Underwater In Situ Local Heat Treatment by Additional Stitches for Improving the Weldability of Steel

Abstract

In this paper the influence of in situ local heat treatment performed by additional stitches on the weldability of high-strength low-alloy (HSLA) S355J2C+N steel was tested. The investigated steel is characterized by high susceptibility to cold cracking. It is necessary to find a method to improve the quality of welded joints. The local heat treatment was applied as an effect of bead-on plate welding made on the face of a Tekken test joint. The specimens were made by the use of covered electrodes in the water environment. For testing weldability, Tekken test specimens were made. Then, the different number of the pad welds with different overlapping were laid on the face of the tested welds. Non-destructive (NDT) visual and penetrant tests were undertaken. During the NDT, imperfections like shape mistakes and spatters were found. Then, metallographic macro- and microscopic testing were performed. The macroscopic observations proved that water environment can generate imperfections like cracking and pores. However, for specimens with additional stitches the number of imperfections decreased. Microscopic tests proved that the proposed technique affected the structure of the heat-affected zone (HAZ). The specimens without the application of additional stitches are characterized by brittle bainitic and martensitic structure. Specimens, in which the additional stitches were applied, contain tempered martensite, fine ferrite and fine pearlite in their HAZ. It was also observed that the number of cracks decreased for in situ local heat-treatment specimens. The final step was Vickers HV10 hardness measurement. These measurements confirmed previous results. The heat from additional stitches affected the steel by significantly decreasing the hardness by 80–100 HV10. The results of experiments showed that the heat from pad welds provided microstructural changes in heat-affected zones and a decrease in the susceptibility to cold cracking, which results in improvement in the weldability of HSLA steel in wet welding conditions.

Effect of Electrode Waterproof Coating on Quality of Underwater Wet Welded Joints

“…These three types of electrodes caused the highest values of hardness in HAZ ( Section 3.3 ). Obtained results confirmed literature information [ 5 , 13 , 34 , 35 , 36 ], that high hardness increases the susceptibility of steel to cold cracking. The lowest number of parallel cracks in HAZ were observed in specimens welded by electrode with impregnate for concrete ( Figure 9 c).…”

“…The usage of paraffin wax caused hardness reducing by 20-40 HV10 in HAZ in comparison to electrode without additional hydrophobic layer and by 40-50 HV10 in comparison to underwater electrode. Expected hardness reducing in HAZ (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40) was also observed in specimens welded with electrodes with concrete impregnate. The significant differences were found in the weld.…”

“…The larger heat input provides a large possibility for a better protective effect and a larger weld penetration. Tomków and Janeczek [36] proposed a temper bead welding technique, which provides underwater in situ local heat treatment for improving the weldability of steel. Yasinta et al [37] tested the effectiveness of the post weld heat treatment as a method to improve underwater wet welded joint properties.…”

Investigation of Welds and Heat Affected Zones in Weld Surfacing Steel Plates Taking into Account the Bead Sequence

“…An experimental analysis of surfaced layers, mainly in the structural aspect as well as corrosion and tribological resistance, was performed in [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ]. The results of metallographic analysis were presented in [ 3 , 4 , 5 , 6 , 7 , 8 ].…”

The influence of welding heat input on the quality and properties of high strength low-alloy dissimilar steel butt joints

“…The use of these steel groups would be impossible without using joining processes. Common welding methods include manual metal arc (MMA) [6], metal active gas (MAG) [7], and self-shielding wire welding [8]. In addition, laser [9], hybrid [10], and friction welding techniques [11] are being developed.…”