Abstract
Vickers hardness, Charpy impact and tensile properties of 16MND5 steel, a bainitic forging steel that is used for nuclear power reactor pressure vessel, were investigated before and after varied thermal aging durations at 350 °C up to 3000 h. After thermal aging for 500 h, the steel exhibits a remarkable increase in the ductile-to-brittle transition temperature (DBTT), a slight increase in the hardness, and slight degradations in the yield stress, ultimate tensile strength and elongation at room temperature. These facts indicate thermal aging induced embrittlement of the steel, which are further evidenced by the intergranular cleavage cracks on fracture surfaces in impact tests and a wheel-spokes like fracture morphology in tensile tests. As thermal aging duration is further extended, the embrittlement seems saturated as manifested by consistent DBTTs and fracture morphologies. Based on the metallographic observations and Rietveld refinements of neutron diffraction patterns under different aging conditions, the possible mechanisms of the thermal aging induced embrittlement are discussed.
| Original language | English |
|---|---|
| Pages (from-to) | 169-175 |
| Number of pages | 7 |
| Journal | Materials Science and Engineering: A |
| Volume | 720 |
| DOIs | |
| State | Published - Mar 21 2018 |
| Externally published | Yes |
Funding
The authors gratefully acknowledge financial support for this work from the National Natural Science Foundation of China (Nos. 51435012 and 51505325 ) and the Science and Technology on Reactor System Design Technology Laboratory, Nuclear Power Institute of China ( SQ-KFKT-02-2016012 ). The neutron diffraction was carried out at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory, supported by the U.S. Department of Energy, Basic Energy Sciences, Scientific User Facilities Division.
Keywords
- Embrittlement
- Low alloy steel
- Neutron diffraction
- Reactor pressure vessel
- Thermal aging