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The study presents the influences of solution treatment temperatures (S.T.T.) on microstructure, tensile and fracture properties of 18 Ni cobalt free maraging steel. The results are thoroughly discussed in light of the prevailing microstructural conditions as revealed by optical and transmission electron microscopy, and detailed scanning electron fractography. It is found that tensile strength in both unaged and aged conditions is independent of solutioning temperature and, consequently, grain size. However, the tensile ductility, CVN and Kie in aged condition get severely affected with the increase in S.T.T. because of a change occurring in the martensitic lath morphology from blocky to stringer type. This transition in the martensitic morphology starts at the prior austenitic grain size of 35-40 µm and is completed at 120-130µm. Solutioning at 1323 K followed by air cooling, however, results in thermal embrittlement of the steel due to grain boundary precipitation of TiCN. The prior austenitic grain size in this reaction plays only an indirect role. Based on these results, it has been suggested that the existing controversies on the effect of S.T.T. grain size on tensile ductility and fracture behaviour of maraging steels can be rationalized if the changes in martensitic lath morphology are considered as an important variable. EinfluB der Temperaturen beim LosungsglOhen auf Mikrostruktur und Festigkeitseigenschaften eines martensitaushartenden Stahls. Die vorliegende Studie berichtet Ober den EinfluB der LosungsglOhtemperaturen auf Mikrostruktur und Festigkeitseigenschaften eines martensitaushartenden, Co-freien Stahls mit 18 % Ni. Die Ergebnisse werden im Hinblick auf die vorherrschenden Mikrostrukturbedingungen diskutiert, wie sie Lichtmikroskopie, TEM und detaillierte Bruchuntersuchungen mit REM widergeben. Es zeigt sich, daB die Zugfestigkeit -unabhangig von einer Alterungsbehandlung -nicht von der LosungsglOhtemperatur -und folglich der KorngroBe -abhangt. Dagegen wird die Zahigkeit der gealterten Probe von steigenden Temperaturen deutlich beeinfluBt. Der Grund hierfOr liegt in einer Veranderung der Morphologie der Martensitlatten von Blockzu Zeilenanordnung. Dieser Wandel beginnt bei einer KorngroBe des ehemaligen Austenits von 35-40 µm und endet bei 120-130 µm. LosungsglOhen bei 1323 K mit nachfolgender LuftabkOhlung !Ohrt zu thermischer Versprodung des Stahls aufgrund der Korngrenzenausscheidung von TiCN. Die KorngroBe des ehemaligen Austenits spiel! in diesem Zusammenhang nur eine indirekte Rolle. Basierend auf diesen Ergebnissen konnen die bestehenden Kontroversen hinsichtlich des Einflusses der KorngroBe nach einer LosungsglOhbehandlung auf Zahigkeit und Bruchverhalten martensitaushartender Stahle nur dann vernOnfig erklart werden, wenn die Veranderung der Martensitlattenmorphologie als eine wichtige Variable angesehen wird.

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Development of the space engines with liquid propellants necessitates the use of bearings of high quality. During recent years, a new family of high strength corrosion resistant steels, with partial replacement of carbon by nitrogen, known as high nitrogen steels were developed having higher impact strength and fracture toughness coupled with high hardness for antifriction bearing of cryopumps in rocket. In this research work, wear characteristics of cryogenically treated high nitrogen martensitic stainless steels were investigated by Pin-on-disc wear testing machine. After conventional hardening treatment, specimens were subjected to cryogenic treatment at −196°C with cryosoaking period varying from 8 to 32 h in the interval of 8 h followed by soft tempering. These specimens were analysed for hardness, wear resistance, subsurface and worn surface features by SEM. It is established that there is a profound influence of nucleation and growth of precipitates on the wear behaviour and the underlying wear mechanisms.