FI56700C - MOTOR ABRASIVES NOETNING MASKINELEMENT AV SEGJAERN FOER BEHANDLING AV MINERALER - Google Patents

Description

- Γαΐ ADVERTISING PUBLICATION. „„ W (11) UTLAGG N I NGSSKRI FT 56700 ‘C Patent .ny3nnctty 10 03 1939

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Patent · oeh registerstyrelsen v Antöktn utiigd och uti. «Krift« n publishederad 30.11.79 (32) (33) (31) Pyydetty etuolkeui — Begird priority (71) Fl) (72) Matti Johansson, Karkkila, Pekka Rikka, Karkkila, Finland-Finland (Fl) (7 * 0 Berggren Oy Ab (5 * 0 Abrasive wear machine made of spheroidal graphite iron for mineral processing - Mot abrasiv nötning bestän-digt masking element from a segment for the processing of mineral e

The invention relates to a machine member made of spheroidal graphite iron, which must withstand in use the abrasive wear caused by a finely divided mineral, such as quartz, which moves relative to it.

Such a machine member is generally hardened carbon steel, hardened alloy tool steel, surface hardened steel, wear layer coated steel, austenitic manganese steel (Hadfield steel), hard cast iron, die cast iron or perlite spheroidal graphite iron.

Said known abrasive-resistant machine members have the following drawbacks. Through-hardened carbon steel and cast iron cannot be used when they may be subjected to shocks during use. The consumption margin of surface-hardened steel, coated steel and die-cast iron is usually too small. Austenitic manganese steel cannot withstand abrasive wear unless it is subjected to surface-modifying impacts during wear. High-alloy tool steel becomes expensive. Wear of perlite spheroidal graphite iron is too great. In addition, several of these are not available C 22 C 37/01 + 2 66700 when the machine body should be manufactured by casting.

The machine element according to the invention is characterized in that it is made of spheroidal graphite iron, the microstructure of which, in addition to spheroidal graphite characteristic of spheroidal graphite iron, contains at least about 8% by volume of residual austenite thermally stable at temperatures between + 300 ° C and -80 ° C. bainite. Most preferably, the residual austenite should be greater than 20% by volume.

It is known from the prior art that the machine member according to the invention withstands well the wear in which cold working, which simultaneously strengthens the surface of the machine member, occurs. Austenitic manganese steel also withstands under such conditions, which is understandable because - the austenite of both is converted to martensite by cold working, whereby the surface hardness rises to about 550 HB and a compressive stress is formed in the surface layer. The essential novelty of the new invention is based on the research result that said spheroidal graphite iron withstands abrasive wear even when its surface does not have to be reinforced by heavy stress. This is not otherwise tolerated by austenitic manganese steel, which behaves in the same way, so the research result can be considered surprising.

The machine member according to the invention is advantageous compared to the known solutions, because it is reasonably wear-resistant throughout the material thickness, impact-resistant, frost-resistant and can be manufactured by casting and cutting.

The machine members according to the invention are, for example, parts of sand processing equipment, those parts of mineral mills which do not have "" working hardening, and plow tips and harrow tines. For example, the tip of the plow can be made of the member according to the invention, in which case it is very durable both in rocky fields and in sandy soil. When using known solutions, a good overall solution of the same metal is not obtained.

In rocky soil, the best metal at the tip of the plow is austenitic manganese steel (Hadfield steel), which is tough and hardens when exposed to rock impacts, but cannot withstand sanding wear. In sandy soil, hardened steel is best suited for the plow tip, but that 3,667,000 would again not withstand rock impacts. The plow blade can also advantageously be made of a member according to the invention.

The abrasive wear-resistant machine member according to the invention can be manufactured, for example, from spheroidal graphite iron according to Finnish patent 49732, which in addition to the usual amounts of carbon, silicon, phosphorus, sulfur and magnesium contains 0.10-0.26% by weight of molybdenum and 0.3- 1.4% by weight of manganese and possibly further tin, copper and / or less than 2.5% by weight of nickel. Other raw materials are doped spheroidal graphite iron in such a way that, by an isothermal heat treatment at a suitable bainitization temperature, its austenite is partly converted into bainite and partly remains thermally stable austenite at the operating temperature. After the heat treatment, the microstructure of such spheroidal graphite iron may contain, in addition to graphite, bainite and austenite, some perlite or martensite, for example.

The abrasive wear-resistant machine member according to the invention can be manufactured, for example, as follows: A cast blank suitable for the manufacture of the machine member is cast from spheroidal graphite iron with 3.6% carbon (C) and 2.25% silicon (Si) in addition to iron (Fe), manganese (Mn) 0.7%, molybdenum (Mo) 0.1%, copper (Cu) 0.5%, magnesium (Mg) 0.045%, phosphorus (P) 0.06% and sulfur (S) 0.015%. The casting is allowed to cool.

The casting is machined by cutting to the dimensions of the designed machine member. The resulting body is heated in a heat treatment furnace at a temperature of 880 ° C to an austenitizing temperature and held there for two hours, during which time its predominantly perlite microstructure is converted to austenite. The piece is transferred from a heat treatment furnace to a salt bath at a temperature of 355 ° C: The salt bath is half sodium nitrite (NaNC 2) and half potassium nitrate (KNO 2). · The salt bath has a thermostatic heating and cooling device and a device for recycling molten salt. The piece is kept in a salt bath for 120 minutes, after which it is allowed to cool freely in air. The body is then spheroidal graphite iron with about 10% by volume of graphite, 50-60% by volume of bainite and 30-40% by volume of residual austenite in the microstructure. The body does not undergo major deformation during heat treatment. However, the machining and heat treatment can be performed in another order, 4,56700, where the cutting is performed after the isothermal heat treatment. In this way, no deformation takes place after cutting, but the cutting is somewhat more difficult due to the working hardening in machining, which is due in part to the conversion of the residual rivet to martensite.

The invention is described in more detail below by way of example.

Example 1

The abrasion resistance of the abrasive wear-resistant machine member according to the invention has been tested under laboratory conditions in an abrasive wear test in which various test pieces are moved in moist sand.

The abrasive wear test is performed as follows. The test pieces are round rods, length 100 mm and diameter 20 mm. The test bars are fixed in a vertical position on the lower surface of a horizontal round plate at the same distance from its center. The plate is rotated by an electric motor about a vertical axis passing through its center. Below the plate is a container and a container of quartz sand with a grain size of 3-7 mm. Quartz sand is moistened with water, which is 20% by weight of quartz sand. As the plate rotates, the test rods have to follow a circular path in quartz sand. The test rods are weighed before the test. In the test, the disc is rotated 120,000 revolutions, corresponding to a distance of 120 km. The average speed of the rods in the sand is 6.25 km / h. Each test has one reference rod of mild steel (Fe 37). After the test, the test bars are weighed and the weight reductions are calculated. For the test result, the weight reductions of the test rod and the reference rod are compared. The test result is the reduction in the weight of the test rod as a percentage of the reduction in the weight of the reference rod. The following representative tests were selected from the abrasive wear tests. Three residual austenitic spheroidal graphite iron according to the invention and one low residual austenitic spheroidal graphite iron, austenitic manganese steel (Hadfield steel), as it is generally a wear-resistant, per-lithic spheroidal graphite iron is a very wear-resistant steel. In addition, two rejuvenation steels were taken because of their high basic strength. High-alloy austenitic steels and cast irons have good corrosion resistance, but do not withstand abrasive wear on 5,567,700. Hardened steels and cast irons were not included in the wear tests due to their brittleness.

The results obtained in the abrasive wear tests are shown in the table below, which describes the test rod and its hardness (HB) and wear as a percentage of the wear of the mild steel (Fe 37). Test rods 2-5 represent the machine members according to the invention and test rods 6-10 represent other possible machine members which are tough. Test rod 1 is the reference rod. Test bars 2, 3 and 4 are spheroidal graphite iron with not only iron (C) 3.6%, silicon (Si) 2.2%, manganese (Mn) 0.7%, molybdenum (Mo) 0.08%, copper (Cu) 0.7% and magnesium (Mg) 0.044%. The test rods are austenitized at 880 ° C for one hour and bainitized in various ways. Test rod 5 is a spheroidal graphite iron with carbon (C) 3.6%, silicon (Si) 2.25%, copper (Cu) 0.77%, magnesium (Mg) 0.045% and the test rod is austenitized at 880 ° C for one hour and bainitized at 210 ° C for 100 min.

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The machine member according to the invention, which has a residual austenite of 26-34% by volume in the microstructure of the spheroidal graphite iron, has a very good wear resistance. When the residual austenite is only 8% by volume, the abrasion resistance is still good, but still slightly weaker than that mentioned above, and when there is even less residual austenite, the abrasion resistance is worse than that of the known perlite spheroidal graphite iron shown in Table 5. It can also be seen from the test results that the residual austenitic spheroidal graphite iron according to the invention withstands wear surprisingly well under experimental conditions in which the residual austenite of the machine member is not converted to martensite by cold working. This is particularly evident when compared to the poor wear resistance of austenitic manganese steel under the same conditions.

The thermal stability of the residual austenite of the microstructure of the machine member according to the invention has been tested on bodies with a residual austenite of 20% by volume. The bodies were kept for 5 hours at 400 ° C, 500 hours at 300 ° C, 20 minutes at -80 ° C and 15 minutes at -190 ° C and no experiment caused a noticeable change in residual austenite.

The upper limit of the permanent residual austenite in the microstructure of the spheroidal graphite iron used in the machine members according to the invention is about 50% by volume, because it is difficult to exceed it without abundant use of expensive alloying elements.

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