Complete Casting Handbook: Metal Casting Processes, Techniques and Design

1242 Pages·2011·26.599 MB·English

by  John Campbell

Complete Casting
Handbook
Metal Casting Processes,
Metallurgy, Techniques
and Design
To Sheila once again. She really deserves it.
Complete Casting
Handbook
Metal Casting Processes,
Metallurgy, Techniques
and Design
John Campbell
OBE FREng DEng PhD MMet MA
Emeritus Professor of Casting Technology,
University of Birmingham, UK
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Contents
Preface................................................................................................................................................xix
Introduction from Castings 1st Edition 1991..................................................................................xxiii
Introduction toCastings2nd Edition 2003.......................................................................................xxv
Introduction toCastingPractice: The10RulesofCastings 2004................................................xxvii
Introduction toCastingsHandbook 2011........................................................................................xxix
Acknowledgments.............................................................................................................................xxxi
VOLUME I CASTING METALLURGY
CHAPTER 1 The melt.......................................................................................3
1.1 Reactions of the melt with its environment..............................................................5
1.2 Transport ofgases in melts........................................................................................9
1.3 Surface film formation.............................................................................................13
1.4 Vaporization.............................................................................................................16
CHAPTER 2 Entrainment................................................................................19
2.1 Entrainmentdefects.................................................................................................24
2.1.1 Bifilms...........................................................................................................24
2.1.2 Bubbles..........................................................................................................28
2.1.3 Extrinsic inclusions.......................................................................................32
2.2 Entrainmentprocesses.............................................................................................42
2.2.1 Surfaceturbulence.........................................................................................42
2.2.2 Oxide skins from melt chargematerials.......................................................52
2.2.3 Pouring...........................................................................................................54
2.2.4 The oxide lap defect I: Surface flooding......................................................57
2.2.5 The oxide lap defect II:Theconfluenceweld..............................................60
2.2.6 The oxide flowtube.......................................................................................64
2.2.7 Microjetting...................................................................................................65
2.2.8 Bubble trails..................................................................................................67
2.3 Furlingand unfurling...............................................................................................77
2.4 Deactivation ofentrained films................................................................................88
2.5 Soluble, transient films............................................................................................92
2.6 Detrainment..............................................................................................................92
2.7 Evidence for bifilms.................................................................................................94
2.8 Theimportance ofbifilms.....................................................................................100
v
vi Contents
CHAPTER 3 Flow......................................................................................... 105
3.1 Effect ofsurface films onfilling............................................................................105
3.1.1 Effectivesurface tension.............................................................................105
3.1.2 Therollingwave..........................................................................................106
3.1.3 Theunzipping wave....................................................................................108
3.2 Maximumfluidity (thescience ofunrestricted flow)............................................110
3.2.1 Mode ofsolidification.................................................................................113
3.2.2 Effect of velocity.........................................................................................126
3.2.3 Effect of viscosity (including effect of entrained bifilms).........................128
3.2.4 Effect of solidificationtime t .....................................................................130
f
3.2.5 Effect of surface tension.............................................................................140
3.2.6 Effect of anunstable substrate....................................................................143
3.2.7 Comparison of fluidity tests........................................................................144
3.3 Extended fluidity....................................................................................................148
3.4 Continuous fluidity.................................................................................................151
CHAPTER 4 Molds and cores....................................................................... 155
4.1 Molds: Inertorreactive.........................................................................................155
4.2 Transformation zones.............................................................................................156
4.3 Evaporation andcondensation zones.....................................................................159
4.4 Mold atmosphere...................................................................................................164
4.4.1 Composition.................................................................................................164
4.4.2 Mold gasexplosions....................................................................................166
4.5 Mold surface reactions...........................................................................................168
4.5.1 Pyrolysis......................................................................................................168
4.5.2 Lustrous carbon film...................................................................................170
4.5.3 Sand reactions..............................................................................................171
4.5.4 Mold contamination....................................................................................171
4.5.5 Mold penetration.........................................................................................173
4.6 Metal surface reactions..........................................................................................178
4.6.1 Oxidation.....................................................................................................178
4.6.2 Carbon(pick-up andloss)...........................................................................179
4.6.3 Nitrogen.......................................................................................................181
4.6.4 Sulfur...........................................................................................................181
4.6.5 Phosphorus...................................................................................................181
4.6.6 Surface alloying...........................................................................................182
4.6.7 Grain refinement..........................................................................................182
4.6.8 Miscellaneous..............................................................................................183
4.7 Mold coatings.........................................................................................................183
4.7.1 Aggregatemolds..........................................................................................183
Contents vii
4.7.2 Permanentmoldsand metal chills..............................................................185
4.7.3 Dry coatings................................................................................................186
CHAPTER 5 Solidification structure.............................................................. 187
5.1 Heattransfer...........................................................................................................187
5.1.1 Resistances to heat transfer.........................................................................187
5.1.2 Increased heat transfer.................................................................................202
5.1.3 Convection...................................................................................................219
5.1.4 Remelting....................................................................................................219
5.1.5 Flowchannelstructure................................................................................220
5.2 Development ofmatrix structure...........................................................................224
5.2.1 General.........................................................................................................224
5.2.2 Nucleation ofthe solid................................................................................225
5.2.3 Growth ofthe solid.....................................................................................228
5.2.4 Disintegration ofthe solid (grain multiplication).......................................236
5.3 Segregation.............................................................................................................241
5.3.1 Planarfront segregation..............................................................................242
5.3.2 Microsegregation.........................................................................................245
5.3.3 Dendriticsegregation..................................................................................247
5.3.4 Gravitysegregation.....................................................................................250
CHAPTER 6 Casting alloys........................................................................... 255
6.1 Zinc alloys..............................................................................................................255
6.2 Magnesium.............................................................................................................260
6.2.1 Films onliquid Mgalloys andprotectiveatmospheres.............................261
6.2.2 Strengthening Mg alloys.............................................................................266
6.2.3 Microstructure.............................................................................................268
6.3 Aluminum..............................................................................................................269
6.3.1 Oxide films onAl alloys.............................................................................271
6.3.2 Entrained inclusions....................................................................................273
6.3.3 Grain refinement(nucleation andgrowth of the solid)..............................274
6.3.4 DAS andgrain size......................................................................................278
6.3.5 Modification of eutectic SiinAl–Sialloys................................................279
6.3.6 Iron-rich intermetallics................................................................................298
6.3.7 Other intermetallics.....................................................................................303
6.3.8 Thermal analysis ofAl alloys.....................................................................305
6.3.9 Hydrogen inAl alloys.................................................................................306
6.4 Copper....................................................................................................................309
6.4.1 Surfacefilms................................................................................................310
6.4.2 Gases inCu-based alloys............................................................................310
6.4.3 Grain refinement..........................................................................................315
viii Contents
6.5 Cast iron.................................................................................................................315
6.5.1 Reactions with gases...................................................................................316
6.5.2 Surface filmson liquid cast irons...............................................................318
6.5.3 Castiron microstructures............................................................................332
6.5.4 Flakegraphite iron (FGI) andinoculation..................................................334
6.5.5 Nucleation and growthof the austenite matrix..........................................343
6.5.6 Coupled eutectic growth ofgraphiteand austenite....................................345
6.5.7 Spheroidal graphiteiron (SGI)(ductile iron).............................................347
6.5.8 Compacted graphite iron (CGI)..................................................................355
6.5.9 Chunkygraphite(CHG)..............................................................................357
6.5.10 White iron (iron carbide)..........................................................................359
6.5.11 General.......................................................................................................360
6.5.12 Summary ofstructure hypothesis..............................................................360
6.6 Steels......................................................................................................................362
6.6.1 Carbonsteels...............................................................................................362
6.6.2 Stainlesssteels.............................................................................................363
6.6.3 Inclusions incarbon and low-alloy steels (general background)...............365
6.6.4 Entrained inclusions....................................................................................367
6.6.5 Primary inclusions.......................................................................................370
6.6.6 Secondary inclusions andsecond phases....................................................374
6.6.7 Nucleation and growthof the solid.............................................................377
6.6.8 Structure developmentinthe solid.............................................................380
6.7 Nickel-base alloys..................................................................................................382
6.7.1 Air melting andcasting...............................................................................383
6.7.2 Vacuum melting and casting.......................................................................383
6.8 Titanium.................................................................................................................386
6.8.1 Tialloys.......................................................................................................387
6.8.2 Meltingand casting Tialloys......................................................................387
6.8.3 Surface filmson Tialloys...........................................................................389
CHAPTER 7 Porosity.................................................................................... 391
7.1 Shrinkage porosity.................................................................................................391
7.1.1 General shrinkage behavior.........................................................................391
7.1.2 Solidification shrinkage...............................................................................392
7.1.3 Feeding criteria............................................................................................399
7.1.4 Feeding:The fivemechanisms....................................................................403
7.1.5 Initiation of shrinkageporosity...................................................................418
7.1.6 Growth ofshrinkage pores..........................................................................436
7.1.7 Shrinkage pore structure.............................................................................436
Contents ix
7.2 Gas porosity...........................................................................................................443
7.2.1 Entrained (external)pores...........................................................................443
7.2.2 Blow holes...................................................................................................445
7.2.3 Gas porosity initiated insitu.......................................................................445
7.3 Porosity diagnosis..................................................................................................461
CHAPTER 8 Cracks and tears...................................................................... 465
8.1 Hot tearing.............................................................................................................465
8.1.1 General.........................................................................................................465
8.1.2 Grain boundary wetting bythe liquid.........................................................469
8.1.3 Pre-tear extension........................................................................................470
8.1.4 Strain concentration.....................................................................................472
8.1.5 Stress concentration.....................................................................................473
8.1.6 Tear initiation..............................................................................................474
8.1.7 Teargrowth..................................................................................................476
8.1.8 Predictionof hottearing susceptibility.......................................................479
8.1.9 Methods oftesting.......................................................................................483
8.1.10 Methodsof control....................................................................................489
8.1.11 Summary ofthe conditions for hottearing and porosity.........................493
8.1.12 Hot tearing instainless steels....................................................................494
8.1.13 Predictivetechniques.................................................................................495
8.2 Cold cracking.........................................................................................................495
8.2.1 General.........................................................................................................495
8.2.2 Crack initiation............................................................................................496
8.2.3 Crack growth...............................................................................................497
CHAPTER 9 Properties of castings............................................................... 499
9.1 Test bars...............................................................................................................499
9.2 Thestatistics offailure........................................................................................504
9.2.1 Background tothe use ofWeibullanalysis..............................................507
9.2.2 Two-parameter Weibullanalysis...............................................................510
9.2.3 Three-parameterWeibullanalysis.............................................................511
9.2.4 Bi-Weibull distributions............................................................................512
9.2.5 Limits ofaccuracy.....................................................................................514
9.2.6 Extremevalue distributions.......................................................................516
9.3 Effect of defects...................................................................................................516
9.3.1 Inclusiontypesand diagnosis...................................................................517
9.3.2 Gas porosity...............................................................................................520
9.3.3 Shrinkage porosity.....................................................................................525
9.3.4 Tears, cracks,and bifilms..........................................................................526