315-paper－T23高压锅炉管的研制(English).doc

The development of ASME SA－213 T23 high pressure boiler tube Wang Qijiang1 Zou Fengming2 Zhang Ke3 （1.Baosteel Technology Cent, R Property; Standard; Power station boiler 1. Introduction ASME SA213 T23 simplified as T23 steel is based on T22 2.25Cr-1Mo steel, substituting W for a part of Mo and adding micro-alloying elements such as V, Nb, B. Due to the solid solution strengthening and the precipitation strengthening, the allowable stress of T23 steel is twice higher than ASME SA213-T22 steel in the creep region from 550℃ to 625℃. The creep rupture strength of T23 steel is approximately 1.4 times higher than 12Cr1MoV steel at 580℃ and approaches that of 12Cr2MoWVTiB（R102）steel developed by our country. Besides, the impact toughness of T23 steel is high, and the weld-ability is improved so greatly that it can be used in as-welded condition without preheating and post-weld heat treatment. Instead of 10CrMo910, T22, 12Cr1MoV and 12Cr2MoWVTiB, it can be used to manufacture the superheater and reheater in power generation boilers with high capacity. With the quick development of power generation boilers in our country towards high capacity and high parameter, more and more T23 steel tubes will be used to manufacture the sub-critical or super-critical boilers with high capacity and high parameter in the industry of boiler. However, all the T23 steel had to be imported since T23 steel could not be produced in China before this research was done. Therefore, the industry of boiler is eager to hope that Baosteel can develop and produce T23 steel in place of import. In order to improve the manufacture capability of high-capacity steam power plants and satisfy the requirement to manufacture sub-critical or super-critical power station boilers in China, Baosteel began to develop T23 steel in April 2001. After experiencing the stages of steel trial production, tube trial rolling, property uation and mass production, Baosteel has the capability of mass production and supply. The main purpose of this study is to discuss the technical process during the development of T23, the product properties and the application of T23 steel produced by Baosteel. 2. The Development of T23 steel 2.1 Chemical compositions Table 1 gives the chemical compositions of T23 steel according to the ASME standard of SA-213. The mechanical property depends on the chemical composition. However, a relatively wide range of every element is given in the standard. In order to obtain the optimum comprehensive property it is necessary to optimize and control the chemical composition. To improve the weld-ability, high creep rupture strength and ductility of T23 steel, it is extremely important to strictly control the elements of C, P, S, Al and so on, for instance, P760℃ for more than 60 minutes. The as-supplied microstructure of T23 steel is tempered bainite after heat treatment, see figure 1. Figure 1. Optical microstructure of T23 steel tubes 3. The properties of T23 steel 3.1 Tensile property at elevated temperatures According to GB/T 4338-1995 standard Metallic materials-Tensile testing at elevated temperature, the specimens were machined from the T23 steel tube in arc proportion, and used for tensile test at elevated temperatures. Figure 2 compares the elevated temperature tensile property of T23 steel tube with the ASME standard. It is seen that the elevated temperature tensile property of T23 steel tube produced by Baosteel is satisfied with the requirement of standard completely. a Elevated temperature tensile strength of T23 tube b Elevated temperature yield strength of T23 tube Figure 2. Elevated temperature tensile property of T23 tube 3.2 Creep rupture strength According to GB/T2039-1997 standard “Metallic materials-Tensile creep testing and creep rupture testing at elevated temperature ”, the creep rupture test was carried out at 550℃, 600℃ and 650℃ respectively using elevated temperature creep rupture machine RD2-3. The test results are shown in figure 3. Figure 3. Creep rupture strength for T23 tube According to the least square theory, the creep rupture strength at 550℃, 600℃ and 650℃ respectively can be calculated by the extrapolation equations as follows Extrapolation equation of the creep rupture strength at 550℃ lgσ＝2.6259-0.1071lgt Then 123MPa Extrapolation equation of the creep rupture strength at 600℃ lgσ＝2.5270-0.1235lgt Then 81.2MPa Extrapolation equation of the creep rupture strength at 650℃ lgσ＝2.5837-0.2120lgt Then 33.4MPa All the creep rupture strength of T23 steel produced by Baosteel at 500℃, 600℃ and 650℃ are higher than the allowable strength in ASME standard of CODE CASE 2199-1 ＞106MPa，＞65MPa，＞31MPa. 3.3 The comparison of oxidation resistance between T23 steel and R102 steel at elevated temperature The comparison of oxidation resistance between T23 steel and R102 steel at elevated temperature was done according to GB/T 13303-1991 standard Steels-Determination of Oxidation resistance. The rectangular specimens 1530mm were used for oxidation resistance test at 600℃, and the oxidation rate was measured through the increase of weight. During test, the actual holding temperature is controlled to be 600℃3℃, and after held for 100h, 200h, 500h, 1000h, 1500h, 2000h, 2500h, 3000h, 3500h, 4000h, 5000h, 6000h, 7000h and 8000h respectively, the weight of the specimens was measured to compare. The measurement results are shown in figure 4. It is found that the average oxidation rate of T23 steel produced by Baosteel is K 0.03410g/m2h and 0.03786mm/year, while G102 steel is K 0.03974 g/m2h and 0.04440mm/year. According to GB/T 13303-91 standard Grade 1 “complete oxidation resistance” ≤0.1g/m2h, both of the two steels belong to complete oxidation resistant steel, and the anti-oxidation property of T23 steel produced by Baosteel is a little better than R102 steel. Figure 4. Curve of anti-oxidation property at 600℃ for T23 and R102 tube 3.4 Aging property The aging treatment temperature of the tube is 600℃3℃. The specimens used for mechanical property test were machined from the tube held for 500h, 1000h, 3000h, 5000h, 8000h and 10000h respectively. Figure 5 gives the mechanical test results. It is seen that the impact toughness of T23 steel doesn’t change obviously after aging for 500h10000h, and still higher than 200J after aging for 10000h. The strength and hardness of T23 steel decrease slightly with the prolonging of aging time, and the decrease is not apparent. There is a slight change of elongation with the ageing time. The ageing of 600℃ for 10000h shows that although the mechanical properties change after aging for a long time at 600℃, the mechanical property of T23 is still higher than the allowable values in the standard of ASME SA-213 Code Case 2199 when T23 steel is aged for 10000h at 600℃. It shows that T23 steel is suitable to manufacture power station boilers due to stable properties. a Variation curves of elongation, hardness and impact toughness after aging b Variation curve of strength after aging Figure 5. Variation of properties after aging 3.5 Impact toughness at different temperatures The specimens for impact toughness test were cut from the as-supplied tube φ60.312.5mm and machined to standard specimens of Charpy V-notched 1010mm. According to GB/T 229-1994 standard Metallic materials- Charpy V-notched impact testing, impact toughness at different temperatures was measured, as shown in Figure 6. It shows the ductile-brittle transition temperature FATT50 is -40℃ -45℃. Figure 6. Impact toughness curve at different temperatures 3.6 Processing property of T23 steel The flattening test and flare test were carried out using T23 tubes φ60.312.5mm following the standard of ASME SA-450. It is confirmed that the processing property of T23 steel produced by Baosteel is excellent see Figure 7, and is satisfied with the requirements of boiler steel. Figure 7. Appearance of flattening and flare test specimens 4. The application in domestic boiler factories T23 steel produced by Baosteel has been used widely in most of the domestic boiler factories since it was developed successfully. Figure 8 gives the application of T23 steel in main domestic boiler factories in 2004 and 2005. The successful development of T23 steel in Baosteel greatly improves the manufacture capability and competitive capability of sub-critical and super-critical power station boilers. At the same time, the gap of heat-resistance steel research between foreign countries and our country is also shortened. Figure 8. Outstanding achievement of application Baosteel’s T23 in Boiler Works 5. Conclusions 1 It is confirmed that all the qualifications and properties of T23 steel produced by Baosteel are satisfied with the standard of ASME SA-213 completely. The domestic T23 steel is suitable to manufacture power station boilers with high capacity. Therefore, the technological design, which is chosen by Baosteel to develop T23 steel, is right. 2 The ductile-brittle transition temperatureFATT50 of T23 steel produced by Baosteel is -40℃ -45℃, and it is anti-oxidiation completely at 600℃. 3 The extrapolated creep rupture strength of T23 steel tube produced by Baosteel at 550℃, 600℃ and 650℃ for 100000h is 123MPa, 81.2MPa and 33.4MPa respectively, which is satisfied with the ASME standard of CODE CASE 2199-1. 4 The successful development of T23 steel in Baosteel greatly improves the manufacture capability and competitive capability of sub-critical and super-critical power station boilers. At the same time, the gap of heat-resistance steel research between foreign countries and our country is also shortened. References 1. Wang Chongbin, Zhou Liping et al. The properties of ASME SA SA213-T23 high-strength boiler tube, Boiler Technology, 1998, 4, 2732 2. ASME SA-213/SA-213M-02a SPECIFICATION FOR SEAMLESS FERRITIC AND AUSTENITIC ALLOY-STEEL BOILER, SUPERHEATER, AND HEAT-EXCHANGER TUBES 340～351. Author Wang Qijiang 1995 , male, professor, works at hot-rolling technology of seamless tube and the development of new high pressure boiler tube for ultra super-critical power station. Tel26647289