Special Grades D6AC
Principal Design Features
D6AC is a low alloy vacuum melted steel containing several other elements and with a carbon content of 0.42 to 0.48%. The hardenability of this alloy is better than that of AISI 4340 and D6AC can be heat treated to strengths ranging from 180 to 260 ksi.
D6AC alloy is a medium-carbon low-alloy ultra high strength steel that was primarily developed for high strength structural applications requiring ultimate tensile strength values up to 280 ksi. The steel has a high yield to ultimate strength ratio, while retaining good ductility. It has good hardenability and excellent impact strength down to –210ºF (-134ºC.)
Chemical Analysis – typical
D6AC is used where its excellent strength, ductility and toughness properties come into play, primarily in structural applications. The alloy’s good hardenability makes it suitable for use in fairly large sections.
Forging of this grade may be carried out from 2000 to 2250ºF (1090 to 1230ºC,) the actual temperature depending upon complexity of the part and the reduction required. A minimum finishing temperature of 1700ºF (930ºC) is recommended. Following forging an equalization treatment at 1200-1300ºF (650-705ºC) is recommended, followed by a furnace cool to 1000ºF (540ºC) and subsequent air cool.
Annealing: Heat uniformly to 1500-1550ºF (815-845ºC) and furnace cool at 50ºF (28ºC) per hour to 1000ºF (540ºC) then air cool to room temperature.
Hardening : Austenitize at 1550-1650ºF (845-900ºC). Small sections up to 1 in (25mm) may be air cooled, but larger sections should be cooled in oil or brine.
Tempering: Temper at 300 – 1200ºF (150-650ºC) for desired properties, using appropriate times according to section size. Double tempering is recommended.
The alloy D6AC has a machinability rating 50-55 percent of that of B1112 screw stock. Either high speed steel or carbide cutting tools are recommended.
The alloy is weldable, even in heavy sections. Preheat and postheat treatments are applicable here for the carbon content in question.
Specific Gravity: 7.8
Specific Heat: 0.116
Melting Point: 2600
Thermal Conductivity: 30
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