CPM M-4 Tool Blade Steel - Heat Treatment Recipe


**Knives should be cleaned by washing with soapy water and then placed into high temperature tool wrap foil (2,200°F+ rated) pouch prior to heat treat if not using Oxygen free heat treat equipment.

***Skipping stages such as pre-heating and equalizing or cryo will result in lower hardness, higher amounts of Retained Austenite (RA), impaired stain resistance or other issues. Ramp AFAP (as fast as possible) between preheating and austenizing temps.

****Clamping flat after quench during cryo or tempering recommended to avoid thermal shock induced warp.

*****Figures represent under quenching under positive pressure with aluminum plates and compressed air to at or below 125°F / 50°C--alternative quenching methods may present lower hardness, high RA, or other issues.



Austenizing temperature

Expected Rc (as

quenched prior to cryo)

1,500°F / 815°C

(hold 5 minutes)

1,800°F / 982°C

(hold 5 minutes)

2,100°F / 1,175°C

Soak 15 minutes

64Rc (65 after Cryo)


Cryogenic Treatment:

A cryogenic treatment is recommended to convert retained austenite, and can either be done before or after the first temper cycle.

While liquid nitrogen is preferred, a sub zero bath with dry ice and kerosene will suffice for -100°F / - 74°C.

Submerge in sub-zero treatment 4-6 hours depending on thickness and number of blades.

**A cryogenic treatment can be done immediately done after quench, but it is recommended blades be clamped flat to avoid thermal shock induced warp--cryo treatment should always be followed by a tempering cycle.



Once blade is quenched and near ambient temperature, blades should be tempered accordingly, the times suggested are to ensure even, consistent temperature.

Figures supplied are as representative of industrial standards.

Note: Final hardness values vary based on initial as-quenched hardness and percentage of conversion to Martensite. Only reliable testing methods, e.g. calibrated Rockwell hardness tester, can provide actual hardness values--hardness calibrated files and chisels are relative testing methods and inaccurate for true hardness value reading.

Temper three times for 2hrs.


Hardness (2 hour x3 guideline):

1,000°F / 537°C


1,025°F / 551°C


1,050°F / 565°C


1,100°F / 593°C



***The included Heat Treat Schedule on this page is formulated based upon Industry standards and data from ASM International, Crucible and other foundry spec sheets, and Kevin Cashen (independent researcher, ferroalloy metallurgist, and bladesmith of Matherton Forge).

Suggested heat treatment is based on the recommended specifications for use in ovens, high temp salts, and similarly, properly calibrated equipment; and in line with proper industrial standards for quenching. Deviation from industry standards for schedules, equipment, quenching mediums; and hardness testing equipment may result in varied results. The supplied information on this page is on a generalized scale with the above mentioned standards and methods, which is why soak times and similar aspects may vary in time length to include a margin for the available heat treating equipment and steel cross section.

If you are unsure if you have the necessary means to heat treat on-site, we recommend professional heat treating services provided by Rob Ridley at HeatTreat.ca  or 403 556 1113. 

CKMS Ltd. is not liable or responsible if proper industry heat treating protocols are not applied; particularly and especially if sending to an independent heat treat provider if they do not follow the intended heat treat schedule or standards for that particular steel; or damage they cause while in their possession.