Abstract:Crevice corrosion behavior of high nitrogen-bearing stainless steels with up to 1.1 mass% nitrogen were investigated in artificial seawater. Specimens were highly purified and contained ultra-high nitrogen of about 1 mass% obtained by using nitrogen gas pressurized electroslag remelting (P-ESR) system. 23%Cr-4%Ni-0 to 2%Mo-0.7 to 1.1%N stainless steels were used as test specimens. Crevice corrosion resistant properties of the stainless steels were evaluated by means of electrochemical corrosion test method usi… Show more
“…High nitrogen alloys as the new class of materials had been the interest of the researchers and industrial sectors for its novel properties [1][2][3][4][5][6][7][8][9][10]. Like carbon in Fe-C alloys, nitrogen is also a good candidate for achieving the similar properties as shown by carbon.…”
In the plasma ionic environment of nitrogen and hydrogen at 4:1 ratio, nitriding had been realized in the plasma laboratory. Nitriding of steel samples was followed at the lower temperature of 450 °C and also at the higher temperature of 550 °C while the sample was biased at the fixed -250 V. Steel nitrided at 550 °C had shown a significantly enhanced resistance to corrosion in comparison to that of steel nitrided at 450 °C. X-ray diffraction studies of nitrided steels had shown the presence of nitrides of iron (FexN). Scanning electron microscopic and the electron dispersive spectroscopic analyses (SEM ? EDS) of the cross section of the nitrided steels had shown the nitrided layer and the elemental distribution from top to the core. Following structural analysis, microhardness and the potentiodynamic polarization tests were performed. A significant improvement in hardness (* 1180 Hv) and the case depth * 150 lm was obtained after nitriding at the higher temperature. Corrosion resistance was also found to be significantly improved. These achievements might be attributed to the presence of FexN, CrN phases and also to the nitrogen solid solution.
“…High nitrogen alloys as the new class of materials had been the interest of the researchers and industrial sectors for its novel properties [1][2][3][4][5][6][7][8][9][10]. Like carbon in Fe-C alloys, nitrogen is also a good candidate for achieving the similar properties as shown by carbon.…”
In the plasma ionic environment of nitrogen and hydrogen at 4:1 ratio, nitriding had been realized in the plasma laboratory. Nitriding of steel samples was followed at the lower temperature of 450 °C and also at the higher temperature of 550 °C while the sample was biased at the fixed -250 V. Steel nitrided at 550 °C had shown a significantly enhanced resistance to corrosion in comparison to that of steel nitrided at 450 °C. X-ray diffraction studies of nitrided steels had shown the presence of nitrides of iron (FexN). Scanning electron microscopic and the electron dispersive spectroscopic analyses (SEM ? EDS) of the cross section of the nitrided steels had shown the nitrided layer and the elemental distribution from top to the core. Following structural analysis, microhardness and the potentiodynamic polarization tests were performed. A significant improvement in hardness (* 1180 Hv) and the case depth * 150 lm was obtained after nitriding at the higher temperature. Corrosion resistance was also found to be significantly improved. These achievements might be attributed to the presence of FexN, CrN phases and also to the nitrogen solid solution.
“…Alloying with nitrogen can increase the corrosion resistance of steel. This is attributed to N combining with H + forming NH + that decreases the hydrogen ion concentration, increases the pH of corrosion solution and slows down the corrosion reaction [22][23][24]. The dissolution of chromium and phosphorus ions in steel has been demonstrated to enhance the uniform formation of amorphous ferric oxyhydroxide which provides corrosion resistance in a different atmosphere.…”
We have studied here the wet/dry cyclic corrosion behaviour of V-N-0.8Cr weathering steel and compared with a reference steel (Q345B) in 0.01 mol/L NaHSO 3 simulated industrial atmosphere. The study indicated that the coherent protective oxide layer formed in the surface of V-N-0.8Cr microalloyed weathering steel, contained corrosion resistant alloying elements (Cr, Ni, Cu, P, Mo). The addition of Cr significantly inhibited the corrosion of weathering steel. The corrosion rate of V-N-0.8Cr and Q345B steel after 360 h corrosion were 1.60 g/(h•cm 2 ) and 2.42 g/(h•cm 2 ) respectively. The major corrosion products in both the steels mainly constituted of α-FeOOH and γ-FeOOH and Fe 3 O 4 . The stratification of the corrosion layer evolved into a dual-layer structure, where the outer layer was dense and the inner layer was a loose and porous structure in V-N-0.8Cr weathering steel. This is different from previous studies. Cr tends to be concentrated in the inner corrosion layer.
“…Nitrogen is well known as a valuable element in steel, improving mechanical properties, 1,2) heat resistance, 3,4) corrosion resistance 5,6) and oxidation resistance. 7) Many kinds of special steels containing nitrogen have been developed over the past 20 years.…”
High-strength Mn-Cr-N steels with high nitrogen content were manufactured using a lab-scale pressurized electro-slag remelting furnace to study the deformability of the steels. Melting experiments were performed under 1.0 MPa pressure N 2 gas in order to have various N contents. Gas porosity and severe macrosegregation were not observed in the remelted ingots. Microstructure observation revealed that nitrides and non-metallic inclusions were small enough not to affect the mechanical properties. After the ESR ingots were heat-treated and forged, the mechanical properties of the steels at a room temperature were measured. The grain sizes were measured in the range from 50 to 300 μm. The results of 0.2% proof stress showed that the steel became stronger with increasing N content according to solid solution hardening mechanism. In addition, with various strain rates, the tensile strain-hardening exponents were determined to be almost the constant values between 0.20 and 0.25. These results suggest that the methods of cold working for conventional 18Mn-18Cr-0.7N steel are applicable to the Mn-Cr-N steels containing over 1.0 mass% nitrogen.
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