Q What is the difference between ASTM F1554 Grade 55 and ASTM A193 B7?
Grade 55 is more elastic and available at a lower cost, rendering it more applicable for general construction needs, while B7 is heat treated and contains alloys that make it more suitable for corrosive environments. Though relevant for many construction applications and certainly more cost-effective than B7, Grade 55 is still a specialty steel that few manufacturers or distributors supply.
The primary difference between ASTM F1554 Grade 55 and ASTM A193 B7 is that Grade 55 is more ductile than B7, but nevertheless is appropriate in high-strength applications. This increased elasticity means that Grade 55 is most frequently used in the construction industry, as buildings and other infrastructure naturally experience displacement over time. On the other hand, B7 is heat treated, increasing strength but rendering the material more brittle.
B7 is an alloy which includes chromium and molybdenum for added strength and corrosion resistance, rendering it suitable for applications that are highly susceptible to corrosion at high temperatures. For example, common uses are in chemical and petroleum facilities. The addition of these alloying elements is costly, and typically means that B7 would be an over-engineered option if used in a general construction application.
F1554 Grade 36
All America Threaded Products (AATP) supplies Grade 55 S1 products that are weldable in accordance to Supplementary Requirement 1 of the F1554 specification. Since AATP’s product meets these requirements, it can be distributed as F1554 Grade 36 while B7 is not considered weldable.
F1554 Grade 55 & ASTM A193 B7
If the application allows for a straight bolt, then B7 can be considered as a substitute for F1554 Grade 105. They are both heat treated parts with near identical mechanical and chemical requirements.