CS226261B1 - Abrasion-resistant cast iron - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to cast abrasion-resistant cast iron which is particularly suitable for highly dynamically loaded machine parts subjected to intensive abrasive wear.

Currently, dynamically stressed machine parts subjected to intensive abrasive wear use podeutectoid low to medium alloyed steels with tempered martensite, which achieve high flexural strength and impact resistance and low relative abrasive wear resistance of 1.6 to 2.3.

A disadvantage of said steels is that casting is followed by quenching and tempering. Hardening consists of heating to a temperature in the range of 20 to 50 ° C above, followed by austenitization, followed by cooling to oil. The tempering of martensite is most often carried out in the I or II tempering zone. In the prevailing number of foundries, heat treatment plants are only equipped with annealing furnaces where it is not possible to ensure a narrow range of quenching temperatures and oil quenching.

Furthermore, chromium-nickel cast irons with an average composition of 2.40 to 2.90% by weight are used for this purpose. % of carbon, 5.50 to 5.00 wt. % nickel and 1.40 to 2.40 wt. chromium, which does not have to be further heat treated after casting.

The cast structure consists of a brittle and hard martensite consisting of plates with a twin substructure and a small amount of austenite. With slow cooling of the metal in sand form, martensite is partially dissolved. In the structure is excluded about 45%

-τ eutectic carbides of the type Fe ^ G. Cast iron achieves high hardness values of 52 to 59 HEC and high relative resistance values

5 'abrasive wear = 2.7 to 5.0.

The disadvantages of the above-mentioned chromium-nickel steels are low impact strengths of max. Furthermore, cast iron is highly susceptible to central porosity, from which cracks propagate during dynamic loading of castings and premature fractures often occur.

_r Said drawbacks are eliminated to cast castings resistant, abrasion of the invention. Cast iron contains,

1.8 to 2.4 wt. % carbon, 0.4 to 1.2 wt. 0.2 to 0.2

0.8 wt. % silicon, 26 to 31 wt. % of chromium, 0.008 to 0.04 wt. % sulfur and 0.008 to 0.05 wt. -phosphorus. The invention is characterized in that 0.05 to 0.2 wt. vanadium, 0.01 to

0.1 wt. % titanium and 0.01 to 0.1 wt. of aluminum. The steel may further comprise 0.4 to 1.2 wt. nickel to suppress the formation of perlite in the austenitic-martensitic metal matrix in thick-walled castings. ,

An advantage of the cast iron according to the invention is that by adding vanadium, titanium and aluminum to the end of the melt, the transcrystallization zone, which causes local fragility of the castings, is suppressed during the crystallization of the castings. Also, the eutectic _Λ carbides do not crumble because they are of the more resilient type (CrFe) γC and are excluded in small formations. The metal matrix of the cast state consists of 50% tough type martensite consisting of needles with dislocation substructure and 50% austenite. When cooled in sand form, martensite is partially tempered. Notch toughness value 6 to 8 J.cm ² , flexural strength 750 to 850 MPa, hardness 46 HRC.

The invention is further described by way of example.

- 4 Example 1

Grinding plates for tube mills for cement grinding were formed from cast iron, which had the following chemical composition by weight.

Carbon 2.06 Manganese * 0.68 Silicon 0.41.

phosphorus 0,027 sulfur 0,030 chrome 29,40 vanadium 0,16 titanium 0,038 aluminum 0,043

The cast iron hardness of this chemical composition was 46 HSC in the cast state, and the impact strength was 7.7 d. cm ² , flexural strength 847 MPa and relative abrasive wear resistance = 2.9.

When grinding cement, occurs in <ø. chamber tube mill about 2.2 GI him grinding, de cut _of only slight wear. The rupture of the plates was not detected even though they were hit by very hard balls. The formation of grooves on the grinding plates was not observed.

Example 2

Grinding plates for cement mills were made of cast iron for the following chemical composition:

% wt.

carbon 2.15 Manganese 0.58 silicon 0.48. phosphorus 0.018 sulfur 0.010 chrome 27.80 vanadium 0.17 titanium 0.030 aluminium 0,036 nickel .0,70

The cast iron of this chemical composition had the same mechanical properties as the cast iron in Example 1. Also in these plates, little wear was found in the 1st chamber of the tubular mill. No plate breaks or grooves were noted.

Claims (2)

1. Abrasive wear resistant cast iron containing 1.8 to 2.4% by weight of cast iron. % carbon, 0.4 to 1.2 wt. 0.2 to 0.8 wt. 26 to 31 wt. chromil, 0.008 to 0.04 wt. % sulfur, 0.008 to 0.05 wt. % phosphorus, characterized in that it contains 0.05 to 0.2 wt. % vanadium, 0.01 to 0.1 wt. titanium and 0.01 to 0.1. % wt. of aluminum. 2. Cast iron according to claim 1, characterized in that it contains from 0.4 to 1.2% by weight. nickel.