Castings Vs Forgings

Relative Properties

WELDABILITY :

Steel castings tend to have better weldability than steel forgings.

PART GEOMETRIES :

Steel castings lend themselves more easily to complex shapes than do steel forgings.

CHEMICAL REQUIREMENTS :

Unique chemistries tend to be better (less expensively produced) with steel castings. Also, the class of steels commonly referred to as “work-hardenable steels” (13% Mn) are not forgeable, but are readily made in a casting.

MECHANICAL PROPERTIES :

Steel castings are ISOTROPIC - meaning “similar properties in all directions”. Steel forgings are ANISOTROPIC - meaning “similar properties in the direction of flow’’. Thus, in the direction of flow (material deformation), a steel forging’s strength is highest along its longitudinal axis, and decreases in the transverse direction. Whereas, in a steel casting, the properties are similar in all directions.

CORROSION RESISTANCE :

In certain stainless steels, castings tend to have better corrosion resistance than equivalent forgings this is due to controlled amounts of ferrite present in castings.

WEIGHT :

ISteel castings are almost always lighter their forged counterparts “redesign from forgings to castings usually results in substantial savings in weight”. For example - a forged cannon muzzle brake weighed 600 lbs; this same part as a casting weighed 400 lbs. (and lasted over three times longer).    
Advantages of Castings
STEEL CASTINGS WILL TEND TO HAVE THE ADVANTAGE OVER EQUIVALENT STEEL FORGINGS WHEN ANY OF THE FOLLOWING INSTANCES OCCUR:

An unusual chemistry is required (i.e., a chemistry other than that which is the norm for steel mills)

The part being considered is relatively large or has complex geometry.

Stresses to be applied to the part are multi-axial.

The material call-out is for a high manganese (approximately 13%), work-hardenable steel.

Minimal set-up and tooling costs are a factor

Sources of Information   “CASTINGS vs FORGINGS - A REALISTIC EVALUATION”, Malcolm Blair, Raymond    Monroe, SFSA “STEEL CASTINGS HANDBOOK”, 5th Edition, SFSA “FORGING HANDBOOK”, Forging Industry Association, ASM “WELDABILITY of CAST STEELS”, Literature Review, SFSA Special Report # 21

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