CS216227B2 - Castings resisting the abrasion and repeated impacts and method of making the same - Google Patents

Abstract

1,218,981. Cast steel grinding members. SOC. ANON. FONDERIES MAGOTTEAUX. Jan. 11, 1968 [Jan.13, 1967], No. 1644/68. Heading C7A. A grinding member such as a ball or lining plate for use in a grinding mill or the like is made of a cast steel having Cr>14% and a metallographic structure which is constituted by a martensitic solid solution, which contains eutectic and pro-eutectoidic carbides and < 3% residual austenite, and which is free from pearlite, A suitable steel has the composition:- C 2-3%, Cr 14-27% with the limitation that Cr-5C = 4-12%, the balance being Fe except for impurties such as Mn, Si, P and S, and incidental ingredients such as Mo, V and W. The steel is heat-treated by hardening in still air or an air blast at a temperature of at least 950‹C., prefer - ably 950‹ -1100‹ C., and then tempering at 440‹ - 530‹ C. A second tempering may follow at a temperature lower than the first. Specification 1, 119, 516 is referred to.

Description

The invention relates to castings which are resistant. against abrasion and repetitive. Impact,. - such as balls and shelves, - and the method of manufacture.

In the material crushing industry, crushers with different compositions and properties are used, including crushers forged from steel, or crushers cast from pearlitic or martensitic white cast iron or chromium alloys.

In most applications, chrome alloy cast crushers are more abrasion resistant than steel or pearlitic white cast iron and are more resistant to repeated impacts than martensitic cast iron crushers. The use of chrome alloy crushers is widespread in the cement industry, where it is particularly advantageous.

Known chromium alloys used in the manufacture of crushers have, in addition to iron, a mass composition of 1.5 to 3% carbon, 0.5 to 1.5 manganese, a maximum of 1% silicon, 0.06% sulfur, 0.06% phosphorus and 11 to 13% of chromium.

In addition, they often also contain up to 0.8% by weight molybdenum and / or up to 0.7% by weight nickel. Depending on the size of the crushing bodies, the known chromium alloys, up to 50 mm in diameter, have a hardness of 50 to 60 HRC and 51 to 53 HRC with a diameter of 50 mm or more, with a residual austenite content of chromium alloys exceeding 3% and often 5%. .

The abrasion resistance of the material is better, the greater the hardness, but the resistance to repeated impacts decreases with increasing residual austenite content, and increases with hardness in the low austenite content range.

Crushing bodies made of these known alloys have greater abrasion resistance than the other known crushing bodies, but do not have sufficient impact resistance when diameters equal to or greater than 50 mm if the alloys used have been manufactured with a hardness greater than 58 HRC. This drawback is due to the fact that, under these conditions, and taking into account the severe shocks to which large crushers are normally subjected, the residual austenite content remains too high, namely 7% or more, and results in internal stresses in the impact. they can cause premature destruction of the crushers by breakage or chipping.

These drawbacks eliminate abrasion and repetitive impact resistant castings, such as chromium alloy balls and lining plates, containing chromium at 14-27 wt%, carbon at 2-3 wt%. and the remainder iron and unavoidable impurities, wherein the casting hardness ranges from 59 to 63 HRC according to the invention. SUMMARY OF THE INVENTION The limit of the chromium content to the carbon content of the casting is 4% by weight Cr-5. and the casting has a martensitic structure containing not more than 3% by weight - residual austenite and primary and secondary carbides.

The invention also relates to a process for the production of said castings, which is characterized in that the castings are heat treated by quenching from 950 to 1100 ° C and tempering at 440 to 530 ° C.

The castings according to the invention are characterized by a high resistance to abrasion and repeated impact and have a long service life, so that they are very well suited for use in the material shredding technique, eg cementitious raw materials and clinkers.

In Figures 1 and 2, the Cr-C diagram shows the quadrilateral composition of the chromium alloys for castings according to the invention.

The chromium and carbon content of the alloys, expressed in weight% / o, lies within the quadrilateral given in Fig. 1

Cr = 22 C - 2 Cr = 27 C = 3 Cr = 14 C = - 2 Cr = 19 C = 3

The presence of other alloying elements, for example molybdenum, vanadium, tungsten, niobium, titanium or tantalum, is not necessary to achieve the minimum desired properties of the castings. However, if the castings are to have particularly good mechanical properties, they must contain these alloying elements.

The content of other conventional elements such as manganese, silicon, sulfur and phosphorus is not critical as long as it falls within the range common to unalloyed steels.

Chromium-carbon-containing alloys, given a quadrilateral with the given coordinates, can be divided into two groups I and II according to the amount of chromium and carbon, as shown in Figure 2. Group I chromium alloys are cheaper than group chromium alloys

II.

In the heat treatment to achieve the desired properties, the castings are quenched in still or blown air from a temperature of 950 degrees Celsius to 1100 ° C. The exact quenching temperature in this range is dependent on the chromium and carbon content of the chromium alloy and should be the higher the value of "% Cr - 5". %C"; all quenching factors should be selected so that after quenching, the chromium alloy structure is free from perlite and bainite and contains not more than 20% stabilized austenite; the hardened chromium alloy is tempered at a temperature of 440 ° C to 530 ° C, the exact temperature within this range being greater the greater the value of% Cr-5. % C ".

The purpose of tempering is to convert the stabilized austenite formed during turbidity. The tempering should take place for a long time and at a temperature such that virtually all stabilized austenite is converted without producing perlite, which would significantly reduce the hardness of the casting. For some Group II chromium alloys whose composition lies at the upper limit of the quadrilateral defining the chromium and carbon contents, the austenite content after quenching may sometimes slightly exceed 20 ° / o. In this case, almost complete conversion of the austenite stabilized during quenching is achieved by two successive tempering, with a slightly lower temperature being used in the second tempering than in the first tempering.

Experiments have shown that after such heat treatment, the castings of the invention have a hardness of 59-63 HRC and a residual austenite content of less than 3%.

The balls and unloading plates for crushers and other castings according to the invention to be subjected to repeated impacts have excellent properties, as shown in the following example.

In the first chamber of the clinker tube mill with a diameter of 3.2 m, the grinding balls were compared simultaneously for 3034 hours with the original diameter of 80 mm, which were divided into four groups of 100 grinding balls each. The first and second groups were comparative and the third and fourth groups have a chemical composition according to the invention. The chemical and structural composition, heat treatment and mechanical properties of these different grinding balls are as follows:

Chemical composition in mass. %:

first group: C2.05 second group: C2.18 third group: C2.16 fourth group:

C 2.15

Si 0.44

Si 0.42

Si 0.49

Si 0.47

Mn 0.52

Mn 0.44

Mn 0.48

Mn 0.47

Cr 12.26

Cr 12.03

Cr 17.46

Mo 0.68

Cr 16.89

Heat treatment:

first group: turbidity in oil second group: turbidity in oil third group: turbidity in blown air from 1000 ° C and tempering at 400 degrees Celsius fourth group: turbidity in blown air from 990 ° C and tempering at 465 ° C

Matrix structure:

first group: martensite + 7% residual austenite second group: martensite + 10% residual austenite third group: martensite + 2 ·% residual austenite fourth group: martensite + 2.5% residual austenite

Hardness:

first group 56 HRC second group 62 HRC third group 61 HRC fourth group 60.5 HRC

During the wear test were found. following the results, the wear being given in g per grinding ball:

first group: second group: third group: fourth group:

286 + 14 g

477 + 21 g

254 + 10 g

491 + 21 g

Claims (3)

1. Abrasion resistant and repetitive impact castings such as chromium alloy balls and lining plates containing 14 to 27% by weight of chromium, 2 to 3% by weight of carbon and the remainder iron and unavoidable impurities, the hardness of the casting being in the range of 59 to 63 HRC, characterized in that the limit ratio of chromium content to carbon content of the casting is 4% by weight Cr-5. and the casting has a martensitic structure containing not more than 3% by weight of residual austenite and primary and secondary carbides. 2. A method for producing castings according to claim 1, characterized in that they are heat treated by quenching from a temperature of 950 to 1100 [deg.] C. and tempering at a temperature; Mp 440-530 ° C. 3. Process according to claim 2, characterized in that the tempering is carried out in two successive stages at a temperature of 440 to 530 ° C.