The Effect of Welding Conditions on Diffusible Hydrogen Content in Deposited Metal

Abstract

The primary limitation of weldability of high strength low alloy steel is susceptibility to cold cracking. The important reason of the formation of cold cracks, besides forming brittle structure and residual stresses, is the presence of diffusible hydrogen in welded joint. The most effective methods reducing the susceptibility to cold cracking are connected with decreasing the amount of potential hydrogen. This process may be carried out in technological (drying welding filler materials, preheating components) or in a metallurgical way (filler metals with austenitic structure, adding rare-earths elements to filler metals as traps for hydrogen atoms in steel). The possibility to minimize the amount of diffusible hydrogen by changing the welding parameters seems to be particularly interesting. The article presents the results of a literature survey and preliminary tests which set out effects of welding conditions on the amount of diffusible hydrogen in deposited metal. Experiments were conducted by using rutile coated electrodes which generate high contents of diffusible hydrogen in deposited metal. The amount of diffusible hydrogen was determined by a glycerin test. Eleven factors were considered: the electrode angle, the grinding of sample, the preheat temperature, the polarity of welding current, the welding current, the welding – cooling time, the electrode usage, the time of welding, the thickness of specimen, the welding – measurement time and thickness of electrode coating. All factors were optimized using a Plackett-Burman design to get the most relevant variables. The results of the preliminary tests indicate that appropriate choice of welding parameters may considerably reduce diffusible hydrogen in deposited metal. However, the range of parameters is limited by the necessity of providing stability of the welding process and obtaining required properties of the welded joint.