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Open Access Thesis

Keywords

Iron -- Effect of temperature on; Materials at low temperatures;

Abstract

The objective of this study was to investigate impact properties of ASTM A897 Austempered Ductile Iron (ADI) grades 125/80/10, 150/100/7, 175/125/4, 200/155/1 and 230/185/- tested at sub-zero temperatures. Final results were compared to impact toughness of ferritic ductile iron (DI) grade 60-40-18 and pearlitic DI grade 100-70-03.

Two series of experiments were conducted: in the first series unnotched specimens of each ADI grade along with ferritic DI grade 60-40-18 and pearlitic DI grade 100-70-03 comparative samples were tested at temperatures of -40°C and -60°C. V-notched samples of ADI grade 1 and ADI grade 5 were tested in the second series at -40°C.

Complex methodology was utilized to study impact behavior and fracture mechanism of ADI at specified temperatures. Impact behavior was evaluated directly as Charpy impact toughness. Fracture surface morphology was analyzed using visual and stereoscopic microscope observation, and scanning electron microscopy (SEM) techniques. Bending angle methodology was used to quantitatively specify ductile constituent in specimens fracture and rupture mode.

Results obtained during this study showed that there is a general trend of decreasing impact toughness for all ADI grades as the testing temperature was decreased from room temperature to -60°C. Also, with the reduction of retained austenite content, the impact toughness of ADI was gradually reduced. However, the difference in impact toughness values was not so noticeable for low retained austenite containing ADI grade 5 at both room and sub-zero temperatures, as it was for ADI grade 1. As expected, the difference in impact toughness values of V-notched experimental specimens tested at -40°C was minimal.

The impact behavior of ADI grade 5 and ferritic DI grade 60-40-18 appeared to be more stable than that of ADI grades 1, 2, 3 and 4 and pearlitic DI grade 100-70-03 when the testing temperature was decreased. The impact toughness of ferritic DI grade 60-40- 18 was higher than that of ADI grades 1 and 2 at both -40°C and -60°C. ADI grade 4 and 5 had the level of impact properties higher than that of pearlitic DI grade 100-70-03 at both -40°C and -60°C.

Visual stereoscopic observations of ADI samples showed that all samples had fractures of light gray color, even though the difference in impact values was quite significant. The SEM study of fractured surfaces revealed that all ADI samples tested at both -40°C and -60°C had mixed ductile and quasicleavage rupture morphology type. With decreasing retained austenite content and ductility, the number of quasicleavage facets increased from ADI grade 1 to ADI grade 5. Testing temperatures applied in this research did not have significant influence on fracture morphology of ADI

Study of the bending angle showed that ductile constituent prevailed in fracture of ADI grades 1 and 2 samples and was 80% and 70% respectively. ADI grade 3 has intermediate ductile-brittle character of fracture with ductile-brittle ratio of approximately 50/50. ADI grades 4 and 5, and pearlitic DI grade 100-70-03 fractured mostly in brittle mode and ductile constituent was calculated as low as 30% and 15% respectively.

Obtained data may be used as a reference by designers and end users of ADI castings

Year of Submission

1999

Degree Name

Master of Arts

Department

Department of Industrial Technology

First Advisor

Yury S. Lerner

Comments

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Date Original

1999

Object Description

1 PDF file (39 pages)

Language

en

File Format

application/pdf

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