Reading wear: crazing, washout, abrasion, adhesive pickup, plastic deformation

Visual: cavity profile changed, edges rounded, surface washed but not eroded, and no cracks. The die feature has moved under load. Sharp corners are rounded, flat surfaces are dished, raised features are flattened. Impression dimension has drifted in the direction of material flow, but without the erosive valley signature of washout. The 2024 Materials review on hot-closed-die-forging tool durability flags plastic deformation as one of the two largest withdrawal causes, comparable in frequency to abrasive wear.

Cause: peak service stress exceeded the substrate's hot yield strength. Three things drive it. Substrate has lost hardness from sustained over-temperature operation (see Lesson 3 on the working ceiling). Substrate was under-tempered or the wrong grade for the load. Forging load exceeded the design envelope, often from a billet that was too cold or too large for the die.

On the shop floor: plastic deformation is the wear mode that looks the least dramatic on the bench and does the most damage when missed. A heat-checked face with a 0.005-inch dimensional drift in a flow region is more often plastic deformation than washout, and the fix for the two is different. Plastic deformation says the substrate has gone soft or the load went out of envelope. Washout says the surface is being eroded by flow. Microhardness on the deformed feature decides which. A surface hardness below the process minimum on a die with no other wear features is plastic deformation almost regardless of what the dimensional measurement says.