Q420GJB steel plate is a high-strength structural steel plate widely used in construction, bridges, ships, automobiles, and other fields. The high construction composition indicators of Q420GJB steel plate are as follows:

1. Carbon content (C): The carbon content of Q420GJB steel plate generally ranges from 0.14% to 0.22%. Carbon is the main strengthening element in steel, which can improve the strength and hardness of the steel, but excessive carbon content will reduce toughness and plasticity.

2. Silicon content (Si): The silicon content of Q420GJB steel plate generally ranges from 0.10% to 0.35%. Silicon can improve the strength and hardness of steel, while also enhancing its oxidation resistance and wear resistance.

3. Manganese content (Mn): The manganese content of Q420GJB steel plate generally ranges from 1.40% to 1.80%. Manganese is an effective deoxidizer that can improve the purity of steel, while also enhancing its strength and hardness.

4. Phosphorus content (P): The phosphorus content of Q420GJB steel plate should not exceed 0.04%. Phosphorus is a harmful element that reduces the toughness and plasticity of steel, while also increasing its cold brittleness and aging sensitivity.

5. Sulfur content (S): The sulfur content of Q420GJB steel plate should not exceed 0.04%. Sulfur is also a harmful element that reduces the toughness and plasticity of steel, while also increasing its corrosion susceptibility and fatigue strength.

6. Nickel content (Ni): The nickel content of Q420GJB steel plate generally ranges from 0.20% to 0.60%. Nickel can improve the strength and toughness of steel, while also enhancing its oxidation resistance and corrosion resistance.

7. Chromium content (Cr): The chromium content of Q420GJB steel plate generally ranges from 0.20% to 0.60%. Chromium can improve the strength and hardness of steel, while also enhancing its wear resistance and corrosion resistance.

8. Molybdenum content (Mo): The molybdenum content of Q420GJB steel plate generally ranges from 0.20% to 0.60%. Molybdenum can improve the strength and toughness of steel, while also enhancing its wear resistance and corrosion resistance.

9. Vanadium content (V): The vanadium content of Q420GJB steel plate generally ranges from 0.10% to 0.50%. Vanadium can improve the strength and toughness of steel, while also enhancing its wear resistance and corrosion resistance.

The above are the detailed information on the high construction composition indicators of Q420GJB steel plate. When selecting and using Q420GJB steel plate, it is necessary to pay attention to these composition indicators to ensure that the quality of the steel plate meets the usage requirements.