عنوان

Superplasticity in ultrahigh carbon steels and their laminates

TLpq303891933

انگلیسی

Superplasticity in ultrahigh carbon steels and their laminates

[Thesis]

H.-C. Tsai

O. D. Sherby

Stanford University

1990

252

Ph.D.

Stanford University

1990

This dissertation is centered on the subject of superplasticity in Ultrahigh Carbon Steel (UHCS) and in laminated composites based on ultrahigh carbon steel. The first topic is on understanding the mechanical behavior of ultrahigh carbon steels containing a large amount of aluminum. The concentration of aluminum is in the order of 10 to 14 weight percent. A principal finding was the attainment of Newtonian-viscous behavior, i.e. ideal superplasticity, at high temperature for the UHCS-10Al. This result can be quantitatively explained by a deformation model based on a grain boundary sliding process accommodated by slip. The results obtained in the present study, and the accompanying proposed model predict that ideal superplastic flow (n = 1) can be achieved in fine-grained Class I solid solution alloys at sufficiently high temperatures. It is shown that the UHCS-high Al are exceptionally oxidation resistant and can be processed to achieve high tensile ductility at room temperature. In the present investigation the superplastic behavior of UHCS laminated composites containing non-ferrous metallic materials are studied. Brass and aluminum bronze are the two non-ferrous components that were investigated. It is shown that high strain rate sensitivity can be achieved in such laminated composites at elevated temperatures. The stability of interfaces between dissimilar metallic materials, however, is shown to play an important role in establishing desirable superplastic properties in these materials. The third topic is on a study of UHCS containing 1.8 weight percent carbon which is nearly the maximum solubility of carbon in austenite. Processing methods were intentionally developed to create surface markings resembling the damask observed in ancient Damascus steel weapons. The basis for this achievement centers on the development of ultrafine structures which consist of submicron spheroidized particles of carbides and coarse spheroidized discontinuous carbide networks in a very fine-grained ferrite matrix (0.5-1.0 mum diameter). Such fine grain size UHCSs not only exhibit superplasticity at temperatures near the A temperature but also show improved strength and remarkable ductility over conventional steels at ambient-temperature. (Abstract shortened with permission of author.)

Applied sciences

Materials science

steels

H.-C. Tsai

O. D. Sherby

p

[Thesis]

276903

a

Y