Precision bright pipe is a kind of high precision steel pipe material which is processed by fine drawing or cold rolling.Because the inner and outer wall of the precision bright tube has no oxidation layer, no leakage under high pressure, high precision, high finish, no deformation in cold bending, flaring, flattening and no crack, etc., it is mainly used to produce products of pneumatic or hydraulic components, such as cylinder or cylinder, can be seamless tube, there are also welded pipe.The chemical composition of precision bright tube includes C, Si, Mn, S, P, Cr.
High-quality carbon steel, fine rolling, non-oxidation bright heat treatment (NBK state), nondestructive testing, the inner wall of the steel pipe is scrubbed by special equipment and washed by high pressure, the steel pipe is treated with antirust oil, and both ends of the cover is treated with dustproof.
The inner and outer wall of the steel pipe has high precision and high finish. After heat treatment, the steel pipe has no oxidation layer, and the inner wall has high cleanliness. The steel pipe bears high pressure, does not deform in cold bending, and has no crack in flared and flattened.Color of steel tube: white medium with bright, with high metallic luster.
3.The main purpose
Automobiles, mechanical parts, etc., which have high requirements for the precision and finish of steel pipes.Precision steel pipe users are not only for precision, smoothness requirements are high users, because of the high precision of precision bright pipe, tolerance can be maintained at 2-8 wire, so many mechanical processing users in order to save labor, material, time loss, seamless steel pipe or round steel is slowly transformed into precision bright pipe.
After quenching the martensite structure, the precision bright tube was tempered in the temperature range of 450~600℃.Or at 650℃ after tempering at a slow cooling rate after 350~600℃;Or after tempering at 650℃, long-term heating in the temperature range of 350~650℃ makes the precision bright pipe embrittlement phenomenon. If the embrittled 20# precision steel pipe is reheated to 650℃ and then quickly cooled, it can restore toughness, so it is also known as %26ldquo;Reversible temper brittleness %26rdquo;The brittleness of high temperature tempering is the toughness of precision bright tube and the increase of brittleness transition temperature.High temperature tempering brittleness.Sensitivity is generally defined as the difference between ductile and brittle transition temperatures (%26Delta;T) to denote.The higher the brittleness of high temperature tempering, the higher the proportion of intergranular fracture on the fracture of precision bright tube.
The effect of the elements in the precision bright tube on the high temperature tempering brittleness is divided into 1) the impurity elements such as phosphorus, tin, antimony and so on that cause the high temperature tempering brittleness of the precision bright tube.(2) Alloying elements that promote or slow down the high temperature tempering brittleness in different forms and to different degrees.Chromium, manganese, nickel, silicon and so on play a promoting role, while molybdenum, tungsten, titanium and so on play a delaying role.Carbon also plays a catalytic role.General carbon precision bright tube on high temperature tempering brittleness.The sensitive degree of binary or multicomponent alloy steels containing chromium, manganese, nickel and silicon is different according to the type and content of alloying elements.
The sensitive degree of the original microstructure of the tempered precision bright tube to the high temperature tempering brittleness of steel is obviously different.Martensite high temperature tempering structure is the most sensitive to high temperature tempering brittleness, bainite high temperature tempering structure is the second, pearlite structure is the least.
The essence of high temperature tempering brittleness of precision bright tube is generally believed to be the result of grain boundary embrittlement caused by segregation of impurity elements such as P, Sn, Sb and As in the original austenite grain boundary.The co-segregation of manganese, nickel, chromium and other alloying elements with the above impurity elements occurs at the grain boundary, which promotes the enrichment of impurity elements and accelerates the embrittlement.On the contrary, molybdenum has a strong interaction with impurity elements such as phosphorus, which can produce precipitate phase in the grain and hinder the segregation of grain boundary of phosphorus, and can reduce the brittle rare earth elements at high temperature.Ti can more effectively promote the precipitation of impurity elements such as phosphorus in the grain, thus weakening the grain boundary segregation of impurity elements and slowing down the tempering brittleness at high temperature.
The measures to reduce the brittleness of high temperature tempering of precision bright tubes are as follows 1) after high temperature tempering, cooling with oil or rapid cooling with water to inhibit the segregation of impurity elements at grain boundaries;(2) When the content of molybdenum in the steel increases to 0.7%, the tendency of high temperature tempering embrittlement is greatly reduced. When the content of molybdenum in the steel exceeds this limit, the special carbides rich in molybdenum are formed in the 20# precision steel pipe. When the content of molybdenum in the matrix decreases, the tendency of embrittlement in the precision bright pipe increases.(3) reduce the content of impurity elements in 20# precision steel pipe;(4) For the parts working in the high temperature tempering embrittlement area for a long time, it is difficult to prevent the embrittlement by adding molybdenum alone. Only by reducing the content of impurity elements in 20# precision steel tube, improving the purity of precision bright tube, and complementing it with the composite alloying of aluminum and rare earth elements, can the high temperature tempering embrittlement be effectively prevented.
5.Standard material delivery status
Main standard :GB/T3639, DIN2391-94/C, DIN2445, EN10305, DIN1630, DIN1629, ASTM A106, ASTM A179, JIS G3445
Main material: 10 #, 20 #, 35,45,40 Cr, 25 mn. 37 mn5, St35 (E235), St37.4, St45 (E255), St52 (E355)
Main delivery status :NBK(+N), GBK(+A), BK(+C), BKW(+LC), BKS(+SR)
Post time: Mar-04-2021