Choosing a Material for an Industrial Part
Material selection starts with load, temperature, corrosion and wear — and ends with one question: can this grade actually be bought here? A practical guide to steels, aluminium, stainless, bronze and engineering plastics.
Material choice is usually either too casual ("just use steel") or over-complicated (forty-column property tables).
The practical route has four questions.
The four questions that decide
1. What load does the part carry? Tensile, compressive, bending, or impact? Impact matters most, because it demands toughness rather than strength alone.
2. What is the service temperature? Below 80 °C almost anything works. Above 200 °C the options narrow sharply.
3. What environment does it work in? Moisture, acid, oil, sunlight, food contact?
4. Does the surface wear? If something slides or rotates against it, surface hardness matters.
And then the fifth question, which in Iran is decisive: can this grade be bought?
Carbon steels — ninety percent of industrial parts
| Grade | Equivalent | Use |
|---|---|---|
| ST37 | S235 / A36 | Structures, sheet, non-load parts. Cheap, weldable, not hardenable. |
| ST52 | S355 | Load-bearing structures, chassis. More strength, same weldability. |
| CK45 | C45 / AISI 1045 | Shafts, pins, machined parts. Hardenable to about HRC 55. |
| MO40 | 42CrMo4 / AISI 4140 | High-duty shafts, gears, heavily loaded parts. Best strength–toughness balance. |
| VCN150 | 34CrNiMo6 | Critical parts under very heavy load. |
Practical rule: if the part is machined and moderately loaded, CK45 is the right starting point. If the load is heavy or impacting, MO40.
Do not pick ST37 for anything that rotates or rubs — it is soft and wears quickly.
Stainless — when it is genuinely needed
304 — the common one. Corrosion resistant in ordinary and humid environments. Suitable for food contact.
316 — 304 plus molybdenum. Resistant to chlorides and seawater. About 30 percent dearer.
The real difference: if the environment is not salty or chlorinated, 316 is wasted money. If it is, 304 will stain within months.
420 and 410 — martensitic stainless, hardenable. For blades and corrosion-resistant wear parts.
Note: austenitic stainless (304/316) is non-magnetic and cannot be hardened. If you need stainless and hard, go to 420, or use ordinary steel with a hard coating.
Aluminium
6061 — the general purpose alloy. Machines well, weldable, moderate strength. Most industrial aluminium parts are this.
7075 — very high strength (approaching mild steel) at a third of the weight. Expensive, poor weldability, less corrosion resistant.
5083 — seawater resistant, for plate and tanks.
Choose aluminium when weight matters or thermal conductivity is needed. If only cost matters, steel is cheaper.
Bronze and brass — for bushings and bearings
CuSn12 bronze — bearing bushings. Partially self-lubricating, wear resistant, will not score a steel shaft.
CuZn39Pb3 brass — very easy to machine, for fittings and decorative parts.
An important rule: never run a steel bushing on a steel shaft. Like metals gall and seize. Use bronze or a polymer bushing.
Engineering plastics
| Material | Character | Use |
|---|---|---|
| POM (Delrin) | Rigid, dimensionally stable, low friction | Gears, bushings, precision parts |
| PA6/PA66 (nylon) | Tough, wear resistant | Gears, rollers. Absorbs moisture |
| PTFE | Lowest friction, to 260 °C | Washers, seals, slide bushings |
| UHMW-PE | Outstanding abrasion resistance | Guide rails, wear plates |
| PC (polycarbonate) | Transparent, impact resistant | Guards, covers |
The fifth question: is it available?
The best grade in the world is useless if the market does not stock it.
In practice these are readily found in Kerman and larger cities:
- Steel:
ST37,ST52,CK45,MO40 - Stainless:
304,316 - Aluminium:
6061, standard profiles - Bronze and brass: bar and tube
- Plastics:
POM,PA6,PTFEas rod and sheet
If a drawing calls for a specific foreign grade, find the local equivalent first. There nearly always is one.
Raw stock shape — the overlooked saving
Before ordering solid bar, ask whether the part could come from tube, profile or plate.
Turning a bushing from 80 mm solid bar turns seventy percent of the material into chips. The same part from 80×60 tube comes out with almost no waste and less machining time.
If you are not sure what your part should be made of, say where it works and what load it carries. Material selection is part of design, not a decision to be made on the shop floor.