High-Chromium Cast Irons
In equipment under wear, ferrous alloys with the highest carbon have the best abrasion resistance. At the same time, due to the numerous stresses that occur during work, the material must be sufficiently tough. Non-alloy or low-alloy steels with a carbon content of about 0.4% have a low toughness when their structure is martensitic. Non-alloy white cast irons, most of which contain cementite carbide, have been used for many years due to their wear resistance. The weakness of these cast irons is in the carbide phase, which forms a continuous network around the austenite grains, causing brittleness and cracking of the part. Increasing the elements that make carbon as a carbide other than cementite with more hardness and more desirable properties not only reduces the amount of carbon in the matrix, but also improves toughness and abrasion resistance. Chromium is the element used for this purpose and its carbide is mostly in the form of M7C3.
Today, high-chromium cast irons are considered as an alternative to high-chromium steels when the parts are subjected to moderate impacts and severe wear. This group of white cast irons, due to the presence of martensite with Carbides precipitate, has been able to show very good abrasion resistance. In conditions where the part is under moderate impact and severe wear, the choice of chromium-nickel cast iron will be appropriate.
Table 1- Chemical composition of three types of high-chromium cast irons.
| Grade | Content of elements % | ||||
| C | Mn | Si | Cr | Ni | |
| ICHH28I2 | 2.7-3 | 0.8-1.4 | 0.5-0.8 | 28-30 | 1.5-3 |
| ICHH15M3 | 3-3.5 | 0.3-0.6 | 0.5-0.9 | 12-18 | – |
| ICHH14G2N | 2-2.4 | 0.5-0.7 | 1.8-3.2 | 13-15 | 1.2-2 |
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Manganese Steel
Manganese steel (Hadfield) is an alloy containing 0.8 to 1.25 percent carbon and 11 to 15 percent manganese, unique non-magnetic steel with wear-resistant properties. This steel has a very high abrasion resistance and this property is due to the tripling of the surface hardness due to impact. This property does not increase brittleness; Which is usually seen with increasing hardness and Leads to high toughness of this steel.
Manganese steels are widely used in the crushing and mill armor of the mining industry, cement industry, load bars and crushers, train rail needles, bulldozer sand, helmets and other applications in abrasive environments, as well as in cases of impact such as shot. These steels have recently been used in the refrigeration industry due to their impact strength at low temperatures. Most grades of manganese steel can be consumed after heat treatment by solution annealing at a temperature of about 1000 ° C and quenching in water, without the need for return treatment. The Brinell hardness in this case is about 200HB (almost similar to 304 stainless steel), but due to its unique properties, after contact with abrasives and consecutive impacts during work, this hardness rises to 550HB and Work hardening is observed in the material. Manganese steel parts often have difficulty machining. These steels cannot be softened by annealing, and usually require special tools for machining. Although capable of hot forging at 1100 ° C, they are likely to break at 1200 ° C during hammering and are generally more tough at high temperatures than carbon steels. For this reason, these steels are usually produced by casting. Manganese steel can be cut by oxyacetylene cutting, but plasma or laser cutting is preferred.
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Heat Resistant Steels
Refractory steels are essentially the same as heat resistant steels. As you know, the strength properties of steels decrease with increasing temperature. Heat resistance means that the steel can withstand temperatures above 500 ° C, so heat-resistant steels are designed for use at temperatures above 500 ° C. These steels, which are rich in chromium and nickel alloying elements, are strengthened by heat treatment (solution annealing and age hardening) and are generally used in places where high temperature corrosion resistance, crack resistance and hot fatigue, and creep resistance are required. These alloys are divided into three categories according to the ASM handbook, which are:
1- Iron-Chromium Alloys:
-Alloys containing 8 to 30% chromium.
– Has a ferrite structure.
– Has ductility and low strength at high temperatures.
– Application in places where the need for corrosion resistance in the presence of gases is considered.
Table 2 – Chemical composition of ferritic heat resistance alloys.
| Steel designation | % by mass | |||||||
| Number | Name | Approximate
AISI/ASTM designation |
C | Si | Mn
Max. |
Cr | Al | Others |
| 1.4713 | X10CrAlSi7 | – | Max. 0.12 | 0.5-1.00 | 1.00 | 6.00-8.00 | 0.5-1.00 | |
| 1.4724 | X10CrAlSi13 | – | Max. 0.12 | 0.7-1.4 | 1.00 | 12.00-14.00 | 0.7-1.2 | |
| 1.4742 | X10CrAlSi18 | – | Max. 0.12 | 0.7-1.4 | 1.00 | 17.00-19.00 | 0.7-1.2 | |
| 1.4762 | X10CrAlSi25 | – | Max. 0.12 | 0.7-1.4 | 1.00 | 23.00-26.00 | 1.2-1.7 | |
| 1.4749 | X18CrN28 | 446 | 0.15-0.2 | Max. 1.00 | 1.00 | 26.00-29.00 | N: 0.15 to 0.25 | |
| 1.4736 | X3CrAlTi18-2 | – | Max. 0.04 | Max. 1.00 | 1.00 | 17.00-18.00 | 1.7-2.1 | 0.2+4.(C+N)≤Ti≤0.8 |
2- Iron-Chromium-Nickel Alloys:
– More than 18% chromium and more than 8% nickel (chromium content is always higher than nickel content).
– Austenitic structure with a very small amount of ferrite.
– Has high strength and ductility at high temperatures and resistant to thermal cycles.
– Can be used in the presence of reducing and oxidizing gases that contain some sulfur.
3- Iron-Nickel-Chromium Alloys:
– More than 10% chromium and more than 23% nickel (nickel content is always higher than chromium content).
– Has a completely austenitic structure.
– Has high strength at high temperatures and resistant to cycles and intense thermal gradients.
– Not usable in places that have a lot of sulfur.
– Can be used in atmospheres that contain carbon and nitrogen. (Due to the high percentage of nickel, they are not easily carbonated and nitrified).
Table 3- Chemical composition of austenitic heat resistance alloys.
| Steel designation | % by mass | |||||||
| Number | Name | Approximate
AISI/ASTM designation |
C | Si | Mn | Cr | Ni | Others |
| 1.4878 | X8CrNiTi18-10 | 321H | Max. 0.1 | Max. 1.00 | Max. 2.00 | 17.00-19.00 | 9.00-12.00 | Ti:5.%C≤Ti≤0.8 |
| 1.4828 | X15CrNiSi20-12 | – | Max. 0.20 | 1.5-2.5 | Max. 2.00 | 19.00-21.00 | 11.00-13.00 | |
| 1.4835 | X9CrNiSiNCe21-11-2 | S30815 | 0.05-0.12 | 1.4-2.5 | Max. 1.00 | 20.00-22.00 | 10.00-12.00 | Ce:0.03-0.08 |
| 1.4833 | X12CrNi23-13 | 309S | Max. 0.15 | Max. 1.00 | Max. 2.00 | 22.00-24.00 | 12.00-14.00 | |
| 1.4845 | X8CrNi25-21 | 310S | Max. 0.1 | Max. 1.5 | Max. 2.00 | 24.00-26.00 | 19.00-22.00 | |
| 1.4841 | X15CrNiSi25-21 | 314 | Max. 0.2 | 1.5-2.5 | Max. 2.00 | 24.00-26.00 | 19.00-22.00 | |
| 1.4864 | X12NiCrSi35-16 | – | Max. 0.15 | 1-2 | Max. 2.00 | 15.00-17.00 | 33.00-37.00 | |
| 1.4876 | X10NiCrAlTi32-21 | – | Max. 0.12 | Max. 1.00 | Max. 2.00 | 19.00-23.00 | 30.00-34.00 | Al:0.15-0.6
Ti:0.15-0.6 |
| 1.4877 | X6NiCeNbCe32-27 | – | 0.04-0.08 | Max. 0.3 | Max. 1.00 | 26.00-28.00 | 31.00-33.00 | Al:max. 0.025
Ce: 0.05-0.1 Nb:0.6-1.00 |
| 1.4872 | X25CrMnNiN25-9-7 | – | 0.2-0.3 | Max. 1.00 | 8.00-1.00 | 24.00-26.00 | 6.00-8.00 | N:0.2-0.4 |
| 1.4818 | X6CrNiSiNCe19-10 | S30415 | 0.04-0.08 | 1.00-2.00 | Max. 1.00 | 18.00-20.00 | 9.00-11.00 | Ce:0.03-0.08 |
| 1.4854 | X6NiCrSiNCe35-25 | S35315 | 0.04-0.08 | 1.2-2.00 | Max. 2.00 | 24.00-26.00 | 34.00-36.00 | N:0.12-0.2
Ce:0.03-0.08 |
| 1.4886 | X10NiCrSi35-19 | N08330 | Max. 0.15 | 1-2 | Max. 2.00 | 17.00-20.00 | 33.00-37.00 | |
| 1.4887 | X10NiCrSiNb35-22 | – | Max. 0.15 | 1-2 | Max. 2.00 | 20.00-23.00 | 33.00-37.00 | Nb:1.00-1.5 |
Ni-Hard Cast Irons
Ni-Hard cast irons are widely used in crushing, pulverizing, rolling and material handling operations. There are two major groups of Ni-Hard cast iron:
Cast iron with 4% nickel and cast iron with 6% nickel and 9% chromium, these two groups are commonly known as Ni-Hard 2 and Ni-Hard 4. Ni-Hard 2 contains M3C Ledeburit eutectic carbides and therefore has low toughness, while Ni-Hard 4 mainly contains M7C3 discontinuous carbides, resulting in higher toughness. Ni-Hard 2 has a lower toughness and is mainly used in the production of metal working rollers. Metallurgy and application of Ni-Hard 4 is almost similar to high chromium cast iron, however, it has been observed that in certain applications, such as ball mills and the shell wall of large-diameter cement mills in which cast parts are subjected to both abrasion and repeated heavy impacts, Ni-Hard 4 does not provide the necessary resistance to failure. In general, the fracture toughness of high-chromium cast irons is higher than that of Ni-Hard cast irons. A characteristic that makes Ni-Hard 4 superior to high chrome cast iron is its excellent Hardness capability.
The chemical composition of all Ni-Hard cast irons is chosen so that most of the structure is solidified as a combination of eutectic and austenite. The amount of eutectic carbide that is formed as well as the structure of the matrix depend on the chemical composition of the cast iron. Ni-Hard 2 has a special Ledeburit structure in which M3C carbide appears continuously in the microstructure, but Ni-Hard 4 has a eutectic structure in which M7C3 carbides are discontinuously present. The advantage of this type of carbide structure is that although the M7C3 carbide is brittle, the cracks that form in it cannot spread much before they enter the much softer matrix.
Table 4- Chemical composition of Ni-Hard cast irons.
| Grade | Chemical composition | |||||||
| C (total) | Si | Mn | S | P | Ni | Cr | Mo | |
| Ni-Hard 1 | 3-3.6 | 0.3-0.5 | 0.3-0.7 | Max 0.15 | Max 0.3 | 3.3-4.8 | 1.5-2.6 | 0-0.4 |
| Ni-Hard 2 | Max 2.9 | 0.3-0.5 | 0.3-0.7 | Max 0.15 | Max 0.3 | 3.3-5 | 1.4-2.4 | 0-0.4 |
| Ni-Hard 4 | 2.6-3.2 | 1.8-2 | 0.4-0.6 | Max 0.1 | Max 0.06 | 4.5-6.5 | 8-9 | 0-0.4 |
Ni-Resist Cast Irons
A well-known group of high-alloy cast irons are known by the brand name Ni-resist and have been produced for a long time to resist corrosion. The excellent resistance of these widely used cast irons to corrosion is due to the presence of 13.5 to 36% nickel and 1.8 to 6% chromium and in one type 5.5 to 7.5% copper in them. Ni-resist cast irons are used to solve corrosion problems related to the pumping and refining of oil from sour salt water wells, some acids and alkalis. Most Ni-resist cast irons
can be produced in the form of gray or ductile iron. These cast irons are resistant to oxidation at high temperatures as well as in corrosive environments. Excessive nickel formation of graphite flakes during solidification, even in the presence of high chromium. The presence of high nickel causes graphite flakes to form during solidification, Even in the presence of a lot of chromium. High levels of nickel also prevent austenitic transformation. Ni-resist cast irons are usually not heat treated, but in some applications and when castings must operate at high temperatures, they must be dimensionally stable. Such heat treatment will not change the structure of the austenitic matrix.
Table 5 – Chemical composition of Ni-resist cast iron with layered graphite.
| Chemical Compositions of Flake Graphite Ni-Resist Alloys, % | |||||||
| Common Name | Ni | Cr | Si | Cu | Mn | C max | Other |
| NiMn 13 7 | 12-14 | 0.2 max | 1.5-3 | – | 6-7 | 3.0 | – |
| Ni Resist 1 | 13.5-17.5 | 1.5-2.5 | 1-2.8 | 5.5-7.5 | 0.5-1.5 | 3.0 | – |
| Ni Resist 1b | 13.5-17.5 | 2.5-3.5 | 1-2.8 | 5.5-7.5 | 0.5-1.5 | 3.0 | – |
| Ni Resist 2 | 18-22 | 1.5-2.5 | 1-2.8 | 0.5 max | 0.5-1.5 | 3.0 | – |
| Ni Resist 2b | 18-22 | 3-6 | 1-2.8 | 0.5 max | 0.5-1.5 | 3.0 | – |
| Ni crosil-al | 18-22 | 1.5-4.5 | 3.5-5.5 | – | 0.5-1.5 | 2.5 | – |
| Ni Resist 3 | 28-32 | 2.5-3.5 | 1-2 | 0.5 max | 0.5-1.5 | 2.6 | – |
| Ni Resist 4 | 29-32 | 4.5-5.5 | 5-6 | 0.5max | 0.5-1.5 | 2.6 | – |
| Ni Resist 5 | 34-36 | 0.1 max | 1-2 | 0.5 max | 0.5-1.5 | 2.4 | – |
| Ni Resist 6 | 18-22 | 1-2 | 1.5-2.5 | 3.5-5.5 | 0.5-1.5 | 3 | 1 Mo |
Table 6- Chemical composition of Ni-resist cast irons with spherical graphite.
| Chemical Compositions of Spheroidal Graphite Ni-Resist Alloys, % | |||||||
| Common Name | Ni | Cr | Si | Cu | Mn | C max | Other |
| Ni Resist D-2 | 18-22 | 1.75-2.75 | 1-3 | 0.5max | 0.7-1.25 | 3 | – |
| Ni Resist D-2w | 18-22 | 1.5-2.2 | 1.5-2.2 | 0.5max | 0.5-1.5 | 3 | 0.12-20Nb |
| Ni Resist D-2B | 18-22 | 2.75-4 | 1.5-3 | 0.5max | 0.7-1.25 | 3 | |
| Ni Crosilal Spheronic | 18-22 | 1-2.5 | 4.5-5.5 | 0.5max | 0.5-1.5 | 3 | |
| Ni Resist D-2C | 21-24 | 0.5 max | 1-3 | 0.5max | 1.8-2.4 | 2.9 | |
| Ni Resist D-2M | 22-24 | 0.2 max | 1.5-2.5 | 0.5max | 3.75-4.5 | 2.6 | |
| Ni Resist D-3A | 28-32 | 1-1.5 | 1-2.8 | 0.5max | 1 max | 2.6 | |
| Ni Resist D-3 | 28-32 | 2.5-3.5 | 1-2.8 | 0.5max | 1 max | 2.6 | |
| Ni Resist D-4A | 29-32 | 1.5-2.5 | 4-6 | 0.5max | 0.5-1.5 | 2.6 | |
| Ni Resist D-428 | 0-32 | 4.5-5.5 | 5-6 | 0.5max | 1 max | 2.6 | |
| Ni Resist D-534 | 0-36 | 0.1 max | 1-2.8 | 0.5max | 1 max | 2.4 | |
| Ni Resist D-5B | 34-36 | 2-3 | 1-2.8 | 0.5max | 1 max | 2.4 | |
| Ni Resist D-5S | 34-37 | 1.15-2.25 | 4.9-5.5 | 0.5max | 1 max | 2.3 | |
| Ni Resist D-6 | 12-14 | 0.2 max | 2-3 | 0.5max | 6-7 | 3 | |
FMU
Chromium-molybdenum steels are one of the most widely used alloys used in the lining of mills, especially iron ore mills, due to their good wear and impact resistance and relatively low production costs.
Depending on the type of lining operation of the mills and the installation location of the lining in the mill, the alloy used must have a suitable combination of wear and impact resistance. Abrasion resistance is a priority in the wall liners used in the mill wall and impact resistance is more important in the floor liners of the mill. In the liners of different mills, different alloys are used such as manganese austenitic steels, high chromium steels and cast irons, Ni hard cast irons and chromium-molybdenum steels.
Recently, a new type of steel known as FMU (Megato brand) has been widely used in the production of cement mill liners. This type of steels has a good combination of wear and impact resistance. Due to the relatively high amounts of alloying elements in this type of steels (especially chromium), the hardness of these alloys is relatively high.
Due to the fact that the alloy used in mills must have the highest wear resistance and sufficient toughness, the structure of tempered martensite offers a good combination of the above properties.
Table 7- Chemical composition of chromium-molybdenum steels.
| Reference Standard | Nominal Chemical Composition (W%) | |||||||
| C | Si | Mn | Cr | Mo | Ni | S | P | |
| FMU-29 | 0.25-0.45 | 0.3-1 | 0.6-1.5 | 6-8 | 0.2-0.4 | – | ≤0.04 | ≤0.04 |
| FMU-11 | 0.9-1.3 | 0.3-1 | 0.6-1.5 | 11-13 | 0.3-0.5 | – | ≤0.04 | ≤0.04 |
| FED- 13 | 0.8-1.3 | 0.4-1.2 | 0.8-1.5 | 11-13 | 0.4-0.8 | – | ≤0.04 | ≤0.04 |
| FED-14 | 1.6-2 | 0.4-1.2 | 0.8-1.5 | 11-13 | 0.6-1 | – | ≤0.04 | ≤0.04 |