D6AC, UNS K24728 Low Alloy Steel


D6AC is a medium carbon low alloy steel acc. to AMS 6431, AMS 2300, AMS-S-8949, MIL-S-8949, UNS K24728, FMS-1011, GM-1013, LCM-05-2190, STM-05-500

D6AC, UNS K24728 Low Alloy Steel - Introduction and Application

D6AC, UNS K24728 is a medium carbon low alloy steel which improved hardenability as compared to 4340 low alloy steel, 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.).  This alloy has very high strength and offers excellent notch toughness.  D6AC has excellent deep hardening characteristics which lend itself well to larger components.  This grade is also widely used in the aerospace industry as landing gear, shafts, and axles requiring a good combination of toughness and strength.


Melted process

  • AOD + VAR
  • VIM + ESR
  • VIM + VAR

D6AC, UNS K24728 Low Alloy Steel - Chemical composition WT %

GradeChemical Composition WT %
CSiMnCrNiMoV
D-6AC Vac Melt N&T0.460.250.751.100.601.000.10

Mechanical Property of D6AC, UNS K24728 Low Alloy Steel

MaterialTempering TreatmentUltimate Tensile Strength (Mpa)0.2 % Yield Strength (Mpa)% Elongation% Reduction of AreaHardness HRC
LESCALLOY D6AC VAC ARC ®316°C (600°F)1931172472353
LESCALLOY D6AC VAC ARC ®510°C (950°F)1572134572546

Heat Treatment of D6AC, UNS K24728 Low Alloy Steel

  • 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.

Welding of D6AC, UNS K24728 Low Alloy Steel

The alloy is weldable, even in heavy sections. Preheat and postheat treatments are applicable here for the carbon content in question.


Machining of D6AC, UNS K24728 Low Alloy Steel

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.


Equivalent grades of D6AC, UNS K24728 Low Alloy Steel

UNS K24728

D6AC, UNS K24728 Low Alloy Steel High-alloy and low-alloy ultra-high-strength steel stock list

Grade Shape Dimensionmm Qty.kg
D6AC Tube 185.00 x 18.00mm 2.768