Work Harden
Is work hardening the same as heat treating?
No. Work hardening is a mechanical strengthening from plastic deformation, while heat treating changes material properties through thermal phase or structural changes. Work hardening occurs at low temperatures and involves dislocation movement, not diffusion or phase transformation.
Why does stainless steel punish light cuts?
Austenitic stainless alloys harden rapidly when rubbed or compressed. An insufficient chip load lets the tool burnish the surface rather than shear it, creating a hardened skin that becomes harder to cut than the parent material. Increasing feed per tooth avoids this.
What is the corrective action sequence for a work-hardened part?
Verify sharp tool condition, increase chip load to stop rubbing, eliminate dwell, and use a toolpath that maintains consistent engagement and chip evacuation. Climb milling and minimal pecking help. If the surface is already glazed, remove the hardened layer with a robust roughing pass.
Work hardening is the localized hardening of a metal surface caused by plastic deformation during machining, not heat treatment. It occurs when a cutting tool rubs, compresses, or dwells against the workpiece instead of cleanly shearing chips. This creates a harder surface layer that resists subsequent cutting, increases tool wear, and degrades surface integrity.
Work hardening typically appears as an unwanted surface condition on stainless steel, titanium, and other hardening-prone alloys. The practical problem begins when a light finishing pass, dull insert, or toolpath dwell causes the cutter to rub rather than shear. That rubbing mechanically compresses the surface grains into a hard, glazed skin. On the next pass, tools must cut through that hardened layer, which spikes cutting forces, promotes chatter, and shortens tool life. Operators often first notice a shiny, polished surface, rising spindle load, or a sudden squeal during re-entry. Corrective action focuses on returning to a true shearing regime: sharp tool geometry, stable fixturing, adequate chip thickness, and consistent feed per tooth. Climb milling, minimal pecking, and avoiding dwell all help. In millwork, similar rubbing or burnishing can create a slick, slippery surface; while not metallurgical, it signals the same need to maintain aggressive, consistent chip formation.
Too-light finishing passes: A skim cut compresses rather than shears the surface, leaving a hardened skin. That skin then overloads the next tool, accelerating edge chipping and forcing premature insert changes.
Dwell or interrupted feed at the cut: Pausing in contact with the workpiece concentrates heat and pressure, creating a localized hardened band. This band causes the tool to squeal, deflect, or break when cutting resumes.
Dull or wrong-geometry tooling: A worn edge increases rubbing and cutting force, so the part work-hardens while tool wear compounds rapidly. Poor chip control, shiny cut marks, and premature insert failure are typical results.