17-4 PH, 1.4542, AISI 630, S17400 — one steel, four names
Half the confusion around this grade is that every region calls it something else, and a drawing can carry any of the names. They are all the same precipitation-hardening stainless: roughly 16% chromium, 4% nickel, 4% copper, stabilised with niobium.
| Designation | Where it comes from | Usually seen on |
|---|---|---|
| 17-4 PH | Original trade name (Armco), now used worldwide | Most drawings and stock lists |
| UNS S17400 | US unified numbering system | Material certificates |
| AISI 630 / Type 630 | USA, ASTM A564 | Aerospace and valve drawings |
| 1.4542 | Europe, material number | German and Italian drawings |
| X5CrNiCuNb16-4 | Europe, EN 10088-3 name | EN material certificates |
| SUS 630 | Japan, JIS G4303 | Japanese machine drawings |
If a drawing says AISI 630 or X5CrNiCuNb16-4, nothing needs converting — order 17-4 PH. What does need deciding is the condition, and that is a separate line on the drawing. A drawing that names the grade but not the condition is not yet buildable.
Chemical composition — ASTM A564 Type 630
| Element | Content | What it is doing |
|---|---|---|
| Carbon (C) | 0.07 max | Kept low so the steel stays weldable and tough |
| Chromium (Cr) | 15.00–17.50 | The corrosion resistance |
| Nickel (Ni) | 3.00–5.00 | Balances the structure to martensite |
| Copper (Cu) | 3.00–5.00 | The whole trick — copper precipitates on ageing and does the hardening |
| Niobium + Tantalum | 0.15–0.45 | Ties up carbon so chromium stays available for corrosion resistance |
| Manganese (Mn) | 1.00 max | Residual |
| Silicon (Si) | 1.00 max | Residual from deoxidation |
| Phosphorus (P) / Sulphur (S) | 0.040 / 0.030 max | Impurities, capped |
| Iron (Fe) | Balance | — |
The copper is what separates this grade from ordinary stainless. It stays dissolved after solution treatment and then comes out as fine particles during a single low-temperature ageing step — which is why 17-4 PH reaches its strength without a quench, and therefore without the distortion that hardening 4140 or 42CrMo4 brings with it.
The condition chart — H900 to H1150
This is the table the grade is really looked up for. The H number is not a code: it is the ageing temperature in degrees Fahrenheit. H900 means one hour at 900 °F. Everything else follows from that — the hotter the ageing, the softer, tougher and more corrosion-resistant the finished part.
| Condition | Ageing | Hold | Tensile min | 0.2% proof min | Elongation min | Hardness min |
|---|---|---|---|---|---|---|
| A (solution annealed) | 1038 °C, air cool | — | — | — | — | 363 HB max (about 38 HRC) |
| H900 | 482 °C / 900 °F | 1 h | 1310 MPa (190 ksi) | 1170 MPa (170 ksi) | 10% | 40 HRC |
| H925 | 496 °C / 925 °F | 4 h | 1170 MPa (170 ksi) | 1070 MPa (155 ksi) | 10% | 38 HRC |
| H1025 | 552 °C / 1025 °F | 4 h | 1070 MPa (155 ksi) | 1000 MPa (145 ksi) | 12% | 35 HRC |
| H1075 | 579 °C / 1075 °F | 4 h | 1000 MPa (145 ksi) | 860 MPa (125 ksi) | 13% | 32 HRC |
| H1100 | 593 °C / 1100 °F | 4 h | 965 MPa (140 ksi) | 795 MPa (115 ksi) | 14% | 31 HRC |
| H1150 | 621 °C / 1150 °F | 4 h | 930 MPa (135 ksi) | 725 MPa (105 ksi) | 16% | 28 HRC |
Read the two ends against each other: between H900 and H1150 the part gives up about 29% of its tensile strength and gains 60% more elongation. That trade is the entire decision, and it is made on the drawing, not in the workshop.
Condition A is not a finished state. It is the delivery condition of the bar — soft enough to machine, and not yet at strength. A part shipped in Condition A because nobody wrote a condition on the drawing is a part that has not been heat treated at all.
Which condition to ask for
The most common question we get on this grade is a one-liner: “The drawing just says 17-4 PH. Which condition do I order?” This table is the short answer.
| What the part has to do | Condition | Why |
|---|---|---|
| Resist wear, hold an edge, take maximum load in a small section | H900 | Hardest of the range — but also the least tough and the most prone to stress-corrosion cracking |
| General strong parts: shafts, pump and valve internals, instrument bodies | H1025 / H1075 | Keeps most of the strength and is far more forgiving. The default when nothing else is specified |
| Chlorides, coastal air, anything left outdoors | H1100 / H1150 | Deliberately over-aged; the best stress-corrosion resistance the grade offers |
| Impact loads, thin sections, anything that must bend rather than snap | H1150 | Highest elongation in the range, at 16% |
| The assembly will be welded | Age after welding | Welding a hardened part destroys the condition in the heat-affected zone |
A 17-4 PH part shrinks when it is aged
Ageing is not dimensionally neutral. The part contracts, and by more at the higher ageing temperatures: roughly 0.05% at H900, rising to about 0.1% at H1150. On a 100 mm length that is 0.05 to 0.1 mm; on a 20 mm bore it is about 0.01 mm.
For a bracket that is nothing. For an H7 bore, a seal groove or a bearing seat it is the whole tolerance. Which is why those features are left with grinding stock and finished after ageing, and everything else is machined complete before it. Ask the heat treater for their own figure when a dimension is critical — it shifts slightly with section thickness.
Machine before ageing or after — the question that sets the price
Route A: machine in Condition A, then age (the normal case)
Bar arrives solution annealed, the part is cut complete, then goes through one ageing cycle. Machinability in Condition A is roughly 45–50% of free-machining steel — sticky and work-hardening, but ordinary carbide tooling handles it. This is the cheaper route, and the only realistic one for H900, because pre-aged H900 bar is rarely stocked.
Route B: buy pre-aged bar and machine to final size
H1075 and H1150 bar can be bought already aged in common diameters. No heat treatment afterwards, no shrinkage to allow for, and the part is finished when it comes off the machine. The cost moves into the cutting: bar at 32–35 HRC is slower, eats tooling, and drills badly.
Where deep holes come in. A small bore that runs a long way — say 6 mm through 130 mm, which is 22 times its own diameter — cannot be done with a standard drill in this material at all. It needs gun drilling, and that one feature can cost more than the rest of the part put together. If the bore does not have to be dead straight and concentric, drilling from both ends roughly halves it. Worth saying so on the enquiry.
Where 17-4 PH loses — and to what
| Compared with | 17-4 PH wins on | 17-4 PH loses on |
|---|---|---|
| 316 / 316L | Three to four times the yield strength — it holds a thread, a bearing surface and a press fit | Chlorides. 316 is far better in salt water, and it is non-magnetic where 17-4 PH is not |
| 410 / 420 martensitic | Better corrosion resistance, and it hardens at low temperature with almost no distortion | Price of the bar |
| 15-5 PH (1.4545) | Availability and cost | Transverse toughness — 15-5 PH is remelted and carries less delta ferrite |
| 4140 / 42CrMo4 | It does not rust in ordinary air, and it hardens without a quench | Top-end strength, and cost per kilo |
The honest limit. If the part sits permanently in sea water, do not specify 17-4 PH at all. It is a strong stainless, not a marine stainless — 316L (1.4404) or a duplex grade will outlast it, and no ageing condition changes that. Above roughly 300 °C in service it also over-ages and quietly loses the strength it was chosen for.
Where the catalogue stops
| What you need | In the catalogue? | What follows |
|---|---|---|
| Round bar, Condition A, common diameters | Yes, every stainless distributor | Buy the bar — you don't need us for that |
| Bar already aged to H1075 or H1150 | Usually, in a few diameters | Buy it if your part fits one of those diameters |
| Bar already aged to H900 | Rarely stocked | Machine from Condition A and age afterwards |
| A finished part in a named condition, 1 to 50 off | No — not a catalogue item in any condition | Machined to your drawing and aged to the condition you name, from 1 piece |
| A small bore deeper than ten times its diameter | No stock equivalent exists | Gun-drilled, and quoted per part |
| A worn 17-4 PH part with no drawing left | No | Send the original — it is measured here, copied, and comes back with the new one |
What to put in the enquiry
Five lines are enough to price a 17-4 PH part, and four of them are usually missing:
- The condition — H900, H1025, H1075, H1100 or H1150. If you genuinely do not know, say what the part has to do and we will suggest one.
- Which dimensions are tight, so they can be left for after ageing.
- Any bore deeper than about ten times its diameter, and whether it has to be dead straight.
- Surface finish on sealing or bearing faces.
- Quantity, even if it is one.
A drawing, a hand sketch, a photo with dimensions or the worn original all work — no CAD file is needed. Quotes come back within 12 hours, and the minimum order is 1 piece. Related grades: 316 / 316L, 304, 4140 alloy steel.
Frequently Asked Questions
H900 is the ageing condition, not a grade. The part is held for one hour at 900 °F (482 °C) and air cooled. The number is simply that temperature in Fahrenheit, which is why the list runs H900, H925, H1025, H1075, H1100, H1150. The lower the number, the harder and the less tough the finished part.
Yes, in every condition. 17-4 PH is martensitic, so it is magnetic whether it is solution annealed or fully aged. If the part has to be non-magnetic, 17-4 PH is the wrong grade and 316L is the usual substitute.
No. In ordinary atmosphere it behaves roughly like 304, and in chlorides it is clearly behind 316. 17-4 PH is chosen for strength that stainless normally cannot give, not for salt water. For permanent seawater immersion, use 316L or a duplex grade instead.
Normally before. Bar is bought in Condition A, machined complete, then aged in one low-temperature step. Ageing involves no quench, so distortion is small. The exception is tight-tolerance features — bores with a fit, sealing diameters, ground surfaces — which are left with grinding stock and finished after ageing, because the part shrinks slightly.
It contracts. Expect roughly 0.05% at H900, rising to about 0.1% at H1150 — so 0.05 to 0.1 mm on a 100 mm length, and about 0.01 mm on a 20 mm bore. Confirm the exact figure with the heat treater when a dimension is critical, because it varies with section thickness.
Same family and almost the same strength. 15-5 PH (1.4545) is remelted and contains less delta ferrite, so it is tougher across the bar rather than only along it. Specify 15-5 PH when the drawing calls out transverse properties; otherwise 17-4 PH is more widely stocked and cheaper.
EKINSUN LTD is a custom parts manufacturer that machines 17-4 PH from 1 piece — turned and milled parts, shafts, valve and pump internals, instrument fittings — and has them aged to the condition named on the drawing. Send a drawing, a sketch or the worn original and the quote comes back within 12 hours.
Get a 17-4 PH Quote
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