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Microstructure of weld metal in a chromium-molybdenum steel
Abstracts of The Scandinavia. Society for Electron Microscopy MICROSTRUCTURE OF WELD METAL CHROMIUM-MOLYBDENUM STEEL Bertil Josefsson, Hans-Olof Andr,~n
IN A
Anders K v i s t and
D e p a r t m e n t of Physics, C h a l m e r s U n i v e r s i t y of Technology, S-412 96 G~teborg, S w e d e n
Chromium-molybdenum steels have been used in the fabrication of pressure vessels and boiler steam pipes since the 1930's. A steel of composition 2.25 CrIMo-O.IC was originally formulated for use at elevated temperatures where creep resistance is required. In the past few years, this steel has also been used in the offshore oil industry because of its resistance to sulfide stress cracking. It is often desirable to use submerged arc welding w h e n fabricating large-size components of this type of steel. However, one p r o b l e m associated with such a high heat input welding m e t h o d is the sometimes low impact strength of the welds. A study of the detailed microstructure of the weld metal was therefore performed, both in the as-welded state and after a commercially used post-weld heat treatment. By optical microscopy we have found that the microstructure can be described as bainite. Transmission electron microscopy showed that the bainite consisted of ferrite, martensite and some cementite precipitates. During heat treatment at 690°C for one hour the martensite completely transformed to ferrite and cementite. Needle-shaped chromium-molybdenum carbides, (CR,Mo)2c , also precipitated. The composition of these precipitates, and of the ferrite, was d e t e r m i n e d by atom-probe microanalysis. The tensile strength was lower after the heat treatment due to, among other things, a lower density of dislocations and the absence of martensite. This also resulted in an improvement of the impact strength: the impact transition temperature d e c r e a s e d from above +20°C to approximately -iO°C. INDUSTRI~ APDTT~TIONS ELECTRON MICROSCOPY
OF
K. Kristiansen Nor~k H y d r o Research P o r s g r u n n Fabrikker, P o r s g r u n n , Norway
Centre, N-3901
71
An electron microscopist involved in industrial applications has to cover a very broad range of applications. Problems related to raw materials, construction materials, intermediate products, environmental samples and final products have to be tackled, usually at very short notice. Results are often required with m i n i m u m expenditure of time. This means that the m i c r o s c o p i s t has to communicate well with people of very different scientific background. Defining the problem well and finding the analytical approach that gives most information relevant to the problem, with as little work as possible, becomes very important. Taking shortcuts often becomes necessary, and therefore the microscopist has to be very conscious about the implications of this. Most of this type of work is done with SEM/EDS systems. The number of TEMs in industrial laboratories is also increasing, but they tend to be involved in more basic development work. Some examples are given to illustrate these points.
EM STUDIES OF ELECTRO-DEPOSITED PROTECTIVE COATINGS
Ni-Zn
Poul Lenvig Hansen and Claus Q u i s t J e n s e n L a b o r a t o r y of A p p l i e d Physics I, Technical U n i v e r s i t y of Denmark; and Laboratory of Process and P r o d u c t i o n Engineering, Technical University of Denmark, 2800 Lyngby, Denmark
Electro-deposited Ni-Zn coatings with 10-15% Ni show good corrosion properties, and they can be used as protective coatings in cars. The microstructure was studied in the 1930's mainly with X-ray diffraction, and not much EM work has been published yet. We have studied the microstructure of electro-deposited Ni-Zn coatings with approximately 10% Ni using HREM, CBED and the dark field imaging technique. The coatings are built up of very small crystals 10-20 nm in diameter. CBED with a small probe gives single crystal patterns which can be indexed ru~-=uzu~uu~=, n±,,~ F=uu=~,= from SAD show the presence of two phases. One is the FCC-structure with lattice parameter a = 0.36 nm, and the other is either the cubic y- or ~-phase both having a large unit cell with a % 0.89 nm. Lattice imaging shows lattice spacings O.21 nm and 0.26 nmo It is also observed that over areas ~ i00 um in
IN A
Anders K v i s t and
D e p a r t m e n t of Physics, C h a l m e r s U n i v e r s i t y of Technology, S-412 96 G~teborg, S w e d e n
Chromium-molybdenum steels have been used in the fabrication of pressure vessels and boiler steam pipes since the 1930's. A steel of composition 2.25 CrIMo-O.IC was originally formulated for use at elevated temperatures where creep resistance is required. In the past few years, this steel has also been used in the offshore oil industry because of its resistance to sulfide stress cracking. It is often desirable to use submerged arc welding w h e n fabricating large-size components of this type of steel. However, one p r o b l e m associated with such a high heat input welding m e t h o d is the sometimes low impact strength of the welds. A study of the detailed microstructure of the weld metal was therefore performed, both in the as-welded state and after a commercially used post-weld heat treatment. By optical microscopy we have found that the microstructure can be described as bainite. Transmission electron microscopy showed that the bainite consisted of ferrite, martensite and some cementite precipitates. During heat treatment at 690°C for one hour the martensite completely transformed to ferrite and cementite. Needle-shaped chromium-molybdenum carbides, (CR,Mo)2c , also precipitated. The composition of these precipitates, and of the ferrite, was d e t e r m i n e d by atom-probe microanalysis. The tensile strength was lower after the heat treatment due to, among other things, a lower density of dislocations and the absence of martensite. This also resulted in an improvement of the impact strength: the impact transition temperature d e c r e a s e d from above +20°C to approximately -iO°C. INDUSTRI~ APDTT~TIONS ELECTRON MICROSCOPY
OF
K. Kristiansen Nor~k H y d r o Research P o r s g r u n n Fabrikker, P o r s g r u n n , Norway
Centre, N-3901
71
An electron microscopist involved in industrial applications has to cover a very broad range of applications. Problems related to raw materials, construction materials, intermediate products, environmental samples and final products have to be tackled, usually at very short notice. Results are often required with m i n i m u m expenditure of time. This means that the m i c r o s c o p i s t has to communicate well with people of very different scientific background. Defining the problem well and finding the analytical approach that gives most information relevant to the problem, with as little work as possible, becomes very important. Taking shortcuts often becomes necessary, and therefore the microscopist has to be very conscious about the implications of this. Most of this type of work is done with SEM/EDS systems. The number of TEMs in industrial laboratories is also increasing, but they tend to be involved in more basic development work. Some examples are given to illustrate these points.
EM STUDIES OF ELECTRO-DEPOSITED PROTECTIVE COATINGS
Ni-Zn
Poul Lenvig Hansen and Claus Q u i s t J e n s e n L a b o r a t o r y of A p p l i e d Physics I, Technical U n i v e r s i t y of Denmark; and Laboratory of Process and P r o d u c t i o n Engineering, Technical University of Denmark, 2800 Lyngby, Denmark
Electro-deposited Ni-Zn coatings with 10-15% Ni show good corrosion properties, and they can be used as protective coatings in cars. The microstructure was studied in the 1930's mainly with X-ray diffraction, and not much EM work has been published yet. We have studied the microstructure of electro-deposited Ni-Zn coatings with approximately 10% Ni using HREM, CBED and the dark field imaging technique. The coatings are built up of very small crystals 10-20 nm in diameter. CBED with a small probe gives single crystal patterns which can be indexed ru~-=uzu~uu~=, n±,,~ F=uu=~,= from SAD show the presence of two phases. One is the FCC-structure with lattice parameter a = 0.36 nm, and the other is either the cubic y- or ~-phase both having a large unit cell with a % 0.89 nm. Lattice imaging shows lattice spacings O.21 nm and 0.26 nmo It is also observed that over areas ~ i00 um in