Type Analysis | Description | Corrosion Resistance | Scaling | Physical Properties
Heat Treatment | Workability | Typical Mechanical Properties

Type Analysis

Description

21Cr-6Ni-9Mn is a high maganese nitrogen strengthened, austenitic stainless steel that combines high strength in the annealed condition, excellent resistance to oxidation at high temperatures, good resistance to lead oxide and a high level of corrosion resistance at ambient temperatures. The alloy can be fabricated and formed much the same as Type 304 and 316, and is readily weldable. It remains nonmagnetic after severe cold work.
21Cr-6Ni-9Mn has been used for chemical process and pollution-control equipment, steam and autoclave applications, and various aircraft engine components, as well as numerous other applications.

Corrosion Resistance

21Cr-6Ni-9Mn has corrosion resistance approaching that of Type 304L. Its low carbon content provides resistance to intergranular corrosion even in the welded condition. For optimum corrosion resistance, surfaces must be free of scale and foreign particles and finished parts should be passivated.

Typical Corrosion Properties
Annealed condition

*5 periods-48 hours each
**ASTM A262 Practice A

Scaling

21Cr-6Ni-9Mn has good resistance to high temperature oxidation in air and to corrosion by molten lead oxide.

Physical Properties

Specific gravity .................................. 7.83
Density
lb/cu in ............................................. 0.283
kg/cu m ............................................. 7830
Mean specific heat
Btu/lb-°F(32/212°F) .......................... 0.12
J/kg-K(0-100°C) ................................. 500
Electrical resistivity (RT)
ohm-cir mil/ft ...................................... 439
microhm-mm ....................................... 730
Modulus of elasticity (E)
ksi ........................................... 28.5 x 10(3)
MPa ...................................... 196.5 x 10(3)

Mean Coefficient of Thermal Expansion

Thermal Conductivity

Magnetic Permeability

Heat Treatment

Stress Relieving
Stress relieving is used to achieve best all-around properties and for operating temperatures below 1300°F. The temperature range for stress relieving is 900/1400°F. Temperatures between 900 and 1250°F will have little effect on the mechanical properties of cold reduced material unless the percent cold reduction is high; then slight increases or decreases in strength will occur. Above 1250°F, the change in mechanical properites will occur more rapidly; a temperature of 1500°F begins to cause rapid softening. The proper stress relief treatment should be selected carefully in order to produce the desired strength levels.

Annealing
Annealing is used for best stress rupture life and for operating temperatures between 1300 and 1600°F. The alloy is not recommended for service above 1600°F. Also, annealing softens the alloy for maximum formability. After the annealing the strength of the material can be increased only by hot/cold working or cold working.
Annealing is generally done in the temperature range of 1800/2150°F. Grain coarsing will occur at the higher temperatures. Lower temperatures such as 1650°F can be used; the temperature must be selected according to the degree of softening required and grain size restrictions.

Workability

Hot Working
21Cr-6Ni-9Mn can be forged, hot rolled, hot headed and upset. An initial forging temperature of 2100/2200°F is normally used. Preheating to an intermediate temperature is not required. Forging can be rapidly cooled without danger of cracking. This alloy can be hot worked as low as 1200°F, and is not susceptible to hot shortness in the entire working range. For best corrosion resistance, anneal after forging.

Cold Working
This alloy is readily cold worked by conventional methods. The alloy's high work-hardening rate and higher initial yield strength dictate greater force than when forming the same part from Type 301, 302, 304, 316, etc.

Hot/Cold Working
This alloy is a solution strengthened alloy and cannot be strengthened by heat treatment. Hot/cold working or cold working can be employed to strengthen this alloy. Hot/cold working is normally done in the temperature range of 1200/1500°F ; reductions in the order of 10 to 14% are used and the percent used is dependent on the strength level required. A stress relief of 900/1400°F is normally applied after hot/cold working operations. Heat treatment of hot/cold worked material, as discussed in the preceding section, will aid in adjusting mechanical properties to the desired levels.

Machining
21Cr-6Ni-9Mn is readily machined using the techniques applied to the austenitic stainless steels. A rigid setup and ample coolant flow should be considered.

Welding
21Cr-6Ni-9Mn can be satisfactorily welded by the shielded fusion and resistance welding processes. Oxyacetylene welding is not recommended., since carbon pickup in the weld may occur. When a filler metal is required, consider AWS E/ER219 welding consumables which should provide welds with strength approaching that of the base metal. If high weld strength is not necessary, then E/ER309 should be considered. Resistance to intergranular corrosion can be restored by a postweld annealing treatment.

Typical Mechanical Properties

Effect of Annealing Temperature on Typical Room Temperature Mechanical Properties of Strip

* Annealing time was approximately 6 minutes

Typical Elevated Temperature Tensile Properties of Anneal Strip

Typical Stress Rupture Strength of Annealed Strip

21-6-9 - Current Inventory Stock