Feeding and risering of high-alloy steel castings

Abstract

A more accurate, less conservative set of feeding distance (FD) and riser sizing rules is developed for high-alloy steel castings produced from alloy grades CF-8M, CA-15, HH, HK, and HP. These rules are designed to produce radiographically sound castings at 2 pct sensitivity. By comparing results between plate casting trials and the corresponding simulations of those trials, a relationship is shown to exist between a local thermal parameter known as the Niyama criterion and ASTM shrinkage X-ray level. This relationship is then used in an extensive set of casting simulations to numerically determine FDs for a wide range of casting conditions. It is shown that the FD rule developed in an analogous earlier study for carbon and low-alloy (C&LA) steels can also be used for these high-alloy grades, provided that the FD is modified by a multiplier that accounts for the high-alloy steel grade. In addition, it is shown that multipliers for superheat, sand mold materials, and the use of chills developed in the earlier work are also valid with these high-alloy steel grades. In comparison with previously published high-alloy FD rules, the present rules are shown to provide longer FDs (and hence higher casting yields) in most casting situations. This study also investigates riser sizing rules. It is determined that for open top risers, the previously published C&LA riser sizing rule is also valid for high-alloy steels. This rule is less conservative than existing high-alloy riser sizing rules, specifying smaller risers that produce higher casting yields. In addition, for vented blind top risers, it is shown that the previously published rules are also overly conservative.