What is the difference between 303, 304, and 316 stainless steel?

303 has sulfur added for superior machinability and is ideal for parts that will not be welded. 304 is the most versatile with good corrosion resistance and excellent weldability. 316 adds molybdenum for superior chloride resistance—marine, chemical, and saltwater environments.

Which stainless steel grade is most machinable?

303 stainless steel offers the best machinability. The added sulfur improves chip breakage and reduces tool wear. Use 303 for screw machine parts, fittings, and shafts that will not be welded.

What is work hardening and why is it a problem?

Work hardening occurs when the surface becomes harder than the base metal from cutting friction. It damages tools and ruins surface quality. Prevention: keep tools sharp, stay in the cut, avoid light cuts, and use climb milling.

What is passivation and when is it needed?

Passivation is a chemical treatment that removes free iron from the surface and restores the protective chromium oxide layer. It is standard for all stainless parts, especially medical, food, and marine applications.

Can you machine hardened stainless steel?

Yes, hardened stainless grades can be machined with carbide tooling, but machining is typically performed in the annealed condition with heat treatment applied after.

How does stainless steel compare to aluminum for CNC machining?

Stainless is stronger, harder, and more corrosion-resistant but machines slower compared to aluminum. Stainless parts cost more due to longer cycle times and greater tool wear.

CNC Stainless

CNC stainless steel machining is the precision processing of stainless steel alloys using computer-controlled cutting tools. Stainless steel is defined by its chromium content—minimum 10.5%—which forms a passive oxide layer that provides exceptional corrosion resistance without coatings. The material is available in multiple families: austenitic grades with excellent corrosion resistance and formability, martensitic grades with high strength and hardness, and precipitation-hardening grades with high strength and good corrosion resistance.

Stainless steel presents unique machining challenges: work hardening during cutting, gummy chip formation, and high cutting forces. 303 stainless is the most machinable grade with added sulfur for chip breakage. 304 is the most versatile all-rounder but work hardens rapidly. 316 offers maximum corrosion resistance with molybdenum addition for marine and chemical applications. Tolerances are held to ±0.02–0.05mm standard, with precision work at ±0.01mm.

Our CNC Machining Services

From prototype to production — reliable quality, on-time delivery

We provide precision CNC machining services for a wide range of materials including aluminum, steel, stainless steel, copper, brass, titanium, PEEK, PTFE, acetal, nylon, and other engineering plastics. Our manufacturing capabilities cover 3-axis, 4-axis, and 5-axis CNC milling, as well as CNC turning, suitable for both prototype development and high-volume production runs.

With ISO 9001:2015 certification and a commitment to quality, we serve customers across aerospace, automotive, medical, electronics, industrial equipment, and consumer goods industries. Our in-house capabilities include surface finishing, anodizing, powder coating, heat treatment, and inspection with CMM and optical measurement equipment.

We offer competitive pricing, flexible lead times, and full material traceability. From simple brackets to complex precision components, we deliver parts that meet your specifications with reliable quality and on-time delivery.

Case StudiesMore+

SLINAR - 316L Stainless Steel Medical Fasteners | CNC Turned Screws & Pins for Orthopedics

316L Stainless Steel Medical Fasteners | CNC Turned Screws & Pins for Orthopedics-stainless_steel

SLINAR - Precision D2 Tool Steel Fixture Fastening Component: High-Accuracy Milling with Superior Flatness for 3C Assembly Tooling

Precision D2 Tool Steel Fixture Fastening Component: High-Accuracy Milling with Superior Flatness for 3C Assembly Tooling-stainless_steel

SLINAR - Precision 304 Stainless Steel Test Fixture Block: High-Stability Milling for Semiconductor Test Equipment

Precision 304 Stainless Steel Test Fixture Block: High-Stability Milling for Semiconductor Test Equipment-stainless_steel

SLINAR - CNC Machined Stainless Steel Precision Gear Components - Group Overview

CNC Machined Stainless Steel Precision Gear Components - Group Overview-stainless_steel

SLINAR - Precision 304 Stainless Steel Semiconductor Cavity Component: High-Accuracy Milling with Strict Perpendicularity and Flatness Control

Precision 304 Stainless Steel Semiconductor Cavity Component: High-Accuracy Milling with Strict Perpendicularity and Flatness Control-stainless_steel

SLINAR - Precision 304 Stainless Steel Knurled Micro-Adjustment Handle Shaft with Passivation and TIR Control for Medical Equipment

Precision 304 Stainless Steel Knurled Micro-Adjustment Handle Shaft with Passivation and TIR Control for Medical Equipment-stainless_steel

Materials

Stainless Steel 15-5 PH

Stainless steel 15-5 PH | 1.4545 | X5CrNiCu15-5

Stainless steel 15-5 has a higher toughness than 17-4, better corrosion resistance and transverse properties compared to other similar martensitic grades.

Understand Stainless Steel 15-5 PH

Stainless Steel 301

Stainless steel 301 | 1.4310 | X10CrNi18-8

Stainless steel 301 is corrosion resistant similar to Stainless steel 304.

Understand Stainless Steel 301

Stainless Steel 430

Stainless steel 430 | 1.4016 | X6Cr17

Stainless steel 430 is magnetic and corrosion resistant.

Understand Stainless Steel 430

Stainless Steel 440C

Stainless steel 440C | 1.4125 | X105CrMo17

Stainless steel 440C has improved toughness and corrosion resistance due to Carbon and Chromium content.

Understand Stainless Steel 440C

Stainless Steel 420

Stainless steel 420 | 1.4028 | X30Cr13

Stainless steel 420 provides high strength and corrosion resistance. It is the hardest of all stainless steels when hardened.

Understand Stainless Steel 420

Stainless Steel 2205 Duplex

Stainless steel 2205 Duplex | 1.4462 | X2CrNiMoN 22-5-3

Stainless steel 2205 Duplex (CNC) is the alloy with the highest strength and hardness. Suitable for applications in severe environments up to 300°C.

Understand Stainless Steel 2205 Duplex

Stainless Steel 416

Stainless steel 416 | 1.4005 | X12CrS13

Stainless steel 416 is magnetic and has a high machinability.

Understand Stainless Steel 416

Stainless Steel 17-4 PH

Stainless Steel 17-4 PH | 1.4542 | X5CrNiCuNb16-4 - Annealed state

Stainless steel 17-4 (CNC) - SAE grade 630 - is a precipitation hardening alloy with good corrosion resistance. Can be hardened up to 44 HRC.

Understand Stainless Steel 17-4 PH

Stainless Steel 303

Stainless steel 303 | 1.4305 | X8CrNiS18-9

Stainless steel 303 (CNC) has excellent toughness, but lower corrosion resistance than 304. Ideal for high volumes, due to its excellent machinability.

Understand Stainless Steel 303

Stainless Steel 316/316L

Stainless steel 316/316L | 1.4401/1.4404 | X5CrNiMo17-12-2/X2CrNiMo17-12-2

Stainless steel 316L (CNC) has similar mechanical properties to 304, with higher corrosion and chemical resistance. Ideal for marine applications.

Understand Stainless Steel 316/316L

Stainless Steel 304/304L

Stainless steel 304/304L | 1.4301/1.4307 | X5CrNi18-10/X2CrNi18-9

Stainless steel 304L (CNC) has excellent mechanical properties and good machinability. Resistant to most environments and corrosive media.

Understand Stainless Steel 304/304L

Applications

Medical Devices

Surgical instruments and tool bodies
Orthopedic implant components
Dental instruments and tooling
Medical device housings and enclosures
Sterilization trays and containers

Food & Beverage

Food processing equipment
Dairy and brewery components
Conveyor system parts
Commercial kitchen equipment
Food-grade fittings and tubing

Marine & Chemical

Marine hardware and boat fittings
Chemical processing equipment
Pump housings and impellers
Valve bodies and actuator components
Heat exchangers and condenser parts

Aerospace & Defense

High-strength structural components
Corrosion-resistant fasteners
Sensor housings and enclosures

Industrial Equipment

Shafts, bushings, and bearings
Hydraulic and pneumatic components
Wear-resistant guide rails and slides

Capabilities

We machine all common stainless steel grades: 303, 304, 316, 17-4PH, 410, 420, and 440C. Equipment includes 3/4/5-axis CNC milling and CNC turning with live tooling. Tolerances held to ±0.02–0.05mm standard, ±0.01mm precision. Surface finishes include as-machined, passivation, electropolishing, and mechanical finishing. ISO 9001:2015 and AS9100D certified. We use specialized carbide tooling and high-pressure coolant to manage work hardening.

Finishes

Passivation

Chemical treatment to remove free iron and restore corrosion resistance
Standard finish for most stainless parts

Electropolishing

Electrochemical removal of surface material to improve finish and corrosion resistance
Enhances surface cleanliness for medical and food applications
Achieves Ra 0.4μm or better

Mechanical Finishes

Bead Blasting: Uniform matte texture
Brushing: Directional grain pattern
Polishing: High-gloss reflective finish
Tumbling: Edge deburring on large quantities

Plating & Coating

Electroless Nickel: Additional wear and corrosion protection
PTFE / Teflon: Low-friction non-stick surface
Powder Coating: Durable decorative finish

Heat Treatment

Annealing: Stress relief for improved dimensional stability
Precipitation Hardening: Strengthening for 17-4PH
Hardening: Increasing hardness for martensitic grades

Technical Specs

Stainless Grade	Type	Machinability	Corrosion Resistance	Key Properties	Common Uses
303	Austenitic	78%	Good	Added sulfur for chip breakage	Fittings, shafts, valve parts, screws
304	Austenitic	45%	Very Good	Most versatile, good weldability	Enclosures, brackets, food equipment
316	Austenitic	36%	Excellent	Molybdenum for chloride resistance	Marine parts, chemical equipment, surgical instruments
316L	Austenitic	36%	Excellent	Low carbon for better weldability	Pharmaceutical equipment, implant devices
17-4PH	Precipitation	50%	Good	High strength, heat-treatable	Aerospace, defense, high-strength parts
410	Martensitic	Good	Moderate	High strength, magnetic	Valves, pump parts, wear-resistant components
420	Martensitic	Moderate	Moderate	High hardness, cutlery grade	Surgical instruments, cutlery, dental tools
440C	Martensitic	Poor	Moderate	Very high hardness, wear-resistant	Bearings, valve seats, wear parts

Parameter	303	304	316	17-4PH
Tensile Strength (ksi)	90	73	80	160+
Yield Strength (ksi)	40	31	30	145+
Hardness (Brinell)	160	170	160	350+
Density (g/cm³)	7.90	7.90	7.90	7.80
Corrosion Resistance	Good	Very Good	Excellent	Good

Parameter	Capability
Max Part Size (Milling)	2,000mm x 800mm x 600mm
Max Part Size (Turning)	600mm diameter x 1,500mm length
Standard Tolerance	±0.02 – 0.05mm
Precision Tolerance	±0.01mm
Surface Finish (As-Machined)	Ra 1.6 – 3.2μm
Surface Finish (Electropolished)	Ra 0.4μm
Surface Finish (Ground)	Ra 0.2 – 0.8μm

FAQs

What is the difference between 303, 304, and 316 stainless steel?

303 has sulfur added for superior machinability and is ideal for parts that will not be welded. 304 is the most versatile with good corrosion resistance and excellent weldability. 316 adds molybdenum for superior chloride resistance—marine, chemical, and saltwater environments.
Which stainless steel grade is most machinable?

303 stainless steel offers the best machinability. The added sulfur improves chip breakage and reduces tool wear. Use 303 for screw machine parts, fittings, and shafts that will not be welded.
What is work hardening and why is it a problem?

Work hardening occurs when the surface becomes harder than the base metal from cutting friction. It damages tools and ruins surface quality. Prevention: keep tools sharp, stay in the cut, avoid light cuts, and use climb milling.
What is passivation and when is it needed?

Passivation is a chemical treatment that removes free iron from the surface and restores the protective chromium oxide layer. It is standard for all stainless parts, especially medical, food, and marine applications.
Can you machine hardened stainless steel?

Yes, hardened stainless grades can be machined with carbide tooling, but machining is typically performed in the annealed condition with heat treatment applied after.
How does stainless steel compare to aluminum for CNC machining?

Stainless is stronger, harder, and more corrosion-resistant but machines slower compared to aluminum. Stainless parts cost more due to longer cycle times and greater tool wear.