High speed continuous turning of hardened steel with newly developed low content PCBN

In this study,newly developed low content PCBN was used to evaluate the cutting performance in high speed turning of hardened steel.Using new PCBN and commercially available PCBN tipped inserts under the same cutting condition,cutting performance with variable cutting speed,feed rate and depth of cuts on tools were measured by observation of flank and crater wear.Its microstructures were analyzed through SEM microscope,measurement of surface roughness on workpiece was also performed. According to cutting performance results,it is shown that new PCBN shows much longer tool life in high speed continuous turning than our conventional PCBN tools,with improved wear and chipping resistance.This result on the machinability of new PCBN for hardened steel will provide effective guidelines to manufacturing engineers,also provide useful economic machining solution for high speed continuous turning for hardened steel.

Microstructural Transformation and Precipitation of an Ultra-high Strength Steel under Continuous Cooling

We investigated phase transition and precipitation of ultra-high strength steel（UHSS）in a new ＂short process＂ with controlled rolling and controlled cooling.Thermalexpansion test combined with metallographic observation was used to research the continuous cooling transformation（CCT）curve.Moreover,the microstructuraltransformation and precipitation law was revealed by morphologicalobservation and alloying elements by electron probe micro-analyzer（EPMA）.Transmission electron microscopy（TEM）was utilized to analyze the composition and grain orientation of microstructure.The study showed that the measured criticaltransformation temperatures of Ac1 and Ac3 were 746 and 868 ℃,respectively.The CCT curve indicated that the undercooled austenite was transformed into proeutectoid ferrite and bainite with HV 520 in a broad range of cooling rate 0.1^（-1） ℃·s^（-1）.When subjected to a cooling rate of 1 ℃·s^（-1）,the undercooled austenite was divided into small-sized blocks by formed martensite.With further increase of cooling rate,micro-hardness increased dramatically,the microstructure of specimen was mainly lathe bainite（LB）,granular bainite（GB）,lath martensite（LM）and residualaustenite.By diffraction test analysis,it was identified that there was K-S orientation relationship between martensite and austenite for {110}_α//{111}_γ,{111}_α//{101}_γ.EPMA clearly showed that carbon diffused adequately due to staying for a long time at high temperature with a lower cooling rate of 2 ℃·s-1.Phase transition drive force was lower and the residualaustenite existed in the block form of Martensite austenite island（M-A）.With the increase of cooling rate to 10 ℃·s^（-1）,the block residualaustenite reduced,the carbon content of residualaustenite increased and α phase around the residualaustenite formed into a low carbon bainite form.

Effect of continuous annealing temperature on the microstructure and mechanical property of an aluminum killed steel

The continuous annealing process of a typical aluminum killed steel was investigated. A cold rolled sheet was annealed continuously at holding temperature ranging from 580 to 760 ℃. The microstructures were analyzed in detail based on contiuous cooling transformation（ CCT） curves that were simulated with JM artP ro softw are. The results show ed that recrystallization and perlitic transformations caused a diversity of microstructures and mechanical properties. In comparison with annealed steel that was produced from insufficient recrystallization,annealed steel produced from sufficient recrystallization had more isometric grains and exhibited low er strength and higher ductility. Higher annealing temperatures than A_1 provided steel with lamellar pearlite zones,large ferrite grains,low strength,and high ductility. The results are attributed to the property optimization of the steel.

Design and Construction Strategy of Arched Continuous Rigid-frame Bridge

With the current rapid development of urbanization in China,people's living standards have been greatly improved.In the context of such a development background,the requirements for road traffic are getting more stringent,especially for bridge projects.The arched continuous rigid-frame bridge was developed under this social background.The advantage of the bridge lies in the design of a bridge model that integrates various functions such as transportation,landscape,and sightseeing.Based on the above,this paper first refers to the case to analyze the design and construction strategy of the arched continuous rigid-frame bridge,in hope of providing a valuable reference for relevant personnel.

Precipitation and growth of titanium nitride during solidification of clean steel

With the help of solidification kinetics, precipitation and growth of TiNhave been studied theoretically and the effect of cooling rate on the growth of TiN has beendiscussed. Through induction electric furnace experiment and electroslag remelting experiment withdifferent cooling rates, the distribution and particle size of TiN were investigated. It is provedthat the higher cooling rate is, the smaller the final size of TiN is and the more TiN particles canbe found in the steel. That TiN can restrain the growth of columnar crystal and enhance theproportion of equiaxed crystals to refine solidification structure as the heterogeneous nucleationsites of δ-ferrite is confirmed preliminarily. A new method to reduce macrosegregation incontinuous cast steel is provided.

Heat Transfer and Central Segregation of Continuously Cast High Carbon Steel Billet

A numerical model of heat transfer was developed to investigate the heat transfer of continuously cast billet with the aid of surface temperature tests by ThermaCAMTM researcher and nail shooting experiments. The effects of secondary cooling practice and casting speed on the solidification process and central segregation of carbon were investigated as well with the actual central segregation tests. The results show that the surface center and billet center temperatures exhibit a different pattern during solidification, and the solidified shell thickness is presented as an ＂S＂ type. With the increase of secondary cooling intensity and the decrease of casting speed, the end points of the solidus line and the liquidus line move forward, and the central segregation level of carbon decreases. The optimal casting condition is suggested for continuously cast high carbon billet with F-EMS （final electromagnetic stirring）.

Simulation of Mould Level Velocities During Continuous Casting of Round Bloom Strands With Mould-Electromagnetic Stirring

In modern continuous casting of round steel blooms rotating electromagnetic fields are commonly employed to improve the product quality.Mould-electromagnetic stirrers(M-EMS)are used to excite a rotary motion along the solidification front in the liquid core.These velocities lead to a better strand surface quality as well as enhancing the transition from columnar to equiaxed solidification.Although the usage of electromagnetic stirrers is widespread,not all effects are fully known or understood.Due to harsh conditions at the plant,measurements are scarce and limited.Water model experiments-an established alternative for investigating continuous casting of steel-cannot be used due to the low electrical conductivity of water.Experiments with liquid metals like mercury,Galinstan or Wood’s metal are either expensive or difficult to perform.Thus numeric simulations are essential to gain a better understanding of the processes involved in continuous casting with electromagnetic stirring.However numeric simulations should always be validated with experiments and/or measurements.While the velocity field inside the liquid core of the bloom cannot be measured at the caster,the velocity at the mould level can be measured by dipping a nail into it.The skull forming at the tip of the nail is directly linked to the occurring surface velocity.These measurements can then be compared with numeric simulations of the nail dipping process.The numeric model is restricted to the upper part of the strand.The lower part of the strand is also taken into account through adjusted boundary conditions(velocity field etc.taken from a simulation of the whole strand).In this work the influence of the stirring field strength on the simulation results will be investigated.In the future these nail dipping simulations will be validated with plant measurements.This can then to a certain extentvalidate the simulation of the strand with M-EMS too,as it serves as the basis for the nail dipping model.

Continuous bending and straightening technology of Q345c slab based on high-temperature creep deformation

A new continuous bending and straightening casting curve with the aim of full using of high-temperature creep deformation was proposed. The curvature of bending and straightening segment varies as sine law with arc length. The basic arc segment is shortened significantly so that the length of bending and straightening area can be extended and the time of creep behavior can be increased. The distance from so lidifying front in the slab was calculated at 1200 ℃ by finite element method. The maximum strain rate of new casting curve at different locations inside the slab is 6.39 × 10 ^-5 s ^-1 during the bending segment and it tends to be 3.70 × 10 ^-5 s ^-1 in the straightening segment. The minimum creep strain rate is 7.45× 10 ^-5 s ^-1 when the stress is 14 MPa at 1 200 ℃. The strain rate of new casting machine can be less than the mini mum creep strain rate. Thus, there is only creep deformation and no plastic deformation in the bending and straightening process of steel continuous casting. Deformation of slabs depending on creep behavior only comes true. It is helpful for the design of the new casting machine and improvement of old casting machine depending on high temperature creep property.