Introduction to AL286 material

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Introduction to Allegheny Ludlum Corporation’s Altemp A-286 super iron-based alloy (UNS S66286): The Altemp A-286 (S66286) alloy, registered by Allegheny Ludlum Corporation, is an iron-based alloy with high temperature resistance. This alloy retains high strength at 704°C, and can be used at higher temperatures under lower stress. The Altemp A-286 produced by Allegheny Ludlum is a heat-resistant and corrosion-resistant alloy that can be age-hardened to achieve higher strength levels. This alloy can also be used as a low-temperature steel; within the temperature range from room temperature to -196°C, it exhibits no magnetic phase transition and possesses good toughness and high strength. This alloy can also be used in aqueous environments with moderate corrosion. The Altemp A-286 alloy produced by Allegheny Ludlum is available in the form of sheets, thin sheets, and strips. This alloy usually specifies the melting composition. All products are supplied in the solid solution state. Solid solution products are most beneficial for equipment manufacturing. The technical documents related to the Altemp A-286 alloy (S66286) are listed below. Furthermore, for alloys whose chemical composition is restricted for special applications, the relevant technical documents include AMS 5858 and others. AMS 5525: plates, sheets, strips; AMS 5858: plates, sheets, strips; AMS 5731: bars, forgings, tubes, forged rings; AMS 5732: bars, forgings, tubes, forged rings; AMS 5734: bars, forgings, tubes, forged rings; AMS 5737: bars, forgings, tubes, forged rings. ASTM A453: screws; ASTM A638: forgings, billets, bars; ASME SA638: forgings, billets, bars. Table 1: Typical chemical composition. Elements: Percentage (%): C 0.04, Mn 0.20, P 0.015, S 0.002, Si 0.20, Cr 14.5, Ni 25.0, Mo 1.25, Ti 2.10, V 0.30, Al 0.15, B 0.006; Fe: remainder. Corrosion resistance and high-temperature oxidation resistance: The contents of alloying elements such as Cr, Ni, and Mo in Altemp A-286 are similar to those in certain austenitic stainless steels; therefore, Altemp A-286 possesses corrosion resistance comparable to that of those austenitic stainless steels. In a high-temperature environment of 704°C, AltempA-286 exhibits excellent resistance to high-temperature corrosion; therefore, engine nozzles manufactured from this material perform well. This alloy can be used continuously at a high temperature of 816°C, and intermittently at 982°C. Table 2 Typical corrosion data
Test conditions, Alloy name: 304L, 316L, Altemp A-286
50% saline spray: No rusting after 100 hours; No rusting after 100 hours; No rusting after 100 hours
U-bend test in 42% MgCl2 solution: Cracking after 8 hours; Cracking after 24 hours; Cracking after 168 hours
Crevice corrosion test in 10% FeCl3 solution (pH 1.5), 21°C: Corrosion; Corrosion; Corrosion

Table 3 Typical corrosion data
Boiling of test solution, Corrosion rate in mm/year:
304L: 316L: Altemp A-286
20% acetic acid: <0.01; <0.01; <0.01
45% formic acid: 1.22; 0.28; 0.21
10% oxalic acid: 1.23; 1.02; 0.37
1% hydrochloric acid: 2.72; >5; 2.14
10% sulfuric acid: >12; >5; 0.75
20% phosphoric acid: <0.01; 0.18; 0.33
10% sodium sulfite: 1.62; 1.06; 0.18

Physical properties:
Density: After solution treatment – 7.9 g/cm³; After aging treatment – 7.94 g/cm³
Melting range: 1370–1430°C
Magnetic permeability: 1.010
Specific heat: 420 J/kg·K

Table 4 Coefficient of linear expansion
Temperature range (°C), Coefficient of linear expansion (10^-6/°C):
21–93: 16.5
21–204: 16.8
21–316: 17.0
21–427: 17.4
21–538: 17.6
21–649: 17.8
21–760: 18.6

Table 5 Thermal conductivity
Temperature (°C), Thermal conductivity W/m·K:
150: 15.1
300: 17.8
500: 21.8
600: 23.9

Table 6 Electrical resistivity
Temperature (°C), Electrical resistivity μΩ/cm:
25: 91.0
540: 115.6
650: 118.8
730: 120.1
815: 122.4

Table 7 Elastic modulus: Modulus of rigidity, Poisson’s ratio
Temperature (°C), Elastic modulus (modulus of rigidity) in MPa, Poisson’s ratio μ:
-196: 204 (80); 0.280
-73: 203 (79); 0.290
24: 201 (77); 0.300
538: 162 (61); 0.330
593: 158 (59); 0.335
649: 153 (57); 0.340
704: 149 (55); 0.345
760: 142 (53); 0.350
816: 137 (50); 0.355
871: 130 (48); 0.360

Mechanical properties: The typical room-temperature tensile properties of the Altemp A-286 alloy after solution treatment at 982°C are as follows: Yield strength, Tensile strength, Elongation: 275 MPa, 620 MPa, 40%. After aging treatment at around 718°C, the strength values of this alloy increase significantly. The short-term tensile properties of this alloy after aging show that it maintains excellent mechanical properties over the temperature range from low temperatures up to 718°C. Figure 1 shows the relationship between the mechanical properties of the AltempA-286 alloy and temperature after solution treatment at 982°C followed by aging at 718°C for 16 hours. The aging effect of AltempA-286 can be achieved in two ways: through solution treatment or by performing cold deformation after solution treatment, the latter resulting in a more significant increase in the material’s strength and hardness. A higher aging treatment temperature can partially reduce the increase in strength and hardness caused by cold working. file:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image003.gif Temperature in °C; Temperature in °F. Figure 1: Relationship between the mechanical properties of AltempA-286 and temperature. file:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image007.gif Aging time. Figure 2: Relationship between aging treatment of AltempA-286 and Vickers hardness. The Charpy impact toughness values of the AltempA-286 alloy across its entire thickness show high values within the temperature range of -196°C to 788°C after aging treatment. The test was conducted after solution treatment at 982°C and aging at 718°C for 16 hours; the test results are listed in Table 8. Table 8 Impact toughness values for V-notch tests. Test temperature, Charpy V-notch impact values: 0°F, 0°C, -320, -196, 77, -100, -73, 92, 80, 27, 87, 410, 210, 81, 810, 432, 70, 1010, 543, 62, 1113, 600, 60, 1250, 677, 56, 1450, 788. High-temperature creep and high-temperature mechanical properties: The AltempA-286 alloy is designed to be used as a superalloy. Under high-temperature conditions, it is not the short-term tensile property values that serve as the basis for design, but rather high-temperature creep or high-temperature fracture strength. file:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image010.giffile:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image012.gif Creep rate: %1 hour. Figure 3: Typical high-temperature creep curve of AltempA-286 alloy. file:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image014.giffile:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image016.gif Time to failure, in hours. Test conditions for the material: 982°C for 1 hour, quenched in oil; 718°C for 16 hours, air-cooled. Figure 4: Typical high-temperature strength curve of AltempA-286 alloy. Manufacturing: In its solution-treated state, AltempA-286 alloy is easy to shape. The formability of the AltempA-286 alloy is comparable to that of austenitic stainless steels. This material has higher strength than standard stainless steel; therefore, a greater loading capacity is required to deform it. During cold working, the work hardening rate of A-286 thin sheets is similar to that of 310 stainless steel; the cold working hardening of A-286 sheets is shown in Figure 5. When cold forming exceeds certain limits, the A-286 alloy may require intermediate annealing at 982°C to soften the material. file:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image018.giffile:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image019.gif Rate of cold shrinkage, % Figure 5: Relationship between the rate of cold shrinkage and mechanical properties of the Altemp A-286 alloy. Welding and brazing of the AltempA-286 alloy should preferably be carried out using the solution-treated material. This alloy is sensitive to thermal cracking, especially after aging treatment. Similarly, due to the tendency for thermal cracking, welding thick sections is more difficult. There is a restricted-component AltempA-286 specifically used for welded parts, listed in the AMS 5858 technical document. The sensitivity to welding thermal cracking can be reduced by strictly controlling welding conditions to avoid restraint, maintaining a minimal welding area, and using A-286 material with restricted composition. Fusion welding is typically carried out using GTAW, GMAW, and SMAW methods; austenitic welding wires and electrodes with various compositions can be used for welding, with nickel-based alloy welding materials being more suitable. Weldments welded with A-286 wire and electrodes can undergo aging treatment after welding to achieve high strength. Inert gas shielding must be used during welding to prevent the burnout of titanium. This is very important, because Ti ensures high strength after aging. Resistance welding and spot welding can be performed using high current and high voltage. The AltempA-286 alloy can be welded to austenitic and martensitic alloys, and inert gas shielding is usually required. The AltempA-286 alloy can be brazed in pure, dry hydrogen or in a vacuum. Placing a nickel plate before brazing helps to improve wetting. Due to the brazing heat cycle at 1149°C, the ductility of the alloy decreases at room temperature and at 649°C. Performing solution treatment at 899°C or 982°C after brazing can improve the ductility of the alloy. After solution treatment, the ductility is only slightly lower than that of the material without copper induction welding. Heat treatment of the AltempA-286 alloy is a type of age-hardening heat-resistant alloy; the best strength properties are achieved by performing aging treatment after solution treatment. Based on performance requirements, AltempA-286 can be solution-treated at 899°C and 982°C. Solid solution treatment at 899℃ yields finer grains, as well as excellent short-term tensile properties at room temperature and high temperatures. After solution treatment at 982°C, the grains of the material are relatively coarse, enabling excellent high-temperature creep and high-temperature fracture properties. For materials with a large cross-sectional area, such as plates, oil cooling is generally used during solution treatment. For materials with a small cross-sectional area, such as thin plates or strips, air cooling can be used during solution treatment. The aging treatment method is as follows: after the material undergoes the aforementioned solution treatment, it is treated at 718°C for 16 hours and then cooled in air. Aging treatment imparts high strength to the AltempA-286 alloy. To achieve higher aging strength, the solution-treated material can be cold-worked prior to aging, as shown in Figure 5. To achieve the highest strength, aging at 718°C can be performed after cold working. Scaling and pickling: During heat treatment, a tightly adhered oxide film forms on the surface of the AltempA-286 alloy. This oxide film can be detached from the metal surface by reduction, oxidation, or molten salt electrolysis, after which the surface is pickled using warm sulfuric acid and nitric acid plus hydrofluoric acid. Machining of the AltempA-286 alloy can be carried out using the same techniques and equipment as those for 18-8 stainless steel. Since the AltempA-286 alloy is soft and sticky in its solution state, after machining ； The material will exhibit a partially aged, fully aged, or over-aged condition. The materials after solution treatment still exhibit good mechanical properties upon cold working.