Dynamic fracture toughness of X70 pipeline steel and its relationship with arrest toughness and CVN

Abstract

The dynamic fracture toughness K 1d and J 1d, arrest toughness K 1a and Charpy V-notched impact toughness (CVN) of a pipeline steel, X70, were studied at different temperatures. It was found that fracture toughness was strongly affected by temperature and loading rate. The fracture toughness decreases with decreasing temperature from 213 to193 K and increasing loading rate from K ̇ =1.0 to 10 5 MPa 1 2 s −1 . At constant temperatures, only increasing loading rate can induce the transition from ductile to brittle. There exists a fracture transition caused by loading rate. Through thermal activation analysis, a quantitative relationship has been derived: J 1d=J a+J 0 K ̇ K ̇ 0 1 n exp Q f nkT . It can describe the fracture process at different temperatures and loading rates. At a loading rate of K ̇ =15 MPa m 1 2 s −1 , the relationship can predict arrest toughness well. It provides the possibility of measuring arrest toughness with small size specimen. An empirical equation has been derived: CVN=4.84×10 6 T −2.8 K 1d( K 1a), which correlates K 1d and K 1a with CVN in one equation. This means that we can calculate K 1d and K 1a when we get CVN.