Different Jobs for Different Steels
NM400 and NM500 belong to the abrasion resistant family defined in GB/T 24186 and are supplied quenched with a surface hardness of 370 to 430 HBW and 470 to 540 HBW respectively. Their purpose is to resist sliding and impact abrasion in mining, quarrying and material handling equipment. ASTM A36, 42CrMo and S45C serve different functions. A36 is a general structural carbon steel with a minimum yield strength of 250 MPa used for frames and supports. 42CrMo is a chromium molybdenum alloy steel that is quenched and tempered to high strength for shafts and gears. S45C is a medium carbon steel per JIS G 4051 used for parts that are surface hardened.
Comparison of Property Data
The table below sets out the reference properties of each steel so that the difference is clear.
| Steel | Governing Standard | Strength or Hardness | Main Function |
| NM400 | GB/T 24186 | 370 to 430 HBW | Abrasion resistance |
| NM500 | GB/T 24186 | 470 to 540 HBW | Severe abrasion resistance |
| ASTM A36 | ASTM A36/A36M | 250 MPa minimum yield | Structural framing |
| 42CrMo | GB/T 3077 | 980 MPa minimum tensile | Loaded machine parts |
| S45C | JIS G 4051 | Surface hardness over 50 HRC after hardening | Hardened machine parts |
Why Wear Plate Cannot Simply Replace Structural Plate
A wear plate has high hardness but relatively low ductility and a limited weldable thickness range. It is not intended to carry primary structural load, and it should not be used as a load path member without a design check. Structural plate such as A36 has lower hardness but much better ductility and weldability. In practice the two are combined. A structural frame in A36 or S355 carries the load, and a NM400 or NM500 liner is bolted or welded on the wearing face. This hybrid arrangement gives long life and safe structural behaviour at the same time.
Selection Rules
Choose a wear grade from the abrasion severity: NM400 for moderate sliding abrasion, NM450 for harder rock and NM500 for high speed impact of sharp material. Choose 42CrMo where the part must transmit torque and also be machined. Choose S45C where a hardened surface on a tough core is needed. Choose A36 where the requirement is simply a weldable structural member. Whichever route is taken, the material certificate should state the standard, the grade, the delivery condition and the test results so that the delivered plate can be verified against the design assumption.
Applications by Steel Type
Dump truck bodies and chute liners in NM400 and NM500.
Building frames and equipment bases in ASTM A36.
Axle shafts, gears and connecting rods in 42CrMo.
Induction hardened pins and bushes in S45C.
Composite wear plates with a structural backing for loaded liners.
Frequently Asked Questions
Q: Can NM500 be used as a structural member?
It should not carry primary structural load without design verification because its ductility and weldability are limited compared with structural steels such as A36.
Q: Which steel is best for a dump truck floor?
NM400 or NM500 plate is normally used for the floor and side liners, with a structural steel frame providing the load path.
Q: How does 42CrMo differ from NM500?
42CrMo is a through hardening alloy steel chosen for strength and toughness in loaded machine parts, while NM500 is chosen for high surface hardness against abrasion.
Q: Is S45C a wear resistant steel?
Not by itself. S45C gains wear resistance only after surface hardening such as induction treatment, and it is used mainly for machine parts.
Q: What should be stated on the mill certificate?
The standard, the grade, the delivery condition and the tested values for hardness or mechanical properties should all appear on the certificate.