Technical guide · 2026-08-14
Mold Steel
Mold steels are tooling steels ordered around polishability, texture response, cleanliness, corrosion exposure, machinability and hardness uniformity across large plastic-mold blocks rather than one universal alloy family.
01
Definition and boundary
This procurement category includes prehardened and corrosion-resistant mold stock; it excludes die steels selected chiefly for hot-metal contact or cutting-edge wear.
Reference information only: final acceptance is controlled by the ordered product specification, condition, dimensions and certified test results.
02
How the material system works
Prehardening provides machinable stock without a final full-block quench.
Inclusion cleanliness and segregation control surface polish and texturing.
Chromium-bearing stainless mold grades resist humid or corrosive molding service.
03
Representative grades and systems
| Grade or system | Selection focus | Qualification |
|---|---|---|
| P20 / 1.2311 | Prehardened general mold steel; exact standard and condition must be stated. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| 1.2738 | Nickel-modified large-block mold system selected for hardenability. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| 420 mold quality | Corrosion-resistant mold steel requiring controlled polish quality. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
04
Properties and trade-offs
Hardness uniformity through block section
Polishability and photo-etch response
Machinability, corrosion resistance and repair weldability
05
Product forms and supply conditions
06
Applications and selection
Applications and selection
- Injection and compression molds
- Large automotive interior molds
- Corrosive-resin and optical mold components
Properties and trade-offs
- Start from finish class, resin chemistry and production volume.
- Match block thickness to verified center hardness and cleanliness.
- Treat trade-name cross references as proposals, not equivalence.
07
Fabrication, durability and inspection
Keep machining strategy symmetric on large blocks to manage stress relief.
Qualify repair welding and post-weld hardness matching.
Use polishing practices appropriate to inclusion rating and texture demand.
08
Procurement checklist
- State block dimensions, hardness range and center-to-surface uniformity.
- Define polish or texture class, cleanliness and ultrasonic acceptance.
- Specify prehardened or annealed state, machining allowance and certification.
09
Standards, sources and review
Standards and designation context
- ASTM A681 alloy tool-steel scope
- ASTM A600 where high-speed grades apply
- Buyer drawing and heat-treatment specification