PSI - Issue 20

Ekaterina M. Maksimova / Procedia Structural Integrity 20 (2019) 174–179 Ekaterina M. Maksimova / Structural Integrity Procedia 00 (2019) 000–000

175

2

for the structure formation of the weld metal and HAZ. As presented by Nerovny (2016) during welding under conditions of low climatic temperatures there is an increase in the cooling rate of the weld pool metal and the HAZ. As the cooling rate increases, the probability of quenching structures formation increases, which can lead to brittle fracture of welded joints by Arzamasov et al. (2008), Li et al. (2013), Saraev and Bezborodov (2013). According to the authors of Lakhtin and Leontyeva (1990), Hromchenko et al. (1980) and Weman (2011), the study of the microstructure of welded joints of structural carbon steel allows to get an idea of the physicochemical phenomena occurring in materials under various conditions of their operation [6-8]. The purpose of research is to study the HAZ microstructure of welded joints of low-alloy steel made by manual arc welding in conditions of positive and negative ambient temperatures. 2. Research material and equipment Rolling sheet of low-alloy structural steel 09G2S, corresponding to State Standard 19281-2014, as the most widely used in structures operated in the conditions of the North and the Arctic, was chosen as the material for research as it was shown by Saraev et al. (2005), Zubchenko (2003). Steels of this grade are well welded in a wide range of welding conditions, regardless of the thickness of the welded elements and the ambient temperature. The chemical composition and mechanical properties of steel are presented in Table 1. The study of the welding conditions influence of on the HAZ structure was carried out on welded joints of plates with a dimensions of 200x300x12 mm. The plates are chamfered with a bevel angle of edges (25 ± 2)°, a bluntness of 2 mm and with a root gap of 1.6 mm for arc welding of a butt joint in accordance with State Standard 5264-80 (Fig. 1, a). For research, manual arc welding of samples with a butt-welded joint with a V-shaped groove was made. Welding was carried out in three passes using UONI 13/Moroz and LB-52TRU electrodes with diameters: 3.0 mm for forming the root layer and 4.0 mm for forming the filling and facing layers. The chemical composition and mechanical properties of the used welding electrodes are shown in Table 2. An inverter welding power source NEON VD-315 was used for welding the samples. The welding modes were selected for research: - direct current (DC) welding at an ambient temperature of – 45° C; - DC welding at an ambient temperature of + 20° С . Parameters of welding are presented in table 3. During the welding, the main energy parameters (arc current and voltage) were recorded with the aid of the welding process recorder AWR-224MD. During the technological experiment, the welding time was estimated and the average heat input was calculated in accordance with the generally accepted method. The linear energies of welding the root layers were 660 ... 980 kJ/m, and the filling and facing layers were 1490-2030 kJ/m.

b

a

Fig. 1. Configuration of the butt-welded specimen (a) butt joint edge preparation scheme, (b) welding process.

Table 1. Chemical composition (wt., %) and mechanical properties of 09G2S grade steel according to State Standart 19281-2014

Impact strength (U-notch) (J/cm 2 )

Tensile strength (MPa)

Elongation (%)

С

Si

Mn

Ni

S

P

Cr

V

N

Cu

As

0,5

1,3

<0,12

<0,3

<0,035

<0,03

<0,3

<0,12

<0,008

<0,3 <0.08

≥ 34 at 70° С

≥ 490

≥ 21

0,8

1,7