17-4 PH vs 15-5 PH vs 13-8 MO Stainless Steel: Which High-Strength Grade Is Best for 2025?

Precipitation Hardening (PH) stainless steels are some of the strongest, toughest, and most corrosion-resistant stainless steels available. Among them, three grades dominate the aerospace, oil & gas, defence, marine, and high-performance engineering sectors:

⭐ 17-4 PH (UNS S17400)
⭐ 15-5 PH (UNS S15500)
⭐ 13-8 MO (UNS S13800)

This blog provides a full comparison to help engineers, buyers, and designers choose the right grade in 2025.

What Are PH Stainless Steels and Why Are They So Strong?

Precipitation hardening stainless steels achieve strength through:

Age-hardening heat treatment
Martensitic microstructure
Alloying elements like Ni, Cu, Al, Mo

PH steels achieve:

Tensile strength up to 1400 MPa
High fatigue resistance
Better corrosion performance than martensitic steels

Chemical Composition Comparison

Element	17-4 PH	15-5 PH	13-8 MO
Chromium	15–17%	14–15.5%	12–14%
Nickel	3–5%	3.5–5.5%	7–8%
Copper	3–5%	2.5–4%	–
Molybdenum	–	–	2–2.5%
Aluminum	~0.2%	~0.2%	~0.1%

Mechanical Properties Comparison

Tensile Strength (H900)

17-4 PH: ~1310 MPa
15-5 PH: ~1310–1370 MPa
13-8 MO: >1400 MPa

Toughness

17-4 PH: Good
15-5 PH: Very High
13-8 MO: Highest

Hardness (HRC)

17-4 PH: 40–44
15-5 PH: 40–45
13-8 MO: 45–49

Corrosion Resistance Comparison

17-4 PH

Good corrosion resistance
Suitable for most industrial environments

15-5 PH

Better SCC resistance
Improved transverse corrosion resistance

13-8 MO

Best chloride SCC resistance
Ideal for marine & aerospace

Weldability Comparison

Grade	Weldability
17-4 PH	Good (aging required)
15-5 PH	Better weldability
13-8 MO	Good (controlled atmosphere)

Applications of Each Grade

17-4 PH

Valves, pump shafts
Marine shafts
Aerospace fasteners

15-5 PH

Aircraft structural parts
Landing gear
High-pressure valves

13-8 MO

Jet engine components
Nuclear reactor parts
Chemical processing equipment

Cost Comparison

17-4 PH: Lowest cost
15-5 PH: Medium cost
13-8 MO: Highest cost

Conclusion

Each PH stainless steel has specific advantages. 17-4 PH delivers cost-effective strength, 15-5 PH offers superior toughness, and 13-8 MO provides maximum performance in critical applications.

FAQ's

Which is stronger — 17-4 PH or 15-5 PH?

Both are similar, but 15-5 PH has better toughness and slightly better strength consistency.

Is 13-8 MO better than 17-4 PH?

Yes — in toughness, SCC resistance, strength, and fatigue performance.

Which grade is most used in aerospace?

15-5 PH and 13-8 MO.

Can 17-4 PH be welded?

Yes, but requires post-weld heat treatment to restore strength.

Which grade is best for marine use?

13-8 MO, followed by 17-4 PH (when properly coated).

At Moksh Tubes & Fittings LLP, we’re dedicated to making your purchases seamless — offering expert advice, a wide inventory of certified products, and global support for every order, large or small.

Get in Touch