KR100431597B1 - Cobalt alloys with improved wear resistance used in the bushes and the sleeves of molten-zinc bath - Google Patents

Abstract

The present invention relates to a cobalt-based alloy for bushes and sleeves of a hot-dip zinc bath having improved wear resistance, which is used for each component used in manufacturing a hot-dip galvanized steel sheet, and exhibits excellent corrosion resistance and wear resistance.

To this end, the present invention is a carbon by weight of 0.1 to 0.3%, chromium (Cr) 15 to 20%, molybdenum (Mo) 25 to 30%, silicon (Si) 3 to 4%, the rest is an unavoidable impurity It provides a cobalt-based alloy for the bush and sleeve of the molten zinc bath with improved wear resistance, characterized in that consisting of and cobalt (Co).

As such, the present invention has an effect of increasing the wear resistance of the parts used in the molten zinc bath to extend the service life of the parts, thereby improving productivity and economy by extending the replacement cycle of the parts.

Description

COBALT ALLOYS WITH IMPROVED WEAR RESISTANCE USED IN THE BUSHES AND THE SLEEVES OF MOLTEN-ZINC BATH}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cobalt-based alloy for bushes and sleeves in a hot-dip zinc bath having improved abrasion resistance. More specifically, the present invention relates to a shrinkage part of a sink roll or a pot roll used in manufacturing a hot-dip galvanized steel sheet. The present invention relates to a cobalt-based alloy for a bush and a sleeve of a molten zinc bath having improved wear resistance, which is used in a sleeve and a bush, and exhibits excellent corrosion resistance and wear resistance.

Currently, hot-dip galvanized steel sheet has a thick plating thickness and is widely used for maintaining corrosion resistance for a long time and being inexpensive, compared to an electroplated steel sheet, and its demand is gradually increasing. In continuous hot dip galvanizing equipment, parts that are in direct contact with hot dip zinc are severely corroded by reaction with hot dip zinc. In addition, the sleeve and the bush, which are the bearing parts of the sink roll, are rubbed with each other under a large load, causing rapid wear and vibration, resulting in poor quality of the plated steel sheet. Therefore, in order to maintain the quality of the coated steel sheet products, it is necessary to stop the line at regular intervals and to replace or repair parts, which leads to a decrease in productivity and economic efficiency. Therefore, if the wear resistance of the bush and the sleeve which are rapidly worn in the molten zinc is improved, the quality of the plated steel sheet as well as contributes to productivity and economics.

In order to solve the problems described above, materials have been made excellent in wear resistance and corrosion resistance in molten zinc baths. One of the materials attempted is to take advantage of the excellent wear and corrosion resistance of ceramics as ceramics. However, ceramic materials are not only vulnerable to mechanical shock and thermal shock, but are also rarely put to practical use at present because of their high manufacturing cost. Currently, the most commonly used material is cast of Stellite 6, a cobalt-based alloy. Alternatively, Stellite 6 material may be used as a Plasma Transferred Arc (PTA).

The growth of the Stellite 6 material by the plasma overlay method results in a finer structure due to the faster solidification rate, resulting in better abrasion resistance, and the lower cost of manufacturing the part due to the use of cheaper stainless steel.

On the other hand, Japanese Patent Laid-Open No. 229103 discloses a technique in which a carbide of tungsten-carbide (WC) or tungsten-carbide-cobalt (WC-Co) is added to a cobalt-based alloy for surface growth using a laser.

The reason why the most expensive cobalt-based alloy, Stellite 6, is used as a part material such as bushes and sleeves in molten zinc is due to its excellent corrosion resistance in the hot-dip zinc bath of cobalt-based alloys compared to other iron- or nickel-based alloys. Cause. The Stellite 6 alloy contains about 28% (by weight) chromium to provide corrosion resistance, about 4 to 5% of tungsten for solid solution strengthening, and about 1% of carbon to form carbides for providing wear resistance. Therefore, as shown in FIG. 1, the tissue shows cobalt-based dendrite tissue in the bright area and eutectic carbide tissue in the dark area. Therefore, the wear resistance improvement is due to the process carbide containing about 20 to 30% (area ratio).

However, since the bush roll and the sleeve part of the sink roll used in the molten zinc bath are parts that are in contact with each other and are worn, if the wear resistance of one side is excellent, the wear of the other is accelerated. In particular, when the Stellite 6 alloy is rubbed with each other at high loads such as a sleeve and a bush, as shown in FIG. 2, process carbides that contribute to improved wear resistance are broken, which eventually acts as a grinding material and wears to each other.

Therefore, even if the microstructure of the Stellite 6 alloy is improved by plasma welding or laser growth, its wear resistance is improved. This is because the addition of carbides such as Cubster-Carbide (WC) to the Stellite 6 alloy to improve the wear resistance, so that the tungsten-carbide acts as a grinding material in the frictional environment. Is insignificant, and sometimes the life is rather deteriorated.

In order to solve the above problems, the present invention is added to the cobalt-based alloy to form an intermetallic compound rather than carbide to improve the corrosion resistance and wear resistance, and the intermetallic compound is not separated from each other during friction An object of the present invention is to provide a cobalt-based alloy for bushes and sleeves of a molten zinc bath with improved wear resistance that can improve the life of components in frictional environments such as bushes and sleeves.

1 is a microstructure photograph of a conventional cobalt-based alloy Stellite 6;

Figure 2 is a microstructure photograph after the molten zinc wear test of the conventional cobalt-based alloy Stellite 6;

3 is a schematic diagram of a tester for corrosion and wear tests in molten zinc;

Figure 4 is a microstructure photograph of the cobalt-based alloy for the bush and sleeve of the molten zinc bath with improved wear resistance according to the present invention;

Figure 5 is a graph showing the results of corrosion test in the molten zinc of the bush and sleeve of the zinc alloy bath and sleeve of the molten zinc bath with improved wear resistance according to the present invention;

FIG. 6 is a graph illustrating abrasion test results in a molten zinc bath and sleeve of a molten zinc bath having improved wear resistance according to the present invention and a conventional material.

In order to achieve the above object, the present invention is a carbon by weight of 0.1 to 0.3%, chromium (Cr) 15 to 20%, molybdenum (Mo) 25 to 30%, silicon (Si) 3 to 4% And, the rest is to provide a cobalt-based alloy for the bush and sleeve of the molten zinc bath with improved wear resistance, characterized in that consisting of inevitable impurities and cobalt (Co).

Hereinafter, the reason for numerical limitation of the alloy composition according to the present invention will be described in detail.

In order to improve corrosion resistance and abrasion resistance in the molten zinc bath, an alloy that forms an intermetallic compound rather than a carbide is added to the cobalt-based alloy. In this case, abrasion resistance is improved by the intermetallic compound, and the intermetallic compound is not detached during friction with each other, so that the lifespan of components in frictional environments such as bushes and sleeves can be improved.

(1) Carbon (C): 0.1-0.3 weight%

In order to form a spherical intermetallic compound instead of carbide in the cobalt-based alloy, carbon (C), which is about 1% or more, is reduced to a range of about 0.1 to 0.3%. That is, when the carbon content is less than 0.1%, the corrosion resistance is lowered, and when it is added in excess of 0.3%, a large amount of carbide appears to act as a grinding material as described above, which adversely affects the wear resistance of the material.

(2) Molybdenum (Mo): 25 to 30% by weight

Instead of tungsten (W) contained in a large amount of conventional cobalt-based alloy, molybdenum (Mo) should be added in a large amount. When the molybdenum content is added less than 25%, the fraction of the intermetallic compound produced is not small, and the wear resistance and corrosion resistance are not improved.When the molybdenum content is added more than 30%, the amount of chromium to be added is reduced too much, and the corrosion resistance It resulted in the result of a fall and limited to the said range.

(3) Chromium (Cr): 15-20 wt%

Since a large amount of molybdenum is contained, the amount of chromium decreases. However, if the amount of chromium decreases too much, the corrosion resistance decreases. Therefore, the amount of chromium is maintained at 15 to 20%. If it exceeds 20%, the production of intermetallic compound by Mo relatively decreases.

(4) Silicon (Si): 3.0 to 4.0 wt%

In the cobalt-based alloy according to the present invention, when the composition range of Si is less than 3.0%, it is not easy to form an intermetallic compound, and the remaining Si is dissolved in cobalt in a range exceeding 4.0% to lower the physical properties of the material.

Cobalt-based alloy manufacturing method according to the present invention having the above composition can be cast or plasma growth welding or growth using a laser or electron beam. A suitable manufacturing method in the present invention is a plasma fusing welding method, which has a finer structure and higher hardness than the casting method, so that the wear resistance may be improved. In the case of using a laser or an electron beam, it has strengths in precision parts but has a disadvantage in that the price increases.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments of the present invention.

Example 1

3 shows a schematic view of a tester for corrosion and abrasion tests in molten zinc shown in FIG. 3.

First, a corrosion test was performed. In the corrosion test, the specimen was fixed on a rotating disk while maintaining the temperature of the molten zinc at 470 ° C., and the weight loss was measured after 24 hours at a rotation speed of 30 m / min without a fixing pin installed.

The measured specimens are shown in Table 1.

Composition of corrosion test specimens (weight ratio) in a molten zinc bath. Co Cr C Si W Mo Remarks Conventional example Balance 26 1.1 - 5 - Stellite 6 Comparative Example 1 Balance 32 1.1 - 12 - Comparative Example 2 Balance 8 0.2 3.0 - 27 Inventive Example 1 Balance 17 0.2 3.5 - 27 Inventive Example 2 Balance 15 0.1 3.5 - 30 Inventive Example 3 Balance 17 0.2 4.0 - 27 Inventive Example 4 Balance 20 0.2 3.0 - 27 Inventive Example 5 Balance 17 0.3 3.3 - 25

Figure 5 is a graph showing the corrosion test results in the molten zinc of the bush and sleeve of the molten zinc bath with improved wear resistance according to the present invention and the conventional material, as shown therein, Comparative Example 1 By adding chromium and tungsten to the example, the structure is almost similar to the conventional example of Stellite 6, but the comparative example 1 manufactured for the purpose of improving the corrosion resistance by chromium and the formation of a lot of carbide by tungsten to increase the wear resistance There is a slight improvement in corrosion resistance than yes. In Comparative Example 2 and each of the inventive examples, molybdenum was added instead of tungsten to prepare an intermetallic compound instead of carbide formation. In the inventive example, more chromium was added to improve corrosion resistance. As shown in the corrosion test results of FIG. 5, Comparative Example 2 and Inventive Example show high corrosion resistance improvement compared to the conventional example, and Inventive Example shows the best corrosion resistance.

On the other hand, Figure 4 shows an internal cross-sectional texture picture of the invention example. In the picture, A is an eutectic lamella, B is an intermetallic compound, commonly called a Laves phase, and C is a cobalt solid solution. Since the hard B phase occupies about 40 to 60%, the hardness is also higher than that of the conventional example, and it is expected that the wear resistance will be improved since these hard phases do not deviate well when friction with each other. For reference, the prior art shows about 350 to 450 in Vickers hardness, and the inventive example shows about 600 to 850.

Example 2

Abrasion test was carried out using the tester shown in FIG. The test temperature was maintained at 470 ° C., and the speed of the disk specimen was fixed at 30 m / min under the fixed pin specimen. The test load was 18.8 MPa as a harsh condition. After a total of 4 hours, the wear resistance was evaluated by measuring the volume reduction of the pin specimen and the weight loss of the disk specimen. At this time, the pin and disk specimens were made of the same material. Table 2 shows the composition and cross-sectional hardness of the test specimens.

Wear test specimen conditions in molten zinc bath. Composition (weight ratio) Manufacturing method Vickers hardness (HV = 5 kg) Conventional example Stellite 6 Plasma Foster Welding 405 Comparative Example 3 Conventional example + 35% WC 〃 480 Comparative Example 4 Conventional example + 35% TiC 〃 590 Comparative Example 5 Conventional example + 45% Cr3C2 〃 802 Comparative Example 6 Conventional example + 40% NbC 〃 621 Comparative Example 7 Invention example + 50% WC 〃 790 Comparative Example 8 Invention example + 50% (WC-Co) 〃 930 Inventive Example 1 Table 1 〃 609 Inventive Example 2 〃 〃 625 Inventive Example 3 〃 〃 612 Inventive Example 4 〃 〃 630 Inventive Example 5 〃 〃 633

FIG. 6 is a graph showing abrasion test results in a molten zinc bath and sleeve of a molten zinc bath having improved wear resistance according to the present invention, and a molten zinc of a conventional material, as shown in FIG. Different carbides were added to the alloys of the prior art and the invention for the purpose of elevation. Therefore, all of the hardness is increased, but in a friction environment, the carbides are released, acting as a grinding material, rather, the wear resistance is reduced. Only the invention example shows the best wear resistance superior to the conventional example.

The improvement of wear resistance of this invention example is because the spherical rigid intermetallic compounds are maintained in a frictionless environment as shown in the cross-sectional tissue image of FIG.

As described above, the present invention has an effect of increasing the wear resistance of the parts used in the molten zinc bath to extend the service life of the parts, thereby improving productivity and economy by extending the replacement cycle of the parts.

Claims (2)

By weight%, it is 0.1 to 0.3% of carbon (C), 15 to 20% of chromium (Cr), 25 to 30% of molybdenum (Mo), 3.0 to 4.0% of silicon (Si), and the rest are inevitable impurities and cobalt (Co). Cobalt-based alloy for the bush and sleeve of the hot-dip zinc bath with improved wear resistance. The method of claim 1. The cobalt-based alloy for sleeves is a bush and sleeve cobalt-based alloy for improved wear resistance, characterized in that produced by the plasma overlay method using an alloy powder.