NM400 vs JFE-EH400 – Composition, Heat Treatment, Properties, and Applications

Introduction

NM400 and JFE-EH400 are widely used high-hardness, quenched-and-tempered wear-resistant steels specified for applications where abrasion resistance is primary. Procurement and engineering teams often decide between them when balancing cost, consistency of mechanical properties, weldability, and delivery chain requirements. Typical decision contexts include selecting a lower-cost, broadly available material for bulk wear parts versus specifying a premium producer grade where tighter mill control and documented toughness are required.

The principal practical distinction is that NM400 represents a class of wear-resistant steels commonly produced to Chinese/Asian specifications (a family of abrasion-resistant steels), while JFE-EH400 is a Japanese proprietary EH (Easy-Handled/Enhanced Hardness) series product from JFE Steel with documented process controls and product provenance. Because both target nominally the same hardness level (≈400 HB), they are compared frequently by designers and buyers for equivalence in chemistry, heat treatment response, mechanical performance, and fabrication behavior.

1. Standards and Designations

• NM400: Commonly supplied to Chinese/Asian standards and commercial specifications (e.g., GB/T and seller-specific certificates). It is a quenched-and-tempered high-hardness low-alloy steel classified as wear-resistant (not stainless). It sits in the category of HSLA variants engineered for abrasion resistance.
• JFE-EH400: Supplied under JFE proprietary designation “EH” series and may be referenced in JIS/JFE product literature. It is likewise a quenched-and-tempered, low-alloy abrasion-resistant steel (HSLA-type for wear service).

Classification: both are low-alloy, quenched-and-tempered wear-resistant steels (not tool steels, not stainless). They are typically referenced by end-use hardness (400 HB nominal).

2. Chemical Composition and Alloying Strategy

The exact chemistry of these steels varies by mill, plate thickness, and specific product option. The table below lists typical compositional ranges reported by mills and industry datasheets for NM400-class steels and for JFE-EH400. These are presented as representative ranges; always verify against the supplier’s mill test certificate (MTC) for the order.

Element (wt%)	NM400 — Typical range	JFE‑EH400 — Typical range
C	0.12 – 0.22	0.10 – 0.20
Mn	0.8 – 1.6	0.7 – 1.4
Si	0.2 – 0.9	0.2 – 0.6
P	≤ 0.035	≤ 0.03
S	≤ 0.035	≤ 0.02
Cr	0.2 – 0.7	0.2 – 0.7
Ni	trace – 0.5	trace – 0.4
Mo	trace – 0.25	trace – 0.2
V	0 – 0.08	0 – 0.08
Nb	0 – 0.03	0 – 0.03
Ti	0 – 0.02	0 – 0.02
B	0 – 0.002	0 – 0.002
N	typically ≤ 0.015	typically ≤ 0.015

Explanation: - Carbon, manganese, and silicon provide baseline strength and hardenability. Slightly higher Mn in some NM400 variants increases hardenability but may reduce weldability if not controlled. - Microalloying elements (V, Nb, Ti) refine grain and improve strength–toughness balance, especially after controlled rolling or tempering. - Small additions of Cr, Mo, and sometimes Ni increase hardenability and temper resistance, aiding uniform hardness through thicker sections. - Trace boron can be used to improve hardenability when present in controlled low-levels.

3. Microstructure and Heat Treatment Response

Typical microstructures for both grades after commercial quench-and-temper processing are tempered martensite with some retained bainitic constituents; microstructure depends on alloy content, cooling rate, and plate thickness.

• NM400: Produced by a range of mills with varying thermo‑mechanical control. Typical microstructure after quenching and tempering is tempered martensite with a dispersion of carbides and fine precipitates if microalloyed elements are present. Variants produced by thermo-mechanical controlled processing (TMCP) can have finer prior austenite grain size, improving toughness.
• JFE‑EH400: JFE emphasizes controlled chemistry and heat treatment to achieve a consistent tempered martensitic matrix with minimized segregation and controlled carbide precipitation. The EH production route typically yields a homogeneous microstructure with predictable hardness and toughness performance across supplied thickness ranges.

Heat-treatment effects: - Normalizing followed by tempering can improve toughness but may lower hardness if tempering parameters are not adjusted. - Quenching & tempering (Q&T) is the commercial route to reach ~400 HB; tempering parameters control the toughness–hardness trade-off. - Thermo‑mechanical controlled processing (TMCP) prior to Q&T yields improved toughness at equivalent hardness due to grain refinement and precipitation control.

4. Mechanical Properties

Mechanical properties vary with thickness, exact chemistry, and the mill’s heat-treatment practice. The table below gives typical property bands for quenched-and-tempered 400 HB class plates.

Property	NM400 — Typical	JFE‑EH400 — Typical
Hardness (HBW)	360 – 440 (nominal 400 HB)	360 – 440 (nominal 400 HB)
Tensile strength (MPa)	~1000 – 1400	~1000 – 1400
Yield strength (0.2% proof, MPa)	~800 – 1200	~800 – 1200
Elongation (A5, %)	~8 – 16	~8 – 16
Charpy V-notch (room or specified temp, J)	Highly processing dependent; typical 20–80 J at room temp; low-temp rating varies	Typically comparable or superior consistency due to controlled processing

Interpretation: - Hardness is targeted to ~400 HB for both; tensile and yield ranges overlap significantly because the same hardness target is being met. - Differences emerge in consistency: JFE‑EH400 is generally specified and delivered with tighter control on toughness and property scatter, especially for critical applications. - For the same nominal hardness, higher alloying/hardenability enables thicker sections to reach target hardness; however, increased hardenability can reduce weldability if not managed.

5. Weldability

Weldability of these high-hardness steels is governed by carbon content, combined alloying (hardenability), thickness, and pre/post-weld heat treatments.

Relevant empirical indices: - Carbon Equivalent (IIW): $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - Pcm (International): $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$

Qualitative interpretation: - Both grades have moderate carbon and alloying; CE and Pcm can be modest to moderate depending on exact chemistry. Higher CE/Pcm indicates higher cold-cracking risk and need for preheat or post-weld heat treatment (PWHT). - JFE‑EH400 often arrives with documented recommendations for preheat/PWHT and sometimes offers versions optimized for improved weldability (controlled low S, P, and tighter C ranges). - NM400 variants vary by mill—some are engineered for weldability (lower C, microalloying) while others prioritize hardenability and wear life. - Best practices: use low-hydrogen consumables, appropriate preheat, controlled interpass temperatures, and tempering PWHT when required by thickness or CE/Pcm thresholds. Qualification of welding procedure (WPS/PQR) is essential.

6. Corrosion and Surface Protection

These are non-stainless wear steels; intrinsic corrosion resistance is limited relative to stainless grades.

• Surface protection methods: painting, industrial coatings, metallizing, sacrificial overlays, or galvanizing for atmospheric protection (galvanizing may be limited by thickness and application). Hardfacing overlays (weld overlays) are frequently used to combine substrate toughness with surface wear resistance.
• PREN (pitting resistance equivalent number) is not applicable to non-stainless steels; for reference, PREN formula is: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$
• Use corrosion-resistant overlays or separate corrosion-resistant components when the service combines heavy wear and aggressive chemical or chloride environments.

7. Fabrication, Machinability, and Formability

• Cutting: Both grades are harder on consumables and tooling; plasma/Oxy-fuel/laser cutting are common; trimming may require post-weld grinding.
• Machinability: Low — these are hardenable steels; machining should be done in the soft-annealed condition if possible. Machining of quenched-and-tempered plates requires carbide tooling and reduced feed rates.
• Bending/forming: Cold forming of delivered quenched-and-tempered plate is limited; formability is low at hardness ~400 HB. Forming should be done in softer, pre-quenched conditions or components should be fabricated from softer blanks and then hardfaced or heat-treated to final hardness.
• Finishing: Grinding and dressing require appropriate abrasives and PPE due to particle generation; flame or plasma cutting require consideration of HAZ and residual properties.

8. Typical Applications

NM400 — Typical Uses	JFE‑EH400 — Typical Uses
Excavator buckets, liners, chutes, hoppers, dump truck beds, crushing equipment in applications where cost-effective abrasion resistance is required	Wear plates and liners for mining machinery, crushers, mill liners, and high-wear components where consistent performance and supplier traceability are prioritized
Agricultural equipment, earthmoving equipment, ore handling where frequent local replacement is acceptable	Critical rotating equipment wear parts, OEMs specifying mill-certified toughness and homogeneous properties for safety-critical installations
Hardfacing substrate (base steel for weld overlays)	Applications requiring validated toughness at temperature and controlled property scatter (e.g., large structural wear components)

Selection rationale: - Choose materials based on wear mode (sliding vs. impact-abrasion), required toughness, and whether localized repair via welding is expected. If impact-abrasion dominates, consider grades with proven toughness or use thicker overlays.

9. Cost and Availability

• NM400-class steels are widely produced by many mills, particularly in China and Asia, and are generally more cost-competitive in bulk plate form and local markets. Availability in common thicknesses and cut-to-size forms is broad.
• JFE‑EH400 is a branded product from a major Japanese mill and may command a premium due to stringent quality control, documented consistency, and export logistics. Availability is global but lead times and cost reflect the premium.
• Product form: Both are available as plates, but JFE product families may provide additional documentation (heat-treatment records, chemical analysis, toughness tests) that add value and cost.

10. Summary and Recommendation

Aspect	NM400	JFE‑EH400
Weldability	Variable; depends on mill chemistry and CE/Pcm	Typically well-documented with guidance; generally comparable or better controllability
Strength–Toughness balance	Good, variable with producer and process	Good with typically tighter control and consistency
Cost	Usually lower / more competitive	Typically higher (premium)
Availability	Broad, especially in Asia	Good, with brand-specific supply chain and documentation

Conclusion / Recommendations: - Choose NM400 if: cost and broad availability are primary drivers, application is dominated by abrasive wear rather than critical impact resistance, and the project tolerates higher variability or you can qualify the specific supplier. NM400 is a practical choice for bulk wear parts where frequent replacement and repair are anticipated. - Choose JFE‑EH400 if: you require tighter property control, documented mill traceability, and consistent toughness across thicknesses; the application is safety‑ or performance‑critical (e.g., heavy mining OEMs, large structures) or you prefer a branded supply with established technical support. JFE‑EH400 is preferable where weld procedure qualification and predictable low-temperature behavior are important.

Final note: Both grades are intended for wear resistance rather than corrosion resistance or extensive cold forming. For any procurement decision, obtain and review the supplier’s mill test certificates, specify required impact temperatures, WPS/PQR needs, and perform trial welds and field validations where service conditions are severe.