Fracture toughness evaluation and material performance optimization model of the low alloy steel at different temperatures
TONG Dihua
XU Yuhao
HUANG Yanqing
ZHOU Song
AN Jinlan
QIAN Zhaoxing
Abstract：[Objective]Low alloy steel for nuclear power is prone to damage under long-term service in high-temperature and heavy-load environments.Existing fracture toughness evaluation methods lack mathematical means for quantifying fracture morphology,and no service temperature optimization method integrating multiple performance parameters has been established.Research on fracture toughness evaluation and performance adaptation optimization of low alloy steel at different temperatures was carried out.[Methods]Firstly,tensile and fracture toughness tests were conducted at 23℃,50℃and 350℃in accordance with ASTM E8/E8M-22,ASTM E21-20 and ASTM E1820 standards to obtain material mechanical properties and fracture toughness data.Secondly,optical microscope and scanning electron microscope were used to analyze the variation laws of material microstructure and fracture morphology at different temperatures.Then,the length ratio of ductile-brittle transition zone was proposed as a new evaluation index of fracture toughness,and the quantitative relationship between it and fracture toughness was established.Finally,the fracture toughness-yield strength-elongation(FYE)optimization model considering fracture toughness,effective yield strength and elongation after fracture was constructed to solve the optimal service temperature.[Results]The results show that when the temperature increases from 23℃to 350℃,the average fracture toughness of low alloy steel decreases from 0.703 9 kJ·mm1/2 to 0.431 6 kJ·mm1/2.The decrease of ferrite content,increase of bainite content and weakening of dislocation hindrance are the main mechanisms for the reduction of fracture toughness.The length ratio of ductile-brittle transition zone has an exponential relationship with fracture toughness,which can quickly predict the fracture toughness of materials.The optimal service temperature calculated by the FYE optimization model is 130℃,which provides reference for the design of key nuclear power components.
Keywords：Low alloy steelFracture toughnessDuctile-brittle transition zone length ratioFYE optimization model
Publication Date：2026-07-31
Online Publishing Date：2026-09-12(First online date of this platform, not the publication date of the document)
Pages：9( 85-93 )