N400 / NM400 Wear Plate vs Hardox 400: Hardness & Application

The short version: N400 and NM400 are Chinese-standard wear plates with a nominal hardness of 400 HBW. Hardox 400 is SSAB’s 400 HBW wear plate. They sit in the same hardness bracket and are often used interchangeably — but “equivalent” here means similar hardness, not identical chemistry or toughness.

What is N400 / NM400?

NM400 is defined under the Chinese standard GB/T 24186 as an abrasion-resistant steel with a nominal Brinell hardness of 400. “NM” stands for 耐磨 (wear-resistant) and “400” is the nominal HBW. In trade, N400, NM400 and “400 wear plate” are used loosely for the same product: a quenched and tempered low-alloy plate hardened to around 400 HBW.

It is designed for one thing — resisting abrasion. It is not a structural steel and it is not meant for high-temperature service.

Hardness comparison

Hardness is the number that matters most for wear life. The table puts the common 400-class plates side by side.

Typical chemistry (low-alloy, boron-treated)

Exact figures vary by mill; the point is that these are low-alloy steels hardened by quenching plus a small boron addition, not stainless or tool steels.

Mechanical properties

• Yield strength: around 1000 MPa
• Tensile strength: around 1250 MPa
• Elongation: around 10%
• Hardness: ~400 HBW nominal (see table above)

These are typical values for the 400 class. Ask for the mill’s actual test report if the part is safety-critical.

Where 400-class wear plate is used

• Dump truck bodies and tipper liners
• Excavator and loader buckets
• Chutes, hoppers and transfer points
• Crusher liners and screen decks
• Conveyor skirts and wear strips

For severe impact, a 400 plate may be too hard and brittle — consider a 360–400 grade with guaranteed impact toughness, or a 450 grade only where abrasion dominates and impact is low.

Cutting and welding notes

• Cutting: plasma, waterjet or laser. Avoid shearing thick plate — it can crack the hardened edge.
• Welding: use low-hydrogen consumables, keep heat input controlled, and preheat thick sections per the mill’s recommendation.
• Machining: hard (400 HBW) — drill and machine before hardening where possible, or use carbide tooling.

How to specify 400 wear plate correctly

1. Give hardness and grade — e.g. “NM400, 400 HBW” or “equivalent to Hardox 400”.
2. State thickness and tolerance — wear plate is often ordered 3–100 mm; thickness tolerance affects wear life.
3. Ask for flatness — quenched plate can distort; flatness matters for liners.
4. Request impact toughness if relevant — Charpy value at the service temperature, for cold or impact duty.
5. Get the MTC — hardness plus chemistry, so you can verify the plate matches the spec.