Precipitation-hardening stainless steel
UNS S17700 Open-die forgings, seamless rolled rings, flanges, shafts and bars in 17-7 PH
UNS S17700 is a chromium-nickel-aluminium semi-austenitic precipitation-hardening stainless steel, known commercially as 17-7 PH and designated AISI Type 631 and DIN 1.4568.
It carries 16.00 to 18.00 percent chromium, 6.50 to 7.75 percent nickel and 0.75 to 1.50 percent aluminium. The grade is formed soft in the austenitic Condition A, then hardened by low-temperature treatments that cause far less distortion than conventional quench and temper. Forgings are ordered to AMS 5644, ASTM A705 or ASTM A579.
Jiangyin Jiangnan Metal melts its own steel and forges to drawing at Zhouzhuang Town, Jiangyin City, Jiangsu Province, China.
- UNS
- S17700
- Also called
- 17-7 PH, AISI 631, DIN 1.4568
- Type
- Semi-austenitic precipitation hardening
- Conditions
- A, T, R-100, C, TH 1050, RH 950, CH 900
- Forging specs
- AMS 5644, ASTM A705, ASTM A579
- Modulus
- 200 GPa (29 x 106 psi)
- Max piece
- 30 t, ring OD to 6,000 mm
- Certificates
- EN 10204 3.1 and 3.2
What the grade is
The designation follows the chemistry. The 17 is the nominal chromium content and the 7 the nominal nickel content, with aluminium acting as the hardening element.
S17700 can be formed in a soft austenitic condition and then hardened to a high strength level by low-temperature heat treatment. Because those temperatures are low, distortion stays small compared with quench-and-temper hardening, which is why the grade turns up in intricate parts, flat springs and aerospace hardware. The alloy has been in commercial use for many years and is also available in vacuum-arc or electroslag remelted form where cyclic stresses call for better fatigue resistance.
Aluminium is a reactive element, so melting, welding and heat-treating practice all have to guard against aluminium loss.
Source: ATI 17-7 technical data sheet (UNS S17700); Superior Tube alloy 17-7 PH data.
Equivalent designations
S17700 is cross-referenced as AISI 631, DIN 1.4568, AMS 5528, AMS 5529, AMS 5568, AMS 5644, AMS 5678, AMS 5824, ASTM A313 (631), ASTM A564 (631), ASTM A579 (631), ASTM A693 (631), ASTM A705 (631), MIL-S-25043, SAE J217 and SAE J467.
Source: AZoM, stainless steel grade 17-7 PH (UNS S17700).
Chemical composition
| Element | Symbol | Content |
|---|---|---|
| Chromium | Cr | 16.00 - 18.00 |
| Nickel | Ni | 6.50 - 7.75 |
| Aluminium | Al | 0.75 - 1.50 |
| Carbon | C | 0.09 max |
| Manganese | Mn | 1.00 max |
| Silicon | Si | 1.00 max |
| Phosphorus | P | 0.040 max |
| Sulfur | S | 0.030 max |
| Iron | Fe | Balance |
Source: ATI 17-7 technical data sheet; aircraftmaterials.com 17-7PH (AMS 5528 / 5529 / 5644). Confirm limits against the specification revision named on your order.
Heat-treatment conditions
Hardening from Condition A takes two stages. An austenite-conditioning treatment lets the relatively stable austenite transform to martensite, then an ageing treatment precipitates the hardening phase. The reaction can be driven past peak strength, so higher ageing temperatures or longer times give lower strength.
| Condition | Austenite conditioning | Transformation | Ageing |
|---|---|---|---|
| A (annealed) | As-supplied austenitic condition, lowest strength and best formability. Anneal at 1066 C (1950 F), 3 minutes per 2.5 mm of section, air cool. | ||
| TH 1050 | 760 C / 1400 F | Transforms to martensite at about room temperature | 565 C / 1050 F |
| RH 950 | 955 C / 1750 F | Hold at -73 C (-100 F) to complete transformation | 510 C / 950 F |
| C then CH 900 | Heavy cold work transforms austenite to martensite directly, giving Condition C | 482 C / 900 F | |
Source: ATI 17-7 technical data sheet; annealing cycle per AZoM.
Material grows by roughly 0.004 in/in moving from Condition A to the TH or RH conditions. Allow for that when machining ahead of final heat treatment.
S17700 does not use the H 900, H 925, H 1025, H 1075, H 1100 or H 1150 temper designations. Those single-step ageing tempers belong to martensitic precipitation-hardening grades such as 17-4 PH and 15-5 PH. Because S17700 is semi-austenitic, it has to be austenite-conditioned and transformed before ageing, so its conditions are A, T, R-100, C, TH 1050, RH 950 and CH 900. Where a drawing calls for S17700 in an H temper we raise it at enquiry stage rather than guess at an equivalent.
Mechanical properties
| Property | Condition A | TH 1050 | RH 950 |
|---|---|---|---|
| 0.2 % yield strength | 345 MPa (50 ksi) | 1205 MPa (175 ksi) | 1380 MPa (200 ksi) |
| Tensile strength | 825 MPa (120 ksi) | 1345 MPa (195 ksi) | 1550 MPa (225 ksi) |
| Elongation | 30 % | 8 % | 7 % |
| Hardness | 85 HRB | 42 HRC | 47 HRC |
Source: ATI 17-7 technical data sheet. Typical values, shown to indicate condition response. Not minimum or maximum values for specification or final design.
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | 1170 MPa | 170,000 psi |
| Yield strength | 965 MPa | 140,000 psi |
| Modulus of elasticity | 204 GPa | 29,600 ksi |
| Elongation at break | 6 % | 6 % |
| Hardness | 38 HRC | 38 HRC |
| Poisson's ratio | 0.27 - 0.30 | 0.27 - 0.30 |
Source: AZoM, grade 17-7 PH, bar and forgings in TH 1050.
Cold rolled and aged
Strength after ageing depends heavily on the cold work put in beforehand. Under AMS 5529, sheet and strip cold rolled to Condition C carries a minimum yield of 1205 MPa (175 ksi) and a minimum tensile of 1380 MPa (200 ksi). Aged to CH 900 those minima rise to 1585 MPa (230 ksi) yield and 1655 MPa (240 ksi) tensile.
Physical properties
| Property | Condition A | TH 1050 | RH 950 |
|---|---|---|---|
| Density | 7810 kg/m3 | 7670 kg/m3 | 7640 kg/m3 |
| Modulus of elasticity | 200 GPa (29 x 106 psi) | ||
| Modulus of rigidity | 75 GPa (11 x 106 psi) | ||
| Thermal expansion, 21 to 93 C | 15.3 x 10-6 /C | 10.1 x 10-6 /C | 10.3 x 10-6 /C |
| Magnetic response | Weakly ferromagnetic | Strongly ferromagnetic | Strongly ferromagnetic |
| Thermal conductivity, 20 to 150 C | about 16.5 W/m.K in the hardened conditions | ||
| Electrical resistivity | about 80 micro-ohm.cm, annealed or hardened | ||
Source: ATI 17-7 technical data sheet.
Corrosion resistance and service temperature
Testing puts the corrosion resistance of S17700 on a par with Type 304 in most media and ahead of the hardenable chromium grades. Looking at it by condition, TH 1050 and RH 950 beat Types 410, 420 and 431 but fall a little short of Type 304, while CH 900 comes close to Type 304 in most environments.
The grade suits fresh water, industrial atmospheres and mild chemical or oxidising service. It is not recommended for salt water or reducing environments.
Published service limits differ depending on the source and the duty. AZoM cites useful strength and mechanical properties in operation up to 427 C (800 F). The Cleveland-Cliffs 17-7 PH product data bulletin states the heat-treated alloy gives exceptional mechanical properties up to 482 C (900 F). For flat springs, aircraftmaterials.com cites excellent properties up to 315 C (600 F). Pick the limit that matches your loading and duty cycle.
Machining, forming and welding
Machining
Machinability runs at about 75 percent of B1112. Chips come off long and gummy, so chip breakers are needed, and slow speeds with a constant feed give the best result. The hardened conditions are much harder to cut, so rough-machine before final ageing wherever the drawing allows it.
Forming
In Condition A the alloy forms much like Type 301. It work-hardens quickly and may need intermediate annealing for deep drawing or intricate shapes, and spring-back is similar to Type 301. In Condition C it is extremely hard and strong, so fabrication methods suited to that strength level have to be used.
Welding
S17700 welds by conventional inert-gas methods. Shielding protects the aluminium from loss and oxidation, since the hardening reaction depends on it. As-welded metal is largely austenitic with properties close to Condition A, and the ductility of that weld removes the preheat and post-weld anneal that martensitic age-hardenable alloys need. Getting a high-strength weld means a full post-weld sequence of solution annealing, austenite conditioning, transformation and precipitation hardening.
Source: ATI 17-7 technical data sheet; AZoM; aircraftmaterials.com.
Specifications
| Specification | Product form |
|---|---|
| AMS 5644 | Bars and forgings |
| ASTM A705 / ASME SA705 | Forgings |
| ASTM A579 | Forgings |
| ASTM A564 / ASME SA564 | Bar, wire and shapes in age-hardening stainless, hot rolled, extruded or forged |
| ASTM A693 / ASME SA693 | Plate, sheet and strip |
| AMS 5528 | Sheet, strip and plate |
| AMS 5529 | Sheet and strip, cold rolled |
| AMS 5568 | Welded tubing |
| AMS 5678 / ASTM A313 | Wire and spring wire |
| AMS 5824 | Welding wire |
Source: ATI 17-7 technical data sheet, specifications and certificates table; aircraftmaterials.com.
The ASTM B series covers nonferrous material, and B564 applies to nickel-alloy forgings, so it is not a valid specification for S17700. Order S17700 forgings to AMS 5644, ASTM A705, ASTM A579 or ASTM A564. The three high-temperature car-bottom furnaces here do cover the solution treatments that ASTM B564 Grade 2 requires, but that work belongs to the nickel alloy range rather than this grade.
What we forge in S17700
Every item below is forged from a single piece of steel melted on site. No welding, no casting, no purchased billet of unknown origin.
Seamless rolled rings
Ring-rolled from a punched preform on a radial-axial mill, rectangular or contoured section, for bearing, gear and pressure-vessel work.
Forged rings
Upset and punched rings for sizes and sections outside the ring-mill envelope, including retaining rings and valve seat rings.
Flanges
Weld neck, blind, slip-on, socket weld, lap joint and orifice flanges for vessels, exchangers and process piping.
Shafts and spindles
Stepped shafts, pinion shafts, eccentric shafts and spindles for pumps, compressors and gearboxes.
Bars and blocks
Round, flat and square forged bar, gear blanks and blocks, supplied black or proof-machined.
Discs and tube sheets
Solid forged discs, tube sheets and covers, proof-machined for volumetric inspection.
Sleeves and bushings
Hollow forged sleeves, bushings and cylinders bored from solid forged blanks.
Valve components
Stems, seat rings, blocks, bodies and bonnets for ball, gate, globe, check and plug valves.
Where the grade is used
Published application data for 17-7 PH covers springs and washers of many kinds, chemical processing equipment, heat exchangers, power boilers, superheater tubes, and parts that have to carry high stress at temperature. The property mix suits aerospace work in particular, including corrosion-resistant springs in hydraulic and fuel systems, actuator parts and latching hardware. Low distortion on heat treatment is also why the grade gets picked for intricate machined parts.
Source: AZoM; aircraftmaterials.com; Coiling Technologies 17-7 PH spring applications.
Working envelope
| Item | Limit | Set by |
|---|---|---|
| Ring outside diameter | up to 6,000 mm | 6 m radial-axial ring mill |
| Single-piece weight | up to 30,000 kg | 60 t maximum heat, 6,300 t press |
| Turned shaft length | up to 14,000 mm | C61160 horizontal lathe, 15 m well furnace for vertical quench |
| Machined disc diameter | up to 5,000 mm | 5,000 mm vertical turning lathe |
| Bored hollow sections | 1,600 mm dia x 10,000 mm | CNC deep-hole drilling machine |
| Minimum ring size | from OD 50 mm | Upset-and-punch route below ring-mill range |
| Minimum order | 10 kg | No minimum piece count |
| Lead time | 20 to 60 days | Section size and heat-treatment route |
Melting, heat treatment and testing
Steel is melted here rather than bought in. Carbon, alloy, stainless and duplex grades run through the 25 t electric arc furnace, are refined in 25 t and 50 t ladle furnaces and decarburised in 30 t and 60 t vacuum oxygen decarburisation units where low carbon or tight nitrogen control is wanted. Protective-atmosphere electroslag remelting is available on 3 t and 6 t furnaces, which is the route to take when the part sees cyclic stress and the specification calls for remelted material.
Fourteen heat-treatment furnaces cover the solution anneal to Condition A along with the austenite conditioning and ageing that TH 1050, RH 950 and CH 900 require. Two well-type furnaces 15 m deep allow long shafts to be quenched vertically. State the condition you need by its correct designation on the order, and tell us at enquiry stage if the sub-zero hold for RH 950 is required, since that step is scheduled separately.
Ultrasonic testing is carried out to ASTM A388 or EN 10228-3, with the acceptance class agreed before production. The on-site laboratory also covers optical emission spectrometry, infrared carbon and sulphur analysis, tensile testing, Charpy V-notch impact to minus 60 C, magnetic particle inspection and metallography. Intergranular corrosion testing to ASTM A262 or ASTM G28 is placed with an accredited third-party laboratory and the report is issued alongside the mill certificate. Certificates are issued to EN 10204 3.1 as standard, with 3.2 witnessed by BV, DNV, LR, SGS, TUV or your own inspector on request. The works holds CCS, BV, DNV, LR and NK approvals.
Questions we get asked
Is UNS S17700 the same thing as 17-7 PH?
Yes. UNS S17700, 17-7 PH, AISI Type 631 and DIN 1.4568 all name the same chromium-nickel-aluminium semi-austenitic precipitation-hardening stainless steel, nominally 17 percent chromium and 7 percent nickel with 0.75 to 1.50 percent aluminium.
How does it differ from 17-4 PH and 15-5 PH?
S17700 is semi-austenitic. It arrives soft and austenitic in Condition A and has to be austenite-conditioned and transformed to martensite before it can be aged, which is why its conditions are TH 1050, RH 950 and CH 900. The martensitic grades are already martensitic after solution treatment and harden in a single ageing step, which is where the H 900 to H 1150 tempers come from.
Which condition should a forged ring or shaft be ordered in?
TH 1050 is the usual hardened condition for bar and forgings, giving around 1170 MPa tensile, 965 MPa yield and 38 HRC. RH 950 is stronger but adds the sub-zero transformation step at minus 73 C. CH 900 relies on heavy cold work and is normally a sheet, strip and wire condition rather than a heavy-forging one. Send the drawing and the duty and we will comment before you release the order.
Can it be used in sea water?
No. Published guidance says 17-7 PH should not be used in salt water or reducing environments. It performs well in fresh water, industrial atmospheres and mild chemical or oxidising conditions, with resistance comparable to Type 304 in most media.
Is S17700 a stock grade at your works?
It is forged to order rather than held in stock. The regular precipitation-hardening grades here are 17-4 PH, 15-5 PH and PH 13-8 Mo, and the plant forges to customer chemistry, so S17700 is quoted against the drawing and the specification you name. Ask before you design around it so the melt route and the heat-treatment cycle can be confirmed.
What do you need in order to quote?
The drawing or finished dimensions, quantity, the governing specification such as ASTM A705 or AMS 5644, the heat-treatment condition, the ultrasonic standard and acceptance class, and whether the certificate is to be EN 10204 3.1 or 3.2. Minimum order is 10 kg with no minimum piece count.
Sources
Material data on this page is taken from the ATI 17-7 technical data sheet for UNS S17700, the Cleveland-Cliffs ARMCO 17-7 PH product data bulletin, the AZoM datasheet for grade 17-7 PH, and the aircraftmaterials.com 17-7PH data sheet covering AMS 5528, AMS 5529 and AMS 5644. Typical values are informational and are not minimum or maximum values for specification or final design. Check every requirement against the revision of the standard named on your order.
Reviewed 4 October 2026. Published by Jiangyin Jiangnan Metal Co., Ltd.