COBEM99

S18 Processos Mecânico-Metalúrgicos

Title:

CORRELATION AMONG THE FRACTURE MODES AND ACOUSTIC EMISSION IN HYDROGEN-ASSISTED CRACKING OF HSLA STEEL WELDMENTS

Summary :

THE AIM OF THE PRESENT PAPER IS TO STUDY THE RELATIONSHIP BETWEEN THE FRACTURE MODES IN HYDROGEN-ASSISTED CRACKING (HAC) IN HIGH-STRENGTH LOW ALLOY STEEL AND THE EMISSION OF ACOUSTIC SIGNALS DURING THE FRACTURING PROCESS. FOR THIS REASON, A FLUX-CORED ARC WELD (FCAW) WAS USED IN A HIGH-STRENGTH LOW-ALLOY STEEL. THE PRODUCTS USED WERE THE COMMERCIALLY AVAILABLE (AWS E120T5-K4) AND HAD A DIAMETER OF 1.6 MM. TWO DIFFERENT SHIELDING GASES WERE USED (CO2 AND CO2+5% H2) TO OBTAIN COMPLETE PHENOMENON CHARACTERIZATION. THE IMPLANT TEST WAS APPLIED WITH THREE LEVELS OF RESTRICTION STRESSES. AN ACOUSTIC EMISSION MEASUREMENT SYSTEM (AEMS) WAS COUPLED TO THE IMPLANT TEST APPARATUS. THE OUTPUT SIGNAL FROM THE ACOUSTIC EMISSION SENSOR WAS PASSED THROUGH AN ELECTRONIC AMPLIFIER AND PROCESSED BY A ROOT MEAN SQUARE (RMS) VOLTAGE CONVERTER. FRACTURE SURFACES WERE EXAMINED BY SCANNING ELECTRON MICROSCOPY (SEM) AND IMAGE ANALYSES. FRACTURE MODES WERE RELATED WITH THE INTENSITY, THE ENERGY AND THE NUMBER OF THE PEAKS OF THE ACOUSTIC EMISSION SIGNAL. THE SHIELDING GAS CO2+5% H2 PROVED TO BE VERY USEFUL IN THE EXPERIMENTS. BASICALLY, THREE DIFFERENT FRACTURE MODES WERE IDENTIFIED IN TERMS OF FRACTURE APPEARANCE: MICROVOID COALESCENCE (MVC), INTERGRANULAR (IG) AND QUASI-CLEAVAGE (QC). THE RESULTS SHOW THAT EACH MODE OF FRACTURE PRESENTS A CHARACTERISTIC ACOUSTIC SIGNAL. KEY WORDS: WELDING, HYDROGEN CRACKING, FRACTURE MODES, ACOUSTIC EMISSION

Author :

Fals, Hipólito Domingo Carvajal
Trevisan, Roseana Exaltação

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