In mold manufacturing, choosing the right steel directly impacts project cost, lead time, and mold life. Many professionals struggle with one question: Pre-hardened or annealed steel – which should I choose?
The key difference lies in the heat treatment state when delivered.
What is Pre-hardened Steel?
Pre-hardened steel is quenched and tempered before delivery, ready to use at working hardness (typically HRC 28-36) Taking P20 as an example, major suppliers like LKM provide pre-hardened P20 at HB 270-340 (approx. HRC 28-36).
Advantages:
No post-processing heat treatment – use directly after machining
Dimensional stability – no deformation from heat treatment
Short delivery time – ready for assembly immediately
Easy modification – can be re-machined without re-heat treatment
Disadvantages:
Slightly harder to machine than annealed steel
Fixed final hardness – cannot be significantly increased
Best for: Low-to-medium volume production, standard plastic molds, tight-deadline projects. P20 pre-hardened steel suits molds up to 500,000 shots.
What is Annealed Steel?
Annealed steel is delivered in a softened state (typically HB ≤ 235, ~HRC 22), making it easy to machine. After machining, it requires quenching + tempering to reach final working hardness (typically HRC 48-60+).
Advantages:
Excellent machinability – annealed P20 offers ~15% better machinability than pre-hardened, longer tool life, ideal for complex cavities
High final hardness – can reach HRC 48+ after heat treatment, better wear resistance and polishability
Wide application range – suitable for high-life, high-wear molds
How to Choose?
Quick Selection Guide:
Under 500,000 shots, tight deadline → Choose Pre-hardened Steel (e.g., P20, P20H, 2311)
Over 500,000 shots, high wear, glass-filled → Choose Annealed Steel + Heat Treatment (e.g., H13, S136, 2083)
Important: Glass-filled plastics wear down molds quickly. Relying on core hardness alone is insufficient – consider nitriding for a 60+ HRC protective shell.
Q&A
Q1: Can pre-hardened steel be used directly?
A: Yes. Pre-hardened steel is delivered at working hardness (typically HRC 28-36) and requires no heat treatment after machining. This saves time, reduces cost, and eliminates deformation risk.
Q2: Why does annealed steel need heat treatment?
A: Annealed steel is delivered soft (~HRC 22) for easy machining, but this soft state cannot meet high-wear, long-life mold requirements. Quenching + tempering increases hardness to HRC 48-60+, significantly improving wear resistance and polishability.
Q3: Can pre-hardened steel be further hardened by heat treatment?
A: Yes, but with caution. P20 can be re-hardened to HRC 48+ via 850-880℃ quenching + 200℃ tempering, or nitrided to 650-700HV (~HRC 57-60). However, secondary heat treatment may cause dimensional changes, and P20 is prone to cracking during quenching. Consult professionals before proceeding