# O1 tool steel

Oil-hardening cold-work tool steel: product identity, condition-dependent properties, heat treatment and dimensional control.

Reviewed: 2026-11-01

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

## Identity and order definition

Carpenter's **O1** typical hardness is **60–63 HRC after a one-hour 204°C temper** and **55–57 HRC after a one-hour 316°C temper**. Both rows follow **oil quenching from 802°C**. Carry the quench and hold time with the reported hardness. [Carpenter O1 tempering table](https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/O1.pdf)

O1 is an oil-hardening manganese-chromium-tungsten tool steel identified as **UNS T31501**. Carpenter's technical sheet lists nominal carbon 0.90%, chromium 0.50% and tungsten 0.50%, with other elements. These are producer analysis values, not the complete acceptance requirements of an arbitrary order. [Carpenter O1 technical sheet](https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/O1.pdf)

Uddeholm Arne and BÖHLER K460 are named products associated with **AISI O1 / 1.2510**. BÖHLER restricts its presented K460 data to **long products**, although it lists plate as another available variant. A designation association does not make every producer property interchangeable across forms. [Uddeholm Arne bulletin](https://www.uddeholm.com/app/uploads/sites/216/productdb/api/tech_uddeholm-arne_en.pdf), [BÖHLER K460 bulletin](https://www.bohler-edelstahl.com/app/uploads/sites/248/productdb/api/k460_de_at.pdf)

Specify grade or producer product, governing standard/edition, form, size, supplied condition, surface allowance and inspection documents. Keep heat identity through cutting and processing. A tool's successful appearance or magnetic response cannot establish the grade of an unidentified offcut.

## Selection and supplied condition

Uddeholm describes Arne as a general-purpose cold-work tool steel and lists **soft-annealed delivery at approximately 190 HB**. The supplied machinable stock and the final hardened tool are different material states. [Uddeholm description and delivery condition](https://www.uddeholm.com/app/uploads/sites/216/productdb/api/tech_uddeholm-arne_en.pdf)

Identify whether the tool's limiting failure is wear, chipping, gross cracking or plastic deformation. Record work material, contact mode, impact, lubrication, clearance and accepted wear limit. Selecting the highest catalogue hardness alone does not resolve that balance. Include machining, grinding, repair and heat-treatment capability in the selection.

A catalogue application such as a die or gauge is a selection lead. It does not establish finished-tool life, dimensional accuracy or an allowable load for a different geometry.

## Property values retain their condition

Uddeholm's **approximate** Arne table gives compressive 0.2% yield strength **2,200 MPa at 62 HRC**, **2,150 MPa at 60 HRC**, and **1,800 MPa at 55 HRC**. The same table's separate compressive-strength column must not be confused with the yield column. These values are reference data, not tensile strengths or guaranteed design allowables. [Uddeholm compressive-strength table](https://www.uddeholm.com/app/uploads/sites/216/productdb/api/tech_uddeholm-arne_en.pdf)

Carpenter separately reports typical hardness after **oil quenching from 802°C and tempering for one hour**: **60–63 HRC at 204°C tempering**, versus **55–57 HRC at 316°C**. These rows describe that test route; they are not a recipe for arbitrary section sizes. [Carpenter tempering table](https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/O1.pdf)

## Heat treatment and geometry

BÖHLER's German K460 bulletin gives **780–820°C hardening**, with **15–30 minutes holding after complete heating**. Its tempering chart uses a **20 mm square specimen**. The bulletin's numerical guidance belongs to its named product and must be read with its quench and tempering instructions. [BÖHLER hardening and chart basis](https://www.bohler-edelstahl.com/app/uploads/sites/248/productdb/api/k460_de_at.pdf)

Uddeholm's Arne tempering curves instead use **15 × 15 × 40 mm oil-quenched samples**. It cautions that actual tools and dies can achieve lower hardness because of tool size and treatment parameters. Its guidance calls for two tempers with cooling to room temperature between them and at least two hours at temperature. [Uddeholm tempering qualifications](https://www.uddeholm.com/app/uploads/sites/216/productdb/api/tech_uddeholm-arne_en.pdf)

Agree on preheat, equalization, quench and tempering with the heat treater.

## Dimensional and surface control

Treat dimensional stability as a manufacturing requirement that needs evidence. Plan rough machining, stress relief where appropriate, heat treatment and final grinding as a sequence. Establish stock allowance and final inspection stages before processing. A supplier's description of low deformation does not guarantee zero change in a finished part.

Inspect geometry and working surfaces after operations that can alter them. Define edge acceptance and any decarburization or surface-damage limits separately from bulk hardness. For EDM, coating, nitriding or repair welding, obtain product-specific guidance compatible with the existing treatment history and verify the affected tool before release.

O1's tooling designation is not a corrosion-service qualification. Specify storage, cleaning and protection for the actual environment. Keep chemical compatibility and protective treatment distinct from wear and hardness requirements.

## Bounded estimate and release record

Carpenter lists density **0.2830 lb/in³**. For an ideal 1 × 2 × 6 inch rectangular blank, original arithmetic gives `V = 12 in³` and `m = 12 × 0.2830 = 3.396 lb`. This excludes tolerances, holes and removed stock; it is an initial stock estimate, not finished-tool acceptance. [Carpenter physical properties](https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/O1.pdf)

Retain producer, heat/lot, specification/edition, supplied/final condition, treatment record, drawing and final inspection. Record substitutions against the complete requirement, including tool quality and processing evidence.

## Source editions

Uddeholm's inspected bulletin prints **Edition 11, 04.2019**. BÖHLER's German-language sheet prints **K460 DE_AT – 09.2026**. Carpenter's sheet prints **Edition Date 05/01/1986** and separately **©2020**; the numeric edition string is retained without assigning an ambiguous day/month interpretation. Confirm current contractual requirements separately.

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