1. Shape: The outer surface of round steel is smooth and circular or tubular, while the outer surface of threaded steel has spiral ribs.
2. Manufacturing process: Round steel is usually made through casting or rolling processes, while rebar is extruded through a die into a shape with spiral ribs during the hot rolling process.
3. Strength: Round steel has relatively low strength and is usually used in the manufacture of building structures and mechanical parts, while threaded steel has higher strength and is usually used in occasions such as bridges and high-rise buildings that require higher load-bearing capacity.
4. Application: Round steel is usually used for reinforcement in reinforced concrete structures, while threaded steel is usually used for connection and reinforcement in steel structures.

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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