NM450 vs JFE-EH450 – Composition, Heat Treatment, Properties, and Applications

Introduction

NM450 and JFE-EH450 are commercially available abrasion-resistant (AR) steels specified for heavy-wear environments where elevated hardness and good toughness are required. Engineers, procurement managers, and manufacturing planners commonly decide between them when balancing wear life, weldability, fabrication costs, and supply chain considerations. Typical decision contexts include selecting a plate for dump truck bodies and liners (wear vs. weight), choosing material for earthmoving buckets (toughness and impact resistance vs. hardness), or specifying sheet for chutes and hoppers (cost and availability vs. service life).

The principal distinction between these two grades lies in their alloying and mill-design heat-treatment strategies: one is often produced to meet a domestic AR-steel specification with flexibility for mill tailoring, while the other is a proprietary grade from a manufacturer with defined composition limits and controlled processing to reach targeted mechanical and microstructural characteristics. That compositional and processing difference drives nuanced variation in hardenability, toughness, and weldability that matters in design and fabrication.

1. Standards and Designations

• NM450
• Commonly referenced in proprietary or national AR steel product lines (often produced to meet customers’ hardness and toughness requirements rather than a single international standard). It is classified as a quenched-and-tempered low-alloy/high-hardness wear-resistant steel.
• JFE-EH450
• JFE’s EH series (e.g., EH400, EH450) are proprietary abrasion-resistant steels produced by JFE Steel Corporation. EH450 is a quenched-and-tempered, high-hardness wear-resistant steel with controlled alloying and heat treatment.
• Relevant standards and families in which comparable grades appear:
• ASTM/ASME: AR400/AR450 are commonly referenced but are product-type designations rather than strict chemical standards.
• JIS: Japanese Industrial Standards reference wear-resistant steels and proprietary grades from Japanese mills.
• EN: EN 10163 / EN 10029 / EN 10051 address structural or wear-resistant steels in broader terms.
• GB: Chinese national standards and manufacturer specifications may list NM-series grades.
• Classification: Both are low-alloy, quenched-and-tempered high-hardness steels (not stainless, not tool steels, not conventional HSLA in the structural sense — they are AR steels designed for wear resistance and acceptable toughness).

2. Chemical Composition and Alloying Strategy

Table: presence/typical role of alloying elements (qualitative; consult mill certificate for exact values)

Explanation - Both grades are tailored to achieve a target hardness (~450 HB) through a combination of carbon, manganese, and small alloying elements (Cr, Mo, Ni) plus thermal processing. The manufacturer-specific approach (proprietary limits and microalloying additions) affects hardenability (ability to form martensite/bainite through section thickness), tempering resistance (retention of hardness after temper), and low-temperature toughness. - Impurity elements (P, S) are minimized because they promote embrittlement and reduce impact toughness in high-hardness steels. Microalloying elements (V, Nb, Ti) are used primarily for grain size control and precipitation strengthening, helping toughness without excessive carbon.

3. Microstructure and Heat Treatment Response

• Typical microstructure: Both NM450 and JFE-EH450 achieve wear resistance chiefly through a tempered martensitic and/or lower bainitic microstructure produced by controlled quench and temper cycles. The exact phase balance (tempered martensite vs. bainite) depends on composition, section thickness, and cooling rate.
• Response to processing:
• Normalizing: Refines grain size and homogenizes microstructure but will not produce the target hardness; used as a preparatory step.
• Quenching & tempering: Primary route to produce ~450 HB. The quench creates hard martensitic/bainitic structure; tempering adjusts toughness and relieves stresses. Tempering temperature and time significantly influence final impact toughness and hardness tradeoff.
• Thermo-mechanical processing: Controlled rolling followed by accelerated cooling can produce fine bainite or tempered martensite with enhanced toughness — a strategy sometimes used in proprietary products to get higher toughness at a given hardness.
• Manufacturer differences: JFE’s EH series typically uses tightly controlled heat-treatment cycles and alloying to ensure consistent through-thickness properties; vendor-to-vendor variations in NM450 supplies can result in slightly different microstructures for the same nominal hardness.

4. Mechanical Properties

Table: qualitative comparison and typical target hardness

Notes - Absolute mechanical numbers vary with supplier, plate thickness, and specific heat-treatment. Hardness is the defining metric (450 HB class). Tensile and impact properties should be verified on the certified mill test report (MTR). - In general, a manufacturer with proprietary control (JFE) aims for a more consistent strength–toughness balance through composition and processing.

5. Weldability

• Considerations: Carbon equivalent and hardenability dictate preheat, interpass temperature, and risk of cold cracking. Microalloying elements and residual stresses also affect weld behavior.
• Common assessment formulas (interpret qualitatively; do not calculate without exact composition):
• Carbon equivalent (IIW form):
  $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$
• Pcm for weldability:
  $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
• Interpretation:
• Both grades will have moderate to elevated carbon equivalents versus mild steel; therefore preheat and controlled interpass temperatures are commonly required for full-penetration welds and to reduce cold-cracking risk.
• JFE-EH450, produced with tighter chemistry control, may offer more predictable welding parameters and consistent HAZ performance. NM450’s weldability depends on the specific supplier chemistry and section thickness.
• Use appropriate filler metals and welding procedures designed for high-hardness AR steels; consider preheat, low hydrogen processes, and post-weld tempering where necessary.

6. Corrosion and Surface Protection

• Both NM450 and JFE-EH450 are non-stainless low-alloy steels primarily selected for wear resistance, not corrosion resistance.
• Typical protection methods: painting, shot blasting plus primers, thermal spray coatings, and galvanizing for mild environments (note: galvanizing can be problematic with high-hardness steels due to thermal effects and possible embrittlement—consult supplier).
• PREN formula is not applicable for these non-stainless steels; for reference, stainless performance is often judged by:
  $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$
• Selection guidance: For combined wear and corrosive environments, consider overlays (hardfacing), sacrificial liners, or specifying a stainless wear-resistant alloy if corrosion is a key driver.

7. Fabrication, Machinability, and Formability

• Cutting: Plasma or laser cutting is common. High hardness requires appropriate consumables and slower feed rates; edge quality and heat-affected zones must be controlled.
• Bending/forming: Limited formability due to high hardness; forming prior to final heat treatment or using local heating techniques may be required. Sharp bending radii increase fracture risk.
• Machinability: Difficult relative to mild steel; tooling wear is higher. Use carbide tooling, reduced cutting speeds, and rigid setups.
• Finishing: Grinding and polishing to remove burrs and improve mating surfaces are common; hardfacing welds may be applied for localized wear protection.

8. Typical Applications

Selection rationale: Choose based on load type (sliding vs. impact), need for predictable through-thickness properties, cost constraints, and supplier support for welding/fabrication.

9. Cost and Availability

• NM450: Often available from multiple domestic mills; typically lower cost and more flexible in lead time for local sourcing. Quality and processing consistency can vary by supplier.
• JFE-EH450: Generally positioned as a premium, proprietary product with consistent material data and tighter process control. May cost more per tonne but offers predictable delivery and documentation. Availability depends on regional distribution and import considerations.
• Product forms: Plates, cut-to-length panels, and fabricated liners are common. Lead times and minimum order quantities vary by supplier.

10. Summary and Recommendation

Table: comparative snapshot (qualitative)

Recommendation - Choose NM450 if you need a cost-effective wear-resistant plate and can accept supplier variation, or if local supply chains and lower unit cost are primary drivers. It suits applications where frequent replacement is acceptable and where welding/fabrication procedures can be qualified locally. - Choose JFE-EH450 if you need higher confidence in through-thickness toughness, consistent mill-controlled chemistry, documented weld procedures, and traceable quality for critical or export applications. Prefer EH450 when predictable performance, reduced qualification effort, and supplier support justify a higher material cost.

Final note: For any critical application, obtain the mill test report, review exact chemical composition and heat-treatment records, and perform application-specific qualification welds and toughness tests. Material names (NM450, EH450) are product-type designations; proper specification should reference the supplier’s technical datasheet and acceptance criteria for hardness, impact energy, and weld procedure qualification.