Stainless Steel CNC Machining Guide: 303 vs 304 vs 316 vs 17-4PH Compared (2026)
Quick recommendation: For general CNC parts, Stainless 303 offers the best machinability (78% rating) and is the most cost-effective. Choose 304 for food and general corrosion resistance, 316 for marine and surgical applications, and 17-4PH when you need high strength (1,100+ MPa after heat treatment).
Stainless Steel Grade Properties Comparison
Property
303 SS
304 SS
316 SS
17-4PH (H900)
Tensile Strength (MPa)
620
515
580
1,310
Yield Strength (MPa)
240
205
290
1,170
Hardness (Brinell)
160
150
175
388
Density (g/cm³)
8.0
8.0
8.0
7.8
Cost per kg (2026)
$4–7
$4–7
$6–10
$8–15
Machinability Rating
78%
45%
40%
35%
Machinability rating relative to 1212 steel (100%). 17-4PH shown in H900 condition (highest strength). Annealed 17-4PH has lower strength but better machinability (~45%).
Corrosion Resistance & Application Guide
Grade
Corrosion Resistance
Weldability
Magnetic
Best Applications
303
★★★☆☆
★★☆☆☆
Slightly
Shafts, nuts, bolts, fittings, bushings
304
★★★★☆
★★★★★
No
Food equipment, kitchen, architecture, general
316
★★★★★
★★★★★
No
Marine hardware, surgical instruments, chemical
17-4PH
★★★★☆
★★★☆☆
Yes
Aerospace, nuclear, high-strength shafts, gears
Machining Time Comparison: Same Part, Different SS Grades
Part: Ø25×80mm Shaft
303 SS
304 SS
316 SS
17-4PH
Material cost (1 pc)
$3.50
$3.50
$5.50
$8.00
Machining time
18 min
28 min
32 min
38 min
Tool wear cost added
$1
$3
$4
$5
Total per part (50 pcs)
$16
$25
$32
$42
Premium vs 303
Baseline
+56%
+100%
+163%
When to Pay the Premium for 316 or 17-4PH
Choose 316 over 304 when: The part will be exposed to chlorides (salt water, pool chemicals, bleach), used in surgical environments, or requires USP Class VI biocompatibility
Choose 17-4PH when: You need strength >1,000 MPa AND corrosion resistance — it’s the only stainless that competes with alloy steel on strength while maintaining stainless corrosion resistance
Stick with 303 when: The part is a mechanical component (shaft, nut, fitting) with no welding requirements. The 78% machinability rating means faster production and lower cost