RU2329324C1 - Iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to development of compositions of high alloyed chromium iron with reduced shrinking porosity. Iron contains, mas.% carbon 1.8-2.3, silicon 1.8-2.1, manganese up to 0.6, chromium 33-35, phosphorus up to 0.06, sulphur up to 0.03, molybdenum 2-2.5, zirconium 0.02-0.1, iron - the rest.

EFFECT: reduction of shrinking porosity.

1 tbl

Description

The invention relates to the metallurgy of foundry, in particular to the development of high-alloy chromium cast irons.

Known chrome cast iron [1] type Sormait with a chemical composition, wt.%:

carbon 2.5-3.5 silicon 2.5-3.5 manganese 1.0-1.5 chromium 28.0-35.0 nickel 3-5 phosphorus up to 0.08 sulfur up to 0.08 iron rest

The tensile strength of this cast iron is 35-40 kgf / mm ² and the hardness is 460-490 HB. The disadvantage of this cast iron is reduced machinability and low working temperature (up to 850 ° C).

Closest to the proposed cast iron in technical essence to the achieved result is chrome cast iron CHX34M [2] with a chemical composition, wt.%:

carbon 1,5-2,2 silicon 1.3-1.7 manganese 0.4-0.8 chromium 32.0-36.0 molybdenum 1.5-2.0 iron rest

Recommended operating temperature CHKh34M 1150-1200 ° C, chrome gives the product high wear resistance at elevated temperatures. The wear resistance of these cast irons increases with an additional alloying of 1.5-2.0% molybdenum. The disadvantage of this cast iron is a large volumetric shrinkage and, as a consequence, the tendency to the formation of shrinkage shells, which grows in proportion to the chromium content. Therefore, the casting must be fed with profits that make up to 20% by weight of the weight of the casting. But if shrinkage shells can be “brought out” in profit, then shrinkage porosity can be excluded only by changing the physicochemical properties of the alloy, changing the chemical composition of the alloy.

The technical problem to which the invention is directed is to improve the quality of castings of high-chromium cast iron.

The technical result of this invention is to reduce casting defects by shrinkage porosity.

The technical result is achieved by the fact that cast iron containing carbon, silicon, manganese, chromium, molybdenum, sulfur, phosphorus and iron, additionally contains zirconium in the following ratio of components, wt.%:

carbon 1.8-2.3 silicon 1.8-2.1 manganese up to 0.6 chromium 33-35 molybdenum 2.0-2.5 phosphorus up to 0.06 sulfur up to 0.03 zirconium 0.02-0.1 iron rest

In the conditions of the foundry, GAZ OAO conducted comparative melts with the known and proposed cast irons, with filling valve seats for the engine. Cast iron was smelted in an electric arc furnace. As a charge, pig-iron cast irons, return of high-chromium cast iron, steel waste, ferromolybdenum, ferromanganese were used. Zirconium was introduced in the form of ferroalloy FSCr45.

The metal was overheated in an oven to 1600 ° C and valve seats with a known and proposed chemical composition were filled in (see table 1). The same table shows the marriage of valve seats by the shrinkage porosity detected by X-ray diffraction of seats on an X-ray machine. As can be seen from table 1, the valve seats of the proposed cast iron (options 5-7) have a rejection (column No. 11) in shrinkage porosity lower than that of the known cast iron (options 1-3) by ~ 10 times, and the optimal content of zirconium is the range of 0.02-0.1%.

When the carbon content is less than 1.8% as a result of secondary oxidation, the metal is intensively coated with a viscous oxide film, which contributes to the formation of marriage casting on junction and non-slit. An increase in carbon content of more than 2.3% leads to an increase in large primary carbides and, as a result, to a deterioration in machining.

To achieve a silicon content of less than 1.8%, it is necessary to use silicon-friendly but very expensive alloying components in the charge, which is not economically feasible. When the silicon content in cast iron is more than 2.1%, the degree of doping of the ferrite base with it increases, which leads to undesirable embrittlement and cracks. With a manganese content of more than 0.6%, the proportion of residual austenite in the base of cast iron increases, which, when machined under the influence of a blade tool, rivets and hardens, as a result of which machining is difficult.

The chromium content in the proposed cast iron is determined based on the need to obtain the optimal combination of wear resistance and heat resistance of the alloy at high temperatures. A chromium content below 30% is impractical, since the proportion of residual austenite increases, the concentration of unbound carbon in the solution increases, the hardness of cast iron increases, and its mechanical processing is difficult.

When the chromium content is more than 35%, the γ-region in the solid solution becomes even more wedged out at high temperature heating, the carbon concentration in the solution decreases, and it is difficult to achieve high hardness of cast iron after quenching.

The upper limits on the content of phosphorus and sulfur are limited by their well-known harmful effect on cast iron.

The introduction of molybdenum into cast iron leads to a significant grinding of carbide inclusions, which increases wear resistance and crack resistance while improving machinability. When the molybdenum content is less than 2.0%, it does not have a positive effect on the structure and properties of cast iron, that is, it does not grind carbide inclusions. With an increase in Mo of more than 2.5%, transcrystallization appears, and the mechanical treatment worsens.

The lower limit on the zirconium content of 0.02% is associated with the beginning of its effective effect on reducing the shrinkage porosity of castings (option 5 of table 1). The upper limit on the content of zirconium - 0.1% (option 7 of table 1) is limited by its effectiveness in reducing rejects by shrinkage porosity. A higher content of zirconium does not affect the decrease in rejects by porosity (option 8 of table 1).

Table 1 Conditional Option Number Number of modifier ФЦЦр45 Chemical composition, wt.% The number of marriage by shrinkage porosity,% FROM Si Mn Cr Mo P S Zr one 2 3 four 5 6 7 8 9 10 eleven Famous 1 - 1,5 1.3 0.4 32 1,5 0.05 0.02 - 25 2 - 2.0 1,5 0.6 34 1.7 0.05 0.02 - 35 3 - 2.2 1.7 0.8 36 2.0 0.05 0.02 - 40 Suggested 4 0.02 1.8 1.8 0.6 33 2.0 0.06 0,03 0.01 10 5 0.05 1.8 1.8 0.6 33 2.0 0.06 0,03 0.02 2,5 6 0.1 2,3 2.1 0.6 35 2,5 0.006 0,03 0.04 2.0 7 0.3 2,3 2.1 0.6 35 2,5 0.06 0,03 0.12 1,5 8 0.4 2,3 2.1 0.6 35 2,5 0.06 0,03 0.16 2.0

Bibliography

1. Shchedrov K.P., Gakman E.L. "Heat-resistant materials", M., Engineering ", 1965.

2. Alexandrov. N.N., Klochnev N.I. "The technology of production and properties of heat-resistant cast irons." M., "Engineering", 1964.

Claims (1)

Cast iron containing carbon, silicon, manganese, chromium, molybdenum, phosphorus, sulfur and iron, characterized in that it additionally contains zirconium in the following ratio, wt.%: carbon 1.8-2.3 silicon 1.8-2.1 manganese up to 0.6 chromium 33-35 phosphorus up to 0.06 sulfur up to 0.03 molybdenum 2-2.5 zirconium 0.02-0.1 iron rest