1. Different lower limits of yield strength: Yield strength refers to the critical stress value at which a material begins to undergo plastic deformation when subjected to tensile force. The lower limit of yield strength of Q235 is 235MPa, while the lower limit of yield strength of Q345 is 345MPa.
2. Different steel categories: Q235 belongs to ordinary carbon steel, which refers to steel with a low carbon content; while Q345 belongs to low alloy steel, which refers to steel with a small amount of alloy elements added to ordinary carbon steel to improve its performance.
3. Different composition: Q235 is made of carbon structural steel, which refers to steel composed of iron and carbon elements without other alloy elements; while Q345 is made of low alloy structural steel, which refers to carbon structural steel with a small amount of alloy elements added.

Answers

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