Anvils-7: Cast Steel vs Forgings

Castings or Forgings in the World of Anvils by Russell Jaqua

• a tool requiring a unique metal composition.
• a tool that is relatively large or complex.
• a tool which may experience multi-axial stresses over the course of its use.

Nimba Anvils uses a specialized 8640 alloy because of its proven toughness and deep-hardening capabilities. 8640 was developed during WWII due to a shortage of Chromium. 8640 is very similar in composition to the more familiar 4140 tool steel except that it has half the amount of Chromium and instead adds Nickel as part of the alloy recipe. It was discovered that the Nickel conferred much greater toughness and wear-resistance when used in conjunction with the Chromium.

Our foundry has a state-of-the-art induction furnace that allows us to mix small batches of 8640 to our precise specifications. Our alloy was designed for maximum hardenability without compromising toughness. This is the best combination of properties for our anvils.

LARGE AND COMPLEX SHAPE OF NIMBA ANVILS

In addition to the massive body that gives superior stability to our anvil design, we are dealing with a particularly wide face that tapers to very fine points in both the conical and pyramidal horns of the double-horn design. The features of this pattern allow tremendous flexibility in a variety of forging applications. To achieve the complexity of shape featured in our pattern, advanced casting methods are far more economical.

CONSISTENT MECHANICAL CHARACTERISTICS FOR MULTI-AXIAL STRESSES ON NIMBA ANVILS

The principle mechanical properties of interest to tool designers are strength, ductility and hardness. The strength of steel forgings lies in the longitudinal axis (or rolling direction used in the process of making the original bar.) However, tensile strength, elongation, and impact properties decrease in the transverse and axial directions. Thus, forgings are anisotropic, i.e. exhibiting different values of a property in different directions. For equivalent alloys, the ductility and impact strength of steel castings generally lie midway between the longitudinal and tranverse values of steel forgings. Additionally, in steel castings, the metal is isotropic, with similar properties in all directions. Thus castings provide more consistent properties in all three axes of possible tool stress. It has been postulated that the inconsistency of wrought steels may be related to the elongation of inclusions. The needle-like inclusions in wrought steels appear to be more likely sites for crack initiation than the round inclusions in casting steels. See Steel Founders' Society of America website article, "Castings or Forgings: A Realistic Evaluation" for more information at:
www.sfsa.org/sfsa/pubs/cvf/ecs.html.

Finally, Nimba Anvils are solid steel castings that are heat-treated as a whole. The anvil is not made in several parts that are welded together as is the case with modern "forged" anvils. Heat treatment is done to Rockwell 50 and the hardness penetrates the anvil on all sides. Thus, the Nimba Anvil provides tremendous structural integrity and consistent properties of toughness and hardness.

Some of our preference for forged comes from hundreds of years of literature telling us forged is better, from an age when forged WAS better. This attitude almost borders on prejudice for most of us that grew up reading the literature of that era. I admit to having that prejudice. It is hard to shake.

However, my first anvil was a Swedish Kohlswa cast steel anvil. It had been sorely abused by its first owner and had serious chips out of the corners of one side that could have only been made by heavy sledges. A similar sized wrought iron body steel faced anvil may have fared a little better but these are no longer manufactured and probably will never again. My prejudice for forgings says a forged steel anvil might have done better.

Currently my "BIG" shop anvil is a 300 pound (135kg) Kohlswa, another cast steel anvil. It has some minor chipping on the edges but also has some mushrooming. Both it would seem are to be expected in used anvils. My second shop anvil is a 200 pound (90kg) Hay-Budden. All of my anvils have been used anvils and the choice of brand or type was never completely in my control. They were what was available at a given sale at the moment. I've had several Hay-Buddens, a Peter Wright, several Mouse Hole, and two Kohlswas and for a brief period a NEW Peddinghaus.

The distance the chipping runs down the side of an anvil is more pronounced in cast steels due to that isotropic structure that is praised above. This lack of "grain" is what makes a good flint chip with controlability in all directions. Chips in a cast steel anvil are very sinilar to presure flakes in flint. Good forged or rolled steel is more resistant to chipping in this one area. Or at least the chips do not run as far. However, forged anvils do not necessarily have the proper grain direction nor is it as predictable as in a rolled piece of steel. In this regard a fabricated anvil MAY be better than both forged or cast.

The important thing to keep in mind is that the quality of materials and heat treating are more important than cast vs. forged. There are both bad castings and bad forgings. The best of both perform very nearly alike.