I can't say anything better than what Mario just said, but as a point of clarification, high strength carbon steel is commonly of higher hardness, and being of higher hardness means higher susceptibility to *cracking* in particular.

H2S + H2O = H+ + HS- + H3O + H2S + H2O and all fluctuate.

How that manifests specifically into cracking, I'm not entirely sure.

I speculate that the entirety has the capability of stripping surface atoms off (corrosion), increasing roughness. The H+ has the capacity to intrude "far" and the metallic electrons look particularly appealing to them. H3O is also thinking those metallic electrons look scrumptious and collects into those rough patches.

When you see a temperature spike, you'll either make more room for more H3O and H or you'll see a crack, depending on whether it gets hot or cold.