# A2 tool steel

Air-hardening cold-work tool steel: grade identity, producer conditions, hardness and dimensional tradeoffs, and fabrication qualification.

Reviewed: 2026-11-01

Tags: materials, steel, tool-steel, cold-work

## Identity and purchasing basis

BÖHLER's **K305** guidance gives **950–980°C** hardening and **15–30 minutes after temperature equalization**. Its tempering chart uses a **20 mm square specimen**. Start the hold when the workpiece has equalized. Check applicability to the actual die section before using the chart. [BÖHLER K305 treatment and chart](https://www.bohler-edelstahl.com/app/uploads/sites/248/productdb/api/k305_en_gb.pdf)

A2 is an air-hardening cold-work tool steel associated with **UNS T30102**. Carpenter lists ASTM A681 among applicable specifications and supplies bar forms. Its nominal analysis includes approximately 1% carbon, 5.25% chromium, 1.1% molybdenum and 0.2% vanadium. These are producer analysis values, not the complete acceptance limits for every A2 order. [Carpenter A2 product page](https://www.carpentertechnology.com/alloy-finder/a2)

Uddeholm Rigor and BÖHLER K305 are named producer products associated with A2/1.2363. BÖHLER expressly restricts its presented K305 data to **long products**, despite listing plates among available variants. A product association does not justify transferring every property to every form. [Uddeholm Rigor](https://www.uddeholm.com/app/uploads/sites/230/2024/05/rigor-eng_p_0419-e10.pdf), [BÖHLER K305](https://www.bohler-edelstahl.com/app/uploads/sites/248/productdb/api/k305_en_gb.pdf)

Order the exact producer or generic grade, product standard and edition, form, size, delivery condition, surface allowance and inspection documents. Keep the heat/lot identification through machining and heat treatment. A grade name does not prove the condition or provenance of an unidentified offcut.

## Where the property balance is useful

BÖHLER positions K305 between lower-alloy cold-work steels and high-chromium grades where through-hardening and wear demands increase. Its examples include blanking/cutting tools, die inserts, thread-cutting tools and industrial knives. These are application leads, not guaranteed tool-life claims. [BÖHLER product description](https://www.bohler-edelstahl.com/app/uploads/sites/248/productdb/api/k305_en_gb.pdf)

Choose A2 against the observed failure mechanism. An edge that chips, a surface that abrades and a punch that plastically deforms require different improvements. Record workpiece material, thickness, clearance, lubrication, impact, contact pressure and the accepted wear limit. Do not choose a replacement only because its catalogue hardness is higher; compare toughness, wear mode, grinding and maintenance cost together.

Carpenter describes its No. 484 A2 wear comparison as **ASTM G65 Procedure A dry-sand/rubber-wheel abrasion**, reported as volume loss, where lower values indicate better abrasion resistance. That test does not establish resistance to every adhesive-wear or impact situation. [Carpenter No. 484 technical sheet](https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/A2.pdf)

## Supplied condition versus working hardness

Uddeholm lists Rigor delivery as soft annealed to approximately **215 HB**. BÖHLER lists K305 annealed hardness **≤240 HB**. Approximate delivery data and a stated maximum are different kinds of information, and neither describes a finished hardened tool. [Uddeholm delivery condition](https://www.uddeholm.com/app/uploads/sites/230/2024/05/rigor-eng_p_0419-e10.pdf), [BÖHLER delivery condition](https://www.bohler-edelstahl.com/app/uploads/sites/248/productdb/api/k305_en_gb.pdf)

## Heat treatment: qualify the complete cycle

BÖHLER's K305 guidance gives a hardening range of **950–980°C**, with 15–30 minutes holding **after temperature equalization**. Its tempering chart uses a **20 mm square specimen**. These conditions matter: a furnace timer started before the workpiece equalizes is not the same treatment, and a chart specimen does not represent every large die. [BÖHLER heat-treatment and chart basis](https://www.bohler-edelstahl.com/app/uploads/sites/248/productdb/api/k305_en_gb.pdf)

Uddeholm likewise says its tempering graphs are valid for small samples and depend on tool size. It recommends two tempers with intermediate cooling to room temperature, a minimum tempering temperature of 180°C and at least two hours at temperature. Its quench options include circulating air, gas cooling and baths; oil is restricted to small, uncomplicated tools. [Uddeholm tempering and quenching guidance](https://www.uddeholm.com/app/uploads/sites/230/2024/05/rigor-eng_p_0419-e10.pdf)

Agree on preheating, atmosphere, quench, tempering and verification for the actual tool section. Specify hardness locations and any core microstructure or toughness requirements.

Carpenter warns that No. 484 is susceptible to decarburization during thermal processing and that overheating can cause adverse size changes. Its guidance calls for suitable protective processing. [Carpenter decarburization and dimensional-change discussion](https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/A2.pdf)

Protecting the surface matters when an edge or wear face must retain its carbon and hardness. Specify whether stock removal after treatment is sufficient and how the final surface is assessed. Do not assume a bright appearance proves acceptable decarburization or that a surface hardness reading establishes the entire section's condition.

## Dimensional control and finishing

Uddeholm's size-change data use a **100 × 100 × 25 mm sample plate**; hardening and tempering changes must be added. It warns that sub-zero treatment can crack intricate shapes. [Uddeholm dimensional stability](https://www.uddeholm.com/app/uploads/sites/230/2024/05/rigor-eng_p_0419-e10.pdf)

Plan rough machining, any stress relief, heat treatment and final grinding as a sequence. Define which dimensions are checked at each stage and which allowance is available for correction. Support slender features and document distortion before deciding whether a process is repeatable. Qualify surface treatments against the underlying tempering condition and dimensional requirements.

Uddeholm calls for an additional temper after EDM on hardened-and-tempered Rigor, about **25°C below the prior tempering temperature**. Incorporate the applicable instruction into the finishing route. [Uddeholm EDM guidance](https://www.uddeholm.com/app/uploads/sites/230/2024/05/rigor-eng_p_0419-e10.pdf)

For repair welding, obtain a producer-supported procedure covering material condition, filler, working temperature, cooling and subsequent treatment. Qualify the repaired edge and geometry before returning the tool to service. A repair changes the local thermal history even when the overall tool still meets its hardness check.

## Bounded estimating example

BÖHLER lists K305 density at 20°C as **7.7 kg/dm³**. An ideal 100 × 50 × 20 mm blank has volume 100,000 mm³ = 0.1 dm³, giving estimated mass **0.77 kg**. [BÖHLER physical properties](https://www.bohler-edelstahl.com/app/uploads/sites/248/productdb/api/k305_en_gb.pdf)

This original arithmetic excludes holes, tolerances, scale and machining allowance. It supports an initial material estimate, not dimensional acceptance or a prediction of tool performance. For costing, use actual stock size and finished CAD volume separately so that purchased mass and removed mass do not become confused.

## Source editions and related reference

Uddeholm's front matter identifies **Edition 10, 04.2019**; its back cover also carries **06.2018**. BÖHLER's footer identifies **K305 EN_GB – 03.2026**. Carpenter's No. 484 sheet prints **Edition Date 11/1/2005** and **©2020**; the copyright is not evidence of a new technical edition. Obtain current order-specific requirements before applying these references to acceptance.

[Grades, tempers and conditions](../grades-tempers-and-conditions.md)