Q08 — TECHNICAL ANSWER
Mild Steel or Stainless for Machined Parts?
Stainless grades go where corrosion or washdown matters; carbon and alloy steels go where strength and wear resistance lead. The position decides it. Choosing on price alone is how a part ends up rusting into the housing it was meant to protect.
The case for carbon and alloy steel
Carbon and alloy steels are specified where strength and wear resistance lead. They take heat treatment, they hold up under load, and in a dry, enclosed, lubricated position they will outlast a stainless part doing the same job.
They also machine predictably and are the conventional choice for shafts, pins and structural parts inside machinery — the positions where a part is protected from the environment by the equipment around it.
Their weakness is exposure. A carbon steel part left in the weather between seasons, or hosed down daily, is corroding when it is not working. On agricultural implements that combination — idle outdoors, then loaded hard — is exactly why material choice there is rarely about peak strength.
The case for stainless
Stainless goes where corrosion or washdown matters. That covers food and grain processing, wet process equipment, and anything cleaned on a schedule with chemistry that would strip a painted or plated steel part.
It is also the answer for food contact regardless of corrosion, because a part shedding rust into product fails on hygiene long before it fails structurally.
Within stainless the choice narrows again: 304 covers most washdown and food-contact positions, 316 is specified where chlorides are present, and 410 and 420 are martensitic and harden by heat treatment — which puts them into wear positions rather than corrosion positions.
Where the decision usually goes wrong
The common error is treating this as a cost decision on the part rather than a service decision on the assembly. A cheaper bush that seizes into its housing costs the housing, and a shaft that pits costs the bearings running on it.
The second error is assuming stainless is always the safer default. Stainless is not automatically harder or stronger, and specifying it in a dry high-load position can shorten service life rather than extend it.
Where a drawing specifies a material we manufacture to it. Where it leaves the material open we raise it before cutting rather than substitute, because the person who owns the equipment knows the environment better than the person cutting the part.
Steel selection — related questions
- Is stainless always stronger than mild steel?
- No. Carbon and alloy steels are specified where strength and wear resistance lead, and they take heat treatment. Stainless is chosen for corrosion resistance, which is a different property.
- Which steels do you machine?
- Stainless 304, 316, 316L, 410 and 420, plus carbon and alloy steel, brass, phosphor bronze and aluminium. Other grades can be arranged on request.
- Can a mild steel part be plated instead?
- It is a common approach, but a plated surface is only protective while it is intact — on a wear part the plating goes first, exactly where protection was wanted.
- What if our drawing leaves the material open?
- We raise it before cutting rather than substitute. Tell us the position, the load and whether it is washed down or left outdoors, and that usually settles it.
Send your drawing with the material if it is specified, or tell us the position, the load and the environment and we will confirm it with you first. An NDA can be arranged before any detailed technical exchange.