Before diving into grades, it's worth understanding that 303, 304, and 316 are fundamentally different materials from 17-4 PH at the microstructural level. This difference explains most of the property gaps and is something every engineer specifying stainless should be aware of.[2]
300-series values shown for annealed bar. 17-4 PH shown for H900 (peak strength). See the full condition table below for all tempers.[1]
303, 304 and 316 values are typical for annealed bar (ASTM A276 minimums are 75 ksi tensile / 30 ksi yield); 17-4 PH values are ASTM A564 / AMS 5643 minimums.[5]
17-4 PH in H900 condition is more than double the tensile strength of the austenitic grades. This is the fundamental reason it exists: when 304 or 316 isn't strong enough, 17-4 PH fills the gap without leaving the stainless family.[1]
303 is chemically identical to 304 with one critical addition: sulfur (and sometimes selenium), which creates manganese sulfide inclusions that act as chip breakers during machining. The result is dramatically better machinability at the expense of weldability and slight corrosion reduction.[1][2]
304 is the most widely produced stainless steel in the world, roughly half of all global stainless output. It contains 18% chromium and 8% nickel (the basis of the informal "18-8" designation), which gives it excellent corrosion resistance and outstanding weldability.[1][3] It work-hardens during machining, so proper tooling and aggressive feeds are essential. 304L (low carbon) is specified when welding is required to prevent sensitization.
316 adds 2 to 3% molybdenum to the 304 base, dramatically improving resistance to pitting and crevice corrosion in chloride environments like saltwater and chemical processing equipment.[1][3] Mechanically it is nearly identical to 304 in annealed condition. Use 316L when welding is required.
17-4 PH (UNS S17400) is a martensitic precipitation-hardening stainless steel containing 17% chromium, 4% nickel, plus copper and niobium. Unlike the austenitic 300-series grades, it can be heat treated to dramatically different strength levels depending on the aging condition specified, ranging from 930 MPa (H1150) to 1310 MPa (H900).[1][4]
17-4 PH machines well across all conditions, from Condition A through H900. A common misconception is that Condition A is the softest state. It is not: Condition A is untempered martensite at roughly 33 HRC (363 HB max), and it machines acceptably but no better than the overaged conditions. The softest and most machinable conditions are H1150-M and H1150; H900 is the hardest. Two approaches work well in practice: rough in Condition A, then age and finish-machine, or buy H1150 or H1025 stock and machine it complete. Shops with experience in precipitation-hardened stainless (like C&W) can comfortably machine 17-4 in any aged condition. Because it is martensitic, 17-4 PH is magnetic in all conditions.[2][4]
The H-number is the aging temperature in degrees Fahrenheit. Lower temperatures produce higher strength with less ductility. Higher temperatures produce lower strength with better toughness and corrosion resistance. Always specify the condition on your drawing.[4]
Strength and hardness values in the table are ASTM A564 / AMS 5643 specification minimums, not typical values. Typical H900 material runs 42 to 44 HRC.[4][5]
| Condition | Aging cycle | UTS | Yield | Hardness | Elong. | Availability | Best for |
|---|---|---|---|---|---|---|---|
| Cond. A |
Solution annealed No aging |
150 ksi
1034 MPa
|
110 ksi | ≤38 HRC (363 HB max; typ. ~33 HRC) | 10% | Widely stocked | Solution annealed, untempered martensite. Machines acceptably, but it is not the softest condition (H1150-M and H1150 are). Common practice: rough in Condition A, then age and finish-machine. |
| H900 |
900°F / 482°C 1 hr + air cool |
190 ksi
1310 MPa
|
170 ksi | 40 HRC | 10% | Somewhat stocked | Peak strength. Lowest toughness. Aerospace fasteners, tooling, high-load structural parts. |
| H925 |
925°F / 496°C 4 hr + air cool |
170 ksi
1172 MPa
|
155 ksi | 38 HRC | 10% | Heat treat required | Slightly lower strength than H900, marginally better toughness. |
| H1025 |
1025°F / 552°C 4 hr + air cool |
155 ksi
1069 MPa
|
145 ksi | 35 HRC | 12% | Heat treat required | Well-balanced strength and toughness. Pump shafts, valve stems, impact-loaded components. |
| H1075 |
1075°F / 579°C 4 hr + air cool |
145 ksi
1000 MPa
|
125 ksi | 32 HRC | 13% | Heat treat required | Good toughness with still-elevated strength. |
| H1100 |
1100°F / 593°C 4 hr + air cool |
140 ksi
965 MPa
|
115 ksi | 31 HRC | 14% | Heat treat required | High toughness, moderate strength. Couplings and flanges. |
| H1150 |
1150°F / 621°C 4 hr + air cool |
135 ksi
930 MPa
|
105 ksi | 28 HRC | 16% | Somewhat stocked | Lowest strength of the single-age conditions, highest ductility. Specified for toughness, low-temperature impact, and stress corrosion cracking resistance. |
| H1150-M |
1400°F + 1150°F Double overage |
115 ksi
793 MPa
|
75 ksi | 24 HRC | 18% | Specialty | Double over-aged. Maximum toughness and SCC resistance. Nuclear, offshore, aggressive chemical environments. |
Toggle between properties to compare all four grades visually. 17-4 PH shown at H900 (peak strength).[1]
300-series values for annealed bar. 17-4 PH shown for both H900 and H1150 to illustrate the full condition range.[1][4]
| Property | 303 | 304 | 316 | 17-4 PH H900/H1150 |
|---|---|---|---|---|
| Microstructure | Austenitic | Austenitic | Austenitic | Martensitic (PH) |
| Magnetic? | No | No | No | Yes, all conditions |
| Tensile strength |
90 ksi
620 MPa
|
84 ksi
579 MPa
|
84 ksi
579 MPa
|
190 / 135 ksi
1310 / 930 MPa
|
| Yield strength |
35 ksi
241 MPa
|
42 ksi
290 MPa
|
42 ksi
290 MPa
|
170 / 105 ksi
1170 / 724 MPa
|
| Hardness | 96 HRB (typical) | 92 HRB (typical) | 95 HRB (typical) | 40 / 28 HRC (min) |
| Elongation | 50% | 55% | 50% | 10% / 16% |
| Density |
0.286 lb/in³
7.93 g/cm³
|
0.285 lb/in³
7.90 g/cm³
|
0.289 lb/in³
8.00 g/cm³
|
0.282 lb/in³
7.78 g/cm³
|
| Machinability | Excellent | Fair (work hardens) | Fair (work hardens) | Good (all conditions) |
| Weldability | Poor | Excellent (304L) | Excellent (316L) | Fair (re-age after) |
| Corrosion resistance | Good | Very good | Excellent (Mo) | Very good |
| Heat treatable? | No | No | No | Yes (H900–H1150) |
| Availability | Excellent | Excellent | Very good | Cond. A widely stocked; H900 and H1150 somewhat stocked; others require heat treat |
| Relative cost | $ (baseline) | $ (similar) | $$ (1.2–1.5×) | $$$ (2–3× + heat treat) |
303, 304 and 316 values are typical for annealed bar (ASTM A276 minimums are 75 ksi tensile / 30 ksi yield); 17-4 PH values are ASTM A564 / AMS 5643 minimums.[5]
Our team at C&W reviews material callouts and can coordinate heat treatment as part of your job.