What Heat-Affected Zone (HAZ) means
Thermal cutting and welding put heat into the part. Immediately around the cut edge or weld pool, the metal gets hot enough to change its microstructure but not to melt. That band is the heat-affected zone, and its width and properties depend on the process, the energy density and how fast the heat is carried away.
Why it matters on the shop floor
A fibre laser produces a narrow HAZ because it delivers energy quickly into a small spot; a plasma or oxy-fuel cut leaves a much wider one. In practice the HAZ is where hardness changes, where residual stress concentrates, and — on stainless steel — where sensitisation can reduce corrosion resistance at the cut edge if heat input is not controlled.
In practice
For most sheet metal work the HAZ is a sub-millimetre consideration that does not need special handling. It becomes a specification item when the part will be welded at high integrity, machined afterwards, or used in a corrosive environment with a cut or welded edge exposed.
What to remember
- Narrower for fibre laser than for plasma or oxy-fuel; wider in thicker material.
- On thin stainless parts it matters mainly where the cut edge is a sealing or welded surface.
- A welded joint carries a HAZ on both sides of the fusion line; on thin sheet the two can overlap.