Alloys or metallic compositions – Ferrous – 1.7 percent or more carbon containing
Patent
1996-09-17
1998-08-18
Yee, Deborah
Alloys or metallic compositions
Ferrous
1.7 percent or more carbon containing
420101, 420 53, 4205861, C22C 3706, C22C 3820, C22C 3842, C22C 3000
Patent
active
057955409
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
It is known in the art to use carbon-containing chromium chill cast parts based on iron for stress from hydroabrasive wear. A cast of that type is distinguished by having a carbon content that is greater than 2.0 percent by weight. However, due to the high consumption of the available chromium to form carbide, those materials are not any more resistant to corrosion than most non-alloy cast iron.
Typically, corrosion resistance is increased by reducing the carbon content and increasing the chromium content of the composition, although reduced wear resistance must be accepted. A typical example of one of these materials is G-X 170 CrMo 25 2. One major disadvantage of these materials is that corrosion resistance in chemically aggressive media, such as, for example, acidic (pH 3) chloride-containing (50 g/l Cl) water from exhaust gas desulfuration equipment cannot be achieved, unless the chromium content is very high. However, high chromium levels in iron-based alloys, such as the known materials G-X 160 CrNiMoCu 42 2 2 2 or G-X 140 CrMnNiMoCu 41 4 2 2 1, have the disadvantage of having poor mechanical properties and impaired casting properties.
For this reason, corrosion-resistant specialty steels whose wear resistance can be easily improved by lowering the carbon content (<0.5%) and the resulting smaller proportion, by volume, of carbides are used for the aforementioned aggressive media. The formation of chromium carbides reduces the chromium content of the basic structure, and the corrosion resistance declines accordingly. Therefore, it is not advisable to increase the carbon content further.
One way to avoid chromium depletion in a composition matrix with higher carbon contents is to add other carbide-forming elements. This is achieved in steels with low chromium contents (<20%), which are exposed to slightly corrosive media. An example is described in DE-A-42 02 339. The addition of niobium was considered to be particularly advantageous, because that alloy element forms pure MC carbide. The element vanadium was not considered beneficial because it reacts with chromium and iron to form composite carbides, which are less wear resistant.
Attempts to increase the chemical-tribologic resistance of the high-chromium material 1.4464 by adding small amounts of niobium, vanadium, or titanium are also known (M. Pohl, A. Ibach, A. Oldewurtel: New Cast and Forged Steel with Improved Chemical/Tribologic Resistance. Proceedings of the Fifth TRIBOLOGY Presentation 1991, Koblenz, pp. 368-376). However, in some cases as a result of the low carbon content, corrosion resistance could be improved only slightly.
SUMMARY OF THE INVENTION
An object of the invention is to provide a metallic casting material (composition) that is distinguished by exhibiting high corrosion resistance in aggressive media and that approaches the wear resistance of parts formed by standard chill casting processes.
This object is achieved by chill casting parts having the composition comprising from 26 to 36 percent Cr; 0 to 10 percent Ni; 2 to 6 percent Mo; 0 to 3 percent Cu; 0 to 0.2 percent N; 0 to 1.5 percent Si; 0 to 1.5 percent Mn; 4 to 9 percent V; and 1.4 to 1.9 percent C; all percents by weight of the total composition; wherein the remainder of the composition is Fe and impurities.
In addition to high resistance to corrosion and wear, this casting material also has good casting properties. Thus, it can be produced in conventional special steel foundries. In addition, this chill casting material has good working properties.
The object of the invention is achieved with a composition comprising a chromium content from 26 through 36 percent by weight and a carbon content of 1.4 through 1.9 percent by weight, which causes a sufficiently high proportion by volume of carbides, and a vanadium content of greater than 4 percent by weight, which reduces chromium depletion in the matrix by forming high-vanadium carbides. This makes it possible to avoid the disproportionate increase in chromium content that would be n
REFERENCES:
patent: 2709132 (1955-05-01), Giles
patent: 3086858 (1963-04-01), Edminster et al.
patent: 4200457 (1980-04-01), Cape
Dwars Anja
Prechtl Wolfgang
Schropfer Jorg
Tischner Hermann
KSB Aktiengesellschaft
Yee Deborah
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