Metal treatment – Stock – Ferrous
Patent
1996-11-18
2000-12-26
Yee, Deborah
Metal treatment
Stock
Ferrous
148326, 148419, 428659, C22C 3844
Patent
active
061652881
DESCRIPTION:
BRIEF SUMMARY
In applications involving hydroabrasive wear it is known to use carbon-containing iron-based, chromium chilled castings. A material of this kind has a carbon content of over 2.0 wt.- %. Examples of this are the materials No. 0.9630, No. 0.9635, No. 0.9645 and No. 0.9655. Since in these materials a large proportion of the chromium is used up in carbide formation, they are only corrosion-resistant to an extent corresponding approximately to unalloyed cast iron.
If now the carbon content is decreased and the chromium content increased, a slight increase of the corrosion resistance can be achieved. An example of this is the material G-X 170 CrMo 25 2. The entire group to which this material belongs has the significant disadvantage that, in chemically aggressive media, such as acidic, chloride-containing waters from flue gas desulfurizing apparatus, for example, corrosion resistance is achieved only at very high chromium contents. High chromium contents in ferritic iron-based alloys, such as the materials G-X 160 CrNiMoCu 42 2 2 2 or G-X 140 CrMnNiMoCu 41 4 2 2 1, however, adversely affect mechanical properties to a decisive extent and substantially impair castability.
Therefore, for aggressive media of the kind described above, corrosion-resistant high-grade steels are used, the wear resistance of which is slightly improved by a low carbon content (<0.5%) and a low volume proportion of carbide that results therefrom. The material 1.4464 is an example of this. The formation of chromium carbides reduces the chromium content of the base structure, whereby the corrosion resistance is correspondingly decreased. Thus any further increase of the carbon content is not advantageous.
The invention is addressed to the problem of creating a metal casting material, the wear resistance of which will correspond approximately to common commercial types of chilled castings, but which additionally will be characterized by high corrosion resistance in aggressive media.
The stated problem is solved in accordance with the invention by a chilled casting with the following composition in weight- %:
In addition to high corrosion and wear resistance, the material according to the invention has good casting characteristics. Consequently it can be produced in conventional high-grade steel foundries. Moreover, this chilled casting has good working characteristics.
The reason for the aforementioned positive qualities is primarily a chromium content of 36 to 42 wt.- % and a carbon content of 1.4 to 1.9 wt.- %, which results in a sufficiently high volume proportion of carbides. The large increase of the chromium content decreases the chromium depletion of the matrix.
Due to the targeted addition of the austenite-former nickel in the concentration range of 5 to 12 wt.- %, it is possible to control the ratio of the ferrite and austenite phases in the matrix in a defined manner. The positive characteristics of a duplex structure in stainless steels are utilized in this case. The normally extremely great brittleness of chilled casting types with high carbon contents and a carbide lattice in a ferritic matrix is avoided by the predominant deposition of the chromium carbides in the austenitic phase. Since the austenitic phase, unlike the ferrite phase, is not embrittled by segregation of intermetallic phases or by segregation processes, the danger of fractures due to stresses between the carbides and the matrix is not as great as it is in the case of a purely ferritic matrix.
In order to achieve a structure consisting of a ferritic-austenitic matrix with embedded carbides, a heat treatment at convventional solution annealing temperatures is necessary; in this manner better workability is simultaneously achieved.
Intermetallic phases in the ferrite, which have a negative influence on the corrosion resistance and increase brittleness, are avoided by the following composition in weight- %: the formation of (secondary) austenite.
The upper limit is established by the requirement, even after air cooling of large components, to obtain a structure wh
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E. Houdremont and R. Wasmuht, Non-Rusting & Heat Resisting
Dwars Anja
Koeper Heinz
Prechtl Wolfgang
Schroepfer Joerg
Tischner Hermann
KSB Aktienegsellschaft
Yee Deborah
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