One of the most misunderstood and confusing steels used in wear resistant applications is Manganese. Manganese steel is used extensively in the mining, aggregate (rock crushing), foundries, metal recycling, and railroad industries.
Recycling, mining and aggregate applications utilize Manganese in the same type of machinery for similar functions in crushing applications. Whether you are shredding junk car bodies, or smashing large rocks into smaller sized rock for specific applications; much of the equipment you use is the same.
The railroad industry uses Manganese for rail switching and crossings. These areas on the tracks take a tremendous pounding. The Manganese rail deforms slightly as the train wheels pound the rail surface. This pounding and deforming causes the surface to harden, and the toughened surface resists future wear; while the rail itself remains ductile so it can flex.
Manganese Steel Properties
Manganese steel stands up to constant impact longer than any other known material, yet has the ability to develop abrasive wear resistance. It will resist impact significantly longer than high carbon steel or cast iron. Of course it will wear, but as the work hardened surface is worn away; the metal beneath becomes hardened from the continual exposure to impact.
The key to Manganese steel effectiveness is beneath the work hardened layer, the steel core remains ductile. When Manganese is exposed to impact, high stress scraping, gouging or pounding; Manganese can last up to 10 times longer than mild steel.
Not Recommended for Abrasion
When sand or other fine materials abrade the surface without impact, the wear resistance is not greater than mild steel. It is also less abrasive resistant than high carbon steel which has been heat treated.
A perfect example of using Manganese steel incorrectly was in a coal crusher feeding a coal fired boiler. When their equipment was first installed they were crushing Eastern Coal, which is very hard. Manganese is perfect for smashing hard materials, allowing the swing hammers and screen to work harden under the constant impact.
The company found they could save fuel costs buying Powder River Basin Coal from Wyoming, rather than the Eastern Coal. PRB coal however is very soft. The change meant the Manganese swing hammers never had a chance to work harden. You can imagine their surprise when the same hammers that were lasting 6 months with Eastern Coal, were totally worn out in 3 weeks using PRB coal.
Don’t Treat The Symptom, Look for the Cause
After initially thinking they received poor quality hammers, investigation into what happened revealed the change in coal was the cause of the dramatic difference in wear. By switching to an alloy steel hammer with a higher initial Rockwell hardness in place of the Manganese steel; their hammer life again returned to normal.
Manganese Steel Properties
The most common Manganese is known as Hadfield Manganese, which was invented by Sir Robert Hadfield in 1882. Hadfield Manganese steel typically has a direct 10 to 1 ratio of Manganese to Carbon. The standard range for Hadfield Manganese contains 11% to 14% Manganese compared to 1.0% to 1.4% Carbon. This ratio is critical for increasing the strength and hardness in Manganese steels.
As cast, Manganese is relatively soft, registering 187 BHN or 10 Rc. Cold working applications such as impact by repeated hammering increases both the hardness and the strength. Surface hardness from impact frequently reaches a maximum of 550 BHN or 55 Rc. The depth of the hardness will depend on the richness of Manganese steel chemistry and the frequency and pressure of the applied stresses. The lower the percentage of Manganese and Carbon, the lower the hardness scores you can achieve.
Yield strength of Manganese steel is about 66,000 PSI and ultimate tensile strength is about 107,000 PSI. Elongation is 35% in 2 inches.
Identification of Manganese Steel
Manganese is identified in the field with a magnet. As produced, Manganese is not magnetic or attracted by a magnet. After being used for a period of time, the impact wear areas will have a slight magnetic pull. The non-impact areas, the sides or back of the casting remain non-magnetic. It is the work hardening that makes the impacted surface slightly magnetic. This is the only known metal to have this magnetic change.
Heat Effects on Manganese Steel
Manganese is usually found as a casting; or wrought into shapes such as bar stock, plate, angles, etc. Manganese steel is expensive to machine, which is why most parts are cast to shape and finished by grinding. As cast, Manganese steel that has not been heat-treated is very brittle because of the Manganese carbides. Standard toughening treatment at the foundries, consists of slowly heating the steel to 1850° and quenching it in water. This heat treatment gives Manganese steel it’s high strength and toughness.
NOTE: If any later fabrication process raises the temperature above 500°F, the toughening treatment MUST be repeated.
Sustained temperatures of 500°F to 800°F may cause the Manganese to become brittle. While carbon steels gain strength from tempering, Manganese steel loses ductility when tempered. And can become brittle and prone to cracking in application.
My Application Has More Abrasion Than Impact, What Should I Use?
Manganese as we discussed, is designed for impact wear resistance. When your application has more abrasive wear with some impact, heat treated alloy steel will perform significantly better.
Most people first turn to an AR400 type steel. Most AR steels typically do not have the same hardness throughout the thickness of the steel. Like an Oreo cookie, they are hard on the surface, but soft as mild steel in the center of the steel thickness.
JADCO’s QT Plus ® is an ideal wear plate to utilize in your most challenging abrasion and impact applications. Here are a few reasons why this is the correct answer for your wear headaches:
QT Plus ® has the same hardness completely through the thickness of the plate. This means your wear is consistent and predictible. Say your ¾” plate has been in use for the past 3 years, and has now worn to ½” thick. You can plan your budget and schedule the labor to replace these plates in another 3 years when they will have worn to ¼”. And schedule the work at your convenience, rather than have an uplanned breakdown.
This way you avoid an unexpected failure when production grinds to a halt. Then it is all hands on deck to try and patch it up. You pray it holds together until you can find the time to replace it properly. Don’t forget you have to buy replacement steel, when your maintenance budget has already run dry. Avoid the drama and stress up front.
QT Plus ® can effectively be formed, machined and welded using the proper welding alloys and correct weld procedures. After comprehensive testing, QT Plus ® has been selected by a highly respected OEM mining equipment as the wear plate they specify for their most challenging applications. We know you will also benefit by using JADCO QT Plus ®.
Isn’t it time for you to invite a JADCO sales professional to review your current applications before it is too late? When we review what you are doing, what you have tried and how it worked previously; we can help you achieve real improvements in your process.