How to weld Hardox wear plate

By Okan Can Kahraman · Updated 2026-10-29

Hardox is a quenched and tempered wear-resistant steel. It welds well with ordinary arc processes, but its hardness comes from a martensitic microstructure, so hydrogen, preheat and heat input need more care than with structural steel.

Short answer

• Use low-hydrogen consumables (H5 or lower) and keep them dry.
• Preheat according to grade and plate thickness: thin Hardox 400 and 450 often need none, harder grades and thicker plates need more.
• Use an undermatching, tough filler metal (for example ER70S-6 / EN ISO 14341 G 42 or G 46) unless the joint itself must be wear resistant.
• Keep the interpass temperature below the maker's maximum so the plate is not tempered soft.
• Keep the heat input moderate; very high heat input widens the softened zone next to the weld.

Why Hardox needs care

The hardness of Hardox comes from quenching and tempering. Two things can go wrong when it is welded. First, the hard heat-affected zone is sensitive to hydrogen cracking, which appears hours after welding. Preheat slows cooling and lets hydrogen escape; low-hydrogen consumables limit how much enters the weld in the first place. Second, heat tempers the plate: if it gets too hot during welding or between runs, the zone next to the weld loses hardness.

Preheat

The required preheat rises with hardness (carbon equivalent) and with thickness. As a rule of thumb, Hardox 400 and 450 in thin plate can usually be welded without preheat at room temperature, while Hardox 500 and above need preheat from much lower thicknesses. When two plates of different thickness or grade are joined, the thicker or harder plate decides. Moisture, cold workshops and highly restrained joints call for more preheat, not less.

The preheat temperature calculator contains SSAB's published preheat recommendations by grade and thickness for Hardox and Strenx. Always check against the steel maker's current data sheet for the plate you have.

Filler metal

For most joints, an undermatching ferritic filler is the better choice: it is tougher and reduces the stress on the hard heat-affected zone. Austenitic stainless consumables (for example 307 or 309 types) dissolve more hydrogen and can allow a lower preheat; they are also used when Hardox is joined to structural steel. Matching-strength fillers are only needed where the weld itself carries high load; hardfacing alloys are used on top when the weld surface must resist wear. The filler metal and shielding gas selector suggests a filler and shielding gas for Hardox against the other base metal.

Interpass temperature and heat input

SSAB specifies a maximum interpass temperature for each grade. Going above it tempers the plate and leaves a soft band beside the weld. Moderate heat input keeps that band narrow; a short t8/5 cooling time keeps the heat-affected zone tough. The heat input check and t8/5 cooling time shows each run's heat input against the window for the materials and calculates t8/5.

Checklist before welding

1. Identify grade and thickness of both parts.
2. Look up preheat and maximum interpass temperature.
3. Choose consumables (H5 or lower) and dry them as the maker specifies.
4. Clean the joint: no oil, rust, paint or moisture.
5. Measure the preheat with a contact thermometer or crayon on both sides, at least 75 mm from the joint.
6. Record the parameters in a WPS.