What NM400 Wear Resistant Plate Is
NM400 wear resistant plate is a quenched and tempered abrasion resistant steel plate produced under GB/T 24186, the Chinese standard that covers wear resistant steel plates for construction machinery. In the designation, NM stands for the Chinese term for wear resistant and the number 400 indicates a nominal Brinell hardness of 400 HBW. Hardness is developed through the full plate section during quenching and tempering, so the working surface does not depend on a welded overlay or a sprayed coating that can spall away.
The structure of the steel is a low carbon martensitic matrix that pairs a hard surface with enough toughness to absorb impact from falling ore, rock and scrap. Delivered hardness normally falls between 360 and 430 HBW. That combination is what places the grade in the 400 HBW class used for truck bodies, buckets, chute liners and crusher parts, where both sliding abrasion and impact loading occur at the same time.
Chemical Composition of NM400
Typical ladle analysis limits for NM400 plate are listed below. Low carbon, low sulphur and low phosphorus keep the steel weldable and reduce the risk of cold cracking, while boron and a modest chromium addition support hardenability during quenching.
| Element | Typical limit | Function in the steel |
|---|---|---|
| Carbon (C) | 0.25% max | Hardness and hardenability |
| Silicon (Si) | 0.70% max | Deoxidation |
| Manganese (Mn) | 1.60% max | Strength and toughness balance |
| Phosphorus (P) | 0.025% max | Weldability control |
| Sulphur (S) | 0.010% max | Cleanliness and impact toughness |
| Chromium (Cr) | 0.80% max | Abrasion resistance |
| Molybdenum (Mo) | 0.50% max | Hardenability in thicker sections |
| Nickel (Ni) | 0.70% max | Toughness |
| Boron (B) | 0.004% max | Hardenability at low carbon content |
Because the plate is delivered in the heat treated condition, the composition is balanced to reach hardness rather than to be used in the as-rolled state. Suppliers of NM400 plate normally issue a mill test certificate that reports heat analysis, product analysis and the measured hardness.
Mechanical Properties and Hardness
Hardness governs acceptance of abrasion resistant plate, because wear life under sliding abrasion tracks surface hardness far more closely than tensile strength. The table below shows a typical property envelope for NM400 plate.
| Property | Typical value | Test basis |
|---|---|---|
| Surface hardness | 360 - 430 HBW | Brinell test on the plate surface |
| Tensile strength | 1200 MPa min | Transverse tensile test |
| Yield strength | 900 MPa min | Transverse tensile test |
| Elongation | 10% min | Tensile test piece |
| Impact test temperature | 0 C or -20 C as ordered | Charpy V notch, longitudinal |
The figures above are the values normally reported by mills for the grade. Final acceptance limits follow GB/T 24186 together with any additional requirements written into the order, and hardness is measured away from the flame cut edge, where the heat affected zone can read differently from the parent plate.
Where NM400 Plate Is Used
Mining haul truck bodies, bed liners, side plates and tailgates
Excavator and wheel loader buckets, cutting edges and wear strips
Crusher liners, hopper liners, transfer chute walls and dead boxes
Conveyor skirt boards, impact beds, screen decks and deflector plates
Scrap containers, demolition shears, shredder housings and recycling equipment
Agricultural implements, mixer blades, silo liners and asphalt plant parts
In each case the aim is the same: place a hard, tough surface in the path of the abrasive material so that a relatively thin plate replaces what would otherwise be a much heavier, faster wearing carbon steel component.
Cutting, Forming and Welding Notes
NM400 plate is usually cut by plasma, laser or abrasive waterjet. Oxy-fuel cutting is workable on heavier gauges but calls for preheating to limit hardening of the cut edge, and cut edges should be dressed where fatigue or impact loading is expected. Cold forming is practical at moderate thickness, and bends should use a generous radius relative to plate thickness to avoid cracking along the bend line. If forming has to be done in cold weather, warming the plate first reduces the risk of brittle behaviour.
For welding, low hydrogen consumables matched to the base metal strength are the normal choice, combined with controlled heat input and a suitable preheat on thick sections. Welding procedures are best qualified before production. A welded joint does not need to match the hardness of the wear plate, since wear performance in the protected zone is set by the hardness of the parent plate.
Frequently Asked Questions
Q: Is NM400 the same as any other 400 HBW wear plate?
NM400 is the GB/T 24186 designation for a 400 HBW class quenched and tempered wear plate. It occupies the same hardness class as other 400 HBW grades, but its chemistry, delivery condition and tolerances are defined by the Chinese standard rather than by another specification.
Q: What is the standard thickness range for NM400 plate?
Common production covers roughly 3 mm to 100 mm. Thin plate is used for liners and chute walls, while heavy plate goes into bucket floors and crusher feed areas. Thickness is chosen from the required wear life and the impact energy in the application.
Q: Does NM400 plate need a wear overlay?
No. The plate is hard through its section, so hardfacing is reserved for small, highly stressed areas such as a bucket lip or a transfer point that wears out faster than the surrounding liner.
Q: How does NM400 compare with ordinary structural steel for liners?
Carbon structural steel of the same thickness has far lower hardness, so it wears several times faster under sliding abrasion. Using NM400 typically means a thinner, lighter liner with a longer replacement interval.
Q: Can NM400 plate be bent and rolled in the workshop?
Yes, within limits. Rolling and bending are done cold on moderate thicknesses with a large radius, and edges are ground smooth afterwards. Forming a very tight radius on thick plate is normally avoided.
Q: How should NM400 plate be stored on site?
Store plates flat on timber dunnage, clear of standing water, and lift with slings rather than dragging them over concrete. Protecting the surface from mechanical damage keeps the full hardness of the working face available.
