O1 vs A2 – Composition, Heat Treatment, Properties, and Applications

Introduction

O1 and A2 are two of the most commonly specified cold-work tool steels. Engineers, procurement managers, and manufacturing planners routinely weigh their choices when specifying punches, dies, gauges, cutters, and tooling components. Typical decision contexts include balancing hardness and wear resistance against toughness and distortion control, accommodating production throughput with heat-treatment constraints, and managing costs and lead times for specific product forms.

The principal metallurgical distinction is their hardenability and quench response: one grade relies on a faster, more severe quench medium to achieve a hardened structure, while the other is designed to harden more uniformly with a slower quench that reduces distortion and improves toughness. This difference drives much of the practical divergence in heat treatment practice, mechanical behaviour, and suitability for specific applications.

1. Standards and Designations

• Common international designations and standards where these grades appear:
• AISI / SAE / ASTM: AISI O1, AISI A2 (often called SAE/AISI tool-steel designations).
• EN / DIN: Equivalent designations vary by producer and exact chemistry; consult EN tool-steel cross-reference tables for precise equivalents.
• JIS / Japanese: JIS equivalents are given in cross-reference tables and vendor datasheets.
• GB / Chinese: Chinese standards list local equivalents; always verify chemical and mechanical spec sheets.

Classification: - O1: Oil-hardening tool steel (plain-carbon / low-alloy tool steel designed for oil quench hardening). - A2: Air-hardening (sometimes called low-alloy, high-hardness, air-quench tool steel) with alloying to increase hardenability and temper resistance.

Note: Exact cross-reference numbers differ by standards body and by supplier. Always consult