Is it reasonable for GBT700 Q235A mild steel quenching to get martensite

GBT700 Q235A mild steel has features of good ductility and plasticity, certain elongation, good welding performance and heat processing property. Q235A mild steel materials are usually delivered in hot rolling condition, and applied in light industry, machinery, transport vehicles, buildings and other general structural parts.

The carbon content of GBT700 Q235A mild steel is 0.14~0.22%. The solid solubility of carbon in Alfa iron at room temperature is only 0.0008%. So, in theory, Q235A mild steel can be quenched to get martensite. However, the hardness of the martensitic carbon is very low, even after quenching, it is only about 170HBS. The hardness of Q235A mild steel itself is about 144HBS.

If use 25# steel, even the carbon content only be increased by 0.05%, but the quenching hardness of the steel can be up to 350HBS.

It can be seen that after quenching, the GBT700 Q235A mild steel has no obvious improvement in strength and hardness, and Q235A mild steel also faces the heat treatment defects such as deformation, cracking, oxidation and decarburization, and Q235A mild steel is rather ineffective for a heat treatment cost. In this aspect, 25# steel do much better than GBT700 Q235A mild steel.