The developed 12. 70 ~ 58. 58 mm SA-516Gr65 steel plate ( /% ： 0. 13C, 0. 26Si, 0. 89Mn, 0. 006P, 0.000 7S,0. 33Ni,0. 062Alt ) is produced by 150 t BOF-LF-RH-CC-TMCP flow sheet. Results show that of the steel plate normalized at 880 ~910 ℃, the yield strength 344 ~417 MPa, tensile strength 485 - 500 MPa, -50 ℃： impact energy 167 ~292 J, to meet the requirement of specification. The non-metallic inclusions in steel are mainly consisted of spherical oxide inclusions, and the size is less than 10 μm. After hydrogen induced cracking ( HIC ) test, no cracks are observed on the specimen, and the average values of CLR ( cracking length ratio ), CTR ( cracking thickness ratio ) and CSR ( cracking sensitivity ratio ) are zero, it is up to the MESC SPE 74/125 technical specification. The main microstructure of the steel plate is pearlite and ferrite, and the grains are refined and dispersed uniformly.

Taking Q460 steel (/% ：0. 17C,0. 35Si, 1. 5Mn, 0. 020P, 0.020S,0. 020Nb, 0. 075V) 3 250 mm x 150 mm wide slab as the research object, the solidification heat transfer model is established by ANSYS software, and the effects of casting speed, specific water rate and superheat etc process parameters on the solidification process of slab are studied. The simulation results show that when the casting speed increases by 0. 10 m/min, the surface temperature of slab at the straightening section increases by 36. 5 ℃ , the slab temperature increases by 50℃，the shell thickness decreases by 2. 4 mm, and the liquid core length increases by 1. 2 m； with increase of superheat of 1 ℃, the center temperature of upper surface of slab at the straightening point increases by 1. 73 °C and the length of the liquid core is extended by 0. 11 m； therefore, the casting speed is the key to quality of slab. Production application shows that by 3 250 mm x 150 mm slab cast speed 1. 20 ~ 1. 25 m/min, with superheat 15 〜20 ℃,the temperature of slab surface at straightening section is more than 950 ℃,to decrease the rating of center porosity and segregation and obviously increase surface quality.

Low carbon (C≤0. 12%) Nb-V microalloying S500QL high strength steel plate has been developed. And 15 ~50 mm steel plate is produced by two-stage controlled rolling (first stage rolling at 950 ~ 1 070 ℃, second stage started rolling at ≤890℃ and finishing rolling at ≤850 ℃,on-line cooling direct-quenching( DQ) with 7 ~20 ℃/s after rolling, and tempering at 620 - 670 ℃ for 3 min/ (mm • T), clean steel smelting process with 120 t BOF + LF + VD. The steel plate has fine granular bainite + small amount of proeutectoid ferrite with yield-tensile strength ratio ≤0. 90, elongation A≥19% and impact energy at -50℃ ≥100 J to meet the market demand. And the welding crack sensitivity test and the welding joint property test of DQ process steel plate was carried out. The results show that the steel plate produced by this process has good welding property.

The continuous cooling transformation ( CCT) curve, microstructure and mechanical properties of Q500qE low yield ratio high strength steel 60 mm thickness plate have been studied by JMatpro software, scanning electron microscope and mechanical property tests. The results show that by control rolling and control cooling process: the final rolling temperature 800-840 °C , the into water temperature 660-680 X. and the final cooling temperature 400-450 °C, the microstnicture of steel is composed of ferrite , bainite and MA( martenite/austenite) island, and many large angle grain boundaries exist in junction of two phases and in bainite. The properties of the steel at 1/4 and 1/2 thickness are yield ratio 0.78-0.79, yield strength ≥500 MPa, tensile strength ≥640 MPa, charpy impact energy of 1/2 thickness at -40 °C ≥ 200 J, for HAZ charpy impact test at -40 °C, the charpy impact energy of HAZ ≥100 J.

220 mm steel blocks were cut at the edge of quenching testing slab of peritectic steel from curving section to straightening section, and then its surface quality and microstructure is anlysized. The result shows that transverse comer cracks appear at straightening section. With the extending of strand from curving section to straightening section,ferrite film at grain boundary of austenite become thicker and clear,and the grain size of austenite is in the range of 1.0 mm to 1.5 mm. Owing to the coarse grain of austenite and thick fragile ferrite film, transverse comer cracks spread along the grain boundary of austenite. With increasing cooling water in single narrow side of mould from original 30 〜32 m ³/h to 34 ~36 m ³/h,and shut the side sprayer of inner arc of straightening sections, transverse comer cracks slab is effectively controlled.

Through the design composition (/% : 0. 09C, 0. 15Si, 1. 15Mn, 0. 58Ni, 0. 47Cr, 0. 44Mo,0. 033V, 0.022Nb,0.0012B,0.036Al,0.014Ti) , the N content of smelting analysis controlled to be ≤ 20 x 10 ^-6 in steel smelting, rolling with ingot maximum heating temperature ≤1 200 °C , and quenching at 930 °C and tempering at 610 °C,the developed 60 mm SX780CF steel plate has yield strength 780 MPa, tensile strength 887 MPa, elongation 18% and 5% strain 250 °C aged -20 °C impact energy (KV ₂) 203 ~ 210 J, which meet the technical requirements of 800 MPa low welding crack sensitivity high strength steel for hydropower station.

The 0. 20% ~0. 25%C high-quality NM450 wear-resistant steel for truck compartment has been designed and developed by using Nb, Ti, Cr and B microalloying composition. The microstructure of 14 mm steel plate queched at 900 °C and tempered at 200 °C is tempered lath martensite and a small amount of dispersed second phase particles, which has the excellent comprehensive properties. The tensile strength of NM450 steel is 1 459 MPa, the elongation is 19% , the impact energy is 104 J, the surface brinell hardness value is 450HBW. With the bending angle 180°and the elbow diameter 168 mm, the bending sample is qualified. CHW-70C welding wire has good welding performance： i. e. the tensile strength of welded joint 839 MPa, the impact energy of weld 113 J, the hardness number of weld 282HV. With the bending angle 90° and the elbow diameter 168 mm, the bending sample is qualified.

By 120 t converter-LF refining-continuous casting-controlled rolling and cooling process,the 750L (Rm≥ 750 MPa)beam steel of 8 mm high strength automobile is succes fully developed. The results show that through 750L steel Nb-Ti composite microalloying(/%:0.074C,0. 11Si,1.51Mn,0.020P,0.002S,0.042Als,0.033Nb,0. 109Ti), combined with control rolling and cooling(finish rolling reduction≥40%),that of produced  750L  steel  strip, the  tensile strength  782～810 MPa, elongation≥17.5%, grain  size11.5～12.5 rating  and  impact  energy ≥90 J, all technical  indexes satisfy the requirements of standard.

The 250 mm casting slab of steel Q355D bearing 0. 14% ~ 0. 18% C and 1.40% ~ 1.60% Mn is hot-rolled by the controlled rolling process. The results show that the microstructure of rolled plate is fine and uniform by rough rolling at 1050 - 1130℃  , finishing rolling at 920℃ and final rolling at 880 ℃ , and the final cooling below 670℃  , the properties of the 70 mm and 80 mm thick plate can meet the requirements of Q355D steel grade and the Z25 reduction of area (RA) is 58% 〜64% to meet the requirement of Z25 direction RA≥25 %.

The properties of Q960E steel 70 mm plate quenched at 890-920 °C and tempered at 560-600 °C are tested, and the microstructure of Q960E steel is analyzed by metallographic microscope (OM) and scanning electron microscope (SEM) . The results show that the strength toughness matching of the steel plate is the best when quenching at 920 ℃ and tempering at 560 °C (UTS 1 048 MPa,YS 1 005 MPa, e1.14% and -40 °C KV ₂ 52-61 J), the performance distribution of the steel plate in the full thickness direction is relatively uniform, and the hardness value is 27.5-33HRC, the microstructure from the surface to the center is tempered sorbite and residual austenite.

 The 150 mm thick steel cladding plate is rolled by two block 365 mm cladding bloom, the delamination crack at 1/2 thickness of quenched-tempered cladding plate occurs when cutting four sides by flame. Analysis results show that quenching delamination crack is induced by the inclusions in central cladding interface together with the quenching stress. When the cladding bloom welding vacuum decreases from 5 x 10 ^-2 Pa to 1 x 10 ^-2 Pa,the cladding plate is not found inclusions in cladding interface and the delamination crack at 1/2 thickness cladding plate does not occur.

Concentrating on the problem that the existing track shoes are vulnerable to rapid wear and tear caused early failure,in this paper,25CrMnB is used as the comparative steel,added 0. 08% ,0. 12% and 0. 16% vanadium respectively, smelted and cast into 50 kg steel ingots in a laboratory using a 150 kg medium frequency vacuum induction furnace. The steel ingot is heated by a box type electric resistance furnace and rolled into a flat steel of 12 mm thickness. The effects of different vanadium contents on the wear resistance is studied by wear resistance test and precipitation phase analysis. The results show that, with increasing vanadium content in the steel,the amount of vanadium precipitates increases,and the hardness as well as wear resistance of the test steel are significantly improved. When the vanadium content in the steel increases from 0.004% to 0.16% ,the HRC hardness value of the test steel increased from 36.5 to 43.5,compared with 25CrMnB steel,and the relative abrasion rate decreases from 100% to 88.2% ,and the relative abrasion rate decreased by 11.8%.

The 1900 MPa Ti microaUyed ultra HSLA steel (/% ：0.34C,0.70Si, 1.50Mn,0.012P,0.004S,0.08Ti, 0. 002 0B,0. 004 ON) is developed by 200 kg vacuum induction furnace and 550 mm slab mill. The results show that with first stage starting and final rolling temperature respectively at 1180 °C and 1030 °C in austenite recrystallization zone, and with second stage starting rolling temperature at 920 ~ 950 °C and final rolling temperature at 850 ~ 890 °C in austenite nonrecrystallization zone,then quenching at (900 ± 10)°C and tempering at 200 〜230 °C , the plate precipitated phase is (Ti, Mo)C,the grain size rating is 10,the structure is tempered martensite,with the mechanical properties are Rm 1930 〜1985 MPa,A 10% ~ 12.5% , -40 T K _v2 200 ~ 230 J.

 4 ~ 100 mm 17Mn plate damping steel plate (/% ： 0. 02C, 0. 08Si, 17.53Mn, 0.014P, 0. 002S, 0.005Als) was developed and produced by Ansteel, with properties of yield strength 311 -407 MPa, 15 〜100 mm plate -20 °C V-notch impact energy 113 ~ 144 J, the tensile strength of welded joint 651 ~654 MPa, and-20°C V-notch impact energy 66 〜84 J after welding. The microstructure of the 17Mn damping steel is residual austenite and e martensite, and its damping property is tested using a dynamic mechanical thermal analyzer. Under the condition of double cantilever strain scanning at 30°C and 50 Hz, the damping values of the different thickness damping steels are greater than 0.02. At 100 Hz, the damping values of damping steels of different thicknesses are all greater than 0.05, and the damping values are higher than those of traditional low-alloy structural steels Q235 and Q345 (0.008 and 0.010 ~0.013).

The yield strength 750 MPa high strength low alloy (HSLA) steel for container (/% : 0.06 ~0.09C, 0.25 ~0.35Si, 1.60 ~1.80Mn, ≤0.015P, ≤0.003S, 0.10 ~0.20Mo, 0.05 ~0.06Nb, 0.09 ~0.llTi, ≥ 0.0015Ca, ≥0.015Alt) has been designed and developed. The process flowsheet for tested steel is 260 t BOF-LF-RH-230 mm slab casting-hot-rolling to 2 ~ 6 mm plate. With the process measures including Nb-Ti compound microalloying and Ca treatment, controlling finishing rolling temperature 840 -880 ℃, lamina flow cooling rate ≥ 60℃ /S, coiling at 520 -580℃ , and hot-rolled coil cooling rate ≤ 10 °C/h， the hot-rolled strip coil has better surface quality, its structure is fine grain ferrite + Nb-Ti carbonitride, and the mechanical properties of strip are upper yield strength 760 〜790 MPa, tensile strength 860 -910 MPa, and elongation 21% ~25% to meet the requirement of user.

The flatness defects of high strength hot rolled wide strip steel AG700L after uncoiling are analyzed in detail. The influences of strip shape and temperature distribution after finishing rolling are discussed, and the influences of the ratio of upper and lower water flow, side spray, cooling methods, edge masking on uncoiling plate and optimization measures are also analyzed. The results show that the main reason of the flatness defects after uncoiling is due to release of the compressive stress caused by the temperature drop of strip edge. The flatness defects could be effectively controlled by optimizing the ratio of upper and lower water flow to 1 ： 1.35 and the angle of side spray, increasing the pressure of side spray to 2.0 MPa, improving the type of cooling and using the edge masking.

The effects of hot-rolled three-stage cooling and temper-rolling processes on mechanical properties of 2.3 mm 700 MPa grade Nb-Ti micro-alloying S600MC high strength steel strip (/% : 0.07C, 0.15Si, 1.50Mn, 0.015P, 0.003S, 0.025Alt, 0.015Nb, 0.08Ti) are studied. When end rolling at 870 as intermediate temperature decreasing from 670 X. to 580 °C , the yield strength increases from 577 MPa to 600 MPa, the tensile strength basically remaines unchanged (774 MPa to 784 MPa) , the elongation decreases from 24% to 21% , and the yield ratio increases by 0.04. When the coiling temperature increases from 150 °C to 250 °C , the mechanical properties remain unchanged. The yield strength of high strength steel with primary temper-rolling process increases by 20 MPa to 43 MPa, while the tensile strength changes slightly and the elongation decreases by 2-5 percentage point. The yield strength increases by the secondary temper-rolling process significantly to 101 MPa, while the elongation decreases by 8 percentage point, which is adverse to comprehensive properties.

The simulated post-weld tensile property, -29 ℃ impact property, metallographic structure and temper embrittlement tendency evaluation of 150 mm thickness SA387Gr22C12 steel plate( /% : 0. 13 ～ 0. 14C, 0. 09Si, 0. 55 ～ 0. 56Mn,0. 004P,0. 001S,2.48 ~2. 49Cr,1.11～1. 12Mo ) are tested. The each property of steel plate with delivered state (normalizing + tempering ), minimum simulated post-weld state, maximum simulated post-weld state and step cooling test are measured. The results show that the temper embrittlement tendency of steel plate is not obvious, the resulf of CvTr55 +2. 5 Δ CvTr55 is -63 ℃ , fully to meets the technical requirements of steel plate for methanol synthesis tower.