M-4 is a super high-speed steel having a very high carbon and vanadium content for exceptional abrasion resistance. It is well suited for premium-cutting tools of all types, and particularly those used for machining abrasive alloys, castings and heat-treated materials.

The higher carbon content enables M-4 to be consistently heat treated in excess of Rockwell C 65. However, this feature and the excess of vanadium carbides means that M-4 is more difficult to grind after heat treatment than M-2 or other super high-speed steels as M-42.

Hardening in properly rectified salt baths or controlled atmosphere or vacuum furnaces is recommended. Preheat thoroughly at 1450-1550° F, then transfer to the high heat of 2175-2225° F in a salt bath or 2200-2250° F in an atmosphere or vacuum furnace. A slight soak at the high heat will assist in developing maximum hardness, but avoid oversoaking. Quench into salt maintained at 1000-1100° F, or warm oil. After equalizing at the quench bath temperature, complete the quench in still air down to at least 150° F prior to beginning the tempering operation. If oil quenched, remove from the oil at about 900° F and air cool.

Large tools made of high vanadium high speed steel such as M-4 may not attain full hardness with a standard interrupted salt quench and it may be necessary to remove from salt bath quench at about 1500° F, then oil quench down to a temperature of about 900° F, or until the tool loses all color. Then complete quench in air. This technique will assist in promoting maximum hardness.

M-4 should be tempered in the range of 1000-1100° F for most applications. Hold at temperature for 2-4 hours. Cooling should be carried out in still air and always allow the tools to reach room temperature before retempering. Double tempering is recommended and a third temper at 800-1000° F after finish grinding is often beneficial.

Hardening happens between 2175-2250° F.

M-4 is an oversized material,

+/- .015 up to .040 on thickness

+/- .080 up to .125 on width

Up to 1" +/- .007 up to .018

1" up to 6" +/- .015 up to .040

6" and up +/- .0625 up to .250