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15-5Ph / 1.4545 / UNS S15500 / AMS 5659

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Corrosion resistance: 15-5 PH has very good corrosion resistance and is used where high mechanical strength and high corrosion resistance are required together. 15-5 PH has somewhat better corrosion resistance than grade 630 (17-4 PH, 1.4542), because unwanted inclusions in the material are minimised by a second melting operation. As the name UGIPURE 155 PH suggests, the material is purer than 17-4 PH, and that purity is a factor in raising its corrosion resistance.

Weldability: This grade is difficult to weld and is not the choice where extensive welding is involved.​‌​​‌​

Machinability: Because the material is heat treated, 15-5 PH materials are hard. Because their internal structure is strong, 15-5 PH materials have very high mechanical values. These two properties make 15-5 PH difficult to machine, and the material is put through various stages in order to machine comfortably.

Heat treatment: Various heat treatments are applied to increase the strength of the 15-5 alloy. After heat treatment, 15-5 stainless can be supplied in eight different conditions: H900, H925, H1025, H1075, H1100, H1150, H1150+1550 and H1150-M.​‌​​‌​

Applications: It is used in corrosive environments, in high pressure environments, in the aerospace industry, in petrochemicals, and in many industrial fields such as chemicals and food equipment.

Standards by Product Form​‌​​‌​

15-5 PH (UNS S15500 / XM-12 / 1.4545) belongs to the same Cr-Ni-Cu precipitation-hardening family as 17-4 PH; the difference is not in the chemistry but in its transverse (through-thickness) toughness. Two points govern the order: which AMS number covers which product form, and which H condition is required.​‌​​‌​

WARNING — two common catalogue errors. (1) AMS 5659 does not cover sheet, plate or tube; its scope is bars, wire, forgings, flash-welded rings, extrusions and stock for forging. Sheet, strip and plate are AMS 5862. Many reseller pages merge the two into one list reading “AMS 5659 · sheet · tube”. (2) ER630 / E630, sold widely as “15-5 PH filler”, actually has the 17-4 PH nominal chemistry (~16–16.75% Cr), not that of 15-5 PH; it is the industry-accepted practical substitute, not a true match. The genuinely matching wire is AMS 5826. AMS 5827, sometimes cited as the matching covered electrode, is also a 17-4 PH-type analysis and has been cancelled since 2000.​‌​​‌​

Composition (ASTM A564 / A693 / A705, XM-12): C ≤0.07% · Mn ≤1.00% · Si ≤1.00% · P ≤0.040% · S ≤0.030% · Cr 14.00–15.50% · Ni 3.50–5.50% · Cu 2.50–4.50% · Nb+Ta 0.15–0.45%. Note: molybdenum is not a controlled alloying element; most mill datasheets do not list it at all. Do not market 15-5 PH as a molybdenum-bearing grade.

H Conditions — the Strength / Toughness Trade-Off​‌​​‌​

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This table is the core of the page. The values below are AMS 5659 minimums for bar; for sheet and plate (AMS 5862 / ASTM A693) the elongation minimums are lower because of the thinner test-specimen geometry. Whenever a ductility figure is published, state which standard and which size class it comes from — reseller datasheets diverge on exactly this point.

Heat Treatment, Welding and Machining

Heat treatment​‌​​‌​

The mechanism is martensitic precipitation hardening: ageing forms finely dispersed copper-rich precipitates within the martensite. Solution treatment (Condition A): 1040 °C ±14, ½ hour, air or oil cool to below 32 °C. Ageing: H900 at 482 °C for 1 hour; H925 / H1025 / H1075 / H1100 / H1150 at their nominal temperature for 4 hours, air cool. H1150M: 760 °C for 2 hours, air cool, then 621 °C for 4 hours, air cool. Dimensional change on ageing is small (roughly 0.05–0.10% shrinkage), so parts are machined close to final size in Condition A and hardened afterwards.

Welding​‌​​‌​

Readily welded by GTAW/GMAW and resistance welding using procedures similar to the 300 series. Preheat is generally not required (the alloy is not air-hardening). Post-weld heat treatment is required: welding heat over-ages or solution-anneals the HAZ, so the specified H condition must be re-applied; for multi-pass welds a solution anneal before final ageing is recommended. Filler: the true chemistry match is AMS 5826; the common practical substitute is ER630 / E630 (a 17-4 PH analysis). Where the weld itself does not need to age-harden, austenitic 308L is used — that deposit will not age and will not match parent-metal strength.

Machining​‌​​‌​

Machine in Condition A, where tool wear and cutting loads are lowest. If a hardened condition must be machined, H1150M gives the best machinability of the standard conditions (lowest hardness). Machinability falls as ageing temperature falls: H900 (388 HB) is the hardest to machine, H1150 and H1150M the easiest.

15-5 PH or 17-4 PH?​‌​​‌​

Service temperature — two different figures, do not conflate them: high strength is retained to about 316 °C; oxidation (scaling) resistance is good to about 593 °C. Quoting only the 593 °C figure as “usable to 593 °C” overstates the load-bearing capability. The grade is magnetic. Typical applications: aerospace components, gears, shafts, valves, cylinders, pumps, nuclear reactor components, chemical, petrochemical and offshore equipment.​‌​​‌​

Frequently Asked Questions

What is the real difference between 15-5 PH and 17-4 PH, and when does it matter?​‌​​‌​

Both are Cr-Ni-Cu martensitic precipitation-hardening stainless steels with practically identical strength and hardness at matching H conditions, and broadly similar corrosion resistance. The real difference is transverse (short-transverse / through-thickness) toughness and the consistency of fracture behaviour: 15-5 PH is designed to minimise the delta-ferrite stringers that make 17-4 PH’s properties direction-dependent, and it is typically produced by remelting (VAR, VIM+VAR or ESR). That difference shows up most in parts loaded across the working direction: thick bar, forgings or plate where the critical stress axis is transverse, and in aerospace, nuclear or offshore work where a toughness floor in the weak direction is required. Where the part is thin, symmetric, or loaded only along the primary working direction, 17-4 PH is usually an equally valid and more economical choice.

Which H condition should I order?​‌​​‌​

A low ageing temperature (H900) gives the highest strength and hardness (≥1310 MPa tensile, ≥388 HB) but the lowest ductility and toughness. As the ageing temperature rises, strength falls while elongation, reduction of area and impact toughness rise markedly: at H1150 tensile is ≥931 MPa but elongation is ≥16% and reduction of area ≥50%. H1150M (the 760 °C + 621 °C double age) gives the lowest strength but the best toughness and machinability of the standard conditions. H1025–H1100 is the common general-purpose compromise. Finally, state which standard governs the condition: the minimum ductility requirements of AMS 5659 (bar) and AMS 5862 (sheet and plate) are not the same.

Can Condition A material be put straight into service?​‌​​‌​

No. Condition A (solution annealed) is a machining condition, not a service condition: it carries no guaranteed minimum tensile or yield strength, and per mill data the untempered martensite in this state is more susceptible to hydrogen embrittlement and chloride stress-corrosion cracking than any properly aged condition. Standard practice is to machine (rough or finish) in Condition A and then age to the specified H condition. Because dimensional change on ageing is small — roughly 0.05–0.10% — machining close to final size beforehand is normal. Always verify that the ageing treatment has been carried out before the part ships or enters service.

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