Material number S17400: 17-4 PH
S17400 is the Unified Numbering System designation for 17-4 PH, martensitic precipitation-hardening stainless steel specified in ASTM A564.
What S17400 means
UNS numbers (ASTM E527 / SAE J1086) use a letter for the alloy family and five digits: G = AISI/SAE carbon and alloy steels (G41400 = 4140), S = stainless and heat-resisting steels (S30400 = 304), K = miscellaneous steels (K02600 = A36), T = tool steels, N = nickel alloys. The UNS number identifies a composition, not a product form or property level, so S17400 appears in several ASTM specifications (plate, bar, pipe) with different mechanical requirements.
17-4 PH at a glance
17-4 PH is the most-used precipitation-hardening stainless steel: a martensitic 17 % Cr / 4 % Ni matrix strengthened by copper precipitates formed during a simple single-step ageing at 480–620 °C. Because the steel is delivered soft-ish (Condition A, ≈ 35 HRC, fully machinable) and hardened afterwards at low temperature with almost no distortion (≈ 0.05 % contraction), it lets shops machine complex parts to size and then age them to 1170 MPa (170 ksi) yield and 44–47 HRC in the H900 condition — or to a tougher 725 MPa / 28 HRC at H1150. UNS S17400, AISI Type 630, EN 1.4542.
Corrosion resistance is close to 304 in most media (better than any conventional martensitic grade), which is why 17-4 is the material of pump shafts and impellers, valve stems and balls, aircraft fittings and landing-gear parts, gears, fasteners, nuclear-reactor components, oil-and-gas downhole tools and, increasingly, additively manufactured parts. The ageing temperature is chosen against the environment: H900 for maximum strength in benign service, H1025–H1150 for toughness and resistance to stress-corrosion and hydrogen embrittlement, H1150M for NACE MR0175 sour service (≤ 33 HRC).
JIS SUS630, GB 05Cr17Ni4Cu4Nb and EN 1.4542 are identical; 15-5 PH is the cleaner, ferrite-free variant preferred for transverse-loaded aerospace forgings.
Full data sheet for 17-4 PH → · Equivalent grades →