Both grades show up on specs for aerospace parts, pump shafts, and precision components. They share the same alloy family but serve different strength requirements. Picking the wrong one wastes time and money. Understanding what separates them helps you make the right call before the order goes in.
If your part needs high strength and solid corrosion resistance in a single bar, you’re already in the right family. We’ve been supplying high-quality steel bars since 1970, and the question we hear most is whether 17-4 PH covers the application or 15-5 PH is the better fit for the strength requirement.
Two Grades, One Family, One Key Difference
Both 17-4 PH and 15-5 PH are martensitic precipitation hardening stainless steels. Engineers specify them when austenitic grades like 304 lack enough strength, and alloy steel corrodes too fast. Both grades combine high strength with meaningful corrosion resistance, which is why they appear in aerospace, hydraulic, and shaft applications regularly.
The separating factor is engineering intent. 15-5 PH was specifically designed to surpass the strength of 17-4 PH. That’s not a subtle difference. If your design is already pushing the upper limit of 17-4 PH, moving to 15-5 PH gives you a real strength gain while staying in the same alloy family.
17-4 PH: The Workhorse Grade
17-4 PH, UNS S17400, is built for highly stressed components in stringent environments where corrosion resistance and high strength must coexist. It responds well to heat treating, so you can target specific mechanical properties by specifying the right condition. It’s widely stocked and well understood across aerospace, pump, and precision shaft applications.
We supply 17-4 PH as a pump shaft quality grade. PSQ bars carry tensile strength of 100 KSI minimum and yield strength of 75 KSI minimum. Bars under 1 inch OD are held to +0 / -0.002 inch diameter tolerance. That dimensional control is what your seals, bearings, and packings depend on for consistent service life.
15-5 PH: When You Need More Strength
15-5 PH, UNS S15500, was designed from the start to exceed 17-4 PH mechanical performance. If your print is written to S15500 or your application is at the edge of 17-4 PH capability, this is the next step. You keep your corrosion resistance, stay in the precipitation hardening family, and gain a higher strength ceiling.
Both grades are available from us as precision-ground round bar stock. If your specification calls for 15-5 PH, we stock it ready to quote. Ordering the right condition from the start saves your shop from secondary processing and rework downstream.
Corrosion Resistance and SCC Performance
High-strength stainless grades in this family hold corrosion resistance comparable to 304 stainless steel. They also carry excellent stress corrosion cracking resistance, which matters for shaft and structural parts under sustained load in wet or chemically active environments. Alloy steel grades simply can’t deliver that combination.
SCC resistance means your parts don’t fail prematurely from cracking under stress in corrosive conditions. For pump shafts, hydraulic components, and aerospace structural parts, that protection is a hard requirement. Both 17-4 PH and 15-5 PH cover it without sacrificing the strength numbers your design needs.
Grinding and Straightening These Grades
Both grades come to you as centerless ground round bar. Centerless grinding achieves the tight diametrical tolerances and surface finish that aerospace and shaft applications require. Our pump shaft quality bars are ground to a super high degree of straightness to prevent harmful vibrations during machining and operation at higher speeds.
Heat treating can introduce warping. Our precision straightening service corrects that before your bar ships. For high-speed shafting applications, straightness is not optional. A bar that arrives straight and on tolerance saves your shop setup time and protects your tooling.
Choosing the Right Grade for Your Part
If your part operates within the strength capability of 17-4 PH and needs reliable corrosion resistance, that’s your grade. It’s well stocked, heat treat response is predictable, and it covers most aerospace, pump, and hydraulic applications without issue. Most shops start here and rarely need to move up.
If your design pushes past 17-4 PH limits or your specification is written to S15500, move to 15-5 PH. The strength advantage is real, corrosion performance stays consistent, and you’re still working in the same familiar alloy family. Our pump shaft quality inventory runs from 1/2 inch to 5 inches in both grades, produced using centerless grinding operations.
Get Precision Ground Bar Stock for Your Next Job
We supply 17-4 PH and 15-5 PH as precision-ground round bar stock from our facility in Palos Hills, IL. We’ve been doing this since 1970. Our bars are ground to tight tolerances, straightened, cut to your specs, and packaged to arrive ready to run.
Call us at (800) 818-0822, Monday through Friday, 8 AM to 5 PM. Or submit a quote online and tell us your grade, diameter, length, and condition. We’ll get back to you with what you need.
FAQs
What is the main difference between 17-4 PH and 15-5 PH stainless bar?
15-5 PH was designed to surpass the strength of 17-4 PH. Both offer high strength and corrosion resistance, but 15-5 PH delivers a higher strength ceiling.
Is 17-4 PH available as a pump shaft quality bar?
Yes. We supply it ground to 100 KSI tensile minimum, 75 KSI yield minimum, and +0 / -0.002 inch tolerance on bars under 1 inch OD.
Do both grades respond to heat treating?
Yes. Both respond well to heat treating, letting you specify the condition before grinding to achieve the mechanical properties your design requires.
What other high-strength stainless grades do you carry?
We also stock 13-8 PH, A286, 455 stainless, Nitronic 60, and duplex stainless as precision-ground round bar.
