Charpy Impact Testing: What JR, J0, J2 and K2 Mean
Charpy V-notch impact testing explained: what toughness is, test temperatures, JR, J0, J2 and K2 subgrades in EN 10025, and when impact-tested steel is needed in Saudi Arabia.
Saudi Steel Work Editorial Team · · 3 min read
Short answer: The Charpy V-notch test measures the energy a notched steel specimen absorbs when broken by a pendulum at a set temperature, indicating toughness and resistance to brittle fracture. In EN 10025, JR means 27 J at +20 °C, J0 means 27 J at 0 °C, J2 means 27 J at −20 °C and K2 means 40 J at −20 °C.
Toughness is a steel's ability to absorb energy and resist brittle fracture. The Charpy test is the standard way to measure it.
How the test works
- A small bar with a machined V-notch is cooled or heated to the test temperature
- A pendulum strikes and breaks it
- The absorbed energy (joules) is recorded
Lower temperatures generally reduce toughness. Steels have a ductile-to-brittle transition range.
EN 10025 subgrades
| Subgrade | Min. energy | Test temperature |
|---|---|---|
| JR | 27 J | +20 °C |
| J0 | 27 J | 0 °C |
| J2 | 27 J | −20 °C |
| K2 | 40 J | −20 °C |
So S355J2 means 355 MPa yield with 27 J at −20 °C.
ASTM approach
ASTM grades often specify impact testing as a supplementary requirement (e.g. A6 S5) or in the grade itself (e.g. A516 with A20 supplementary requirements). Pressure codes specify impact testing based on thickness and minimum design metal temperature.
When to require impact-tested steel
- Thick plates and sections
- Fatigue-loaded structures (crane girders, bridges)
- Dynamically loaded or seismic elements
- Pressure equipment per code
- Low-temperature service (e.g. some gas processing)
- Where the design standard's steel selection rules require it
Welds too
Weld metal and heat-affected zone toughness are qualified in the PQR where required (WPS and PQR).
Check the certificate
Impact energy and temperature should appear on the mill certificate for J0/J2/K2 grades (MTC guide).
See S275 vs S355 and steel plate grades.