This NASA component for the space shuttle crawler transporter, produced with modified 4320 steel alloy via V-process casting, met reduced surface hardness requirements while maintaining high material strength when compared to its previous design.


such as salt water and chemical process- ing, require high-alloy stainless steels or nickel-based alloys. Generally, higher contents of chromium and molybdenum are needed as the environment becomes more severe. Corrosion-resistant materi- als heavily depend on the end-use envi- ronment for selecting the correct alloy; thus, a metallurgist should be consulted. Wear materials are found in ASTM A128, A351, A532, A743, A744, A890 and A494. Carbon or alloy steels may be used in less severe environments.


Keys to Steel Use With cast steel, engineers can design com-


ponents to increase different performance characteristics, such as corrosion resistance and wear resistance, through alloying and heat treatment. Mechanical properties, such as strength and elongation, also can be ad- justed. When purchasing parts, supplying a part design with material and requirements is important, and material should be des- ignated with a specification and grade (i.e. ASTM A 27/A 27M-95 Grade 60-30 Class 1). Requirements should call out both the test method and acceptance criteria specifi- cations. Mechanical properties typically are obtained from separately cast test bars. Designers should observe three keys


to selecting the right steel casting alloy for optimized performance and cost. One, utilize the geometry of the steel casting to uniformly carry the loading. Two, start with carbon steel for most applications, modify the heat treat- ment and then add alloying elements to improve properties. Three, know the design limit for an application and work with a metalcasting facility to design the part and select a material.


METAL


For more information, consult “Steel Casting Handbook,” Malcolm Blair and Tom Stevens, 6th


edition, 1995; “Specifying Steel Cast- ings—Keeping Alloy Composition in Mind,” J. Carpenter and B. Hanquist, ECS Fall 2001, p. 41-44; and the Steel Founders’ Society of America web site at: www.sfsa.org.


26 Metal Casting Design & PurChasing 2010 Casting sourCe DireCtory


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