Abstract
The article presents tests aimed to verify the possibility of Thermomechanically Controlled Processed (TMCP) steels T-joints laser welding. The 10 mm thick high-yield-point steel S700MC obtained in an industrial manufacturing process was used for tests of laser welding. The joints made during the tests were single- and double-sided. Subsequent nondestructive tests revealed that the laser-welded joints represented quality level B in accordance with PN-EN ISO 13919-1. Single-sided welding performed at the output laser beam power of 11 kW provided the penetration depth of just 8 mm without visibly deforming of the joint. The double-sided welded joints were characterized by proper geometry and the presence of gas pores in the welds not compromising the requirements of quality level B (strict requirements). The identified weld structure was bainitic-ferritic. The weld hardness was by approximately 60 HV1 higher than that of the base material (280 HV1). The HAZ (Heat Affected Zone) area was slightly softer than the base material. The tests of thin foils performed using a high-resolution scanning transmission electron microscope revealed that, during welding, an increase in the content of the base material in the weld was accompanied by an increase in contents of alloying microagents Ti and Nb, particularly near the fusion line. The above-named alloying microagents, in the form of fine-dispersive (Ti,Nb)(C,N) type precipitates, could reduce plastic properties of joints.
Highlights
Laser welding is one of many technologies enabling the joining of materials
The HAZ (Heat Affected Zone) area was slightly softer than the base material
Technical and economic aspects resulting from the possibility of using high-yield-point Thermomechanically Controlled Processed (TMCP)
Summary
Laser welding is one of many technologies enabling the joining of materials. Because of its unquestionable advantages, the above-named technology has proved successful when joining small-sized and -shaped elements. In addition to its high precision (previously quite paradoxically regarded as a disadvantage because of very precise and expensive preparations required prior to welding), enables the very fast welding of elements without the use of filler metals while not affecting the properties of the base material [4,5,6,7]. The authors state that the narrow width of the above-named area does not significantly affect mechanical properties of welded joints It appears that, in terms of high-yield-point steels, the above-named area could undergo sensitisation to brittle and fatigue cracking and become characterised by worsened plastic properties [8,9,10,11,12,13,14,15,16,17]. The application of laser welding enables high-quality T-joints to be obtained without the necessity of using filler metals, significantly lowering production costs and reducing welding strains in the aforesaid types of joints [28,29,30]
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