Proceedings of the Value-Added Niobium Microalloyed Construction Steels Symposium CBMM and TMS, 2015 DEVELOPMENT AND PROSPECT OF APPLICATIONS OF NIOBIUM MICROALLOYED STEELS TO BUILDING STRUCTURES IN CHINA Mingxuan He1, Yaohua Wu2 and Houxin Wang3 1Baosteel Construction Co., Ltd. Shanghai 201900, China 2Central Research Institute of Building and Construction, MCC, Beijing 100088, China 3CITIC-CBMM Microalloying Technology Center, Beijing 100082, China Keywords: Niobium Microalloyed Steel, High-rise Buildings, Large Span Structure, Steel Standards, Case Studies, Mechanical Properties Abstract The Chinese steel industry has been developing at an amazing rate for over ten years, providing great quantities of steel materials to downstream industries and also stimulating the development of these industries. In recent years, with the further development of urbanization and modernization, many high-rise buildings and large span structures have been built in China, and a large amount of steel has been used in those buildings. Before giving some examples of the buildings in which niobium microalloyed steels have been used, Chinese steel standards are reviewed. The new version of the code for the design of steel structures allows more steel grades to be considered for building structures. There is no doubt that niobium microalloyed steels, with outstanding mechanical properties, will play a very important role in the booming era of high- rise buildings in China. Present Situation and Development of Building Steel Structures in China In recent years, China's economy has been growing continuously at high speed, and urbanization is similarly increasing. China has been the biggest steel producer in the world for over 15 years. To achieve light weight, high strength, better seismic performance, improved usable floor area, faster construction, energy conservation, environmental protection and other comprehensive economic advantages, more and more steel is used in building constructions. The development of steel structure buildings has become a principal engineering construction policy in China. The steel construction industry chain has been formed on the basis of the steel production, steel structure design, steel components production, installation and related industries. While the lower strength steel Q235 dominated in the past, Q345 and higher strength low alloy steels are now the major steel grades being used. The number of high-rise buildings and large span steel structure buildings in China will be the largest in the world in the next ten years, and accordingly niobium-bearing microalloyed high strength steel should be widely used. 13 China’s Steel Output and Steel in Building Structures China’s steel output exceeded 100 million tons in 1996, becoming the world’s biggest steel producer. At present, within the domestic steel market, supply exceeds demand. According to the 2009 census, the steel consumption in segments was: building (including rebar and structural steel plates) 52%, industries 34%, transportation 6% and others 8%. Steel output and steel consumption in building structures in 2009 and 2010 are shown in Table I. From the table, the proportion of steel used in building steel structures to the total steel output is too low (accounting for only about 4%), while it is approximately 10% or more for developed countries and more than 30% for Japan and the United States. Therefore, there is much space and great potential for the development of building steel structures using niobium-bearing high strength steels. Table I. Steel Output and Steel Consumption by Building Steel Structures Steel Output Steel Consumption by Building Steel Structures Proportion Year (million ton) (million ton) (%) 2009 565 23 4.1 2010 626 26 4.2 2011 683 30 4.4 Steel structures consist of buildings, railway and highway bridges, power plant construction, municipal construction, etc., according to China’s steel construction society statistics [1,2]. The usage distribution of steel structures is as follows. Proportions according to the applications are shown in Table II and Figure 1. Table II. Proportions According to Applications (%) Year Building Bridge Tower Mast Others 2009 54 9 7 30 2010 66 11 6 17 14 Figure 1. Steel construction proportions according to applications in (a) 2009 and (b) 2010. Proportions according to steel grades are shown in Table III and Figure 2. Table III. Proportions According to Steel Grades (%) Year Q235 Q345 Q390 Q420 Q460 2009 35 53 7 3 2 2010 31 62 4 2 1 15 Figure 2. Steel construction proportion according to steel grade in (a) 2009 and (b) 2010. Proportions according to the steel products are shown in Table IV and Figure 3. Table IV. Proportions According to the Steel Products (%) Year Plates Shapes Cold Forming Pipes Others 2009 64 15 5 10 6 2010 60 15 6 15 4 16 Figure 3. Steel construction proportions according to the steel products in (a) 2009 and (b) 2010. In building structures, steel consumption can be divided by building types into public buildings, industrial plant, high-rise buildings, multistory buildings and so on. The steel distribution is thus shown in Table V and Figure 4. Table V. Proportions of Steel Consumption According to Building Type (%) Year Public High-rise Multistory Factory 2009 21 17 13 49 2010 21 14 12 53 17 Figure 4. Steel consumption proportions according to building types in (a) 2009 and (b) 2010. Building Structure Steel Standards Ten years ago, the major steel used in building structures was Q235 carbon structural steel produced as per the national standard “Carbon Structural Steel” GB/T 700-88 [3] and a small amount of Q345 steel as per “High Strength Low Alloy Steels” GB/T 1591-94 [5]. Along with the continuous development of China’s steel industry, the level of technology, processing, equipment and management for steel production has been constantly advancing. More high strength steel grades such as Q390 steel, Q420, Q460, Q345GJ, Q390GJ, Q420GJ and others are used in domestic large-scale projects, such as CCTV’s new tower, the national swimming center (water cube), Beijing’s international trade building and other large constructions. The leading position of Q235 in constructions has been replaced by Q345 steel in recent years. The quality and strength level of structural steels for buildings and construction has been improved. The current steel material standards for steel structures in China are introduced briefly as follows. “Carbon Structural Steel” GB/T 700 Q235 steel is the most widely used among the carbon structural steels listed in the national standard GB/T 700 “Carbon Structural Steels”. The mechanical properties of Q235 in the 2006 edition almost remain as per the 1988 edition [4]. Table VI shows the mechanical properties of Q235 in the 2006 edition of GB/T 700. 18 Table VI. Mechanical Properties of Q235 Steel in GB/T 700-2006 Yield Strength ReH Elongation A %, Impact Test m Cold Bending (MPa) ≥ (V-notch) Thickness or Thickness or Thickness Diameter (mm) Diameter (mm) (mm) nergy nergy E C) (MPa) ° (J) ( Steel Grades Steel ≤60 ≤16 ≤40 Absorbed Absorbed Quality Grades Quality >16~40 >40~60 >40~60 Temperature >60~100 >60~100 Tensile Strength R Strength Tensile Impact >100~150 >150~200 >100~150 >150~200 A ─ ─ Longitudinal/ B 20 370~500 26 25 24 22 21 (0.5a) C 235 225 215 215 195 185 0 ≥27 Q235 Transverse/(a) D -20 “High Strength Low Alloy Steels” GB/T 1591 The mechanical properties and chemical composition of “High Strength Low Alloy Steels” (HSLA steels) are listed in Table VII and Table VIII respectively. Comparing the last version of “High Strength Low Alloy Steels” (GB/T 1591-94) [5] with the current edition (GB/T 1591- 2008) [6] has changed in the following areas: Modified thickness classification; Increase in Q345’s yield strength; The yield strength decrease with thickness has become smaller (the drop of typically 20 MPa reduced to 10 MPa), as seen in Figure 5; The absorbed impact energy of E grade steels increased from 27 Joules to 34 Joules; The CEV and Pcm requirement index added; Lower sulfur and phosphorus content required and increase in allowable niobium and vanadium contents. 19 Q460 Q420 Q390 Q345 Steel Grades D C D C B A D C B A D C B A E E E E Quality Grades Table VIITable 460 420 390 345 ≤16 (mm) or Diameter Thickness Yield Strength R Yield Strength 440 400 370 335 >16~40 . Mechanical Properties of HSLA Steels Mechanical Properties HSLASteels of in GB/T 420 380 350 325 >40~63 400 360 330 315 >63~80 eH (MPa) 400 360 330 305 >80~100 380 340 310 285 >100~150 20 550~720 520~680 490~650 470~630 Tensile Strength Rm (MPa) Thickness or Diameter or Diameter Thickness 17 19 20 20 ≤16 ≥ (%), A Elongation 16 18 19 19 >16~40 (mm) 16 18 19 19 >40~63 16 18 18 18 >63~80 1591 - - - 17 >80~100 - 2008 +20 +20 +20 (V - - - - - - - - 40 20 40 20 40 20 20 40 0 0 0 0 Impact Impact - - - - Test Temperature (°C) n otch) 34 34 34 34 - - - Absorbed Impact Energy (J) ≥ Table VIII. Chemical Composition of HSLA Steel in GB/T 1591-2008 Chemical Composition (wt.%) P S Nb V Ti Cr Ni Cu N Mo B Als C Si Mn Steel Level -2 Grades ≤ ≤ ≤ ≤ ≤ (x10 ) ≥ A 0.035 0.035 - B 0.20 0.035 0.035 Q345 C 0.50 1.70 0.030 0.030 7 15 20 30 50 30 1.2 10 - D 0.030 0.025 .015 0.18 E 0.025 0.020 A 0.035 0.035 - B 0.035 0.035 Q390 C 0.20 0.50 1.70 0.030 0.030 7 20 20 30 50 30 1.5 10 - D 0.030 0.025 .015 E 0.025 0.020 A 0.035 0.035 - B 0.035 0.035 Q420 C 0.20 0.50 1.70 0.030 0.030 7 20 20 30 80 30 1.5 20 - D 0.030 0.025 .015 E 0.025 0.020 C 0.030 0.030 Q460 D 0.20 0.60 1.80 0.030 0.025 11 20 20 30 80 55 1.5 20 0.4 .015 E 0.025 0.020 C 0.030 0.030 Q500 D 0.18 0.60 1.80 0.030 0.025 11 12 20 60 80 55 1.5 20 0.4 .015 E 0.025 0.020 C 0.030 0.030 Q550 D 0.18 0.60 2.00 0.030 0.025 11 12 20 80 80 80 1.5 30 0.4 .015 E 0.025 0.020 21 Chemical Composition (wt.%) P S Nb V Ti Cr Ni Cu N Mo B Als C Si Mn Steel Level -2 Grades ≤ ≤ ≤ ≤ ≤ (x10 ) ≥ C 0.030 0.030 Q620 D 0.18 0.60 2.00 0.030 0.025 11 12 20 100 80 80 1.5 30 0.4 .015 E 0.025 0.020 C 0.030 0.030 Q690 D 0.18 0.60 2.00 0.030 0.025 11 12 20 100 80 80 1.5 30 0.4 .015 E 0.025 0.020 Als = Soluble Aluminum Figure 5.