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Developing the Relationship Between Micro Hardness, Instrumented Indentation, and Impact Toughness in Structural Steels

 

  • Temper Bead Welding (TB) techniques are often used as an alternative to PWHT when welding hardenable steels mainly when equipment is too large for PWHT to ensure an acceptable heat affected zone (HAZ) fracture toughness.
  • The Charpy V-notch test has been used historically to determine fracture toughness in the HAZ; however, in 2004 there was a provision to ASME Section IX (QW-290) that permits TB qualification through tensile, bend, and peak hardness without impact testing requirements.
  • This addition allows for qualification testing based on a single hardness value measurement, and does not take into account the full thermal history leading to possible acceptance of temper bead processes that produce poor fracture toughness.
  • EPRI proposed an alternative TB qualification procedure through microhardness testing to address the shortfalls of the new ASME code, but these testing parameters are still undefined, there are no qualifications for steels that are not fully martensitic, and there is no clear definition regarding the amount of tempering.

This project deals with creating three correlations to impact toughness. These correlations are instrumented indentation, the Hardness Drop parameter, and the critical brittle volume fraction to tell where hardness indents should be taken, giving a quantitative impact toughness estimate from just hardness, and how many brittle zones can be present before it becomes detrimental to the mechanical properties respectively. Together these correlation will lead to a specific TB Qualification Criteria through only hardness measurements making qualification safer, quicker, and cheaper thus saving millions of dollars in resources. 

 

Industry Sponsor: EPRI

Faculty: Antonio Ramirez (OSU)

Graduate Student: Boeing Smith

Faculty Contact: Steve McCracken