Mechanical Properties of Rapidly Solidified High Carbon Iron Base Alloys
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MECHANICAL PROPERTIES OF RAPIDLY SOLIDIFIED HIGH CARBON IRON BASE ALLOYS D. BURCHARDS, K.U. KAlNER, B.L. MORDIKE Institut fUr Werkstoffkunde und Werkstofftechnik, Technische Universitdt, Agricolastr. 2, 3392 Clausthal-Zellerfeld, FRG ABSTRACT High carbon content iron base alloys (2-4 wt%) with various alloying additions ,eg., Cr, Ni, Si or Te were produced in powder form by water atomisation. Depending on the alloying addition the powder particles solidify, microcrystalline with either dendritic or cellular microstructures with supersaturated solid solution and eutectic. The proportion of carbide is dependent on the composition and atomizing conditions. The powder, after suitable preparation, was consolidated by extrusion or hot isostatic pressing. The consolidation behaviour of the powders is influenced by the composition and particle size distribution. The microstructures and hardness values of the powder in the as quenched state are compared with those of the consolidated state with particular emphasis on the thermal stability. The mechanical properties of extruded powders are compared with those for hot isostatically pressed. INTRODUCTION During atomization alloys solidify in metastable states [11. They can be characterized as follows: finely dispersed microstructures, high degree of supersaturation of matrix, metastable phases and homogeneous distribution of phases and elements. The as-quenched powder is then extruded or hot isostatically pressed to semi finished products and this can lead to changes in the microstructural state. Alloying elements can be chosen so that the fine microstructure is retained producing materials with good properties [2]. Such materials possess high strength and at the same are very ductile. An alloy with 3% C and 1.5% Cr exhibited superplastic behaviour at 700'C [ 3,4].
EXPERIMENTAL DETAILS The powders were prepared using a water atomizer from Davy McKee, Sheffield, Table I. The liquid alloy stream was atomized with a 20 MPa water jet producing powders d = 38 pm. After drying in vacuum the powder was classified 9y sieving and air classifying into the particle sizes 10 p'm, 20 4m, 35 4m, 70 4m. Billets for extrusion were prepared by filling steel containers and cold compressing. The containers were evacuated and sealed and extruded at temperatures between 860 and 920 0 C at a pressure of 780 MPa. For comparative purposes some alloys were hot isostatically pressed at Vacuum Generators, Hastings, England. The powder was again put into containers, sealed under vacuum and consolidated under 200 MPa at 675'C for 5 h. Metallographic and mechanical testing was carried out on the compacted rods.
Mat. Res. Soc. Symp. Proc. Vol. 58.
1986 Materials Research Society
442
TABLE I
Chemical Analysis of the Alloys Prepared
No. C Si Mn P 5 2.60 2.03 0.12 0.011 6 3.40 1.98 0.08 0.016 8 2.76 0.64 0.48 0.017 10 2.65 0.60 0.57 0.014 11 3.20 0.89 0.59 0.035 12 3.80 0.17 0.03 0.025 13 3.70 0.18 0.03 0.026 14, 3.70 0.20 0.04 0.022 15 3.85 0.19 0.03 0.025 * inoculated with 0.01% Te
S 0.008 0.007 0.1
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