Welding Abrasion-Resistant (AR/NM) Wear Plate: Keeping the Hardness You Paid For

The central trade-off

Wear plate is supplied quenched and tempered at 360–550 HBW. Two opposing risks govern welding:

• Too cold (no preheat, low heat input, thick plate): the joint and its heat-affected zone (HAZ) can harden further and crack, especially on the higher grades.
• Too hot (high heat input, high interpass temperature): the HAZ softens below the delivered hardness, creating a groove of soft material next to every weld that wears preferentially in service.

Plate makers publish welding recommendations per grade and thickness; those take precedence over general rules, but the pattern below is typical.

Preheat: moderate, not extreme

Unlike structural steels of similar hardness, wear plate usually needs only moderate preheat, because its carbon content is modest and its toughness is engineered in. Indicative practice:

Plate	Typical minimum preheat
NM360 / AR400, thin (<20 mm)	Often none above ~10 °C ambient
NM400–NM450 / AR450, 20–40 mm	75–125 °C
NM500 / AR500 and heavier sections	100–175 °C

Always confirm against the mill's data sheet for the actual grade and thickness. Over-preheating is itself harmful: unnecessary preheat plus slow welding is exactly what produces a wide, soft HAZ.

Consumables and heat input

• Low-hydrogen fillers throughout — basic electrodes or controlled wires, stored dry.
• Joint strength is usually undermatched deliberately: ordinary E70-class (or equivalent) fillers are standard for attachment welds, because a ductile, softer deposit accommodates the plate's movement and resists cracking. Reserve high-strength matching fillers (and hardfacing) for wear surfaces.
• Limit heat input to the maker's window (often around 1.0–2.0 kJ/mm or lower for the hardest grades) and keep interpass temperature within the specified ceiling — commonly no more than about 200–250 °C.
• Use sequences that spread heat: skip welding, backstep, and avoid concentrating passes in one spot.

Wear-side considerations

• Welds on the wear face are sacrificial points: where a weld must cross the wearing surface, cap it with a hardfacing deposit or accept locally faster wear. Better design puts joints and attachments on the back face.
• Repair welding follows the same rules as fabrication; grinding out a crack must not overheat the surrounding plate (blueing means tempering has begun).
• Cutting and edge preparation: thermally cut edges of high-hardness plate can carry microcracks — grind edges back to sound metal before welding, and never weld over a cracked cut edge.
• Do not flame-straighten or hot-form wear plate without the maker's guidance; local reheating above the original tempering temperature permanently softens the spot.

In one sentence

Treat wear plate like a finished heat-treated component that happens to need joining — moderate preheat, low hydrogen, restrained heat input, and design the welds off the wear face wherever possible.