General
13-8 Stainless Steel [PH 13-8 Mo (tm),Vasco13-8 (tm)(UNS S13800) is a precipitation hardening stainless steel that combines excellent strength, good toughness, and good general corrosion resistance. It is a through-hardening alloy, which allows it to be used in parts with large cross sections, where yield strengths in excess of 200 ksi. (1,380 MPa) may be required. Good transverse toughness properties are achieved by tight chemical composition control (to prevent the formation of delta phase), low carbon content (to minimize grain boundary precipitation), and double vacuum melting (to reduce alloy segregation). Since the rate of cooling from the solution temperature is not critical, large cross sections can be air-cooled. This alloy is produced by a primary vacuum induction melt process (VIM), followed by a consumable vacuum arc remelting (VAR) step. Typical uses are aircraft parts, rocket engine mounts, nuclear reactor parts, landing gear components, high performance shafts, and petrochemical parts that require high strength combined with good resistance to stress corrosion.

 

Specifications

PH 13-8 Mo AMS 5629 - Bars, forgings, rings, and extrusions
PH 13-8 Mo AMS 5864 - Plate

 

Physical properties
Melting Range: 2,560 to 2,680F (1,404 to 1,471C)
Density: 0.279 lbs/in3(

7.76 gm/cc)

Heat Treatment
Solution treatment from 1,675 to 1,725F (913 to 941 C) for 15 to 30 minutes at temperature. Air cool or oil quench to below 60F (15C) to ensure complete transformation to martensite. Aging is normally carried out from 950 to 1,150F (510 to 621C), depending upon the desired final properties. Heat treatment is usually performed in air. Heat treatment of brazed components maybe done in inert atmospheres. Reducing atmospheres should not be used because of the potential for nitrogen contamination.

 

HARDNESS
Hardness in the solution annealed condition is approximately Rockwell C 33.

 

OXIDATION AND CORROSION RESISTANCE
PH13-8MO alloy has excellent oxidation resistance up to 1,500F (816C). Corrosion resistance decreases slightly as the aging temperature is raised. This alloy has the best resistance to stress corrosion cracking of all of the precipitation hardenable stainless steels. Its resistance to general corrosion is greatest in the fully-hardened condition. The alloy shows very little rusting when exposed to a 5 percent salt fog at 95F (35C).

FORGEABILITY/ FORMABILITY
PH13-8MO alloy has good hot working characteristics, and can be forged over a wide temperature range. Temperatures up to 2,200°F(1,204C) may be used. For optimum properties, forging temperature should not exceed 1,900F(1,038C). Hot working shouldnot be done below 1,700F (927C). After forging, parts should be cooled to room temperature, then solution treated prior to aging.The alloy can be cold formed in the annealed condition, utilizing conventional cold forming techniques.

 

MACHINABILITY
PH 13-8 MO alloy can be machined in both the annealed and hardened conditions. In the annealed condition, use
machine speeds 20 to 30 percent lower than those used on 304 stainless steel.

 

WELDABILITY
PH13-8MO alloy is normally welded using inert gas tungsten arc techniques, although most other welding processes may be used. These include plasma arc, electron beam, gas metal arc, and shielded metal arc processes. Helium is the preferred shielding gas.

 

SPECIAL PRECAUTIONS
All lubricants and coolants, particularly sulfur-bearing, should be removed prior to heat treatment, brazing and pickling.