Automobile precision bright tube factory
Precision bright tube is a kind of high-precision steel tube material after fine drawing or cold rolling. Because there is no oxide layer on the inner and outer walls of the precision bright pipe, no leakage under high pressure, high precision, high finish, no deformation in cold bending, flaring, flattening and no cracks, it is mainly used to produce products of pneumatic or hydraulic components, such as air cylinder or oil cylinder, which can be seamless pipe or welded pipe. The chemical composition of precision bright tube includes carbon C, silicon Si, manganese Mn, sulfur s, phosphorus P and chromium CR. High quality carbon steel, finish rolling, non oxidizing bright heat treatment (NBK state), nondestructive testing, brushing and high-pressure washing of steel pipe inner wall with special equipment, antirust treatment with antirust oil on steel pipe, and dustproof treatment with covers at both ends. The inner and outer walls of the steel pipe are of high precision and high finish. After heat treatment, the steel pipe has no oxide layer and high cleanliness of the inner wall. The steel pipe bears high pressure, does not deform during cold bending, and has no cracks during flaring and flattening. The precision steel pipe can be processed for various complex deformation and machining. Steel pipe color: white with bright, with high metallic luster. Automobile and mechanical accessories have high requirements for the accuracy and finish of steel pipes. Precision steel pipe users are not only users with high requirements for precision and finish. Because precision bright pipe has high precision and the tolerance can be maintained at 2-8 wires, many machining users are slowly transforming seamless steel pipe or round steel into precision bright pipe in order to save labor, material and time losses.
The martensite structure is obtained by quenching of precision bright tube and tempered in the temperature range of 450 ~ 600 ℃; Or after tempering at 650 ℃, pass through 350 ~ 600 ℃ at a slow cooling rate; Or after tempering at 650 ℃ and heating for a long time in the temperature range of 350 ~ 650 ℃, the precision bright tube will produce embrittlement. If the embrittled 20# precision steel tube is reheated to 650 ℃ and then cooled quickly, the toughness can be restored. Therefore, it is also called% 26ldquo; Reversible temper brittleness%26rdquo; The brittleness of high temperature tempering shows the increase of toughness brittleness transformation temperature of precision bright tube. High temperature tempering brittleness. The sensitivity is generally determined by the difference between the ductile brittle transition temperature in the toughened state and the brittle state (% 26delta; T) To show. The more severe the brittleness of high temperature tempering, the higher the proportion of intergranular fracture on the fracture of precision bright tube.
The effects of elements on high temperature tempering brittleness in precision bright tube are divided into: (1) impurity elements causing high temperature tempering brittleness of precision bright tube, such as phosphorus, tin, antimony, etc（ 2) Alloy elements that promote or slow down the brittleness of high temperature tempering in different forms and degrees. Chromium, manganese, nickel and silicon play a promoting role, while molybdenum, tungsten and titanium play a delaying role. Carbon also plays a catalytic role. General carbon precision bright tubes are not brittle to high temperature tempering. The binary or multicomponent alloy steel containing chromium, manganese, nickel and silicon is very sensitive, and its sensitivity varies according to the type and content of alloy elements.
The sensitivity of the original structure of the tempered precision bright tube to the high temperature tempering brittleness of the steel is significantly different. Martensite high-temperature tempering structure is most sensitive to high-temperature tempering brittleness, bainite high-temperature tempering structure is the second, and pearlite structure is the smallest.
The essence of high temperature tempering brittleness of precision bright tube is generally considered to be the result of the segregation of impurity elements such as phosphorus, tin, antimony and arsenic at the original austenite grain boundary, resulting in grain boundary embrittlement. The alloy elements such as manganese, nickel and chromium are co segregated with the above impurity elements at the grain boundary, which promotes the enrichment of impurity elements and intensifies embrittlement. On the contrary, molybdenum has strong interaction with phosphorus and other impurity elements, which can produce precipitation phase in the crystal and hinder the grain boundary segregation of phosphorus, which can reduce the brittleness of high temperature tempering. Rare earth elements also have a similar effect as molybdenum. Titanium can more effectively promote the precipitation of phosphorus and other impurity elements in the crystal, so as to weaken the grain boundary segregation of impurity elements and slow down the high-temperature tempering brittleness.
The measures to reduce the high temperature tempering brittleness of precision bright tubes are as follows: (1) after high temperature tempering, oil cooling or water rapid cooling is used to inhibit the segregation of impurity elements at the grain boundary (2) When the molybdenum content in the steel increases to 0.7%, the embrittlement tendency of high-temperature tempering is greatly reduced. Beyond this limit, 20# precision steel tubes form special carbides rich in molybdenum, the molybdenum content in the matrix decreases, and the embrittlement tendency of precision bright tubes increases (3) Reduce 20# the content of impurity elements in precision steel pipe (4) It is difficult to prevent embrittlement of parts working in high-temperature tempering embrittlement area for a long time by adding molybdenum alone. Only by reducing 20# impurity element content in precision steel pipe, improving purity of precision bright pipe, supplemented by composite alloying of aluminum and rare earth elements, can high-temperature tempering embrittlement be effectively prevented.
