Grades of Stainless Steel - Grade 321

SX 321 Technical Data

Summary

SX 321 is a titanium-stabilised version of SX 304, used in particular applications within the sensitizing temperature range.  Its resistance to sensitization, coupled with its higher strength at high temperature makes it suitable in application where SX 304 will become sensitized, or where SX 304L has insufficient hot strength.  It is not subject to weld decay (intergranular corrosion) when exposed to mildly corrosive environments.  However, welded SX 321 must never be used in highly oxidising environments as it is liable to 'Knife-line' attack.

Typical Applications

SX 321 is today used almost exclusively for service within the sensitizing temperature range (450-850^oC).  In welded ambient temperature applications it has been replaced by SX 304L.  Some typical areas of application are:
                Furnace components.
                Superheater and afterburner parts.
                Compensators and expansion bellows.

Chemical Composition (ASTM A240)
 

	C	Mn	P	S	Si	Cr	Ni	Ti
SX Analysis	0.08 max	2.0 max	0.045 max	0.030 max	1.0 max	17.0 - 19.0	9.0 - 12.0	5X%C min 0.5 max
Typical	0.06	1.2	0.020	0.020	0.5	17.5	9.4	0.48

Typical Properties in the Annealed Condition

The properties quoted in this publication are typical of mill products.  Unless otherwise indicated they should not be regarded as guaranteed minimum values for specification purposes.

1. Mechanical Properties at Room Temperature
 

	Typical	Minimum
Tensile Strength, MPa	580	515
Proof Stress (0.2 % offset), MPa	280	205
Elongation (Percent in Lo = 5.65 So)	60	40
Hardness (Brinell)	163	-
Endurance (fatigue) limit, MPa	260	-

2. Properties at Elevated Temperatures
Short Time Elevated Temperature Tensile Strength

Temperature, oC	600	650	700	750	800	850
Tensile Strength, MPa	390	329	280	230	190	140

Creep data
Stress to develop a creep rate of 1% in the indicated time at the indicated temperature.

Time	Temperature oC	550	600	650	700	800
10 000 h	Stress MPa	180	100	70	40	10
100 000 h	Stress MPa	120	80	50	25	5

Creep Rupture Stress

Time	Temperature oC	500	600	650	700	800
1 000 h	Stress MPa	270	180	140	70	30
10 000 h	Stress MPa	240	130	90	50	10
100 000 h	Stress MPa	200	90	50	15	5

Recommended Maximum Service Temperature
(Oxidising Conditions)

Continuous Service            950^oC
Intermittent Service             870^oC

Thermal Processing
1.    Annealing Heat  from 1050 to 1150^oC and cool in air.  This ensures maximum ductility of the steel.
2.    Stress Relieving SX 321 can be stress-relief annealed within the sensitization temperature range
       450-800^oC without carbide precipitation occurring, thus avoiding the possibility of intergranular corrosion.
3.     Hot working
        Initial forging and pressing temperature:              1150  - 1250^oC
        Finishing temperature:                                                   950^oC
 
 

Note:  Soaking times to ensure uniformity of temperature are up to 12  times that required for carbon steel.  Care must be exercised with this grade, and long soaking times to ensure even distribution of carbides should be employed.  The initial reductions must be light to allow dispersion of carbides in the flow pattern during forging.

 Info by  :  http://www.askzn.co.za/tech/tech_grade_321.htm