Q420GJC high-strength construction steel is a low-alloy high-strength structural steel widely used in bridges, buildings, ships, aerospace, and other fields. Due to its high yield strength and tensile strength, good toughness, and welding performance, the performance changes of Q420GJC high-strength construction steel in low-temperature environments have attracted significant attention.

In low-temperature environments, the performance of Q420GJC high-strength construction steel undergoes changes, mainly in the following aspects:

1. Yield strength and tensile strength: In low-temperature environments, the yield strength and tensile strength of Q420GJC high-strength construction steel increase. This is because, at low temperatures, atomic motion in the steel slows down, and dislocation movement is hindered, thereby enhancing the steel's strength.

2. Toughness: In low-temperature environments, the toughness of Q420GJC high-strength construction steel decreases. This is because, at low temperatures, dislocation movement in the steel becomes difficult, making the steel prone to cracking and fracturing under impact loads.

3. Impact toughness: Impact toughness is an important indicator for evaluating a material's resistance to impact in low-temperature environments. In low-temperature environments, the impact toughness of Q420GJC high-strength construction steel decreases, which may affect the processing and service performance of the steel plate.

4. Low-temperature bending performance: Low-temperature bending performance is an important indicator for evaluating a material's load-bearing capacity in low-temperature environments. In low-temperature environments, the low-temperature bending performance of Q420GJC high-strength construction steel is affected, which may impact the processing and service performance of the steel plate.

Factors affecting the performance changes of Q420GJC high-strength construction steel at low temperatures mainly include chemical composition, microstructure, and stress state. Chemical composition is one of the important factors influencing the low-temperature performance of Q420GJC high-strength construction steel. The content of elements such as carbon, silicon, and manganese in the steel affects its strength, hardness, toughness, and other properties. For example, carbon can increase the strength and hardness of steel but reduces its toughness. Silicon and manganese, on the other hand, can improve the strength and toughness of steel.

Microstructure refers to the microstructural characteristics of the steel, such as grain size, morphology, and phase composition. Different microstructures directly affect the performance of Q420GJC high-strength construction steel at low temperatures. For example, a fine-grained structure can enhance the low-temperature toughness of steel.

Stress state also affects the performance of Q420GJC high-strength construction steel at low temperatures. Under complex stress states, the low-temperature performance of the steel plate may be compromised.

In summary, the performance changes of Q420GJC high-strength construction steel at low temperatures are multifaceted and require comprehensive consideration of factors such as chemical composition, microstructure, and stress state. When using Q420GJC high-strength construction steel in low-temperature environments, it is necessary to fully consider its performance changes and make corresponding design adjustments based on actual engineering needs. For example, measures such as increasing structural redundancy, improving material microstructure, and implementing temperature control can be taken to enhance the performance of Q420GJC high-strength construction steel in low-temperature environments.