Stainless Steel PH Grades 15-7MO

General Characteristics

This alloy is a semi-austenitic precipitation and age hardening stainless steel with high strength and good corrosion resistance.

Chemical Analysis

C% Mn% P% S% Si% Cr% Ni% Al% Mo%
0.09 max 1.00 max 0.040 max 0.040 max 1.00 max 14.00/16.00 6.50/7.75 0.70/1.50 2.00/3.00

Applications

The alloy is used for retaining rings, springs, diaphragms, aircraft bulkheads, welded and brazed honeycomb paneling and other aircraft components requiring high strength at elevated temperatures.

Forging

This alloy may be forged in the region of 2000/2100ºF (1090/1150ºC.) At forging temperatures above 2000ºF, followed by heat treating, these semi-austenitic grades have a tendency to retain an austenitic structure at room temperature. To achieve uniform grain refinement it is often necessary to promote transformation of austenite to martensite by heating forgings in the region of 1400ºF (760ºC). Such a treatment causes carbide precipitation, rendering the austenite less stable, and promotes complete transformation to martensite on cooling to room temperature.

Heat Treatment

A wide range of properties may be achieved with this grade following solution annealing at 1950ºF +/- 25ºF (1065ºC +/- 14ºC).

Hardening Treatments

Following solution annealing, the two most common heat treatments performed on this alloy are soaks at 1050ºF +/- 10ºF (565ºC +/- 6ºC) and at 950ºF +/- 10ºF (510ºC +/- 6ºC) followed by air cooling. Properties obtained by these treatments are:

1050 treatment        210 ksi UTS (1448Mpa)  200 ksi YS (1379Mpa)  7% El

950 treatment            240 ksi UTS (1655Mpa)  225 ksi YS (1552Mpa)  6% El

It will be noted that ductility is certainly given up for strength in this alloy following hardening treatments.

Machinability

The alloy may be machined in both the solution annealed and hardened conditions, using carbide tooling and positive speeds and feeds.

Weldability

The high aluminum content of this alloy reduces weldability by favoring weld slag formation and degrading penetration. Additionally austenite conditioning and precipitation heat treatments are required following welding to achieve high strength levels.

Annealing

1900 F (1038 C) for 1 hour, rapid cooling. Also known as ” solution treating.”

Density: 0.282

Specific Gravity: 7.804

Specific Heat: 0.11

 

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