UNS S45500 · W.Nr. 1.4543 · X3CrNiCuTiNb12-9 · ASTM Type XM-16 · Carpenter CarTech Custom 455® · ~12% Cr – 8.5% Ni – 2% Cu – 1.1% Ti. ASTM A564 Type XM-16 range: 11.00-12.50% Cr – 7.50-9.50% Ni – 1.50-2.50% Cu – 0.90-1.40% Ti – 0.10-0.50% Nb+Ta – Mo ≤ 0.50% – C ≤ 0.03% – Mn ≤ 0.50% – Si ≤ 0.50% – P ≤ 0.015% – S ≤ 0.015%. The producer (Carpenter / AMS 5617) type analysis is wider: C ≤ 0.05% – P ≤ 0.040% – S ≤ 0.030% – Ti 0.80-1.40%.
A martensitic precipitation-hardening stainless steel that hardens with a single-step aging treatment. The part is machined or cold formed in the soft solution-treated state (Condition A), then hardened in one cycle between 482 and 566 °C.
Forms
Round bar · Flat bar · Plate · Sheet · Tube · Forging
Standards
AMS 5617 (bars, wire, forgings — vacuum induction plus vacuum consumable electrode melted) · AMS 5860 (sheet, strip, plate) · AMS 5578 (welded tubing) · AMS 5672 (spring temper wire) · ASTM A564 / ASME SA-564 Type XM-16 (bars and shapes) · ASTM A693 Type XM-16 (plate, sheet, strip) · ASTM A313 Type XM-16 (spring wire) · ASTM F899 (surgical instrument steel) · W.Nr. 1.4543 THE MOST IMPORTANT DIFFERENCE: ASTM A564 defines ONLY H900, H950 and H1000 for Type XM-16. There is NO XM-16 equivalent of the H1025 / H1075 / H1100 / H1150 conditions that exist for 17-4 PH and 15-5 PH.
Advantage
A two-sided advantage, measured with the minimum values of the same standard (ASTM A564) in the same condition. STRENGTH: in H900 the XM-16 minimum is 1620 MPa tensile / 1515 MPa yield;
Welding
Process: shielded fusion welding and resistance welding are suitable. Oxyacetylene welding is NOT recommended — carbon pickup occurs in the weld (Carpenter). Preheat: not required; Carpenter states that preheating is not required to prevent cracking during welding.
Limits
TEMPERATURE: Carpenter’s only numerical limit reads “short exposures to elevated temperatures can be considered, provided the maximum temperature is at least 28 °C (50 °F) LESS than the aging temperature”. For a part aged at H900 (482 °C) that means roughly 454 °C for short exposure, and it is NOT a continuous service rating.
Compiled from manufacturer data sheets · confirm against the current specification before ordering
On this page · click to jump
Standards by Product FormConditions and Mechanical PropertiesHeat Treatment, Welding and MachiningWhere It Belongs, and What It Compares ToFrequently Asked Questions
Custom 455 is a martensitic stainless steel hardened by ageing. It belongs to the precipitation hardening stainless steel family; its UNS designation is S45500.
It draws its strength from the copper-rich intermetallic precipitates that form during ageing. The copper and titanium levels in the alloy are critical to this mechanism, while the low carbon content limits carbide precipitation at the grain boundaries and reduces the risk of cracking after welding.
Within this group it is most often compared with 17-4 PH. The difference is this: Custom 455 keeps corrosion resistance similar to 17-4 PH while offering markedly higher tensile and yield strength, and it also has better weldability and heat treatment stability. Where a PH application is pushing against its strength limit, 455 is the next step up.
It is used in aerospace for propeller shafts, fasteners and landing gear parts; in defence systems for missile attachment hardware; and in chemical processing and in oil and gas in H₂S-bearing environments (grades compliant with NACE MR0175 / ISO 15156 are available).
ASTM A313 was verified with three sources; for a spring wire order it must be confirmed from the standard text. AMS 5672 is a SPRING TEMPER WIRE specification, not bar; it must not be used for a bar order. AMS 5578 covers WELDED tubing only. MIL-S-83311 appears in some distributor lists; it could not be verified with 4 independent sources and was left out of the table.
Custom 455 (UNS S45500 / XM-16) is a proprietary martensitic precipitation-hardening stainless steel originated by Carpenter Technology. Two features define it: very high yield strength for a PH stainless, and almost no dimensional change on hardening — the second of which lets parts be finish-machined soft and hardened afterwards.
Standards by Product Form · Custom 455 (S45500 / XM-16)
— (no dedicated AMS filler-wire specification was found for Custom 455)
Surgical-instrument bar
ASTM F899 — single-sourced, not independently confirmed
Military
MIL-S-83311 — single-sourced
ASTM A579
— not associated with S45500 in any source reviewed; do not list it
Composition: C ≤0.05% · Mn ≤0.50% · Si ≤0.50% · P ≤0.040% · S ≤0.030% · Cr 11.00–12.50% · Ni 7.50–9.50% · Mo ≤0.50% · Cu 1.50–2.50% · Nb+Ta 0.10–0.50% · Ti 0.80–1.40%. The low carbon together with the titanium, copper and niobium additions is what makes the alloy harden by intermetallic precipitation rather than by carbides. (The precipitating phase is not named in the mill and service-centre sources reviewed, so no specific phase is claimed here.)
Conditions and Mechanical Properties
STRENGTH BY AGEING CONDITION
DEFENCE METAL
Condition
Hardness
Yield MPa
Tensile MPa
Elongation
Condition A (solution treated)
36 max
—
—
—
H900
≥ 47
1515
1620
8% (3 sources — see conflicts)
H950
≥ 44
1415
1515
10%
H1000
≥ 40
1275
1415
10%
DEFENCE METAL
Additional information
H1050 note
The H1050 (566 °C) condition is NOT DEFINED for Type XM-16 in ASTM A564, so there is no standard minimum row for it.
All rows are ASTM A564/A564M Type XM-16 (ASME SA-564) STANDARD MINIMUM values, for the LONGITUDINAL direction and sections up to 150 mm (6 in.). They are NOT manufacturer TYPICAL values. This table gives ASTM A564 minimums. Manufacturer typical values lie above these minimums, but a typical-value table could not be verified with 4 independent sources and is therefore not published here (see omissions). The H900 minimum elongation is 8%. For 17-4 PH and 15-5 PH in the same condition it is 10% — Custom 455 reaches its higher strength with a lower elongation minimum. Hardness is a MINIMUM in the H conditions and a MAXIMUM limit in Condition A. The values apply to sections up to 150 mm and to the longitudinal direction.
HEAT TREATMENT — SCHEMATIC
1 · SOLUTION TREATMENT
830 ± 15 °C (1525 ± 25 °F) — ASTM A564 Type XM-16. Carpenter’s bulletin gives the same window as 816/843 °C (1500/1550 °F). section dependent; the bulletins give no numerical holding time
2 · COOL
cool rapidly; water quenching is preferred for small sections
3 · AGEING
see the table below
DEFENCE METAL
Solution treatment
Step
Condition A (solution treated — as-delivered)
Temperature
830 ± 15 °C (1525 ± 25 °F) — ASTM A564 Type XM-16. Carpenter’s bulletin gives the same window as 816/843 °C (1500/1550 °F).
Time
section dependent; the bulletins give no numerical holding time
Cooling
cool rapidly; water quenching is preferred for small sections
Result
36 HRC / 331 HB maximum. The part is machined and cold formed in this state.
Note
NOTE: this temperature is 210 °C LOWER than the 1040 ± 15 °C that ASTM A564 gives for 17-4 PH (Type 630) and 15-5 PH (Type XM-12).
DEFENCE METAL
H900
Step
H900
Temperature
480 °C (900 °F)
Time
4 hours
Cooling
air cool
Standard
ASTM A564 Type XM-16
DEFENCE METAL
H950
Step
H950
Temperature
510 °C (950 °F)
Time
4 hours
Cooling
air cool
Standard
ASTM A564 Type XM-16
DEFENCE METAL
H1000
Step
H1000
Temperature
540 °C (1000 °F)
Time
4 hours
Cooling
air cool
Standard
ASTM A564 Type XM-16
DEFENCE METAL
H1050
Step
H1050
Temperature
566 °C (1050 °F)
Time
4 hours
Cooling
air cool
Note
Carpenter states that aging is done by holding for four hours at a SELECTED temperature between 482/566 °C (900/1050 °F) and air cooling; 566 °C is the top of that range. There are no standard minimum values for it, but it can be ordered against a special specification.
Status
NOT DEFINED for XM-16 in ASTM A564
Schematic; the time axis is not to scale. No published TTT/CCT curve was used. Aging is SINGLE-STEP: four hours at the selected temperature plus air cooling. There is no XM-16 equivalent of the multi-step cycles of 17-4 PH such as H1150-M or H1150-D. Schematic; the time axis is not to scale. ASTM A564 defines only H900, H950 and H1000 for Type XM-16. H1050 is not in the standard. The aging time is four hours in all three conditions; H900 for 17-4 PH is one hour. The two must not be confused. A welded part is welded in the solution-treated condition and, for the best property combination, solution treated again before aging.
The values below are typical room-temperature properties for 25 mm bar.
Custom 455 · Typical Mechanical Properties by Condition
WARNING — a real transcription error in circulation. On a widely used service-centre page the H900 row is shifted by one: the values shown there for H900 (yield ~1516 MPa, tensile ~1585 MPa, ~48 HRC) are in fact the manufacturer’s H950 figures, and the H950 row on that same table is blank. The real H900 values are markedly higher (see the table above). If a supplier’s table shows H900 and H950 almost identical, or leaves H950 empty, the table has shifted.
Heat Treatment, Welding and Machining
Heat treatment
Solution treatment (Condition A): 816–843 °C (1500–1550 °F), cooled rapidly; water quenching is preferred for small sections. Ageing:4 hours at the selected temperature between 482 and 566 °C, air cool. The number in the condition name is the ageing temperature in °F. Standard delivery is Condition A. The grade’s headline property is that dimensional change during hardening is only about −0.001 in./in., which the manufacturer describes as permitting “close-tolerance finish machining in the annealed state”. In practice this largely removes the need for post-hardening grinding allowances.
Welding
It can be welded by the shielded fusion and resistance welding processes; oxyacetylene welding is not recommended. Preheat is not required to prevent cracking. Interpass temperature and a specific filler-alloy designation are not stated in the manufacturer’s datasheet, so no filler number is invented here. Because the alloy is normally welded in the annealed (Condition A) state and only reaches full strength after ageing, weldments must be re-aged after welding, or the HAZ will not reach parent-metal strength.
Machining
Machine in the annealed (Condition A) state; the hardness after ageing markedly reduces machinability. The manufacturer’s guidance is rigid tool and work supports, slower speeds, positive cuts and ample coolant, and describes the machining behaviour as resembling nickel maraging steels. Carbide tooling is required for aged material, allowing 2–3× the surface speed of HSS. No numeric machinability index (for example a percentage of B1112) could be verified — the sources publishing a percentage for this grade were not reliable.
Where It Belongs, and What It Compares To
COMPARISON IN THE H900 CONDITION USING ASTM A564 MINIMUMS
DEFENCE METAL
Alloy
Solution treatment
Condition A hardness
H900 tensile mpa
H900 yield mpa
H900 elongation
H900 reduction of area
H900 hardness
Chromium
Custom 455 (Type XM-16 · S45500)
830 ± 15 °C
36 HRC / 331 HB max
1620
1515
8% (3 sources)
30%
≥ 47 HRC / 444 HB
11.00-12.50%
17-4 PH (Type 630 · S17400)
1040 ± 15 °C
38 HRC / 363 HB max
1310
1170
10%
40%
≥ 40 HRC / 388 HB
15.00-17.50%
15-5 PH (Type XM-12 · S15500)
1040 ± 15 °C
38 HRC / 363 HB max
1310
1170
10%
35%
≥ 40 HRC / 388 HB
14.00-15.50%
One source, one standard, one condition: ASTM A564/A564M, H900, longitudinal direction, sections up to 150 mm. No manufacturer typical values are used. In H900 Custom 455 is 24% higher in minimum tensile and 30% higher in minimum yield strength, and its solution treatment is 210 °C lower. The price: the elongation minimum drops to 8%, the reduction-of-area minimum to 30%, and the chromium band stays at 11.00-12.50% — general corrosion resistance is below both competitors. The comparison is taken from the same table of the same standard; typical values from different manufacturers are not mixed in. The H1025-H1150 conditions of 17-4 PH and 15-5 PH have no XM-16 equivalent; the comparison is valid for H900 only. The chromium band is not the only determinant of corrosion resistance, but it is the main difference between these three alloys.
Custom 455 · Properties and Comparison
DEFENCE METAL
Service temperature
Good oxidation resistance to approximately 593 °C (manufacturer data)
Corrosion resistance
The manufacturer states only this: superior to the 12% chromium grades (Type 410) and approaching the 17% chromium grades (Type 430). No mill document claims superiority over 17-4 PH or 15-5 PH; because Custom 455 carries less chromium (11–12.5%), its general corrosion resistance is expected to sit somewhat behind theirs — that is an inference from composition, not documented data
Yield strength
Even in the softest aged condition (H1050) about 1206 MPa; ~1634 MPa at H900 — roughly three times the yield strength of annealed 304
Dimensional stability
About −0.001 in./in. on hardening — one of the strongest selling points in this family
Magnetic
Ferromagnetic, as a martensitic PH grade (no numeric permeability data could be verified)
Typical applications
Aerospace fasteners and fittings, hydraulic actuator components, shafting and pins; also sporting goods such as golf club faces where strength-to-weight matters
Higher chromium → better general corrosion resistance, and far wider stock and specification support. Custom 455 is not a corrosion upgrade but a strength and precision upgrade
Carpenter’s own comparison positions Custom 465 as giving a superior combination of strength, toughness and stress-corrosion resistance “compared with other high-strength precipitation hardenable stainless alloys such as Custom 455 or 13Cr-8Ni”
Frequently Asked Questions
When is Custom 455 the right choice over 17-4 PH?
Choose Custom 455 when the application needs a yield strength above what 17-4 PH delivers in its standard aged conditions, combined with tight dimensional control through heat treatment. The documented ~−0.001 in./in. dimensional change lets parts be finish-machined soft (Condition A) and aged afterwards, which is a substantial manufacturing advantage for close-tolerance aerospace fittings, hydraulic actuator components and fasteners. Where general corrosion resistance is the priority, 17-4 PH remains the better default: its chromium content is materially higher (15–17.5% versus 11–12.5%) and it is far more widely stocked and specified. Custom 455 is a specialty upgrade for strength-critical, precision-machined parts — not a general corrosion upgrade.
Which H condition should be specified?
H900 (482 °C) gives the highest strength available (~1634 MPa yield, ~1689 MPa tensile, ~49 HRC) but the lowest ductility and toughness (11% elongation), which suits highly loaded fasteners and studs. H1000 (538 °C) is a common general-purpose aerospace condition, balancing ~1345 MPa yield with better ductility (14% elongation) and higher toughness, and most published reference data is built around it. H1050 trades a little more strength for maximum ductility and toughness. The general rule: specify the lowest H number — that is, the highest strength — that still meets the part’s toughness and fatigue requirements. In every case the condition must be called out explicitly on the drawing and the order, and confirmed against the AMS 5617 class.
Is generic “S45500” from a non-Carpenter mill equivalent?
Not necessarily. Custom 455 is a Carpenter Technology-originated proprietary grade; UNS S45500 and ASTM A564 Type XM-16 define only the compositional and mechanical envelope. Any mill melting to that chemistry and meeting AMS 5617 or ASTM A564 requirements can legitimately ship “S45500”. However the melting practice (Carpenter typically uses VIM + VAR), the cleanliness and the published typical properties — such as the documented −0.001 in./in. dimensional stability — are products of the process, not of the chemistry, and are not guaranteed by the UNS number. For aerospace or specification-critical work, require certification to the specific AMS number, and where the manufacturer’s documented behaviour is what matters, specify CarTech Custom 455 by name.
→ Contact us for Custom 455 stock availability, sizes and AMS 5617 / AMS 5860 certified supply.
