Abstract
This paper presents a failure analysis on welding of bucket adapter for an excavator that made of low carbon steel with Ideal Diameter (DI) value 341 and Carbon Equivalent 0.73. The bucket component is stated OK as the final inspection, but four months later found cracked and even it has not been used yet. Adapter mounted to bucket through CO2 gas shielded Gas Metal Arc Welding (GMAW) process, filler metal MG-50 (AWS A5.18 ER70S-G), pre-heating and post-heating. Crack occurred on the boundary of weld metal and adapter casting. The metallurgical examination was conducted in the crack origin and the adapter casting. Nondestructive test (NDT) covered visual and magnetic test (MT), while destructive test (DT) covered fractography, mechanical properties, and Electron Probe Micro Analyzer (EPMA). The investigation resulted in that crack initiated from slag inclusion in the weld metal due to insufficient cleaning on weld joint. The higher hardness of martensite structure in the heat affected zone (HAZ) of adapter indicates high cooling rate that gen erates high residual stress. High stress that caused by insufficient post heating triggered severe crack propagation. By its characteristic, crack is called the cold cracking, delayed cracking, or hydrogen-induced cracking (HIC).
Highlights
The biggest problem in welding is crack, whether it is hot or cold cracking
One of the cracked adapters was taken by gas cutting with enough distance, about 100mm, to prevent structure changing near the crack line
Hacksaw cutting performed in both tip of a crack to observe the fracture surface, small size sample taken from adapter casting and crack initiation site for chemical composition, mechanical properties, macroscopic observation, and microscopic observation
Summary
The biggest problem in welding is crack, whether it is hot or cold cracking. Hot cracking is caused by a considerable portion of nonmetallic inclusion and a higher concentration of Phosphor (P) and Sulphur (S). Cold cracking is generated by the presence of little stresses arising from austenite to martensite transformation in the heat affected zone (HAZ). Minimizing of Sulphur, Phosphor, and nonmetallic inclusion provide low susceptibility to hot cracking, otherwise higher susceptibility to cold cracking [1]. Hot cracking obviously can be detected after weld finished. May appear a few days or even months after welding
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
