The bake‐hardening behaviour of a deep drawing steel sheet was investigated. Aging experiments after different prestrains were carried out in the temperature range from 50 to 180°C. The change of mechanical properties, especially the increase in yield stress, was measured by tensile tests. It was found that the increase in the yield stress by simulated baking treatment occurs in two successive steps. It is assumed that the first rise is based on the Cottrell‐effect and the further strengthening in the second step is caused by the precipitation of coherent carbides. A kinetic interpolation‐model of the bake‐hardening effect is introduced and this allows a description of the experimental data and a calculation of the bake‐hardening behaviour.
The microstructures of three steels with metastable austenite with mass contents of 10‐14 % Cr, 10‐15 % Mn and O.1‐0.35 % C were optimized by a simulation of the cavitation load. Results of cavitation tests show that the microstructure should be fine grained, to avoid the arise of cracks in the early stages. The materials were pretreated by a thermomechanical treatment. Criteria for a selection were the mechanical properties and the microstructure. According to the results a steel with mass contents of 13 % Cr, 10 % Mn and O.35 % C (X 35 CrMn 13 10) should have the best cavitation resistance. In this steel a deformation of 400 °C produces a dislocation network that forces a transformation of austenite to very fine martensite plates during cavitation and gives a smooth abrasion. The cavitation resistance of steel X 35 CrMn 13 10 in a pretreated condition is in the range of published values of a Steinte 6B, but the production of the steel is more versatile and less expensive than that of a Stellite.
For the calculation of the transformation of steels during continuous cooling a new method is proposed. For isothermal transformation the temperature dependence of 1% and 99% transformation of austenite is described by a function which can well be fitted to measured values. This function allows an extrapolation beyond the measured values giving good agreement between calculated and measured TTT-diagrams. For continuous cooling it is possible to calculate the transformation below Ms. The agreement between calculated and measured values of the volume fractions of different microstructural constituents at room temperature after continuous cooling is good. Eine verbesserte Berechnung des Umwandlungsverhaltens von Stahlen. Fur die Berechnung der Umwandlung in Stahlen wiihrend kontinuierlicher Abkuhlunq wird ein neues Verfahren vorgeschlagen. Die Temperaturabhiingigkeit der isothermischen Umwandlung des Austenits wird fur 1% und 99% umgewandelte Menge durch eine Funktion beschrieben, die sehr gut den MeBwerten angepaBt werden kann. Diese Funktion ermoqlicht eine Extrapolation uber MeBwerte hinaus und liefert eine gute Obereinstimmung zwischen gemessenen und auf diese Weise berechneten Zustandsschaubildern fur isothermische Umwandlung. Bei kontinuierlicher Abkiihlunq ist eine Berechnung der Umwandlung unterhalb M s rnoqlich. Die Obereinstimmung zwischen berechneten und gemessenen Volumenanteilen der einzelnen GefUge bei Raumtemperatur nach kontinuierlicher Abkuhlung ist gut.
For the general calculation of the transformation of steels the transformation diagram for isothermal transformation must be known. It is described, how from dilatometric measurements with continuous cooling the transformation at a constant temperature can be calculated. To do this, the simplex method must be used as iteration process to achieve sufficient precision. Even when measuring data are scattered around an ideal value by ± 5% the transformation diagram for isothermal transformation can be calculated with considerable accuracy. Berechnung des ZTU-Schaubildes fur isothermische Umwandlung aus Dilatometer-Messungen mit kontinuierlicher Abkuhlung. Fur die allgemeine Berechnung des Umwandlungsverhaltens von Stahlen ist die Kenntnis des ZTU-Schaubildes fur isothermische Umwandlung erforderlich. Es wird -zunachst fur ein Gefuqe -eine M6glichkeit gezeigt, aus Dilatometer-Messungen mit kontinuierlicher Abkuhlunq das Umwandlungsverhalten bei isothermischer Temperatur-Zeit-FOhrung zu berechnen. HierfOr muB als Iterationsverfahren die Simplex-Methode eingesetzt werden, um ausreichende Genauigkeiten zu erzielen. Auch bei einer Streuung der MeBwerte von ±5% urn einen idealen Wert kann das ZTU-Schaubild fiir isothermische Umwandlung mit guter Genauigkeit berechnet werden.
Karbidmengenbestimmung mit dem quantitativen Fernsehmikroskop (QFM). Automatische Registrierung der örtlichen Karbidverteilung. Möglichkeiten sur Gewinnung einer objektiven Kennzahl der Karbidzeiligkeit. Karbidgehalte von weichgeglühten bzw. gehärteten Werkzeugstahlen.
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