Changes in Mechanical Properties of Holding Magnet Type LS50 in Liquid Metal Transfer Ladle Due to Repeated Use

Inside a ladle there is one component of the material that often gets damaged, namely the Holding Magnet Type LS50, which has corrosion (damage) on the surface due to temperatures that reaches 1500 °C with a time limit of 150 minutes. Test shows the material contained in the Holding Magnet Type LS50 are steel, copper (CuZn), and magnet. The Steel of Holding Magnet Type LS50 has a chemical composition with the main ingredient of iron (Fe) around 97.961% and other elements such as carbon, silicon, manganese, chromium and other alloy elements. As for the microstructure, CuZn has a microstructure in the form of an α (alpha) phase and a s (betha) phase. The average of Holding Magnet hardness test results shows only CuZn experienced a very drastic decrease in the hardness value due to continuous heat exposure while the temperature for CuZn melting point is only 1084 ° C. Keywords: Chemical Composition, Metallography, Hardness. DOI: 10.7176/CMR/12-7-08 Publication date: October 31st  2020


INTRODUCTION
As we already know that with the development of this era and its human needs, the industrial world has a very important role. In the mechanical engineering field, steel processing industry is one of them.
Metal processing industry cannot be separated from the importance of using ladle, which is an item or tool of a die casting machine that functions to take liquid metal from the holding (liquid metal reservoir) and pour the liquid metal according to the needs of production. This ladle has many sizes and types just like the casting machine. The bigger the machine size, the bigger the ladle size used. Mostly, the ladle used is the one with a capacity of 100 tons.
The pouring technique using ladle is much more profitable, because there is no need for excessive human labor to meet abundant consumer demands. However, to support this activity, treatments must be taken so that the ladle can work properly.
Inside the ladle, there is one component of the material that is often damaged, namely the Holding Magnet. Holding Magnet is a component that attached to the bottom of the ladle. The function of the Holding Magnet itself is as an adhesive for Slid Gate components or Slid Gate binders, it can be interpreted as a substitute for bolts.
There are several types of ladles, but this study will be carried out on the Holding Magnet Type LS50. Type LS50 is the serial number of the ladle used with a capacity of 100 tons.

Ladle
Ladle is an item or tool of die casting machine that functions to move liquid metal from the liquid aluminum reservoir continue with pouring the liquid aluminum in accordance to the needs of production. Ladle comes in many sizes and types adjusting the casting machine. The bigger the machine size, the bigger the size of ladle used.

Holding Magnets on Ladle
Holding Magnets is an adhesive or a binder component. It is a substitute for bolts and clamps. Holding magnets provide an economical solution for many material handling applications involving ferrous products, through the removal of expensive clamps and fixtures. These magnets can increase productivity in the application process that includes: feeding part, automatic part transfer, welding, and holding parts in metal forming operations.
Standard holding magnets are supplied with its flat extended and ground precision mild steel poles, which can be customed by the machine to fit irregular shapes. These magnets are unaffected by vibration and are completely isolated for direct mounting to steel surfaces.

Function of Magnet Holding on Ladle
Holding Magnet is a component that is attached to the bottom of the ladle, it serves as the adhesive for the Sliding Gate component or the Sliding Gate binder

Magnet Holding Parts
The holding magnet has 3 items in it, namely:

Copper (Cu)
Copper is an alloy made of copper (Cu) and zinc (Zn). This material is used in many equipment such as decorative items, screws, musical instruments, and small nails. The mixture is between copper (Cu) with zinc (Zn) levels varying between 10% -40%. The higher the brass metal content, the more zinc content is.
If the zinc (Zn) content exceeds 40%, the zinc will experience a decrease in strength and when it is smelted, the zinc (Zn) will evaporate and make the copper (Cu) better. The copper will become harder so therefore it will be better to use machine. Zinc alloy that reaches 39% will give a mixture that is more resilient so that in cold temperatures, brass can be easily formed and it resistant to corrosion.
Copper-zinc alloys or called as brass metals can be used for heat exchangers, which is a part that strong, has a good resistant to corrosion and have a fairly high ductility. Copper-zinc alloys or brass alloys mixed with a third element can be used to improve corrosion resistance, wear resistance and machinability properties.
The manufacture of brass by casting is the only method commonly used in the small metal industry and the large metal industry. Metal casting is a smelting process or melting a metal, where the liquid metal is poured into a mold then the molten metal is allowed to cool. The casting process includes mold making, preparation, smelting, pouring the metal into the mold and further processing of the casting results.
In the process of casting brass metal within the existing small industrial environment, most of them still use the sand molding system. And in this brass metal smelting, they generally still use some used materials that are melted with a crucible furnace or with a low frequency induction furnace.

Magnets
The word magnet comes from the word magnesia (Greek) which means magnesian stone. Magnesia is the name of a region in Greece in the past which is now called Manisa (now in the territory of Turkey) where there are magnetic stones found since ancient times in the region. The first magnetic stones found were natural magnets (fixed magnets). Magnets that exist today are almost all artificial magnets.

Types of Magnets
Based on the type of material used, magnets can be divided into four types: Magnetic properties of this type are hard and have a very strong attractive force. Mixed permanent magnets are divided into: -Alcomax magnets, made from a mixture of iron with aluminum -Alnico magnets, made from a mixture of iron and nickel -Ticonal magnets, made from a mixture of iron and cobalt b) Ceramic Permanent Magnets This type of magnet is also called a magnadur, it is made of ferrite powder and is hard and has a strong attractive force. c) Malleable Iron Magnets This type of soft iron magnet is also called stalloy, it is made of 96% iron and 4% silicon. Its magnetic properties are not harsh and temporary. d) Protective Magnets This type of magnet, also known as mumetal, it is made of 74% nickel, 20% iron, 5% copper, and 1% manganese. These magnets are not hard and are temporary.

Steel
Steel is a vital base material for industry. All segments of life, from kitchen utensils, transportation, generators, to building frames and bridges are using steel. The exploitation of steel is ranked first among the mining and metal goods. Its products cover almost 95% of metal products used in everyday human life. day.
Steel is a metal alloy composed of iron as the main element and carbon as the reinforcing element. The carbon element plays a large role in increasing hardness. Heat treatment can change the physical properties of steel from soft like a wire to hard like a knife. The reason is that heat treatment changes the microstructure of steel and the crystal structure from BCC to FCC which is alloy and when cooled suddenly there is a change in crystal structure from FCC to BCC. Low Alloy Steel As in low carbon steel added with alloying elements of less than 4% such as Cr, Ni, Mo, Al and others.

Medium Alloy Steel
As in low alloy steel with the number of alloying elements between 5 -10% High Alloy Steel With a total of more than 10% of alloying elements.

Tool Steel
As in low alloy steels but the number of alloying elements is above 5%.

Carbon Steel Mechanical Properties
The mechanical properties of metals can be controlled by heating, called as heat treatment. The mechanical properties of steel include: a) Hardness which is the resistance of a material to plastic deformation due to local loading on the surface in the form of scratches or presses. b) Strength is indicated by the resistance of the material to the loads imposed on it so that it changes shape or size. Part of the strength includes tensile strength, yield strength and fracture strength. c) Ductility is the metal's ability to deform. Ductile materials usually have large cross-sectional shrinkage before fracturing occurs. d) Deformation so the fracture of a metal takes place quickly without knowing the propagation direction e) Toughness is the ability of a metal to maintain its shape by absorbing energy affecting it until it breaks. Chemical composition testing was carried out at B2TKS-LUK BPPT, aiming to determine the amount of chemical element composition in the Holding Magnet Type LS50. In this test, the Holding Magnet will be checked first, then the surface is cleaned so that the testing process can run well. The testing process for the Steel of Holding Magnet Type LS50 is carried out using a spectrometer, while the Ring of Holding Magnet Type LS50 use Niton for the chemical composition test tools.  This test is done to get the relationship between the microstructure changes that occur in the holding magnet. In this case, the type of Holding Magnet material is observed from the aspect of its operating temperature, then the anticipated change in the metallurgical structure can occur decarburasim due to oxidation, growth of spherodized carbide metal grains, and corrosion. Figure 4 is the optical microscope for metallographic testing tool.

Hardness Testing (Vickers)
Hardness testing is a mechanical test that aims to determine the hardness value of the material being tested due to heat treatment. Figure 5 is the picture of the hardness test equipment (Vickers). This hardness test uses an indenter that is pressed on the test object with a certain load. This stress will cause the metal to undergo plastic deformation. The value of hardness is expressed by HV (Diamond Pyramid Number -VPN), which is the ratio between the load (P) and the compressive footprint (A). With the formula: (1) d is the average diagonal in μm, P is the load given in gf, and α is the surface angle (136 °). Hardness can be calculated by the formula above or by converting the diagonal average in the HV (Hardness Vickers Number) conversion table book.

Steel of Holding Magnets Chemical Composition Analysis
After testing the chemical composition of the Holding Maget Type LS50 steel, it was found that in fact its chemical composition used the main ingredient of iron (Fe) around 97.961%. In addition to these elements, there are also several elements as support, these elements include carbon, silicon, manganese, chromium and other alloying elements. Inside the steel, there is an element of Manganese (Mn) that quite large, as big as 1.39% which functions to increase the fluidity, strength, and hardness of the Holding Magnet Type LS50.

Ring of Holding Magnet Type LS50 Chemical Composition Analysis
After the chemical composition test was carried out on the Ring of Holding Maget Type LS50 with 3 tests, it resulted in different element values using the Niton tool as shown in Table 4. Thus, from the results of the chemical composition testing above, the average value of the ring of holding magnet type LS50 chemical composition will be taken as above. 52 By examining the 50x and 200x magnification of the Holding Magnet Type LS50 -A in Figure 6, it shows it is in a good condition. It has a 3 mm CuZn ring, the CuZn microstructure is in the good condition of α (alpha) phase and ß (betha) phase and there are no defects. (Etching: K2CrO7). In Figure 7, the microstructure of location 2 CuZn is in the form of α (alpha) and ß (betha) phases. It is in good condition and there are no defects.  As Seen in Figure 9 on the magnetic material of the holding magnet with a magnification of 12 times and 200 times, there are holes and cracks caused by heat.    In figure 13, picture number 2 with 500x magnification for the microstructure on the magnetic cover shows there is no change, it is still ferrite-pearlite. In picture number 3 with 50x magnification shows between the magnet and the magnetic cover there is a deposit. From the micro structure in Figure 14 with magnification of 50x and 500x on the magnetic casing, it is still in form of ferrite-pearlite and there is a defect in the material, namely sulfide, where this type of sulfide corrosion defect is caused by various sulfur compounds at temperatures of 260 -540 °C (500 -1000 °F) In Figure 16, the macro photo of the Holding Magnet Type LS50 -C with damaged condition in the CuZn ring, it can be seen that the CuZn material surface is not visible because it experiences corrosion in its operating temperature.  In Figure 21, examining the Holding Magnet Type LS50 -D, it shows the microstructure of the casing has undergone a change from ferrite (white) and lamellar pearlite to pearlite (spherical) spheroidization, this is due to the fact that the casing is continuously exposed to high temperatures. (Etching: l2% nita) Figure 21. Magnetic casing microstructure.

Hardness Testing Analysis (Vickers)
After the hardness test is carried out on the Holding Magnet Type LS50, it produces a comparison value for hardness, both for steel, CuZn, and Magnet materials.  Table 5 shows the hardness value of the steel on the Holding Magnet Type LS50. After knowing the value of the hardness test on the Steel of Holding Magnets Type LS50, the average value is taken, thus the hardness graph will be known as shown figure 23.  Figure 23 is the graph of the hardness test average value on the Steel of Holding Magnets Type LS50. It shows that the hardness level is higher due to continuous exposure to heat, both from each type of damage. From Table 6 can be seen that in samples A and B on CuZn (ring) of Holding Magnet Type LS50 has different hardness values. After testing, the average value of the hardness can be taken. The graph can be seen in Figure 24. Judging from the Figure 24 which shows the graph of the hardness average value in CuZn samples A and B has decreased seen from the level of damage. Based on Table 7, it is known from several hardness tests on magnet of Holding Magnet Type LS50 has different hardness value. From the hardness value, the average hardness value in samples A, B and C can be taken. The graph for the average value of hardness on the Magnet Type LS50 can be seen in Figure 25.  Judging from the figure 25,. the graph of the hardness test average value on a magnet shows that the hardness level has decreased in terms of the level of corrosion.

CONCLUSION
7. In the magnetic material made from the casting process, there are porous defects, the microstructure is in the form of ferritic with carbide grains spread evenly, experiencing transgrannular corrosion and corrosion through the grain boundaries (intergrannular corrosion).
8. From the average hardness test results of the Holding Magnet Type LS50 on steel (casing) still have very hard mechanical properties as well as magnets. The average value of the hardness test on the Steel of Holding Magnets Type LS50 shows that the hardness level is higher due to continuous exposure to heat, both from the type of damage.
9. The CuZn material has an average value of hardness in CuZn samples A (180.5) and B (61.5) which has a quite drastic decrease in hardness. For the magnetic material, the Holding Magnet Type LS50 has an average hardness value that decreases in terms of its corrosion rate.