Chemical Composition

Identification Symbol	Grade	Elements	Composition %
Grade LF6	26 chromium, 6 nickel, 3.5 molybdenum with nitrogen and copper 255	Carbon	0.22 max
		Manganese	1.15–1.50 max
		Phosphorus	0.025 max
		Sulfur	0.025 max
		Silicon	0.15–0.30 max
		Nickel	0.40 maxB
		Chromium	0.30
		Molybdenum	0.12 maxB,C
		Copper	0.40
		Columbium	0.02
		Vanadium	0.04–0.11
		Nitrogen	0.01–0.030

Mechanical Properties

Property	Class 1	Class 2 and 3
Tensile Strength, min, ksi [MPa]	66–91[455–630]	75–100[515–690]
Yield Strength, min, ksi [MPa]	52 [360]	60 [415]
Elongation in 2 in. [50mm] or 4D, min, %	48t + 15	48t + 13
Reduction or Area, min, %	40	40

Charpy V-Notch Energy Requirements and Standard Impact Test Temperature for Standard Size [10 by 10 mm] Specimens

Grade	Test Temperature, °F [°C]	Minimum Impact Energy Required for Average of Each Set of Three Specimens, ft·lbf[J]	Minimum Impact Energy Permitted for One Specimen only of a Set, ft·lbf[J]
LF2, Class 1	−60 [−51]	15 [20]	12 [16]
LF2, Class 2	−60 [−51]	20 [27]	15 [20]
LF2, Class 3	0 [−18]	20 [27]	15 [20]

Heat Treatment

• After hot working and before reheating for heat treatment, the forging shall be allowed to cool substantially below the transformation range.
• Forgings of grades other than Grade LF787 shall be furnished in the normalized, or in the normalized and tempered, or in the quenched and tempered condition described by the following procedures:
  • Normalize—Heat to a temperature that produces an austenitic structure, holding sufficient time to attain uniform temperature throughout. Cool uniformly in still air.
  • Normalize and Temper—Subsequent to normalize, reheat to 1100 °F [590 °C] minimum, holding at temperature a minimum of 30 min/in. [30 min/25 mm] of maximum thickness, but in no case less than 30 min. Cool in still air.
  • Quench and Temper—The procedure for quenching shall consist of either (1) fully austenitizing the forgings followed by quenching in a suitable liquid medium or (2) using a multiple stage procedure whereby the forging is first fully austenitized and rapidly cooled, then reheated to partially reaustenitize, followed by quenching in a suitable liquid medium. All quenched forgings shall be tempered by reheating to a temperature between 1100 °F [590 °C] and the lower transformation temperature, holding at temperature a minimum of 30 min/in. [30 min/25 mm] of maximum thickness but in no case less than 30 min.
• The heat treatment procedures shall be as follows:
  • Normalized-and-Precipitation Heat Treated—Heat to a temperature in the range from 1600 to 1725 °F [870 to 940 °C], hold at the temperature for a time sufficient to attain uniform temperature throughout, soak at the temperature for not less than 1⁄2 h, and remove from the furnace and cool in air. Subsequently, heat to a temperature in the range from 1000 to 1200 °F [540 to 650 °C], soak at the temperature for not less than 1⁄2 h, and cool at any convenient rate.
  • Quenched-and-Precipitation Heat Treated—Heat to a temperature in the range from 1600 to 1725 °F [870 to 940 °C], hold at the temperature for a time sufficient to attain uniform temperature throughout, soak at the temperature for not less than 1⁄2 h and quench in a suitable liquid medium by immersion; reheat to a temperature in the range from 1000 to 1225 °F [540 to 665 °C], hold at the temperature for not less than 1⁄2 h, and cool at any convenient rate.