Developed in 1990, Fast-Cut 20 and 45 steels, available in two nominal carbon levels, provide the highest level of machinability because of their elevated sulfur levels. Fast-Cut steels are primarily used in thicknesses under 6 inches in machining-intensive applications, such as tire and other rubber molding equipment.

Due to the higher sulfur content of Fast-Cut steels, they are limited to a maximum thickness of 8 inches. Occasional internal porosity may be encountered in heavier thicknesses. This condition is not considered a cause for rejection.

Because of the deoxidation practices used by Bethlehem's Fast-Cut steels have been found to perform better than competitive products in surface roughness and tool wear, as noted in Figure 5.

Developed in 1978, Clean-Cut carbon steels provide free-machining characteristics and are available in two carbon levels as Clean-Cut 20 and Clean-Cut 45. Additionally, Clean-Cut steels are calcium treated to reduce the influence of oxide inclusions on tool wear. These steels are available to 15 inches in thicknesses and can be inspected for internal soundness to the requirements of ASTM A435 when so specified. Used primarily in thicknesses greater than 6 inches, these steels are widely used in manifold blocks and surface-critical mold applications.

Clean-Cut alloy steels are sold predominantly through Steel Service Centers. Bethlehem offers Clean-Cut steels in AISI grades 4140, 4142, 4150, 8620 and in the Bethlehem prehardened steels, MTD� #1, #2, and #4. These steels are produced with a sulfur content of .02-.04% and exhibit improved machinability over the lower sulfur steels, particularly in milling and drilling. This improvement is also assisted by the calcium treatment given these steels. Milling test comparisons are shown in Figure 6.

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