TEMPERATURE-STABLE CAST-IRON ALLOY AND ITS USE

The present invention relates to a temperature-stable cast-iron alloy having a high wear resistance at temperatures ranging between 500 and 900°C.

Many industries use machines containing machine parts which incur significant wear at relatively high temperatures in excess of 500 °C. For example, in the cement manufacturing industry a so-called clinker cooler is used for cooling cement clinker which is introduced to the clinker cooler from a preceding kiln at a temperature ranging between 1300 and 1450° C. The cement clinker is directed through the clinker cooler by means of appropriate means of conveyance which are typically made up of some form of elements which are reciprocated in the direction of movement of the cement clinker, and thus exposed to significant wear at temperatures ranging between 500 and 900 °C.

From WO 2004/104253 is known a wear-resistant cast-iron alloy having the following composition expressed in weight percentages: chromium: 12-25 %, carbon: 1.5-6 %, manganese: 2-7 %, silicon: up to 1.5%, molybdenum: up to 2 %, nickel: up to 4 %, micro alloying elements selected from the group consisting of titanium, zirconium, niobium, boron, vanadium, and tungsten: up to 2 % of each of one or more of the elements, and balance iron.

According to the publication, the alloy is subjected to heat treatment in order to give it a martensitic matrix. This type of matrix is very hard and brittle, and machine elements manufactured from such material are prone to cracking if subjected to impacts or blows. Furthermore, this type of matrix lacks thermal stability due to its softening at temperatures in excess of 400° C.

The applicant of the present patent application also has experience with regard to a cast-iron alloy according to European standard 10295 (2002), material: G-X40 CrNiSi25-12, Material No. :1.4837, which has the following composition expressed in weight percentages: chromium: 24.0-27.0 %, carbon: 0.3-0.5 %, manganese: up to 2.0 %, silicon: 1.0-2.5 %, molybdenum: up to 0.5 %, nickel: 1 1.0-14.0 %, phosphorous: up to 0.040 % and sulphur: up to 0.030 %

and a modified version hereof having the following composition expressed in weight percentages: chromium: 24.0-26.0 %, carbon: 0.7-0.9 %, manganese: 0.6-1.0 %, silicon: 1.5-2.0 % and nickel: 2.5-3.5 %

Experience with these two materials has shown that after prolonged heating to temperatures between 500 and 900 °C both materials tend to form a sigma phase which is a brittle inter-metallic phase consisting of equal parts of iron and chromium, and hence be brittle, and that they are not particular wear resistant.

It is the objective of the present invention to provide a cast-iron alloy having a higher wear resistance and a reduced tendency to form a sigma phase at temperatures between 500 and 900 °C as compared to the cast-iron alloys currently available.

According to the invention this is achieved by a cast-iron alloy according to the invention having the following composition expressed in weight percentages:

chromium: 15.0-20.0 %, carbon: 1.0-2.0 %, manganese: 1.5-2.0 %, silicon: 0.8-1.2 %, nickel: 8.0-10.0 %, molybdenum: 0.8-1.2 % balance iron and unavoidable metallic and non-metallic contaminants, where the non-metallic contaminants comprise nitrogen, oxygen, phosphorous and sulphur.

Hereby is obtained a cast-iron alloy having a higher wear resistance and a reduced tendency to form the undesired sigma phase when heated to temperatures between 500 and 900 °C as compared to the previously mentioned known alloys.

Laboratory experiments carried out by the applicant of the present patent application have indicated that the alloy according to the invention has significantly improved wear characteristics compared to the alloy according to the European standard 10295 and the modified version hereof, both defined above. The test results show that the alloy according to the invention has a wear resistance which is approximately four times higher than that of the alloy according to European standard 10295 and twice as high as that of the modified version hereof. The improved wear resistance is mainly ascribable to the optimization of the carbon-chromium ratio, resulting in optimum formation of chromium carbides which constitute the wear-resistant component of the alloy.

Furthermore, laboratory experiments during which the alloy according to the invention over a period of 8 weeks underwent heat treatment at a temperature of 500 °C with a subsequent microscopy examination, have shown that the alloy exhibits significant heat stability, given the absence of any signs of sigma phase formation.

In order to avoid significant deterioration of the mechanical characteristics of the iron alloy, the non-metallic contaminants comprising nitrogen, oxygen, phosphorous and sulphur should not exceed the maximum limits specified below: maximum 0.020 N, maximumi O ppm O, maximum 0.040 P, and maximum 0.030 S.

The cast-iron alloy according to the invention preferably comprises 16.5-19.5 weight percentage, most preferably 17.0-19.0 weight percentage chromium.

Furthermore, the cast-iron alloy according to the invention preferably comprises 1.25-1.85 weight percentage carbon, most preferably 1.5- 1.7 weight percentage carbon.

The cast-iron alloy according to the invention preferentially has an austenitic matrix.

The cast-iron alloy can be manufactured and cast into blanks using generally known techniques.

The described cast-iron alloy is particularly suitable for use in connection with machine parts in clinker coolers for cooling cement clinker.