Technical knowledge
17-4PH and 15-5PH: precipitation hardening stainless for strength
Composition, heat treatment conditions, strength and toughness differences between 17-4PH and 15-5PH, with guidance on using precipitation hardening stainless for flanges and bolting.
The condition letters matter more than the grade
| Condition | Approximate age | Character |
|---|---|---|
| Condition A | Solution annealed, not aged | Soft, for machining and forming |
| H900 | About 480 C | Maximum strength, lower toughness |
| H1025 | About 550 C | Balanced |
| H1150 | About 620 C | Best toughness and stress corrosion resistance |
Tip Never order 17-4PH flanges without naming the condition. The same part can differ by more than 400 MPa in yield strength depending on the age.
17-4PH versus 15-5PH
15-5PH has a more tightly controlled composition and a cleaner structure, which gives more uniform hardness and toughness through thick sections and better transverse properties. For large flanges and heavy forgings where properties must hold through the section, 15-5PH is usually the safer specification. For smaller parts, 17-4PH remains widely available and economical.
Limits you should know before specifying
- Chloride resistance is modest. These are not seawater alloys, especially in the higher strength conditions.
- Avoid H900 in sour service. The higher strength conditions are more susceptible to sulphide stress cracking.
- Welding requires a full re-age. The heat affected zone will not otherwise reach the specified properties.
- Dimensional change. Allow for movement during ageing and finish machine critical faces where possible.
Questions about this topic
Are 17-4PH flanges suitable for seawater?
Generally no. Their chloride resistance is limited and they are more prone to localised attack and stress corrosion cracking in the higher strength conditions. Use duplex, super duplex or a nickel alloy for seawater duty.
Which condition should I choose?
Choose H900 only where maximum strength is essential and the environment is benign. For most process and marine adjacent duty, H1100 or H1150 gives a far better balance of toughness and stress corrosion resistance.
Can I weld 17-4PH and keep the properties?
Only with a full solution anneal and re-age of the whole component. Local repair welds on aged material will leave a softened heat affected zone unless the part is re-treated.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email [email protected] or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
Talk to an engineer
Share your duty conditions and we will shortlist candidate alloys within one working day.