17-4 PH Stainless Steel
Also: 17-4PH, UNS S17400, Type 630, AISI 630, 1.4542, X5CrNiCuNb16-4, SUS630, Armco 17-4 PH, H900 stainless, CB7Cu-1 (cast)
17-4 PH is the most used precipitation-hardening stainless: machine it soft, then age it at 480-620 °C to 28-47 HRC with almost no distortion. Corrosion near 304.
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At a glance
| Density | 7.8 g/cm³ (0.282 lb/in³) |
|---|---|
| Tensile strength | H900 1310-1380 MPa (190-200 ksi); H1025 1070-1170 MPa (155-170 ksi); H1150 930-1000 MPa (135-145 ksi); Condition A about 1030 MPa (150 ksi) |
| Yield strength | H900 1170-1275 MPa (170-185 ksi); H1025 1000-1140 MPa (145-165 ksi); H1150 725-860 MPa (105-125 ksi); Condition A about 760 MPa (110 ksi) |
| Hardness | H900 40-47 HRC; H1025 35-38 HRC; H1150 28-33 HRC; Condition A about 33 HRC (363 HB maximum) |
| Elongation | H900 10-14%; H1025 12-15%; H1150 16-19%; Condition A about 10% |
| Modulus of elasticity | 196 GPa (28.5 Msi) |
| Thermal | Melts at 1400-1440 °C (2560-2625 °F); thermal conductivity ~18 W/m·K; expansion ~10.8 um/m·K; service to about 315 °C (600 °F) before the age overages |
| Composition | Fe, 15-17.5% Cr, 3-5% Ni, 3-5% Cu, 0.15-0.45% Nb (+Ta), up to 0.07% C, up to 1% Mn, up to 1% Si |
Typical values, Aged conditions, ASTM A564 minimums to typical upper values: H900 = 482 °C (900 °F) 1 h; H1025 = 552 °C (1025 °F) 4 h; H1150 = 621 °C (1150 °F) 4 h; Condition A = solution annealed at 1040 °C (1900 °F). Confirm against the mill certificate and the purchase spec.
- MachinabilityFair
- About 45-50% of B1112 in Condition A, H1150 or H1025; many shops find the overaged conditions cut cleaner than Condition A. H900 at 44 HRC is a hard-milling and grinding job. Coated carbide, positive geometry, flood coolant; machine soft, age, then finish critical features.
- WeldabilityGood
- Welds by TIG, MIG and laser with 17-4 PH filler (AMS 5825 / ER630) and no preheat; the low carbon avoids hardening cracks. Weld in Condition A or an overaged condition, then age the whole part; a weld in aged stock needs re-solution treatment plus age to match the base metal.
- FormabilityFair
- Sheet arrives in Condition A at about 33 HRC, so bends want 2-3t inside radii and heavy tonnage; form first, age after. Nothing forms once aged.
- Corrosion resistanceGood
- Close to 304 in atmosphere and fresh water, better than any 400-series martensitic grade, below 316 in chlorides. Resistance rises with aging temperature: H900 is the worst for stress-corrosion and hydrogen cracking, H1150 the best. Passivate after machining.
17-4 PH is a martensitic precipitation-hardening stainless with about 4% copper and a niobium addition. As supplied in Condition A (solution annealed at 1040 °C / 1900 °F) it is already martensitic at about 33 HRC. A single low-temperature age then precipitates copper-rich particles: H900 (482 °C / 900 °F, 1 hour) for peak strength around 1310-1380 MPa (190-200 ksi) at 40-47 HRC, or the overaged conditions H1025, H1075, H1100 and H1150 (up to 621 °C / 1150 °F, 4 hours) that trade strength for toughness and stress-corrosion resistance.
That cycle is why it is everywhere: aerospace fittings, pump shafts, valve stems, firearm parts, oilfield tools, gears and fasteners. There is no quench, so a finished part ages in an air furnace and comes out with a predictable contraction of roughly 0.05% (H900) to 0.1% (H1150) and almost no warp. Strength rivals quenched-and-tempered 4140 while corrosion resistance sits close to 304 in most atmospheres and fresh water. It welds, forges, casts (CB7Cu-1), molds by MIM and prints on laser powder-bed machines.
The rules to respect: Condition A is not a service condition (low toughness, poor stress-corrosion resistance; the specs prohibit using it unaged). H900 is the most prone to hydrogen embrittlement and chloride stress-corrosion cracking, so sour-service and marine parts use H1150 or the double-aged H1150M, and NACE MR0175 caps hardness at 33 HRC. Large bar and thick plate have low transverse ductility, which is the reason 15-5 PH exists. It is magnetic in every condition.
Heat treatment
Solution treat at 1040 °C (1900 °F) and cool below 32 °C (90 °F) to form martensite (Condition A). Then one age, air cooled: H900 482 °C (900 °F) 1 h; H925 496 °C (925 °F) 4 h; H1025 552 °C (1025 °F) 4 h; H1075 579 °C (1075 °F) 4 h; H1100 593 °C (1100 °F) 4 h; H1150 621 °C (1150 °F) 4 h; H1150M 760 °C (1400 °F) 2 h then 621 °C 4 h for maximum toughness. Parts contract about 0.05% at H900 and about 0.1% at H1150, predictably enough to machine before aging. Follow AMS 2759/3. Never put Condition A parts into service.
Tempers and conditions
- Condition A (solution annealed, as purchased)
- H900
- H925
- H1025
- H1075
- H1100
- H1150
- H1150M and H1150D (double overaged)
Stock forms
- Round, square and flat bar (Condition A)
- Plate and sheet (Condition A)
- Forgings
- Investment castings (CB7Cu-1, ASTM A747)
- MIM feedstock and metal 3D printing powder
- Tube and wire (limited)
Relative cost
Tier 4 of 5. About 1.5-2x 304 bar per pound, close to 316, plus a heat-treat lot charge; far cheaper than titanium or Inconel for the same strength. MIM and printing make small complex parts economical.
Typical applications
- Aircraft and helicopter structural fittings, hinges and actuator parts
- Pump shafts, impellers and valve stems
- Firearm receivers, bolts and slides
- Oil and gas wellhead and downhole components (overaged conditions)
- Gears, shafts and fasteners in food and chemical plants
- Surgical and dental instruments
- Nuclear reactor internals and fasteners
- High-strength MIM and 3D-printed parts
Process compatibility
How 17-4 PH takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | FairFair | Machine in Condition A or H1150, age, then finish bores and threads; allow 0.05-0.1% contraction. H900 stock is a hard-milling job. Can 17-4 PH be machined in the hardened condition? |
| CNC Turning | FairFair | Shafts and stems turn well in Condition A or H1150 with coated carbide; hold size for the aging shrink if turned before aging. |
| Wire EDM | GoodGood | Cuts aged material at any hardness without stressing it; the way to profile H900 parts. Passivate after to clear the recast layer. |
| Heat Treating | ExcellentExcellent | One low-temperature age in an air or vacuum furnace, no quench, minimal distortion; specify the condition (H900, H1025, H1150) and AMS 2759/3. How is 17-4 PH stainless heat treated? |
| Vacuum Heat Treating | GoodGood | Solution anneal and age in vacuum for a bright, scale-free surface on finished parts. |
| Welding | GoodGood | ER630 / AMS 5825 filler, no preheat; weld soft, then age the assembly so weld and base metal match. Can 17-4 PH stainless be welded? |
| TIG Welding | GoodGood | The usual process for fittings, thin sections and repairs; ER630 filler, then age. |
| Passivation | ExcellentExcellent | ASTM A967 after final machining and aging; the copper can dull under long nitric exposure, so citric is the safer default. |
| Electropolishing | GoodGood | Brightens and removes the light aging scale; less mirror-like than 316 but standard on medical instruments. |
| Metal 3D Printing | ExcellentExcellent | The most printed stainless after 316L (laser powder bed and binder jet); printed parts need a solution treatment before aging to reach H900 numbers. |
| Investment Casting | GoodGood | Cast as CB7Cu-1 (ASTM A747) and aged the same way; castings run a step lower in ductility than bar. |
| Forging | GoodGood | Forge at about 1150-1200 °C (2100-2200 °F) and solution treat after; large forgings show low transverse ductility, which is what 15-5 PH fixes. |
| Hard Chrome Plating | FairFair | Possible on wear surfaces, but bake within hours (190 °C / 375 °F, 3 h or more) to drive off hydrogen; H900 parts are the most embrittlement-prone. |
| Hot-Dip Galvanizing | Not recommendedNot recommended | Zinc will not bond to the passive oxide, the coating adds nothing, and the bath temperature overages the alloy. |
Compare 17-4 PH
Design and sourcing tips
- Always specify the aged condition on the drawing ("17-4 PH per ASTM A564, Condition H1025"), never just "17-4"; Condition A is not a service condition.
- Pick the condition by the job: H900 for maximum strength and wear, H1025 for the best strength-toughness balance, H1150 or H1150M for impact, chlorides, sour service and welded parts.
- Machine in Condition A (or H1150), age, then finish-machine bores and threads; allow 0.05-0.1% linear contraction on aging.
- Keep hardness at or under 33 HRC (H1150 double aged) for hydrogen sulfide or hydrogen exposure; NACE MR0175 / ISO 15156 sets the limits.
- Specify 15-5 PH (AMS 5659) instead for large forgings, thick plate and parts loaded across the grain.
- Add passivation per ASTM A967 after aging; the age leaves a light oxide that stains if it is left on.
Frequently asked questions
- Is 17-4 PH stainless magnetic?
- Yes, strongly, in every condition. It is martensitic, so a magnet sticks to Condition A, H900 and H1150 stock alike. If the part must be non-magnetic, use an austenitic grade such as 316 and accept a quarter of the strength, or a cold-worked austenitic.
- What does H900 mean for 17-4 PH?
- It is the aging treatment: hold at 900 °F (482 °C) for one hour and air cool. H900 gives the highest strength and hardness, about 1310-1380 MPa (190-200 ksi) tensile at 40-47 HRC, with the lowest toughness and the least resistance to stress-corrosion and hydrogen cracking. H1025 and H1150 are the same idea at higher temperatures for tougher, more corrosion-tolerant parts.
- Is 17-4 PH stronger than 304 stainless?
- By a wide margin. Aged 17-4 PH yields at 725-1275 MPa (105-185 ksi) depending on condition, against about 205-290 MPa (30-42 ksi) for annealed 304, so three to six times the yield strength. It gives up some chloride corrosion resistance and all of the ductility and non-magnetic behaviour that 304 offers.
- Can 17-4 PH be welded?
- Yes. Its low carbon means it does not crack like the 400-series martensitics, so it welds by TIG, MIG and laser with 17-4 PH (ER630) filler and no preheat. The catch is matching properties: weld in Condition A or an overaged condition and age the whole assembly afterward. Welding aged parts and leaving them as welded gives a soft, under-strength weld zone.
- What is the difference between 17-4 PH and 15-5 PH?
- Same chemistry family, same heat treatments and the same strength minimums per condition. 15-5 PH is made by remelting with slightly less chromium and more nickel, which removes the ferrite stringers that give 17-4 PH poor toughness across the grain in large bar, forgings and thick plate. Choose 15-5 for those; 17-4 is cheaper and more widely stocked for everything else.
Processes that commonly use it
Related materials
Where to verify these values
- ASTM A564 and ASTM A693 (minimums by condition)
- AMS 5643, AMS 5604 and AMS 5622; AMS 2759/3 for heat treatment
- ASM Handbook, Volume 4 (heat treating) and Volume 1
- MMPDS design allowables and producer data sheets (Cleveland-Cliffs / AK Steel, Carpenter)
