Alloys or metallic compositions – Containing over 50 per cent metal but no base metal – Iron containing
Patent
1991-04-10
1992-06-30
Dean, R.
Alloys or metallic compositions
Containing over 50 per cent metal but no base metal
Iron containing
420443, 420452, C22C 3848
Patent
active
051261073
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an iron-, nickel-, chromium base alloy having an austenitic structure and good high temperature features, including a very high resistance against oxidization in oxidizing atmosphere and against carburizing in carburizing atmosphere at high temperatures, as well as a high creep fracture resistance.
BACKGROUND OF THE INVENTION
High alloyed, stainless, austenitic steels or nickel base alloys containing up to 60% nickel conventionally have been used for objects which during a long period of time are subjected to high temperatures in combination with mechanical loading in oxidizing environments. These alloys usually have a high oxidization resistance and often also a very high creep fracture resistance, but because of the increasingly high demands which are raised upon materials for the present field of use there has arisen a need of materials having still better oxidization resistance in oxidizing environments in combination with very good creep fracture resistance, a combination of features which has not satisfactorily been achieved with presently known alloys.
Another problem with known alloys of the above mentioned kind is that they have a comparatively great tendency to take up carbon and nitrogen when exposed in carburizing atmosphere or in environments which involve a risk for the taking up of nitrogen at high temperatures. This particularily concerns austenitic steels but to an essential degree also nickel base alloys. Also attacks from gaseous halides and metal oxides in certain environments may involve problems.
The above mentioned problems will be particularily accentuated in those cases when the material is subjected alternatingly to carburizing and to oxidizing media at high temperatures, or, which sometimes even may occur, in environments which at the same time may act oxidizing as well as carburizing. Those situations when the material in hot condition is exposed to ambient air after having been subjected to carburizing in an furnace at a high temperature are examples of alternatingly carburizing and oxidizing exposures. Similar conditions may occur in furnaces where it from some reason is difficult to maintain a balanced atmosphere. Further may be mentioned furnace linings which are subjected to coke depositions. It is conventional to remove such depositions by burning them off, wherein air is supplied for the combustion, which is a further example of exposure to alternatingly carburizing and oxidizing media. Finally, treatment of poorly degreased goods in oxidizing atmosphere at high temperatures is an example of a situation where carburizing and oxidizing may occur at the same time.
DESCRIPTION OF THE INVENTION
The invention aims at providing an alloy having a composition which brings about an improved resistance at high temperatures against carburizing as well as against oxidizing, and which also gives a good creep fracture resistance. The material according to the invention also has a good resistance to the taking up of nitrogen and also has good resistance to attack from gaseous halides and metal oxides. It can advantageously be used in the form of sheets, plates, bars, rods, wires and tubes in various kinds of furnaces, as for example carburizing furnaces, sintering-, annealing-, and tempering stoves, where also non degreased goods are heat-treated, and it can also be used for accessories for furnaces and stoves, for example charging-baskets, -grates and -buckets. Further it can be used in burners, combustion chambers, radiant-tubes, reaction rooms in the petrochemical industry and in fluidized beds, exhaust gas filters for motor cars, etc.
The following table shows the broad range for the elements which are included in the alloy according to the invention, and also the preferred, and the suitably chosen ranges. The contents are expressed in weight-%. The balance is iron, unavoidable impurities in normal amounts and normally existing accessory elements. For example there is a negligible amount of aluminum and calcium in the steel as
REFERENCES:
patent: 3758294 (1973-09-01), Bellot et al.
patent: 3833358 (1974-09-01), Bellot et al.
patent: 3989514 (1976-01-01), Fujioka et al.
patent: 4224062 (1980-09-01), Darnfors
patent: 4448749 (1984-05-01), Sugitani et al.
patent: 4530720 (1985-07-01), Moroishi et al.
Avesta Aktiebolag
Dean R.
Ip Sikyin
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