AR550 is a high-hardness abrasion-resistant steel plate engineered for severe wear environments where sliding abrasion and high-velocity impact quickly destroy conventional steels. With a typical Brinell hardness range of 530 to 570 BHN and a minimum surface hardness of 530 BHN, it outperforms AR500 in resisting sliding abrasion, making it a strong candidate for ballistic and extreme-wear applications. The higher hardness also lets engineers specify thinner plates without sacrificing durability, reducing weight and extending operational life. This article details the composition, mechanical properties, availability, and fabrication considerations of AR550.
What Is AR550 Steel?
AR550 belongs to the family of abrasion-resistant plates whose designation indicates the nominal Brinell hardness class. The 550 class sits above AR500 and is chosen when service conditions involve severe sliding abrasion, gouging, or high-velocity impact. Typical uses include liners for chutes, hoppers, buckets, crushers, and ballistic protection. Because hardness drives wear life, AR550 components usually last longer than AR400 or AR500 parts in the same application, which reduces downtime and replacement cost.
Chemical Composition
The alloy is designed to achieve maximum hardness with controlled weldability. Maximum contents are carbon 0.35 percent, manganese 0.95 percent, phosphorus 0.020 percent, sulfur 0.010 percent, and silicon 0.50 percent. The hardening elements are limited to chromium 0.75 percent, nickel 0.55 percent, molybdenum 0.75 percent, and boron 0.003 percent. This balanced composition contributes to the plate's high hardness, impact resistance, and abrasion performance while keeping the plate formable in the mill and weldable with proper procedures.
Hardness and Mechanical Properties
The Brinell hardness is 530 to 570 BHN with a minimum surface hardness of 530 BHN. Tensile and yield testing are not standard for this product but are available on request, with typical values around 220 ksi yield strength and 265 ksi tensile strength. Elongation measured over 2 inches is typically about 7 percent, reflecting the trade-off between hardness and ductility. Impact testing using the Charpy V-notch longitudinal direction shows an average of 14 foot-pounds at minus 40 degrees Fahrenheit, evidence of useful low-temperature toughness for a plate of this hardness.
Plate Availability and Dimensions
AR550 plates are typically available in thicknesses from 0.125 inch to 0.405 inch, widths from 48 to 60 inches, and lengths from 96 to 120 inches, supplied as flat plates. Because the product is marketed primarily on hardness and wear performance, chemical and mechanical verification should be confirmed against the mill certificate for each lot. Availability of specific dimensions should be checked with the supplier, as rolling programs concentrate on the sizes most used in the mining and material-handling industries.
Fabrication Guidelines and Applications
Fabrication of AR550 requires procedures suited to high-hardness steel. Cutting is normally done by plasma or water jet, and machining demands rigid setups, sharp tooling, and adequate cooling. Welding should use low-hydrogen consumables with controlled heat input and, where required, preheat to avoid cracking in the heat-affected zone; when wear performance is critical, hardfacing and overlay techniques can be applied. Primary applications include liners for chutes and hoppers, excavator buckets, crusher components, wear plates in mining, and ballistic panels.
Frequently Asked Questions
How hard is AR550 steel? R550 has a typical Brinell hardness of 530 to 570 BHN with a minimum surface hardness of 530 BHN.
How does AR550 compare with AR500? R550 is harder than AR500, which gives it better resistance to sliding abrasion and high-velocity impact, at the cost of lower ductility and more demanding fabrication.
What is the yield strength of AR550? Tensile and yield testing are not standard for AR550, but typical values available on request are about 220 ksi yield strength and 265 ksi tensile strength.
What thickness range is available? R550 plates are typically available from 0.125 inch to 0.405 inch thick, in widths of 48 to 60 inches and lengths of 96 to 120 inches.
Can AR550 be welded? Yes, with low-hydrogen consumables and controlled heat input, and preheat where required, although welding reduces local hardness in the heat-affected zone.
What applications use AR550? R550 is used for chute liners, hopper liners, excavator buckets, crusher components, mining wear plates, and ballistic protection where extreme abrasion occurs.