P20 mold steel

Identify the actual product

Uddeholm's Impax Supreme at 325 HB gives approximate yield/tensile strengths of 900/1020 MPa at 20°C and 800/930 MPa at 200°C, tested on 90 × 300 mm flat bar. A deeper cavity or another producer's block requires its own property and hardness-location evidence. Uddeholm Impax Supreme specimen data

P20 is a mold-steel designation used alongside several producer-specific modifications. A purchase described only as “P20” leaves important questions unresolved. For example, Uddeholm calls Impax Supreme AISI P20 modified, Finkl calls MD AISI P20+Ni, and Böhler labels M200 ~P20, with material number 1.2312 and designation 40CrMnMoS8-6. These labels should not be collapsed into a single guaranteed chemistry or processing specification. Uddeholm Impax Supreme, p. 3; Finkl MD, p. 1; Böhler M200, pp. 1–2

ASTM's active A681-24 specification covers wrought alloy tool-steel products and requirements including chemistry, hardness, macrostructure and decarburization. A catalogue's approximate grade correspondence is not itself certification to an ordered ASTM grade and edition. Establish the product specification, producer designation and any permitted modification in the purchase agreement. ASTM A681-24, scope and abstract

Select the stock for the resin, fillers, wear, corrosion, block size and required polish or texture.

Named products and supplied condition

These are separate supplier entries, not a hardness-conversion table. Check the ordered condition and inspection location. Impax, p. 3; MD, p. 1; M200, pp. 1–2

Böhler describes M200 as non-corrosion-resistant and publishes average sulfur of 0.08%. Its sheet warns that other product variants, including plates, may differ in technical data and delivery condition. Do not transfer the long-product values to an unspecified mold plate without confirmation. M200 datasheet

Prehardening can remove the need to harden a finished cavity as part of the planned manufacturing route. It does not establish that machining, welding or later thermal treatment causes zero movement. Define machining allowance, roughing sequence, any stress relief and final inspection around the actual block and geometry.

Mechanical properties need condition and specimen context

For Impax Supreme at 325 HB, Uddeholm gives approximate tensile data from a 90 × 300 mm flat bar:

These are product-specific approximate data, not guaranteed minima for every P20 block. Impax, p. 4

Finkl separately publishes typical properties for a 4 in. (101.6 mm) thick MD plate and cautions that size, chemistry and heat-treatment variations can change results. Its brochure also limits its stated surface-to-core hardness-loss claim to the identified MD product and mold-size conditions. A surface hardness result cannot establish an arbitrary deep cavity's core properties. MD, pp. 1–2, 4

Machining, repair and surface finishing

Uddeholm provides stress-relief, hardening and surface-treatment guidance specifically for Impax Supreme. A complete route is needed if changing its delivered condition; a small-specimen tempering curve does not validate the response of a large finished mold. Impax heat-treatment guidance, pp. 4–5

Qualify repair filler and thermal controls for the actual grade and hardness. Match the repaired zone to the required polish or texture.

Finkl warns that EDM can leave a rehardened white layer and advises removing it. It also warns against overpolishing and recommends different named products for especially demanding polishing or texturing. Those recommendations qualify the individual MD product rather than guaranteeing an optical finish for the entire P20 family. MD, pp. 3–4

Agree surface acceptance with the mold owner and finishing specialist. Preserve the cavity's required geometry through layer removal and polishing. Qualify nitriding, local hardening or a coating as a complete surface system, including case/supporting substrate and final finish. A high surface hardness is not the same as through-hardening the mold.

Bounded thermal-expansion example

Böhler reports M200's mean thermal-expansion coefficient from 20 to 200°C as 13 × 10⁻⁶/K. M200 physical properties, p. 2

For an illustrative freely expanding 500 mm length heated uniformly from 20 to 200°C, ΔL = 500 × 13 × 10⁻⁶ × 180 = 1.17 mm. The estimated hot length is 501.17 mm. This arithmetic uses the cited M200 value; it is not a generic P20 coefficient or predicted mold-cavity error. A real mold has temperature gradients, constraints and mating components. Use the actual thermal field and product data when establishing clearances or dimensional compensation.

Source versions and purchasing boundary

The currently hosted Impax brochure prints Edition 7, 09.2011; its 2024 upload directory does not make it a 2024 edition. Finkl MD prints May 2018. Böhler's two-page sheet prints M200 EN_GB – 09.2026. ASTM lists A681-24 as active. Obtain current order confirmation for binding properties, availability and processing guidance rather than treating these explanatory brochures as acceptance certificates.

See also grades, tempers and conditions.