Uddeholm’s Formvar heat-treatment guide pairs five tempering temperatures with expected hardness ranges for this hot-work tool steel. Use the table only when the grade and heat-treatment conditions match the manufacturer’s guidance. The schedule is a reference for discussion with a qualified heat treater, not a universal tool-steel recipe: a different grade, section, furnace, austenitizing condition, or quench can produce a different result.

Uddeholm Formvar tempering temperature and hardness

How to read the values

Temperature is shown in degrees Fahrenheit, and hardness is a range in Rockwell C. For example, the guide associates a 1,090°F temper with 44–48 HRC. The endpoints are a reported range, not a promise that every production tool will land at either value. The chart is specific to Uddeholm Formvar; do not substitute it for H13, H11, D2, or another hot-work steel based on a similar alloy description.

The guide calls for at least two tempers. It specifies a holding time of one hour per inch of wall thickness, with at least two hours at temperature. It also notes that some intended final hardness values in the 500–550°C tempering band can reduce toughness. The table shows the manufacturer’s listed Fahrenheit values; use the current full guide for the complete sequence, temperature conversions, and process details.

A practical selection example

Suppose a die is confirmed as Formvar and the heat treater is targeting roughly 46–50 HRC. The manufacturer’s chart points to 1,070°F as the corresponding tempering condition. The heat treater must still follow the full grade-specific procedure, including hardening, quench, hold duration, repeat tempering, and cooling between tempers. Selecting a temperature from this small table alone does not establish that the finished part will meet a drawing or service requirement.

Before starting, confirm the grade on the material certificate, the condition in which it was supplied, the section thickness, and the required final hardness. If a tool has a thin edge and a heavy core, local geometry and heat-transfer differences can affect the outcome. Ask the heat treater how hardness will be checked and whether the test location represents the critical section.

Two common mistakes

First, do not apply the Formvar chart to any steel simply called “tool steel.” Tempering response varies by grade and composition. Second, do not read the hardness range as an exact guaranteed result. Uddeholm states that real tools can finish softer than the test samples because tool size and heat-treatment parameters differ. Use the specification and process qualification that apply to the actual part.

Values and process notes are from Uddeholm’s Formvar Heat Treatment Guidelines. The guide’s sample hardness values should be interpreted with its stated test conditions and the complete heat-treatment procedure.

Before specifying a heat-treatment cycle

Hardness is only one requirement. A drawing may also control dimensional change, toughness, wear behavior, surface condition, and the condition of a critical edge. Tell the heat treater the exact steel designation, section size, required property range, and any limits on distortion. The heat treater should use the latest manufacturer instructions and process controls suited to the part rather than treating one temperature entry as a complete procedure.

Check whether the hardness target applies to the core, the surface, or a test coupon. A coupon does not automatically represent the largest or thinnest section of the tool. When a result falls outside the expected interval, investigate the full cycle and test method before changing temper temperature; changing one parameter can affect toughness and dimensional stability as well as hardness.

Ask how hardness readings will be taken and reported, including the test scale and location. A Rockwell C number is meaningful only when the surface and specimen support the test method. Document the selected temper, number of cycles, hold duration, and final measurements with the part record so later rework can be compared with the same procedure.