Understanding NM Wear Resistant Steel Plate Grades
NM wear resistant steel plate is a quenched and tempered abrasion resistant plate produced in China. The designation NM comes from the pinyin initials of the words "nai" and "mo", and the number that follows the letters is the nominal Brinell hardness of the plate in the as-delivered condition. The series described here covers NM360, NM400, NM450, NM500, NM550 and NM600, all of which are supplied in a hardened and tempered state rather than as-rolled.
The practical consequence of that treatment route is a hard, wear-facing surface supported by a tough, crack-resistant core. The plate resists sliding abrasion from ore, coal, clinker, gravel and sinter, while still absorbing impact and being cuttable and weldable with conventional shop equipment.
Chemical Composition Requirements
The compositions below are the maximum values given for NM wear plates. Because the grades are hardened rather than micro-alloy strengthened, carbon, manganese and the micro-alloying additions of chromium, molybdenum and titanium together determine how deep the plate hardens through its thickness.
| Grade | C max | Si max | Mn max | P max | S max | Cr max | Ni max | Mo max | Ti max |
|---|---|---|---|---|---|---|---|---|---|
| NM300 | 0.23 | 0.70 | 1.60 | 0.025 | 0.015 | 0.70 | 0.50 | 0.40 | 0.050 |
| NM360 | 0.25 | 0.70 | 1.60 | 0.025 | 0.015 | 0.80 | 0.50 | 0.50 | 0.050 |
| NM400 | 0.30 | 0.70 | 1.60 | 0.025 | 0.010 | 1.00 | 0.70 | 0.50 | 0.050 |
| NM450 | 0.35 | 0.70 | 1.70 | 0.025 | 0.010 | 1.10 | 0.80 | 0.55 | 0.050 |
| NM500 | 0.38 | 0.70 | 1.70 | 0.020 | 0.010 | 1.20 | 1.00 | 0.65 | 0.050 |
| NM550 | 0.38 | 0.70 | 1.70 | 0.020 | 0.010 | 1.20 | 1.00 | 0.70 | 0.050 |
| NM600 | 0.45 | 0.70 | 1.90 | 0.020 | 0.010 | 1.20 | 1.00 | 0.80 | 0.050 |
Residual element control is equally important: boron is held in the range 0.0005 to 0.006 percent and the acid-soluble aluminium minimum is 0.010 percent, which keeps grain size under control during austenitising and limits hardness scatter across a plate.
Mechanical Properties and Hardness
Hardness is the primary acceptance criterion for wear plate, with tensile and elongation values controlling how the plate behaves under impact and bending. The values below apply to plates within the thickness limits shown for each grade.
| Grade | Thickness limit | Hardness (HBW) | Elongation | Tensile strength |
|---|---|---|---|---|
| NM300 | 80 mm and below | 270-330 | 14 percent min | 1000 MPa min |
| NM360 | 80 mm and below | 330-390 | 12 percent min | 1100 MPa min |
| NM400 | 80 mm and below | 370-430 | 10 percent min | 1200 MPa min |
| NM450 | 80 mm and below | 420-480 | 7 percent min | 1250 MPa min |
| NM500 | 70 mm and below | 470 HBW min | - | - |
| NM550 | 70 mm and below | 530 HBW min | - | - |
| NM600 | 60 mm and below | 570 HBW min | - | - |
NM400 and NM450 type plates also deliver yield strengths above 950 MPa, so they can carry structural loads in equipment such as hopper walls and truck beds rather than acting only as a sacrificial liner.
Thickness Range and Plate Supply Formats
| Item | Common range | Extended range |
|---|---|---|
| Thickness | 2 mm to 100 mm | 1 mm to 300 mm |
| Width | 600 mm to 2500 mm | 10 mm to 2500 mm |
| Length | 100 mm to 12000 mm | Cut to order |
| Delivery condition | Quenched and tempered (hardened and tempered), flat and free of roll scale | |
| Surface | Cleaned, edge-machined, blast cleaned or primed to requirement | |
Applications in Mining, Cement and Bulk Handling
Wear plate is specified wherever a steel surface is abraded by moving bulk material. Typical duties include:
Excavator and loader bucket liners, cutting edges and wear strips
Dump truck body liners and tailgate plates
Chute liners, hopper walls, transfer points and impact zones
Crusher feed plates, screen decks and grizzly bars
Cement mill liners, fan housings and clinker handling equipment
Sinter plant, coke oven and steelworks discharge equipment
Recycling shredder feed tables, baler liners and scrap handling plant
Grade choice follows the abrasion mechanism. Free-flowing fine material with low impact calls for NM360 or NM400, whereas sharp, coarse or high-velocity material and thick sections justify NM450, NM500 or above. Where impact energy is high, a lower hardness grade with better elongation often outlasts a harder plate that cracks.
Cutting, Forming and Welding Practice
Cutting. Plasma, laser and abrasive waterjet cutting are suitable; oxy-fuel cutting requires preheat on thick sections and a controlled cool-down.
Forming. Rolling and press braking need generous bend radii, typically at least three times the plate thickness for the higher hardness grades, and are best done transverse to the rolling direction.
Welding. Low-hydrogen consumables, controlled heat input and preheat on thick sections limit hardness loss in the heat affected zone; a ductile buffer layer is used where a hard overlay would otherwise crack.
Machining. Drilling and countersinking are feasible with carbide tooling at low speed and steady feed.
FAQ
Q: What does NM stand for in wear resistant steel plate?
NM is formed from the pinyin initials of the Chinese words "nai" (wear) and "mo" (grinding), and the trailing number indicates the nominal Brinell hardness of the plate.
Q: What is the difference between NM360, NM400, NM450 and NM500?
They differ mainly in hardness and therefore in wear life: NM360 is 330-390 HBW, NM400 is 370-430 HBW, NM450 is 420-480 HBW and NM500 is 470 HBW minimum, with elongation and toughness falling as hardness rises.
Q: Which standard covers NM wear plates?
NM wear resistant steel plate is specified by GB/T 24186, which sets the chemical composition, hardness, tensile properties and thickness limits for each grade in the series.
Q: How thick can NM plate be supplied?
Common production runs from 2 mm to 100 mm, with an extended range from 1 mm to 300 mm, although the hardness grades in the standard are qualified only up to 80 mm for NM360 to NM450, 70 mm for NM500 and NM550, and 60 mm for NM600.
Q: How should the correct grade be selected?
Match the grade to the abrasion severity and impact level; use lower hardness with higher elongation where impact dominates, and higher hardness where fine abrasive material slides at speed with low impact energy.
Q: What documentation is supplied with the plates?
A mill test certificate covering heat number, chemical composition, hardness and mechanical properties is issued for each heat, and third-party inspection before loading can be arranged.