The alloys in this group, in terms of cost and in maximum service temperature, generally fall between the austenitic stainless steels and the nickel- and cobalt-base alloys. They are used in airframes, principally, in the temperature range 1000 to 1200°F, in those applications in which the stainless steels are inadequate and service requirements do not justify the use of the more costly nickel or cobalt alloys.
Composition — The complex-base alloys comprising this group range from those in which iron is considered the base element to those which border on the nickel-base alloys. All of them contain sufficient alloying elements to place them in the “Superalloy” category, yet contain enough iron to reduce their cost considerably.
Chromium, in amounts ranging from 10 to 20 percent or higher, primarily increases oxidation resistance and contributes to strengthening of these alloys. Nickel and cobalt strengthen and toughen these materials. Molybdenum, tungsten, and columbium contribute to hardness and strength, particularly at elevated temperatures. Titanium and aluminum are added to provide age-hardening.
Heat Treatment — The complex-base alloys are heat treated with conventional equipment and fixtures such as would be used for austenitic stainless steels. Since these alloys are susceptible to carburization during heat treatment, it is good practice to remove all grease, oil, cutting, lubricant, etc., from the surface before heating. A low-sulfur and neutral or slightly oxidizing furnace atmosphere is recommended for heating.
The iron-chromium-nickel-base alloys closely resemble the austenitic stainless steels insofar as forging, cold forming, machining, welding, and brazing are concerned. Their higher strength may require the use of heavier forging or forming equipment, and machining is somewhat more difficult than for the stainless steels. Pertinent comments are included under the individual alloys.
A-286 is a precipitation-hardening iron-base alloy designed for parts requiring high strength up to 1300°F and oxidation resistance up to 1500°F. It is used in jet engines and gas turbines for parts such as turbine buckets, bolts, and discs, and sheet metal assemblies. A-286 is available in the usual mill forms.
A-286 is somewhat harder to hot or cold work than the austenitic stainless steels. Its forging range is 2150 to 1800°F; when finishing below 1800°F, light reductions (under 15 percent) must be avoided to prevent grain coarsening during subsequent heat treatment. A-286 is readily machined in the partially or fully aged condition but is soft and “gummy” in the solution-treated condition. A-286 should be welded in the solution-treated condition. Fusion welding is difficult for large section sizes and moderately difficult for small cross sections and sheet. Cracking may be encountered in the welding of heavy sections or parts under high restraint. A dimensional contraction of 0.0008 inch per inch is experienced during aging. Oxidation resistance of A-286 is equivalent to that of Type 310 stainless steel up to 1800°F.
Some material specifications for A-286 alloy are presented in Table 6.2.1.0(a). Room-temperature mechanical and physical properties are shown in Table 6.2.1.0(b). The effect of temperature on physical properties is shown in Figure 6.2.1.0.
Elevated-temperature data are presented in Figures 6.2.1.1.1, 6.2.1.1.3, and 6.2.1.1.4(a) through (c). Stress rupture properties are specified at 1200°F; the appropriate specifications should be consulted for detailed requirements. Figures 6.2.1.1.8(a) through (e) are fatigue S/N curves for several elevated temperatures.
| Specification | Form | Condition |
|---|---|---|
| AMS 5525 | Sheet, strip, and plate | Solution treated (1800°F) |
| AMS 5731 | Bar, forging, tubing, and ring | Solution treated (1800°F) |
| AMS 5732 | Bar, forging, tubing, and ring | Solution treated (1800°F) and aged |
| AMS 5734 | Bar, forging, and tubing | Solution treated (1650°F) |
| AMS 5737 | Bar, forging, and tubing | Solution treated (1650°F) and aged |
Figure 6.2.1.0. Effect of temperature on the physical properties of A-286.
| Specification | AMS 5525 | AMS 5731 AMS 5732 | AMS 5734 AMS 5737 | ||
|---|---|---|---|---|---|
| Form | Sheet, strip, and plate | Bar | |||
| Condition | Solution treated and aged | ||||
| Thickness or diameter, in. | >0.004 | <2.499 | 2.500-5.000 | <2.499 | 2.500-5.000 |
| Basis | Sa | S | S | S | S |
| Mechanical Properties: | |||||
| Ftu, ksi: | |||||
| L | ··· | 130 | 130 | 140 | 140 |
| LT | 140 | 130b | 130 | 140b | 140 |
| ST | ··· | ··· | 130 | ··· | 140 |
| Fty, ksi: | |||||
| L | ··· | 85 | 85 | 95 | 95 |
| LT | 95 | 85b | 85 | 95b | 95 |
| ST | ··· | ··· | 85 | ··· | 95 |
| Fcy, ksi: | |||||
| L | ··· | 85 | 85 | 95 | 95 |
| LT | 95 | ··· | ··· | ··· | ··· |
| Fsu, ksi | 91 | 85 | 85 | 91 | 91 |
| Fbru, ksi: | |||||
| (e/D = 1.5) | 210 | 195 | 195 | 210 | 210 |
| (e/D = 2.0) | 266 | 247 | 247 | 266 | 266 |
| Fbry, ksi: | |||||
| (e/D = 1.5) | 142 | 127 | 127 | 142 | 142 |
| (e/D = 2.0) | 171 | 153 | 153 | 171 | 171 |
| e, percent: | |||||
| L | ··· | 15 | 15 | 12 | 12 |
| LT | 15 | 15b | 15 | 12b | 12 |
| ST | ··· | ··· | 15 | ··· | 12 |
| RA, percent: | |||||
| L | ··· | 20 | 20 | 15 | 15 |
| LT | 15 | 20b | 20 | 15b | 15 |
| ST | ··· | ··· | 20 | ··· | 15 |
| E, 103 ksi | 29.1 | ||||
| Ec, 103 ksi | 29.1 | ||||
| G, 103 ksi | 11.1 | ||||
| μ | 0.31 | ||||
| Physical Properties: | |||||
| ω, lb/in.3 | 0.287 | ||||
| C, K, and α | See Figure 6.2.1.0 | ||||
| a Test direction longitudinal for widths less than 9 inches; transverse for widths 9 inches and over. | |||||
| b Applicable to widths ≥2.500 inches only. | |||||
Figure 6.2.1.1.1. Effect of temperature on the tensile yield strength (Fty) and tensile ultimate strength (Ftu) of A-286 alloy (1800°F solution treatment temperature).
Figure 6.2.1.1.3. Effect of temperature on the bearing ultimate strength (Fbru) and the bearing yield strength (Fbry) for A-286 alloy (1800°F solution treatment temperature).
Figure 6.2.1.1.4(a). Effect of temperature on the tensile and compressive moduli (E and Ec) for A-286 alloy (1800°F solution treatment temperature).
Figure 6.2.1.1.4(b). Effect of temperature on the shear modulus (G) of A-286 alloy.
Figure 6.2.1.1.4(c). Effect of temperature on Poisson’s ratio (μ) for A-286 alloy.
Figure 6.2.1.1.8(a). Best-fit S/N curves for unnotched A-286 bar at 800°F, longitudinal direction.
| Correlative Information for Figure 6.2.1.1.8(a) | |
|
Product Form: Bar, air melted Properties: TUS 141.4 ksi, TYS 95.3 ksi, 800°F Specimen Details: Unnotched Heat Treatment: 1650°F for 2 hours, oil quenched and 1300°F for 16 hours, air cooled. Surface Condition: Not given Reference: 6.2.1.1.8 |
Test Parameters: No. of Heats/Lots: 1 Equivalent Stress Equation: Sample Size: 17 [Caution: The equivalent stress model may provide unrealistic life predictions for stress ratios beyond those represented above.] |
Figure 6.2.1.1.8(b). Best-fit S/N curves for notched, Kt = 3.4, A-286 alloy bar at 800°F, longitudinal direction.
| Correlative Information for Figure 6.2.1.1.8(b) | |
|
Product Form: Bar, air melted Properties: TUS 141.4 ksi, TYS 95.3 ksi, 800°F Specimen Details: Notched, V-Groove, Heat Treatment: 1650°F for 2 hours, oil quenched and 1300°F for 16 hours, air cooled. Surface Condition: As machined Reference: 6.2.1.1.8 |
Test Parameters: No. of Heats/Lots: 1 Equivalent Stress Equation: Sample Size: 13 [Caution: The equivalent stress model may provide unrealistic life predictions for stress ratios beyond those represented above.] |
Figure 6.2.1.1.8(c). Best-fit S/N curves for unnotched A-286 bar at 1000°F, longitudinal direction.
| Correlative Information for Figure 6.2.1.1.8(c) | |
|
Product Form: Bar, air melted Properties: TUS 137.2 ksi, TYS 100.6 ksi, 1000°F Specimen Details: Unnotched Heat Treatment: 1650°F for 2 hours, oil quenched and 1300°F for 16 hours, air cooled. Surface Condition: Not given Reference: 6.2.1.1.8 |
Test Parameters: No. of Heats/Lots: 1 Equivalent Stress Equation: Sample Size: 18 [Caution: The equivalent stress model may provide unrealistic life predictions for stress ratios beyond those represented above.] |
Figure 6.2.1.1.8(d). Best-fit S/N curves for notched, Kt = 3.4, A-286 alloy bar at 1000°F, longitudinal direction.
| Correlative Information for Figure 6.2.1.1.8(d) | |
|
Product Form: Bar, air melted Properties: TUS 137.2 ksi, TYS 100.6 ksi, 1000°F Specimen Details: Notched, V-Groove, Kt = 3.4 Heat Treatment: 1650°F for 2 hours, oil quenched and 1300°F for 16 hours, air cooled. Surface Condition: As machined Reference: 6.2.1.1.8 |
Test Parameters: No. of Heats/Lots: 1 Equivalent Stress Equation: Sample Size: 17 [Caution: The equivalent stress model may provide unrealistic life predictions for stress ratios beyond those represented above.] |
Figure 6.2.1.1.8(e). Best-fit S/N curves for unnotched A-286 bar at 1250°F, longitudinal direction.
| Correlative Information for Figure 6.2.1.1.8(e) | |
|
Product Form: Bar, air melted Properties: TUS 109.6 ksi, TYS 96.5 ksi, 1250°F Specimen Details: Unnotched Heat Treatment: 1650°F for 2 hours, oil quenched and 1300°F for 16 hours, air cooled. Surface Condition: Not given Reference: 6.2.1.1.8 |
Test Parameters: No. of Heats/Lots: 1 Equivalent Stress Equation: Sample Size: 13 [Caution: The equivalent stress model may provide unrealistic life predictions for stress ratios beyond those represented above.] |
N-155 alloy, also known as Multimet, is designed for applications involving high stress up to 1500°F. It has good oxidation properties and good ductility and can be fabricated readily by conventional methods. This alloy has been used in many aircraft applications, including afterburner parts, combustion chambers, exhaust assemblies, turbine parts, and bolting.
N-155 is forged readily between 1650°F and 2200°F. It is easily formed by conventional methods; intermediate anneals may be required to restore its ductility. This alloy is machinable in all conditions; low cutting speeds and ample flow of coolant are required. The weldability of N-155 is comparable to that of the austenitic stainless steels. The oxidation resistance of N-155 sheet is good up to 1500°F.
Some materials specifications for N-155 are presented in Table 6.2.2.0(a). Room-temperature mechanical and physical properties for N-155 sheet and tubing in the solution-treated (annealed) condition are presented in Table 6.2.2.0(b). Bars and forgings are not specified by room-temperature properties but have specific elevated-temperature requirements. The effect of temperature on physical properties is shown in Figure 6.2.2.0.
| Specification | Form | Condition |
|---|---|---|
| AMS 5532 | Sheet | Solution treated |
| AMS 5585 | Tubing (welded) | Solution treated |
| AMS 5768 | Bar and forging | Solution treated and aged |
| AMS 5769 | Bar and forging | Solution treated |
Elevated-temperature curves are presented in Figures 6.2.2.1.1(a) and (b), as well as 6.2.2.1.4(a) and (b). Stress-rupture properties are specified at 1500°F for sheet and at 1350°F for bars and forgings; the appropriate specifications should be consulted for detailed requirements.
Figure 6.2.2.0. Effect of temperature on the physical properties of N-155 alloy.
| Specification | AMS 5532 | AMS 5585 | |
|---|---|---|---|
| Form | Sheet | Strip and plate | Tubing |
| Condition | Solution treated | ||
| Thickness, in. | ≤0.187 | ··· | ··· |
| Basis | Sa | Sa | S |
| Mechanical Properties: | |||
| Ftu, ksi: | |||
| L | ··· | ··· | 100 |
| LT | 100 | 100 | ··· |
| Fty, ksi: | |||
| L | ··· | ··· | 49b |
| LT | 49b | ··· | ··· |
| Fcy, ksi: | |||
| L | ··· | ··· | ··· |
| LT | ··· | ··· | ··· |
| Fsu, ksi | ··· | ··· | ··· |
| Fbru, ksi: | |||
| (e/D = 1.5) | ··· | ··· | ··· |
| (e/D = 2.0) | ··· | ··· | ··· |
| Fbry, ksi: | |||
| (e/D = 1.5) | ··· | ··· | ··· |
| (e/D = 2.0) | ··· | ··· | ··· |
| e, percent: | |||
| L | ··· | ··· | c |
| LT | 40 | 40 | ··· |
| E, 103 ksi | 29.2 | ||
| Ec, 103 ksi | 29.2 | ||
| G, 103 ksi | 11.2 | ||
| μ | See Figure 6.2.2.1.4(b) | ||
| Physical Properties: | |||
| ω, lb/in.3 | 0.300 | ||
| C, Btu/(lb)(°F) | 0.103 (70 to 212°F) | ||
| K, Btu/[(hr)(ft2)(°F)/ft] | See Figure 6.2.2.0 | ||
| α, 10-6 in./in./°F | See Figure 6.2.2.0 | ||
| a Test direction longitudinal for widths less than 9 inches; transverse for widths 9 inches and over. | |||
| b Typical value reduced to minimum. | |||
| c Strip = 35. Full section 0.625 thick = 40. Full section >0.625 thick = 30. | |||
Figure 6.2.2.1.1(a). Effect of temperature on the tensile ultimate strength (Ftu) of N-155 alloy.
Figure 6.2.2.1.1(b). Effect of temperature on the tensile yield strength (Fty) of N-155 alloy.
Figure 6.2.2.1.4(a). Effect of temperature on the tensile and compressive moduli (E and Ec) of N-155 alloy.
Figure 6.2.2.1.4(b). Effect of temperature on Poisson’s ratio (μ) for N-155 alloy.
- 6.2.1.1.8Blatherwick, A. A. and Cers, A., “Fatigue, Creep and Stress-Rupture Properties of Nicrotung, Super A-286, and Inconel 718”, AFML-TR-65-4447 (June 1966) (MCIC 65927).