Forged rounds are some of the most common forgings made. With just two dimensions to protect, the round is also one of the easiest forgings to make.
Round forging consists of starting with billet or bar. The easiest way to estimate material needed for the round is to add the finishing allowances, which helps to guarantee the part can be machined from the gaurantee. In most situations, these allowances are 0.250" to 0.500" per side. For instance, if the guarantee needed is 4" Dia x 6" Long, then the forging size would be 4.5" Dia x 6.5".
Once the forging dimensions have been developed, a billet needs to be selected.
For optimum properties (to receive greatest benefit of forging process), you want a forging that has at least 25% work in it. Some companies will also indicate a MHWR or "Minimum Hot Working Ratio", which helps a forger to understand the total amount of work the piece has received since it was cast.
Calculate the total width, which is normally the diameter. For our example this dimension is 4.5" Dia, but we also need the work added. To add the work amount, we need the area of the finished round and add at least 25% to the area. This would be Ao=Af*1.333. Notice how we are adding 25% to the final area of the round? We must use the inverse of 3/4, which comes out 4 thirds or multiply final area by 1-1/3. So the pre-forging area we want is 15.9*1.333=21.19in^2. To get back to the radius, we must divide by PI, and then take the square root. SQRT(21.19/PI) = 2.59" Radius, which means we are looking for round or billet at least 5.25" Dia, as 5.18" Dia probably doesn't exist. We use this measurement as a minimum Diameter to match up billet or bar to use.
If you wish to calculate the amount of work the piece would see, it is fairly easy to calculate also - using the original area and the final area of the piece. The effective reduction for this piece would be original area minus the final area, all divided by the original area. Using our example it would be ( AoPI*r^2 - AfPI*r^2 ) / AoPI*r^2 = ( 21.19 - 15.9) / 21.19 = 25% Reduction.
Why do rounds need more work than blocks? Rounds have more on-die time, due to the rounding up of corners.
Superalloy rounds usually have demanding applications in nuclear, aerospace, defense environments. This means that once the forging is made, we usually need to test it for properties. Non-critical applications may only need a hardness verification that the material exhibits similar properties to known samples. Critical applications require a full mechanical test (destructive) that may also entail a stress rupture test to qualify the lot. If mechanical testing is required, a sample piece will be needed to submit for testing. Usually the specification that requires the testing indicates where the sample should be from, and the size of the samples needed. I mention this, as the material for a sample usually requires additional material, which can add to the overall length of the part being made - or in some cases another piece long enough to obtain the sample from. Typical samples can be 6" long, while in some cases a sub-sample of 3" is all that is required. ASME samples require at least 8" of material.