Grades

There are several grades within the A193 specification. Each grade possesses unique chemical requirements, strength requirements, testing requirements, and applications. This website summarizes the similarities and differences between many of the grades. For more specific information, please refer to the actual ASTM A193 specification which can be purchased directly from ASTM International.

Grade B7b7

ASTM A193 Grade B7 bolts and threaded studs are manufactured from a chromium-molybdenum steel and are quenched and tempered (heat treated) to develop the desired mechanical properties (strength). Grade B7 is the most common grade of A193 bolts used in construction. B7 threaded studs and short, headed bolts are readily available in the marketplace. Grade B7 bolts are commonly used in pipe flange connections. These bolts are typically bought and sold in a plain, bare metal finish but are often hot-dip galvanized, zinc plated, Xylan coated, PTFE coated, or otherwise coated for corrosion resistance. Note that coated bolts may not be able to withstand the high temperatures that uncoated B7 bolts can be subjected to.

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

Grade B8b8

ASTM A193 Grade B8 Class 1 bolts and threaded studs are manufactured from AISI 304 stainless steel. Type 304 is the most common grade of stainless steel used in the fastener industry. Fasteners manufactured using this austenitic stainless steel require carbide solution treatment on bars to be threaded or after the heading operation for bolts with forged heads.  Carbide solution treatment, also referred to as solution annealing, is a process in which fasteners or stainless bars are heated and then water-quenched to assure maximum corrosion resistance.  A193 Grade B8 Class 2 bolts are strain hardened after carbide solution treatment to achieve increased strength characteristics and reduce the potential for galling. Class 2 bolts are marked “B8SH” with the grade symbol underlined.

Grade Size Tensile ksi, min Yield, ksi, min Elong, %, min RA % min HBW HRC
B8 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

Grade B8Mb8m

ASTM A193 Grade B8M Class 1 fasteners are similar to Grade B8 but instead are manufactured from AISI 316 stainless steel as opposed to AISI 304 stainless steel. Type 316 stainless offers superior corrosion resistance to type 304 stainless due to the added molybdenum. Grade B8M Class 1 fasteners require carbide solution treatment, while Class 2 fasteners require an additional strain hardening operation which increases the strength and reduces the susceptibility to galling. Class 2 fasteners are marked “B8MSH” with the grade symbol underlined.

Grade Size Tensile ksi, min Yield, ksi, min Elong, %, min RA % min HBW HRC
B8M Class 1 All 75 30 30 50 223 max 96 max
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

Grade B7Ma193-b7m

ASTM A193 Grade B7M bolts and studs are identical in chemistry to Grade B7 (quenched and tempered medium carbon alloy steel), but have lower strength requirements and require 100% hardness testing of all fasteners manufactured in the lot. Grade B7M bolts resist chloride, sulfide, and hydrogen stress corrosion cracking (SCC) and are frequently used in sour gas service.

Grade Diameter Tensile ksi, min Yield, ksi, min Elong, %, min RA % min HBW HRC
B7 Up to 4 100 80 18 50 235 max -
Over 4 - 7 100 75 18 50

Grade B16

a193-b16

ASTM A193 Grade B16 bolts and threaded studs are manufactured from a chromium-molybdenum-vanadium alloy steel. Although A193 Grade B16 bolts and studs have similar strength requirements as Grade B7, the vanadium and higher tempering temperature helps the fasteners retain their molecular structure and strength under higher ambient temperatures than Grade B7. Grade B16 bolts and studs are used in the power and petrochemical industries on boilers, turbines, and other pressurized equipment with elevated temperatures. Unlike the stainless steel grades within the A193 specification, Grade B16 has no corrosion-resistant properties unless they are coated.

Grade Diameter Tensile ksi, min Yield, ksi, min Elong, %, min RA % min HBW HRC
B16 Up to 2-1/2 125 105 18 50 321 max 35 max
Over 2-1/2 to 4 110 95 17 45
Over 4 to 8 100 85 16 45

Grade B5a193-b5

ASTM A193 Grade B5 bolts and threaded studs are manufactured from AISI 501 stainless steel which has been quenched and tempered to increase strength. These bolts and studs are often used in high temperature flanged connections in highly corrosive environments.

Grade Diameter Tensile ksi, min Yield, ksi, min Elong, %, min RA % min HBW HRC
B5 Up to 4, incl 100 80 16 50 - -

Grade B6a193-b6

ASTM A193 Grade B6 bolts and threaded rods are manufactured from AISI 410 stainless steel which has been quenched and tempered to increase strength. Because these bolts are manufactured from stainless steel, they are used in highly corrosive environments with elevated ambient temperatures.

Grade Diameter Tensile ksi, min Yield, ksi, min Elong, %, min RA % min HBW HRC
B6 Up to 4, incl 110 85 15 50 - -
B6X 90 70 16

Grade Variations

Grade variations of the A193 specification which are rarely used and therefore not addressed on this site include: B6X, B8A, B8C, B8CA, B8MA, B8M2, B8M3, B8P, B8PA, B8N, B8NA, B8MN, B8MNA, B8MLCuN, B8MLCuNA, B8r, B8RA, B8S, B8SA, B8LN, B8LNA, B8MLN, B8MLNA, B8CLN, B8CLNA, B8T, and B8TA. If you need more information about these variations, contact me.