S11212-321

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Technical Parameter Table: Carbon Steel Tube S11212-321

Product Name: Carbon Steel Tubes for Machine Structural Purposes
Designation: S11212-321 (JIS G 3445: STB 321)
Standard: JIS G 3445 (Japanese Industrial Standard)
Note: This is a high-carbon cold-drawn seamless tube designed for applications requiring higher strength and wear resistance.

Parameter Category	Parameter	Value / Description	Notes & Interpretation
Designation Decoding	S11212	Indicates a carbon steel tube.	The “12” refers to a general carbon steel category.
	-321	The suffix “-321” specifically denotes the grade “STB 321” under JIS G 3445.	The “3” indicates the highest standard carbon content in this series.
Mechanical Properties	Tensile Strength (Rm)	≥ 585 MPa	Significantly higher than both STB 021 and STB 121.
	Yield Strength (Rp0.2)	Not Specified (N/S)	For this grade, yield strength is typically not the primary specified property, but it will be high due to the carbon content.
	Elongation (A), min	≥ 15%	Noticeably lower ductility than the lower carbon grades, which is a trade-off for its high strength.
	Hardness	Not Specified (N/S)	But will be relatively high (likely in the range of ~170-200 HB).
Chemical Composition (Max %)	Carbon (C)	0.32 – 0.39%	High carbon content. This is the key feature, providing high strength and wear resistance.
	Manganese (Mn)	0.30 – 0.60%	Similar range to other grades in the standard.
	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, but this grade is most commonly produced as seamless.
	Tolerances	Strict dimensional and wall thickness tolerances.	Governed by JIS G 3445. Known for excellent dimensional accuracy.
Physical Properties	Surface Finish	Smooth, bright finish	Characteristic of cold-drawn tubes.
	Density	7.85 g/cm³	Standard for carbon steel.
Processing & Applications	Weldability	Poor (Requires Strict Procedures)	High risk of cracking due to high carbon content. Pre-heating and post-weld heat treatment are often mandatory. Low-hydrogen electrodes are essential.
	Formability	Fair (Limited)	Can be bent, but requires a larger bend radius and is more prone to cracking during forming than lower carbon grades.
	Machinability	Fair	Can be machined, but its higher strength requires more power and reduces tool life compared to softer steels.
	Typical Applications	– High-strength shafts and axles – Pins, bolts, and studs – Sleeves and bushings – Machine components requiring wear resistance – Automobile components (e.g., shock absorber cylinders, steering parts)	Used in static or dynamic structural applications where high strength, hardness, and wear resistance are more critical than weldability or extreme formability.