Structure and Consolidation Properties of Some Melt Extracted Steels
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STRUCTURE AND CONSOLIDATION PROPERTIES OF SOME MELT EXTRACTED STEELS J.V. Wood and C. Gagg Department of Materials Science, The Open University, Walton Hall, Milton Keynes MK7 6AA, England. ABSTRACT A range of Fe-Mn and Fe-Ni steels have been processed by melt extraction to give fibres and particulate. The consolidation and sintering performance of these alloys are presented. Densities of up to 95% can be achieved with hardnesses in the range 400-500 Hv while possessing grain sizes less than 20m. Salient features of the sintered structures are described and it is concluded that sintering of pre-annealed short fibres compares favourably with a more conventional approach using powders.
INTRODUCTION The amount of data reported for rapidly solidified crystalline steels has increased dramatically in the Dast three years, with most emphasis on commercial applications (1-4). However, there still appears a gap between these reports and more fundamental papers dealing with phase stability and structure (e.g. 5-7). It is the purpose of this paper to attempt to bridge this divide by considering the consolidation properties of some model alloys. In this investigation the technique of pendant drop melt extraction has been employed (8) to produce fine fibres which can subsequently be consolidated by traditional powder metallurgical methods. Initial results on some Fe-Cr steel (9), demonstrated that acceptable consolidates could be made by this route. The subsequent hardnesses of sintered and heat treated compacts of Fe-12%-Cr-C steels compared favourably with more complex chromium base die steels made by conventional methods. The structure of the present series of Fe-Mn and Fe-Ni alloys have been widely studied after rapid solidification (e.g. 5, 6, 11, 12). 1.
Experimental Details
1.1
Rapid Solidification Processing
Pre-alloyed ingots were processed by pendant drop melt extraction in a chamber which had been previously evacuated to 10-2 Pa prior to back-filling with inert gas. Semi-continuous clean fibres of between 30-iO0pm in diameter were produced by means of a sharp edged wheel. The compositions and structure of these alloys are given in Table 1. 1.2
Fibre Treatment
Semicontinuous lengths were chopped to between 1-3mm in length. Some of this particulate was subsequently ground to powder in a vibratory mill. In view of the initial hardness of the melt extracted product, a proportion of chopped fibres and powder was subsequently annealed at 9000 C for 3 hours followed by furnace cooling. Thus four types of particulate are referred to, viz: i) Chopped fibre ii) Annealed fibre iii) Ground powder iv) Annealed powder. These were then consolidated either in a uniaxial mechanical press or in cold isostatic press.
Mat.
Res.
Soc.
Symp.
Proc. Vol.
28 (1984)
OElsevier Science Publishing Co., Inc.
a
152
TABLE 1.
Composition and Structure of Melt Extracted Steels.
Alloy compositions in wt% (balance iron) Alloy No 1 2 3 4 5 6 7 1.3
Phases present in RS steels
C
Mn
Ni
V
0.1 0.1
19.3 19.4 20 19.5 -
16.o 22.5 20.4
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