NM550 / NM550D / NM550E Abrasion Resistant Steel Plate

⚙️ Chinese high strength wear-resistant steel for construction machinery — GB/T 24186-2022
🔥 Delivery: Quenched | Quenched+Tempered | TMCP+Tempered | Tempered | Hot rolled

📌 Designation method (GB/T 24186-2022)

The designation consists of the pinyin initial letters "NM" for "wear-resistant" and the specified surface Brinell hardness value. For steel requiring low-temperature toughness, the designation includes the quality class symbol (D, E).

Example 1: NM550 — NM: wear-resistant; 550: nominal surface Brinell hardness (HBW).

Example 2: NM550D — D grade: impact test temperature -20°C.

Example 3: NM550E — E grade: impact test temperature -40°C.

📏 Thickness Range

NM550 / NM550D / NM550E: Thickness ≤100 mm (per GB/T 24186-2022 Table 1)

🧪 Chemical Composition (mass fraction / %) — Standard Grade (Table 2)

Grade C ≤ Si ≤ Mn ≤ P ≤ S ≤ Cr ≤ Ni ≤ Mo ≤ Ti ≤ B Als ≥
NM550 0.38 0.70 1.70 0.020 0.010 1.50 1.50 0.70 0.05 0.0005~0.006 0.010

🧪 Chemical Composition — Low-Temperature Toughness Grades D/E (Table 3)

Grade C ≤ Si ≤ Mn ≤ P ≤ S ≤ Cr ≤ Ni ≤ Mo ≤ Ti ≤ B Als ≥ CEV ≤ (≤50mm) CEV ≤ (>50mm)
NM550D / NM550E 0.38 0.70 1.70 0.015 0.005 1.50 1.50 0.70 0.05 0.0005~0.006 0.015 0.72 0.82
ⓘ CEV formula: CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15. D/E grades have stricter P, S limits for low-temperature toughness.

📊 Brinell Hardness (GB/T 24186-2022 Table 4)

Grade Thickness (mm) Surface Brinell Hardness (HBW) Center Section Hardness (HBW)
NM550 / NM550D / NM550E ≤70 520~580 475~580
NM550 / NM550D / NM550E >70~100 500~580 —

📊 Impact & Tensile Properties

Grade Thickness (mm) Longitudinal Impact Energy KV2 (J) Tensile Rm (MPa) Elongation A (%)
NM550 ≤70 — (not required) By agreement By agreement
NM550D ≤70 By agreement (test temperature -20°C) By agreement By agreement
NM550E ≤70 By agreement (test temperature -40°C) By agreement By agreement
NM550 / D/E >70~100 By agreement By agreement By agreement
📌 Note: Per GB/T 24186-2022 Table 5 and Table 6, tensile strength, elongation and impact energy for NM550/NM550D/NM550E shall be agreed upon between the supplier and buyer and specified in the contract. Brinell hardness (520~580 HBW) is the guaranteed property.
🔬 Impact specimen size (per 7.4.2.4): Standard specimen 10mm × 10mm × 55mm. When insufficient to prepare standard specimen, 7.5mm × 10mm × 55mm or 5mm × 10mm × 55mm specimens shall be used.
⚙️ Delivery condition: quenched; quenched+tempered; TMCP+tempered; tempered or hot rolled (as agreed).
⚠️ Bend test (per Table 7): Not applicable to NM550 and NM550D/E.

⚙️ Technical requirements (GB/T 24186-2022)

7.1.2 On the premise of ensuring the steel properties, the alloying elements Cr, Ni, Mo specified in Table 2 and Table 3 may be added individually or in combination. Other alloying elements not specified in Table 2 and Table 3 may also be added. Their alloying elements and contents shall be indicated in the quality certificate.

7.1.3 When Cu is present as a residual element in the steel, its content shall not be greater than 0.30%; the As content shall not be greater than 0.08%. If the supplier can guarantee it, analysis is not required.

7.1.4 The carbon equivalent of steel requiring low-temperature toughness shall comply with the requirements of Table 3. The carbon equivalent is calculated according to formula (1):
CEV = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15

7.1.5 When using total aluminum (Alt) content calculation, the Alt content shall not be less than 0.015%, and for steel requiring low-temperature toughness (D/E grades), the Alt content shall not be less than 0.020%.

7.1.6 After negotiation between the supplier and the buyer and specified in the contract, the chemical composition of TiC-reinforced steel shall comply with Appendix A.

7.1.7 When the buyer requires finished product chemical composition analysis, the allowable deviation of the finished product chemical composition shall comply with the provisions of GB/T 222.

7.2 Smelting method
The steel shall be smelted in a converter or electric furnace and subjected to ladle refining.

7.3 Delivery condition
The steel shall be delivered in the quenched, quenched + tempered, TMCP + tempered condition, or in the hot-rolled condition (hot-rolled steel before heat treatment).

⚖️ NM550 vs AR550 / Hardox 550 — Global Grade Comparison

Parameter NM550 (China GB/T 24186) AR550 / Hardox 550 Comparison
Surface Hardness (HBW) 520~580 (≤70mm)
500~580 (>70~100mm)		 520~580 Equivalent range
Tensile Strength (MPa) By agreement (optional) ≥1600 (typical) Consult supplier
Elongation (%) By agreement (optional) ≥7 (typical) Consult supplier
Impact Toughness (D/E grade) By agreement (-20°C / -40°C) By agreement Both by agreement
Carbon Equivalent (CEV) 0.72~0.82 (D/E grade) 0.70~0.80 Similar weldability
Bend Test (90°) Not applicable (per Table 7) Not recommended Bending not recommended
Typical Applications Ultra-high wear: crusher liners, slurry lines, extreme abrasion Same applications globally Fully interchangeable
⏱️
Service Life Extension
Field data indicates NM550 extends service life by 800%~1200% in extreme sliding abrasion applications compared to structural steel, directly reducing maintenance frequency and component replacement intervals.
💰
Total Cost of Ownership
Despite higher procurement cost, the total cost of ownership is 60%~80% lower for NM550 in high-wear environments due to extended operational life and reduced downtime.
🏗️
Design Consideration
Select NM550 for extreme abrasion conditions where maximum hardness is required. For thickness >70mm, hardness range is 500~580 HBW. Bend test not applicable. Tensile and impact properties to be agreed upon with supplier.

📋 Standards and Inspection — GB/T 24186-2022

📄
Applicable Standard
GB/T 24186-2022
Engineering machinery high strength abrasion resistant steel plate and strip
🔍
Inspection Items (per Table 8)
  • Chemical composition (1 sample per heat)
  • Surface Brinell hardness (1 sample per batch) — 520~580 HBW (≤70mm) / 500~580 HBW (>70~100mm)
  • Impact test for D/E grades — values by agreement
  • Flatness — Class H per GB/T 709-2019 (or L / PF.A by agreement)
🎯
Sampling & NDT
Sampling: One sample per 60 tons max. per batch.
NDT: Available upon agreement — standard and acceptance level to be specified in contract.

🔥 Welding & Processing Notes — Practical Guidelines

✅ Weldability
Acceptable with low-hydrogen process (SMAW, GMAW, FCAW).
Consumables: ISO 18275 E69X X X / AWS A5.5 E11018M.
HAZ hardness limit: ≤400 HBW for field welding.
Consult welding procedure specification.
🌡️ Preheat Requirement
Required for thickness ≥20mm.
Minimum preheat: 200°C~250°C (CEV ~0.72~0.82)
Interpass temperature: ≤250°C
For restrained joints: up to 250°C.
✂️ Cutting Methods
• Plasma cutting (recommended ≤50mm)
• Abrasive waterjet — minimal HAZ (recommended)
• Laser cutting with preheating
• Oxy-fuel — with preheat, hardened edge up to 4mm
🛠️ Post-cut treatment: HAZ removal by grinding is recommended. Stress relief at 550°C~600°C for 2 hours if dimensional stability is critical. Bending is not recommended for NM550 due to high hardness.
📘 NM550 / NM550D / NM550E Approximate Grade Lookup Table →
📄 NM550 / NM550D / NM550E technical data sheet — CEHE Steel — Compiled from GB/T 24186-2022
Mill test certificates available upon request. Third-party inspection accepted.