PH Grades 13-8MO – Stainless Steel Type 13-8Mo

Principal Design Features

13-8 MO is a precipitation, age hardenable stainless steel. It’s principal features are high transverse toughness, good resistance to general and stress corrosion cracking, and high strength that is developed by a single low temperature heat treatment.


General Characteristics

Type 13-8 Mo stainless is a martensitic precipitation and age hardening grade capable of high strength and hardness levels coupled with good ductility and toughness. The grade’s mechanical properties are obtained by a combination of cold work and heat treatment.

Chemical Analysis

C% Mn% P% S% Si% Cr% Ni% Al% Mo% N%
0.05 max 0.10 max 0.010 max 0.008 max 0.10 max 12.25/13.25 7.50/8.50 0.90/1.35 2.00/2.50 0.01 max



This alloy is used for forged valve parts and fittings, for cold-headed and machined fasteners, forged shafts, landing gear parts, pins and lockwashers, aircraft components, nuclear reactor components and petrochemical applications requiring resistance to stress corrosion cracking.


Heat uniformly to 2150/2200ºF (1175/1205ºC) and soak for one hour before forging. Do not forge below 1750ºF (955ºC.) For optimum grain size and mechanical properties, air cool forgings to 60ºF (16ºC) before further processing and solution treat prior to hardening.

Heat treatment

The alloy is hardened by heating solution treated material to 950ºF (510ºC) to 1150ºF (620ºC) for 4 hours and air cooling.

Solution treatment or anneal is carried out at 1700ºF (927ºC) +/- 15ºF (+/- 8ºC) and air cooling to below 60ºF (16ºC) to ensure complete transformation to martensite.

To obtain condition RH 950 – precipitation or age hardened – cold treat solution treated material at -100ºF (-73ºC) for 2 hours minimum, to transform any retained austenite. Air warm to room temperature. This must be done within 24 hours after solution treatment. Heat the cold treated material to 950ºF (510ºC) for 4 hours and air cool.

To obtain conditions H 950, H 1000, H 1050, H1100, and H 1150, precipitation or age hardened, heat the solution treated material at the appropriate temperature for 4 hours and air cool.


The alloy can be machined in the solution-annealed and in the various age-hardened conditions. To obtain optimum machinability, treat solution annealed material at 1400ºF (760ºC) for 2 hours and air cool, then heat to 1150ºF (620ºC) for 4 hours and air cool.


The alloy may be welded by shielded fusion or resistance methods. If a filler metal is required a 13-8 type should be used. Heat treatment before and after welding will depend upon required strength levels in both the parent and weld metals.

Density: 0.28

Specific Gravity: 7.76

Specific Heat: 0.11

Electrical Resistivity: 613

MoETensile: 28.3


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