Susceptibility of iron castings to heat absorption from an electric arc and to hardened-layer shaping
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10/30/03
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Susceptibility of Iron Castings to Heat Absorption from an Electric Arc and to Hardened-Layer Shaping ANTONI WLADYSLAW ORLOWICZ and ANDRZEJ TRYTEK Surface fusions were performed by the gas tungsten arc welding (GTAW) surfacing process on plate castings of spheroidal graphite cast iron with a travel speed from 200 to 800 mm/min. Their geometry and hardness were measured. Calorimetric measurments of the net heat input for the GTAW process have been conducted. A stepwise regression method was used to develop the relationship between GTAW process parameters and those of fusion geometry, microhardness, arc efficiency, and melting efficiency for the obtained data set.
I. INTRODUCTION
ANALYSIS of materials used in the machine building indicates a broad use of cast iron, which has both good casting characteristics and satisfactory operating properties. Not unimportant is also the fact that cast iron is one of the cheapest foundry materials. Iron castings are frequently required to be highly resistant to frictional wear. In the industrial practice, surface hardening of iron castings may be realized through introducing small additions of magnesium, bismuth, or tellurium (i.e., elements having a particularly strong effect on the creation of cementite in cast iron) into the surface layer of castings, the use of chills in a casting mold, or casting-surface fusion with a concentrated heat flux. In case of iron-casting surface hardening with the use of a concentrated heat flux, sudden heat removal from the molten pool to the cast iron substrate takes place immediately after concentrated heat-flux displacement, thus enabling starting of rapid crystallization of the fusion zone. Research found that the laser-fusion-refined surface layer of spheroidal graphite castings had 65 to 70 pct austenite and 16 to 20 pct cementite, while the remainder was martensite.[1] Besides, it was shown that, under suitable fusion process parameters, graphite underwent complete dissolution with consequential austenite enrichment with carbon (to 1.8 pct C). Thus, the results of a number of research works indicate that surface treatment of iron castings realized with the use of a concentrated heat flux creates conditions for rapid crystallization with the resulting structure, which should guarantee them high operating properties. Presently, a laser, electron beam, or electric-arc plasma are used as a heat source for the realization of rapid crystallization of surface-layer areas. In the recent period of time, gas tungsten arc welding (GTAW) has enjoyed more and more interest. Such factors as the low price of equipment and easy availability, as well as the lack of special requirements for the preparation of a heated surface, speak for its application.
ANTONI WLADYSLAW ORLOWICZ, and ANDRZEJ TRYTEK, are with the Department of Foundry and Welding Engineering, Technical University Rzeszów, 35-959 Rzeszów, Poland. Contact e-mail: zois@ prz.rzeszow.pl Manuscript submitted March 4, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
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