For years, machining stainless steel has been a time consuming and costly enterprise. The desirable combination of corrosion resistance and mechanical strength of stainless steel is challenging to productively and economically machine. Many applications today also require that the stainless steel be hardened, which can make machining these materials with indexable carbide inserts an even more difficult enterprise.

One of the more common stainless steels encountered today is 17-4 PH, which is widely used in the Aerospace, Petrochemical, Pulp and Paper, and Food Processing industries. 17-4 PH is a precipitation hardening martensitic stainless steel offering a good combination of oxidation and corrosion resistance as well as strength and toughness. In the solution treated state, 17-4 PH can be milled using traditional methods and materials, but for critical applications, 17-4 PH is used in the 
hardened condition. Often, this material is in the 38-42 R/c hardness range which lowers carbide tool life, requires slower cutting speeds, and increased process times.
Using Greenleaf’s whisker reinforced ceramic to mill hardened 17-4 PH it is possible to increase cutting speed from 4 times to as much as 10 times that of coated carbide. Insert life can also be increased due to the heat resistance of WG300 when milling these hardened stainless steels at increased surface speeds.

In a recent example, a western New York customer milling a hardened 17-4 PH component, switched from a 2” cutter using indexable carbide inserts with 2 cutting edges to a 2” Greenleaf Excelerator mill using round inserts with 6 cutting edges. Not only was the cycle time reduced by 200 percent, but the WG300 ceramic inserts average 60 percent more tool life at four times the cutting speed of carbide.
Alloys like nickel and chrome that are present in stainless steels also demand particular attention to feed rates when milling. If the proper chip thickness is not achieved at the cutting edge, work-hardening can occur, chips can be re-cut and insert life dramatically reduced. In another example of milling 42 R/c 17-4 PH stainless, a 2” Greenleaf Excelerator mill outperformed a high feed cutter using carbide inserts in a pocketing application. The carbide high-feed cutter was able to run at 363 SFM and a feed rate of 110 IPM. Due to the varying widths of cut in the pocketing routine, and the chip thinning effect of the round WG300 inserts in the Greenleaf cutter, cutting speed was increased as much as 10X, and the feed rate was optimized at 152 IPM!
Milling stainless steels such as 17-4 PH in the hardened state can be done efficiently and cost effectively if you combine the right cutting tools with the proper operating parameters using Greenleaf’s WG300 whisker reinforced ceramic inserts.

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