A193 B8 CL2 vs A193 B16

[TurboME]

How does the high temperature performance (above 1000 degrees) differ between these two grades? According to ASTM A193 the yield strength for B8 class 2 (strain hardened 304) is almost the same as B16 (cr-mo-va), 100 ksi vs. 105 ksi. My understanding is 304 shouldn't be used above 900 degrees. Does this apply to B8?

The application is under hood automotive, the fastener should be exposed to little moisture and no harsh chemicals. Should corrosion failure of B16 be a major concern?

 

[metengr]

No. The B16, which is a Cr-Mo-V alloy steel, should perform well at 900 deg F because the maximum service temperature for this stud material is typically 1000 deg F. The AISI 304 ss (A 193 Grade B8 stud material) at service temperatures above 850 deg F will have a reduction in corrosion resistance over time because of a phenomenon called sensitization. Based on your post, I would not expect the sensitization to be a problem for your application.

However, it is important to note that these are two dissimilar materials with different coefficients of expansion. The AISI Type 304, which is an austenitic stainless steel, will expand at a greater rate (9.2 X E^-6 in/in degF) in comparison to B16 (7.4 X E^-6 in/in/degF), which is a ferritic material. This should be taken into account when used in bolting applications. I personally would avoid using dissimilar materials for bolting connections.