What are the differences between F593 and A193 stainless steel headed bolts?

There are many differences between these two specifications.  In order to understand these dissimilarities there are overviews of each specification below followed by a short summary of these variances.  For the purposes of this FAQ we will be focusing on A193 Grades B8 (Type 304) and B8M (Type 316) versus  F593 Alloy Group 1 (Type 304) and Alloy Group 2 (Type 316).

ASTM A193

The fasteners under the ASTM A193 specification are designed to be used in high temperature or high pressure service, often in flanges and piping systems.  Headed fasteners in this specification require a heavy hex pattern head unless otherwise specified. Also, threads above 1” in diameter are specified as 8 threads per inch (8UN).

Hot-forged headed stainless steel bolts under the A193 specification require solution annealing after forging to restore full corrosion-resistant properties. If a scale-free bright finish is required, this must be specified in the purchase order. A193 bolts require ASTM A194 heavy hex nuts in the matching stainless steel type.

A193 Marking Requirements include grade symbol and manufacturer’s identifier.

ASTM A193/A320 Grade B8 A193/A320 Grade B8 Class 1
ASTM A193/A320 Grade B8M A193/A320 Grade B8M

The mechanical properties are listed below.

Grade Size Tensile ksi, min Yield, ksi, min Elong, %, min RA % min HBW HRC
B7 Up to 2-1/2 125 105 16 50 321 max 35 max
2-5/8 - 4 115 95 16 50
4-1/8 - 7 100 75 18 50
B8 Class 1 All 75 30 30 50 223 max 35 max
B8M Class 1 All 75 30 30 50 223 max 96 max
B8 Class 2 Up to 3/4 125 100 12 35 321 max 35 max
7/8 - 1 115 80 15 35
1-1/8 - 1-1/4 105 65 20 35
1-3/8 - 1-1/2 100 50 28 45
B8M Class 2 Up to 3/4 110 95 15 45 321 max 35 max
7/8 - 1 100 80 20 45
1-1/8 - 1-1/4 95 65 25 45
1-3/8 - 1-1/2 90 50 30 45

ASTM F593

The F593 specification is more of a general purpose stainless steel specification used in all different applications.  The headed bolts in the F593 specification require a standard hex head pattern (as opposed to heavy hex) unless otherwise specified.  Diameters above 1” require Unified National Coarse (UNC) threads unless otherwise specified.

Hot-forged headed stainless steel bolts under the F593 specification are manufactured to either Condition A or Condition CW which both require solution annealing after forging to restore full corrosion-resistant properties.   F593 bolts require ASTM F594 hex nuts in the matching stainless steel type.

One primary difference between A193 and F593 hot-forged bolts is that F593 requires an additional test for susceptibility to intergranular corrosion, which the A193 specification does not.  This test adds to both the cost and lead time to produce this grade of stainless headed bolt.

F593 Marking requirements include grade symbol and manufacturer’s identifier. The mechanical properties for these two alloy groups are listed below.

Alloy Group Condition Marking Diameter Range Tensile, ksi Yield, ksi min Rockwell Hardness
1 AF F593A 1/4 to 1-1/2 65 to 85 20 B85 max
A F593B 1/4 to 1-1/2 75 to 100 30 B65 to 95
CW1 F593C 1/4 to 5/8 100 to 150 65 B95 to C32
CW2 F593D 3/4 to 1-1/2 85 to 140 45 B80 to C32
2 AF F593E 1/4 to 1-1/2 65 to 85 20 B85 max
A F593F 1/4 to 1-1/2 75 to 100 30 B65 to 95
CW1 F593G 1/4 to 5/8 100 to 150 65 B95 to C32
CW2 F593H 3/4 to 1-1/2 85 to 140 45 B80 to C32

Summary

There are multiple differences between these two specifications.  The A193 specification is designed for use in high-temperature, high-pressure applications whereas F593 is used as more of a generic, all-purpose use fastener.  There are varying mechanical properties between the two specifications along with configuration differences for headed bolts and varying thread pitch requirements.  There are also additional testing requirements for F593 which are not required under the A193 specification.

Do you have a job that requires A193 or F593 stainless steel fasteners?  Give Portland Bolt a call – our experts are standing by to assist you with all of your stainless steel fastener needs.

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