Determination of the Key Microstructural Parameter for the Cleavage Fracture Toughness of Reactor Pressure Vessel Steels in the Transition Region

Min Chul  Kim; Bong Sang Lee; Won Jon Yang; Jun Hwa Hong

doi:10.4028/www.scientific.net/KEM.297-300.1672

Paper Titles

Evaluation of Nuclear Piping Failure Frequency in Korean Pressurized Water Reactors
p.1645

Bottom-Mounted Nozzle Failure Modes of a Nuclear Reactor Pressure Vessel under Severe Accident Conditions
p.1652

Alternative Fatigue Evaluation of Nuclear Piping Designed by ANSI B31.1 Code
p.1659

Analysis Technology on the Temperature and Thermal Stress of the Cask for Radioactive Material Transport
p.1666

Determination of the Key Microstructural Parameter for the Cleavage Fracture Toughness of Reactor Pressure Vessel Steels in the Transition Region
p.1672

Surface Crack Behavior in Socket Weld of Nuclear Piping under Fatigue Loading Condition
p.1678

Critical Temperatures for Initiating and Arresting Delayed Hydride Cracking in a Zr-2.5Nb Pressure Tube
p.1685

Evaluation of the Fracture Characteristics with Thermal Aging on Dissimilar Welds in Reactor Coolant System
p.1691

Annealing Effect of Thermal Conductivity on Thermal Stress Induced Fracture of Nuclear Graphite
p.1698

HomeKey Engineering MaterialsKey Engineering Materials Vols. 297-300Determination of the Key Microstructural Parameter...

Determination of the Key Microstructural Parameter for the Cleavage Fracture Toughness of Reactor Pressure Vessel Steels in the Transition Region

Abstract:

The effects of the microstructural parameters, such as the prior austenite grain size and carbide size, on the cleavage fracture toughness were investigated in the transition region of Mn-Mo-Ni bainitic low alloy steels. Cleavage fracture toughness was evaluated by the ASTM standard E 1921 Master curve method. In order to clarify the effects of each microstructure, the grain size and carbide size of the test materials were independently controlled by modifying the heat treatment process. Firstly, the grain sizes were changed from 25㎛ to 110㎛ without any significant changes in the carbide size and shape. Secondly, the average carbide sizes were changed from 0.20 ㎛ to 0.29㎛ but maintaining the initial grain sizes. As a result, the fracture toughness in the transition region did not show any significant dependency on the austenite grain size, while the carbide size showed a close relation to the fracture toughness. Fracture toughness was decreased with an increase of the average carbide size. From the microscopic observation of the fractured surface, the cleavage initiation distance (CID) from the original crack tip showed no direct relationship to the prior austenite grain sizes but a strong relationship to the carbide sizes. However, the measured cleavage fracture toughness was strongly related to the distance from the crack tip to the cleavage initiation site. From the viewpoint of the weakest link theory, the particle size and their distribution in front of the crack tip is probably more important than the grain size in the transition temperature range where the fracture was controlled by the cleavage crack initiation.