1. Different shapes:
Round steel has a smooth outer surface.
Rebar has spiral ribs on its outer surface.

2. Different production standards:
In current standards, round steel refers to HPB235 grade rebar, and its production standard is "Hot-rolled plain steel bars for reinforced concrete" (GB13013).
Rebar generally refers to HRB335 and HRB400 grade rebar, and its production standard is "Hot-rolled ribbed steel bars for reinforced concrete" (GB1499).

3. Strength Differences:
The design strength of round steel (HPB235) is 210 MPa.
Rebar has higher strength than round steel. The design strength of HRB335 is 300 MPa, and the design strength of HRB400 is 360 MPa.

4. Different steel grades (chemical compositions):
Round steel (HPB235) is a carbon steel, grade Q235.
Rebar is a low-alloy steel. HRB335 grade rebar is 20MnSi (20 manganese silicon); HRB400 grade rebar is 20MnSiV, 20MnSiNb, or 20MnTi, etc. 5. Different physical and mechanical properties:
Due to differences in the chemical composition and strength of steel bars, their physical and mechanical properties vary. Round steel has better cold bending performance and can be made into 180-degree hooks, while rebar can only be made into 90-degree straight hooks. Round steel has better weldability and can be made with ordinary carbon welding rods, while rebar must use low-alloy welding rods; rebar has better toughness and fatigue resistance than round steel.

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