Stainless Steel vs. Steel Inserts: Why One Tool Doesn't Fit All
It’s a common temptation in a busy CNC shop: you have a steel turning insert (like an NC3120) already loaded, and a stainless steel job comes in. You think, "It’s just metal, right? It should work."
The truth? Using a dedicated steel insert on stainless steel is one of the fastest ways to destroy your tool life and ruin your surface finish. Here is the science behind why you need material-specific grades.
1. The "Sticky" Nature of Stainless Steel
Unlike carbon steel, stainless steel is notoriously "sticky." During cutting, it has a high tendency to weld itself to the cutting edge—a phenomenon known as Built-Up Edge (BUE).
- Steel Inserts (NC Series): Usually feature thicker CVD coatings designed for heat resistance in dry cutting. These can be too "rough" for stainless, encouraging material adhesion.
- Stainless Inserts (PC5300): Use specialized PVD coatings and ultra-smooth surface treatments that act like "non-stick pans," allowing chips to slide off without welding.
Shop Best-Seller: Korloy CCMT09T304 PC5300 for Stainless
2. Work Hardening: The Silent Killer
Stainless steel hardens instantly when it is compressed or heated. If your insert isn't sharp enough to "shear" the metal cleanly, it will "rub" the surface, making the next pass nearly impossible to cut.
- Steel Geometry: Often has a slightly rounded, "honed" edge to handle the impact of hard steel.
- Stainless Geometry: Features a razor-sharp cutting edge to slice through the material before it has a chance to work-harden.
3. Heat Dissipation: CVD vs. PVD
| Feature | Steel Grades (NC3120/NC3020) | Stainless Grades (PC5300) |
|---|---|---|
| Coating Type | Thick CVD (Heat Shield) | Thin, Tough PVD (Sharpness) |
| Edge Prep | Strong / Honed | Sharp / Positive |
| Best For | Stable High-Speed Steel Turning | Stainless, Ti, and Superalloys |
When Can You Cross-Over?
If you absolutely must use one insert for everything, look for a Universal Grade like the Korloy PC5300. While it is optimized for stainless steel, its high-toughness PVD coating allows it to perform respectably on general steel and even some cast iron.
However, an NC-series steel insert should never be your first choice for a long stainless steel production run.
Conclusion
Using the right tool saves you money by preventing broken inserts and reducing machine downtime. Stop fighting your material and start using the grade designed for it.
