PSI - Issue 16

Yevstakhiy Kryzhanivskyy et al. / Procedia Structural Integrity 16 (2019) 237–244 Yevstakhiy Kryzhanivskyy et al. / Structural Integrity Procedia 00 (2019) 000 – 000

240

4

zone of thermal impact can be explained by their structural state and the localization of deformation processes in the Charpy specimen.

3.2. Stage-like nature of fracture of Charpy specimens

It was found that specimens cut from the weld zone were fractured with the impact toughness of the material close to the ductility of the base material; therefore, they were not investigated further in the research. More dangerous situation was for the specimens cut from the fusion zone, which was associated with the low plasticity of the weld metal and the near-weld zone. The general energy of impact failure of the material (A) was considered as the initiation (A i ) and propagation of the crack (A p ), Table 1. In this series of tests, it has been shown that the impact toughness of the welds and the zone of thermal impact of the welds is (KCV > 55 J/cm 2 ) and even higher for the base metal. For welds with defects, the impact toughness does not generally exceed KCV <30 J/cm 2 .

Table 1. Macro-characteristics of Charpy specimens cut from X70 pipe steel tested for impact toughness Charpy specimens t, o C А, J A i , J A p , J KCV, J/cm 2 20 300 76 224 376

0

267 168 279

61 55 54 62 52 51 56 54 42 51 52 52 49 41

206 113 225

334 210 150

-20 -40

Base metal (BM)

-60

88

26 89

110

20

141 157

176.78 157.73

0

106

-20 -40 -60

90

34 51

112.8

Fusion zone (W1)

105

132.07

47

5

58.93

20

161 128 134 100

110

201 164 168 124

0

76 82 51 31

-20 -40 -60

Fusion zone (W2)

72

90

The results obtained are useful, first of all, from the viewpoint of the analysis of the temperature effect on an increase in values (А р /А)·100% in t he temperature range from - 60 °C to 20 ° C, Fig. 3. Thus, the specific ratio (A p /A )·under conditions of fracture increase d with an increase in the test temperature, and at temperatures 20 ° C; 0 ° C; -20 ° C; -40 ° C; -60 ° C it was, respectively:

 For BM: 74.7 %; 77.2 %; 67.3 %; 80.6%; 29.5 %.  For W1: 63.1 %; 67.5 %; 37.8 %; 48.6 %; 10.6 %.  For W2: 68.3 %; 59.4 %; 61.2 %; 51.0 %; 43.1 %.

The results prove that, in case of dynamic loads, the most dangerous zone is the near-weld zone, in particular, the zone of thermal influence. The analysis of weld test results at different temperature-force conditions allowed finding fracture parameter А р /А , which can be used successfully in numerical analysis of the elastic-plastic fracture of gas pipe steels.