Standard Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure Service and Other Special Purpose Applications

ASTM A193 specification covers alloy and stainless steel bolting for pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications. Several grades are covered, including ferritic steels and austenitic stainless steels designated B5, B6, B7, B8, B8M, etc. Selection will depend upon design, service conditions, mechanical properties, and high temperature characteristics. This specification is expressed in both inch-pound units and in SI units; however, unless the purchase order or contract specifies the applicable A193M specification designation (SI units), the inch-pound units shall apply

Bolting Grades

Grade Tensile Class Raw Material Description
B5 4-6% Chromium Ferritic Steel
B6 13% Chromium Ferritic Steel
B6X 13% Chromium Ferritic Steel
B7 Chromium Molybdenum Alloy Steel, Quenched & Tempered
B7M Chromium Molybdenum Alloy Steel, Quenched & Tempered
B16 Chromium-molybdenum-vanadium Alloy Steel, Quenched & Tempered
B8 Class 1 AISI 304 Stainless Steel, Carbide Solution Treated
B8 Class 2 AISI 304 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8A AISI 304 Stainless Steel, Carbide solution treated in the finished condition
B8C Class 1 AISI 347 Stainless Steel, Carbide Solution Treated
B8C Class 2 AISI 347 Stainless Steel, Carbide Solution Treated and Strained Hardened
B8CA AISI 347 Stainless Steel, Carbide Solution Treated in Finished Condition
B8M Class 1 AISI 316 Stainless Steel, Carbide Solution Treated
B8M Class 2 AISI 316 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8MA AISI 316 Stainless Steel, Carbide Solution Treated in Finished Condition
B8M2 AISI 316 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8M3 AISI 316 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8P Class 1 AISI 305 Stainless Steel, Carbide Solution Treated
B8P Class 2 AISI 305 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8PA AISI 305 Stainless Steel, Carbide Solution Treated in Finished Condition
B8N AISI 304N Stainless Steel, Carbide Solution Treated
B8N AISI 304N Stainless Steel, Carbide Solution Treated and Strain Hardened
B8MLCuN AISI 304N Stainless Steel, Carbide Solution Treated and Strain Hardened
B8MLCuN UNS S31254 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8MLCuNA UNS S31254 Stainless Steel, Carbide Solution Treated
B8T Class 1 AISI 321 Stainless Steel, Carbide Solution Treated
B8T Class 2 AISI 321 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8TA AISI 321 Stainless Steel, Carbide Solution Treated in Finished Condition
B8R Nitronic 50/UNS S20910 Stainless Steel, Carbide Solution Treated
B8RA Nitronic 50/UNS S20910 Stainless Steel, Carbide Solution Treated in Finished Condition
B8S Nitronic 60/UNS S21800 Stainless Steel, Carbide Solution Treated
B8SA Nitronic 60/UNS S21800 Stainless Steel, Carbide Solution Treated
B8LN AISI 304LN Stainless Steel, Carbide Solution Treated
B8LNA AISI 304LN Stainless Steel, Carbide Solution Treated in Finished Condition
B8MLN AISI 316LN Stainless Steel, Carbide Solution Treated
B8MLNA AISI 316LN Stainless Steel, Carbide Solution Treated in Finished Condition
B8CLN AISI 347LN Stainless Steel, Carbide Solution Treated
B8CLNA AISI 347LN Stainless Steel, Carbide Solution Treated in Finished Condition

ASTM A193 Chemical Composition

Each alloy shall conform to the chemical composition requirements.

Ferritic Steels
Element Grade B5 Grade B6, B6X Grade B7, 7M Grade B16
Carbon 0.10 min 0.08-0.15 0.37-0.49 0.36-0.47
Manganese, max 1.00 1.00 0.65-1.10 0.45-0.70
Phosphorus, max 0.040 0.040 0.035 0.035
Sulfur, max 0.030 0.030 0.040 0.040
Silicon 1.00 max 1.00 max 0.15-0.35 0.15-0.35
Chromium 4.00-6.00 11.5-13.5 0.75-1.20 0.80-1.15
Molybdenum 0.40-0.65 -- 0.15-0.25 0.50-0.65
Vanadium -- -- -- 0.25-0.35
Aluminium, max -- -- -- 0.015
Austenitic Steels, Classes 1, 1A, 1D, and 2
Element Grade B8, B8A Grade B8C, B8CA Grade B8M, B8MA, B8M2, B8M3
Carbon, max 0.08 0.08 0.08
Manganese, max 2.00 2.00 2.00
Phosphorus, max 0.045 0.045 0.045
Sulfur, max 0.030 0.030 0.030
Silicon, max 1.00 1.00 1.00
Chromium 18.0-20.0 17.0-19.0 16.0-18.0
Molybdenum -- -- 2.00-3.00
Columnium + Tantalum -- 10 x carbon content, min – 1.10 max --
Austenitic Steels, Classes 1A, 1B, 1D, and 2
Element Grade B8N, B8NA Grade B8MN, B8MNA Grade B8MLCuN, B8MLCuNA
Carbon 0.10 min 0.08-0.15
Manganese, max 1.00 1.00
Phosphorus, max 0.040 0.040
Sulfur, max 0.030 0.030
Silicon 1.00 max 1.00 max
Chromium 4.00-6.00 11.5-13.5
Molybdenum 0.40-0.65 --
Columnium + Tantalum --
Austenitic Steel, Classes 1, 1A and 2
Element Grade B8T, B8TA
Carbon 0.10 min
Manganese, max 1.00
Phosphorus, max 0.040
Sulfur, max 0.030
Silicon 1.00 max
Chromium 4.00-6.00
Molybdenum 0.40-0.65
Austenitic Steels, Classes 1C and 1D
Element Grade B8R, B8RA Grade B8S, B8SA
Carbon, max 0.10 min 0.08-0.15
Manganese 4.00-6.00 1.00
Phosphorus, max 0.040 0.040
Sulfur, max 0.030 0.030
Silicon 1.00 max 1.00 max
Chromium 4.00-6.00 11.5-13.5
Molybdenum 0.40-0.65 --

ASTM A193 Mechanical Properties

The material as represented by the tension specimens shall conform to the requirements at room temperature after heat treatment. Alternatively, stainless strain hardened fasteners (Class 2, 2B, and 2C) shall be tested full size after strain hardening to determine tensile strength and yield strength and shall conform to the requirements prescribed in Table 2 and 3. Should the results of full size tests conflict with results of tension specimen tests, full size test results shall prevail.

Grade Diameter Tensile Strength Yield Strength Elongation Reduction Hardness
Grade B5 Up to M100, inclusive 690 550 16 50 --
Grade B6 Up to M100, inclusive 760 585 15 50 --
Grade B6X Up to M100, inclusive 620 485 16 50 26 HRC
Grade B7 M64 and under 860 720 16 50 321 HBW or 35 HRC
Grade B7 Over M64 to M100 795 655 16 50 321 HBW or 35 HRC
Grade B7 Over M100 to M180 690 515 18 50 321 HBW or 35 HRC
Grade B7M M100 and under 690 550 18 50 235 HBW or 99 HRB
Grade B7M M100 and over 690 515 18 50 235 HBW or 99 HRB
Grade B16 M64 and under 860 725 18 50 321 HBW or 35 HRC
Grade B16 Over M64 to M100 760 655 17 45 321 HBW or 35 HRC
Grade B16 Over M100 to M180 690 585 16 45 321 HBW or 35 HRC
Grade B8, B8M, Class 1, 1D All Diameters 515 205 30 50 223 HBW or 96 HRB
Grade B8, B8C, B8T, Class 2 M20 and under 860 690 12 35 321 HBW or 35 HRC
Grade B8, B8C, B8T, Class 2 M20 to M24, inclusive 690 550 20 45 321 HBW or 35 HRC
Grade B8, B8C, B8T, Class 2 M24 to M30, inclusive 655 450 25 45 321 HBW or 35 HRC
Grade B8, B8C, B8T, Class 2 M30 to M36, inclusive 620 345 30 45 321 HBW or 35 HRC
Grade B8, B8M2, Class 2B M48 and under 655 515 25 40 321 HBW or 35 HRC
Grade B8, B8M2, Class 2B M48 to M64, inclusive 620 450 30 40 321 HBW or 35 HRC
Grade B8, B8M2, Class 2B M64 to M72, inclusive 550 380 30 40 321 HBW or 35 HRC
Grade B8A, B8MA, B8CA, B8TA, B8MLCuNA, Class 1A All Diameters 515 205 30 50 192 HBW or 90 HRB
Grade B8M, B8MLCuN, Class 2 M20 and under 760 655 15 45 321 HBW or 35 HRC
Grade B8M, B8MLCuN, Class 2 M20 to M24, inclusive 690 550 20 45 321 HBW or 35 HRC
Grade B8M, B8MLCuN, Class 2 M24 to M30, inclusive 655 450 25 45 321 HBW or 35 HRC
Grade B8M, B8MLCuN, Class 2 M30 to M36, inclusive 620 345 30 45 321 HBW or 35 HRC
Grade B8M3, Class 2C M48 and under 585 450 30 60 321 HBW or 35 HRC
Grade B8M3, Class 2C Over M48 585 415 30 60 321 HBW or 35 HRC
Grade B8C, B8T, Class 1 All Diameters 515 205 30 50 192 HVW or 90 HRB
Grade B8R, Class 1C, 1D All Diameters 690 380 35 55 271 HBW or 28 HRC
Grade B8RA Class 1C All Diameters 690 380 35 55 271 HBW or 28 HRC
Grade B8S, Class 1C, 1D All Diameters 655 345 35 55 271 HBW or 28 HRC
Grade B8SA Class 1C All Diameters 655 345 35 55 271 HBW or 28 HRC

Heat Treatment

Ferritic steels shall be allowed to cool to a temperature below the cooling transformation range immediately after rolling or forging. Materials shall then be uniformly reheated to the proper temperature to refine the grain (a group thus reheated being known as a quenching charge), quenched in a liquid medium under substantially uniform conditions for each quenching charge, and tempered. The minimum tempering temperature shall be as specified in Tables 2 and 3.

ASTM A193 Marking Requirements

Class Grade Grade Symbol
Class 1 B8
B8C
B8M
B8P
B8T
B8LN
B8MLN
B8CLN
B8
B8C
B8M
B8P
B8T
B8F or B8LN
B8G or B8MLN
B8Y or B8CLN
Class 1A B8A
B8CA
B8MA
B8PA
B8TA
B8LNA
B8MLNA
B8NA
B8MNA
B8MLCuNA
B8CLNA
B8A
B8B or B8CA
B8D or B8MA
B8H or B8PA
B8J or B8TA
B8L or B8LNA
B8K or B8MLNA
B8V or B8MA
B8W or B8MNA
B9K or B8MLCuNA
B8Z or B8CLNA
Class 1B B8N
B8MN
B8MLCuN
B8N
B8Y or B8MN
B9J or B8MLCuN
Class 1C B8R
B8RA
B8S
B8SA
B9A or B8R
B9B or B8RA
B9D or B8S
B9F or B8SA
Class 1D B8
B8M
B8P
B8LN
B8MLN
B8N
B8MN
B8R
B8S
B8CLN
B94
B95
B96
B97
B98
B99
B100
B101
B102
B103
Class 2 B8
B8C
B8P
B8T
B8N
B8M
B8MN
B8MLCuN
B8SH
B8CSH
B8PSH
B8TSH
B8NSH
B8MSH
B8YSH
B0JSH
Class 2B B8M2
B8
B9G or B8M2
B9
Class 2C B8M3 B9H or B8M3

Recommended Nuts & Washers

Bolting Grade Nut Grade Washer Grade
ASTM A193 Grade B6, B6X ASTM A194 Grade 6 Mild Steel
ASTM A193 Grade B7,7M ASTM A194 Grade 2H, 2HM ASTM F436
ASTM A193 Grade B16 ASTM A194 Grade 16 ASTM F436
ASTM A193 Grade B8 ASTM A194 Grade 8 SS 304
ASTM A193 Grade B8M, B8MA, B8M2, B8M3 ASTM A194 Grade 8M, 8MA SS 316
ASTM A193 Grade B8C, B8CA ASTM A194 Grade 8C, 8CA SS 347
ASTM A193 Grade B8T, B8TA ASTM A194 Grade 8T, 8TA SS 321
ASTM A193 Grade B8MLCuN, B8MLCuNA ASTM A194 Grade 8MLCuN, 8MLCuNA 254SMO / UNS S31254
ASTM A193 Grade B8R, B8RA ASTM A194 Grade 8R, 8RA Nitronic 50/UNS S20910
ASTM A193 Grade B8S, B8SA ASTM A194 Grade 8S, 8SA Nitronic 60/UNS S21800