Research on Flange Spread of H-Beamon Universal Mill

The deformation process of H-beams was simulated by explicit dynamic FEM, and the influence of deformation parameters on the spread of rolling piece was obtained. The results show that the flange width, elongation ratio between flange and web and flange thickness are the maior influencing factors on the spread of rolling piece, and the inclination and diameter of vertical roll together with web inner width can also influence to some extent on the spread of rolling piece.

Microstructures and Properties of 550 MPa Grade High Strength Thin-walled H-beam Steel

The microstructures and mechanical properties of 550 MPa grade lightweight high strength thin-walled H-beam steel were experimentally studied. The experimental results show that the microstructure of the air-cooled H-beam steel sample is consisted of ferrite, pearlite and a small amount of granular bainites as well as fine and dispersive V（C,N） precipitates. The microstructure of the water-cooled steel sample is consisted of ferrite and bainite as well as a small amount of fine pearlites. The microstructure of the water-cooled sample is finer than that of the air-cooled sample with the average intercept size of the surface grains reaching to 3.5 gna. The finish rolling temperature of the thin-walled high strength H-beam steel is in the range of 750 ~C-850 ~C. The lower the finish rolling temperature and the faster the cooling rate, the finer the ferrite grains, the volume fraction of bainite is increased through water cooling process. Grain refinement strengthening and precipitation strengthening are used as major strengthening means to develop 550 MPa grade lightweight high strength thin- walled H-beam steel. Vanadium partially soluted in the matrix and contributes to the solution strengthening. The 550 MPa grade high-strength thin-walled H-beam steel could be developed by direct air cooling after hot rolling to fully meet the requirements of the target properties.

棚锚联合抗压支护技术的应用

谢一矿472块段掘进过程中,工作面巷道压力显现非常明显。为此,巷道采取留设小煤柱沿空掘巷,其巷道采用棚锚联合支护方式,克服了原来单一工字钢梯形棚支护的缺点。实践证明,本块段采用棚锚联合支护后,巷道顶板下沉量、两帮移近量及底鼓量都较小,支护效果好,提高了矿压大块段掘进单进水平,确保安全生产。

Effect of Cooling Rate and Deformation on Microstructures and Critical Phase-Transformation Temperature of Boron-Nickel Added HSLA H-Beams

Microstructures and critical phase-transformation temperature of boron-nickel added Nb-treated high strength low alloy （HSLA） H-beams cooled at different cooling rate, with different deformation were investigated. Continuous cooling transformation （CCT） diagram of this new type of steel was obtained by using Gleeble 1500 ther- momechanical simulator. Microstructures and hardness, especially micro-hardness of the experimental steel were in- vestigated by optical microscopy （OM）, scanning electron microscope （SEM）, Rockwell and Vickers hardness tests. Phase analysis was also studied by X^ray diffraction （XRD）. The results indicated that with increase of cooling rate, microstructures of continuous cooled specimens gradually transformed from polygonal ferrite and pearlite, grain boundary ferrite and bainite, bainite and martensite to single martensite. The CCT diagram revealed that slow cool- ing was needed to avoid austenite-bainite transformation to ensure toughness of this steel. By plastic deformation of 40%, austenite-ferrite transformation temperature increased by 46℃, due to deformation induced ferrite transfor- mation during continuous cooling, but Rockwell hardness has little change.

Effect of Controlled Cooling on Microstructure and Mechanical Properties of H-Beam

Based on ANSYS, an analytical model was established for H beam during controlled cooling. The tempera-ture fields during controlled cooling and air cooling were analyzed and the microstructure and mechanical properties for different parts of H-beam were discussed in detail. After the H-beam was controlled cooled for 4.5 s, its mean surface temperature decreased from 850 to 460 ℃, and the lowest and the highest temperatures were measured at edge of flange and at R corner, respectively. Whereas, for the H-beam air cooled for 30 s, the mean temperature at R corner and web was 700 and 540 ℃, respectively. The microstructures for different parts of H-beam consisted of ferrite and pearlite, and the grain size at R corner was coarser than those at flange and web. The difference of yield and tensile strengths of web, flange and R corner was within 30 MPa, and the elongation was similar. The changes of microstructure were in good agreement with that of temperature field. In addition, the results show that the uni formity of microstructure and mechanical properties can be improved by increasing water flow rate at R corner.

Dynamic recrystallization behavior and finite element analysis of a low-alloy high-strength steel

The axial single-pass high temperature compression test of a hot-rolled extra-large heavy H-beam steel continuous casting billet (Q420 steel) under different deformation conditions through the Gleeble-1500D thermomechanical simulator was carried out. The modified Johnson–Cook model and the Arrhenius model based on strain-compensated of Q420 steel were established. The latter can more accurately reflect the flow behavior of Q420 steel. For the simulation of thermal compression, dynamic recrystallization (DRX) correlation models were developed and imported into DEFORM-3D software. According to simulation results, high temperatures and low strain rates are conducive to DRX. Due to the uneven distribution of equivalent strain and temperature in different parts of the same section, DRX volume fraction and grain size are unevenly distributed. At the center, the DRX volume fraction is the largest and the grain size is the smallest. The upper and lower edges are vice versa, and the left and right edges are centered. Optical microscopy and electron backscatter diffraction characterization methods were used to study the hot compression microstructure under different deformation conditions. As the deformation amount increases, complete DRX is gradually reached. The original austenite grain gradually becomes smaller. Local average misorientation decreases with the progression of DRX but increases with the amount of deformation after completion of DRX. As the temperature increases and the rate decreases, low angle grain boundaries and medium angle grain boundaries gradually decrease, and high angle grain boundaries gradually increase, indicating that dislocation decreases gradually, DRX grains increase gradually, and martensitic multilayer structure is obvious. As austenite grain size increases, the length of martensite lath increases, and the number of martensite blocks decreases.