Maintenance options: polish, repolish, weld repair, re-nitride, re-coat, scrap

Weld repair lives in a narrow window between "right call" and "guaranteed to fail in production." The window is defined by three things: substrate weldability, post-weld heat treatment, and the discipline to treat the repair as a metallurgical event rather than a quick fix.

H13 and similar 5% chromium hot-work tool steels weld. The standard practice, captured in the ASM Welding Handbook Vol. 6 tool-steel repair chapter and confirmed in the 2025 Lachowicz et al. work on martensitic hardfacing for forging tools, is preheat to roughly 300 to 450°C, hold interpass in the same band, use a matched H13 filler or a hardfacing alloy chosen for the wear mode, then post-weld heat treat the entire die at the substrate's original tempering temperature for full stress relief and microstructure recovery. Lachowicz's measurement matters here: as-welded martensitic deposits on three different hot-work substrates showed extreme hardness peaks (700 to 800 HV) and depressed valleys across the heat-affected zone. After PWHT, all three converged to a uniform tempered martensite around 500 HV. That uniformity is the point. A welded zone with a 300 HV gradient over 5 mm is a stress riser that cracks under the first hundred thermal cycles.

Weld is the right call when (a) the worn region is localized and well-defined, ideally less than about 5% of die face area, (b) the substrate at and around the repair is sound, with no propagating cracks running into the area, (c) the shop has preheat, interpass, and PWHT equipment under control, not a hand torch and a hope, and (d) the die has enough remaining service life elsewhere to justify the lost weeks of turnaround. Closed-die forge dies in H13 with washed-out detail or chipped corners are the classic weld repair candidates.

Weld is a coin flip when the substrate has accumulated thermal-fatigue cracking near the repair, when the shop has done preheat but is approximating PWHT with an air-cool, or when the filler chemistry was chosen for general hardfacing rather than matched to the substrate. These dies sometimes hit 25,000 to 30,000 post-repair hits. They sometimes fail within 5,000.

Weld is never the right call in four conditions, covered in the closing subsection.