Chemical composition of steel: The chemical composition of steel is one of the most important factors affecting the performance of seamless black steel pipes, and it is also the main basis for formulating process parameters for rolling and heat treatment of seamless black steel pipes.

1) Alloying elements: intentionally added, according to the application

2) Residual elements: brought into steelmaking, properly controlled

3) Harmful elements: strictly controlled (As, Sn, Sb, Bi, Pb), gases (N, H, O)

Out-of-furnace refining or electroslag remelting: improve the uniformity of the chemical composition in the steel and the purity of the steel, reduce the non-metallic inclusions in the tube blank and improve their distribution.

Seamless black steel pipe geometric accuracy and shape

1) The accuracy of the outer diameter of the seamless black steel pipe: depends on the method of determining (reducing) the diameter, the operation of the equipment, the process system, etc.

Outer diameter tolerance δ=(D-Di)/Di ×100%
D: maximum or minimum outer diameter mm
Di: Nominal outer diameter mm

2) Seamless black steel pipe wall thickness accuracy: related to the heating quality of the tube blank, the process design parameters and adjustment parameters of each deformation process, the quality of tools and their lubrication quality, etc.

Wall thickness tolerance: ρ=(S-Si)/Si×100%
S: Maximum or minimum wall thickness in cross section
Si: nominal wall thickness mm

3) Ovality of seamless black steel pipe: It indicates the degree of out-of-roundness of the seamless black steel pipe.

4) Seamless black steel pipe length: normal length, fixed (multiple) ruler length, length tolerance

5) Seamless black steel pipe bending degree: Indicates the bending degree of the seamless black steel pipe: the bending degree of the steel pipe length per meter, the bending degree of the full length of the seamless black steel pipe

6) The inclination of the end face of the seamless black steel pipe: indicates the inclination of the end face of the seamless black steel pipe and the cross section of the seamless black steel pipe

7) Bevel angle and blunt edge of seamless black steel pipe end face

Surface quality of seamless black steel pipe: requirements for surface smoothness

1) Dangerous defects: cracks, inward folds, outward folds, rolling, delamination, scarring, concave pulls, convex hulls, etc.

2) General defects: pits, blue lines, scratches, bumps, slight inner and outer straights, roll marks, etc.

Cause

1) Due to surface defects or internal defects of the tube blank.

2) Produced in the production process, such as incorrect design of rolling process parameters, unsmooth die surface, poor lubrication conditions, unreasonable pass design and adjustment.

3) In the process of heating, rolling, heat treatment and straightening of the billet (steel pipe), if the heating temperature is not properly controlled, the deformation is uneven, the heating and cooling rate is unreasonable or the straightening deformation is too large, resulting in excessive residual stress, Then it may also cause surface cracks in the seamless black steel pipe.

Steel management properties: normal temperature mechanical properties, high temperature mechanical properties, low temperature properties, corrosion resistance. The physical and chemical properties of the seamless black steel pipe mainly depend on the chemical composition of the steel, the structure of the steel, the purity of the steel, and the heat treatment method of the seamless black steel pipe.

Seamless black steel pipe process performance: flattening, flaring, crimping, bending, welding, etc.

Metallographic structure of seamless black steel pipe: low magnification (macro), high magnification (micro) M, B, P, F, A, S