Of T22 Alloy High-pressure Boiler Tubes Developed

In the paper, the whole trial-produce process of higher pressure boiler tubes T22 using tube rounds from horizontal continuous casting is introduced. The trial-produced sample tube is analyzed synthetically. Based on the development trend of seamless steel tubes used for boilers in power stations, we think that the main trend for development of boiler steels is heat-resistance, lower Cr content, higher creep resistance, better weldability and lower cost, which can be used to produce heavy thickness and heat-exchange components in large scale power generator sets under a working temperature of 600°C. This kind of steel can be developed by multi-element strengthening method.At first, this paper introduced that the whole process of higher pressure boiler tubes of alloy steel T22, processes including Cross-rolling piercing, semi-floating continuous rolling, Stretch-reducing, heat treating.Then the trial-produced process is analyzed synthetically, process parameter of higher pressure boiler tubes T22 is assured:1. Adopting the particular steel billet of alloy steel T22 make from horizontal continuous casting in HENGYANG STEEL TUBE (GROUP) CO., LTD. ,for its good surface qualify , steady geometric size and chemical component; no defect of white spots,shrinkage hole,laminar,crack,bubble,entrapped slag, surface peeling and subsurface blowhole, etc; it can be used to make higher pressure boiler tubes.2. Heating method including preheating along with furnace,four places heating,1280±5°C soaking, choosing appropriate molding parameter and deformation parameter to cross-roll piercing, and now we had made good winning in rolling rough tube which wall thickness from 12 to 13.5mm.3. Adopting 112mm mandrel, by appropriate increased the viscosity of lubricant, we succeeded in rolling tube which outer diameter is 123.5¹25.8mm, wall thickness is 5.1～5.9mm with the 6 stand semi-floating mandrel mill, and inside and outside surface quality can meet the needs.4. adopting five places heating ,by choosing appropriate molding parameter and deformation parameter , finish rolling alloy steel T22 seamless tubes ofφ60.3×5.2 with 24 stand differential transmission Stretch-reducing mill. Acquired seamless tubes has good dimensional homogeneity, conformed to the requirements of ASME SA213/SA213M-01.5. Normalizing and tempering in non-oxidizing continuous heat treating roller-hearth electric furnace with the protection of N₂. Normalizing choosing 940±10°C heating,25min holding time,120°C/min cooling velocity , Tempering choosing 740±10°C heating,85min holding time . The online heating process of higherpressure boiler tubes T22 is finished.According to above process parameters, We succeeded in produced higher pressure boiler tubes T22.At last, The trial-produced product was thoroughlytested according to the natronal《standard of seamless steel tubes for high pressure boilers》and requirements of a domestic boiler maker. The result shows that tube rounds produced by the process of EBT (electric steelmaking) + LF (secondary steelmaking processes) + VD (vacuum degassing) + HCC (horizontal continuous casting) are suitable for producing seamless steel tubes used to manufacture boilers of thermal power generators. The properties and performances of the trial-produced tubes are full qualified and can be used for manufacturing of power station boilers.