304 Vs 316 Stainless Steel CNC Machining Guide
February 12, 2026
In precision manufacturing, the success of stainless steel CNC machining often hinges on material selection from the outset. As quintessential austenitic stainless steels, 304 and 316 exhibit performance differences that directly impact part corrosion resistance, machining costs, and ultimate applications. Faced with an array of stainless steel grades, engineers frequently grapple with a dilemma: how to balance material costs, machining difficulty, and performance requirements? This article provides an in-depth comparison across three critical dimensions—chemical composition, corrosion resistance, and machining costs—while offering practical CNC material selection strategies to facilitate informed decisions and avoid unnecessary economic losses or performance compromises.
304 Stainless Steel: As a general-purpose stainless steel, its primary composition includes 18% chromium (Cr) and 8% nickel (Ni). The presence of chromium enables the formation of a dense chromium oxide protective layer, granting resistance to atmospheric, weak acid, and food-grade environmental corrosion. However, in chloride-rich environments (e.g., seawater or salt spray), 304 stainless steel is highly susceptible to pitting corrosion, leading to localized rapid deterioration that significantly compromises service life.
316 Stainless Steel: Distinguished from 304 by the addition of 2%–3% molybdenum (Mo) and increased nickel content (10%–14%), 316 stainless steel exhibits markedly enhanced pitting resistance. Experimental data reveal that in a 3.5% sodium chloride solution, 316 stainless steel corrodes at a rate of merely 0.001 mm/year—ten times slower than 304's 0.01 mm/year—underscoring molybdenum's pivotal role in corrosion resistance.
- Passivation Layer Repair and Strengthening: Molybdenum accelerates the repair of the passive film, maintaining its integrity even under chloride attack.
- Pitting Inhibition: Alters electrochemical conditions within potential pits, reducing initiation likelihood.
- Passivation Layer Stability: Synergizes with chromium to enhance the passive film's resilience.
High-Temperature Performance: At 800°C, 316 retains a yield strength of 150 MPa—20% higher than 304—making it preferable for aerospace components and other high-temperature applications.
Work Hardening Rate: 316's work hardening rate exceeds 304's by 15%, increasing machining difficulty. Precise control of cutting parameters is essential to mitigate tool wear and part deformation.
Due to molybdenum's relative scarcity (1/50th of chromium's global reserves), 316 stainless steel typically costs 30%–50% more than 304, necessitating careful budget considerations.
304 Machining: With excellent machinability, 304 permits cutting speeds of 120–150 m/min and extended tool life, ideal for mass production. However, excessive cutting heat must be avoided to maintain precision.
316 Machining: Requires carbide tools, reduced speeds (80–120 m/min), and increased coolant flow to counteract work hardening, raising labor costs by ~15%.
A desalination equipment manufacturer opting for 316 pump bodies saw a 40% initial cost increase but achieved a 15-year lifespan (versus 304's 5 years) and 60% lower maintenance costs, proving 316's superior TCO.
Recommended: 304 stainless steel (e.g., kitchenware, appliance housings).
Advantages: Cost-effective, easy machining, surface roughness up to Ra 0.8 μm.
Recommended: 316 stainless steel (e.g., ship components, chemical piping).
Enhancement: Electrolytic polishing (Ra 0.4 μm) improves corrosion resistance by 30%.
Implantable Devices: 316L (low-carbon variant) meets ASTM F138 for biocompatibility.
Food Equipment: 304 suffices for general use, but 316 excels in acidic/high-salt environments (e.g., juice filling systems).
304: TiAlN-coated carbide tools, 150 m/min speed, 0.15 mm/tooth feed.
316: Diamond-coated tools, 100 m/min speed to minimize work hardening.
Coolant: High-penetration, extreme-pressure additives for 316, with 20% increased flow.
Post-Processing: Sandblasting (Ra 1.6 μm) or electrolytic polishing (Ra 0.4 μm) enhances longevity.