Which statement about welding medium carbon steels is true?

• A. May include preheat, postheat and controlling interpass temperatures
• B. Lower carbon % is easier to weld, but as it increases, there is a greater tendency towards brittleness
• C. To reduce hardness, keep work hot and cool slowly
• D. All of the above

Answer: (D)

Welding medium carbon steels is all about controlling heat input and the cooling rate to prevent cracking and excessive hardness. Preheating and keeping interpass temperatures within a suitable range slow down cooling, which reduces thermal gradients and hydrogen-related cracking in the heat-affected zone. Post-weld heating can temper hardened regions after welding to restore ductility and relieve residual stresses. Carbon content also matters: steels with lower carbon are easier to weld because they form softer, more ductile weld metal, but as carbon content increases, weldability decreases and the tendency toward brittleness grows, especially if cooling is rapid. To reduce hardness, keeping the work hot and cooling more slowly allows the microstructure to temper rather than form hard, brittle martensite. Since these principles all hold together for medium carbon steels, all of the above statements are true.