Mold Steel Selection Guide

Selecting the right steel for your injection mold is one of the most critical decisions affecting tool life, part quality, and production cost. The wrong choice can lead to premature wear, corrosion, heat checking, or even catastrophic mold failure.

This guide covers the most common mold steel grades, their properties, and how to select the right material for your specific application.

Common Mold Steel Grades

P20 (1.2311) — General Purpose Mold Steel

P20 is the most widely used mold steel for general-purpose injection molds. It comes pre-hardened to 28-32 HRC, eliminating the need for heat treatment after machining. P20 offers good machinability, reasonable wear resistance, and moderate polishability. Best for: prototype molds, low-to-medium volume production (up to 500,000 cycles), and molds with simple geometries.

H13 (1.2344) — Hot Work Tool Steel

H13 is the standard for high-performance injection molds and die casting dies. It offers excellent toughness, high heat resistance, and good thermal fatigue resistance. Through-hardened to 46-52 HRC, H13 maintains its hardness at elevated temperatures. Best for: high-volume production (500,000+ cycles), molds running abrasive materials, and die casting applications.

D2 (1.2379) — High-Carbon, High-Chromium Steel

D2 offers exceptional wear resistance due to its high carbide content. Through-hardened to 58-62 HRC, it is one of the hardest conventional mold steels. However, D2 has lower toughness than H13 and can be challenging to machine and polish. Best for: highly abrasive materials (glass-filled nylon), stamping dies, and applications where wear is the primary concern.

S7 (1.2358) — Shock-Resistant Tool Steel

S7 is designed for applications requiring high impact toughness. It offers excellent shock resistance combined with good wear properties. Through-hardened to 54-58 HRC. Best for: molds with thin inserts, sharp corners, high-stress applications, and cold heading tools.

420SS (1.2083) — Stainless Mold Steel

420 stainless steel offers excellent corrosion resistance and the best polishability of any mold steel. It can be polished to a mirror finish (SPI A-1 grade). Through-hardened to 48-54 HRC. Best for: medical molds, optical lenses, clear plastic parts, and corrosive material processing.

Selection by Production Volume

Selection by Material Processed

• Unfilled plastics (ABS, PP, PE): P20 or H13 — standard wear resistance sufficient
• Glass-filled materials (GF30 PA66, GF PBT): H13 or D2 at 54+ HRC — abrasive fillers accelerate wear
• Corrosive materials (PVC, POM): 420SS — corrosion resistance is essential to prevent pitting
• Optical/clear materials (PC, PMMA): 420SS polished to SPI A-1 — highest polishability required
• High-temperature materials (PEEK, PEI): H13 (ESR) — excellent hot hardness and thermal fatigue resistance

Surface Treatments

Surface treatments can significantly extend mold life beyond the base steel properties:

• Nitriding: Creates a hard case (65+ HRC) on H13 and P20 surfaces. Improves wear resistance by 2-3x.
• PVD Coating (TiN, TiAlN, CrN): Thin ceramic coating reduces friction and improves wear resistance. Best for abrasive materials.
• Chrome Plating: Hard chrome plating provides corrosion resistance and a low-friction surface. Common for PVC molds.
• EDM White Layer Removal: After EDM machining, the recast layer must be removed by polishing or etching to prevent premature cracking.