[1]
Where KJc is the fracture toughness corresponding to Pf, K0 is the characteristic fracture toughness corresponding to 63.2% cumulative failure probability and Kmin is minimum value of fracture toughness for the probability density function. The relationship between fracture toughness and temperature under different failure probabilities of materials is determined using the reference temperature T0 with an equation Eq. 2.
DOI: 10.1115/pvp2005-71346
Google Scholar
[2]
The curve that the fracture toughness with temperature failure probability is 50% is called the master curve, and the expression is Eq.3. The temperature corresponding to the fracture toughness of the master curve at 100 MPa is defined as the reference temperature T0, which is the characterization parameter of the macro fracture properties of the material.
DOI: 10.1016/j.engfailanal.2020.104713
Google Scholar
[3]
Experimental The material used in this article is from the CAP1400 CV, which has a quenching and tempering condition. The microstructure of the material is mainly granular tempered bainite plus a small amount of ferrite, as shown in Fig.1. The main chemical composition is shown in table 1. Fig. 1 Microstructure of SA738Gr.B: optical micrograph Table 1 The chemical of SA738Gr.B steel (mass fraction, %) (10mm×10mm×50mm) C Si Mn P S Ni Cr Mo Cu 0.09 0.32 1.5 0.01 0.002 0.52 0.28 0.23 0.02 Charpy impact tests were performed on standard Charpy V-notch specimens (10×10×50, mm) in the temperature range from -120℃ to 50℃ following ASTM E23-10a procedure. In order to cope with the dispersion of data, regression analysis for absorbed impact energy with large scatter was conducted using a hyperbolic tangent curve fitting. Rob type tensile specimens with a gage diameter mm and a gage length mm were tested in the room temperature at a loaded speed 0.5mm/min. The fracture toughness were obtained with CT specimen, in which the initial fatigue crack length is about 2mm and total crack length is 25.4mm. Fig. 2 shows the structure and dimensions of the specimen. Experimental temperatures were set to -120℃ and -110℃, respectively, and temperature was controlled within ±3℃ using a regulated liquid Nitrogen flow in an insulated chamber equipped with PID controller. The results of tests were analyzed following ASTM E1921-15a. Fig. 2 Specimen used in tests Results and Discussion Mechanical properties. Charpy impact test results of the relationship between impact energy and temperature are shown in the Fig.3. Steel exhibits a significant ductile-brittle transition and has a large dispersion of impact energy. The impact energy of the upper shelf energy (USE) is about 400J, indicating that the steel has a high toughness reserve. Characteristic temperatures T28J, T41J are -120.4°C and -112.9°C, respectively. According to the ASME codes, the impact properties of this kind of steel meet the standard requirements.
Google Scholar
