PSI - Issue 33

Saki Hayashi et al. / Procedia Structural Integrity 33 (2021) 1162–1172 Hayashi et al / Structural Integrity Procedia 00 (2019) 000 – 000

1166

5

this study, strictly speaking, the use of CTOD is not appropriate because no fatigue cracking ahead of machine notch. However, test results were simply calculated and summarized by CTOD calculation formula as shown in eq. (3)-(5), which were suggested by ISO15653 and Kawabata et al (2016). CTOD tests were carried out at -40 ~ -130 ℃ , wh ere vapored liquefied nitrogen was used to control the temperature as shown in Fig. 4. An example of load-clipgage displacement curve is shown in Fig. 5. Then, the ductile-to-brittle transition temperature was calculated from the relationship between the temperature and critical CTOD values for all heat treatment conditions and all steels, and we evaluated the temperature change, Δ T between the transition temperature for double cycle specimens from the transition temperature for single cycle specimens. Considering the nature of the transition temperature, the better the toughness, so the smaller the Δ T , the better the toughness and smaller the toughness deterioration by tempering. quasi,cr = cr 2 (1 − 2 ) YS + ∙ 0.43( − 0 ) p 0.43( − 0 ) + 0 (3) = cr ∙ ∙ 3⁄2 (4) = 3√ 0 1.99 − ( 0 ⁄ ){1 − ( 0 ⁄ )}{2.15 − 3.93( 0 ⁄ ) + 2.7( 0 ⁄ ) 2 } 2{1 + 2( 0 ⁄ )}{1 − ( 0 ⁄ )} 3⁄2 (5) = 4.9 − 3.5 ( YS TS ) (4) = {−1.4 ( YS TS ) 2 + 2.8 ( YS TS ) − 0.35} [0.8 + 0.2exp{−0.019( − 25)}] (5)

10

60 °

1.5

5

60

2

60 ° , R=0.20

Fig. 3. Configuration of specimen for fracture test.

Fig. 4. Appearance of the test machine used.

Fig. 5. An example of load-clipgage displacement curve.

2.4. Results Fig. 6 and Fig. 7 show the transition temperature change with tempering holding time. It is clear that the Δ T is small when the Sn content is 0.01%, while temper embrittlement clearly occurs when the Sn content is 0.1% or higher