Structural Stability of Austenitic CrMn(Mo)N Steels for High-Strength, Corrosion-Resistant Retaining Rings

Abstract

The improved temperature resistance of insulating materials enables the service temperature of retaining rings on electric generator shafts to be raised from 90 to 130°C. Therefore the structural stability of two high nitrogen austenitic steels in respect to cold expansion and ageing was investigated by XRD, STEM and internal friction. Cold working caused the formation of about 5 to 10 % ε‐martensite, which was promoted by the low stacking fault energy of about 30 mJ/m2. Ageing between 90 and 170°C was accompanied by the precipitation of Fe3N which dissolved during subsequent aging at 400°C because of the stronger bond of nitrogen to dislocations. Their pinning prevented long‐term structural changes of a ring which was shrink fitted at 400°C and more than 60.000 h in service.

Nichtmagnetisierbarer warmbeständiger nichtrostender Stahl für Wälzlager

“…Die hohe Warmbeständigkeit der kaltverfestigten CN-Stäh-le ist zum einen in der geringeren Diffusionsgeschwindigkeit der interstitiellen Elemente im kubischflächenzentrierten Gitter begründet, zum anderen behindert die starke Wechselwirkung von gelösten Stickstoffatomen und Versetzungen die Bildung von Eisenkarbiden [14]. Wie nah man mit den neuen CN-Stählen bezüglich Betriebstemperatur und -dauer an sekundärgehärtete Stähle wie z.…”

Fatigue and Structural Changes of High Interstitial Stainless Austenitic Steels

“…Aging of a cold worked austenitic CrMnN steel with 0.45 mass% N was accompanied by the precipitation of Fe 3 N nitrides starting after four months at room temperature in samples of high reduction by cold rolling but was also apparent in X‐ray diffraction patterns after 2 years, if the degree of cold working was within the range of the present study 15. In CrMnN steels with about 0.55 to 0.8 mass% N the Fe 3 N precipitates were detected after aging at temperatures between 90 and 170 °C for 30 h 16. They redissolved during aging at 400 °C as shown by Snoek‐like relaxation.…”

Wear Behavior of Roller‐Burnished High Interstitial Austenitic Stainless Steel Parts in Glass‐Reinforced Plastic Melt

“…[12,13] Decreased corrosion resistance of FeCrNi austenites after cold working is related to strain-induced phase transformation or decreased stability of passive layers. [14][15][16] In turn, the reason for the high resistance of HIS even in highly cold-worked condition can be attributed to their high austenite stability [16] as well as a very stable passive layer. [10] Consequently, the described combination of properties makes high interstitial austenitic stainless steels promising candidates for application in processing of plastics.…”

“…[ 12,13 ] Decreased corrosion resistance of FeCrNi austenites after cold working is related to strain‐induced phase transformation or decreased stability of passive layers. [ 14–16 ] In turn, the reason for the high resistance of HIS even in highly cold‐worked condition can be attributed to their high austenite stability [ 16 ] as well as a very stable passive layer. [ 10 ]…”