Hot and cold composite formed square and rectangular steel tube with thickened corners and production method

A steel tube, comprising:

• a square and rectangular steel tube with thickened corners formed by hot and cold composite, wherein a cross section of the square and rectangular steel tube is in a square or a rectangular shape, the square and rectangular steel tube further comprises a straight tube and four corners, and radius of an outer corner of the square and rectangular steel tube meets one of following conditions:
• when wall thickness (t) of the straight tube of the square and rectangular steel tube is less than or equal to 6 mm, radius (R) of each of outer corners of the four corners of the square and rectangular steel tube is greater than 0 and less than 2.0 t;
• when t is greater than 6 mm and less than or equal to 10 mm, R is greater than 0 and less than 2.5 t;
• and
• when t is greater than 10 mm, R is greater than 0 and less than 3.0 t;
• and
• wherein wall thickness of each corner of the square and rectangular steel tube is in a range of 1.0 t to 1.8 t.