Annealing is the American standard seamless steel pipe heated to slightly higher or lower than the critical temperature, to maintain a period of time (ie, insulation), and then slowly cooling a process. Common annealing process classification: diffusion annealing, complete annealing, isothermal annealing, spheroidizing annealing, incomplete annealing, recrystallization annealing, stress relief annealing.
American Standard seamless steel pipe annealing as follows:
(1) Reduce the hardness, improve machinability.
(2) Eliminate residual stress, stabilize size, reduce deformation and crack tendency;
(3) Grain refinement, adjust the organization, eliminate tissue defects.
(4) Uniform material organization and composition, to improve the material properties or for future heat treatment to do the organizational preparation.
Precision seamless pipe is a cold drawn or hot-rolled after a high-precision steel pipe material. Because the inner and outer wall of the precision steel tube are free of oxide layer and bear the features of high pressure without leakage, high precision, high finish, cold deformation, flaring, flattening and no cracks, so it is mainly used to produce pneumatic or hydraulic components such as cylinder or Cylinder, can be seamless, but also welded pipe.
Precision seamless tube production process
Precision seamless pipe is usually cold-rolled production process. The specific process is as follows:
Round steel → perforated → pickling → cold-rolled → saw head → baling seamless pipe → pickling → cold-rolled → sawing → baling
Precision seamless pipe features
1, High precision, saving the loss of machining workers when the material.
2, Many specifications, wide range of applications.
3, High precision cold-rolled products, surface quality, good straightness.
4, Pipe diameter can be made of hexagonal.
5, Pipe superior performance, metal is more dense.
To ensure that the perfect welding of straight seam welded pipe in winter need to follow the following steps:
First, increase the welding current positioning welding, slowing down the welding speed, the appropriate increase in cross-sectional area and length of the weld, if necessary, preheat.
Second, should not be grooved on the parent material for arc, arc extinguishing need to fill the crater.
Third, as far as possible not under the conditions of low temperature bending, correction and assembly of welding parts.
Fourth, preheating before welding, the welding process strictly maintain the interlayer temperature should not be lower than the preheating temperature.
Fifth, the use of low hydrogen or ultra-low hydrogen welding materials.
Sixth, the entire weld should be continuous welding finished, to avoid interruption.
Generally the latest production technology of seamless steel tube is divided into oblique rolling method (mennesmann method) and kneading method.
Slanting method (Mennesmann method) is the first use of oblique roller seamless steel pipe perforation, and then use the mill to extend it. This method of production speed, but the seamless steel tube billet machining requirements higher, mainly for the production of carbon steel and low alloy steel pipe.
Kneading method is to use perforation machine seamless steel tube or ingot perforation, kneading machine and then kneaded into seamless steel pipe, this method is lower than the power of the cross rolling method, suitable for producing high strength alloy seamless steel pipe.
Slanting method and kneading method must be the first tube or ingot heating, the production of steel known as hot-rolled seamless steel pipe. The seamless pipe produced by hot working sometimes can be cold worked according to the need. Cold-working in two ways: one is the cold-drawing method, that is, through the drawing of seamless steel pipe drawing, the pipe gradually thinning, elongation; another method is the cold-rolled method, it is Mengnei Man Brothers invented the hot-rolling machine used in cold-working methods. Cold-rolled seamless steel pipe, pipe can advance the standard accuracy and finish, improve the mechanical properties of the material.
Seamless steel pipe (hot-rolled seamless steel pipe) production process
Seamless steel pipe mainly through the tension reducing to the end of the process of reducing the diameter of the hollow base metal without mandrel continuous rolling process. In the premise of ensuring the quality of the mother pipe welding, the pipe tensile reduction process is the overall heating pipe to 950 degrees Celsius, and then by tension reducing machine (stretch reducing machine a total of 24 times) rolling into a variety of outer diameter and wall thick finished seamless pipe, the use of this technology produced by the hot-rolled steel pipe and the usual high-frequency welded seamless pipe is essentially different from the heating furnace after the weld and the parent metal structure and mechanical properties can be completely consistent. In addition, the standard accuracy of the steel pipe (especially the tube roundness and wall thickness accuracy) is superior to the similar seamless steel pipe through the multi-pass tension reducer rolling and automatic control. The world's developed countries produce fluid pipe, boiler seamless pipe has many welded pipe seamless steel pipe technology, with the community started, the domestic hot-rolled pipe gradually replace the seamless steel pipe situation has now been formed.
The stringent requirements of the quality of the tube and pipe varieties, uses and perforation methods. Tube quality requirements for general-purpose pipe can be relaxed, while the important use of steel and high-alloy steel pipe of the quality requirements must be strict. Perforation methods with better stress conditions or smaller deformations may require slightly lower surface and internal quality requirements of the tube without affecting the performance of the tube.
If the perforation deformation is large, the surface quality and internal quality of the tube should be strictly required. In short, the technical requirements of the tube is to ensure the quality of the steel pipe and the smooth progress of the production process as the basis to determine, and will vary with the perforation method, with the technical conditions of the pipe increased. The technical conditions of various tube can be found in the standard and technical agreement. For example, automatic tube rolling machine tube blank requirements are as follows:
(1) Bending of any part of the tube is less than or equal to 6mm / m, the incision gradient of the tube end is less than or equal to 6 ~ 8mm, and the end flattening of the tube is less than or equal to 8% Dp.
(2) The tube surface shall not be cracked, Scales, folds, non-metallic inclusions and shrinkage cavities. Not allowed to have a height or depth of more than 0.5mm of small grooves, pockels, ears and the height of more than 1mm double-sided ears. Tube blank defect cleaning depth of not more than 0.05Dp;
(3) Tube microstructure: not allowed to have ≥ 1 level shrinkage hole, air bubbles, skin, white spots and cracks. For the general carbon structural steel billet, the general loose ≤ 3, the center loose ≤ 3, segregation ≤ 3, subcutaneous bubbles ≤ 2.