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

Visual: smooth, progressive erosion of die material in flow regions. The surface is matte or polished rather than scratched, and the impression dimension has grown in the direction of metal flow. Deepest near gates, narrow transitions, and the flash land where hot metal accelerates and shears against the die wall. The eroded surface is shaped by the flow itself, so the pattern is directional and traces the material flow lines.

Cause: hot scaled billet flowing under load. Oxide scale on the billet is harder than the die surface, and at high flow velocity the scale acts as a continuous abrasive medium. Lube film thickness drops at the high-velocity regions where contact stress is highest, so the die surface meets the scaled billet directly. The 2024 Materials review on hot-closed-die-forging tool durability ranks abrasive wear (including washout) as the single largest contributor to tool withdrawal, with roughly 70 percent of tools pulled for plastic deformation or abrasive wear combined.

On the shop floor: washout is the wear mode that progressively kills dimensional tolerance. The part grows in flow regions until the dimension drifts out of spec. A washout valley is not a defect to fix in isolation, it is a signal that the lube film failed in that region. Zone the spray pattern to put more film at the high-velocity flow regions, descale the billet more aggressively, or accept that the die has reached the end of its dimensional life in that feature. Welding the valley back to size buys hits, but the underlying cause stays the same and the welded zone washes faster than the rest of the die.