Black Square Tube | Carbon Steel Square Tube | Structural & Construction Grade

🟧 Product Overview

Black Square Tube is a carbon steel square hollow section widely used in construction, structural frameworks, machinery, and general engineering applications.

Produced through hot‑rolled or cold‑formed processes, black square tubes offer excellent strength, weldability, and dimensional accuracy. The uncoated black surface provides a cost‑effective solution for indoor or coated applications where corrosion resistance is not the primary requirement.

Black square tubes are available in a wide range of sizes and thicknesses to meet structural, mechanical, and fabrication needs.

🟧 Standards

• ASTM A500
• ASTM A36
• EN 10219
• GB/T 6728
• JIS G3466

🟧 Available Grades

• Q195
• Q235
• Q345
• S235
• S275
• S355

🟧 Product Specifications & Available Sizes

Specification	Details
Size Range	10×10–500×500 mm
Wall Thickness	0.8–20 mm
Length	6 m / 12 m / custom
Type	Hot Rolled / Cold Formed
Surface	Black (uncoated)
Ends	Plain End / Custom Cut
Tolerance	As per ASTM / EN / GB standards

Type	Specifications （mm）	Thickness （mm）
Square tube	10*10-15*15	0.24-0.31
	17*17-50*50	0.24-0.31
	17*17-50*50	0.33-0.38
	17*17-50*50	0.40-2.0
	17*17-50*50	0.24-0.31
	17*17-50*50	0.33-0.38
	17*17-50*50	0.40-2.0
	60*60-250*250	0.5-3.0
Rectangular Pipe	10*20-75*45	0.24-0.31
	10*20-75*45	0.33-0.38
	10*20-75*45	0.40-2.0
	10*20-75*45	0.24-0.31
	10*20-75*45	0.33-0.38
	10*20-75*45	0.40-2.0

🟧 Mechanical Properties

Property	Value
Tensile Strength	375–630 MPa (depending on grade)
Yield Strength	235–355 MPa
Elongation	≥ 20%
Hardness	As per grade

🟧 Chemical Composition (Typical Carbon Steel Grades)

Element	Q235 (%)	Q345 (%)
C	≤ 0.22	≤ 0.20
Mn	≤ 1.40	≤ 1.70
Si	≤ 0.35	≤ 0.50
P	≤ 0.045	≤ 0.035
S	≤ 0.045	≤ 0.035

🟧 Manufacturing Processes

• Hot Rolled Square Tube
• Cold Formed Square Tube
• ERW Welded Tube
• Straightening & Sizing
• Cutting & End Finishing

🟧 Primary Industry Usage

• Construction and building structures
• Steel frames and support systems
• Machinery and equipment manufacturing
• Automotive and trailer frames
• Furniture and fabrication projects
• General engineering applications

🟧 Why Use Black Square Tube

• High structural strength
• Excellent weldability and formability
• Cost‑effective for large‑scale projects
• Wide size range for multiple applications
• Ideal for indoor or coated environments

🟧 Why Choose WelSteels

• Full range of black square tubes in stock
• Precise sizing and strict quality control
• Custom cutting and fabrication services
• SGS / BV inspection available
• Export‑grade seaworthy packaging
• Fast delivery and stable

International Steel Standards

China	America	Germany	Japan	France	Britain	International
GB3077	AlSI	DIN	JIS	NE	BS	ISO
20Mn2	13201221	20Mn5	SMn21	20M5	150M19	–
30Mn2	1330	30Mn5	SMn24	32M5	150M28	–
35Mn2	1335	36Mn5	SMnl	35M5	150M36	–
40Mn2	13401341	–	SMn2	40M5	–	–
45Mn2	1345	46Mn7	SMn3	45M5	–	–
50Mn2	1052	50Mn7	–	55M5	–	–
20MnV	–	20MnV6	–		–	–
30Mn2MoW	–	—	–		–	–
27SiMn	–	27MnSi5	–		–	–
35SiMn	–	37MnSi5	–	38MS5	–	–
42SiMn	–	38MnSi446MnSi4	–	38MS5	–	–
20SiMn2MoV	–	–	–	–	–	–
25SiMn2MoV	–	–	–	–	–	–
37SiMn2MoV	–	–	–	–	–	–
40B	14B35	35B2	–	–	–	–
45B	50B46H	45B2	–	–	–	–
50B	14B50	–	–	–	–	–
4OM∏B	15B41	–	–	–	–	–
45MnB	15B4850B44	–	–	–	–	–
20Mn2B	–	–	–	–	–	–
20MnMoB	80B20	–	–	–	–	–
15MnVB	–	–	–	–	–	–
–	–	–	–	–	–	–
–	–	–	–	–	–	–
20MnVB	–	–	–	–	–	–
40MnVB	–	–	–	–	–	–
20MnTiB	–	–	–	–	–	–
25MnTiBRE	–	–	–	–	–	–
2OSiMnVB	–	–	–	–	–	–
15Cr	50155115	15Cr3	SCr21	12C3	523A14523M15	–
15CrA	–	–	–	–	–	–
20Cr	5120	20Cr4	SCr22	18C318C4	527A19527M20	683/1120Cr420CrS4
30Cr	5130	28Cr4	SCr2	28C432C4	530A30530A32	–
35Cr	5135	34Cr437Cr4	SCr3	38C4	530A36	683/83、 3a、 3b
40Cr	5140	38Cr441Cr4	SCr4	42C4	530A40530M40	683/14、 4a^ 4b
45Cr	5145	42Cr4	SCR5	45C4	–	–
50Cr	51505152	–	–	50C4	En48	–
38CrSi	–	–	–	–	–	–
12CrMo	4119	13CrMo44	–	12CD415CD2	–	–
15CrMo	ASTMA-387Gr. B	15CrMo516CrMo44	SCM21	15CD4. 05	BS1653	–
20CrMo	4118	20CrMo522CrMo4	SCM22	18CD420CD4	CDS 12CDSllO	–
30CrMo	4130	25CrMo4	SCM2	30CD4	CDS 13	–
30CrMoA	–	32CrMol23ICRMo12	–	–	–	–
35CrMo	41354137	34CrMo435CrMo4	SCM3	35CD4	78A37	683/1C35eaC35eb
42CrMo	41404142	41CrMo442CrMo4	SCM4	40CD442CD4	708M40708A42709M40	683/13
12CrMoV	–	–	–	–	–	–
35CrMoV	–	35CrMoV5	–	–	–	–
12CrlMoV	–	13CrMoV4.2	–	–	–	–
25Cr2MoVA	–	24CrMoV5.5	–	–	–	–
25Cr2MolVA	–	–	–	–	–	–
20CR3MoWVA	–	21CrVMoW12	–	–	–	–
38CrMoΛl	6370 (ΛMS)	34CrAlMo541CrAlMo7	SACM645	40CAD6.12	905M39	683/1041CrAlMo74
20CrV	6120	22CrV4	–	22CrV4	–	–
40CrV	6140	42CrV	–	42CrV4	–	–
50CrVA	6150	50CrV4	SUPlO	50CV4	735A50	–
15CrMn	–	16MnCr5	–	16MC5	–	–
20CrMn	5120	20MnCr5	SMC21	20MC5	–	–
40CrMn	5140	–	SMC3	–	–	–
20CrMnSi	–	–		–	–	–
25CrMnSi	–	–	SMKl	–	–	–
30CrMnSi	–	–	–	–	–	–
30CrMnSiA	–	–	–	–	–	–
35CrMnSiA	–	–	SMK2	–	–	–
20CrMnMo	4119	20CrMo5	SCM23	–	–	–
40CrMnMo	4140	–	–	–	–	–
20CrMnTi	–	–	SMK22	–	–	–
30CrMnTi	–	30MnCrTi4	–	–	–	–
20CrNi	3120	20NiCr6	–	20NC6	637A16637M17	–
40CrNi	3140	46NiCr6	SNCl	35NC6	640A35640M40	–
45CrNi	3145	45NiCr6	–	–	–	–
50CrNi	3150	–	–	–	–	–
12CrNi2	3115	14NiCrlO	SNC21	IONCll14NC11	–	–
12CrNi3	3310	13NiCrl2	SNC22	10NC1214NC12	655A12655M13	–
20CrNi3	–	22NiCrl4	–	20NC11	–	–
30CrNi3	–	28NiCrlO31NiCrl4	SNC2	30NC1130NC12	–	–
37CrNi3	–	35NiCrl8	SNC3	35NC15	–	–
12Cr2Ni4	E3310	14NiCrl8	–	12NC15	–	–
20Cr2Ni4	E3316	22NiCrl4	–	20NC14	659A15659M15	–
20CrNiMo	8620    8720	20NiCrMo221NiCrMo2	–	20NCD2	805A20805M20	–
40CrNiMoA	4340     9840	36NiCrMo440NiCrMo6	SNCM8	35NCD540NCD3	817M40816M40	–
45CrNiMoVA	4437	–	SNCM9	–	–	–
18Cr2Ni4WA
25Cr2Ni4WA