Corrosion behaviour and mechanical properties of supermartensitic stainless steels all-weld-metals

A. BURGUEÑO, S. ZAPPA, H. G. SVOBODA, E. S. SURIAN Y L. A. DE VEDIA

Buenos Aires

Conferencia; New Developments on Metallurgy and Applications of High Strenght Steels International Conference; 2008

Techint

The supermartensitic stainless steels (SMSS) have been rather recently developed as a promising technological alternative. The SMSS 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 (SCC), toughness and weldability. The objective of the present work is to analyze the corrosion behavior, particularly resistance to stress corrosion cracking (SCC) and pitting corrosion of the all weld metal obtained under different welding conditions. 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 (AW) and post weld heat treated (PWHT) conditions were studied. In order to characterize the susceptibility of the material to SCC, tests were performed based in the NACE 0177-05 standard, method B. A solution concentrated in Cl- (100gL-1 of Cl dissolved) and saturated with CO2 was used. The chemical composition of the deposits was determined. For evaluation of pitting resistance, potentiodynamic polarization curves were determined for the different welding conditions. The microstructural characterization was carried out by means of optical and scanning electron microscopy, and x-rays diffraction. The micro-hardness, tensile strength and Charpy-V notch tests for the different conditions were also determined. Results relating chemical composition and microstructure with mechanical properties, pitting resistance and SCC resistance are discussed.