---
title: "Stainless Steel CNC Machining & Fabrication | 303, 304, 316, 17-4 | OpenSpindle"
description: "Get quotes for custom stainless steel parts from independent machine shops. 303, 304, 316, 17-4 PH and more, machined, turned, cut, and passivated. Upload a drawing."
canonical: https://openspindle.com/materials/stainless-steel
---

# Custom stainless steel parts from independent machine shops

Stainless steel is the default when a part has to resist corrosion, take heat, or stay clean. Upload a drawing and hear back from shops that machine and fabricate 303, 304, 316, and 17-4 every day.

## Stainless steel shops on OpenSpindle

Real shops that machine and fabricate stainless steel. See their equipment and talk to the person making your part.

[Browse all stainless steel shops](https://openspindle.com/manufacturers?material=304%20%2F%20304L%2C316%20%2F%20316L%2C303%2C17-4%20PH)

## Stainless steel grades shops run most

The grade sets corrosion resistance, strength, and how easily it machines. These are the ones you will see quoted; if yours is not here, ask when you request a quote.

### 303

The free-machining austenitic grade. Sulfur added to 304 chemistry lets it cut fast and clean, at the cost of some corrosion resistance and weldability. The default when you need many turned stainless parts.

**Best for:** Turned fittings, shafts, fasteners, and high-volume machined parts

### 304 / 304L

The general-purpose stainless. Excellent corrosion resistance, non-magnetic, and food-safe, though it work-hardens and machines slower than 303. 304L has lower carbon for better weldability.

**Best for:** Enclosures, brackets, food and dairy, general fabrication

### 316 / 316L

Adds molybdenum for far better resistance to chlorides, salt water, and harsh chemicals. The marine and medical grade. More expensive and gummier to machine than 304.

**Best for:** Marine, chemical process, medical, and outdoor coastal parts

### 17-4 PH

A precipitation-hardening stainless with strength approaching alloy steel plus good corrosion resistance. Machined in the annealed condition then heat treated (H900, H1075) to spec. Magnetic.

**Best for:** High-strength shafts, valve and pump parts, aerospace hardware

### 15-5 PH

Similar to 17-4 but with better toughness and transverse properties from a more refined microstructure. Also precipitation-hardened to a range of tempers. Common in aerospace structure.

**Best for:** Aerospace structural parts, high-strength corrosion-resistant hardware

### 440C / 416

Hardenable martensitic grades. 440C reaches high hardness (~58 HRC) for wear and edge retention; 416 is the free-machining martensitic grade that heat treats and takes magnetism.

**Best for:** Knife blades, bearings, valve seats, wear parts, magnetic components

## Material Properties

Representative values for 304 in the annealed condition, the most common machining grade. Exact numbers vary by grade and temper.

| Property | Value |
| --- | --- |
| Density | 8.0 g/cm³ (0.29 lb/in³) |
| Tensile strength (304) | ~73-90 ksi (515-620 MPa) |
| Yield strength (304) | ~30 ksi (205 MPa) |
| Tensile strength (17-4 H900) | ~190 ksi (1310 MPa) |
| Hardness (304 annealed) | ~70-85 HRB |
| Max service temp | ~870 °C (1600 °F) intermittent for 304 |
| Machinability | Moderate; 303 best, 304/316 work-harden and run gummy |
| Corrosion resistance | Excellent; 316 outperforms 304 in chlorides |
| Weldability | 304L/316L good; avoid welding 303 |

Stainless work-hardens, so it wants sharp tools, rigid setups, and steady feeds. That is why a stainless part costs more to machine than the same part in aluminum or mild steel.

## Stock Forms

- **Plate & block** -- Milled and 5-axis parts machined from solid.
- **Round bar** -- Turned shafts, fittings, and cylindrical parts.
- **Sheet** -- Laser, waterjet, and press-brake sheet metal.

## Processes That Run This Material

- [CNC Machining](https://openspindle.com/capabilities/cnc-machining.md) -- Milled housings, brackets, and prismatic parts from plate and block.
- [CNC Turning](https://openspindle.com/capabilities/cnc-turning.md) -- Turned shafts, fittings, and fasteners from round bar, often in free-machining 303.
- [Sheet Metal & Press Brake](https://openspindle.com/capabilities/sheet-metal-fabrication.md) -- Cut, bent, and welded enclosures and panels from 304 and 316 sheet.
- [Waterjet Cutting](https://openspindle.com/manufacturers?capability=Waterjet%20cutting) -- Cold cutting for thick stainless plate with no heat-affected edge.
- [Laser Cutting](https://openspindle.com/manufacturers?capability=Laser%20cutting) -- Fast, precise flat cuts in thinner stainless sheet.
- [Welding](https://openspindle.com/manufacturers?capability=Welding) -- TIG welding of 304L and 316L assemblies and weldments.

## Finishes

Stainless is usually left bare because the metal itself resists corrosion. Finishing focuses on restoring that resistance and setting surface texture, not adding a coating.

- **Passivation** -- A nitric or citric acid bath that dissolves free iron from the surface and lets the natural chromium oxide layer reform. Standard on medical and food parts (ASTM A967). Does not change dimensions.
- **Electropolish** -- An electrochemical process that removes a thin surface layer for a bright, smooth, ultra-clean finish. Improves corrosion resistance and cleanability, common in medical and semiconductor parts.
- **Bead blast** -- A uniform matte texture that hides machining marks. Often specified as a cosmetic finish before passivation.
- **Tumbling / deburr** -- Mass finishing that breaks edges and evens the surface on small turned or stamped parts. Good for high-volume runs.
- **As-machined** -- No finish beyond deburring. Fine for internal or non-cosmetic parts, though passivation is still recommended for corrosion service.

Stainless does not anodize like aluminum. If a part needs color or a hard coating, call it out and the shop confirms what is possible for the grade.

## Applications

- Medical & surgical
- Food & beverage
- Marine
- Chemical & process
- Aerospace
- Firearms
- Architectural
- Industrial / OEM

Stainless shows up wherever corrosion, hygiene, heat, or strength rule out aluminum and plain steel.

## How It Compares

How stainless steel stacks up against the other metals shops quote most.

### [Aluminum](https://openspindle.com/materials/aluminum.md)

- Stainless is far stronger and harder, and resists corrosion without any coating
- Aluminum is about one-third the weight and machines several times faster
- Stainless holds up better at high temperature and in food, marine, and chemical service

**Verdict:** Choose stainless for strength, hygiene, and corrosion in tough environments. Choose aluminum for light weight, speed, and cost.

### [Carbon steel](https://openspindle.com/materials/carbon-steel.md)

- Stainless resists corrosion on its own; carbon steel rusts and needs a coating or oil
- Carbon steel is cheaper per pound, machines more easily, and can reach very high hardness
- Stainless keeps its properties in wet, salty, or sanitary environments where carbon steel fails

**Verdict:** Choose stainless when corrosion or cleanliness matters. Choose carbon steel for lower cost and easier machining where a finish handles rust.

### [Titanium](https://openspindle.com/materials/titanium.md)

- Titanium has a much higher strength-to-weight ratio and is roughly half the weight of stainless
- Stainless is several times cheaper and easier to source and machine
- Both resist corrosion well and are biocompatible, but titanium leads in seawater and implant use

**Verdict:** Choose stainless for cost and general corrosion service. Choose titanium when weight, seawater, or biocompatibility justify the premium.

## Frequently Asked Questions

### What is the difference between 304 and 316 stainless steel?

Both are austenitic, non-magnetic, and corrosion resistant, but 316 adds molybdenum that greatly improves resistance to chlorides, salt water, and harsh chemicals. 304 is the general-purpose default and costs less; 316 is the marine, medical, and chemical grade. Use 304 for most parts and 316 when the part sees salt, acids, or coastal exposure.

### Which stainless steel is easiest to machine?

303 is the free-machining grade: sulfur is added to 304 chemistry so it cuts fast and clean with good chip breaking. The trade-off is slightly lower corrosion resistance and poor weldability, so avoid 303 where the part must be welded or sees aggressive corrosion. For turned parts in volume, 303 is usually the cheapest stainless to run.

### Is stainless steel magnetic?

It depends on the family. Austenitic grades like 303, 304, and 316 are essentially non-magnetic, though cold working can make them slightly magnetic. Martensitic and precipitation-hardening grades such as 416, 440C, and 17-4 are magnetic. If magnetic properties matter for your part, note them on the drawing.

### Does stainless steel need passivation?

For corrosion-critical, medical, or food parts, yes. Machining leaves free iron on the surface that can rust and seed corrosion; passivation dissolves that iron and lets the protective chromium oxide layer reform (ASTM A967). It does not change dimensions or appearance. As-machined stainless still resists corrosion, but passivation restores full performance.

### Can stainless steel be heat treated for strength?

The precipitation-hardening and martensitic grades can. 17-4 PH and 15-5 PH are machined soft then aged (for example H900 or H1075) to reach strengths near alloy steel while keeping corrosion resistance. 440C and 416 harden by quench and temper. The common austenitic grades (304, 316) do not harden by heat treatment and are strengthened only by cold work.

### Why does stainless cost more to machine than aluminum or mild steel?

Stainless work-hardens as it is cut, so it needs sharp tooling, rigid setups, slower speeds, and generous coolant. Austenitic grades like 304 and 316 also run gummy and are hard on tool life. The result is longer cycle times and more tool wear, which raises the machined cost even before the higher material price.

### What file formats should I send for a stainless steel part?

STEP, IGES, X_T, DWG, DXF, or a dimensioned PDF. Include the grade and any temper (for example 316L or 17-4 H900), critical dimensions and tolerances, quantity, and any finish or spec such as passivation, electropolish, or a surface roughness callout.

## Related Materials

- [Aluminum](https://openspindle.com/materials/aluminum.md)
- [Carbon Steel](https://openspindle.com/materials/carbon-steel.md)
- [Titanium](https://openspindle.com/materials/titanium.md)
- [Brass](https://openspindle.com/materials/brass.md)
- [Copper](https://openspindle.com/materials/copper.md)
- [Delrin](https://openspindle.com/materials/delrin.md)

## Get stainless steel part quotes

Upload a drawing once and compare quotes from independent shops that machine, cut, and finish stainless steel.