6.3.2.1 Increasing tempering temperature

6.3.2.2 Intercritical quenching

6.3.2.3 Ausforming process

6.3.3 Effect of Mo alloying

6.3.3.1 Mo raising tempering temperature

6.3.3.2 Mo carbide as hydrogen trap

6.3.3.3 Mo controlling impurities and strengthening grain boundaries

6.3.3.4 Influence of Mo content

6.4 Controlling of Hydrogen Trap in Martensitic Steels to Improve Its DF Resistance

6.5 Effect of Cleanliness on the Fatigue Performance of High Strength Martensitic Steels

6.6 New Developed High Strength Martensitic Steels and Their Industrial Application

References

7 Carbide-free Bainite/Martensite(CFB/M) Duplex Phase Steel

7.1 CFB/M Duplex Phase Structure

7.2 Alloy Design of CFB/M Duplex Phase Steel by Tsinghua University Bainitic Steel R＆D Center

7.2.1 Alloy design of CFB/M duplex phase steel and its structure

7.2.2 Effect of cooling rate on CFB/M duplex phase microstructure

7.2.3 Effect of CFB/M duplex phase microstructure on strength and toughness of the steel

7.3 Effect of Tempering on Strength and Toughness of CFB/M Duplex Phase Steel

7.3.1 Effect of CFB/M duplex phase microstructure on the initial temperature of temper embrittleness the first kind

7.3.2 Effect of CFB/M duplex phase microstructure on yield-tensile ratio of steel

7.4 Susceptibility to Hydrogen Embrittlement for CFB/M Duplex Phase High Strength Steel

7.4.1 Effect of hydrogen content on susceptibility to hydrogen embrittlement for CFB/M duplex phase high strength steel

7.4.2 Effect of heat treatment process on susceptibility to hydrogen embrittlement for CFB/M duplex phase high strength steel

7.4.2.1 Effect of BU and CFB

7.4.2.2 Effect of CFB quantity on fracture surface topography

7.4.3 Influence of microstructure refinement and retained austenite on susceptibility to hydrogen embrittlement for CFB/M steel

7.5 Stress Corrosion of CFB/M Duplex Phase High Strength Steel

7.5.1 Stress corrosion cracking property of CFB/M duplex phase high strength steel

7.5.2 Stress corrosion fracture of CFB/M duplex phase high strength steel

7.6 Hydrogen in CFB/M Duplex Phase High Strength Steel

7.6.1 Measure hydrogen diffusion coefficient using double electrolysis cell

7.6.2 Hydrogen trap in CFB/M duplex phase high strength steel

7.6.2.1 Bainitic/martensite lath boundary

7.6.2.2 Retained austenite

7.7 Mechanism of Resistance to Delayed Fracture of CFB/M Steel

7.7.1 Relationship between susceptibility to hydrogen embrittlement and hydrogen trap for CFB/M steel

7.7.2 Relationship between stress corrosion and hydrogen trap in steel

7.7.3 Crack propagation model of CFB/M duplex phase steel

7.8 Fatigue Behavior of 1500MPa CFB/M Duplex Phase High Strength Steel

7.8.1 Fatigue behavior of CFB/M duplex phase steel

7.8.1.1 Fatigue strength of CFB/M duplex phase steel

7.8.1.2 Fatigue crack propagation behavior

7.8.1.3 Fatigue fracture of CFB/M duplex phase high strength steel

7.8.2 Effect of microstructure characteristics of CFB/M duplex phase steel on fatigue behaviors

7.8.2.1 Effect of microstructure characteristics on fatigue strength

7.8.2.2 Effect of microstructure characteristics on △Kth and da/dN

7.8.3 Effect of retained austenite on fatigue behaviors of CFB/M duplex phase steel

7.8.3.1 Retained austenite content and cyclical stability

7.8.3.2 Effect of retained austenite and its cyclical stability on fatigue strength

7.8.3.3 Effect of retained austenite film on fatigue crack propagation

7.8.4 Fatigue fracture mechanism of CFB/M duplex phase steel

7.9 Application Prospect of CFB/M Duplex Phase Steel

References

8 Extra Low Sulfur and Non-metallic Inclusions Control for Ultra Fine Grain High Strength Steels

8.1 Introduction

8.2 Refining Technology for Extra Low Sulfur Steels

8.2.1 Hot metal De-S pretreatment

8.2.2 Reducing[S]pick up in BOF steelmaking

8.2.3 Desulfurization in secondary refining of liquid steel

8.2.3.1 Desulfurization during BOF tapping

8.2.3.2 Desulfurization in ladle furnace refining(LF)

8.2.3.3 Powder injection desulfurization methods

8.3 Extra Low Oxygen and Non-metallic Inclusions Control of High Strength Alloying Steels

8.3.1 Influence of non-metallic inclusions on fatigue property of steel

8.3.2 Refining and non-metallic inclusion control of extra low oxygen alloy steels

8.3.3 Deformable non-metallic inclusions for tyre cord and valve spring steels

8.3.3.1 Deformable non-metallic inclusions

8.3.3.2 Control of[Al]in liquid steel

8.3.3.3 Slag control

8.3.4 Steel with premium cleanliness

References

9 Fundamental Study on Homogeneity of Solidification Structure of Steel

9.1 The Structure of Liquid Fe-C Alloy

9.1.1 Experimental

9.1.2 Data analysis

9.1.3 Medium-range order structure in liquid Fe-C alloy

9.1.4 Conclusions

9.2 Observation and Analysis of Heterogeneous Nucleation Phenomena

9.2.1 Experimental

9.2.2 Effects of vibration frequency and amplitude

9.2.3 Effects ofsolid substrate temperature and surface roughness

9.2.4 Conclusions

9.3 Homogeneity and Equiaxed Grain Structure of Steels

9.3.1 Relation of segregation and equiaxed grain structure

9.3.2 Titanium-based inoculation technology

9.3.2.1 Precipitation of TiN particles

9.3.2.2 Competitive precipitation between TiN and Ti2O3

9.3.2.3 Particles for nucleus ofδ-ferrite dendrites

9.3.3 Small temperature gradient technology

9.3.4 Conclusions

References

10 Welding of Ultra-Fine Grained Steels

10.1 Introduction

10.2 Simulation of Welding of Fine-grained Steel

10.2.1 Simulation of grain growth in HAZ

10.2.1.1 The monte carlo model of the HAZ

10.2.1.2 The EDB model

10.2.1.3 MC simulation ofgrain growth in HAZ of fine-grained steels

10.2.1.4 Experimental identification

10.2.2 Fluid flow in welding pool of ultra fine grain steel

10.2.2.1 Mathematical model

10.2.2.2 Numerical method

10.3 Welding of Fine Grained Carbon Steel Plate

10.3.1 Laser welding of low carbon steel

10.3.1.1 Experiment material and equipment

10.3.1.2 Weld shape and microstructure of welded joints

10.3.1.3 Mechanical properties of laser welded joint

10.3.1.4 Conclusions

10.3.2 Arc welding of fine grained low carbon steel

10.3.2.1 Experiment material and method

10.3.2.2 Experiment results and discussion

10.3.2.3 Conclusions

10.3.3 Arc welding of fine grained atmospheric corrosion resistant steel

10.3.3.1 Experiment materials and procedure

10.3.3.2 Experiment results and discussion

10.3.3.3 Conclusions

10.3.4 Welding of 400 MPa grade fine grained rebar

10.3.4.1 Experiment material and procedure

10.3.4.2 Experiment results and discussion

10.3.4.3 Conclusions

10.4 Welding of Ultra-Fine Structure Bainite Steel

10.4.1 Development of ultra-low carbon bainitic high strength welding wire

10.4.1.1 Designing principles of the ULCB welding wires

10.4.1.2 Compositions and mechanical properties of ULCB wire deposited metals

10.4.1.3 Optical microstructure of the ULCB deposited metals

10.4.1.4 Fine microstructure of ULCB wire deposited metals

10.4.1.5 Conclusions

10.4.2 Microstructures and properties of the GMAW welded joint of the ultra fine structure bainitic steel

10.4.2.1 Weld microstructure of ultra fine grained bainitic steel

10.4.2.2 Mechanical properties of weld metal in ultra-fine grained bainitic steel

10.4.2.3 Conclusions

10.4.3 Laser welding of ultra-fine microstructural bainitic steel

10.4.3.1 Chemical composition and microstructure of base metal

10.4.3.2 Experimental procedure

10.4.3.3 Grain size

10.4.3.4 Microstructure of CGHAZ

10.4.3.5 Hardness and strength of CGHAZ

10.4.3.6 Toughness of CGHAZ

10.4.3.7 Conclusions

References

Subject Index