Lost Foam Casting Surface Alloying

In this paper, a novel surface alloying technique was developed in which a coatingfor surface alloying was pasted on an evaporative polystyrene pattern, thus a wear-resistant casting surface was formed during the pouring and solidification process onvacuum conditionFirstly, orthogonal tests were carried out to investigate the effects of the fac-tors, such as pouring temperature, alloy powder size , flux content and binder contenton surface alloying process of evaporative polystyrene pattern castings Ingredients ofthe coating were determined by the experiments simultaneously. On the basis, mi-crostructure and properties of the alloying layer were studied Lastly, the possibilityof non-binder surface alloying of evaporative polystyrene pattern castings was dis-cussed The main results were that:(1 ) A suitable coating for surface alloying consists of Cr-Fe powder with a diam-eter of 0. 127mm~ 0. l8lmm (l00wt. %), phenolic resin and plastics (2wt. %),the compound flux (l5wt. % ), CMC (0. 5wt. % ), water and some trace additives;(2) Among the factors acting on the process of surface alloying, pouring tem-perature is the most prominent, alloy powder size secondary, flux content the third,and binder content the least ;(3) Microstructure of the alloying layer is mainly composed of (Cr, Fe)7C3phase, (Fe,Cr)3C phase and a-Fe phase. With the increase of the distance from thesurface, Cr content and carbide content in the alloying layer decrease, and the car-bide is transformed from M7C3 to M3C gradually;(4) The thicker the casting thickness is, the more hypereutectic carbide exists inthe alloying layer. A little addition of RE can refine the carbide;(5) With the increase of the distance from the surface, the hardness of the al-loying layer decreases by degrees. After heat treatment, the hardness is higher ;(6) Wear-resistant property of the alloying layer is high, and 2. 8 times as highas that of normalized 45# steel ;(7) It is feasible that a surface alloying layer in evaporative polystyrene patterncastings be formed without binder.