Choosing Steel for a Mold Base
Hardness sets machinability and wear
Both P20 and 718H are pre-hardened plastic mould steels and are the two most common choices for mold bases and core inserts. P20 is typically supplied pre-hardened to HRC 28-32, which gives good machinability and higher material removal rates. 718H sits around HRC 30-36 with greater strength and wear resistance, better suited to larger production volumes or glass-filled resins. The difference shows up over a long run, where wear rather than the initial price decides the outcome.
Pre-hardened supply is the reason these grades dominate mold base work. Steel that arrives already hardened can be machined straight to finished size - no quenching after roughing and no re-finishing afterwards - which removes an entire heat-treatment loop from the schedule. Where a programme genuinely needs through-hardening or a different grade, that belongs on the drawing rather than becoming a change part-way through production.
Polishability, corrosion and the rest of the list
Transparent parts and high-gloss cosmetic parts demand high polishability, which generally means cleaner and more homogeneous material; for ordinary structural parts, P20 is sufficient. Beyond those two grades our common materials are 45#, 40Cr, P20, 718H, S136, NAK80 and S50C, and we also machine to a customer-specified grade or an in-house standard. Tell us the part resin, the surface finish required and whether the tool will run a corrosive or glass-filled material.
Volume then settles the choice in practice. Low volumes and trial tooling usually favour P20 on cost-performance; medium to high volumes and glass-filled material favour 718H; high transparency or high-gloss surfaces are selected by polish grade separately. Saying which of those three applies is generally more useful than naming a grade, because it lets our engineers propose the material with the price difference shown at review.
Traceability from incoming inspection to dispatch
Mould steel arrives by batch and is inspected before it reaches a machine tool: material certificates and hardness checks are recorded, and a batch that fails incoming inspection is not put into production. That record follows the finished plates, so a question raised months later can be traced back to a specific melt rather than argued from memory. Heat-treatment records are traceable by batch for the same reason.
Send the 2D drawing and 3D model with the material requirement, or a note that it is still open, along with plate size and quantity. Drawing review is free of charge with feedback within 24 hours, and we will recommend a grade and state the cost difference. Standard mold bases are delivered from 7 days, within an overall window of 7 to 20 days depending on specification.
FAQ
What is the difference between P20 and 718H?
P20 is typically supplied pre-hardened to HRC 28-32 with good machinability, while 718H sits around HRC 30-36 with higher strength and wear resistance. P20 suits low volumes and trial tooling; 718H suits medium to high volumes and glass-filled resins.
Which other grades do you machine?
Common materials are 45#, 40Cr, P20, 718H, S136, NAK80 and S50C, and we also work to a customer-specified grade or in-house standard. Send the resin, the required surface finish and the annual volume and we will recommend one.
Is material traceability provided?
Yes. Steel is inspected by batch on arrival with material certificates and hardness checks recorded, and heat-treatment records are traceable by batch. A batch that fails incoming inspection does not enter production.
How fast can a standard mold base be delivered?
Commonly used specifications are held in stock and delivered from 7 days, within an overall window of 7 to 20 days. Non-standard projects follow the schedule agreed at drawing review, and we flag schedule risks early.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.