17-4 PH vs 304 Stainless Steel plate -What's the Difference？

What is 17-4 PH Stainless Steel Plate?

17-4 PH stainless steel plate is a precipitation-hardening martensitic stainless steel, containing 15–17% chromium, 3–5% nickel, 3–5% copper, and a small amount of niobium, with a low carbon content (≤0.07%). It undergoes solution annealing (around 1040°C followed by quenching) and age hardening (at 480–620°C) to form fine copper-rich precipitates, significantly increasing its strength. It offers tensile strength exceeding 1100 MPa, combining high strength with moderate corrosion resistance. Common applications include aerospace, petrochemical, and other high-strength environments. However, its resistance to chloride-induced pitting is lower than 304, making it more suitable for low-chloride conditions.

 

What is 304 Stainless Steel Plate?

304 stainless steel plate is a widely used austenitic stainless steel, containing 18–20% chromium and 8–10.5% nickel, with a maximum carbon content of 0.08%. Its austenitic structure makes it non-magnetic in the annealed condition, with excellent ductility, and it is easy to form and weld. It cannot be hardened by heat treatment, but cold-worked properties can be restored by solution annealing. 304 is widely applied in food processing equipment, home appliances, and construction, offering better corrosion resistance than 200 series stainless steels at a moderate cost, making it a mainstay grade in industry.

Specifications & Standards

Grade	Type	ASTM	EN	UNS	Common Forms
17-4PH	Precipitation-hardening	ASTM A564	1.4542	S17400	Bars, forgings, fasteners
304	Austenitic	ASTM A240	1.4301	S30400	Sheets, pipes, coils

Chemical Composition

Element (%)	17-4PH	304
Chromium (Cr)	15–17.5	18–20
Nickel (Ni)	3–5	8–10.5
Copper (Cu)	3–5	–
Molybdenum (Mo)	–	–
Carbon (C)	≤0.07	≤0.08
Niobium (Nb)	0.15–0.45	–

 Mechanical Properties

Property	17-4PH (H900 Condition)	304 (Annealed)
Tensile Strength	1,310 MPa (190 ksi)	515 MPa (75 ksi)
Yield Strength	1,170 MPa (170 ksi)	205 MPa (30 ksi)
Elongation	10%	40%
Hardness	40–45 HRC	70–90 HRB

 

What is the difference between PH and stainless steel?

Precipitation-hardening stainless steels (often called PH steels) offer similar characteristics to stainless steels and nickel alloys but with one fundamental difference. Small traces of aluminium, phosphorus, copper and titanium is included in the alloying mix.

 

Corrosion Resistance
17-4 PH, as a precipitation-hardened martensitic stainless steel, performs well in mild environments like air and water, but due to its lower chromium content (15–17%), it is less resistant to chloride corrosion than 304.

 

Heat Treatment
17-4 PH requires precipitation hardening, involving solution annealing followed by aging at 480–620°C, forming copper precipitates that boost tensile strength beyond 1100 MPa.
In contrast, 304 cannot be hardened by heat treatment; it only undergoes solution annealing (1010–1120°C water quench) to restore ductility and corrosion resistance after cold working, with no significant increase in strength.

Machinability and Fabrication
17-4 PH offers good machinability in the annealed condition, but becomes more difficult to machine after hardening, requiring sharp tooling and low speeds.
304 stainless steel, with high ductility and low work hardening rate, is easier to process, form, and weld in the annealed condition.
 

Need high-strength or corrosion-resistant stainless steel plates?

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(What GNEE Offers)：
✅ Full range of 17-4 PH & 304 stainless steel plates, from 3mm to 100mm thickness
✅ Custom sizes with laser cutting, waterjet cutting, and shearing
✅ Surface finishes: 2B, No.1, Brushed, Mirror Polish, or Custom
✅ Heat treatment services: Solution annealing, age hardening (for 17-4 PH)
✅ Mill Test Certificates (EN 10204 3.1/3.2) and third-party inspections (SGS, BV)
✅ Fast global shipping with seaworthy wooden pallets and protective packaging

 

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