A193-B8M and A320-B8M are specifications for stainless steel stud bolts
A193 is the Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for High-Temperature Service.
A320 is the Standard Specification for Alloy/Steel Bolting Materials for Low-Temperature Service. The former is the "standard" most commonly used for valve and flange bolting. The latter usually requires better control on grain structure and passing certain destructive tests to measure low temperature ductility.
B8M designates a chemistry similar to 316 (where the M stands for molybdenum).
316 is the standard 18Cr-10Ni-2Mo with 0.08C max
316L is basically 316 with .03C max.
The L grade is to increase resistance to intergranular corrosion after welding. (Less carbon means less chance of sensitization). Since bolting is not welded I am not sure you can get it that way.
Grade B8M has the same compostion in both ASTM A193 and ASTM A320 Standard.
However,there are some difference between ASTM A193 B8M and ASTM A320 B8M stud bolt,even they are the same B8M grade
1. Temperature Range
- ASTM A193-B8M:
- Operates well at elevated temperatures (up to 1200°F or 650°C depending on conditions).
- ASTM A320-B8M:
- Optimized for low-temperature performance, maintaining toughness at temperatures as low as -150°F (-100°C).
2. Mechanical Properties difference
- A193-B8M:
- Focused on tensile and creep strength at high temperatures.
- Higher yield strength compared to A320-B8M.
- A320-B8M:
- Prioritizes impact toughness at low temperatures.Charpy V-notch impact test is required for A320 B8M
- May have slightly reduced tensile strength due to the emphasis on ductility.,
3. Heat Treatment
- A193-B8M: Solution annealing is typically done to enhance corrosion resistance and strength.
- A320-B8M: Similar heat treatment but with specific controls to meet low-temperature toughness criteria.
4. Markings
- Both bolts are marked with their grade for easy identification.
- A193 bolts are stamped “B8M” (possibly with an “A” or “C” suffix for Class 1 or 2).
- A320 bolts are stamped “B8M” with a low-temperature designation.
How to choose the Stud bolt between A193-B8M and A320-B8M stud bolts
if you are looking for a 316 bolt for high temp ,A193-B8M would be recommended
For low temperature applications, A320-B8M is recommended
