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 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 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.

 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).

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.

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.

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 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.

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.

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 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.

The effect of heat treatment process on metallographic structure and mechanical properties of SA-738Gr. B steel plate has been studied. And the factors led to instability of tensile test performance in delivery state and low tensile strength after SPWHT are analyzed. At the same time, technological measures to improve the stability of steel plate SA- 738 Gr. B have been worked out. The test results show that steel plate SA-738Gr. B quenched at 915 ~935 ℃ and tempered at 675℃ ,and simulated post-welded heat-treated (SPWHT) has excellent mechanical properties to meet the using requirement.

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.

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 production process and actual product performances of ASTM A 387M Gr. 11 CL2 steel 24 mm plate for pressure vessels produced by Chongqing Iron and Steel Co Ltd are introduced. The rolling process and heat treatment of test steel (/% ：0.13C,0.56Si,0.56Mn,0.036Alt,0.005P,0.001S,l.02Cr,0.50Mo)300 mm x2010 mm casting slab are rough rolling at >1000 °C , thicknees of middle bloom 72 mm, finishing rolling at 880 ~ 940 °C , end finish rolling at 850 ~870 °C,laminar cooling to 690 -710 °C , air cooling to room temperature and normalizing at 890 〜910 °C, tempering at 650 ~ 670 °C. Practice shows that the performance indexes of the steel meet the technical requirements and the steel has good impact toughness at low temperature, i. e. the impact energy of test steel at -40°C is 149 ~ 172 J.

For improving the problem of non-metallic inclusions in low carbon aluminum killed steel produced by CSP process at Jiuquan steel Co,with sampling at each phase of steelmaking and continuous casting,the study of inclusions in steel is carried out by metallographic analysis, electron probe and scanning electron microscopy. The results show that under the current process conditions,the casting slab T[0] is more than 30 x 10 ^-6 ,by BOF blowing N ₂/Ar exchange process,LF soft blowing 36 min and lable heel 2% ~4% ,the 2μm inclusions ≥66% and spherical inclusions ≥94% ,and the type of inclusions is mainly calcium aluminate plus a certain amount of CaS. After the process optimization, all indexes meet the requirements of DQ deep drawing steel production.

The microstructure and mechanical properties of controlled rolling and controlled cooling 0. 31% Ni and 0. 88% Ni two Nb-Ti microalloyed NiCr steel are investigated. The results show that granular bainite, upper bainite, acicular ferrite, polygonal ferrite and a little of pearlite in marine steel are obtained by controlled rolling-cooling. Controlled rolling and control! cooling result in the refinement of the feirite grain and the increase of M-A islands. Both steels have high tensile strength,yield strength,elongation and hardness,and the mechanical properties of 0. 88Ni- 0.32Cr steel are higher than those of 0. 31Ni- 0.33Cr steel. The impact energy of longitudinal direction all of the marine steels exceeds 200 J,and that of 0.88Ni- 0.32Cr steel exceeds 300 J at _80℃. 0. 88% Ni is optimum of containing nickel of steel. This is attributed to the ferrite grain refinement strengthening, M-A islands compound strengthening, precipitation strengthening and dislocation strengthening due to controlled rolling and controlled cooling. Nickel effectively improves low-temperature impact toughness of marine steel.

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.