The morphological microstructure, the density and dispersion of high angle boundaries, morphology and micro chemical composition of precipitates and the volume fraction of retained austenite of a commercial super martensitic stainless steel (SMSS) normalized and tempered at various temperatures were characterized by optical microscope, scanning electron microscope (SEM), electron backscattered diffraction (EBSD), transmission electron microscope (TEM) and X-ray diffraction (XRD) in the light of equilibrium phase diagram of the alloy calculated using Thermo-Calc software. The mechanical properties and pitting corrosion resistance were determined to correlate with microstructures. Two kinds of morphology of precipitate were observed in tempered commercial super martensitic stainless. Besides the globular Nb and V rich carbo-nitride precipitates, rod-like Cr rich nitrides were formed due to excess N content. While high density of high angle boundaries and precipitates contribute to strength properties, the dislocation softening of the matrix and retained austenite from tempering restore the ductility and impact toughness properties. The poor resistance to pitting corrosion is attributed to the occurrence of Cr rich precipitates. It is demonstrated that by lowering the nitrogen content and adding niobium, the Cr rich precipitates can be suppressed and the mechanical properties and resistance to pitting corrosion can be significantly improved.

Microstructure and properties of 13Cr5Ni1Mo0.025Nb0.09V0.06N super martensitic stainless steel

Laser surface melting of AISI 440C martensitic stainless steel was achieved using a 2.5-kW continuous wave Nd:YAG laser. The pitting corrosion behavior of laser surface-melted specimens processed under different processing conditions in 3.5% NaCl solution at 23 °C was studied by potentiodynamic polarization technique. The corrosion resistance of all laser surface-melted specimens was significantly improved, as evidenced by a shift from active corrosion to passivity, a wide passive range and a low passive current density. The pitting potential of the laser surface-melted specimens P08-440C-25 (laser power=0.8 kW, scanning speed=25 mm/s) and P12-440C-25 (laser power=1.2 kW, scanning speed=25 mm/s) was increased to 260 and 200 mV (SCE), respectively, and was much higher than that of the conventionally heat-treated AISI 440C. The pitting corrosion characteristics of the laser surface-melted specimens were strongly dependent on the processing conditions which resulted in different microstructures. The enhanced corrosion resistance was attributed to the dissolution or refinement of carbide particles and the presence of retained austenite. The amount of carbides in the melt layer, which indirectly determine the Cr content in solid solution and hence, the corrosion resistance, was related to the amount of C remaining in solid solution and to decarburization. The pit morphology of the laser surface-melted specimen was also studied.

Effect of processing conditions on the corrosion performance of laser surface-melted AISI 440C martensitic stainless steel

This paper discusses the corrosion behavior of supermartensitic stainless steel in CO 2 -saturated synthetic seawater. A comparison is also made with an aerated solution. Potentiodynamic polarization measurements were taken in synthetic seawater with five different chloride contents: 20 000, 30 000, 40 000, 60 000 and 80 000 ppm, and at three different temperatures: 5, 25 and 60 °C. The pitting potential decreased in a logarithmic relation with the chlorine concentration. The pitting potential decreased linearly with increasing temperature. XPS measurements indicated that the presence of CO 2 enriches the Cr content in the oxide layer and that the temperature also favors this enrichment. The pitting potential depends on the stability of passive film. Otherwise, stability is dependent on the composition. So pitting potential is affected by a synergy between the chloride concentration and the saturated CO 2 solution.

Corrosion behavior of supermartensitic stainless steel in aerated and CO2-saturated synthetic seawater

Microstructure and pitting corrosion of 13CrNiMo weld metals

Microstructure and corrosion behavior of a novel additively manufactured maraging stainless steel

Effect of retained austenite on the corrosion performance of modified 13% Cr martensitic stainless steel (0.025%C-13%Cr-[4% to 6%]Ni-[1% to 2%]Mo) seamless pipe is investigated. Retained a...

Yoshikazu Kitahaba

Papers

Effect of Retained Austenite on Corrosion Performance for Modified 13% Cr Steel Pipe