X7CrNiAl17-7 (EN 1.4568 / UNS S17700 / 17-7 PH) Forgings Forged rings, seamless rolled rings, flanges, shafts, discs, bars, sleeves and tube sheets, made to drawing by Jiangyin Jiangnan Metal Co., Ltd., China.
X7CrNiAl17-7 is the EN designation (material number 1.4568) of a chromium-nickel-aluminium precipitation hardening stainless steel, known elsewhere as 17-7 PH, AISI/SAE 631 and UNS S17700. It is austenitic and easily formed in the annealed condition, and is then hardened to high strength by heat treatment to Condition TH1050, RH950 or CH900, with good corrosion resistance, excellent fatigue properties and little distortion during heat treatment.
Jiangyin Jiangnan Metal Co., Ltd. (No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu, China) is an open-die forging factory producing X7CrNiAl17-7 forgings to EN, ASTM and customer drawings, with EAF plus VOD melting, optional ESR, ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, and EN 10204 3.1 or 3.2 certification. Enquiries: +86-189-2135-9659, sales@steelforgepieces.com.
1. What X7CrNiAl17-7 is
X7CrNiAl17-7 is a semi-austenitic precipitation hardening stainless steel containing nominally 17 % chromium, 7 % nickel and about 1 % aluminium. The aluminium is what makes the grade work. In the solution annealed condition the structure is austenitic and soft enough to form and machine; conditioning and low temperature ageing then transform the matrix to martensite and precipitate an aluminium rich phase, which raises strength sharply while keeping dimensional movement small.
Within the PH family, this grade carries the highest chromium and nickel compared with 15-5 and 17-4. Its corrosion resistance is close to that of AISI 301 / 1.4310, while its strength and fatigue behaviour make it the better choice for highly stressed parts. After ageing the material is magnetic.
For forged components the practical benefit is sequencing: a part can be forged, rough machined and drilled while soft, then hardened, which avoids the tool wear and distortion that come with machining fully hardened stock.
2. Designations and equivalents
| System | Designation |
|---|---|
| EN material number | 1.4568 |
| EN name | X7CrNiAl17-7 |
| UNS | S17700 |
| AISI / SAE | 631 |
| JIS | SUS 631 |
| Trade name | 17-7 PH |
| ASTM product specifications | A564, A693, A313, A579, A705 (ASME SA705) |
| AMS specifications | 5528, 5529, 5644, 5678 and related |
| European standard | EN 10088 |
For forgings the usual reference documents are ASTM A705 / ASME SA705 for age hardening stainless steel forgings and ASTM A564 for hot finished and cold finished bars and shapes. Sheet, strip and plate fall under ASTM A693 and wire under ASTM A313. Please state the specification and condition required on the enquiry.
3. Chemical composition
The EN limits for 1.4568 are tighter on silicon and sulphur than the UNS S17700 limits, so a heat ordered to EN will normally also meet UNS, although the reverse is not always true. Both sets are shown below.
| Element | EN 1.4568 / X7CrNiAl17-7 | UNS S17700 (17-7 PH) |
|---|---|---|
| Carbon, C | < 0.09 | < 0.09 |
| Silicon, Si | < 0.70 | < 1.00 |
| Manganese, Mn | < 1.00 | < 1.00 |
| Phosphorus, P | < 0.040 | < 0.040 |
| Sulphur, S | < 0.015 | < 0.030 |
| Chromium, Cr | 16.0 to 18.0 | 16.0 to 18.0 |
| Nickel, Ni | 6.5 to 8.3 | 6.5 to 7.75 |
| Aluminium, Al | 0.7 to 1.5 | 0.75 to 1.50 |
| Iron, Fe | Balance, roughly 70 to 75 | Balance |
Published nickel ranges for the EN grade differ slightly between data sheets, some quoting a narrower band than 6.5 to 8.3 %. We work to the range given in the edition of the standard named on the order, so please confirm the governing specification at enquiry stage. The ASTM 17-7 PH limits are narrower again, at 16.00 to 17.25 % chromium and 0.75 to 1.25 % aluminium.
4. Heat treatment conditions
This grade is not quenched and tempered like a martensitic stainless steel. It is supplied solution annealed as Condition A, and strength is developed by austenite conditioning, transformation of austenite to martensite, and finally ageing.
| Condition | Route | Purpose |
|---|---|---|
| A | Solution annealed at about 1065 C | Soft austenitic delivery condition for forming and machining |
| TH1050 | Condition at 760 C (1400 F) for about 1.5 h, cool to about 15 C (60 F) for about 0.5 h, age at 566 C (1050 F) for about 1.5 h | High strength with better ductility and toughness |
| RH950 | Condition at 954 C (1750 F) for about 10 min and air cool, cool to minus 73 C (minus 100 F) for about 1.5 h, age at 510 C (950 F) for about 1 h | Highest strength and hardness of the two standard aged conditions |
| C | Cold rolled, flat product | Heavily cold worked high strength strip |
| CH900 | Condition C followed by ageing at 482 C (900 F) for about 1 h and air cooling | Very high strength where limited ductility is acceptable |
Annealing is carried out at about 1066 C (1950 F), holding roughly 3 minutes per 2.5 mm of section, followed by air cooling. Parts must be clean and free of scale before ageing if results are to be consistent. For open-die forgings we run solution treatment and ageing in sequence in our own furnaces and can supply the time and temperature chart with the certificate.
5. Mechanical properties
Properties depend entirely on condition, so a single tensile figure for this grade means little. The minimum requirements per condition are listed separately below.
| Condition | Tensile strength | 0.2 % proof strength | Elongation | Reduction of area | Hardness |
|---|---|---|---|---|---|
| A (annealed) | 1035 MPa max | 380 MPa | 20 % | - | 92 HRB max |
| TH1050 | 1170 MPa (170 ksi) | 965 MPa (140 ksi) | 6 % | 25 % | 38 HRC / 352 HB |
| RH950 | 1280 MPa | 1030 MPa | 6 % | 10 % | 41 HRC / 388 HB |
| C (cold rolled) | 1380 MPa | 1205 MPa | 1 % | - | 41 HRC |
| CH900 | 1655 MPa | 1580 MPa | 1 % | - | see specification |
| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | 1170 MPa | 170,000 psi |
| Yield strength | 965 MPa | 140,000 psi |
| Hardness | 38 HRC | 38 HRC |
| Elongation at break | 6 % | 6 % |
| Modulus of elasticity | 204 GPa | 29,600 ksi |
| Poisson ratio | 0.27 to 0.30 | 0.27 to 0.30 |
For reference, 1.4568 in the solution annealed delivery condition is listed at 900 to 1100 N/mm2 tensile strength, 280 N/mm2 minimum 0.2 % proof strength, 35 % minimum elongation and 230 HB maximum. Those are supply condition figures, not the properties of the finished hardened part.
6. Physical properties
| Property | Value |
|---|---|
| Density | 7.81 g/cm3 |
| Modulus of elasticity | 200 kN/mm2 |
| Thermal conductivity | 16 W/m K |
| Specific heat capacity | 500 J/kg K |
| Electrical resistivity | 0.8 ohm mm2/m |
| Maximum temperature, heat treated | about 480 C (900 F) |
| Usual service limit | about 427 C (800 F) |
| Magnetic response | Austenitic in Condition A, magnetic after ageing |
7. Corrosion resistance and where not to use the grade
X7CrNiAl17-7 gives good general corrosion resistance, better than the hardenable straight chromium stainless steels in both TH1050 and RH950. It performs well in fresh water, industrial atmospheres and mild chemical and oxidising environments.
It is not recommended for salt water or reducing environments. Where the duty involves seawater, hot chlorides or sour service we will normally propose a duplex, super duplex, super austenitic or nickel alloy grade instead. Tell us the medium, temperature and pressure and we will say so rather than quote this grade by default.
8. Machining, forming and welding
Machining
Machinability is rated at about 75 % of B1112. The alloy produces long gummy chips, so chip breakers are needed, and slow speeds with constant uninterrupted feeds give the best results. Our normal practice is to rough machine in Condition A and finish machine after ageing, because turning, drilling and milling become much harder work once the part is fully hardened. In machining character the grade resembles 302, 303, 410, 420 and 430F, but it is far stronger than any of them.
Forming
Forming behaviour in the annealed condition is similar to grade 301. Severe forming sequences may need intermediate annealing.
Welding
Common arc and resistance welding methods can be used. Inert gas shielding matters during fusion welding to limit oxidation of the aluminium, and a matching 1.4568 filler is normally specified. Where the design allows, welded assemblies should be heat treated as a unit so that weld and parent metal end up in the same condition.
9. Forging capability
We make X7CrNiAl17-7 forgings to customer drawings rather than from a fixed catalogue. A typical order runs through steel sourcing and melt approval, open-die forging or ring rolling, heat treatment, rough or finish machining, NDT and certification.
- Melting route: EAF plus VOD as standard, with ESR remelt where cleanliness and segregation control are specified.
- Forging methods: open-die forging, seamless ring rolling, upsetting, and hollow forging by trepanning or boring.
- Delivery conditions: Condition A, TH1050 and RH950, with solution treatment and ageing carried out in house.
- Non-destructive testing: ultrasonic examination to EN 10228-3, SEP 1921 or ASTM A388, plus PT or MT, hardness survey and dimensional report on request.
- Mechanical testing: tensile, impact and hardness, with grain size and intergranular corrosion testing where specified.
- Certification: EN 10204 3.1 works certificate, or EN 10204 3.2 witnessed by a third party such as TUV, BV, DNV, SGS or LR.
- Machining: rough turning with allowance, or finish machining to drawing tolerance.
- Size range: outside diameter up to XXX mm, single piece weight XXX kg to XXX kg.
- Equipment: forging presses and hammers of XXX t, ring rolling mill XXX, heat treatment furnace XXX mm.
- Quality system: ISO 9001 certificate No. XXX.
10. Forged product range in X7CrNiAl17-7
11. Applications
Because the grade combines corrosion resistance with high strength and good fatigue behaviour, and moves little during heat treatment, it is widely used for intricate and highly stressed parts. Established uses include aircraft structures and hardware, springs, spring washers and thrust washers, diaphragms, knives and blades, chemical processing equipment, heat exchangers, power boilers and superheater tubes, valve components, tanks and fittings, and machine components.
In forged form our customers use X7CrNiAl17-7 for pump and compressor shafts and sleeves, valve stems, seat rings and bodies, flanges and tube sheets for heat exchangers and pressure equipment, rolled rings and bushings for rotating assemblies, and high strength fastener and spindle blanks. For chloride bearing or seawater service, see section 7 first.
12. Frequently asked questions
What is X7CrNiAl17-7 equivalent to?
Is X7CrNiAl17-7 the same as 17-4 PH?
Should I order TH1050 or RH950?
Can you supply third party inspected material?
What do you need in order to quote?
Can X7CrNiAl17-7 be used in seawater?
Quotation for X7CrNiAl17-7 forgings
Send the drawing or dimensions for X7CrNiAl17-7 / 1.4568 / UNS S17700 forged rings, flanges, shafts, discs, bars, sleeves or tube sheets. We quote custom open-die forgings worldwide and reply within one working day.
Jiangyin Jiangnan Metal Co., Ltd., Open-Die Forging Factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Related grades
Composition, condition and property data on this page are taken from published material data sheets for EN 1.4568 and 17-7 PH and from the condition requirements of ASTM A1082. The figures are for guidance at design and enquiry stage and are not a guarantee of the properties of any individual heat or component. The governing document is the specification and revision stated on the purchase order, and the properties achieved are those recorded on the material test certificate supplied with the goods.
Page last reviewed 10 October 2026. Published by Jiangyin Jiangnan Metal Co., Ltd., open-die forging factory, Jiangyin, Jiangsu, China.