High Mn Stainless Steel Research Articles

Manganese Constituent in Stainless Steels Oxidized in Oxygen Containing Water Vapor at 800 °C: High Temperature Oxidation and Volatilization

Many industrial operations, such as solid oxide fuel cells (SOFCs) or combustion processes, have water vapor environments. Stainless steel was applied as part of these applications at high temperatures. The present work investigates high and low manganese content stainless steel that oxidized in an oxygen-containing 5% water vapor at 800 °C. SEM and EDX were performed to analyze oxide formation and ICP-OES was used to detect the volatile species that evaporated from steel surfaces. The results show that manganese in steel increases spallation and reduces Cr volatilization rates in high Mn stainless steel. The average Cr volatilization of high Mn samples is 0.09 × 10-11 g cm-2 s-1, which is about 14 times lower than the ones (1.25 × 10-11 g cm-2 s-1), while Fe and Mn volatilization rates increase by 10 and 62 times, respectively.

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.

Investigation of the effect of grain size on the strain-induced martensitic transformation in a high-Mn stainless steel using nanoindentation

The formation of strain-induced martensite (SIM) during nanoindentation experiments was investigated in a Ti-bearing high-Mn stainless steel with three different grain sizes, e.g. coarse-grained, ultrafine-grained and nano-grained structures. In the nanoindentation load–displacement curves, there was clear distinction in the number of pop-ins from five in the coarse-grained structure to one in the nano-grained structure representing the difference in the susceptibility to formation of SIM. It was found that grain refining down to the nano scale leads to a significant restriction in the formation of SIM. This can be attributed to the increased stability of austenite as a result of increase in the stacking fault energy by reducing grain size.

Degradation of MgO–C refractories by MnO-rich stainless steel slags

In order to identify the influence of MnO on the wear rate of MgO–C bricks for the production of high Mn stainless steel, MgO–C refractory samples were exposed to slags containing different MnO levels (up to 26 wt.%). Although the investigations of the worn brick microstructures revealed the presence of numerous Mn-rich metal particles and the formation of a (Mg,Mn)O solid solution at the slag/refractory interface, no clear evidence of wear rate enhancement was observed due to high MnO concentration in the slags. With respect to refractory wear, the MgO content in the slag is the dominant factor. The degradation processes are discussed by combining experimental results and thermodynamic calculations.

Manganese and Chromium Distribution between CaO–SiO2–MgOsat.–CrO1.5–MnO Slags and Fe–Cr–Mn Stainless Steel

The Mn and Cr equilibria between a Mn rich stainless steelmaking slag (CaO–SiO2–MgOsat.–MnO–CrO1.5) and Fe–Cr–Mn stainless steel were investigated in a temperature range from 1823 to 1873 K under Ar atmosphere. The partition ratios LMn and LCr between liquid slag and steel were determined as a function of slag composition and temperature. By combining the experimental results with thermodynamic calculations, it was found that, as basicity increases, LMn decreases, while LCr increases. The elevated basicity leads to a high MnO activity coefficient. On the other hand, the CrO1.5 activity coefficient decreases with higher slag basicities. The influence of MnO and CrO1.5 contents on the activity coefficients was also considered. It is concluded that in order to maximize Mn recovery during high Mn stainless steel production, a basic slag with a high MnO activity coefficient must be employed whereas high temperatures should be avoided.

高Ｍｎステンレス鋼の真空中ガス放出特性に及ぼす表面処理の影響

高Ｍｎステンレス鋼の真空中ガス放出特性に及ぼす表面処理の影響

Proposals for the Final Design of the ITER Central Solenoid

The ITER central solenoid (CS) is 12 m high and 4 m in diameter. The CS consists of a stack of 6 electrically independent modules to allow control of plasma shape. The modules are compressed vertically by a pre-compression structure to maintain contact between modules. The CS conductor is CIC conductor with Nb/sub 3/Sn strands and a steel conduit. The CS model coil and insert coil test results have shown that the conductor design must be modified to achieve an operation margin. This required either to increase the cable diameter or to use strand with a higher current capability. A bronze-process (NbTi)/sub 3/Sn strand is proposed to achieve a higher critical magnetic field. A square conduit with a high Mn stainless steel is proposed as it can satisfy fatigue requirements. The inlets are in the high stress region and any stress intensification there must be minimized. The preload structure is composed of a set of tie-plates, flanges, buffer plates, and wedges. These design proposals satisfy all ITER operational requirements.

Effect of Cold Working and Aging on High Temperature Deformation of High Mn Stainless Steel

By the addition of N, the strength of high Mn stainless steel can be increased. Cold rolling and aging are effective to increase its strength further, and with those treatments this grade is often used for high temperature applications. In this study, creep deformation behavior and high temperature strength of the high Mn stainless steel in cold rolled and aged conditions are discussed as compared to Type 304 stainless steel. It has been revealed that as-rolled specimens show instant elongation at the beginning of creep tests and its amount is larger in the high Mn grade than in Type 304. Also, the creep rate of the high Mn stainless steel is smaller than that of Type 304. These facts may be related to the change in microstructure.

Effect of applied potential on the nature of surface film and SCC of a high Mn stainless steel in 1 M HCl

The Stress Corrosion Cracking (SCC) behavior of a high Mn austenitic stainless steel (SS) with 14.67 wt % Mn was studied in 1 M hydrochloric acid at room temperature as a function of potential. At open circuit potential (OCP) thick black surface film formation and a transgranular mode of cracking were observed. At all applied anodic potentials general dissolution and ductile cracking were observed. X-ray photoelectron spectroscopy (XPS) studies were conducted to characterise the surface films formed at different potentials. The nature of the surface film was found to be different with a change in potential. The nature of the film formed was found to govern the dissolution behavior and therefore the fracture morphology of the alloy.

Mechanical effects of simulated plasma disruptions in Cr-Ni and Cr-Mn stainless steels

Plasma disruptions were simulated on three materials of interest for fusion purposes (a Cr-Mn low activation austenitic steel (AMCR 0033), an age-hardenable high-Mn stainless steel (VA 64) and the European 316 L fusion reference composition stainless steel) by single electron beam spots reaching a power of several KW on an area of few millimeters. The resulting damage on the resolidified region of AMCR-0033 and AISI 316 L samples was primarily constituted of solidification cracking, which however had little effect for the various combinations of process parameters, whereas in VA 64 samples extensive cracking occurred and an equiaxed dendrite structure formed with an embrittlement effect.