PSI - Issue 30

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

97 5

Table 6. Plates marking, welding modes and conditions for St3sp steel.

Pulse current (I p , A), Background current (I b , A), Voltage (U, V)

Electrode pass, diameter (mm)

Weld heat input (kJ / m)

Marking of welded samples (No)

Ambient air temperature (° С )

Electrode grade

Welding mode

1) 707 2) 1475 1) 719 2) 1253 1) 743 2) 1404 1) 1083 2) 1522

1) I p =136, I b =50, U=29 2) I p =200, I b =60, U=25

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

WCM-1,67 with cooling

1

+20

LB-52TRU

1) I=94, U=28,5 2) I=143, U=23,4

DCW with cooling

2

+20

LB-52TRU

1) I p =136, I b =50, U=29,5 2) I p =200, I b =60, U=24,5

WCM-1,67 with cooling

4

-40

LB-52TRU

5

-40

LB-52TRU

DCW with cooling

1) I=94, U=28,7 2) I=145, U=23,4

WCM-1,67 (-45 °C)

WCM (-45 °C)

DCW (-45 °C)

DCW (+20 °C)

a

b

Fig. 1. Microstructure of the HAZ of the welded joint of 09Mn2Si steel at a distance of 0.5 mm from the fusion line obtained using the following electrode grades: (a) UONI 13/Moroz; (b) LB-52TRU.

Thus, a study of the structures of the HAZ of welded joints obtained by welding at low climatic temperatures of ambient air showed that in areas of incomplete melting and overheating, welding at -45 °C forms more highly dispersed ferrite-carbide mixtures with a high content of quenching bainitic mixtures compared to welding at room temperature (Fig. 1). A broadening of the distribution zone of quenching structures (bainite) and carbides is observed. The WCM-5 mode had minimal heat input (1291 kJ/m) at an ambient air temperature of -45 °C, which led to the formation of quenching structures in the HAZ in the form of bainite up to 90%. The samples, which were obtained by welding with LB-52TRU electrodes at a temperature of -45 °C, formed a finer-grained structure in the HAZ compared to welding at room temperature. Bainite content was up to 30% in the HAZ. Investigation of the effect of current modulation frequency in adaptive pulse arc welding on the HAZ structure at low temperatures has revealed that the HAZ structures do not differ from each other significantly when welding

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