Selection of energy-technological modes of submerged-arc welding with silicomanganese slag for parts of mining equipment

The paper presents studies of the influence of energy-technological modes of welding on the physical and mechanical properties of welded joints obtained by submerged-arc welding, with the use of slag from silicomanganese production for parts of mining equipment. To study the welding and technological properties, we used a welding flux of 0.45-2.5 mm fraction based on a silicomanganese slag with a chemical composition, wt. %: 0.42 FeO, 16.22 MnO, 29.00 CaO, 41.34 SiO2, 6.53 Al2O3, 1.33 MgO, 0.24 S, 0.022 P, 0.008 ZnO, 0.031 C, 0.31 F, 0.15 TiO2, 0.025 Cr2O3. Automatic welding of 09G2S low-alloy steel under this flux was carried out by Sv-08GA wire. Various welding modes were investigated to ensure the required penetration depth and the absence of external defects (pores, cracks, cavities). Based on the data obtained, the dependences of the influence of the parameters of the welding mode on the mechanical properties of welded samples are plotted. It is shown that changes in the parameters of the current strength, welding speed and voltage can affect the physical and mechanical properties of the weld, as well as the transition of sulfur and hydrogen into the weld.).


Introduction
At present, welding fluxes made on the basis of manganese oxides such as AN-348A, AN-67, AN-39S are widely used in the Russian Federation [1][2][3]. At SibSIU a number of works on the use of silicomanganese slag as analogues of such welding fluxes has been carried out [4][5][6][7][8][9][10]. In this case, welding modes have a significant effect on the quality indicators of the weld. The purpose of this work is to study the effect of energy-technological modes of submerged-arc welding with the use of silicomanganese slag on the physical and mechanical properties of the welded seam obtained by automatic welding with wire Sv-08GA of low-alloy steel 09G2S.
To study the welding and technological properties, a welding flux was manufactured based on a slag produced by silicomanganese with a chemical composition, wt. %: 0. Previous studies [11] showed that for these fluxes, the most acceptable is the use of fraction 0.45-2.5mm. The research used the equipment of the Scientific and Production Center "Welding Processes and Technologies" and the Center for Collective Use "Materials Science" of Siberian State Industrial University.

Research methods
Samples for studies of macro-and microstructure, hardness, wear resistance were prepared according to the technique including cutting out samples on KKS 315L cut-off machine, grinding on 3D725 surface grinder, polishing on FROMMIA 835 SE polishing machine.
Welding of specimens of steel 09G2S 20 mm thick was carried out by butt welding without cutting edges with Sv-08GA welding wire using ASAW-1250 welding tractor and the manufactured flux. For comparison, the plates were welded with AN-348 submerged arc. The scheme of cutting samples from welded plates is shown in figure 1. The used flux was dried in the thermal electric furnace for 2 hours at a temperature of 300 ˚С. Before the surfacing process, the metal plates were cleaned with an angle grinder. Preservation agents, dirt, rust and oxide films were removed from the metal surface. After welding, the surface of the weld metal and the slag crust on the side adjacent to the weld were examined by the visual method and the chemical composition was determined. The chemical composition of slag crusts and fluxes was determined by the X-ray fluorescence method on XRF-1800 spectrometer. The chemical composition of the welds was determined by the atomic emission method on DFS-71 spectrometer. Chemical composition of a number of weld metal samples was determined by chemical methods: for carbon content according to GOST 12344-2003, sulfur according to GOST 12345-2001 and phosphorus according to GOST 12347-77.
Metallographic studies of polished microsections were carried out using OLYMPUS GX-51 optical microscope in a bright field in the magnification range from × 100 to × 1000. The microstructure was revealed by etching the samples in the solution of 4% HNO 3 in ethyl alcohol. The grain size was determined in accordance with GOST 5639-82 at × 100 magnification. Investigation of samples of the deposited layer for the presence of nonmetallic inclusions was carried out in accordance with GOST 1778-70. The polished surface was examined at a magnification of × 100 using a LaboMet-1I metallographic microscope. Macrosections with the size of 20 × 55 × 14 mm were made from the cut samples. The hardness of the samples under study was measured by the Brinell method using an ultrasonic hardness tester USIT-3 in accordance with the requirements of GOST 9012-59.

Results and discussion
Various welding modes were investigated to ensure the required penetration depth and the absence of external defects (pores, cracks, cavities). The welding modes of the samples were selected by the method of planning experiment 3 (3-1), mode 0 was taken as the basis: current I = 700A, voltage U = 28V, welding rate v = 30 cm/min [12][13][14]. The investigated modes are presented in table 1.  0  700  28  30  42000  1  600  28  28  36000  2  600  30  32  33750  3  600  32  30  38400  4  650  28  32  34125  5  650  30  30  39000  6  650  32  28  44571  7  700  28  30  39200  8  700  30  28  45000  9 700 32 32 42000 The chemical composition of the investigated welded samples and the parameters of hydrogen concentration are given in table 2.  The mechanical properties of the samples under study are presented in table 3.       As it can be seen from figures 7-9, the hardness values depend on the welding modes.    Figure 9. Dependence of HB hardness on welding rate.

Conclusion
The paper presents studies of the influence of energy-technological modes of welding on the physical and mechanical properties of welds obtained by submerged-arc welding, made on the basis of silicomanganese production slag for parts of mining and metallurgical equipment. Automatic welding of 09G2S low-alloy steel under this flux was carried out by Sv-08GA wire. Various welding modes were been investigated to ensure the required penetration depth and the absence of external defects (pores, cracks, cavities). It is shown that a change in the parameters of the current strength, welding speed and voltage can affect the physicomechanical properties of the weld, as well as the transition of sulfur and hydrogen into the weld.