The production flowsheet for Ti-Nb Microalloy high strength steel plate is 206 t top and bottom combined blown converter-LF-RH-230 mm slab casting-rolling 3 〜7 mm plate process. Through optimizing the original 0.45 Nh- 0. 015Ti microalloy steel to 0. 070Ti-0. 015Nb microalloy steel has excellent welding and low temperature impact toughness properties and has better comprehensive mechanical properties. Service results show that the 0. 07Ti-0. 015Nb microalloy steel is identical to 0. 045Nb-0. 015Ti microalloy steel, satisfactory to requirement of process and service, while the production cost decreases obviously.

The metallurgy flowsheet of developed steel Q460D (/% : 0. 16 - 0. 18C, 0. 42 ~ 0.48Si, 1.40 ~ 1.46Mn, 0.012 ~0. 020P, ≤ 0.005S, 0.11 ~12V, 0.020 ~ 0.050A1, 0.0102 ~0.0139N) is ≥40% hot metal + scrap- 50 t EAF-LF-VD-260 mm x 300 mm bloom casting- hot rolling to 070 ~ 100 mm products. With the process measures including controlling EAF end [C] 07% and [P]≤0.015% , LF refining slag basicity ≥ 3.0, feeding Al and Ca wire, controlling Al 0. 030% ~ 0. 05% and [S]≤0.005% , and feeding manganese-nitride wire before LF tapping, the mechanical properties of steel is stable i. e. yield and tensile strength, elongation and impact energy of steel being respectively 470 - 504 MPa, 576 ~ 695 MPa, 19.0% ~ 27. 5% and 32 ~ 60 J, the qualified rate of nondestructive testing is 93. 7% , and the stability of composition and each performance of steel is high to meet the of high cleanliness, high homogeneity and high stability of properties of steel for auto axle head.

The 5. 0 mm strip of developed tested steel 510CL (/% : 0. 08C, 0. 07Si, 1. 25Mn, 0. 008P, 0. 005S, 0. 023Nb, 0. 018Ti) is produced by semi-steel desulphurization- 200 t top and bottom combined blowing converter-LF-230 mm x 1 650 mm slab casting-continuous rolling process. In order to ensure the better welding performance of wheel steel, the 500 MPa high strength wheel steel is developed by low carbon Nb-Ti microalloying combined TMCP ( Thermo-Mechanical Control Process) technology. The hole-expansion rate of tested steel is more than 100% , the welding performance is better, the cold-forming performance and the fatigue life of steel all meet the user technical index, and after application the test steel is up to design requirement.

The production process flowsheet of steel C38N2 (/% : 0. 36 〜0.40C, 0. 50 ~0. 65Si, 1.40 ~ 1. 55Mn, ≤ 0.025P, 0.010 ~0.040S, 0. 10 ~0,25Cr, ≤ 0.01A1, 0.015 ~0.020N) is 120 t-BOF-LF-RH-410 mm x 530 mm bloom casting-continuous rolling to Φ170 mm products. The statistics of effect of refining slag basicity (2. 0 ~ 2. 5 ) , Ca content in finished steel (0 ~ 0.075%), tundish shielding agent basicity (5. 94 and 1.70), secondary cooling water (0. 14 ~0. 24 L/kg) and mould electromagnetic stirring current (250 A and 100 A) on sulfide in steel has been analyzed. With process measures including using 2 ~3 low basicity slag .in refining, controlling [ Ca]/[ S]>0. 03 , using tundish shielding agent basicity 1. 70, secondary cooling water rate 0. 24 L/kg and mould electromagnetic stirring current 100 A, the ratio of rating ≤2. 5 of A-thin series sulfide in steel increases from 80% before process improvement to 95% , and the fine, dispersed distributed spheroidal and spindle-shaped sulfide in steel increases markedly.

Non-quenched and tempered steel C38 + N for automobile can be used into not only crank shaft materials, but also produced engine connecting rods. By optimizing chemical composition (/% ：0.36 ~ 0.40C ,0.50 ~ 0.65Si, 1.40 ~ 1.55Mn,0.10 ~0.20Cr,0.015 ~0.020N,0.020 ~0.035S, ≤ 0.025P,0.003 ~0.015Al) and by feeding S wire to control sulfur content in steel etc, measures, the mechanical properties of steel C38 + N are Rp 0.2506 ~ 544 MPa Rm 854 ~ 879 MPa,A 12% ~23.5% and Z 26% - 30% to meet the requirement of standard.

The new energy automobile motor shaft made of non-quenched and tempered steel 50MnSiV (/% ：0.50C, 0.52Si, 1.20Mn, 0.010P, 0.025S, 0.15Cr, 0.10V, 0.015Ti, 0.015N) by eliminating traditional carburizing heat treat¬ment, straightening and finishing process of steel 20CrMnTiH, can not only improve 95% materials utilization rate and 2 delivery days and can also reduce 25% costs. With tensile strength 1100 MPa, yield strength 858 MPa and impact energy 48 J, its static torque (4697 Nm),fatigue life ( ±1600 Nm bidirectional torsion 120 ,000 times, ± 1400 Nm bidirectional torsion 270,000 times) increased by 27% and 93% 〜140% respectively than that of carburized 20CrMnTiH motor shaft, and its performance index and 80,000 km road test results meet motor shaft technical requirements.

The technological process  of C70S6BY  steel  for automobile  engine  connecting rod is  130 t BOF-LF-RH- CCM-Heating-Rolling.   The content   of   S   and   N   in   steel(0.064%～0.068%Sand   136×10 ^-6～142×10 ^-6N) can   be   accurately  controlled  by  using1.5~2.0  low  basicity  CaO-SiO ₂-Al ₂O ₃-MgO  slag  system  in  LF  refine,nitrogen  driving  in  RH and for 5～10 min circulation after pump withdrawal. The microstructure of the steel is pearlite and a small amount of fer- rite by slow cooling in pit after rolling,the non-metallic inclusions in the steel are mainly MnS and composite inclusions.Of 1050℃  30  min  air  coling   steel,the  tensile   strength  is 995~1018  MPa,the  yield   strength  is   586~611  MPa,the  elongation   is   11.5%～13.0%,the   reduction   of  area   is   22%~24%,and   the   HB  brinell   hardness   number   is   285~301. All   indexes meet the requirements of breaking connecting rod.

The application status and processing technology of cold extrusion forming steel for steering tie rod at home and abroad are described. The main technical indicators and the performance of the corresponding parts of ordinary quenched and tempered steel, pre-quenched and tempered steel and non-quenched and tempered cold heading steel for steering tie rod are introduced. Production practice shows that compared with ordinary quenched and tempered steel ML40Cr and pre-quenched and tempered steel ESW90, the strength and plasticity of automobile steering tie rods produced by non-quenched and tempered cold heading steel 30MnVS6 can reach the same level, but the impact toughness is significantly lower. The research progress of improving the strength and toughness of non-quenched and tempered cold heading steel is discussed from the four aspects of chemical composition, microstructure, non-metallic inclusion and segregation. By normalizing treatment, the impact energy KV2 of steel 30MnVS6 increases from hot-rolled status 62 ~67 J to 108 ~ 115 J.

10 heats of non-quenched-tempered steel 49MnVS3 (/% : 0.46 ~ 0.48C, 0,30 ~ 0.40Si, 0.88〜0.92Mn, 0.001~0. 014P, 0.004 ~ 0.005S, 0.09~ 0.10V, 0.19 ~ 0.22Cr) are produced by 100 t EBT DC EAF-LF- VD-260 mm x 340 mm bloom casting-Φ140 〜150 mm round bar rolling process flowsheet. With using the process measures including charging 75% hot metal, in EAF earlier period dephosphorizing to ≤0.015%P, before tapping controlling 0.20% ~0. 30% [C] , in refining adding 150 ~200 kg silicon carbide, controlling LF refining slag basicity 2. 80 ~2. 95 and ( CaO)/( Al ₂O ₃) = 1.2 ~ 1. 6, after VD feeding 1. 5 m/t calcium-iron wire and soft argon blowing for ≥15 min, the [N] , [H] and [O] of steel 49MnVS3 are respectively 130 x 10 ^-6 - 220 x 10 ^-6, 1.2 x 10 ^-6 - 1.5 x 10 ^-6 and 5 x 10 ^-6 ~ 11 x 10 ^-6 , finished products grain size is N5 rating, nonmetallic inclusions and macrostructure are all ≤ 1. 5 rating, the structure (banded orientation ≤1 rating) and the mechanical properties (R _m 803 ~883 MPa, R _el 517 〜590 MPa, A 16% ~21%, A _ku39~59J) all meet the requirement of standard.

The production flowsheet for non-quenched and tempered steel F45MnVS is 50 t UHP EAF-LF-VD-260 mm x300 mm and 180 mm x 220 mm billet casting-rolling to Φ20-Φ160 mm products. According to analysis on micro structure of steel, the hot heading crack is caused by block and lamella MnS and attached with Al ₂O ₃ -MnO-FeO compound oxide. With using the process measures including controlling Al content in steel 0.010%-0.030% , EAF end [C]≥0.20% and end [P]≤0.025% ,[Mn]/[S]＞20, LF refining slag basicity ≥3.0, after VD soft argon blowing for ≥ 12 min, ensuring homogeneous distribution of sulfur in steel, superheating extent of liquid in tundish 20-30 °C, controlling casting speed to prevent MnS segregation, and controlling finishing rolling temperature 850-1000 °C and cooling rate after rolling 2-4℃/s, the main inclusions in steel is long lath MnS, the hot heading test is all qualified without crack and other defects.

The tested non-quenched-tenipered steel 48MnVS (/% ： 0.48C, 0.60Si, 1.50Mn, 0.35Cr, 0.14V, 0.05S, 0.020Al, 0.0150N) is melted by an 100t EAF, cast to 280 min x 360 mm bloom and rolled to Φ100 mm bar products. The recrystallization precess of austenite in vanadium microalloying non-quenched-tempered steel 48MnVS singlepass compressed with defonnation 60% and deformation rale 0.1-10 s ^-1 temperature at 950-1150℃ is studied by using a Gleeble-3800 thermal simulation tests machine lo gel true stress-true strain curves, and the dynamic recrystallization grain size model and the dynamic recrystallization slate diagram in tested sleel are obtained by calculation. Results show that with higher deformation temperature ant lower deformation rate, the stored energy of deformation for occurring dynamic recrystallization is lower therefore dynamic recrystallization of vtuiadium microalloying non-quenched-tempered steel 48MnVS occurs more easily. The activation energy Q _d for dynamic recrystallization of tested steel 48MnVS is 343.202 kJ/mol.

The production flowsheet of Φ35 mm bar of non-quenching-tempering steel C70S6 (/% ： 0.72C, 0.20Si, 0.58Mn, 0.015P，0.065S，0.12Cr，0.05Ni， 0.035V， 0.008Al) is 60 t UHP EAF-LF-VD-240 mm x240 mm bloom casting-rolling process. The analysis on structure, fracture and shearing technology of cracking bar during shearing process is carried out. It is obtained that the structure and hardness of cracking bar are no-obvious different to the non-cracking bar during shearing, and during shearing process by shearing stress action the shift of bar along horizontal plane occurs led to increasing the interval between flat cutter and round cutter, the deformation of bar shearing plane curving and deforming, finally causing crack at end of bar. With the measures including decreasing the interval between cutters from 0.5 mm to 0.3 mm, increasing clamping force from 3 t to 3.5 t and carried out spraying water on steel bar to enlarge coefficient of wear as installing cutters, the results of cutting 30 t steel C70S6 Φ35 mm bar products show that the rate of cutting cracking decreases to 0 from original 10% .