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Materials comparison

17-4 PH vs 15-5 PH Stainless Steel

Choose 17-4 PH for lightly or axially loaded parts, castings, and jobs where cost and stock matter most. Choose 15-5 PH for parts loaded across the grain, large sections, or salt air with sustained stress, where its remelted, low-ferrite structure and Table I rating at H1000 and above earn the premium.

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17-4 PH vs 15-5 PH side by side

15-5 PH is 17-4 PH rebalanced and remelted: same copper precipitation hardening, same single-step aging, similar strength, but with delta ferrite minimized and inclusions controlled so toughness across the grain is better. The table pulls the differences that change a material decision.

Item17-4 PH (UNS S17400, Type 630)15-5 PH (UNS S15500, Type XM-12)
Chromium, nickel, copper, percentCr 15.00 to 17.00, Ni 3.00 to 5.00, Cu 3.00 to 5.00, Cb plus Ta 0.15 to 0.45 (producer data)Cr 14.00 to 15.50, Ni 3.50 to 5.50, Cu 2.50 to 4.50 (distributor data)
Main aerospace bar specAMS 5643AMS 5659
Melting stated in the AMS titleNo consumable electrode melting in the AMS 5643 titleConsumable electrode melted (AMS 5659); producers use ESR or VAR
Delta ferritePresent in S17400, per ATIMinimized by composition and processing; distributor data calls the VAR product essentially ferrite free
Transverse toughnessBaselineDesigned for greater toughness, especially short transverse (ATI)
Minimum strength by H condition190 ksi UTS, 170 ksi yield at H900 (ASTM A564)Same A564 minimums at H900; see the next table
MSFC-STD-3029 stress corrosionTable II, moderate, all conditions; aging at 1150 F recommendedTable I, high, at H1000 and above; Table II below H1000
General corrosionEquivalent to Type 304 in most media (producer data)Comparable to Type 304 in most media (ATI)
MachinabilityMachined in Condition A at rates similar to 304; H900 machined moderately if at allCondition A about 50 percent of B1112 at about 80 ft/min; H1150 about 125 ft/min (distributor data)
Investment casting specsAMS 5342 (H1100, 130 ksi), AMS 5343 (H1000, 150 ksi), AMS 5344 (H900, 180 ksi)AMS 5400 (H935, 170 ksi)
DensityNot compared in our sourcesAbout 7.8 kg/dm3

Composition and machining notes for 17-4 come from the North American Stainless Type 630 long products sheet; 15-5 composition, density and cutting speeds from the Smiths Metal Centres AMS 5659 data sheet (2023); toughness, delta ferrite and corrosion statements from the ATI 15-5 technical data sheet (Version 1, March 15, 2012); stress corrosion ratings from NASA MSFC-STD-3029 Revision A; casting spec titles from SAE and BSI listings.

H900 to H1150: strength by condition

Both alloys are bought in Condition A (solution treated at about 1900 F) and aged at the temperature named in the condition. Lower aging temperature means higher strength and lower toughness and stress corrosion resistance; higher temperature means the reverse. Minimums for bar from an ASTM A564 summary, plus the figures one AMS 5659 distributor publishes for 15-5:

ConditionAgingA564 minimum, Type 630 (17-4): UTS / yield / elongation / RA15-5 per AMS 5659 distributor sheet: UTS / 0.2 percent proof
H900900 F, 1 hour190 ksi / 170 ksi / 10 percent / 35 percent (same for XM-12)1,310 MPa / 1,172 MPa
H925925 FNot in our A564 summary1,172 MPa / 1,069 MPa
H10251025 F, 4 hours155 ksi / 145 ksi / 12 percent / 45 percent1,069 MPa / 1,000 MPa
H10751075 FNot in our A564 summary1,000 MPa / 862 MPa
H11001100 FNot in our A564 summary965 MPa / 793 MPa
H11501150 F, 4 hours135 ksi / 105 ksi / 16 percent / 50 percent931 MPa / 724 MPa

The distributor labels its 15-5 figures typical, but they convert to 190/170, 170/155, 155/145, 145/125, 140/115 and 135/105 ksi, which match the A564 minimum set where we could check it. Treat them as a guide and take acceptance values from the controlling spec, its size range and its test direction. Strength is not the reason to pick 15-5; at a given condition the two alloys land on the same minimums. The reasons are toughness, stress corrosion and inspection behavior.

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Why 15-5 PH exists: delta ferrite and remelting

15-5 was developed to fix 17-4's weak direction. ATI's data sheet states that 15-5 was designed for greater toughness than S17400, especially through the thickness, achieved by reducing delta ferrite and controlling inclusion size and shape through electroslag remelting. Delta ferrite is a high-temperature phase retained in the martensite of 17-4. In rolled or forged product it is elongated along the working direction, which is why the penalty shows up across the grain, the short transverse direction ATI singles out.

The fix has two parts. The chemistry is shifted, with less chromium and slightly more nickel, so the alloy solidifies and is solution treated with little or no ferrite. Then the ingot is remelted. AMS 5659 is titled consumable electrode melted, and producers make it by electroslag remelting (ESR) or vacuum arc remelting (VAR). Distributor data for the VAR product describes an essentially ferrite free structure with excellent transverse notch toughness and better properties in large sections than 17-4.

When does this matter? Lugs and clevises loaded across the grain, thick sections machined from large bar where the part's critical direction is transverse, landing gear and actuator parts, and any fracture critical part where the analysis uses transverse properties. For a small turned pin loaded along its axis, 17-4 is often adequate.

Stress corrosion and hydrogen embrittlement

For salt air with sustained tension, 15-5 at H1000 or above is the only one of the two that needs no NASA stress corrosion approval. MSFC-STD-3029 lists 15-5 PH at H1000 and above in Table I, high resistance, and below H1000 in Table II. It lists 17-4 PH in Table II for all conditions, with a note recommending aging at 1150 F for better resistance. Table II materials need approval and may not be proposed for high installation stress uses such as springs and fasteners.

The standard also states the general rule for this class: susceptibility of precipitation hardening stainless steels increases as the aging temperature decreases. ATI gives the matching producer advice: where chloride stress corrosion is possible, age at the highest temperature that still meets the required minimum properties.

Treat hydrogen embrittlement with the same caution: the higher the strength condition, the more care plating and acid cleaning need. ATI warns that Condition A material, which is untempered martensite, is more sensitive to hydrogen embrittlement and chloride cracking than aged material and should not generally be put into service. Practical controls:

  • Never let a part ship in Condition A by accident. Put the H condition on the drawing and require it on the heat treat cert.
  • Prefer H1025 or higher for parts that will be plated, and require the bake the plating spec calls for. Bake rules are on the plating and cadmium alternatives page.
  • Passivate after final aging, using the method in the stainless and specialty steels page.

Choose 17-4 when, choose 15-5 when

Choose 17-4 PH when

  • Loads are mainly longitudinal and the section is modest: pins, shafts, small fittings, valve stems.
  • The part is protected from salt or is not under sustained tension, so a Table II rating is acceptable, ideally at H1150 per the MSFC note.
  • A complex shape is better cast than machined, since 17-4 has three AMS investment casting specs by strength level.
  • Cost and stock breadth matter more than transverse toughness.

Choose 15-5 PH when

  • Transverse or short transverse loads govern, or the part is cut from large bar or forgings.
  • The part sees salt air with sustained stress and you want Table I at H1000 or above.
  • The program or the prime's design manual calls for remelted material.
  • You need better large-section properties and forgeability, which the AMS 5659 distributor sheet credits to 15-5 over 17-4.

Castings: 17-4 cast specs and the 15-5 option

17-4 has AMS investment casting specs at three strength levels; 15-5 castings are covered by AMS 5400. The SAE titles define each by condition and minimum tensile strength:

SpecAlloy and formCondition in titleTensile strength in title
AMS 534217-4 investment castingsHomogenized, solution and precipitation heat treated, H1100130 ksi (896 MPa)
AMS 534317-4 investment castingsH1000150 ksi (1,034 MPa)
AMS 534417-4 investment castingsHomogenized, solution and precipitation heat treated, H900180 ksi (1,241 MPa)
AMS 540015-5 investment castingsSolution and precipitation heat treated, H935170 ksi (1,172 MPa)

Note that the cast H900 level in AMS 5344 is 180 ksi against 190 ksi for wrought H900, and the stress corrosion and hydrogen points above apply to castings at high strength too. Castings bring their own buying issues: radiographic grade, separately cast versus integral test bars, and weld repair limits. See the casting page for those. Confirm the current revision of each spec on ASSIST or SAE.

Machining, aging shrinkage and welding

Machine both alloys in Condition A or an overaged condition, then age, and plan for shrinkage. North American Stainless states Type 630 machines in the solution treated condition at rates similar to 304 and at lower rates in other conditions, and that H900 material should be machined moderately if at all. For 15-5, a distributor sheet gives about 80 ft/min in the annealed condition, about 50 percent of B1112, and about 125 ft/min at H1150.

  • Shrinkage. Aging from Condition A contracts the part. Producer data for 17-4 gives 0.0004 to 0.0006 in/in to H900; the stainless steels page covers H1150 figures and how to size parts.
  • Soft condition for heavy work. ATI describes a two-step 1400 F plus 1150 F treatment per ASTM A693 for maximum softness when forming or heavy machining is needed, followed by re-solution treatment and final aging.
  • Cutting thick plate. ATI warns that plasma cutting Condition A plate over about 1 inch can crack it, and recommends saw or water jet, or aging at 1150 F before torch cutting.
  • Welding. Both weld by conventional inert gas methods without preheat. Matching filler plus post-weld aging restores strength; an austenitic filler such as 308L gives a ductile weld that will not harden.
  • Heat treat control. Aging is a controlled heat treat operation with pyrometry and furnace class requirements. See heat treatment.

Cost and availability drivers

Expect 15-5 to cost more and offer fewer stock sizes than 17-4, because the remelting step and the narrower aerospace market both add cost. We do not quote material prices here; these are the drivers:

  • Melt practice. AMS 5659 requires consumable electrode melting, an extra process step over the primary melt. A drawing that also names ESR or VAR narrows the eligible heats further.
  • Market breadth. 17-4 is sold widely as commercial ASTM A564 Type 630 bar for industrial parts as well as aerospace, so non-AMS stock is easy to find. AMS-certified bar of either alloy is a smaller pool.
  • Size. Large diameters and forgings are where 15-5's advantages show, and also where stock is thinnest.
  • Condition and processing. Bar is normally bought in Condition A, so aging, hardness testing, passivation and any plating bake are separate operations with their own lead time and certs.
  • Castings. Investment castings carry pattern tooling and qualification cost, offset by less machining on complex shapes.
  • Specialty metals. Both alloys are DFARS specialty metals, so a contract carrying 252.225-7009 limits you to compliant melt sources.
  • Certified surplus. Remnant bar with traceable mill certs can shorten lead time if the cert shows the right spec, revision and melt practice.

Callouts for the drawing and PO

Name the alloy, spec, form and H condition, and say who ages the part. Examples:

  • Salt-exposed actuator fitting: MATL: CRES 15-5PH BAR PER AMS 5659. HEAT TREAT TO H1025 AFTER MACHINING. PASSIVATE PER AMS 2700.
  • General shaft: MATL: CRES 17-4PH BAR PER AMS 5643, COND H1150. Use H1150 or H1150M where stress corrosion margin matters.
  • Cast housing: MATL: 17-4PH INVESTMENT CASTING PER AMS 5344, with radiographic grade and test bar requirements stated.
  • High-strength 15-5 casting: MATL: 15-5PH INVESTMENT CASTING PER AMS 5400.

On the PO require: the spec and revision, the mill cert with heat number and melt practice, the heat treat cert showing condition, time and temperature, hardness or tensile results after aging, and DFARS 252.225-7009 compliance where the contract carries it, since both alloys are specialty metals. Our DFARS specialty metals and certs and traceability pages explain what to check. For the aluminum equivalent of this decision, see 6061 vs 7075 aluminum.

Get 17-4 or 15-5 material quoted

Send the spec, condition, form and size through a certified material request. We source AMS 5643 and AMS 5659 bar and AMS cast product from qualified suppliers with traceable mill certs, confirm the melt practice and condition on the certs before shipment, and can add aging, passivation and machining on the same PO. See also bar and rod and the materials hub.

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Questions

Is 15-5 PH stronger than 17-4 PH?

Not at the same condition. ASTM A564 sets the same H900 minimums for Type 630 and XM-12, 190 ksi ultimate and 170 ksi yield, and published 15-5 figures track the 17-4 minimums at the other conditions. 15-5 is chosen for better transverse toughness from low delta ferrite and remelting, and for its Table I stress corrosion rating at H1000 and above in MSFC-STD-3029, not for more strength.

What is the difference between AMS 5643 and AMS 5659?

AMS 5643 covers 17-4 PH bars, wire, forgings, mechanical tubing and rings in the solution treated condition. AMS 5659 covers 15-5 PH bars, wire, forgings, rings and extrusions, and its title requires consumable electrode melting, which producers meet with ESR or VAR. They are not interchangeable on a drawing. Confirm the current revision of each on ASSIST or SAE before release.

Which H condition should I specify for salt air service?

Use the highest aging temperature that still meets your strength need. MSFC-STD-3029 rates 15-5 PH at H1000 and above as highly resistant, and rates 17-4 PH moderate in all conditions while recommending 1150 F aging for better resistance. ATI gives the same advice for 15-5: age at the highest temperature that produces the required minimum properties where chloride stress corrosion is possible.

Can I use 17-4 PH in Condition A?

Generally no. Producers state Condition A material should not be put into service because it is untempered martensite with lower ductility, and ATI adds that it is more sensitive to hydrogen embrittlement and chloride stress corrosion than aged material. Condition A is the machining state. Put the final H condition on the drawing and require the heat treat cert to show it.

Is there a cast version of 15-5 PH?

Yes. AMS 5400 covers 15-5 PH investment castings solution and precipitation heat treated to H935 with 170 ksi tensile strength in its title. 17-4 castings are more common, with AMS 5342 at H1100 and 130 ksi, AMS 5343 at H1000 and 150 ksi, and AMS 5344 at H900 and 180 ksi. Confirm the current revisions on ASSIST or SAE.

Do 17-4 and 15-5 shrink during aging?

Yes, both contract when aged from Condition A. Producer data for 17-4 gives 0.0004 to 0.0006 in/in when aged to H900, with larger contraction at higher aging temperatures. Shops either finish machine after aging or size the Condition A part so it lands on tolerance after shrinkage. State on the drawing which approach applies to tight dimensions.

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