Clean Steel and Machinability.

Cleanliness of steel remains an important issue, as was evident among the seven presentations by the Steel Div. at the Casting Congress. Microporosity persists as a vital factor.

In the first panel discussion on clean steel, various methods for cleanersteel were suggested. Discussing parting lines, R. Duncan, Casteel Technical Service, recommended wide, thin cross sections, multiple ingates and bottom ingates, especially against a core. S. Kulkarni, ABC Naco, Inc., discussed pouring practices. In a designed experiment, he recorded a 60% improvement when adding aluminum and "blowing" down the carbon. Based on studies in an acid foundry, J. Griffin, Univ. of Alabama-Birmingham, indicated that silicon was the controlling deoxidizer with silicon dioxide governing the equilibrium of oxygen concentration at higher temperatures and silicon dioxide dominating at lower temperatures.

During another panel on nitrogen and hydrogen control, T. Oakwood, Professional Metallurgical Services, said that invisible nitrogen and hydrogen cause casting quality problems too.

When the mold cools faster, a nitrogen problem occurred while a slow cool resulted in a hydrogen problem, he said. To control hydrogen and nitrogen within the melting process, he suggested minimizing the holding, avoiding deoxidizing in the furnace, tapping fast and keeping the scrap and alloys as low as possible.

In their paper on the effect of abrasive inclusions on the machinability of cast steel (01-112), M. Murshed, E. Eleftheriou, R.D. Griffin and C.E. Bates, Univ. of AlabamaBirmingham, concluded that the basic melted steel had the lowest inclusion count and better machinability than all the acid melted steel. Hardness decreased with both the number and size of inclusions.