What is NM400 wear-resistant steel plate?
NM400 is a high-strength wear-resistant steel plate under the Chinese national standard system, and is one of the core grades of the NM series of wear-resistant steels. Its grade naming follows a clear and logical rule: "NM" is the first letter of the Chinese pinyin for "wear-resistant" (Nai Mo), and "400" indicates the nominal Brinell hardness value of 400 HBW.
NM400 is one of the core grades in GB/T 24186-2022 "High-strength Wear-resistant Steel Plates for Engineering Machinery". This standard covers seven hardness grades from NM300 to NM600, with a hardness range of 270–640 HBW. NM400 is the most widely used among all NM series grades, accounting for more than 50% of consumption. It achieves an optimal balance between wear resistance, impact toughness, weldability, and cost, making it the preferred material for medium to heavy wear conditions in mining, engineering construction, and material handling.
mplementation Standards and Systems
NM400 wear-resistant steel plates are manufactured according to GB/T 24186-2022 (replacing the 2009 version), the standard title of which is "High-strength Wear-resistant Steel Plates for Engineering Machinery". This standard specifies all technical requirements, including chemical composition, mechanical properties, dimensional tolerances, surface quality, and inspection methods.
Chemical composition and mechanical properties
1.Chemical properties
The superior performance of NM400 stems from its carefully balanced chemical composition. The table below shows the typical composition range and the specific role of each alloying element:
| Element | Content Range (wt%) | Role and Mechanism |
|---|---|---|
| Carbon (C) | 0.20–0.30 | Core strengthening element; forms high-hardness carbides that directly contribute to wear resistance; contributes to martensite formation during quenching. |
| Silicon (Si) | 0.10–0.50 | Deoxidation agent; provides solid-solution strengthening and improves oxidation resistance. |
| Manganese (Mn) | 1.00–1.60 | Enhances hardenability to ensure thorough transformation throughout thicker sections; inhibits hot cracking during thermal processing. |
| Chromium (Cr) | 0.30–1.20 | Critical wear-resistance element; forms (Cr,Fe)₇C₃ hard phases that greatly improve abrasion resistance; also improves hardenability and tempering stability. |
| Phosphorus (P) | ≤0.025 | Strictly controlled harmful impurity; can induce cold brittleness and degrade weldability if excessive |
| Sulfur (S) | ≤0.025 | Controlled to maintain toughness and hot workability; forms nonmetallic inclusions that can cause anisotropy. |
| Boron (B) | 0.0005–0.005 (trace) | Dramatically improves hardenability even in very small quantities; ensures deep hardening in thicker plates. |
2.Mechanical properties
NM400 delivers an optimal combination of hardness, strength, and toughness, carefully balanced to suit a wide range of heavy-wear applications. The following table summarizes typical mechanical property values for NM400 in the quenched and tempered condition：
| Property | Typical Value | Remarks |
|---|---|---|
| Brinell Hardness (HBW) | 370–440 (typical 380–440) | Equivalent to HRC 38–46 on the Rockwell C scale; actual varies with plate thickness. |
| Tensile Strength (Rm) | ≥1200–1250 MPa | Far exceeding standard structural grades such as Q345或Q460. |
| Yield Strength (Rel) | ≥1000–1050 MPa | High resistance to plastic deformation under heavy loads. |
| Elongation (A₅) | ≥10% | Sufficient ductility to absorb impact and vibration without brittle failure. |
| Impact Toughness (-20℃ KV₂) | ≥24 J | Guarantees resistance to brittle fracture under cold-weather impact conditions. |
NM400
Production process flow
The production of NM400 is a sophisticated, multi-stage process requiring precise control at every step:
Smelting: Primary smelting is carried out in a converter or electric furnace, followed by ladle refining (LF/VD, etc.). Strict control is maintained over the narrow range of fluctuations in the purity and chemical composition of the molten steel, minimizing the content of harmful elements such as phosphorus and sulfur.
Continuous Casting and Slab Heating: Molten steel is cast into slabs using a continuous casting machine, and then heated in a heating furnace to a specific temperature range to prepare the microstructure for subsequent rolling.
Controlled Rolling：A two-stage controlled rolling process is used to refine prior austenite grains: coarse rolling in the recrystallization region to break down the as-cast structure, followed by finish rolling in the non-recrystallization region to accumulate deformation energy-which provides more nucleation sites for ferrite transformation and results in finer final grain sizes typically ≤50μm. The finishing rolling temperature is typically maintained between 800–900℃ to optimize grain refinement
Quenching (Core Step of Tempering): Immediately after rolling, the plate undergoes direct quenching using high-pressure water jets, achieving a cooling rate exceeding 30℃/s to promote martensite formation. Quenching temperatures are controlled in the range of 900–930℃ to achieve nearly complete austenitization. This process must be carefully balanced: the plate thickness, chemical composition, and cooling water intensity all influence the final hardness and through-thickness uniformity.
Tempering: Quenched plates then undergo low-temperature tempering at 180–250℃. This step relieves quenching-induced residual stresses, slightly adjusts the hardness-toughness balance, and stabilizes the microstructure for consistent in-service performance. Tempering temperatures must be kept below 300℃ to prevent excessive loss of hardness through over-tempering and martensite softening
Processing technology
Cutting
Flame cutting, plasma cutting, or laser cutting can be used. During flame cutting, due to the high hardness and high carbon equivalent, there is a significant tendency for cold cracking; preheating is necessary before cutting. Preheating to 150~200℃ is recommended, and preheating is mandatory for thicknesses exceeding 30mm. Plasma cutting is suitable for medium-thin plates (<50mm), offering fast cutting speeds and a small heat-affected zone. Laser cutting is suitable for thin and medium-thick plates, achieving an accuracy of ±0.1mm, and is suitable for machining complex-shaped parts.
Welding
NM500 has a high alloy composition and high carbon equivalent, making it sensitive to welding processes and exhibiting a significant tendency for cold cracking. Weldability is poor (20†L2-L3). Preheating to an appropriate temperature (usually above 100~150℃) is essential before welding. Low-hydrogen welding rods or wires should be used, and heat input must be strictly controlled. During welding, the principle of "selecting welding material strength according to the material with lower strength and determining the preheating temperature according to the material with higher strength" should be followed. Post-weld stress-relief annealing is recommended to eliminate residual stress in the weld joint.
Main application scenarios
NM400 is widely used in wear-resistant parts of industrial equipment, providing wear-resistant protection for critical components. Its core applications include:
Mining Machinery: Excavator buckets, cutting edges, and side cutting edges; crusher liners; dump truck bodies and bottom plates; transfer conveyor troughs and screw feeders.
Construction Machinery: Bulldozer bucket plates, loader cutting edges, scraper conveyor troughs, etc.
Metallurgical Machinery: Sintering machine trolleys, blast furnace bells, and wear-resistant liners for coking equipment, capable of withstanding high-temperature wear conditions up to 400℃.
Coal and Power Machinery: Pulverized coal conveying pipelines, coal mill liners, dust collector flues, fan impeller housings, coal crusher liners, coal hoppers, and screw feeders, etc.
Building Materials Machinery: Cement mill liners, brick machine molds, reducing production costs by improving wear resistance.
In addition, NM400 is also used in small quantities in the manufacture of precision parts such as abrasives and bearings. With the continuous development of technology, high-end grades such as NM500D and NM500E have been successfully applied to new equipment fields such as large intelligent crushers and wide-body mining cars.
Grade Comparison and Selection Guide
| Grade | Hardness Range (HBW) | Wear Resistance | Toughness | Applicable Working Conditions |
|---|---|---|---|---|
| NM400 | 370–440 | Baseline | Excellent | Moderate wear, balanced overall performance, suitable for heavy impact loads |
| NM450 | 410–480 | High (15–30% higher than NM400) | Good | Comprehensive performance, good balance between toughness and hardness |
| NM500 | 470–540 | Extremely high | Limited | High wear, low to medium impact scenarios; preferred for extreme wear environments |
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FAQ:
What is NM400 steel?
NM400 Plates is a high-strength, wear-resistant steel known for its superior durability and toughness. NM400 is a Chinese GB standard steel grade. The NM 400 material is widely used in industries where resistance to abrasion (abrasion resistant) is important, such as in the construction and mining sectors.
Is NM400 the same as AR400?
No. NM400 and AR400 are both 400 HB-class wear plates, but they are not exactly the same grade or standard.
Is NM400 equivalent to AR400?
NM400 may be used as an AR400 alternative in many wear applications, but the MTC and project requirements should be checked first.
What is the hardness of NM400 vs AR400?
NM400 is commonly about 370–430 HBW, while AR400 is commonly about 360–444 BHN.
Can NM400 replace AR400 for liners and chutes?
Yes. In many sliding abrasion applications, NM400 can be considered for liners, chutes, hoppers, and similar wear parts.