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What is a Precision Bright Tube?

Date:2021-09-28    keywords:precision bright tube, tempering brittleness
Precision bright tube is a kind of high-precision steel tube material processed by ordinary seamless steel tube (or reduced-diameter welded steel tube) through fine drawing or cold rolling. Because the inner and outer walls of the precision bright tube have no oxide layer, withstand high pressure without leakage, high precision, high finish, cold bending without deformation, flaring, flattening and no cracks, it is mainly used to produce pneumatic or hydraulic components, such as cylinders. Or the oil cylinder, which can be a seamless tube or a welded tube.

precision bright tube


The chemical composition of the precision bright tube includes carbon C, silicon Si, manganese Mn, sulfur S, phosphorus P, and chromium Cr. High-quality carbon steel finish rolling, non-oxidation bright heat treatment (NBK state), non-destructive testing, the inner wall of the steel pipe is brushed with special equipment and subjected to high-pressure washing, the steel pipe is treated with rust-proof oil for rust prevention, and the two ends are sealed for dust-proof treatment. The inner and outer walls of the steel pipe have high precision and high smoothness. After heat treatment, the steel pipe has no oxide layer, and the inner wall has high cleanliness. The steel pipe bears high pressure, cold bending does not deform, flaring and flattening without cracks, the color of the steel pipe: white with bright, with high metal luster. The precision steel pipes provided by Permanent Steel Manufacturing Co.,Ltd can be used for various complex deformations and mechanical processing.

The main purpose of precision bright tube:
Automobiles, machinery parts and other machinery that have high requirements on the precision and smoothness of steel pipes. The precision bright tube has high precision and the tolerance can be maintained at 2-8 wire. Therefore, in order to save labor, material, and time loss, many machining users are slowly turning seamless steel pipes or round steel into precision bright tubes.

Tempering brittleness of precision bright tube:


After the precision bright tube is quenched to obtain the martensite structure, it is tempered in the temperature range of 450-600℃; or after tempering at 650℃, it passes through 350-600℃ at a slow cooling rate; or after tempering at 650℃, it is tempered at 350-650℃ Long-term heating in the temperature range of ℃ will cause embrittlement of the precision bright tube. If the embrittled 20# precision steel pipe is reheated to 650℃ and then cooled quickly, the toughness can be restored, so it is also called %26ldquo;reversible temper brittleness%26rdquo;high temperature temper brittleness is expressed as the "toughness-brittleness of the precision bright tube" "The increase in transformation temperature. High temperature temper brittleness. The sensitivity is generally expressed by the difference (%26Delta; T) between the "toughness-to-brittle" transition temperature between the toughened state and the brittle state. The more serious the brittleness of high temperature tempering, the higher the ratio of the upper crystal fracture of the precision bright tube.

The effect of the elements in the precision bright tube on the high temperature temper brittleness is divided into:


(1) Impurity elements such as phosphorus, tin, antimony, etc. that cause high temperature tempering brittleness of precision bright tubes.
(2) Alloy elements that promote or slow down the brittleness of high temperature tempering in different forms and degrees. Chromium, manganese, nickel, silicon, etc. play a promoting role, while molybdenum, tungsten, titanium, etc. play a retarding role. Carbon also plays a catalytic role.

Generally, carbon precision bright tubes are not sensitive to high-temperature temper brittleness, while binary or multi-element alloy steels containing chromium, manganese, nickel, and silicon are very sensitive. The degree of sensitivity varies depending on the type and content of alloy elements.

The sensitivity of the original structure of the tempered precision bright tube to the high temperature temper brittleness of steel is significantly different. The martensite high temperature tempered structure is the most sensitive to high temperature temper brittleness, the bainite high temperature tempered structure is the second, and the pearlite structure is the smallest.

The high-temperature temper brittle nature of precision bright tubes is generally believed to be the result of the segregation of impurity elements such as phosphorus, tin, antimony, and arsenic in the original austenite grain boundaries, which leads to the embrittlement of the grain boundaries. However, alloying elements such as manganese, nickel, chromium and the above-mentioned impurity elements co-segregate at the grain boundary, which promotes the enrichment of impurity elements and aggravates embrittlement. On the contrary, molybdenum has a strong interaction with phosphorus and other impurity elements, which can produce a precipitation phase in the crystal and hinder the segregation of phosphorus at the grain boundary, which can reduce high temperature temper brittleness. Rare earth elements also have a similar effect to molybdenum. Titanium more effectively promotes the precipitation of impurity elements such as phosphorus in the crystal, thereby weakening the grain boundary segregation of impurity elements and slowing down the high temperature temper brittleness.

Measures to reduce the high temperature temper brittleness of precision bright tubes include:

(1) After high temperature tempering, use oil cooling or water rapid cooling to inhibit the segregation of impurity elements in the grain boundaries;
(2) When the molybdenum-containing precision bright tube is used, when the molybdenum content in the steel increases to 0.7%, the high temperature temper embrittlement tendency is greatly reduced, and the precision steel tube forms a molybdenum-rich special carbide when it exceeds this limit. When the molybdenum content in the matrix decreases, the embrittlement tendency of the precision bright tube increases instead;

(3) Reduce the content of impurity elements in precision steel tube;
(4) For parts that work in the embrittlement zone of high temperature tempering for a long time, it is difficult to prevent embrittlement by adding molybdenum alone. The only way to reduce the content of impurity elements in the precision steel tube is to improve the purity of the precision bright tube, supplemented by aluminum and rare earth. The compound alloying of the elements can effectively prevent high temperature temper brittleness.

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