Inconel X-750 Introduction

Overview

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INCONEL® alloy X-750 (UNS N07750 / W.Nr. 2.4669) is a precipitation-hardenable nickel-chromium alloy used for its corrosion and oxidation resistance and high strength at temperatures to 1300°F. Although much of the effect of precipitation hardening is lost with increasing temperature over 1300°F, heat-treated material has useful strength up to 1800°F. Alloy X-750 also has excellent properties down to cryogenic termperatures.

The economics of INCONEL alloy X-750 coupled with its availability in all standard mill forms has resulted in applications in a wide variety of industrial fields. In gas turbines, it is used for rotor blades and wheels, bolts, and other structural members. INCONEL alloy X-750 is used extensively in rocket-engine thrust chambers. Airframe applications include thrust reversers and hot-air ducting systems. Large pressure vessels are formed from INCONEL alloy X-750. Other applications are heat-treating fixtures, forming tools, extrusion dies, and test machine grips. For springs and fasteners, INCONEL alloy X-750 is used from sub-zero to 1200°F.

Depending on the application and the properties desired, various heat treatments are employed. For service above 1100°F, particularly where loads are to be sustained for long times, optimum properties are achieved by solution treating (2100°F) plus stabilization treating (1550°F) plus precipitation treating (1300°F). For service below 1100°F, the alloy may be strengthened by precipitation treating after hot or cold working or by precipitation treating after equalizing or solution treating. A furnace-cooling treatment is also used to develop optimum properties for some applications.

The various heat treatments and the properties developed are described under the section on Mechanical Properties. Property values in this bulletin – the results of extensive testing – are typical of the alloy but, unless shown as limiting, should not be used as specification values.

Mechanical Properties

INCONEL alloy X-750 may be given any one of a variety of heat treatments. Each develops special properties and puts the product form in the best condition for its intended application. In all conditions, alloy X-750 is resistant to oxidation up to 1800°F. The most often used heat treatments have been incorporated by the Society of Automotive Engineers in their AMS specifications* for various product forms.

Corrosion Resistance

INCONEL alloy X-750 is resistant to a wide variety of industrial corrosives under both oxidizing and reducing conditions. It resists oxidation and attack by other hightemperature corrosion mechanisms.

In hot corrosion tests for automotive applications, weight loss after exposure for 100 hours in 90% Na2SO4 + 10% NaCl mixture in air was about 5%. Samples precoated with sodium chloride (by dipping in a hot saturated salt solution), suspended in a furnace at 1700°F and exposed for 100 hr to a moving gas stream of air containing 1% SO2 exhibited a corrosion penetration of approximately 0.007 in.

An interesting feature of this alloy is its high resistance to chloride-ion stress-corrosion cracking even in the fully precipitation-hardened condition. Standard U-bend specimens of precipitation-hardened material (hardness, 33 Rc) showed no signs of cracking when exposed to boiling 42% magnesium chloride for 30 days.

Physical Properties

Density		g/cm3	8.28
		lb/in.3	0.299
Melting Range		°F	2540 - 2600
		°C	1393 - 1427
Curie Temperature	As hot-rolled	°F	-225
	Triple-heat-treated (2100°F/2 hr, A.C.,+1500°F/24 hr, A.C., + 1300°F/20 hr, A.C.)	°F	-193
Emissivity, oxidized surface	600°F		0.895
	2000°F		0.925

Mechanical Properties

Rods, Bars and Forgings
Size, in.	Tensile Strength, ksi	Yield Strength (0.2% offset), ksi	Elongation in 2 in., %	Reduction of Area %
Under 4.0	165	105	20	25
4.0 and over	160	100	15	17
Under 2.50	170	115	18	18
2.5 to 4.00, excl.	170	115	15	15
4.0 and over	–	As agreed upon between purchaser & vendor
Sheet, Strip and Plate
Form and Size, in.	Tensile Strength, ksi	Yield Strength (0.2% offset), ksi	Elongation in 2 in., %	Hardness, Rc
Annealed Condition
Strip
Under 0.010	140 max.	–	–	–
0.010 to 0.025, excl.	130 max.	–	20 min.	–
0.025 & over	As agreed upon between purchaser & vendor
Sheet
0.010 to 0.024, incl.	140 max.	–	30 min.	–
Over 0.024-0.125, incl.	130 max.	60 max.	40 min.	–
Over 0.125-0.250, incl.	130 max.	65 max.	40 min.	–
After Precipitation Treating (1300°F/20 hr, A.C.)
Strip
Under 0.010	150 min.	–	–	30 min.(0.005 & over)
0.010 to 0.025, excl.	155 min.	–	15 min.	30 min.
0.025 & over	155 min.	–	15 min.	30 min.
Sheet
0.010 to 0.025, incl.	165 min.	105 min.	20 min.	32 min.
Plate
0.187 to 4.000, excl.	155 min.	100 min.	20 min.	30 min.
Seamless Tubing
Tensile strength				155 ksi
Yield strength (0.2% offset)				100 ksi
Elongation in 2 in.
	Strip specimen			15%
	Full tube specimen			20%
Rupture life (1350°F/45 ksi)				23 hr
Wire

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