Most ingots, however, are sent to semifinishing mills (also known as slabbing or blooming mills) for reduction and shaping into slabs, blooms, or billets. A slab is generally a large flat length of steel wider than a bloom, a bloom is a length of steel either square or rectangular with a cross-sectional area larger than 36 in (90 cm), and a billet is generally two to five inches square, although some billets can be round or rectangular. The exact sizes of slabs, blooms, and billets depend on the requirements of further processing.

In slabbing and blooming mills, the steel ingot is gradually squeezed between heavy rolls. To make billets, the steel is first shaped into blooms, then further reduced in a billet mill. Each time the ingot is forced through the rolls, it is further reduced in one dimension. Blooming mills can be classified as either two-high or three-high, depending on the number of rolls used. The two rolls of the two-high mill can be reversed so that the ingot is flattened and lengthened as it passes back and forth between the rolls. The top and bottom rolls of the three-high mill turn in one direction while the middle roll turns in the opposite direction. The ingot is flattened first between the bottom and middle rolls and ends up on a runout table. The table rises and the steel is then fed through the top and middle rolls. The continuous, or cross-country, mill is a third type of blooming mill. This mill has a series of two-high rolls. As many as 15 passes may be required to reduce an ingot 21 in2 (135 cm2) in cross section to a bloom 8 in2 (52 cm2) in cross section. The twoand three-high blooming mills roll the top and bottom of the steel in every pass. After one or two passes, mechanical manipulators on the runout table turn the steel to bring the side surfaces under the rolls for a more uniform material. After the steel is rolled, the uneven ends are sheared off, and the single long piece is cut into shorter lengths.

Read more: http://science.jrank.org/pages/6484/Steel-Manufacturing-proc...
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Note added at 56 mins (2009-11-08 16:10:48 GMT)
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BLOOM:

A semi finished piece of steel resulting from the rolling or forging of an ingot. A bloom is square or not more than twice as wide as thick and usually not less than 36 square inches in cross-sectional area.
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