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

Visual: a distributed network of fine cracks across the highest-temperature regions of the die face. Looks like cracked mud, alligator skin, or a dry lakebed under a hand magnifier. Crack spacing is roughly uniform within the network, typically 0.2-1 mm cell size on an H13 die that has run 10-40K hits. Individual cracks are shallow, typically under 0.1 mm deep on the working network, and run in no preferred direction. The pattern follows the temperature map of the die, not the geometry, not the flow.

Cause: thermal fatigue from the cyclic gradient between hot billet contact and the cooler die bulk plus cooling spray. Each cycle puts the surface into compression on contact and tension on release. The surface accommodates the strain by cracking, and once the network is established it accommodates further strain without growing the individual cracks much.

On the shop floor: crazing is expected on every H13 forge die past the break-in window. A fine, uniform, network-pattern at 20K hits is the die surface working as designed. The danger is not the network. The danger is a single crack that has propagated out of the network, deeper and longer than its neighbors, and that is mechanical fatigue (Step 5) or a propagating thermal crack, not crazing. A working crazing pattern reads uniform under a 10x loupe. A failing pattern has one or more cracks visibly different from the network around them.