How to process high-speed steel raw materials into milling cutters

High-speed steel (such as W18Cr4V, M2, etc.) needs to go through a series of precise heat treatment and machining steps from raw materials to milling cutters. The following is a typical processing flow:

1. Cutting and forging
Cutting: Cut the high-speed steel bar into blanks of the required size.

Forging: Improve the internal structure of the material through hot forging (heating to 1000~1150℃), eliminate carbide segregation, and improve density and mechanical properties. Slow cooling is required after forging to avoid cracking.

2. Annealing treatment
Purpose: Reduce hardness (to HB200~250) to facilitate subsequent machining.

Process:

Heat to 850~880℃ and keep warm for 2~4 hours.

Slowly cool (furnace cooling) to below 500℃, and then air cool.

Result: Obtain spherical pearlite structure and reduce residual stress.

3. Machining
Turning/milling: Processing the initial geometric shapes of the milling cutter, such as the shape, groove, and tooth shape.

Grinding: Precision grinding of key parts (such as the cutting edge) to ensure dimensional accuracy and surface finish.

4. Heat treatment (key steps)

(1) Quenching
Preheating: Preheating in two stages (500~600℃ and 800~850℃) to avoid cracking caused by direct high-temperature heating.

High-temperature heating: Heating to quenching temperature (such as 1260~1300℃ for W18Cr4V) to fully dissolve carbides.

Cooling:

Oil quenching: Suitable for simple shapes, cooling to about 300℃ and then air cooling.

Graded quenching: Short stay in a 500~600℃ salt bath, then air cooling to reduce deformation.

Vacuum quenching: Commonly used for high-end cutting tools to avoid oxidation and decarburization.

(2) Tempering
Process: Temper 3 times at 540~570℃, 1~2 hours each time, air cooling.

Function: Eliminate residual austenite, improve hardness (HRC63~66) and toughness.

Cryogenic treatment (optional): -80℃ or -196℃ treatment to further transform residual austenite.

5. Finishing and sharpening
Grinding: Use diamond grinding wheel to precisely grind the edge to ensure sharpness and geometric accuracy.

Coating (optional): Apply TiN, TiAlN and other coatings through PVD (physical vapor deposition) process to improve wear resistance and life.

6. Quality inspection
Hardness inspection: Ensure that the hardness meets the standard (HRC63 or above).

Dimension inspection: Use a projector or three-coordinate measuring machine to check the tolerance.

Metallographic analysis: Observe the distribution of carbides and grain size to ensure uniform structure.

Key considerations
Temperature control: Quenching heating needs to be precise to avoid overheating (coarse grains) or underheating (undissolved carbides).

Anti-oxidation and decarburization: Salt bath furnaces or vacuum furnaces can protect the surface.

Stress relief: Stress relief annealing is required between each processing stage (such as after rough processing).

Edge treatment: Burrs need to be removed after grinding to avoid micro cracks.

Through the above process, the high-speed steel raw material is finally transformed into a high-performance milling cutter with high hardness, red hardness (maintaining hardness at high temperatures) and wear resistance, suitable for metal cutting processing.