It depends on a number of factors:

1. What is the stress on the fastener?
2. What is the expected duration of the loading?
3. What "class" from A 193 is the fastener, i.e. Class 1D, Class 2, etc.?

For applications involving short-term exposure to temperatures below about 480 C (900 F), the short-time tensile properties are usually sufficient in the mechanical design of steel components.  For temperatures above 480 C, the design process must include other properties such as creep rate, etc.  Class 1D fasteners are restricted to applications at less than 455 C.

ASME Boiler codes use the following relationship:

maximum allowable stress based on yield strength = 0.67 * 0.2% offset yield strength

maximum allowable stress based on creep and rupture strength = creep strength for 0.01% per 1000 hours

Some data on the high temperature strength of a typical 18-8 stainless steel:

              425 C        650 C
YS       ~ 300 MPa    ~ 190 MPa

TS       ~ 650 MPa    ~ 450 MPa

This data is based on room temperature properties of YS ~ 450 MPa and TS ~ 900 MPa.