It has high strength and hardenability. The critical hardenability diameter in oil is 4-22 mm, and in water is 11-40 mm, but the toughness is poor. There is still a tendency of grain growth when carburizing this steel. The impact toughness is greatly affected by direct quenching after cooling. Therefore, secondary quenching after carburizing is needed to improve the core toughness of the parts without tempering brittleness. The cold strain plasticity of steel is high and can be drawn in cold state; the machinability is good at high temperature normalizing or tempering, but poor after annealing; the weldability is good, and heat treatment is generally not needed after welding, but parts thicker than 15mm need to be preheated to 100-150 C before welding.