1. Difference in mechanical properties
Q235 steel phase transition point temperature (approximate value) Ac1=735℃, Ac3=855℃, Ar3=835℃, Ar1=680℃; normalizing specification temperature 920~950℃, air cooling after leaving the furnace. Hardness 131~156HBS.
20# steel cold pressed blank softening treatment specification temperature 700~720℃, holding time 8~15h, then cooling at a cooling rate of 50~100℃/h, cooling with the furnace to ≤550~600℃, air cooling after leaving the furnace. Both steels are low carbon steels. From the data, the carbon content of 20# steel is slightly higher, and the metallographic structure of both is pearlite + ferrite.
2. Use difference
Q235 steel: The yield point of steel is 235MPa, and the elongation is 21-26%. It is widely used to make general mechanical parts with certain strength and elongation, such as pins, shafts, tie rods, connecting rods, rings, bolts, nuts, cylinders, gears, brackets, racks and welded parts.
No. 20 steel: The yield point in the normalized state is 245MPa, and the elongation is >25%; the yield point in the quenched and tempered state is 280MPa, and the elongation is >22%. It is widely used to make parts with small loads and high toughness requirements, such as forged tie rods, sleeves, fixtures and gaskets in heavy and general machinery, and small and medium-sized carburized and cyanided parts in general machinery, automobiles and tractors.
No. 20 steel is high-quality carbon structural steel, Q235 is carbon structural steel, and the price of No. 20 steel is higher than that of Q235. Depending on the application, the two steels are generally interchangeable when the load is not large and the requirements are not high.
