PSI - Issue 30

K.V. Stepanova et al. / Procedia Structural Integrity 30 (2020) 167–172 Stepanova K.V., , Petrov P.P., Platonov A.A. / Structural Integrity Procedia 00 (2020) 000–000

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unequal expansion and compression of the metal. Internal stresses in the weld arise mainly because of structural phase changes of the metal in the weld and heat-affected zones. Taylor (1961) reported that determination of internal (residual) stresses by X-ray diffractometry methods is based on recording changes in the interplanar spacings of the stressed crystallite. Modern approaches to the study of X-ray diffraction methods are described by Hauk (1997), Welzel (2002, 2005), Genzel (2001). Residual stresses in metals and alloys in certain cases reach the yield strength and even the tensile strength and cause cracking during thermomechanical processing of the material (hardening, grinding, etc.). On the one hand, tensile residual stresses in the surface layers combined with external ones can induce destruction of parts during operation. On the other hand, the occurrence of compressive residual stresses on the surface complicates the formation of cracks and significantly increases the fatigue strength of parts and assemblies of equipment and constructions, as noted by Dudarev (1988) and Ivanova (1986). The interest in methods of weld metal alloying with rare-earth elements is growing now, so the issue of evaluating the residual stresses in a weld and a heat-affected zone with rare-earth metals is very important. Lazko (1981), Efimenko (1980), Cai (2014), Zhang (2007), Li (2017) showed that rare earth elements such as yttrium, cerium, lanthanum, praseodymium, etc. affect on the crystallization process and the formation of the primary weld structure during welding and surfacing of various steels. Therefore, the determination of the mechanisms of the influence of rare earth metals at various concentrations in the weld on the occurrence of internal residual stresses helps to control some properties of the weld metal, such as strength, hardness, impact strength and corrosion resistance. In this research, the residual stresses were studied in the weld metal and HAZ, obtained by deposition with flux cored wires with different contents of rare-earth elements from the Tomtor deposit (Yakutia, Russia) and the optimal composition of flux-cored wires with a modifying additive with rare-earth metals for forming a weld with increased strength properties with reduced stress-strain state was selected. 2. Experimental procedures A commercial grade 09G2S steel plate with a thickness of 12 mm was used as the base metal. Alloy powders with 10 different concentrations of REE (see Table 1) were designed and mixed with the filler material of UONI 13/55 covered electrode. Rare earth material added to the mixture in an amount of 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 0.9; 1% of the total mass of filler wire. Then experimental flux-cored wires (FCW) with diameters of 5 mm, with 15% fill factor were manufactured and weld beads were deposited to steel plates. Manual arc welding experiments were conducted using a VD 306E welding machine at current of 180 A and voltage of 40 V.

Table 1. Chemical composition of experimental flux-cored wires.

Compositions of flux-cored wires

Chemical elements (wt.%) Si Ti V

Mn

Fe

Y

Nb

Pr

Nd

Comp1 Comp2 Comp3 Comp4 Comp5 Comp6 Comp7 Comp8 Comp9 Comp10

9.51 9.21 9.16

2.91

0.009

4.13 4.19 4.03 4.11 4.62 4.15 4.02 4.18 3.85 4.07

2.62 2.78 2.73 2.93 3.58 3.32 3.47 3.66 3.52 3.91

0.0051 0.0087

0.04

0.036 0.057 0.085

0.037 0.067 0.097

3.1

0.01

0.052

2.88

0.013 0.016 0.017 0.022 0.028 0.029 0.031 0.041

0.012 0.014 0.032 0.025 0.033 0.043 0.032

0.0652

9.1

3.3

0.058 0.155 0.117 0.148 0.192 0.129 0.228

0.11 0.18 0.18 0.24 0.25 0.26 0.31

0.14 0.21

-

3.35 3.48

8.83 8.72 8.67 8.53 8.53

0.2

3.2

0.25

3.39 3.07 3.48

0.3

0.31 0.35

0.0538

X-ray diffraction spectra for all samples were detected on a Rigaku Ultima IV X-ray diffractometer with a high precision horizontal goniometer where sample is fixed horizontally. The sample is scanned by an X-ray generator and a sensor, which is a scintillation counter located on the goniometer lever with rotation over a vertical area.