Welding Hardox and other high-strength wear steels is a completely different discipline from welding standard structural steel. The hardness and wear resistance of these steels come from special quenching and tempering treatments applied during production. Uncontrolled heat input during welding can disrupt this structure, and incorrect technique leads to cold cracks that appear days later. This article covers the technical rules of welding Hardox and the points to watch for in field application.
What Is the Core Challenge in Welding Hardox?
The hardness of wear steels comes from a martensitic internal structure. During welding, the joint area is melted and the surrounding material is exposed to high temperature. As this zone cools, it re-hardens, and significant residual stresses build up inside it.
Three risks come into play at exactly this point: softening of the material in the heat-affected zone due to excessive heat input, excessive hardening and embrittlement due to rapid cooling, and hydrogen-induced cold cracking. The correct welding procedure aims to keep all three risks in balance at the same time.
Cold Cracking: The Sneakiest Risk
Cold cracking (hydrogen cracking) is the most dangerous type of damage in welding Hardox. What makes it so treacherous is that it can appear not immediately after the weld is completed, but hours or even days later. A weld that looks clean under visual inspection can be cracked two days later.
Three conditions must come together for cold cracking to occur: hydrogen present in the weld metal, a hard and brittle internal structure, and high residual stress. Eliminating any one of these three prevents cracking; the entire welding procedure is essentially built around fighting these three factors.
Why Is Preheating Critical?
Preheating is the most important step in welding Hardox. Heating the material before welding serves two functions: it slows the cooling rate, preventing excessive hardening, and it gives hydrogen in the weld metal time to diffuse out.
The main factors that determine preheat temperature:
- Material thickness: the required temperature rises as thickness increases
- The steel's hardness grade: harder grades require higher preheat
- Joint geometry and rigidity: restrained joints carry higher risk
- Ambient temperature and humidity: requirements increase in cold, damp field conditions
Temperature needs to be maintained not just along the weld line but across sufficient width on both sides of the joint and through the material thickness. Quickly heating the surface with a torch is not enough; time must be allowed for the heat to penetrate the full wall thickness. Temperature should be verified with a contact thermometer or temperature-indicating crayon.
Electrode and Filler Metal Selection
Hydrogen control in welding Hardox starts directly with consumable selection. For this reason, low-hydrogen (basic) electrodes or suitable wire-gas combinations for MIG/MAG welding should always be used.
A common misconception is that the weld metal needs to be as hard as the base material. In reality, the opposite is preferred in most applications: a softer, more ductile weld metal absorbs stresses through plastic deformation, reducing crack risk. The weld seam itself is not the surface exposed to wear — the wear resistance is provided by the plate itself.
Keeping electrodes free of moisture is critical. Opened basic electrodes should be stored in an oven at the temperature specified by the manufacturer and carried to the field in a heated quiver. A damp electrode can undo even the best preheating.
Heat Input and Interpass Temperature
Heat input is a value determined jointly by welding current, voltage, and travel speed, and it has an upper limit in welding Hardox. Excessive heat input widens the heat-affected zone and creates permanent softening in that region, locally reducing the plate's wear resistance around the weld.
For this reason, a thin, controlled multi-pass technique is used instead of thick, single-pass wide beads. Interpass temperature also has an upper limit; temperature should be measured after every pass, and if necessary, the operator should wait before starting the next pass. Weaving increases heat input and should be kept as limited as possible.
Joint Preparation and Cleanliness
Correctly preparing the weld groove is decisive for both penetration and crack resistance. The joint surface must be completely free of oil, paint, rust, moisture, and slag left over from cutting. All of these contaminants are sources of hydrogen and directly raise crack risk.
Correctly opening the groove geometry also determines weld quality. On grooves prepared by thermal cutting, grinding away the hardened cut edge is recommended.
After Welding: Slow Cooling
The job isn't finished the moment welding ends. Controlled, slow cooling of the part gives hydrogen the time it needs to escape the structure. Placing the welded part on a cold floor, spraying it with water, or exposing it to wind can undo everything achieved up to that point. In critical applications, the part is wrapped in insulating blankets and left to cool slowly.
Welded Fabrication with Hardox at DMK Makina
As a Hardox Wearparts partner, DMK Makina carries out the entire process — from cutting wear steels to welding them — with certified welders and written welding procedures. Preheat temperatures are verified by measurement, heat input is recorded, and non-destructive testing is applied on critical joints. We support your wear-part and heavy-duty equipment projects in the Thrace and Marmara region with project-specific engineering solutions.