UNS S45000 Hardness: 278-410 Brinell Guide

UNS S45000 Hardness: 278-410 Brinell Guide

Published: November 7, 2025 | Updated: November 7, 2025By Gangsteel Engineering Team – 25+ Years in Stainless Steel Export Excellence

Hardness is a critical property in stainless steels, dictating everything from wear resistance to machinability, and for UNS S45000—a precipitation-hardening martensitic grade—the Brinell range of 278-410 HB offers a sweet spot for demanding applications. As a premier producer and exporter based in China, Gangsteel has melted, processed, and shipped thousands of tons of UNS S45000 (also known as Custom 450 or XM-25) to global clients in aerospace, oil & gas, and medical industries. If you've ever puzzled over how to hit that ideal hardness for a turbine blade or surgical tool, or why 278-410 HB makes this grade so versatile, this guide is your roadmap. We'll explore the hardness specifics, how it's achieved, influencing factors, and practical tips, all drawn from our mill's daily operations and client feedback.

Imagine a scenario from our 2024 records: a U.S. aerospace supplier needed UNS S45000 bars hardened to 350 HB for landing gear components. Our tailored precipitation aging process not only nailed the range but boosted fatigue life by 25%, as confirmed by their cyclic tests. UNS S45000 isn't your standard martensitic like 410—it's age-hardenable, meaning you can machine it soft then harden it via low-temp aging for properties that rival more exotic alloys. In this comprehensive guide, we'll break down the 278-410 HB Brinell window, link it to overall properties, cover applications, and answer common questions. Grounded in standards like ASTM A564 and our ISO-certified testing, this isn't abstract—it's actionable insight for your next spec.

What is UNS S45000? A Quick Overview

UNS S45000, commonly branded as Custom 450, is a precipitation-hardening (PH) martensitic stainless steel developed for high strength with excellent corrosion resistance and toughness. Unlike traditional martensitics that harden via quenching, S45000 uses copper precipitates during aging to achieve its properties, allowing for distortion-free hardening at lower temperatures (around 480-620°C). This makes it easier to fabricate complex parts without post-machining warpage.

At its core, UNS S45000 offers:

• Corrosion Resistance: Similar to 304 in many environments, thanks to 14-16% Cr and Mo additions.
• Strength: Up to 1,310 MPa ultimate tensile after H900 aging.
• Toughness: Good impact values even at sub-zero temps.
• Density: 7.76 g/cm³, lighter than many martensitics for weight-sensitive uses.

Gangsteel produces this grade in bars, plates, sheets, and forgings per ASTM A564, A693, and AMS 5864, with dual certs for global compliance. Its age-hardening nature is key to the hardness guide: start soft (around 270 HB annealed), then age to 278-410 HB depending on condition.

The Brinell Hardness Range: 278-410 HB Explained

Brinell hardness (HB) measures resistance to indentation, and for UNS S45000, the 278-410 HB range spans its most common heat-treated conditions, making it adaptable for various uses. This range corresponds to Rockwell C (HRC) 28-44, offering a spectrum from moderately hard (for machinability) to very hard (for wear).

How Hardness is Achieved

• Annealed/Condition A: ~270-280 HB – Soft for forming/machining; solution treated at 900-950°C, air cooled.
• Aged Conditions:
  • H900 (480°C/4hrs): 410-440 HB – Max hardness/strength; for high-wear parts, but lower ductility.
  • H1000 (540°C/4hrs): 360-390 HB – Balanced; good strength with better toughness.
  • H1150 (620°C/4hrs): 278-320 HB – Softer for max ductility; ideal for impact-heavy uses.
• Over-Aging: Beyond H1150 (e.g., double aging), hardness drops below 278 HB for specialized toughness.

Factors influencing hardness:

• Aging Time/Temp: Higher temp/longer time softens (reduces HB by 20-50 per 50°C increase).
• Section Thickness: Thicker parts (>50mm) may need adjusted times for uniform HB.
• Prior Work: Cold working before aging can boost HB by 10-20%.

From our lab tests, 350 HB (H950 condition) is a sweet spot for many clients—strong (1,100 MPa yield) yet tough (40 J impact at -40°C). Avoid over-aging, as HB <278 can compromise strength.

Full Properties of UNS S45000: Beyond Hardness

While hardness is key, UNS S45000's properties interlink for holistic performance.

Chemical Composition

Balanced for PH hardening via Cu precipitates.

PREN ~25-28 for good corrosion in mild acids/seawater.

Properties (H900 to H1150 Conditions)

Vary by aging; H1000 typical.

Gangsteel's lots often hit upper ends, with H1000 at 360 HB for balanced uses.

Physical Properties

• Density: 7.76 g/cm³
• Thermal Conductivity: 18-25 W/m·K
• Specific Heat: 460 J/kg·K
• Expansion Coefficient: 10.9 × 10^-6 /°C (20-100°C)
• Modulus: 200 GPa

Stable for thermal apps; magnetic in all conditions.

Hardness Optimization: Guide for Achieving 278-410 HB

To hit the range:

1. Solution Treat: 900-950°C, air cool to form martensite (soft ~270 HB).
2. Age: 480°C (H900, 410 HB) to 620°C (H1150, 278 HB) for 4 hours.
3. Test: Use Brinell (ASTM E10) for large parts; convert to HRC if needed (278 HB ~ HRC 28, 410 HB ~ HRC 44).
4. Factors: Thicker sections need longer soak; over-aging drops HB below 278.
5. Tips: For NACE, aim <352 HB; consult Gangsteel for custom cycles.

Common issue: Uneven hardness—solved by our uniform furnaces.

Corrosion and Fabrication Properties

Corrosion: Good in atmospheres, fresh water, mild acids; PREN 25 resists pitting better than 410. NACE-compliant for H2S. Weldable with matching fillers, minimal preheat; machinable at 60% of carbon steel in annealed state.

Applications and Equivalents

Uses: Aerospace (gears), medical (instruments), oil & gas (valves), where 278-410 HB provides wear without brittleness.

Equivalents: AMS 5864, EN 1.4594, Custom 450.

Gangsteel supplies for a turbine project at 350 HB, boosting efficiency.

Sourcing UNS S45000: Pricing and Tips

Price: $2,600-2,800 USD/ton FOB; custom hardening +$200/ton. MOQ 1 ton; lead 7-30 days. Certs: 3.1/3.2, third-party.

Why Gangsteel? Tailored hardness, global shipping.

FAQ: UNS S45000 Hardness and Properties Answered

Q: What is the Brinell hardness range for UNS S45000, and how is it achieved?A: UNS S45000's Brinell hardness typically ranges from 278-410 HB, depending on the aging condition. In the H1150 condition (aged at 620°C/4hrs), it's 278-352 HB for maximum ductility; in H900 (480°C/4hrs), it reaches 388-410 HB for peak strength. This range is achieved through precipitation hardening: solution treat at 900-950°C to dissolve precipitates, air cool to form martensite, then age to form copper-rich phases that harden the matrix. Gangsteel's process ensures uniformity, with tests showing <5% variation across sections—vital for consistent wear in applications like gears.

Q: How does hardness affect the properties and uses of UNS S45000?A: Higher hardness (e.g., 410 HB in H900) boosts wear resistance and strength (1,310 MPa tensile) but reduces ductility (10% elongation), suiting uses like cutting tools or high-abrasion parts. Lower hardness (278 HB in H1150) enhances toughness (41 J impact) and machinability, ideal for structural components like valves or shafts. The 278-410 HB range allows versatility—too low (<278) sacrifices strength, too high (>410) risks brittleness. In our experience, 350 HB (H1000) is optimal for aerospace, offering 1,070 MPa yield with 12% elongation for fatigue-prone parts.

Q: What are the full mechanical properties of UNS S45000 across hardness ranges?A: Mechanicals vary by condition: For 278-352 HB (H1150), tensile 965 MPa min, yield 795 MPa min, elongation 14% min, impact 41 J min at -46°C. For 388-410 HB (H900), tensile 1,310 MPa min, yield 1,170 MPa min, elongation 10% min, impact 20 J min. Hardness correlates inversely with ductility but directly with strength. Gangsteel's data sheets show mid-range (H1000, ~360 HB) at 1,070 MPa tensile, 965 MPa yield, 12% elongation—balanced for most uses, with our tests confirming 30-40% better fatigue than softer grades.

Q: How does the chemical composition contribute to UNS S45000's hardness?A: UNS S45000's chemistry—C 0.05 max, Cr 14-16%, Ni 5-7%, Mo 0.5-1%, Cu 1.25-1.75%, Nb 0.15-0.45%, Mn/Si 1 max, P/S 0.03 max, Fe balance—enables precipitation hardening via Cu phases, driving the 278-410 HB range. Low C prevents over-hardening, Cr/Mo enhance corrosion without affecting hardening, Ni stabilizes for toughness, and Nb refines grains for uniform hardness. The Cu is key: during aging, it forms precipitates that pin dislocations, increasing hardness by 100-150 HB. Gangsteel's low-impurity melts (<0.01% P/S) ensure consistent hardening, avoiding hotspots.

Q: What heat treatment achieves the 278-410 Brinell hardness in UNS S45000?A: Start with solution annealing at 900-950°C (1 hr/25mm thickness), air cool to dissolve phases (soft ~270 HB). Then age: H900 (480°C/4hrs) for 388-410 HB max hardness; H1150 (620°C/4hrs) for 278-352 HB max ductility; intermediates like H1000 (540°C/4hrs) for ~360 HB balance. Aging time/temp inversely affects hardness—over-aging drops below 278 HB. For NACE, aim <352 HB. Gangsteel's vacuum furnaces achieve precise control, with full cycles documented in our data sheets for repeatability.

Q: What are common applications for UNS S45000 at different hardness levels?A: At 278-352 HB (softer), it's used for ductile parts like medical instruments or pump shafts needing impact resistance. At 388-410 HB (harder), it suits wear-heavy apps like aerospace gears or mining tools. Mid-range (350 HB) is popular for oil & gas valves, offering strength without brittleness. Gangsteel has supplied for U.S. landing gear at 410 HB (high wear) and Brazilian reactors at 300 HB (toughness focus), with hardness tailoring extending service life 25-40% in corrosives.

Q: How does UNS S45000's hardness compare to other stainless steels?A: UNS S45000's 278-410 HB is higher than austenitic 304 (160-200 HB, better corrosion but softer) but tunable like 17-4PH (310-450 HB, similar but pricier). Vs. 410 martensitic (200-400 HB), it offers better toughness at equivalent hardness due to Ni/Mo. The range allows matching duplex strength without duplex cost. In tests, Gangsteel's S45000 at 350 HB outperforms 410 in impact by 50% while equaling 304's machinability.

Q: Where can I get a full PDF data sheet for UNS S45000?A: Gangsteel provides customizable PDF data sheets with chem/mech details, heat treat guides, and mill test reports. Contact us for a free download—includes our production variants with enhanced properties. For sourcing, our stock ranges 1-200mm thick at $2,600-2,800/ton FOB, with equivalents like EN 1.4594 available.