The Characteristic of Cold Metal Transfer (CMT) and its application For Cladding

Abstract

Corrosion and wear has been a major challenge in most of our industries. CMT process has been selected as a weld technique because of its low heat inputs that makes it a promising technique for industrial application. However, the aim of this thesis is to study the competence of CMT welding process in cladding of mild stainless steel and performing a qualitative fault tree analysis. Furthermore, the most critical aspect of anticorrosion overlay, such as penetration into the substrate and level of dilution, that usually comprises the essential corrosion resistance of the coating, were analysed.

In the first stage of this thesis, literature review of the welding process, CMT, synergic line and welding defects was discussed. In the second stage, two experiments and various tests have been carried out. The result demonstrates that with Corocarb Ni –WC wire filler, an increased in wire feed speed to 6m/min in test 2 and adjusting of arc length correction (ALC) and dynamic correction (DC) parameter, there was probably dissolve in carbides present in the bead for stringer motion and single bead. Moreover, the level of hardness achieved while adjusting ALC and DC value, for wire feed speed variation from (5-11m/min) is (HV1 356 - 393) for test 4. In fact, for test 4 straight beads were not produced. Finally, in test 5, the shielding gas was changed, the bead went quite straight and the melt spread well. Comparing, CMT process to Pulse MAG in test 5, CMT process gives hardness value of 422HV1 and deposition rate equal to 3.3kg/hr. Also, CMT process produces small dilution and no cracks while pulsed MAG produced significant crack.

Furthermore, with Inconel 625, the arc power calculated from average current and voltage related well with the AIP value that were determined by oscilloscope while adjusting parameter ALC and DC are around the middle of the scale. However, with respect to the results, it is advantageous to use large negative value of DC. DC Value of -5 did not probably produce spattering, but it increases melting range, contact angle values, without significant effect on penetration and dilution. Moreover, positive value of DC value does not show positive effect. Also, it is possible to set WFS to 10m/min, this will give the same result instead of bringing more heat to the system.