Converter-RH-LF-continuous casting technique for producing pipe line steel

Abstract

The invention belongs to the field of metallurgy, is a process for producing pipeline steel by converter-RH-LF-continuous casting, comprising converter process and terminal control, oxygen-remaining steel-tapping process, RH decarburization desaeration process, RH deoxidation alloying process and LF desulfurization process. By using RH oxygen-remaining natural decarburization, the invention can reduce the burden of converter decarburization and lower the oxidizability of molten steel, better meet the quality requirements of X70, X80 pipeline steel to low carbon and high purity. Pipeline steel produced by the converter-RH-LF-continuous casting has carbon content stably controlled in a range of 0.035% to 0.050% in accordance with objective composition requirement, no more than 0.006% of N,no more than 0.0003% of H, 0.013% of P, 0.002% of S, no more than 1.5 levels of inclusion thick series and no more than 1.5 levels of inclusion fine series.

Description

Converter-RH-LF-continuous casting process for producing pipeline steel technical field The invention belongs to the field of metallurgy and relates to a production process of pipeline steel, in particular to a converter-RH-LF-continuous casting process for producing pipeline steel. Background technique The RH cycle vacuum degassing method was jointly developed by Ruhrstahl and Heraeus in 1957. It has good degassing effect, natural decarburization with oxygen retention or oxygen blowing decarburization, treatment Large amount of molten steel, alloy fine-tuning and other functions, suitable for smelting low-carbon, ultra-low-carbon high-purity steel. In order to meet the requirements of high toughness, good welding performance and HIC and SCC resistance of X65, X70 and above grade pipeline steel, low carbon and high purity of molten steel must be ensured in the smelting process, C ≤ 0.070% or even ≤ 0.050%, N ≤0.0060%, H≤0.0003%, P≤0.013%, S≤0.002%, reduce the total amount...

AI Technical Summary

Problems solved by technology

In the LF-RH process, due to the use of alloys, covering agents, mold slag and other carbon-containing materials and corrosion of refractory materials during the process from converter tapping to pouring, it is inevitable to cause carburization of molten steel. According to relevant information, the carburization amount is in 0.002-0.004%, in order to meet the requirements of C≤0.070% of the finished product, the converter must decarbonize to less than 0.003%, according to the iron-carbon selective oxidation relationship, when C≤0.003%, it will cause peroxidation of molten steel in the furnace and a large amount of blown iron According to the results of oxygen determination by rifle gun and slag analysis, molten steel T.O≥1200ppm and slag T.Fe are between 25-30%, which will have adverse effects on technical and economic indicators such as molten steel quality, furnace lining life, and steel material consumption.

For the second West-East Gas Pipeline and the X80 pipeline steel commonly used in foreign countries, in order to control the strength, toughness and welding performance at a good level, the requirement of C≤0.050% for the finished product is put forward, which cannot be achieved only by decarburization of the converter and control of carbon increase in the subsequent process. Stable batch production

If the nitrogen content of pipeline steel is too high, it will reduce the toughness, welding performance and toughness of the thermal stress zone of the steel, and increase the brittleness of the steel. The original LF-RH process is not good for the control of molten steel nitrogen, mainly because of the high nitrogen content of the molten steel at the end of the converter, Severe nitrogen absorption during the tapping process: With the decarburization reaction of the converter, there are two opposite processes of denitrification and nitrogen absorption in molten steel. The CO bubbles generated by the carbon-oxygen reaction are equivalent to a small vacuum chamber for nitrogen in molten steel. At the same time, the temperature of the reaction zone High (about 2600 ℃) eliminates the inhibitory effect of surface active element oxygen in molten steel on denitrification, and has a good denitrification effect. However, during deep decarburization in the later stage of blowing, the reaction speed of carbon and oxygen slows down, and the molten steel takes nitrogen as the main Mainly, when the end point C≤0.003%, the nitrogen content will reach 25-30ppm; Oxygen is a surface active element, which will be adsorbed on the surface of molten steel, hindering the interface reaction of nitrogen absorption and denitrification in molten steel. The nitrogen absorption process has a decisive influence, and its content determines the nitrogen absorption rate of the molten steel. During the tapping process of the LF-RH process, the molten steel is fully deoxidized, the oxygen activity is low, and the kinetic conditions are good, and the nitrogen absorption tendency is very strong. obvious