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 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 metallurgical flowsheet of 230 nun casting slab of 700 MPa Ti microalloying low carbon steel is KR metal pre-desulphurization-210 t BOF-LF-RH-CC process. It is found that the median position of cross section of slab in laid up is breaking. The results by analysis on casting slab composition, structure, gas content, inclusions and hot plasticity show that the composition of median position is same as that in other part of slab (/% : 0.075 ~ 0.084C, 0.53 ~ 0.56Si, 1.97~2.05Mn, 0.025 ~0.026P, 0.002-0.004S, 0.134 ~ 0.136Ti, 0.20Mo, 0.064 ~0.069Nb, 0.001V, 0.008 9N) , and the structure of breaking area and base metal is all fenite + minor pearlite with same grain size； the micro crack in breaking area is formed by local plasticity deformation in main crack expanding process ； the formed network proeutectoid ferrite, TiC and TiN are key reason to effect on hot plasticity of casting slab of high Ti microalloying steel. With the measures including in prerequisite of qualified strength of plate to decrease the Ti content in steel from 0. 13% to 0. 11%, secondary water ratio ≤0.9L/kg, temperature of slab at straightening region being more than 950℃ (second brittle zone of the steel- 950 ~ 850 ℃.), adding holding bell and using slow cooling pit to decrease the cooling rate of slab, the breaking rate of high Ti slab decreases from 10% to 0 to avoid the occurrence of slab breaking.

The depressed defects of scales with dimension (10~40) mm x (3~10) mm and depth 1~3 mm occur at 30 mm plate hot-rolled from 230 mm casting slab of steel Q235B (/% : 0.18C, 0.20Si, 0.34Mn, 0.015P, 0.005S, 0.07Cr). The primary scale formation mechanism and removability at high temperature in high-pressure water descaling operation are analyzed and the measures to optimize the process are forward including (1) with optimizing heating process to insure the casting slab surface temperature being more than 1170 °C for high-pressure water descaling； (2) with optimized high-pressure water parameters i. e. increasing spray-water pressure from 18 MPa to 20 MPa and flow velocity from 161.2 m/s to 170.0 m/s, in order to increasing the impact force from 116.3 N to 122.7 N. The test and commercial production results by 26 heats show that after process optimization the closing off rate of slab caused by rolled-in scales reduces to less than 2% , it is obvious to improve the rolled-in scales defects.

The steelmaking process of 700 MPa microalloying steel (/% : 0.05C, 0.18Si, 1.80Mn, 0.010P, 0.003S, 0.15Mo, 0.l0Ti, 0.075Nb, 0.035V, 0.030Al, 0.0020Ca) is 240 t BOF-LF-2150 mm slab casting. The structure and mechanical properties of hot-rolled 10 mm strip of 700 MPa microalloying high strength steel air-cooling processcoiling at 600℃. and direct sampling air-cooling for 3.7 h to ambient (25℃ ) and slow-cooling process-coiling at 600℃ and coils stacked slow-cooling for 36.2 h to ambient (25℃)are observed and tested by using optical microscope, scanning electron microscope, energy spectrometer and tensile tester. Results are obtained that with slow-cooling process the a mount of bainite in steel strip is relatively less, the steel strip has higher yield strength (732~740 MPa) , lower tensile strength (793~799 MPa) and larger elongation (21.0% 〜23.0% ) ； and with air-cooling process the amount of bainite in steel strip is rather more, the steel strip has lower yield strength (647〜654 MPa) , higher tensile strength (811〜831 MPa) and rather lower elongation (15.0%~17.0% ). Comprehensive consideration, the mechanical properties of steel strip with slow-cooling process are better than that with air-cooling process.

The 300 mm slab of tested steel EH460 (/% : 0.06~0.08C, 0.20~0.33Si, 1.51~1.52Mn, 0.003〜0.013P, 0.002S, 0 〜0.18Mo, 0.34~0.36Ni, 0.04~0.05Nb, 0.05~0.06V, 0.013~0.015Ti, 0.006~0.026Als) is rolled to 60 mm plate by Φ550 mm mill, end rolling temperature at 798~817 °C. and cooling rate 5~20 °C/s. The effect of no-bearing Mo and bearing 0.18% Mo on structure and mechanical properties of the steel has been studied. Test results show that with cooling rate 15 ℃/s, of no-adding Mo steel the tensile strength is 645~655 MPa, -40 ℃ impact energy is 168~200 J, and of 0.18% Mo steel the tensile strength is 677~679 MPa, -40℃ impact energy is 48~64 J. For the high strength hull steel EH460, the strength of plate shall be increased by adding Mo in steel to meet the ships' classification society standard requirement for strength of steel ( yield strength ≥460 MPa, tensile strength 570~720MPa and impact energy at -40 ℃ ≥46 J) , but the impact energy of higher Mo content steel decreases more, therefore in real production the Mo content in high strength bull steel EH460 should be ≤0.15%.

The casting slab corner transverse cracks of steel Q550D (/% ： 0.15C, 0.25Si, 1.40Mn, ≤0.010P, ≤0.002S, 0.03Nb, 0.06V, 0.015Ti, 0.020Alt) have been analyzed to get the comer transverse cracks form in mold and further develop at secondary cooling area, besides at bending part ( Ⅲ brittle zone) of slab, the tensile-stress action of outer face of slab is also an important factor for corner cracking. With the process measures including decreasing water flow rate of width face of mold by 200 L/min and of narrow face by 20 L/min, improving precision of arc each other from ±0.5 mm to ±0.3 mm, improving the amplitude and vibration frequency respectively from 4~5 mm and 130~136 opm to 3.6~4.5 mm and 140~146 opm, increasing the mold taper from 0.9%~1.0% to 1.0%~1.1% , improving edge natural cooling at secondary section to nozzle cooling, and decreasing nitrogen content in steel from ≤60 x 10 ^-6 to ≤40 x 10 ^-6 the occurring rate of comer cracks markedly decreases.

The production flowsheet of 240 mm slab of tested steel 1500MS (/% : 0.20C, 0.31Si, 1.39Mn, 0.011P, 0.001S, 0.028Als, 0.26Cr, 0.028Ti, 0.0018B, 0.0048N) is 250t BOF-LF-RH-slab CC process. The mechanical properties of tested steel at 1350 ~600°C have been measured by using Gleeble-1500 thermal simulation machine to get I-bnttle zone at 1350 ~ 1250°C , and Ⅲ-brittle zone at 650〜750°C，and at 800〜1200 °C the tested steel has better hot plasticity ； and the mathematical model of slab solidification heat transfer is established and the surface temperature of casting slab in solidification process is calculated. The temperature of tested steel of steel 1500MS at straightening zone should be controlled at 800〜1150°C.

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 flowsheet of 236 mm x 1 350 mm casting slab of tested steel CR1030/1300MS (/% : 0. 13C, 0. 26Si, L53Mn, 0.011P, 0.002S, 0.31Cr, 0.047Als, 0.029Nb, 0.032Ti, 0.002 5B, 0.003 2N) is 260 t BOF-LF-RH-CC process. With using Gleeble3500 thermal simulation test machine the thermoplasticity curves of test slab at 650 ~ 1 300 °C has been measured and the structure of high temperature tensile specimen fracture is analyzed. The test results obtain that the two brittle zones in test steel are melting point 〜1 120 °C and 800 〜650 °C , and the better plasticity occurs at 1 120 ~ 800 °C , in this zone the reduction of area of steel is more than 85%. The fracture of tensile of steel at 900 °C. is transgranular toughness fracture and at 700 °C it is toughness and along crystal fracture. The structure near fracture of tensile of steel at 1 250 °C and 900 °C is martensite and with increasing temperature the martensite lath is coarser. The basic reason to form crack is that the proeutectoid ferrite occurs in original austenite grain boundary at 750 °C.Straightening at 1 120 ~ 800 °C is available to avoid the casting bloom forming crack.

Surface crack on micro-alloyed steel plate produced by hot charging process was investigated by means of metallographic analysis, energy spectrometer analysis and contrast test of HCR and CCR. The results show that the main factors of surface crack on micro-alloyed steel plate produced by hot charging process are not the cracks on slab but the precipitation of a large of fine carbon and nitrogen compound at the boundary of the austenite grains,which decreases the strength of the grain boundary sharply.

The effect of C and Si content on mechanical property of low carbon cold-rolled steel(/% ：0.0051 ~0.0344 C,0.008 ~0.054 Si,0.28 ~0.30 Mn,0.023 ~0.026 P,0. 004 - 0.007 S. 0.044 ~0. 060 Al)has been studied. Industrial process is hot metal pretreatment-80tBOF-RH-continuous casting - hot rolling-acid pickling-cold rolling. Results show that the higher the C or Si content, the higher the strength and hardness, the lower the elongation. Cold rolling test was carried out in the laboratory,the test material was low carbon steel hot rolled (/% :0.0112C,0.009Si,0.30Mn,0.025P,0.006S,0.052Al) which produced in plant. Results of cold rolling test show that when the cold rolling reduction ratio increases from 41% to 57% , strength and hardness gradually increase, the elongating slightly elevate, When the content of C was 0. 005% ~ 0. 010% ,Si was ≤0.012% and cold rolling rate was 40% ~ 50% ,the tensile strength (Rm) of cold rolled sheet was less than 660 MPa and hardness (HRB) was 86 - 89. meeting technical requirement.

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 Q690E steel plate for engineering machinery (/% ：0. 10 ~0. 15 C,0. 20 - 0. 40 Si, W0. 015 P, W 0.005 S,0.30 ~ 0. 40 Cr,0. 20 ~ 0. 30 Mo,0. 035 ~ 0. 045 V,0. 01 ~ 0. 02 Ti,0. 001 ~ 0. 002 B) has been developed through low carbon and a “Mn-Cr-Mo-B-V-Ti” microalloyed components design, rolling and heat treatment technology selecting. The microstructure of Q690E steel plate guenched at 880 ~910 ℃ + tempered at 570 ~610 ℃ is tempered sorbite with yield strength 811 ~ 891 MPa,tensile strength is 852 -938 MPa and - 40 ℃ impact energy 132 ~ 167J. It ean meet the requirements of GB/T16270-2009 on mechanical properties for Q690E Steel. The result is that, while meeting the increasingly stringent requirements of users,the production costs are reduced.

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%.