Cold drawn seamless tube

Cold drawn seamless tube (CDS) is a cold drawn 1018/1026 steel tube which offers uniform tolerances, enhanced machinability and increased strength and tolerances compared to hot-rolled products.

Cold drawn steel tube is with hot-rolled steel coil as raw material, and tandem cold rolling pickled to remove oxide scale, its finished rolling hard roll, rolling hard volumes due to the continuous cold deformation caused by cold hardening strength, hardness increased indicators declined tough plastic, stamping performance will deteriorate, which can only be used for simple deformation of the parts.

Round tube → heating → ​​perforation → Heading → ​​annealing → ​​pickling → ​​oiled (copper) → multi-pass cold drawn (cold rolled) → blank tube → heat treatment → straightening →hydrostatic testing (testing) → mark → storage.

Condition on delivery of steel pipe

Term	Symbol	Explanation
Cold-finished/hard (cold-finished as-drawn)	BK	No heat treatment after the last cold-forming process. The tubes therefore have only low deformability.
Cold-finished/soft (lightly cold-worked)	BKW	After the last heat treatment there is a light finishing pass (cold drawing) With proper subsequent processing, the tube can be cold-formed (e.g. bent, expanded) within certain limits.
Annealed	GBK	After the final cold-forming process the tubes are annealed in a controlled atmosphere or under vacuum.
Normalized	NBK	The tubes are annealed above the upper transformation point in a controlled atmosphere or under vacuum.

The general cold strip mills, volume should go through continuous annealing (CAPL unit) to eliminate cold hardening and rolling stress, or batch annealing reach the mechanical properties of the corresponding standard specifies. Cold rolled steel surface quality, appearance, dimensional accuracy better than hot-rolled plate, and right-rolled thin product thickness is about 0.18mm, so the majority of users favor.

Cold rolled steel coil substrate products deep processing of high value-added products. Such as electro-galvanized, hot dip galvanized, electro-galvanized fingerprint resistant, painted steel roll damping composite steel, PVC laminating steel plates, etc., so that the excellent quality of these products has a beautiful, high resistance to corrosion, has been widely used.

Cold rolled steel coil finishing after annealing, cut the head, tail, trimming, flattening, smooth, heavy volume, or longitudinal clipboard. Cold-rolled products are widely used in automobile manufacturing, household electrical appliances, instruments, switches, buildings, office furniture and other industries. Steel plate strapping package weight of 3 to 5 tons. Flat sub-volume typically 3 to 10 tons / volume. Coil diameter 6m.

It is produced by the thermal cracking of a liquid to a solid state crystallization process in the weld metal, mostly generated in the weld metal. The main causes of its low-melting substance is present in the weld, which weakens the contact between the grains when subjected to high welding stress, it is easy to cause breakdown between the grains. Weldments and welding rod containing S, Cu impurities such a long time, it is prone to hot cracking.

Thermal cracking characteristic distribution along the grain boundaries. When the crack through the surface and the outside world, it is a clear tendency hydrogenation. Cold cracks are generated in the cooling process after welding, mostly produced in the base metal or base metal and the weld fusion line junction. The main reason is due to its generation or the weld heat affected zone formed within the quenched structure, under high stress, causing rupture of grains, the higher the carbon content of the welding elements, or more easily hardened alloy steel, the most prone to cold cracking. Excessive weld melt into hydrogen, can also cause cold cracking. A defect of the most dangerous cracks, which in addition to reducing the cross-section than the bearing, but also produce severe stress concentration at the crack will gradually expand in use, may eventually lead to the destruction member. So welded structures are generally not permitted the existence of such defect has been found to be a shovel to re-welding.

Steel pipe internal defects of weld lack of penetration is refers to the workpiece and the weld metal or weld layer between local incomplete fusion of a defect. Incomplete penetration welds weakened section of the work, causing serious stress concentration, greatly reduce joint strength, it is often a source of weld cracking. Weld slag sandwiched nonmetallic slag, that is called slag. Weld slag reduces work-section, resulting in stress concentration will reduce weld strength and toughness.

Porosity of the weld metal at high temperatures, the absorption due to too much gas or gas dissolved within the cell is generated by the reaction of metallurgical, too late when the bath is discharged is cooled and solidified, and the weld hole is formed inside or the surface, i.e. pores. The presence of pores reduces the effective work of the weld cross-section, to reduce the mechanical strength of the joint. If penetrating pores or continuity exists, it will seriously affect the tightness of the weldment. After cracking during welding or welding metal in the welded joints appearing partial rupture area called crack. Cracks may occur in the weld may also be produced in the weld heat affected zone on both sides. Sometimes occurs on the metal surface, the metal may be generated internally.

Cold-rolled tube refers to steel product that is through cold drawing, cold-formed, cold drawn, cold plate or strip processed at room temperature.

• good quality. Cold drawn tube production principle is a stretch, from the shortage of pipe to finished tube to pull at least 3,4 Road, more than a dozen waste pipe continuously variable length, thinning of the material internal defects which inevitably extended organization loose structure; cold-rolled tube production principle is compressed, so that the waste pipe longer, thinner, thereby increasing the compactness of the material, another advantage is that good surface quality, dimensional accuracy.
• high production efficiency. By the material pull the scalability limitations, each deformation is not too much, otherwise you will pull off, pull the break, the general deformation control in about 25%.
• low cost. Cold drawn on a needs annealing, pickling, on a gray, dry, (sometimes also need straightening), a pass to go two days, but the cost increased by 200 ~ 300 yuan, cold rolled pass to reduce not only to shorten the production cycle, and eliminates the need for repeated annealing, pickling, on a gray,drying the material and labor costs, the cost of in this area compared with cold-drawn, you can lower half, or even more.

The annealing of cold drawn steel is commonly used in the production of preliminary heat treatment process. The majority of machine parts and engineering, mold rough can eliminate internal stress and composition of casting, forging and weldment inhomogeneity; can improve and adjust the steel mechanical properties, and organizational preparations for the next process to make after annealing. Performance of less demanding, less important parts and some ordinary castings, weldments, annealing can be used as the final heat treatment.

The annealing of the steel is heated to a suitable temperature, holding a certain period of time, and then slowly cooled in order to get close to the heat treatment process of a balanced organization. The purpose of annealing is uniform chemical composition, to improve the mechanical properties and process performance, eliminate or reduce stress and make the organization ready for the final heat treatment of parts.

The annealing process is many types of steel, the heating temperature can be divided into two categories: one is in the annealing above the critical temperature (Ac3 or Ac1), also known as phase change recrystallization annealing. Including the fully annealed, fully annealed, isothermal annealing, the ball annealing and diffusion annealing; the other is in critical temperature (Ac1) following annealing, also known as low-temperature annealing. Including the recrystallization annealing, to stress and dehydrogenation annealing. The cooling method can be divided into continuous cooling annealing and isothermal annealing.

Cold drawn steel quenching is very important in the heat treatment process, is widely used processes. Quenching can significantly improve the strength and hardness of the steel. If matched to a different temperature tempering can eliminate or mitigate the quenching stress, but also the strength, hardness and toughness with, to meet different requirements. Therefore, the quenching and tempering is inseparable from the two heat treatment process. Quenching the steel is heated to above the critical point is greater than the critical cooling rate (Vc) in the insulation after cooling, in order to get the heat treatment process of the martensite or lower bainite.