Cementite in the Fe-N-C system [Elektronische Ressource] / vorgelegt von Marc Nikolussi

Nikolussi

Informations

• Publié par: universitat_stuttgart
• Publié le: 01 janvier 2008
• Nombre de lectures: 9
• Langue: English
• Poids de l'ouvrage: 4 Mo

Extrait

Max-Planck-Institut für Metallforschung
Stuttgart

Cementite in the Fe–N–C system

Marc Nikolussi
Dissertation
an der
Universität Stuttgart

Bericht Nr. 220
November 2008

2

Cementite in the Fe–N–C system


Von der Fakultät Chemie der Universität Stuttgart zur
Erlangung der Würde eines Doktors der Naturwissenschaften (Dr. rer. nat.)
genehmigte Abhandlung


vorgelegt von

Marc Nikolussi

aus Ehenbichl


Hauptberichter: Prof. Dr. Ir. E.J. Mittemeijer
Mitberichter: Priv.-Doz. Dr. J. Bill
Prüfungsvorsitzender: Prof. Dr. H. Bertagnolli

Tag der Einreichung: 28.08.2008
Tag der mündlichen Prüfung: 18.11.2008




INSTITUT FÜR METALLKUNDE DER UNIVERSITÄT STUTTGART
MAX-PLANCK-INSTITUT FÜR METALLFORSCHUNG, STUTTGART
STUTTGART, 2008 2
Table of contents
1 General Introduction.............................................................................................. 7
1.1 Cementite formation; a literature overview........................................................ 11
1.2 Thermodynamic considerations.......................................................................... 12
1.2.1 Gaseous nitriding ......................................................................................... 12
1.2.2 Gaseous carburising..................................................................................... 15
1.2.3 Gaseous nitrocarburising ............................................................................. 18
1.3 Outline of the work ............................................................................................. 19
1.3.1 Formation of massive cementite compound layers
and its growth kinetics................................................................................. 19
1.3.2 Orientation relationships of cementite and ferrite and the consequences ... 22
1.3.3 Diffusivity of nitrogen and activation energy
of nitrogen diffusion in cementite ............................................................... 22
1.3.4 New information on the Fe–N–C system .................................................... 23
1.3.5 Elastic constants of cementite...................................................................... 24
References................................................................................................................. 25
2 Formation of massive cementite layers on iron by ferritic carburising
in the additional presence of ammonia................................................................ 29
2.1 Introduction......................................................................................................... 30
2.2 Experimental procedure...................................................................................... 31
2.2.1 Specimen preparation and thermochemical treatment................................. 31
2.2.2 Analysis of the (nitro-)carburised specimens .............................................. 32
2.3 Results and discussion ........................................................................................ 34
2.3.1 Influence of the ammonia content in the atmosphere
on the layer constitution .............................................................................. 34
2.3.2 Cementite layer-growths kinetics ................................................................ 39
2.4 Conclusions......................................................................................................... 41
References................................................................................................................. 42
4 Contents
3 Growth of massive cementite layers;
thermodynamic parameters and kinetics............................................................ 45
3.1 Introduction......................................................................................................... 46
3.2 Experimental....................................................................................................... 47
3.3 Results and evaluation ........................................................................................ 49
3.4 Discussion........................................................................................................... 52
3.4.1 Parabolic layer growth for interstitial compounds....................................... 52
3.4.2 Thermodynamics of gaseous nitrocarburising............................................. 53
3.4.3 Interpretation of the “apparent” activation energy ...................................... 57
3.5 Conclusions......................................................................................................... 61
References................................................................................................................. 62
4 Microstructure and crystallography of massive cementite layers
on ferrite substrates............................................................................................... 65
4.1 Introduction 66
4.2 Experimental....................................................................................................... 67
4.2.1 Specimen preparation and gaseous nitrocarburising ................................... 67
4.2.2 Microstructural and crystallographic analysis ............................................. 68
4.3 Experimental results ........................................................................................... 71
4.3.1 Morphology of cementite compound layers ................................................ 71
4.3.2 Orientation relationship cementite-ferrite.................................................... 72
4.3.3 Preference of orientation-relationship variants............................................ 73
4.4 Discussion........................................................................................................... 75
4.4.1 The Bagaryatsky orientation relationship; cementite/ferrite misfit............. 75
4.4.2 Surface misfit-strain energy of cementite grains;
orientation favouritism ................................................................................ 77
4.4.3 Orientation relationship of adjacent cementite grains;
consequence for the cementite-layer growth............................................... 79
4.4.4 Comparison with γ’-Fe N ......................................................................... 81 4 1-y
4.5 Conclusions......................................................................................................... 83
Acknowledgement .................................................................................................... 84
References................................................................................................................. 84
4
Contents 5
5 Nitrogen diffusion through cementite layers...................................................... 87
5.1 Introduction......................................................................................................... 88
5.2 Experimental....................................................................................................... 89
5.2.1 Specimen preparation and gaseous nitriding/nitrocarburising .................... 89
5.2.2 Microstrcutural and hardness analysis......................................................... 91
5.3 Experimental results and evaluation:
hardness measurements and chemical analysis .................................................. 94
5.4 Modelling nitrogen concentration-depth profile development........................... 98
5.4.1 General assumptions.................................................................................... 98
5.4.2 Simulation of nitrogen concentration-depth profiles;
numerical procedure .................................................................................. 104
5.5 Results of the simulation................................................................................... 104
5.6 Concluding discussion ...................................................................................... 107
5.6.1 Hardness/concentration-depth profiles ...................................................... 107
5.6.2 Simulation of nitrogen concentration-depth profiles................................. 108
5.7 Conclusions....................................................................................................... 110
Appendix................................................................................................................. 112
References............................................................................................................... 115
6 Examination of phase transformations in the system Fe–N–C by mean