PSI - Issue 30

Nikolay I. Golikov et al. / Procedia Structural Integrity 30 (2020) 93–99 Author name / Structural Integrity Procedia 00 (2020) 000–000

96

4

During welding, the main energy parameters (current and arc voltage) were recorded using the AWR-224MD welding process recorder. During the technological experiment, the welding time was estimated, and the average heat input was calculated according to the established practice. Structural studies of welded joints were accomplished using JEOL JSM-7800F high-resolution scanning electron microscope with a Schottky cathode and a super-hybrid objective lens. A cross-section of the welded joints was cut to analyze the structure, and thin sections were prepared. To reveal the structure of the samples, chemical etching of the surface with a 4% solution of nitric acid in ethanol was implemented. Structural studies were performed at the middle level of the cross-section of the welded joint with a research step of 0.5 mm.

Table 5. Marking of welded plates, welding conditions and modes of 09Mn2Si steel.

Pulse current (I p , A), Background current (I b , A), Voltage (U, V) 1) I p =135, I b =50, U=25,7 2) I p =200, I b =60, U=26,3 3) I p =200, I b =60, U=26,3 1) I p =120, I b =50, U=24,5 2) I p =180, I b =60, U=23,1 3) I p =180, I b =60, U=23,1

Weld heat input (kJ / m)

Marking of weld samples (No)

Ambient air temperature (° С )

Electrode grade

Electrode pass, diameter (mm)

Welding mode

1) Root – 3 2) Fill – 4 3) Cap – 4 1) Root – 3 2) Fill – 4 3) Cap – 4 1) Root – 3 2) Fill – 4 3) Cap – 4 1) Root – 3 2) Fill – 4 3) Cap – 4 1) Root – 3 2) Fill – 4 3) Cap – 4 1) Root – 3 2) Fill – 4 3) Cap – 4 1) Root – 3 2) Fill – 4 3) Cap – 4 1) Root – 3 2) Fill – 4 3) Cap – 4

1) 984 2) 1527 3) 1805 1) 665 2) 1318 3) 1891 1) 973 2) 1681 3) 1698 1) 804 2) 1489 3) 1796 1) 794 2) 1529 3) 2008 1) 850 2) 1783 3) 2006 1) 660 2) 2028 3) 1597 1) 682 2) 1514 3) 1729

UONI 13/Moroz

1

-45

WCM -1,67

UONI 13/Moroz

2

-45

WCM -5

1) I=98, U=23,6 2) I=154, U=24,4 3) I=154, U=24,4 1) I=98, U=26,2 2) I=145, U=25,5 3) I=146, U=25,0

UONI 13/Moroz

3

-45

DCW

UONI 13/Moroz

7

+20

DCW

1) I p =136, I b =50, U=28,1 2) I p =200, I b =60, U=23,6 3) I p =200, I b =60, U=22,7 1) I p =126, I b =50, U=25,6 2) I p =180, I b =60, U=23,9 3) I p =180, I b =60, U=22,8

4

-45

LB-52TRU

WCM -1,67

5

-45

LB-52TRU

WCM -5

1) I=87, U=26,5 2) I=141, U=23,3 3) I=141, U=22,6 1) I=99, U=26,8 2) I=136, U=24,1 3) I=136, U=24,3

6

-45

LB-52TRU

DCW

8

+20

LB-52TRU

DCW

3. Research results and discussion Welding of 09Mn2Si low alloy steel. It has been established that the proportion of bainite varies from 16 to 45% in the HAZ when welding in cold weather (-45 °C) with an average heat input of 1440 kJ/m. In the HAZ areas, a ferrite-carbide mixture is observed. Moreover, bainite is observed in the area up to 2.5 mm from the fusion line. The size of ferritic grains is on average 8-12 microns. When welding at positive temperatures (+ 20 °C) with an average heat input of 1335 kJ/m, the proportion of bainite in the HAZ ranges from 5 to 15% in the area up to 1.5 ... 2 mm from the fusion line. The structure of the HAZ consists of a ferrite-carbide mixture. The size of the ferrite grains is 1.5-3 times larger at 2 ... 4 mm marks than when welding at low temperatures. The carbide content decreases at a distance of 3 mm from the fusion line and further, and pearlite grains form.