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The ladle treatment technique for molten Hadfield steel was utilized by using four groups of CaSi inoculants and Mg metal in order to exclude the most hard-control conventional heat treatment process. The effect of ladle treatment on the morphology of Cementite networks, hardness, impact strength, and wear abrasion resistance were investigated. The SEM indicates that cementite is dispersed throughout the austenite matrix in a new eutectic. This eutectic grows on heterogeneous nuclei either SiO2 or MgS. Impact strength of modified as cast Hadfield steel exceeds the as heat-treated steel. The wear abrasion resistance of modified steel is 350% in excess of the conventional Hadfield steel.

Reverse transformation at 725–800°C × 0–35 s from a ferrite/pearlite to austenite was investigated in spring steel 60Si2MnA with various pearlite fineness obtained by isothermal transformation. Then, its influence on the structure inheritance in the spring steel during heat treatment process was discussed. The results indicated that various pearlite fineness influences clearly start temperature of the reverse transformation. Austenite preferentially nucleates at the ferrite/cementite interface within pearlite, the neighboring pearlite colony boundary and the proeutectoid ferrite/pearlite boundary during the reverse transformation process. And the angle between pearlite lamellae and austenite growth direction has an important influence on austenite growth rate. Besides, the ferrite/pearlitic structure has structure inheritance phenomenon, because various hot-rolled microstructure affect the austenite nucleation and growth during heat treatment process.

Using self-made electromagnetic centrifugal casting machine, optical microscopy (OM) and D/max2200pc X-ray diffraction, the solidification microstructure and phases of as-cast high speed steel(HSS) roll made by sand casting, centrifugal casting and electromagnetic centrifugal casting were investigated. The experiment results show that the phases of as-cast high speed steel (HSS) roll are alloy carbide (such as W2C, VC, Cr7C3), martensite and austenite. The centrifugal casting and electromagnetic centrifugal casting can apparently improve the solidification structure of HSS roll. With the increase of electromagnetic field intensity (B), the volume fraction of austenite in the HSS solidification structure increased obviously and eutectic ledeburite decreased, the secondary carbide precipitated from the austenite is more fine and distribution of secondary carbide is more even.

Development of TRIP aided ferrous alloys is one answer to the demand for weight decrease in the automotive industry. The microstructure of hot rolled and cold rolled TRIP steels is quite complex and the optimisation of such steel products requires a detailed understanding of the mechanisms of phase transformation, during thermomechanical treatment as well as during mechanical testing or metal forming. We present in this paper the results obtained at Irsid concerning the study of austenite stabilisation through bainitic transformation during thermal treatment and its transformation into martensite during mechanical testing. First of all, the characterisation methods are presented. An effort has to be put on this point due to the refinement of the microstructure of TRIP steels, especially the size of austenite and martensite islands. Carbon replicas for the observation by means of transmission electron microscopy (TEM) are used to analyse the morphological features of the microstructure - nature of the constituents, size and shape - and the composition of cementite particles present in the steels. The mean value for this carbon content in retained austenite is deduced from X-ray diffraction measurements. Then the kinetics of bainitic transformation are discussed as well as cementite precipitation. The typical composition of the steel studied is 0.5 % C, 1.5 % Mn. The use of 0.5 % C steels facilitates the study of bainitic transformation by avoiding the ferrite formation usually occurring in TRIP steels. Cementite nucleation appears at the ferrite/austenite interface without any partitionning of substitutional elements. To satisfy thermodynamic equilibrium at the interface, the silicon content on the cementite side is very low and high on the austenite side. Then, carbon diffusion towards austenite is delayed and, as a consequence, cementite growth is also delayed. As the diffusion kinetics are low at 400 °C, cementite keeps this non partitioned composition, even after 3 hours holding. At 500 °C, diffusion kinetics are higher and cementite composition approaches that predicted by equilibrium. Finally, the stability of retained austenite during mechanical testing is studied. Before and after mechanical testing the morphological characteristics of the microstructure (austenite island size and elongation) are analysed by TEM replicas and image analysis. There is a high density of very small austenite islands but they represent only a small fraction of the total retained austenite. These results confirm and quantify the size effect on austenite stabilisation during deformation.

Transformation induced plasticity (TRIP) effects associated with austenite dispersions in low alloy Fe-Mn-Sl steels can be enhanced by austenite stabilisation. Austenite which forms during conventional intercritical annealing does not possess the required stability in order to exhibit TRIP effects. In this work, thermodynamic calculations indicated that it is feasible to form austenite by a cementite to austenite conversion which occurs under paraequilibrium conditions, i.e with partition of carbon but with no partition of substitutional alloying elements. In this way the austenite inherits the manganese content of cementite and is chemically stabilised. A treatment consisting of a two-step annealing has been examined. In the first step, soft annealing, an Mn-enriched cementite dispersion in ferrite is formed. In the second step, intercritical annealing, austenite nucleates on the cementite particles, which are consumed to form austenite. It was experimentally determined that this austenite has been enriched in manganese and carbon and, therefore, is stabilised. The conversion reaction is followed by the conventional austenite nucleation at ferrite grain boundaries. This austenite is lean in manganese and is not stable. The net effect of the two-step annealing treatment is a significant austenite stabilisation relative to simple intercritical annealing, indicating a potential for enhanced TRIP effects in this class of steels.

The identity of carbide precipitates resulting from autotempering in as-quenched 3. 5 NiCrMoV rotor steel has been rigorously examined. Tempering for 5 hrs at 500 degree C produces only marginal coarsening of Widmanstaetten carbides, but results in the appearance of additional carbides at the boundaries of microtwins. Carbides in the tempered steel are readily identified as cementite, and have provided an understanding of the relationship between the diffraction patterns produced by double difraction and cementite at microtwin boundaries. This relationship is found in some cases to result in coincidence of the two types of pattern, so that cementite spots are obscured by double diffraction spots. This partly explains the lack of unequivocal cementite spots in the as-quenched steel. Dark field imaging and statistical analysis have shown that in the tempered steel, in some of the diffraction patterns which have contributions from both double diffraction and cementite, the contribution from cementite is major. By contrast, the contribution to such patterns in the as-quenched steels is minor.

Unter „Wachsen” des Guseisens versteht man eine auf verschiedene erorterte Ursachen zuruckzufuhrende unerwunschte Volumenzunahme des Guseisens bei Einwirkung hoherer Temperaturen. Mit dieser Eigenschaft haben sich zahlreiche Forscher beschaftigt, deren Meinungen nach hemmenden, neutralen und fordernden Einflussen zusammengefast dargelegt wurden. Bei der Behandlung des Problems sind im einzelnen folgende Kennzeichen der Guseisensorten und Einwirkungen auf diese zu berucksichtigen: Chemische Zusammensetzung, der Carbidzerfall, die Oxydations durch Feuerungsgase und Wasserdampf, Druck oder Oxydation der im Guseisen eingeschlossenen Gase, die Graphitteilchengrose, das besondere Verhalten von weisem ledeburitischem Guseisen, die Dichte, Einwirkungen zunehmender Temperaturen, Schmelzverfahren und Gattierungen, Vakuumeinflusse, Oberflachenbearbeitung, Spannungen und Wirkungen sich stark ausdehnender Einschlusse, z. B. Gase und Oxyde. Von entscheidendem Einflus ist der Zementit-(Carbid)-zerfall und um wenigstens diesen auszuschalten, empfiehlt sich die Verwendung durch Gluhen ferritisierter Guseisensorten, die aus erorterten Grunden durch Gattierungsmasnahmen erzeugten ferritischen Guseisen mit ihrem zu groben Graphit uberlegen sind, weil letztere das Eindringen korrodierender, das Wachsen fordernder Mittel begunstigt. Bei starr mit anderen Werkstucken fest verschraubten, hoheren Temperaturen ausgesetzten Guseisen-Werkstucken hat sich dieses Gluhen mit Uberfuge instabiler carbidhaltiger Guseisengefuge in den stabilen Ferrit und Graphit-Gefugezustand praktisch recht gut bewahrt. “Swelling” of cast iron – Its causes, and a remedy „Swelling” of cast iron is the undesirable increase in volume, due to a number of causes here discussed, of cast iron exposed to high temperatures. The phenomenon has been investigated by many research workers. Their opinions are summarized, distinguishing between inhibiting, neutral and promoting influences. In dealing with the problem, account must be taken, in particular, of the following characteristics of the cast iron, and of the influences acting on it: — Chemical composition, carbide disintegration, oxidation by flue gases and steam, pressure or oxidation of the gases occluded in the cast iron, size of the graphite particles; the special behaviour of white Ledeburite cast iron, density, effects of increasing temperatures, smelting and charging, vacuum influences, surface treatment, stresses and effects of markedly expanding occlusions, e. g. gases and oxides. Of decisive influence is the cementite (carbide) disintegration. To eliminate at least this influence, it is recommended to use cast iron which has been ferritised by annealing. For reasons explained here, this type of cast iron is superior to ferritic cast iron obtained by charging control where the coarse graphite favours the penetration of corrosive agents which promote swelling. With cast iron components which are firmly screwed to other parts and exposed to high temperatures, this annealing process, causing the transition from unstable cast iron structure with carbide contents to stable ferrite and graphitic structure, has been found very successful in practice.

Mit Hilfe einer Mikrokapillarmethode in Verbindung mit gleichzeitiger metallographischer Beobachtung wurden mit einer Potentialsonde in alkoholischen Sauren die Oberflachenpotentiale von Roheisen, CrNi-Stahl 188, 17% Cr-Stahl (Schweisnaht) und einer AlCuLegierung bestimmt. Dabei konnte Zementit von Ledeburit, nicht hingegen von Austenit unterschieden werden. Beim Lochfras von 188 Stahl nimmt das Potential linear mit der Lochtiefe ab. Das Auftreten von Potentialminima in der Schweisnaht ferritischer Stahle ist ein Indiz fur das Auftreten von interkristalliner Korrosion in dem betreffenden Medium. In AlCuLegierungen wirken die bei etwa 150 °C entstehenden Ausscheidungen von CuAl2 an den Korngrenzen als Anode und fuhren dadurch zu interkristalliner korrosion. Surface potential profiles of metals Using a microcapillary method in connection with simultaneous metallographic observation surface potential profiles have been determined with the potential probe in alcoholic acid solutions on cast iron, CrNi aciers steels 188, Cr steel with 17% Cr (welded) and an AlCu alloy. It was possible to distinguish cementite from ledeburite, not however, from austenite. The potential of 188 steel under pitting conditions decreases as a linear function of pit depth. The appearance of potential minima in a weld of ferrite steels is evidence of a intercrystalline corrosion in that particular medium. The precipitation of CuAl2 in AlCu alloys at 150 °C at the grain boundaries forms an element with the grain boundary as the anode giving rise to intercrystalline corrosion.