Quick Answer
Casting material selection reduces to three questions asked in order. First: what does the environment do to the part — nothing (dry, lubricated), water, chlorides, acids, or heat? Second: what does the load ask — mass, stiffness, strength, impact, or wear? Third: what does the budget allow? Answer those and the family picks itself; the grade inside the family is then a data lookup. This page is the map; each family links to its detailed guide.
The Decision Map
| Environment → Load | First-choice family | Deep dive |
|---|---|---|
| Benign + mass/damping | Gray iron (A48) | A48 classes |
| Benign + strength/impact | Ductile iron (A536) | A536 grades |
| Benign + high stress / welding | Carbon steel (A216) | WCB guide |
| Benign + extreme stress/wear | Low alloy steel, Q&T | Low alloy grades |
| Cold climate (<−29°C) | A352 LCB/LCC family | WCB vs LCB vs WCC |
| Water/food, no chlorides | CF8 (cast 304) | CF8 family compared |
| Chlorides, marine, CIP | CF8M / CF3M (cast 316) | CF8M guide |
| Chlorides + high stress/abrasion | Duplex CD4MCu | CD4MCu guide |
| Sulfuric/phosphoric acid | CN7M (Alloy 20) | CN7M guide |
| Wear + moderate corrosion | 17-4 PH (CB7Cu-1) | 17-4 PH guide |
| Weight-critical | Aluminum A356-T6 | A356 guide |
| Heat >425°C, pressure | A217 chrome-moly (WC6/WC9) | Ask with design temperature |
The Three Cross-Family Rules
- Buy the environment first. Under-specifying corrosion is the expensive direction — a corroded CF8 part in chloride service costs a warranty claim; an over-specified CF3M part in clean water only costs a premium. When in doubt between two families, price both and state the media honestly in the RFQ.
- Strength is heat treatment as much as chemistry. The same low-alloy casting spans 500–1,100 MPa depending on its cycle — specify grade and condition and hardness window. The mechanics are in our heat treatment guide.
- Weldability is binary at design time. Iron families: assume no structural welding. Steel families: weldable with procedure discipline. This single fact sorts many part-material pairs immediately.
Material × Process: The Second Axis
Family choice constrains process choice: aluminum favors gravity/low-pressure casting; steels and stainless run investment or sand casting by size and finish; irons live in sand and shell molding. If a material-process pair looks exotic, the price will say so — sometimes switching family beats forcing a process.
What to Send a Foundry for a Material Recommendation
- Part drawing or model, with functional surfaces marked
- Media, temperature range, and cleaning chemicals if any
- Load case in plain words: static, cyclic, impact, abrasive
- Annual volume and target price context
- Any code (ASME, API, PED) governing the assembly
With those five items, a competent foundry returns a grade recommendation with DFM notes in days — ours come with the inspection plan attached.
FAQ
What is the cheapest casting material overall?
Gray iron, nearly always — lowest melt cost, best castability, fastest machining. Every step away from it buys a property gray iron lacks.
Can I switch material without new tooling?
Within a family (iron to iron, steel grade to steel grade) usually yes with shrinkage checks; across families (iron to steel, steel to aluminum) shrinkage differences typically require pattern rework.
Who should own material selection — designer or foundry?
The designer owns the requirement; the foundry validates castability and often knows a cheaper equivalent grade. The best results come from stating requirements and inviting counter-proposals.