Solid manufacturers can customize precision bright tubes
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.
At present, there are more than 5100 production plants under more than 1850 companies in more than 110 countries, including more than 260 plants under more than 170 companies in 44 countries. In 2000, the apparent consumption of seamless pipe in China was 4.18 million tons, including 3.821 million tons of domestic supply, accounting for 91.4% of the total domestic demand. The import was 359000 tons, accounting for 8.59% of the total domestic demand. In the same year, the consumption of oil pipes was about 910000 tons. The import is about 252000 tons. Imported pipes account for about 70% of the total domestic consumption, of which imported pipes account for 27.69% of the total domestic consumption, and oil pipes account for about 70% of the total imports of seamless pipes. Oil pipes imported from Japan account for more than half of the total imports. Tianjin steel pipe company, China's largest oil casing production base, produced 522000 tons of steel pipe products in 2000, including 364100 tons of oil casing. Casing accounts for more than half of the national oil production. It ranks first in China's casing Market in terms of output and sales volume.
From the international and domestic markets, the existing production capacity of seamless pipes (including special oil pipes) has exceeded the demand. Therefore, in the future, the focus should be on giving full play to the capacity of existing units and developing products such as oil pipes, high-pressure boiler pipes and gas cylinder pipes with high strength grade, high damage resistance and high corrosion resistance. It is also the content of optimizing product structure for China's steel market. This is also the key to increase the competitiveness of products at home and abroad and expand market share. That is to say, improving the market competitiveness of domestic steel pipe enterprises is the long-term task and the key to successful development of domestic enterprises after China's accession to the WTO.
