What is NM500 wear resistant steel plate?
China's wear-resistant steel grade naming system adopts the concise logic of "NM + hardness value," covering seven basic grades from NM300 to NM600, with a hardness range extending from 270 HBW to 640 HBW. NM500, with a hardness range of 470~540 HBW, is positioned as a high-strength wear-resistant grade, suitable for harsh wear scenarios such as hard rock mining and vibrating screen plates.
NM500 is a high-strength wear-resistant steel plate grade in China's national standard system. Its name has a clear engineering meaning: "N" represents "wear-resistant," "M" represents "wear-resistant," and the number "500" indicates that the steel plate's average Brinell hardness value reaches approximately 500 HBW. As a high-end grade in the wear-resistant steel series, NM500 is specifically designed for heavy-duty wear conditions in engineering machinery, mining machinery, and other applications. With its excellent wear resistance, it can provide effective protection for equipment in wear-resistant areas, extending equipment lifespan and reducing maintenance downtime and financial investment.
mplementation Standards and Systems
The main standard for NM500 wear-resistant steel plates is GB/T 24186-2009 "High-strength Wear-resistant Steel Plates for Engineering Machinery," which applies to steel plates with a thickness not exceeding 80mm and primarily serves wear-resistant structural components for engineering machinery in mining, construction, and agriculture. In 2022, this standard was updated to GB/T 24186-2022, further refining the technical requirements and quality grade system for wear-resistant steel.
Regarding quality grades, based on the requirements for low-temperature impact toughness, the NM series adds D/E grade designations after the basic grade: Grade D guarantees an impact energy of 21~24 J at -20℃, suitable for mining equipment in northern winters; Grade E still achieves an impact energy of 21~24 J at -40℃, making it ideal for equipment in extremely cold regions such as Northeast China and Siberia.
Chemical composition and mechanical properties
1.Chemical properties
The chemical composition of NM500 is precisely designed to ensure high hardness while minimizing excessive brittleness. Its typical chemical composition range and the roles of key elements are shown in the table below.
| Element | Content Range (mass fraction, %) | Main Function / Role |
|---|---|---|
| Carbon (C) | 0.20–0.38 | Provides base hardness; forms wear‑resistant carbides with alloying elements |
| Silicon (Si) | 0.30–0.70 | Deoxidation and solid‑solution strengthening; improves oxidation resistance and strength |
| Manganese (Mn) | 1.00–1.80 | Increases hardenability, ensures core hardening of thick plates, and improves toughness |
| Phosphorus (P) | ≤0.025 | Strictly controlled harmful element; avoids low‑temperature brittleness and weld cracks |
| Sulfur (S) | ≤0.015 | Lowers hot workability and toughness; must be kept at very low levels |
| Chromium (Cr) | 0.80–1.50 | Forms wear‑resistant chromium carbides; improves hardenability and corrosion‑wear resistance |
| Molybdenum (Mo) | 0.20–0.60 | Refines grain size; enhances high‑temperature strength and tempering stability |
| Nickel (Ni) | 0.50–1.00 | Key toughness element; reduces ductile‑brittle transition temperature; ensures low‑temperature impact resistance |
| Vanadium/Niobium (V/Nb) | ≤0.10 (total) | Added in trace amounts to refine grains; further increases strength and wear resistance |
2.Mechanical properties
The mechanical properties of NM500 embody a balance of "high hardness + high strength + limited toughness".
| Property | Typical Value | Remarks |
|---|---|---|
| Brinell hardness (HBW) | 480–525 (for thickness ≤70 mm) | Key wear‑resistance indicator; surface hardness slightly decreases when thickness exceeds 70 mm |
| Tensile strength (MPa) | ≥1300 | Far exceeds ordinary structural steel; ensures no deformation under heavy loads |
| Yield strength (MPa) | ≥500 | Strong resistance to plastic deformation |
| Elongation after fracture (%) | ≥7–16 | Lower than lower‑grade wear‑resistant steels, but sufficient to avoid brittle fracture |
| Impact absorbed energy (-20℃, J) | ≥24 |
Guarantees resistance to brittle fracture in low‑temperature environments |
NM500
Production process flow
The production process of NM500 wear-resistant steel plate integrates several key aspects of modern metallurgical technology. Its core objective is to obtain a uniform, high-hardness martensitic microstructure through precise microstructural control.
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 and Controlled Cooling: High-precision controlled rolling technology is employed. By precisely controlling the rolling passes, deformation amount, and temperature, the grain structure is refined. The final rolling temperature has a significant impact on the microstructure of medium-manganese martensitic NM500 steel, directly affecting its mechanical properties after heat treatment.
Quenching (Core Step of Tempering): This step is crucial for achieving the high hardness of NM500. Online quenching is widely adopted to rapidly cool rolled steel plates, transforming the austenitic structure into high-hardness martensite. In recent years, advanced manufacturers have introduced a two-stage temperature-controlled quenching and cooling process: a high-pressure stage followed by a low-pressure stage. In this process, the high-pressure stage rapidly cools the steel to below 500°C at a rate greater than the critical cooling rate to induce the martensitic transformation, while the low-pressure stage uses intermittent cooling at medium to low rates. This controls the uniformity of martensite dimensions, resulting in excellent formability.
Tempering: After quenching, tempering heat treatment is performed (typically at 200-300°C for 1-2 hours) to eliminate quenching stress, improve toughness, stabilize microstructure, and prevent excessive hardness loss.
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
NM500 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, NM500 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 the difference between Hardox 500 and NM500?
Hardness: NM500 typically has a hardness range of around 470-540 HBW (Brinell hardness), while Hardox 500 typically falls within the range of 470-530 HBW. The hardness level indicates their ability to withstand abrasive wear and impact.
What is the difference between AR500 and NM500?
AR500: Higher carbon (C: ~0.38–0.45%), chromium (Cr: ~1.5%), and boron (B: 0.0005–0.006%) for enhanced hardness and corrosion resistance . NM500: Lower carbon (C: ≤0.38%), added nickel (Ni: ≤1.0%) and molybdenum (Mo: ≤0.65%) for balanced weldability and toughness.
Can NM500 be welded?
NM500 is weldable but demands strict welding procedures. It needs preheating at 100–150°C, matched low-hydrogen welding materials, and proper post-weld tempering treatment to guarantee welding quality.