CORROSION BEHAVIOUR AND MECHANICAL PROPERTIES OF SUPERMARTENSITIC STAINLESS STEEL ALL-WELD METALS

摘要

The supermartensitic stainless steels which have been rather recently developed as a promising technological alternative, offer an economic option, good corrosion resistance and suitable mechanical properties, mainly in the applications related to the gas and oil industry. In this respect, welding of these materials plays a crucial role, influencing its resistance to stress corrosion cracking, strength and toughness. The objective of the present work is to analyze the resistance to stress corrosion cracking of the all weld metal obtained under different welding conditions, in a solution with high Cl- content and saturated in CO2. Two all-weld-metal test coupons were prepared according to standard ANSI/AWS A5.22-95, using a 1.2 mm diameter tubular wire. The shielding gases used were Ar - 5 % He and Ar - 18 % CO2. The welds were made in the flat position and the nominal heat input was of 1 kJ/mm. The as welded and post weld heat treated conditions were studied. The chemical composition of the deposits was determined. The microstructural characterization was carried out by means of light and scanning electron microscopy, and x-rays diffraction. The micro-hardness, tensile strength and Charpy-V notch tests values for the different conditions were also determined. In order to characterize the corrosion behavior, tests of pitting corrosion and stress corrosion cracking were made. For evaluation of pitting resistance, potentiodynamic polarization curves were determined for the different welding conditions. In order to assess the susceptibility of the material to stress corrosion cracking, tests based in the NACE 0177-05 standard, method B, were performed. A concentrated solution Cl- (165 gL-1 of NaCl diluted in water) and saturated with CO2 was used. Results relating chemical composition and microstructure with mechanical properties and SCC resistance are discussed.