上游充通大率 SHANGHAI JIAO TONG UNIVERSITY Principles of Materials Processing Part Ill 全属材料热处理原理 Heat Treatment Principles of Metals Lecturer:Ke Chen 2017-05-18
Principles of Materials Processing Part III - 金属材料热处理原理 Heat Treatment Principles of Metals Lecturer: Ke Chen 2017-05-18
Outline for Chapter 10 上游充道大粤 SHANGHAI JIAO TONG UNIVERSITY Chapter 10:Shear Transformation 10.1 Martensite Transformations 10.1.1 Characteristics 10.1.2 Thermodynamics 10.1.3 Crystallographic Theory 10.1.4 Kinetics 10.2 Martensite Transformations in Steels 10.3 Bainite Transformations K.Chen 2
K. Chen Chapter 10: Shear Transformation 10.1 Martensite Transformations 10.1.1 Characteristics 10.1.2 Thermodynamics 10.1.3 Crystallographic Theory 10.1.4 Kinetics 10.2 Martensite Transformations in Steels 10.3 Bainite Transformations Outline for Chapter 10 2
Intro 上游充道大粤 SHANGHAI JIAO TONG UNIVERSITY Heat treatment process for hardening of steel? √Quenching! Rapid enough from the austenitic phase field> insufficient time for diffusion-controlled decomposition processes to occur Transform to martensite!>Diffusionless transformation! NG UNN Where will be the C atoms? > Solid solution of C in fcc y-Fe>Solid solution of C in a-Fe (Supersaturated!) K.Chen 3
K. Chen Heat treatment process for hardening of steel? Quenching! Rapid enough from the austenitic phase field insufficient time for diffusion-controlled decomposition processes to occur Transform to martensite! Diffusionless transformation! Where will be the C atoms? Solid solution of C in fcc γ-Fe Solid solution of C in α-Fe (Supersaturated!) 3 Intro
上游气通大粤 SHANGHAI JIAO TONG UNIVERSITY Shear/Displacive Transformation: In this transformation,atoms change position(lattice reconstruction)in an ordered military manner,by a shear mechanism. Military: The regimented/coordinated manner in which atoms change position In contrast to diffusion-controlled transformations which are termed civilian Two types of shear transformations: Diffusionless:individual atomic movements less than one interatomic spacing >Martensite transformation Diffusional:Bainite transformation (Fe:shear;C:diffuse) K.Chen 4
K. Chen Shear/Displacive Transformation: In this transformation, atoms change position (lattice reconstruction) in an ordered military manner, by a shear mechanism. Military: The regimented/coordinated manner in which atoms change position In contrast to diffusion-controlled transformations which are termed civilian Two types of shear transformations: Diffusionless: individual atomic movements less than one interatomic spacing Martensite transformation Diffusional: Bainite transformation (Fe: shear; C: diffuse) 4
上游充通大粤 Martensite transformation SHANGHAI JIAO TONG UNIVERSITY Any diffusionless transformation in which from start to completion of the transformation individual atomic movements are less than one interatomic spacing ■Only in steel? 层月 In principle,all metals and alloys,even ceramics can be made to undergo this transformation Complex process;the mechanism is not properly understood Growth of martensite with increasing cooling below M. K.Chen 5
K. Chen Martensite transformation Any diffusionless transformation in which from start to completion of the transformation individual atomic movements are less than one interatomic spacing Only in steel? • In principle, all metals and alloys, even ceramics can be made to undergo this transformation Complex process; the mechanism is not properly understood 5 Growth of martensite with increasing cooling below Ms
歌 上游充通大粤 Martensite transformation SHANGHAI JIAO TONG UNIVERSITY Morphologies in iron alloys 10oum 20 um 20um Low C (lath) Medium C(plate) Fe-Ni(plate) K.Chen 6
K. Chen Martensite transformation Morphologies in iron alloys 6 Low C (lath) Medium C (plate) Fe-Ni (plate)
Characteristics 上游充道大粤 SHANGHAI JIAO TONG UNIVERSITY 1.Shear mechanism and surface relief effect Where the martensite plates intersect the surface of a polished specimen they bring about an elastic deformation,or tilting of the surface The transformed regions coherent with the surrounding austenite The intersection of the lenses with the surface of the specimen does not result in any discontinuity Structure of the interface:a high level of continuity, normally semi-coherent K.Chen 7
K. Chen Characteristics 7 1. Shear mechanism and surface relief effect Where the martensite plates intersect the surface of a polished specimen they bring about an elastic deformation, or tilting of the surface The transformed regions coherent with the surrounding austenite The intersection of the lenses with the surface of the specimen does not result in any discontinuity Structure of the interface: a high level of continuity, normally semi-coherent
Characteristics 上浒充通大￥ SHANGHAI JIAO TONG UNIVERSITY 1.Shear mechanism and surface relief effect Surface Surface Relief (a) M A Invariant plane in austenite Martensite Schematic for Martensite Transformation habit plane (b) Fig.6.2 Illustrating how a martensite plate remains(macroscopically coherent with the surrounding austenite and even the surface it intersects. Lines on a polished surface are displaced, but remain continuous after the transformation Surface Reliefs K.Chen 8
K. Chen Characteristics 8 Schematic for Martensite Transformation Surface Reliefs 1. Shear mechanism and surface relief effect Lines on a polished surface are displaced, but remain continuous after the transformation Surface
Characteristics 上游充道大粤 SHANGHAI JIAO TONG UNIVERSITY 2.Diffusionless Austenite Martensite:only crystal structure change but no composition change Atoms change position in a regimented manner (coordinated movement)>neighboring atoms keep the same after transformation Experimental support:martensite transformation can occur at temperature as low as 4K,when the atomic diffusion rate is so small that transformation can not take place through atomic diffusion at all! K.Chen 9
K. Chen Characteristics 9 2. Diffusionless Austenite Martensite: only crystal structure change but no composition change Atoms change position in a regimented manner (coordinated movement) neighboring atoms keep the same after transformation Experimental support: martensite transformation can occur at temperature as low as 4K, when the atomic diffusion rate is so small that transformation can not take place through atomic diffusion at all!
Characteristics 上游充道大粤 SHANGHAI JIAO TONG UNIVERSITY 3.Orientation relationships and habit planes The formation of martensite involves the coordinated movement of atoms. Austenite and martensite lattices will be intimately related All martensite transformations therefore lead to a reproducible orientation relationship between the parent and product lattices. It is frequently the case that a pair of corresponding close- packed planes in the ferrite and austenite are parallel or nearly parallel,and it is usually the case that corresponding directions within these planes are roughly parallel. K.Chen 10
K. Chen Characteristics 10 3. Orientation relationships and habit planes The formation of martensite involves the coordinated movement of atoms. Austenite and martensite lattices will be intimately related. All martensite transformations therefore lead to a reproducible orientation relationship between the parent and product lattices. It is frequently the case that a pair of corresponding closepacked planes in the ferrite and austenite are parallel or nearly parallel, and it is usually the case that corresponding directions within these planes are roughly parallel
