Structures and tempering behavior of rapidly solidified high-carbon iron alloys
- PDF / 1,349,507 Bytes
- 8 Pages / 597 x 774 pts Page_size
- 1 Downloads / 175 Views
I.
INTRODUCTION
IT is
expected that rapidly solidified high-carbon iron alloys could reveal a fine structure in which solute elements such as carbon are retained in solution at a high concentration due to the rapidness of cooling rate. Ruhl and Cohen m have reported that the structure of highcarbon iron alloys, which are rapidly solidified through a splat quenching from liquid state, consists of metastable phases of e phase and austenite. The e phase, which was originally observed in materials treated under high pressures, [2] has a hexagonal close-packed structure and a large amount of carbon in solid solution ranging from 3.8 to 4.8 pct at atmospheric pressure and temperature. The authors t3-6] have already shown that coatings of high-carbon iron alloys obtained by thermal spraying have e phase in the as-solidified condition and decompose only slightly upon tempering at temperatures as high as 800 K, provided that the alloy contains carbide formers of chromium and/or molybdenum. On tempering above this temperature, the metastable phases decompose to very fine carbide and ferrite, which causes the coatings to achieve a fairly high hardness. Thus, the rapidly solidified high-carbon iron alloys can be applied as wearresistant coatings for high-temperature service. In this study, the goal was to obtain metastable phases such as e phase and austenite through rapid solidification by means of a single roller method which brought about relatively homogeneous structures. The metastable phases obtained in this manner also have a large amount of carbon in solid solution so that there is a possibility for the carbide precipitation structure of these alloys to be very refined upon decomposition, giving rise to a high hardness at high temperatures. Furthermore, only a few reports on tempering behavior of rapidly solidified high-carbon iron alloys have been offered. [7.8,9]Also, the effect of carbide formers on the decomposition of metaK. KISHITAKE, Professor, and H. ERA, Associate Professor, are with the Department of Materials Science and Technology, Faculty of Engineering, Kyushu Institute of Technology, Kita-Kyushu 804, Japan. F. OTSUBO, formerly Graduate Student, Kyushu Institute of Technology, is Metallurgical Engineer, Sumitomo Metal Industries Ltd., Osaka, Japan. Manuscript submitted April 20, 1990. METALLURGICALTRANSACTIONSA
stable phases and the resulting hardness has not been clarified yet. The present work was carried out to investigate how the carbide formers and carbon in rapidly solidified high-carbon iron alloys can affect the decomposition behavior and the hardness change. II.
EXPERIMENTAL PROCEDURE
The high-carbon iron alloys were prepared by melting in an ordinary way, from electrolytic iron, ferro-silicon (75 pct Si), ferro-chromium (60 pet Cr), and ferromolybdenum (60 pct Mo) alloys and a graphite electrode. The alloys were remelted in a silica capsule with a nozzle size of 1 x 5 mm in an argon atmosphere. The remelted alloys were solidified in the form of ribbon 50to 100-/~m thick by a single roller
Data Loading...
