15-5PH is a martensitic precipitation-hardening stainless steel built around one specific problem: 17-4PH loses toughness through the thickness of heavy sections. If you are buying 15-5PH pipe or plate, the drawing almost certainly specifies it because the part sees multi-directional stress, or because a Saudi Aramco or ADNOC material specification rules out a grade that cannot hold its transverse properties across a thick cross-section.
This page covers what the grade actually is, which specification applies to which product form, how the aging condition you choose changes both strength and cracking risk, and where the advantage over 17-4PH stops being real.
What 15-5PH Is, and Why It Exists at All
15-5PH is registered as UNS S15500, designated Type XM-12 in ASTM A564, and known in Europe as 1.4545 (X5CrNiCuNb15-5). The composition change versus 17-4PH is small and deliberate: chromium drops to 14.0–15.5 %, nickel rises to 3.5–5.5 %, with copper 2.50–4.50 % and niobium+tantalum 0.15–0.45 % doing the strengthening.
Carbon stays at 0.07 % maximum. Density is about 7.78 g/cm³ and the grade is magnetic in every condition. Those chromium and nickel numbers are the whole story - shifting the balance toward nickel suppresses retained delta ferrite, making 15-5PH a delta-ferrite-controlled version of 17-4PH.
Pipe, Plate, Bar: Matching the Product Form to the Right Specification
This is where a large share of published 15-5PH material gets it wrong, and where a mistake costs you a rejected purchase order.
Why the Bar Specification Does Not Cover Plate
AMS 5659 is correct for round bar, wire, forgings, rings and extrusions - it does not cover flat-rolled product. Sheet, strip and plate are covered by AMS 5862. Seamless and welded tubing is supplied to ASTM A511, with AMS 5659 applied by agreement or to customer specification. The chemistry windows are identical, but test requirements, specimen orientation and documentation differ.
Product Form to Specification Table
| Product form | Applicable AMS | Applicable ASTM | As-delivered |
|---|---|---|---|
| Bar, wire, forgings, rings, extrusions | AMS 5659 | ASTM A564 (XM-12) / A705 (forgings) | Condition A |
| Sheet, strip, plate | AMS 5862 | ASTM A693 (XM-12) | Condition A |
| Seamless and welded tubing | AMS 5659 by agreement / customer spec | ASTM A511 | Condition A |
| Welding wire | AMS 5826 | - | - |
Product Forms
Bar & Rod
Plate & Sheet
Coil & Strip
Pipe & Tube
Fitting: Flange, Tee, Elbow, Reducer etc.
Forging: Ring, Shaft, Circle, Block etc.
The chemistry-to-strength chain
|
Element (wt %) |
15-5PH range |
What it does for the pipe |
|
Cr |
14.0–15.5 |
Passive film; corrosion resistance near 304 level |
|
Ni |
3.5–5.5 |
Stabilizes austenite on heating, enables full martensite on quench |
|
Cu |
2.5–4.50 |
Forms the ε-Cu precipitates that do the hardening on aging |
|
Nb + Ta |
0.15–0.45 |
Grain refinement, reduces sensitization risk |
|
C |
≤ 0.07 |
Kept low to protect toughness and weldability |
|
Fe |
Balance |
Matrix |
How Aging Temperature Sets Strength, Toughness and Cracking Risk
15-5PH is supplied in Condition A, a solution-treated state soft enough to machine. Final properties come from a single low-temperature aging step. Choosing the aging temperature is the single most consequential decision in the specification.
The H900 to H1150 Ladder
| Condition | Aging | Tensile, min | 0.2% Yield, min | Elong. min (L/T) | Hardness | Suitable for |
|---|---|---|---|---|---|---|
| Condition A | 1038 °C solution | Not a service state | 363 HB max | Machining only | ||
| H900 | 480 °C / 4 h | 1310 MPa | 1170 MPa | 10 % / 6 % | 40–47 HRC | Peak strength, benign env. |
| H1025 | 552 °C / 4 h | 1070 MPa | 1000 MPa | 12 % / 8 % | 34–42 HRC | Balanced default |
| H1075 | 579 °C / 4 h | 1000 MPa | 862 MPa | 13 % / 9 % | 31–38 HRC | Some SCC risk |
| H1100 | 593 °C / 4 h | 965 MPa | 793 MPa | 14 % / 10 % | 30–37 HRC | Wet chloride cycling |
| H1150 | 621 °C / 4 h | 930 MPa | 724 MPa | 16 % / 11 % | 28–37 HRC | Seawater, salt spray |
| H1150M/D | 760 °C + 621 °C | 795 MPa | 520 MPa | 18 % | 33 HRC max | NACE MR0175 sour |
Values are minimum specified per AMS 5659 / ASTM. As aging temperature rises, strength falls and elongation, toughness and SCC resistance rise. Long-term service temperature should stay at or below about 315 °C.
Condition A Is a Machining State, Not a Service State
Condition A is untempered martensitic with low fracture toughness and poor SCC resistance; it must never be a part's final condition. Plan the sequence as: rough machine in Condition A, age, finish machine. Linear change is about 0.05 % for H900 and 0.10 % for H1150.
15-5PH Pipe: Sizes, Delivery Condition and Forming Limits
15-5PH tubing is produced to ASTM A511 in both seamless and welded-and-drawn routes, from small instrumentation sizes up to roughly 500 mm OD, wall 1–25 mm depending on diameter; larger diameters are made-to-order. Almost all tubing is supplied in Condition A and aged after forming. It is magnetic in every condition, so MPI works directly on finished parts.
15-5PH Plate: Thickness Range and Flat-Rolled Supply
Plate and sheet to AMS 5862 arrive in Condition A at roughly 38 HRC maximum, from thin sheet ~0.5 mm up to plate ~100 mm, widths to ~1500 mm and lengths to 6000 mm, cut-to-size available. Plate is cross-rolled through a thick section - exactly where delta-ferrite stringers form in 17-4PH - so for a part loaded through its thickness, the transverse properties decide survival.
Delta Ferrite and Transverse Toughness: The Real Reason to Specify 15-5PH
What Chromium and Nickel Do in a Martensitic Matrix
In a martensitic stainless steel, chromium stabilises ferrite and nickel stabilises austenite. 17-4PH's chromium-rich balance promotes delta ferrite stringers aligned with the working direction - crack-initiation sites under through-thickness load.
15-5PH lowers chromium to 14.0–15.5 % and raises nickel to 3.5–5.5 %, producing a more isotropic structure. VAR/ESR remelting removes sulphide inclusions. Published transverse Charpy values for 15-5PH run roughly 30–50 % above 17-4PH at equivalent conditions.
Where the Advantage Disappears
- Thin sheet and fine wire: fast solidification leaves little room for delta ferrite; the grades are close to interchangeable and 17-4PH is cheaper.
- Purely longitudinal load on a modest section: the transverse advantage has no load case to act on.
- Service temperature: 15-5PH is a high-strength alloy at ambient and moderately elevated temperature, not a heat-resisting alloy (≈315 °C ceiling).
- On corrosion: 15-5PH performs at roughly 304 level and clearly better than 400-series martensitic grades, but it is not a substitute for 316 or a duplex grade in high-chloride or strongly oxidising acid service.
Regional Supply: Middle East and Europe
Middle East - Saudi Arabia & UAE
15-5PH in H1025 or H1150 is a routine choice for downhole tools, wellhead valves and pump shafts specified to Saudi Aramco and ADNOC material requirements. The chloride environment rules out peak-strength H900, and NACE MR0175 sour-service limits often push the spec toward H1150M.
Europe - Germany & Italy
The grade is specified for aerospace structural plates and precision valve and pump components, almost always with EN 10204 3.1 certification and PED 2014/68/EU consideration for pressure parts. We supply both regions from stock and made-to-order programs with full heat traceability.
Ordering 15-5PH: What to Put on the Purchase Order
| Field | What to state | Why it matters |
|---|---|---|
| Alloy and grade ID | 15-5PH, UNS S15500, XM-12 | "A564" alone does not distinguish XM-12 from Grade 630 |
| Product form | Seamless tube / welded tube / plate / sheet | Determines the applicable specification |
| Specification | ASTM A511 (tube), AMS 5862 (plate), AMS 5659 (bar) | Form and specification must match |
| Delivery condition | Condition A, or aged H900/H1025/H1150/H1150M | Condition A is not a service condition |
| Melt practice | VAR or ESR, declared on certificate | Drives transverse properties and cleanliness |
| Certification | EN 10204 3.1 minimum, heat traceability | Required for aerospace and nuclear end use |
FAQ
Q1: Is 15-5PH pipe stronger than 316L pipe?
Yes, by a wide margin - 15-5PH H1025 yield is about 1000 MPa versus ~170–310 MPa for 316L. But 316L wins on formability and uniform corrosion in many media; 15-5PH is chosen where strength-to-weight and hardness matter.
Q2: Can I substitute 17-4PH for 15-5PH pipe?
Only if the design does not rely on transverse or short-transverse toughness or large-section uniformity. 17-4PH can carry delta-ferrite that weakens those directions. If the drawing calls out 15-5PH, do not swap without engineering sign-off - the grade name is not the full specification.
Q3: Which heat-treatment condition resists chloride stress corrosion best?
H1150, the over-aged condition, gives the highest SCC threshold stress and is direction-independent because there are no ferrite stringers. H900 is the most sensitive.
Q4: What standard covers 15-5PH pipe?
Pipe/tube is commonly supplied to ASTM A511 (seamless mechanical tubing) or per aerospace spec AMS 5659 / AMS 5862, or to customer specification; plate is ASTM A693 (XM-12), bar ASTM A564, forgings ASTM A705.
Q5: Does aging distort the pipe dimensions?
Minimally. Aging is a low-temperature precipitation step, not a phase transformation, so distortion is small. The standard practice is to machine in Condition A and age last, which is why "Condition A + age to H1025" is a common supply route.
CTA
Need a 15-5PH pipe or plate quote with the right aging condition for your pressure and environment? Send your size, schedule and service condition to market@htpipe.com - we will confirm the condition and the wall, not just the grade.
