304 vs 316L for CNC Machining: Choosing the Stainless Grade

The most common stainless selection decision in CNC machining is the one between the general-purpose austenitic grade and its molybdenum-bearing sibling. Both machine as tough, work-hardening alloys; both strengthen by cold work only; and the property envelopes overlap far more than their prices differ. What separates them is environmental: the molybdenum in the higher-alloy grade is there for chlorides, and a part that never meets chlorides is paying for chemistry it does not use.

This page compares the two as machining selections — the collected property envelope side by side, the decision rule that settles most cases, and where the machining behavior actually differs. The linked grade pages and knowledge articles carry the depth; this page carries the decision.

CNC machined metal parts packed in a blue tote bin on a workshop bench — Product illustration, actual appearance confirmed at quotation

Side by side

Property	304	316 / 316L
Tensile strength	515–620 MPa (annealed)	≥485 MPa (316/316L); 316 ≈570 MPa (annealed)
Yield strength (0.2% offset)	≈205–215 MPa (annealed)	316 ≈290 MPa; 316L ≈170 MPa (0.2% offset) (annealed)
Hardness	≈70–85 HRB (annealed)	160–201 HB (annealed)
Density	8.0 g/cm³ (0.29 lb/in³) (annealed)	—
Elongation	—	≥40% (annealed)
Detail page	304 machining	316 / 316L machining

Values above are read from the collected evidence and catalog data at build time — heat-treatment condition is stated where the source carries one, and a dash means the value is not established rather than not applicable. Cost is quoted per part, not banded here: request a quotation for the specific geometry.

Choose which one

Choose 304 when…	Choose 316 / 316L when…
Ambient, indoor or washdown service with no chloride exposure Food-contact and sanitary hardware outside brine or chemical lines Cost-sensitive machined hardware where the environment is benign Parts that will be passivated and live indoors for their service life	Marine, coastal or de-icing-salt exposure — open or crevice Chlorinated process fluids, brine handling or chemical lines Repeated-sterilization medical and laboratory hardware Anything welded in assembly that must cite a low-carbon variant

The decision rule, and when it does not settle it

Map the environment, not the budget: chlorides in service push the selection to the molybdenum grade, and their absence usually keeps the general-purpose grade. The unsettled middle is smaller than buyers expect but real — intermittent spray, indoor pools of process water, or environments that may change over the part's life. There the honest move is to quote both and let the price delta inform a risk decision, rather than to guess once and re-source after the first stain or pit.

Machining behavior: same family, slightly different difficulty

Both grades work-harden, form continuous chips, and punish dwell and rubbing. The higher-alloy grade runs a step harder on tool life and heat at the edge, so identical geometry prices with slightly more cycle time and tooling. Neither difference is a feasibility boundary — the practical machining consequence is concentrated in the features that already stress the family: deep small bores, thin walls and fine cosmetic finishes.

Strength is not the differentiator

The collected envelopes overlap closely, and neither grade responds to hardening heat treatment — if a design fails on strength, moving between these two grades solves nothing. Strength-driven stainless selection belongs to the precipitation-hardening family, at a real corrosion cost. Choosing between the two grades on this page is a corrosion decision; dragging strength into it usually signals that a third grade should be on the table.

What to state on the RFQ

The service environment, in plain words — this is the single input that validates the grade choice. Whether the part is welded in your assembly (it decides the low-carbon variant and any post-weld treatment), the finish and passivation callouts, and the tolerance class on critical features. An RFQ with the environment stated gets a grade confirmation instead of a guess.