Manganese Steel Buyer's Guide (keep update)

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Part 1: Introduction of manganese steel
History
Sir Robert Hadfield’s discovery of manganese steel came to limelight in 1882. He was looking for a steel, which possessed the properties of hardness, and toughness a combination of which was then very rare to come by. His first attempt was based on 3–4 percent manganese addition to a low carbon steel, the result of the tested piece was hard and brittle. The second attempt was 10- 14 percent manganese. After a suitable heat treatment, the steel possessed the properties of toughness combined with a remarkable resistance to wear and abrasions This gave birth to Hadfield’s Steel. Hadfield`s steel is unique in that it combined high toughness and ductility with high work-hardening capacity and, usually, good resistance to wear. Consequently, it rapidly gained acceptance as a very useful engineering material. Hadfield`s austenitic manganese steel is still used extensively, with minor modifications in composition and heat treatment, primarily in the fields of earthmoving, mining, quarrying, oil well drilling, steelmaking, railroading, dredging, lumbering, and in the manufacture of cement and clay products. Austenitic manganese steel is used in equipment for handling and processing earthen materials (such as rock crushers, grinding mills, dredge buckets, power shovel buckets and teeth, and pumps for handling gravel and rocks). Other applications include crusher hammers and grates for automobile recycling and military applications such as tank track pads.
Typical composition of Austenitic manganese steel

Characteristics of austenitic manganese steel
Austenitic manganese steel remains tough at subzero temperatures. The steel is apparently immune to hydrogen embrittlement. There is gradual decrease in impact strength with decreasing temperature. The transition temperature is not well defined because there is no sharp inflection in the impact strength-temperature curve down to temperatures as low as -85oC. At a given temperature and section size, nickel and manganese additions are usually beneficial for enhancing impact strength, while higher carbon and chromium levels are not. Resistance to crack propagation is high and is associated with very sluggish progressive failures. Because of this, any fatigue cracks that develop might be detected, and the affected part or parts removed from service before complete failure occurs. Yield strength and hardness vary only slightly with section size. The hardness of most grades is about 200 HB after solution annealing and quenching, but this value has little significance for estimating machinability or wear resistance.
Key Factors
Austenitic manganese steel was discovered by R. A. Hadfield in 1882 and since then it has become one of the most important steels where erosion of components takes place by continued abrasion and impact. It is a 1.2% carbon – 12% manganese alloy steel heat treated to an austenitic condition, which is stable at room temperature. Outstanding toughness, high strain hardening capacity and paramagnetism are the principle virtues of manganese steel.

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Part 2: Application of manganese steel

Why Manganese steel
Although austenitic manganese steels are universally known as the most useful abrasion resistant material, there is a general misconception amongst both the manufacture and the user about the basic characteristic of manganese steel for its choice for usual applications. The primary reason for selecting manganese steel for any particular application is not abrasion resistance. Manganese steel does have a good abrasion resistance, but if, abrasion resistance is the only criterion, there are a number of materials available which are much superior E.g. Martensitic white cast iron. The overriding reason for its choice is the tremendous toughness of manganese steel. The wear resistance of Hadfield manganese steel, having a fully austenitic structure obtained by water quenching from 1050 cent-degrees, depends entirely upon the amount of work hardening which it subsequently experiences. An intriguing feature of austenitic manganese steel is its ability to work hardens rapidly in the locality of sudden deformation. Superficial work hardening of crusher liners maintains surface hardness of Rc 45 to 55 over a base of high toughness. This combination cannot be duplicated by heat treatment. The work hardened profile depends on the nature of deforming force. Typical effected depths are 0.5mm from shot preening, 2.5mm from crushing hard rock and 38mm from explosive hardening (this is why in some extreme cases manganese steel parts were pre hardened by applying explosion).
It is understood that performance of manganese steel will depend on the type of wear i.e. the wear is associated with heavy or moderate impact or no impact at all because deformation is a necessary pre-requisite for work hardening of manganese steel. Three different types of wear can occur in service i.e. Gouging abrasion, Grinding or high stress abrasion, and Scratching or low stress abrasion.
Three different types of wear
In the first case, impact is always involved, such as in case of digger teeth cutting into rock, in gyratory crusher or impact crusher. In such cases manganese steel would be able to absorb huge amount of energy and undergo extensive plastic deformation without cracking. Even if crack is eventually developed, manganese steel has such a unique resistance to crack propagation that early detection is possible before equipment damage occurs. In the second type of wear, high stresses results from a crushing action such as in a ball mill. In such applications, logical choice, so far, has been manganese steels, mainly to avoid premature failures due to, either mishandling at user’s end, or, negligence at manufacturer’s end. But, by making judicious compromise on toughness for hardness, hard martensitic white cast irons, such as high chromium irons as well as other materials, are replacing manganese steels in this type of applications. The third type of wear is no way connected to impact and the scratching results from loose particles lightly abrading the steels. During this type of low stress abrasion austenitic manganese steel, as there is no chance of deformation, will not harden sufficiently to prevent surface erosion.

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Part 3: How it’s made?
Melting process

The melting components include some ferroalloys such as Fe-Mn, Fe-Si, and Fe- Mn-C and with few additions of lime or charcoal. The melting is carried out furnace When the melting is completed a small sample from the melt is taken for chemical examination. Another sample is taken for metallographic examination confirming the phases present in the castings. The pouring temperature of all the castings produced from this class of steel lies around and the pouring time must be as short as possible.

Heat Treatment
Heat treatment strengthens austenitic manganese steel so that it can be used safely and reliably in a wide variety of engineering applications. Solution annealing and quenching, the standard treatment that produces normal tensile properties and the desired toughness, involves austenitizing followed quickly by water quenching. Variations of this treatment can be used to enhance specific desired properties such as yield strength and abrasion resistance.
Usually, a fully austenitic structure, essentially free of carbides and reasonably homogeneous with respect to carbon and manganese, is desired in the as-quenched condition, although this is not always attainable in heavy sections or in steels containing carbide-forming elements such as chromium, molybdenum, vanadium and titanium. If carbides exist in the as-quenched structure, it is desirable for them to be present as relatively innocuous particles or nodules within the austenite grains rather than as continuous envelopes at grain boundaries.
Mechanical Properties after Heat Treatment
As the section size of manganese steel increases, tensile strength and ductility decrease substantially in specimens cut from heat-treated castings. This occurs because, except under specially controlled conditions, heavy sections do not solidify in the mold fast enough to prevent coarse grain size, a condition that is not altered by heat treatment. Fine grain specimens may exhibit tensile strength and elongation as much as 30% greater than those of coarse-grain specimens. Grain size is also the main reason for the differences between cast and wrought manganese steels -- the latter are usually on fine grain size. Mechanical properties vary with section size. Tensile strength, tensile elongation, reduction in area and impact strength are substantially lower in 102 mm (4 inches) thick sections than in 25 mm (1 inch) thick sections. Because section thicknesses of production castings are often from 102 to 152 mm (4 to 6 inches), this factor is an important consideration for proper grade specification.

 

[coalrulz]

Thanks for the posts. Found them to be very interesting.

 

[oceanobob]

If I may request: during your research of these steels, would it be possible to add a couple things. I am wondering if a list of popular trade names would be available such as T1 steel etc so we can relate the information to the buckets and etc steels. And while I am asking, any general information about how to weld (and weld repair) these items would also be handy.

 

[Dimonsof]

Hi.

Do you make bucket tips like K-type on CAT equipment? On your web-site there are only J-type teeth.

Regards,
Dima

 

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Part 4: The evolving of manganese steel
Many variations of the original austenitic manganese steel have been proposed, often in unexploited patents, but only a few have been adopted as significant improvements. These usually involve variations of carbon and manganese, with or without additional alloys such as chromium, nickel, molybdenum, vanadium, titanium, and bismuth. The figures below show two variations that are commonly used in recent years:

The mechanical properties of austenitic manganese steel vary with both carbon and manganese content. As carbon is increased it becomes increasingly difficult to retain all of the carbon in solid solution, which may account for reductions in tensile strength and ductility. Nevertheless, because abrasion resistance tends to increase with carbon, carbon content higher than the 1.2% midrange may be preferred even when ductility is lowered. Carbon content above 1.4% is seldom used because of the difficulty of obtaining an austenitic structure sufficiently free of grain, boundary carbides, which are detrimental to strength and ductility. Carbides form in castings that are cooled slowly in the molds. In fact, carbides form in practically all as cast grades containing more than 1.0% C, regardless of mold cooling rates. They form in heavy-section castings during heat treatment if quenching is ineffective in producing rapid cooling throughout the entire section thickness. Carbides can form during welding or during service at temperatures above about 275°C. If carbon and manganese are lowered together, for instance to 0.53% C with 8.3% Mn or 0.62% C with 8.1% Mn, the work-hardening rate is increased because of the formation of strain-induced a (body-centered-cubic, or bcc) martensite. However, this does not provide enhanced abrasion resistance (at least to high-stress grinding abrasion) as is often hoped.
Higher Manganese Content
Austenitic steels with higher manganese contents (>15%) have recently been developed for applications requiring low magnetic permeability, low temperature (cryogenic) strength and low temperature toughness. This applications stem from the development of superconducting technologies used in transportation systems and nuclear fusion research and to meet the need for structural materials to store and transport liquefied gases.
Chemical composition explained
Here we will spend some time to look at the different chemical compositions and their roles in manganese steel:
Manganese contributes a vital austenite-stabilizing effect. It sharply depresses the austenite-ferrite transformation and thus helps to retain 100% austenite structure at room temperature after water quenching. It is widely held that Manganese: Carbon ratio of 10 was optimum without reference to exact levels. This was probably inherited from earlier steel making limitations as it is apparent that the fixed ratio has no basic significance. Manganese within the range of 10 to 14%, has almost no effect on yield strength, but it does benefit tensile strength and ductility. Below 10% Mn the tensile properties decline rapidly to perhaps half the normal level at about 8% manganese
For critical requirements 11%Mn is desirable as a minimum; though the improvement over 10% is slight. The maximum is rather arbitrary and probably depends more on the cost of the alloy than on metallurgical results, since acceptable properties may be produced up to at least 20% manganese. Austenitic steels with higher manganese contents (>16%) are being manufactured
for applications requiring low magnetic permeability, low temperature strength (cryogenic strength) and low temperature toughness. For low magnetic permeability, these alloys have lower carbon and the corresponding loss in yield strength is compensated by alloying with chromium, molybdenum, vanadium and titanium.
Phosphorus: Although phosphorus content of 0.08% is permitted in specifications, experienced foundry men will hold phosphorus to much lower levels. The most serious problem faced with high phosphorus contents is the effect upon “in plant cracking” rather than the effect on the mechanical properties. Phosphorus above 0.02% progressively promotes intergranular cracking in manganese steels as in austenitic stainless steels. Above 0.06%, the high temperature plasticity of manganese steel is severely reduced and the steel becomes extremely susceptible to hot tearing. At such a high phosphorus level, microstructural evidence of grain boundary films of phosphide eutectic can be observed. Below 0.06% phosphorus, no microstructural evidence can be observed but phosphorus still affects the hot tearing propensity. The maximum tolerable phosphorus content is depended upon the severity of the stress system which is related to casting design, size and riser location. For massive, complex castings it is advisable to hold the phosphorus below 0.04%.
Sulfur is seldom a factor in 13% manganese steel, since the scavenging effect of manganese, for which it is customarily added in simple steels, operates to eliminate it by slagging or fixing it in the form of innocuous rounded inclusions of manganese sulfide. Elongation of these inclusions in wrought steels may contribute to directional properties: in cast steels they are considered harmless.
Chromium increases yield strength and flow resistance, which can be useful in certain applications: however, on the other side of the ledger, chromium is very detrimental to toughness and is extremely sensitive to section size variation.
Nickel: It has been shown that adding nickel to plain austenitic manganese steel decreases the tensile strength slightly increases the ductility but has no effect on yield strength. However, nickel improves the toughness of such steel by inhibiting the precipitation of grain boundary carbides during reheating and cooling. This produces a steel less susceptible to hot tearing and more amenable to welding.
Molybdenum: An important contribution made by molybdenum additions is the significantly improved as cast mechanical properties and the enhanced resistance to carbide embitterment which occurs if manganese steel is re-heated. In foundry terms, this translates into easier shop handling with reduced propensity for cracking, especially during the removal of gates and risers, arc air flushing and weld repair. For this reason, molybdenum (usually a 1% addition) is a valuable contributor to the production of massive crusher castings.

 

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Part 5: Finding of the right supplier
Since austenitic manganese steel castings have a big share of total demand of castings all over the world, innumerable foundries, right from the highly sophisticated and quality conscious foundries to even a foundry that carries out melting in a small crucible, produce manganese steel castings today. As a result there has been a wide scatter in the performance of standard austenitic manganese steel castings. This is because, except a few, most of the foundries do not have knowledge of metallurgy of manganese steel and not aware of the strict controls required to produce good quality manganese steel castings. And when complaints start coming from the users or the performance is compared with the products of the few good foundries, most foundries, almost blindly, start trying different modifications of manganese steels with different costly alloys, instead of trying to improve the manufacturing process. That is why it is so important for end users to choose their suppliers so carefully.
Tips on finding the right supplier:
1.First determine your requirements. This will help you figure out whether a supplier can meet your requirements. If you don’t know what your specific requirements are, the chances of choosing the wrong suppliers are high. Once you are clear about your requirements, you should make it known to potential suppliers.
2.Look at total cost (price plus costs incurred before or after product or service delivery) instead of choosing the supplier with the lowest price, as it is important to balance other important elements such as quality, delivery, and service. You don’t want to choose the lowest-price supplier, only to discover hidden costs of doing business, such as poor quality or poor service that drive up your real costs.

3.Consider making a site visit to a potentially key or critical supplier to see their operation firsthand, meet their management, and help increase your knowledge of and comfort level with the supplier.
4.In some cases, using a distributor may be a good option for small companies, particularly those who want to buy in smaller quantities than buying directly from manufacturers will permit. This will help keep one’s inventories lower. Keep in mind that most distributors deal with multiple suppliers, you also need to make your expectations clear.
5.Develop good relationships with suppliers and keep the lines of communications open to help work through changes and problems as they occur. Suppliers with whom you have developed good relationships are often more willing to work through challenges with you than those whom you either don’t know or those with whom your interactions have been adversarial. Developing relationships with your key suppliers is one of the most proactive ways to avoid risk and unpleasant surprises and sometimes even get more favorable terms.