Tempering temperature affects the hardness, toughness and stability of tool steel, but a useful value only makes sense with the steel grade and hardening cycle attached. This reference summarizes five published points from Uddeholm’s Formvar hot-work tool-steel heat-treatment guide. The hardness ranges are specific to Formvar and the supplier’s stated test conditions; they are not a recipe for another tool steel or a promise of the result on a production die.

Tool Steel Tempering Temperature Reference

The table lists five points from the Formvar guide: temperature in degrees Fahrenheit and the reported hardness interval in Rockwell C. For example, 1,090°F corresponds to 44–48 HRC in the published data. The range matters: one nominal temperature does not identify a single guaranteed hardness value, even under the source conditions.

Uddeholm’s guideline uses an austenitizing temperature of about 1,850°F for the listed treatment and calls for tempering at least twice. It specifies a minimum two-hour hold at temperature; tempering time and cooling between cycles matter alongside the furnace set point. Apply the schedule only after confirming that the material is Formvar and that the actual austenitizing, quench and tool section match the supplier’s guidance.

These points describe a manufacturer heat-treatment chart for a named product. They do not cover every tool steel, every section size or every furnace. Large or complex tools may respond differently from laboratory samples because section size, heat transfer, decarburization, quench severity and dimensional requirements affect the result. Uddeholm notes that hardness on actual tools and dies can be lower than the curve values because the test specimens are small.

For a worked selection, suppose a Formvar hot-work die needs a target near 45 HRC. The 1,090°F row reports 44–48 HRC, so it is a candidate point for discussion with the heat treater, not an automatic pass criterion. Confirm the drawing’s required hardness range, measurement location, load-bearing surface, finishing allowance and any later surface treatment. If the die will be nitrided, the core tempering condition must also account for the nitriding temperature so the treatment does not soften the underlying material.

Use the row together with the exact grade designation and the full heat-treatment sequence. Check the certificate and the supplier’s current product data before programming a furnace. Record the austenitizing temperature, time at temperature, quench method, temper count, hold duration and final hardness test. If the material is a different Uddeholm grade or a substitute from another supplier, locate that grade’s own tempering chart rather than transferring these values.

One common mistake is reading a tempering graph as a universal relation between temperature and hardness. It is specific to alloy chemistry and processing. Another is carrying over the right temperature but omitting the required second temper. A further risk is using a table point as a certified acceptance limit when the source presents a typical product response, not the contract drawing or material certification requirement.

Tool steel selection also involves toughness, wear, dimensional stability and the failure mode of the tool. The hardest point is not always the best operating point. Check whether the application prioritizes resistance to plastic deformation, thermal checking, chipping or wear, then consult the full grade guide and heat treater. This small table is a quick reference to five listed Formvar points; it does not replace a grade-specific heat-treatment procedure.

Keep the heat-treatment record with the part identification. If a measured result falls outside the drawing band, investigate furnace calibration, temperature uniformity, quench history and hardness-test preparation before changing the temper schedule. A supplier chart helps frame that review, but it cannot determine the cause of a specific out-of-range measurement.

Sources

Values and processing limits are summarized from Uddeholm’s Formvar Heat Treatment Guidelines. The guide identifies the austenitizing condition, tempering chart, specimen-size limitation and repeated tempering instructions.