Precision bright tube is a type of high-precision steel tube material that is derived from ordinary seamless steel pipes (or welded pipes with reduced diameter) through precision drawing or cold rolling processing. Due to its advantages such as the absence of oxidation layers on the inner and outer walls, resistance to high pressure without leakage, high precision, high cleanliness, no deformation during cold bending, and resistance to flaring and flattening without cracking, it is mainly used for the production of pneumatic or hydraulic components such as cylinders or oil cylinders. It can be either seamless or welded.

 

 

The chemical composition of precision bright tubes includes carbon (C), silicon (Si), manganese (Mn), sulfur (S), phosphorus (P), and chromium (Cr). High-quality carbon steel, precision rolling, oxygen-free bright heat treatment (NBK state), non-destructive testing, and specialized equipment for cleaning the inner wall of the steel tube followed by high-pressure flushing are involved in the manufacturing process. Rust prevention oil is applied to the inner and outer walls of the steel tube for rust protection, and the ends are sealed to prevent dust. The steel tube has high precision and high cleanliness on both the inner and outer walls. After heat treatment, there is no oxidation layer on the steel tube, and the cleanliness of the inner wall is high. The steel tube can withstand high pressure, has no deformation during cold bending, and shows no cracks during flaring or flattening. Precision steel tubes provided by Changzhou Rencheng Metal Products Steel Tube Factory can undergo various complex deformations and mechanical processing. The color of the steel tube is white with brightness, exhibiting a high metallic luster.

 

 

Precision steel tubes are used in machinery such as automobiles and mechanical parts that require high precision and cleanliness of the steel tube. Precision steel tube users are not limited to those with high requirements for precision and cleanliness. Due to the high precision of precision bright tubes, tolerances can be maintained at 2-8 threads. Therefore, many mechanical processing users, in order to save labor, material, and time losses, are gradually transitioning from seamless steel pipes or round steel to precision bright tubes.

 

 

(1) Impurity elements that induce high-temperature temper embrittlement in precision bright tubes, such as phosphorus, tin, antimony, etc.

(2) Alloy elements that promote or retard high-temperature temper embrittlement in different forms and degrees. Chromium, manganese, nickel, and silicon have a promoting effect, while molybdenum, tungsten, titanium, etc., have a retarding effect. Carbon also has a promoting effect.

 

Generally, carbon precision bright tubes are not sensitive to high-temperature temper embrittlement, while dual or multiple alloy steels containing chromium, manganese, nickel, and silicon are very sensitive. The sensitivity depends on the type and content of alloy elements.

 

The sensitivity of the original structure of tempered precision bright tubes to high-temperature temper embrittlement varies significantly. Martensitic high-temperature temper structures are the most sensitive, followed by bainitic high-temperature temper structures, and pearlitic structures are the least sensitive.

 

The essence of high-temperature temper embrittlement of precision bright tubes is generally believed to be the result of impurity elements such as phosphorus, tin, antimony, arsenic, etc., segregating at the grain boundaries of the original austenite, leading to embrittlement. Alloy elements such as manganese, nickel, chromium, etc., undergo co-segregation with these impurity elements at the grain boundaries, promoting the enrichment of impurity elements and exacerbating embrittlement. On the other hand, molybdenum has the opposite effect, forming a strong interaction with impurity elements such as phosphorus, which can precipitate in the grain interior and hinder the grain boundary segregation of phosphorus, thereby alleviating high-temperature temper embrittlement. Rare earth elements also have a similar effect to molybdenum. Titanium more effectively promotes the precipitation of impurity elements such as phosphorus in the grain interior, thus weakening the grain boundary segregation of impurity elements and slowing down high-temperature temper embrittlement.

 

 

(1) Rapid cooling with oil or water after high-temperature tempering to suppress impurity element segregation at grain boundaries;

(2) The use of precision bright tubes containing molybdenum. When the molybdenum content in steel increases to 0.7%, the tendency for high-temperature temper embrittlement is significantly reduced. Beyond this limit, special carbides rich in molybdenum are formed in 20# precision steel tubes, the molybdenum content in the matrix decreases, and the embrittlement tendency of precision bright tubes increases;

(3) Reducing the content of impurity elements in 20# precision steel tubes;

(4) For components working in the high-temperature temper embrittlement zone for a long time, the addition of molybdenum alone is difficult to prevent embrittlement. Only by reducing the content of impurity elements in 20# precision steel tubes, improving the purity of precision bright tubes, and supplementing with aluminum and rare earth elements, can high-temperature temper embrittlement be effectively prevented.