AR400, AR500, and Hardox welding guide: preheat requirements, low-hydrogen electrode selection, HAZ softening prevention, and hardfacing overlay procedures.
Abrasion-resistant plate (AR400, AR500, Hardox 450/500) gets its hardness from quench-and-temper processing. Welding re-introduces heat that softens the HAZ and risks hydrogen cracking if you don’t follow proper procedure. The plate costs too much to crack with sloppy technique.
Preheat is mandatory on all AR grades. AR400 needs 200-300F minimum. AR500 needs 300-400F. Thicker sections and higher carbon equivalents push preheat higher. Verify with a contact pyrometer or temperature crayon, not a hand-feel guess. The preheat slows cooling enough to prevent the HAZ from forming untempered martensite that cracks under residual stress.
Low-hydrogen consumables are the only option. 7018 for stick, ER70S-6 or ER80S-D2 for MIG, E71T-1 (gas-shielded) for flux-core. Self-shielded flux-core works in a pinch but has higher hydrogen potential. Keep stick rods in an oven at 250-300F. Moisture in the flux deposits hydrogen in the weld, and hydrogen cracking on AR plate can propagate across the entire joint.
Heat input control determines how wide the soft zone gets. Every AR plate weld has a softened HAZ band where the quench-temper hardness drops by 5-15 HRC. You can’t eliminate it, but you can minimize the width with stringer beads (no weaving), controlled interpass temperature (under 400F), and moderate amperage. Fast passes with less heat spread produce a narrower soft zone.
Hardfacing overlay is a separate application where you deposit wear-resistant alloy (chromium carbide, complex carbide) onto the surface of worn plate. This rebuilds abrasion resistance on excavator buckets, crusher liners, and chute plates. Hardfacing wires and electrodes have their own selection criteria based on the type of wear (abrasion, impact, erosion) the part sees in service.
Hardfacing for wear resistance on AR plate. Chromium carbide, tungsten carbide, and complex carbide electrodes. Stringer, dot, and crosshatch patterns. Stress-relief cracking explained.
AR400 and AR500 abrasion resistant plate welding guide. Preheat (150-400F), low-hydrogen filler (E7018, ER70S-6), HAZ softening control, and joint design.