Interstitial Stainless Steels Research Articles

Effects of Iron Oxidation State and Chromium Distribution on the Corrosion Resistance of High Interstitial Stainless Steel for Down-Hole Application

The corrosion properties of Fe-Cr-Mn-C-N high interstitial austenitic stainless cast steels were investigated for down-hole application in sour environments. The two cast alloys contained 0.66% and 0.71% of total nitrogen and carbon. The corrosion properties of the alloys that were solution-treated and fast-cooled were directly responsible for high corrosion resistance in NaCl solution, including resistance to pitting corrosion resulting from a better distribution of chromium chemical compound in the high interstitial stainless cast steel. However, the sour corrosion resistance of the alloys decreased with the fast cooling rate, which can be attributed to the increased amount of ferrite containing Fe2+, which causes iron sulfide precipitate formation in H2S.

Development of High Interstitial Stainless Steel and Evaluation of Its NaCl Corrosion Resistance

High interstitial Fe–Cr–Mn–C–N stainless steels, CN66 (0.38 wt% N + 0.28 wt% C) and CN71 (0.44 wt% N + 0.27 wt% C), were cast under atmospheric pressure to develop a new drill collar for use in petroleum industry. To evaluate the corrosion property, CN66 and CN71 were compared with high-Mn stainless steel, P550, which is currently being used as a drill collar material. Through the measurement of the corrosion resistance based on the chemical compositions, CN71 exhibited the highest corrosion property, a mean of 35.74, corresponding to strong corrosion resistance. However, CN71 exhibited a mean of 0.517 mpy for the corrosion rate compared to 0.37 mpy for P550, after the immersion experiment in 3.5 wt% NaCl. With high C content, the formation of carbide along the grain boundaries in CN71 and CN66 caused intergranular corrosion. However, this could be restricted by heat treatment at 1050 °C and 1180 °C with uniform distributions of chemical compositions via air cooling, decreasing the corrosion rates significantly.

Evaluation of the Protective Ability of Air-formed Oxide and Passive Films Formed on Nb-Bearing High Interstitial Stainless Steels

Evaluation of the Protective Ability of Air-formed Oxide and Passive Films Formed on Nb-Bearing High Interstitial Stainless Steels

Wear Evaluation of High Interstitial Stainless Steels

A new series of high nitrogen-carbon manganese stainless steel alloys are studied for their wear resistance. High nitrogen and carbon concentrations were obtained by melting elemental iron-chromium-manganese (several with minor alloy additions of nickel, silicon, and molybdenum) in a nitrogen atmosphere and adding elemental graphite. The improvement in material properties (hardness and strength) with increasing nitrogen and carbon interstitial concentration was consistent with previously reported improvements in similar material properties alloyed with nitrogen only. Wear tests included: scratch, pin-on-disk, sand-rubber-wheel, impeller, and jet erosion. Additions of interstitial nitrogen and carbon as well as interstitial nitrogen and carbide precipitates were found to greatly improve material properties. In general, with increasing nitrogen and carbon concentrations, strength, hardness, and wear resistance increased.

Microstructure Refinement of a Low Interstitial Ferritic Stainless Steel by Cold Rolling and Annealing of Martensite

Several studies have shown that recrystallization of cold rolled martensite results in low carbon steels with very fine microstructures. Correspondingly, these materials exhibit promising combinations of strength and elongation. Most of the work on this processing route has focused on low carbon steels (0.1-0.2wt% carbon) where the interstitial content may play an important role in the microstructure refinement. In this note we describe experiments performed on a low interstitial stainless steel containing 0.02wt%C. It has been possible to achieve materials with high strengths (UTS > 1 GPa) and significant uniform elongation (> 8%), however, the microstructures associated with these properties are very different from those previously reported for low carbon steels.

EBSD investigation of intergranular corrosion attack on low interstitial stainless steel

AbstractGrain boundary effect on corrosion behaviour of low interstitial AISI 316LN austenitic stainless steel after homogenization and heat treatment at 700 and 800°C was investigated by means of Electron Backscattered Diffraction (EBSD) technique. Rapid oxalic acid etch test (ASTM A262‐ practice A) was used to determine steel susceptibility to intergranular corrosion. An attempt to quantify oxalic acid etch test results was also made.Beneficial effect of low carbon and nitrogen content on grain boundary precipitation and corrosion was observed. No changes neither in grain orientations nor in grain boundary types between sensitised and non‐sensitised steel states using orientation measurements were recorded. Twin boundaries were found in all samples with highest amount and only small occurrence changes. CSL categorizations showed only little increase of special boundary fractions with increasing time and temperature of heat treatment. Irrespective to annealing conditions a continued network of random boundaries was retained. Additionally, based on misorientation measurement of 50 grooved grain boundaries, a tendency for preferred attack of high angle boundaries (30–55°) was noted.

Processing maps for hot working of commercial grade wrought stainless steel type AISI 304

The hot-working behaviour of commercial grade wrought stainless steel type AISI 304 is characterized using processing maps developed on the basis of the dynamic material model and hot compression data in the temperature range 600–1250°C and strain rate range 0.001–100 s –. The material exhibits a dynamic recrystallization (DRX) domain in the temperature range 1000–1200°C at a strain rate of 0.01 s −1. Optimum hot workability occurs at 1100°C and 0.01 s −1, which corresponds to a peak efficiency of 32% in the DRX domain. Finer grain sizes are obtained at 1000°C and all strain rates. In comparison with low interstitial stainless steel type AISI 304 L, the DRX occurs at lower strain rate and temperature. This result is attributed to the strong primary effect of interstitial carbon enhancing the rate of DRX nucleation. Flow instabilities occur in the entire region above the DRX domain. Flow localization occurs in the regions of instability at temperatures lower than 1000°C and ferrite formation is responsible for the instability at higher temperatures.