304 vs 17-4 PH Stainless
304 is the austenitic all-rounder: soft, ductile, weldable, non-magnetic and corrosion resistant, with a yield strength around 205 MPa annealed. 17-4 PH is a martensitic precipitation-hardening grade: a simple furnace age at 480 to 620 °C takes it from about 760 MPa yield in Condition A to well over 1100 MPa in H900, and it is magnetic throughout.
They rarely compete on corrosion, where 304 wins in most environments. They compete on strength. If a stainless part is yielding, wearing or flexing in 304, 17-4 PH in H900 or H1025 usually fixes it in the same envelope, at higher material cost and with more heat-treat steps.
| Property | 304 | 17-4 PH |
|---|---|---|
| Type | Austenitic | Martensitic precipitation-hardening |
| Chromium / Nickel | 18-20% / 8-10.5% | 15-17.5% / 3-5% |
| Key additions | None | 3-5% Cu, 0.15-0.45% Nb |
| Yield | 205 MPa (30 ksi) min, annealed | 1170 MPa (170 ksi) min, H900 |
| Tensile | 515 MPa (75 ksi) min, annealed | 1310 MPa (190 ksi) min, H900 |
| Hardness | ~80 HRB annealed | ~44 HRC H900; ~35 HRC H1150 |
| Elongation | 40% min | 10% min (H900) |
| Density | ~8.0 g/cm³ | 7.8 g/cm³ |
| Magnetic | No (annealed) | Yes |
| Heat treatment | None (anneal only) | Solution treat + age (H900 to H1150) |
| Typical uses | Sheet metal, tanks, food equipment | Shafts, valve parts, aerospace fittings, firearms |
Typical values for the stated conditions. Confirm against the mill certificate and your spec.
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Decision matrix
A check marks the side with the edge on that dimension.
| Dimension | 304 | 17-4 PH |
|---|---|---|
| Machining | Fair; gummy, work-hardens | ✓ Good in Condition A or H1150; fair at H900 hardness |
| Welding | ✓ Excellent; 308L filler | Good; weld in Condition A, re-age afterward; 17-4 filler |
| Forming | ✓ Excellent; deep draws, tight bends | Poor; limited even in Condition A |
| Strength | 205 MPa yield annealed | ✓ 1170 MPa yield H900, 725+ MPa H1150 |
| Corrosion resistance | ✓ Good in most atmospheres and foods | Fair to good; roughly 304 in H1150, below it at H900 |
| Finishing | ✓ Passivates, electropolishes, bright finishes | Passivates; usually left machined or bead blasted |
| Material cost | ✓ Baseline stainless | About 1.5-2.5x plus heat treat |
| Availability | ✓ Every form | Bar and plate common in Condition A and H1150; sheet limited |
Choose 304 when
- Sheet metal, tanks, enclosures and anything formed or deep drawn
- Heavy welding with no post-weld heat treatment
- Corrosion resistance is the reason for stainless and strength is secondary
- Non-magnetic behavior matters
Choose 17-4 PH when
- Stainless shafts, pins, fasteners, valve stems and fittings that would yield in 304
- Aerospace, medical or firearms parts specified to AMS 5643 or a listed H condition
- Wear resistance with corrosion resistance: 40-45 HRC is available in H900
- Dimensional stability after hardening matters; aging at H900 moves parts very little
Frequently asked questions
- Is 17-4 PH stronger than 304?
- Much stronger. Aged to H900, 17-4 PH reaches a minimum of 1170 MPa yield against 205 MPa for annealed 304, about five to six times. Even the softest common condition, H1150, sits at three times the yield of 304.
- Which has better corrosion resistance, 304 or 17-4?
- 304 in most environments. 17-4 PH in the overaged H1100 to H1150 conditions comes close to 304; at H900 it is noticeably less resistant and more sensitive to stress corrosion. Neither should be used in chloride-rich service where 316 or a duplex grade belongs.
- Is 17-4 PH magnetic?
- Yes, in all conditions, because it is martensitic. Annealed 304 is non-magnetic. If a part must not attract a magnet, 17-4 is the wrong choice.
- Can 17-4 PH be welded?
- Yes. Weld in Condition A with matching 17-4 filler, then solution treat or at least re-age so the weld zone reaches the same condition as the base metal. Welding after aging softens the heat-affected zone. 304 is simpler: weld it and use it.
