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The effect of prior austenite grain size on the machinability of a pre-hardened mold steel. : Measurement of average grain size using experimental methods and empirical models. / Machinability of pre-hardened mold steels and the effect of prior-austenite grain size,hardness,retained austenite content and effect of work hardening. : Chemical etchants used for revealing prior austenite grains.Irshad, Muhammad Aatif January 2011 (has links)
The use of pre-hardened mold steels has increased appreciably over the years; more than 80% of the plastic mold steels are used in pre-hardened condition. These steels are delivered to the customer in finished state i.e. there is no need of any post treatment. With hardness around ~40HRC, they have properties such as good polishability, good weldability, corrosion resistance and thermal conductivity. Machinability is a very important parameter in pre-hardened mold steels as it has a direct impact on the cost of the mold. In normal machining operations involving intricate or near net shapes, machining constitutes around 60% of the total mold cost. Efforts are underway to explore every possible way to reduce costs associated with machining and to make production more economical. All the possible parameters which are considered to affect the machinability are being investigated by the researchers. This thesis work focuses on the effect of prior austenite grain size on the machinability of pre-hardened mold steel (Uddeholm Nimax). Austenitizing temperatures and holding times were varied to obtain varying grain sized microstructures in different samples of the same material. As it was difficult to delineate prior-austenite grain boundaries, experimental and empirical methods were employed to obtain reference values. These different grain sized samples were thereafter subjected to machining tests, using two sets of cutting parameters. Maximum flank wear depth=0.2mm was defined for one series of test which were more akin to rough machining, and machining length of 43200mm or maximum wear depth=0.2mm were defined for second series of tests which were similar to finishing machining. The results were obtained after careful quantative and qualitative analysis of cutting tools. The results obtained for Uddeholm Nimax seemed to indicate that larger grain sized material was easier to machine. However, factors such as retained austenite content and work hardening on machined surface, which lead to degradation of machining operations were also taken into consideration. Uddeholm Nimax showed better machinability in large grained samples as retained austenite(less than 2%) content was minimal in the large grained sample. Small grained sample in Uddeholm Nimax had a higher retained austenite (7+2%) which resulted in degradation of machining operation and a lesser cutting tool life.
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Oberflächenfeinwalzen von Förderelementen auf ProfilwalzmaschinenForke, Erik 10 September 2021 (has links)
Es wird untersucht, ob in Schneckenextrudern verwendete Förderelemente aus Stahl durch das
Oberflächenfeinwalzen der schraubförmigen Mantelfläche gleichzeitig geglättet und verfestigt
werden können. Steigungsprofile, zu denen auch die Förderelemente zählen, werden bislang oft
nach der Hauptformgebung wärmebehandelt und im harten Werkstoffzustand spanend
feinbearbeitet. Formgebung, Wärmebehandlung und Feinbearbeitung sind voneinander
getrennte Prozessschritte. In dieser Arbeit besteht das Ziel, die Verfahrenseingangsgrößen für
die Kombination aus Formgebung und definierter lokaler Werkstoffverfestigung beim Walzen
zu erarbeiten. Zu diesem Zweck werden sowohl am Steigungsprofil selbst als auch an einem
davon abgeleiteten Rotationsprofil simulative, experimentelle sowie analytische
Untersuchungen durchgeführt. Es werden geometrische, kinematische und werkstofftechnische
Gesichtspunkte beleuchtet. Aufbauend auf dem Vergleich zwischen Simulationsergebnissen
mit der Finite-Elemente-Methode und im Versuch ermittelten Daten werden
Haupteinflussfaktoren auf die geometrischen Abweichungen sowie die Härtesteigerung in der
Bauteilrandschicht ermittelt. Mit Hilfe eines neu entwickelten sensorischen Werkstückträgers
wird die Drehbewegung des Werkstücks erfasst. Aus den analytischen Betrachtungen wird
schließlich ein Modell zur qualitativen Beschreibung des Walzkraftverlaufs abgeleitet, das zur
Vorauswahl von Verfahrenseingangsgrößen genutzt werden kann. Im Ergebnis wiederholter
Messungen wird deutlich, dass mit der geometrischen Gestaltung einer Walzvorform gezielt
Einfluss auf Umformgrad und damit Verfestigung im Bauteil genommen werden kann. An den
untersuchten hochfesten korrosionsbeständigen austenitischen Stählen ist eine Verdopplung der
Halbzeughärte möglich. Die beim Spanen der Vorformen auftretenden Formabweichungen
haben großen Einfluss auf die Beschaffenheit der Zielgeometrie sowie die erzielbare
Härtesteigerung. Durch Kenntnis der realen Werkstückdrehbewegung während des Walzens
lassen sich Rückschlüsse auf die Werkzeuggestaltung und die Walzparameter ziehen. Aufgrund
der Untersuchungsergebnisse wird das Verfahren für die Anwendung an korrosionsbeständigen
Bauteilen mit mittleren Verschleißschutzanforderungen empfohlen.:1 Einleitung
2 Stand der Technik
3 Zielstellung der Arbeit
4 Beschaffenheit der Werkstücke und Werkzeuge
5 Modellbildung mit Hilfe der FEM
6 Versuchsvorbereitung und Eingangsgrößen
7 Vergleich der Verfahrenskenngrößen in Simulation und Experiment
8 Analytisches Modell zur qualitativen Vorhersage der Walzkraft
9 Bauteileigenschaften nach dem Walzen
10 Zusammenfassung und Ausblick / A combined surface burnishing and mechanical hardening process for steel conveying elements
in screw extruders is examined. Helical profiles, that also comprise conveying elements, are
often heat treated after shaping followed by fine processing. Shaping, heat treatment and fine
processing are sequential process steps. This work deals with the investigation of rolling process
parameters that enable both low geometrical deviations and high work hardening of the screw
material. For this purpose, helical and axisymmetric profiles are analyzed with simulative,
experimental and analytical methods. The investigations highlight geometrical, kinematical and
material-related aspects. The main factors with influence on screw geometry and hardness
increase in the component subsurface are investigated by means of the comparison between
simulative and experimental results. An intelligent workpiece carrier is applied to analyze the
part rotation. Based upon analytical observations, a calculation model for the prediction of the
rolling force curve over workpiece rotation is developed. This model supports predefining the
process input variables. Repeated measurements indicate that the geometrical design of the
machined preforms allows for individual strain and hence hardness distributions in the part
subsurface. Hardness can be doubled in the investigated corrosion resistant austenitic high
strength steels. Form deviations of the part and hardness increase are strongly dependent on
geometrical deviations of the preform. Knowledge of part rotation during rolling enables to
draw conclusions for tool design and rolling parameters. Based on the results it is suggested to
apply the rolling procedure to parts in environments which require high corrosion resistance
and moderate wear resistance.:1 Einleitung
2 Stand der Technik
3 Zielstellung der Arbeit
4 Beschaffenheit der Werkstücke und Werkzeuge
5 Modellbildung mit Hilfe der FEM
6 Versuchsvorbereitung und Eingangsgrößen
7 Vergleich der Verfahrenskenngrößen in Simulation und Experiment
8 Analytisches Modell zur qualitativen Vorhersage der Walzkraft
9 Bauteileigenschaften nach dem Walzen
10 Zusammenfassung und Ausblick
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強ひずみ加工法による銅合金の結晶粒微細化機構に関する研究 / キョウヒズミ カコウホウ ニヨル ドウゴウキン ノ ケッショウリュウ ビサイカ キコウ ニカンスル ケンキュウ浅野 真由, Mayu Asano 18 September 2021 (has links)
FCC組織を有する純金属と合金において強ひずみ加工法の1つである側方押出し加工(ECAP)法を用いて超微細結晶材を作製し,ECAPの各段階における力学特性と微細組織を調査した.微細組織形成過程におけるセル壁の形成から結晶粒界の形成に着目し,積層欠陥エネルギーと固溶原子による固溶強化の効果の観点から,強ひずみ加工における加工硬化ステージの推移と微細組織形成の関係を議論した. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University
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Strengthening Mechanisms in Microtruss MetalsNg, Evelyn 18 December 2012 (has links)
Microtrusses are hybrid materials composed of a three-dimensional array of struts capable of efficiently transmitting an externally applied load. The strut connectivity of microtrusses enables them to behave in a stretch-dominated fashion, allowing higher specific strength and stiffness values to be reached than conventional metal foams. While much attention has been given to the optimization of microtruss architectures, little attention has been given to the strengthening mechanisms inside the materials that make up this architecture. This thesis examines strengthening mechanisms in aluminum alloy and copper alloy microtruss systems with and without a reinforcing structural coating. C11000 microtrusses were stretch-bend fabricated for the first time; varying internal truss angles were selected in order to study the accumulating effects of plastic deformation and it was found that the mechanical performance was significantly enhanced in the presence of work hardening with the peak strength increasing by a factor of three. The C11000 microtrusses could also be significantly reinforced with sleeves of electrodeposited nanocrystalline Ni-53wt%Fe. It was found that the strength increase from work hardening and electrodeposition were additive over the range of structures considered. The AA2024 system allowed the contribution of work hardening, precipitation hardening, and hard anodizing to be considered as interacting strengthening mechanisms. Because of the lower formability of AA2024 compared to C11000, several different perforation geometries in the starting sheet were considered in order to more effectively distribute the plastic strain during stretch-bend fabrication. A T8 condition was selected over a T6 condition because it was shown that the plastic deformation induced during the final step was sufficient to enhance precipitation kinetics allowing higher strengths to be reached, while at the same time eliminating one annealing treatment. When hard anodizing treatments were conducted on O-temper and T8 temper AA2024 truss cores, the strength increase was different for different architectures, but was nearly the same for the two parent material tempers. Finally, the question of how much microtruss strengthening can be obtained for a given amount of parent metal strengthening was addressed by examining the interaction of material and geometric parameters in a model system.
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Strengthening Mechanisms in Microtruss MetalsNg, Evelyn 18 December 2012 (has links)
Microtrusses are hybrid materials composed of a three-dimensional array of struts capable of efficiently transmitting an externally applied load. The strut connectivity of microtrusses enables them to behave in a stretch-dominated fashion, allowing higher specific strength and stiffness values to be reached than conventional metal foams. While much attention has been given to the optimization of microtruss architectures, little attention has been given to the strengthening mechanisms inside the materials that make up this architecture. This thesis examines strengthening mechanisms in aluminum alloy and copper alloy microtruss systems with and without a reinforcing structural coating. C11000 microtrusses were stretch-bend fabricated for the first time; varying internal truss angles were selected in order to study the accumulating effects of plastic deformation and it was found that the mechanical performance was significantly enhanced in the presence of work hardening with the peak strength increasing by a factor of three. The C11000 microtrusses could also be significantly reinforced with sleeves of electrodeposited nanocrystalline Ni-53wt%Fe. It was found that the strength increase from work hardening and electrodeposition were additive over the range of structures considered. The AA2024 system allowed the contribution of work hardening, precipitation hardening, and hard anodizing to be considered as interacting strengthening mechanisms. Because of the lower formability of AA2024 compared to C11000, several different perforation geometries in the starting sheet were considered in order to more effectively distribute the plastic strain during stretch-bend fabrication. A T8 condition was selected over a T6 condition because it was shown that the plastic deformation induced during the final step was sufficient to enhance precipitation kinetics allowing higher strengths to be reached, while at the same time eliminating one annealing treatment. When hard anodizing treatments were conducted on O-temper and T8 temper AA2024 truss cores, the strength increase was different for different architectures, but was nearly the same for the two parent material tempers. Finally, the question of how much microtruss strengthening can be obtained for a given amount of parent metal strengthening was addressed by examining the interaction of material and geometric parameters in a model system.
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