---
title: Heat-Affected Zone (HAZ): Definition | Wolf Machine Reno
url: https://wolfmachinenv.com/glossary/heat-affected-zone/
business: Wolf Machine & Fabrication, Inc.
address: 4812 Longley Ln, Reno, NV 89502
phone: (775) 359-5570
hours: Shop Monday-Friday 7:00 am-3:30 pm; closed Saturday and Sunday
type: Metal and plastic fabrication and machining (custom and CNC machining, welding, metal and plastic fabrication, gearbox and part repair, align boring, metal spray)
---

[Photo: Stock photo: arc welding with a stick electrode, sparks in a dark shop]

- [Home](https://wolfmachinenv.com/)
- [Glossary](https://wolfmachinenv.com/glossary/)
- Heat-affected zone (HAZ)

# Heat-affected zone (HAZ)

The heat-affected zone is the band of base metal next to a weld that did not melt but was heated enough to change its structure and properties. It is where many weld repairs crack or soften, which is why heat is controlled on cast iron, hardened steel and thick sections.

Stock photo: arc welding with a stick electrode, sparks in a dark shop

When you weld, the weld metal melts and the metal beside it gets hot, with the temperature falling off with distance. The part of that gradient that changes the metal is the HAZ. You cannot see its edge, but its effects are real.

## What happens in the zone

In steel, the metal closest to the weld can be heated high enough to harden when it cools quickly, which makes it brittle. Farther out, heat can soften steel that was hardened or cold worked. In stainless steel, a long stay in a certain heat range can reduce corrosion resistance. In aluminum, heat can reduce the strength gained from heat treatment.

The width of the zone grows with the amount of heat put in, so a welder who controls travel speed and bead size controls the zone. Slow travel, big welds and thick, hot parts make a wider zone.

## Why it matters on a repair

Cast iron is the clearest case. It cracks easily in and beside the HAZ, so castings are warmed first and cooled slowly. The same logic applies to hardened shafts and high-carbon steels. Read the entry on [preheat and interpass temperature](https://wolfmachinenv.com/glossary/preheat-and-interpass/) for the usual way of controlling it.

After a repair weld, the HAZ is also a part of the metal that will be machined or loaded, so it is considered when planning how much material to leave. See [cast iron welding repair](https://wolfmachinenv.com/services/cast-iron-welding/) for an example.

### Sources

- [Heat-affected zone (overview)](https://en.wikipedia.org/wiki/Heat-affected_zone) (2026-10-18)

### Talk to the shop

[(775) 359-5570](tel:(775)%20359-5570)

| Monday to Friday | 7:00 am - 3:30 pm |
|---|---|
| Saturday and Sunday | Closed |

[Request a quote](#quote)

### Keep reading

- [Cast iron welding repair](https://wolfmachinenv.com/services/cast-iron-welding/)
- [Welding, all types](https://wolfmachinenv.com/services/welding/)
- [Stainless steel welding](https://wolfmachinenv.com/services/stainless-steel-welding/)

## See also

[Preheat and interpass temperature](https://wolfmachinenv.com/glossary/preheat-and-interpass/) [Rockwell hardness](https://wolfmachinenv.com/glossary/rockwell-hardness/) [Tolerance](https://wolfmachinenv.com/glossary/tolerance/)

## Where this comes up

[Stainless steel welding](https://wolfmachinenv.com/services/stainless-steel-welding/) [Metal spray, sleeve or weld: rebuilding a worn surface](https://wolfmachinenv.com/guides/metal-spray-sleeve-or-weld/) [Cast iron welding repair](https://wolfmachinenv.com/services/cast-iron-welding/)

[Photo: Stock photo: a lathe turning a bar, hot chips flying]

## Request a quote

Tell us what you need, attach a drawing or photos of the part, and we will get back to you during shop hours. Free consultations; prompt estimates.

[Call (775) 359-5570](tel:(775)%20359-5570)

- From your specifications, drawings or samples. We can also assist you in designing your product or part.
- Free consultations and prompt estimates
- Stands behind the work: Our rates are very competitive and our quality is second-to-none. Wolf Machine stands behind the work we perform.
- Company accounts: all major credit cards, or we can open an account for your company

Shop hours Monday to Friday, 7:00 am to 3:30 pm. Send your request any time and we will get back to you during shop hours.

Stock photo: a lathe turning a bar, hot chips flying