This specification deals with continuous grain flow carbon and alloy steel crankshaft forgings intended for medium speed diesel and natural gas engines. The steel used in the manufacture of the forgings is required to be vacuum degassed. Heat treatment, which may be done either before or after rough machining, shall consist of normalizing followed by tempering at a subcritical temperature, or austenitizing, liquid quenching and subcritical tempering. Charpy impact and tensile tests, which shall be performed at a frequency of one test per heat treatment load, shall be used to evaluate tensile strength, yield strength, elongation, reduction of area, and Brinell hardness requirements of forgings. Chemical composition requirements shall also be examined by heat analysis. Grain size tests and non-destructive magnetic particle examinations shall be conducted as well. When required by the purchaser, crankshafts may be surface hardened in designated areas for the purposes of enhanced wear resistance and fatigue strength.

1.1 This specification covers continuous grain flow forged carbon and alloy steel crankshafts for medium speed diesel and natural gas engines.

1.2 The steel used in the manufacture of the forgings is required to be vacuum degassed.

1.3 The choice of steel composition grade for a given strength class is normally made by the forging supplier, unless otherwise specified by the purchaser.

1.4 Provision is made for treatment of designated surfaces of the crankshaft to provide enhanced fatigue strength, or wear resistance, or both.

1.5 Except as specifically required in this specification, all provisions of Specification A788/A788M apply.

1.6 Unless the order specifies the applicable “M” specification designation, the material shall be furnished to the inch-pound units.

1.7 The values stated in either inch-pound units or SI (metric) units are to be regarded separately as standard. Within the text and tables the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.