1. The Hardness Range of Wear Plates
Wear resistant plates are grouped by their Brinell hardness, and the common range runs from about 360 HB up to 540 HB. NM400 and AR400 sit at the lower end with about 360 to 450 HB, NM450 and AR450 cover about 410 to 480 HB, and AR500 and NM500 reach 450 to 540 HB. The hardness is measured on the plate surface and reported on the certificate, and it is the primary specification value for these grades.
2. How Hardness Affects Wear Life
For sliding abrasion, the wear resistance of a steel plate rises roughly in line with its hardness, so AR500 and NM500 typically last longer than NM400 in the same chute or hopper. The relationship is not linear, and the actual life depends on the abrasive material, the impact angle and the particle speed. A field trial with a test patch is the most reliable way to compare grades, and the plate thickness can also be increased to extend the life of the component.
3. Surface and Rust Behaviour
Wear plates are supplied with a mill scale surface or a protective primer, and they can develop surface rust during storage and transport. Surface rust does not reduce the hardness of the plate, but it should be removed before welding and painting, and the plate should be stored under cover or oiled for long periods. The rust on the surface is removed by grinding or blasting at the fabrication stage, and the cut edges are prepared for welding in the same operation.
4. Cutting and Welding Practice
Wear plates are cut with plasma or waterjet cutting, and thin plates can be cut with laser. The heat affected zone of a plasma cut edge is hard and can crack, so the edge should be ground before welding or forming. Welding is carried out with low hydrogen consumables and a preheat of 150 to 250°C, and the interpass temperature is controlled. The plate is not normally bent after hardening because the high hardness limits the formability.
5. Selection for Abrasive Service
NM400 for liners with moderate abrasion and some impact.
NM450 for a balance of wear life and toughness.
AR500 and NM500 for severe sliding abrasion in chutes and hoppers.
Thicker plates for heavy impact and gouging wear.
Higher hardness for fine, fast-moving abrasive particles.
Frequently Asked Questions
Q: What is the hardness of NM500 plate? NM500 has a typical Brinell hardness of 450 to 540 HB, which is the top of the common wear plate range.
Q: Does a harder plate always give a longer wear life? For sliding abrasion, yes in general, but for impact wear a tougher plate with slightly lower hardness often lasts longer because it resists cracking.
Q: Does surface rust affect the performance of the plate? Surface rust does not change the hardness or the mechanical properties, but it should be removed before welding and painting.
Q: Why is preheating needed when welding wear plates? The hardened microstructure is sensitive to cracking, and preheating slows the cooling of the weld zone so that hard, brittle structures do not form.
Q: Can wear plates be bent to shape? Bending is limited because the high hardness reduces formability; the plates are normally cut and welded into shape rather than bent.