SUS630 (17-4PH): Choosing H900, H1025 or H1150 for CNC Parts

SUS630, also known as 17-4PH or Type 630, is a martensitic precipitation-hardening stainless steel. A part's performance depends not only on the alloy name but also on its final heat-treatment condition. Stock is commonly supplied solution treated as Condition A and then aged to an H condition. H900, H1025 and H1150 identify nominal aging temperatures in degrees Fahrenheit and produce different combinations of strength, hardness, ductility and toughness. A drawing that says only “SUS630” may therefore be incomplete for a load-bearing part. State the governing material specification, product form, incoming condition and final acceptance condition.

Start with tension, bending, torsion, impact, cyclic loading and service temperature. A steady-torque shaft does not present the same design problem as an impact-loaded pin or a valve body in a corrosive medium. Corrosion behaviour also depends on condition, surface, stress and environment; the stainless designation does not guarantee immunity from pitting, crevice attack or stress-corrosion cracking. Industry requirements such as NACE, aerospace or medical specifications may impose additional restrictions. VietTech does not substitute one H condition for another without written design approval.

A common route is rough machining in Condition A, leaving controlled stock, aging through a qualified specialist partner, then finish machining or grinding critical surfaces. It is not the only valid route. Completing more machining before aging may reduce later work but requires an allowance for dimensional change and residual stress. Finishing after aging allows correction of functional dimensions but changes cutting conditions, tool life and burr risk. Threads, precision bores, seals and long datum chains need a clear pre- and post-treatment acceptance plan. VietTech performs CNC machining and inspection within the confirmed scope and coordinates specialist heat treatment with an appropriate partner.

Dimensional change during aging may be modest compared with quenching many tool steels, but it is not zero. Slender geometry, uneven sections, deep pockets, machining stress and furnace loading can still influence the result. Define datums, critical dimensions, measurement state, measurement temperature and inspection timing. A heat-treatment certificate or hardness result does not replace dimensional inspection, while a CMM report does not prove the H condition without material and treatment records.

Do not stop at the alloy name. Provide the material standard and form, incoming and final condition, required mechanical property or hardness, surfaces finished before and after aging, GD&T and datums, and required records. Terms such as SUS630, 17-4PH, UNS S17400 and 1.4542 appear in different supply chains, but their specifications and product requirements should not be treated as automatically interchangeable.

This guide was checked against Carpenter Technology's Custom 630 datasheet and Nippon Yakin Kogyo's NAS630 technical information. ASTM A564/A564M is a commonly referenced specification for heat-treated precipitation-hardening stainless bars and shapes, but the contractual drawing, cited edition and product form govern. The table is for screening choices only; the responsible design authority must approve the final condition for the actual load and environment.