---
term: "Ductile-to-Brittle Transition"
category: "impact-testing"
shortDefinition: "Temperature range where ferritic steels shift from high absorbed impact energy (ductile) to low energy (brittle) fracture; mapped with Charpy or Izod energy versus test temperature."
relatedStandards: ["ISO 148-1","ASTM E23"]
url: "https://vectorbtc.com.tr/resources/glossary/ductile-brittle-transition/"
---

## What it measures

The **ductile-to-brittle transition (DBTT)** curve shows how **impact absorbed energy** changes with **test temperature**. Ferritic steels often exhibit an upper shelf (ductile), a transition region, and a lower shelf (brittle).

## How it is tested

Notched bars are broken in a **pendulum impact tester** at multiple temperatures (often after conditioning in a thermal chamber). Energy versus temperature is plotted; project specs may define acceptance at a reference temperature or require 50% shelf energy criteria.

## Standards and reporting

ISO 148-1 and ASTM E23 govern specimen geometry, striker, and energy calculation. Report notch type, specimen size (KV2, etc.), and thermal soak time because transition position shifts with microstructure and strain rate.

## Common errors

Insufficient temperature control, misaligned specimens, and comparing energies from different notch sizes or sub-size bars without standard conversion rules.