The Carbon Equivalent value is a crucial parameter evaluated when selecting structural steel for a heavy industrial shed. What primary property does the CE value predict?
- AThe ultimate tensile strength of the steel under dynamic loading.
- BThe exact coefficient of thermal expansion for the steel section.
- CThe weldability of the steel and its susceptibility to cold-cracking in the heat-affected zone.Correct
- DThe resistance of the steel to galvanic corrosion in marine environments.
Solution
Concept
Carbon equivalent and steel weldability
Formula
CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
Step-by-step solution
1. The Carbon Equivalent (CE) formula calculates the combined hardening effect of carbon and alloying additions (Mn, Cr, Mo, V, Ni, Cu). 2. As the CE value rises, steel forms hard, brittle martensite more readily in the heat-affected zone (HAZ) during weld cooling. 3. High CE values indicate increased susceptibility to hydrogen-assisted cold cracking and require preheating. 4. Thus, the CE value primarily predicts the weldability of the steel and susceptibility to HAZ cold-cracking. Answer: C
Explanation
The Carbon Equivalent (CE) formula converts the alloy content of structural steel (manganese, chromium, molybdenum, vanadium, nickel, and copper) into an equivalent carbon value. A higher CE value increases steel hardenability, promoting brittle martensite formation and susceptibility to hydrogen-induced cold cracking during cooling after welding. Evaluating the CE value ensures proper preheat temperatures and welding procedures to maintain structural weldability.
Why the other options are wrong
A) Ultimate tensile strength is determined directly from tensile coupon tests, not solely from CE. B) Thermal expansion coefficient is an intrinsic physical constant, not predicted by CE. D) Galvanic corrosion resistance depends on environmental exposure and protective coatings.
Shortcut
Carbon Equivalent (CE) = Predicts steel weldability and cold cracking susceptibility.
Common mistake
Believing CE measures ultimate tensile strength or corrosion resistance rather than weldability.
Correct answer: C) The weldability of the steel and its susceptibility to cold-cracking in the heat-affected zone.