S11212-121

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Technical Parameter Table: Carbon Steel Tube S11212-121

Product Name: Carbon Steel Tubes for Machine Structural Purposes
Designation: S11212-121 (JIS G 3445: STB 121)
Standard: JIS G 3445 (Japanese Industrial Standard)
Note: This grade has a higher carbon content than the STB 021, making it stronger but less ductile.

Parameter Category	Parameter	Value / Description	Notes & Interpretation
Designation Decoding	S11212	Indicates a carbon steel tube.	The “12” refers to a general carbon steel category.
	-121	The suffix “-121” specifically denotes the grade “STB 121” under JIS G 3445.	The “1” indicates a specific chemical group with higher carbon.
Mechanical Properties	Tensile Strength (Rm)	≥ 415 MPa	Higher than STB 021 (≥315 MPa) due to increased carbon content.
	Yield Strength (Rp0.2)	Not Specified (N/S)	For this grade, yield strength is typically not the primary specified property.
	Elongation (A), min	≥ 25%	Good ductility, though slightly lower than STB 021 (≥30%) due to higher strength.
	Hardness	Not Specified (N/S)
Chemical Composition (Max %)	Carbon (C)	0.18 – 0.23%	Significantly higher than STB 021 (0.08-0.13%). This increases strength but reduces weldability.
	Manganese (Mn)	0.30 – 0.60%	Similar range to STB 021.
	Phosphorus (P)	≤ 0.040%	Impurity, controlled.
	Sulfur (S)	≤ 0.040%	Impurity, controlled.
	Silicon (Si)	Remarks: May be added as a killing agent.	Typically, Silicon is not specified but may be present.
Dimensional Standards	Manufacturing Process	Seamless or Welded & Cold-Drawn	The standard covers both.
	Tolerances	Strict dimensional and wall thickness tolerances.	Governed by JIS G 3445. Defines deviations for outer diameter, wall thickness, and length.
Physical Properties	Surface Finish	Smooth, bright finish	Characteristic of cold-drawn tubes.
	Density	7.85 g/cm³	Standard for carbon steel.
Processing & Applications	Weldability	Good (with precautions)	The higher carbon content requires more care than STB 021. Pre-heating and low-hydrogen electrodes may be necessary for thicker sections to prevent cracking.
	Formability	Good	Can be bent and formed, but requires more force than STB 021.
	Typical Applications	– Medium-strength mechanical structural parts – Automobile and bicycle components (e.g., frames, shafts) – General machinery parts requiring higher strength than STB 021. – Low-pressure hydraulic cylinders	Used in applications where a balance of strength, formability, and a good surface finish is required.