24 July 2021 Hardware Tool Steel Bar
ASTM A193 Grade B7 Hardware Tool Steel Bar
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.
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 |
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 |