17-4 PH Stainless Steel
Fasteners
Manufacturer India
17-4 PH Explained — Composition, Chemistry & What Makes It Unique
17-4 PH (UNS S17400) is a martensitic precipitation-hardened (PH) stainless steel — the designation “17-4” refers to its nominal composition of 17% chromium and 4% nickel. It is the most widely used PH stainless steel in engineering, manufactured to ASTM A564 Grade 630 for bar stock used in fastener manufacture and to AMS 5643 for aerospace procurement.
What makes 17-4 PH unique among stainless steels is the combination of mechanical properties achievable by age hardening alone — no cold work needed. In the H900 condition (aged at 900°F / 482°C), 17-4 PH achieves ≥1310 MPa UTS and ≥1170 MPa yield strength — properties that exceed Grade 12.9 alloy steel in absolute UTS terms, while retaining the corrosion resistance of 17% Cr stainless. The tensile properties are directly controlled by the ageing temperature: lower ageing temperature = higher strength, lower toughness; higher ageing temperature = lower strength, higher toughness and corrosion resistance. This is the H-condition selection principle.
The 17-4 PH alloy is martensitic in the solution-annealed (Condition A) state — unlike austenitic 316L, it is magnetic in all heat-treated conditions. It is not suitable for applications requiring non-magnetic stainless steel. For non-magnetic high-strength stainless, Duplex 2205 (non-magnetic, but lower strength) or cold-worked austenitic grades are used instead.
| Element | Min % | Max % |
|---|---|---|
| Chromium (Cr) | 15.00 | 17.50 |
| Nickel (Ni) | 3.00 | 5.00 |
| Copper (Cu) | 3.00 | 5.00 |
| Niobium + Tantalum (Cb+Ta) | 0.15 | 0.45 |
| Carbon (C) | — | 0.07 |
| Silicon (Si) | — | 1.00 |
| Manganese (Mn) | — | 1.00 |
| Iron (Fe) | Balance | |
17-4 PH H-Condition Profiles — Strength vs Toughness
The H-number designates the ageing temperature in degrees Fahrenheit. Lower ageing temperature = higher strength, lower ductility/toughness. Higher ageing temperature = better ductility, toughness, and corrosion resistance at lower strength. All five conditions available from Akbar Fasteners from ASTM A564 Gr 630 certified bar stock.
17-4 PH Fastener Types & Standards
All forms in all H-conditions from ASTM A564 Gr 630 certified bar stock. H1025 and H900 are primary stocking conditions. H925, H1075, H1150 available on order with typically 2–3 week lead time. NABL hardness certificate per ASTM A370 on every lot.
17-4 PH Stud Bolts
Fully threaded stud bolts in H1025 (most common), H900, and H1150 conditions. ASME B16.5 Class 150–2500, M12–M100, lengths to 3,000mm. For high-pressure flange joints in oil and gas wellheads, aerospace test rigs, pharmaceutical autoclaves, and marine platform equipment requiring higher strength than SS 316L without specifying exotic alloy.
Hex Bolts
Full thread and partial thread hex bolts in all H-conditions. M6–M100. H1025 for chemical and marine equipment covers requiring strength beyond 316L. H900 for precision mechanical bolting, injection moulding equipment, and high-load structural connections where 17-4 PH’s combination of stainless corrosion resistance and alloy steel strength is specified.
Hex Nuts
Standard hex and heavy hex in H1025 and H1150 (nuts are typically supplied in H1150 for higher ductility during tightening, matching the stud bolt in H1025 or H900 for strength). M6–M100. Food processing equipment, pharmaceutical vessel body nuts, and marine hardware where 17-4 PH is the specified nut material to match the stud bolt grade.
Socket Cap Screws
Hex socket cylindrical head cap screws — the most common 17-4 PH fastener form in aerospace and precision mechanical service. H900 socket cap screws to AMS 5643 for aerospace structural fastening requiring magnetic stainless steel. H1025 for food processing equipment internal fastening, pharmaceutical mixer shafts, and marine instrument connections. M3–M36.
Washers
Plain flat washers in all H-conditions. M6–M100. 17-4 PH washers for matched-grade assemblies where the washer-nut-bolt galvanic potential must be minimised — aerospace structural joints, pharmaceutical autoclave cover assemblies, and marine deck equipment where the specific H-condition hardness is part of the engineering design file.
Threaded Rods
Full thread threaded rods in H1025 and H1150 conditions. M6–M100, lengths to 3,000mm. 17-4 PH threaded rods for marine structural tie-rod systems, pharmaceutical equipment support rods, and high-strength food processing equipment frames where 316L threaded rod strength is insufficient and exotic alloy cost is not justified.
AMS 5643 & Custom
AMS 5643 certified bar stock for aerospace and defence procurement. Inch UNC/UNF thread (ASME B18.6.7), non-standard head forms, flanged hex, drawing-specific configurations. Contact sales@akbarfasteners.in with your condition, size, thread pitch, and documentation requirement.
Matched Sets
17-4 PH stud bolts + hex nuts + washers from the same ASTM A564 Gr 630 certified heat, same H-condition. Single MTC, hardness certificate, and COC for the complete assembly. For pharmaceutical, food processing, and aerospace assembly documentation where individual fastener and nut traceability is a QA requirement.
17-4 PH vs SS 316L vs Inconel 718 — Grade Matrix
17-4 PH sits between standard SS 316L (lower strength, better general corrosion) and Inconel 718 (higher strength, better high-temperature corrosion). Use this matrix to confirm whether 17-4 PH is the correct specification for your service environment.
| Property / Criterion | 17-4 PH H1025 This Page | SS 316L | Inconel 718 |
|---|---|---|---|
| MECHANICAL PROPERTIES | |||
| Min UTS | ≥1030 MPa | ≥515 MPa | ≥1241 MPa |
| Min YS (0.2%) | ≥862 MPa | ≥205 MPa | ≥1034 MPa |
| Strength vs cost | Excellent value | Low cost, low strength | High cost, max strength |
| Magnetic | Yes (martensitic) | No (austenitic) | No |
| CORROSION RESISTANCE | |||
| Mild chloride / marine deck | Good (comparable 316L) | Good | Excellent |
| Seawater immersed | Limited — pit risk | Limited | Excellent |
| High-temp oxidising acid | Not suitable | Limited | Excellent |
| Food contact / pharma CIP | H1150 compliant | Standard | Overkill / cost |
| SERVICE ENVIRONMENT | |||
| Temperature limit | ~315°C (H900/925) | ~300°C (creep onset) | ~650°C |
| Aerospace structural | H900 / AMS 5643 | Insufficient strength | Yes (extreme cases) |
| Oil & gas wellhead | H925 — good choice | Insufficient strength | 718 if HPHT extreme |
Need higher strength for extreme HPHT: Inconel 718 (≥1241 MPa) · Need exotic alloy for seawater: Monel K500
17-4 PH Application Areas
High-strength stainless steel service where SS 316L lacks the mechanical properties and exotic alloy is not justified by the corrosion environment — the precise niche 17-4 PH fills.
Aerospace
structural stainless bolts
Oil & Gas Wellhead
wellhead structural fasteners
Pharmaceutical
pharma vessel cover fasteners
Food Processing
food-grade high-strength bolts
Marine Equipment
high-strength marine hardware
Nuclear
reactor internals fasteners
Pumps & Compressors
compressor body bolts
Defence
H900 tactical equipment bolts
17-4 PH Standards Coverage
NABL-accredited hardness testing per ASTM A370 on every lot. Same ISO 9001:2015 quality system as our exotic alloy range.
Complete Documentation Package
Grade 630 · H-Condition
ASTM A370 · NABL Lab
Conformance
Accredited Laboratory
TÜV · BV · Lloyds
Related High-Strength Fasteners
17-4 PH for strength + stainless. Inconel 718 for strength + extreme corrosion. Monel K500 for strength + seawater. SS 316L for corrosion + economy.
Inconel 718 Fasteners
When 17-4 PH H900 (≥1310 MPa) is still insufficient, or when the corrosive environment is beyond 17-4 PH’s stainless rating — Inconel 718 (≥1241 MPa) with its Ni-Cr alloy corrosion resistance is the next step.
View Page →Monel K500 Fasteners
For seawater service requiring high strength — Monel K500 (≥1000 MPa age-hardened) provides seawater immunity that 17-4 PH’s 17% Cr cannot match in aggressive seawater or marine immersion service.
View Page →SS Fasteners Range
For applications where 17-4 PH’s strength is not required — SS 316L for standard corrosion, Duplex 2205 for higher chloride resistance, 904L for H₂SO₄ service where the base stainless steel family is correct.
View SS Range →High Tensile Fasteners
When corrosion resistance is not required and pure mechanical strength is the criterion — ISO 898 Grade 12.9 alloy steel (1,220 MPa) provides equivalent or greater strength than 17-4 PH H900 at significantly lower material cost in non-corrosive environments.
View Page →Need 17-4 PH Stainless
in Any H-Condition?
H-condition · product form · size · quantity · AMS or ASTM cert · documentation. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Export: +91 8696 32 4646 · Support: +91 800 9315 333 · export@akbarfasteners.in