Research on Heredity of Coarse Ferrite Grains

The changes in austenite grain size of the specimens with coarse ferrite grains under different heat treatment process were investigated.The focus was on studying the effect of annealing on refining coarse ferrite grains,as well as the influence of the ferrite grain size on the main technical indicators of gas carburizing.The results show that coarse ferrite grains may not necessarily cause the coarse austenite grains,but may result in mixed austenite grains.After annealing treatment,the coarse ferrite grains can be significantly refined and homogenized.Moreover,the coarse ferrite grains have no significant effects on hardnessand intergranular oxidationof gas carburizing.

Effects of Ta C on microstructure and mechanical properties of coarse grained WC-9Co cemented carbides

Coarse grained WC-9Co cemented carbides with 0-1.0% TaC(mass fraction) were fabricated by HIP-sintering and gas quenching. The effects of TaC on the microstructures and mechanical properties were investigated using scanning electron microscopy(SEM), energy dispersive X-ray analysis(EDS), X-ray diffractometry(XRD) and mechanical properties tests. The results show that the maximum values of hardness and strength are HV 1124 and 2466 MPa respectively when 0.4% TaC is added. When the content of TaC is more than 0.6%, the grain size of WC is no longer affected by the amount of TaC, and(W,Ta)C occurs as well. Moreover, the strength and fracture toughness increase and the(Ta+W) content decreases with the increase of TaC content. The dependence of(Ta+W) content on the mechanical properties indicates that(Ta+W) content in Co should be decreased as low as possible to improve the mechanical properties of coarse grained WC-TaC-9Co cemented carbides with the microstructure of WC+γ two phase regions.

Precision Grinding of Reaction Bonded Silicon Carbide Using Coarse Grain Size Diamond Wheels

Reaction bonded SiC（RBSiC） is attractive for optical application because of its favorable properties and low fabrication cost. However, the difficultness and cost involved in RBSiC grinding limit its application. The investigation on high efficient and low-cost machining with good grinding quality is desired. Generally, high efficient machining for RBSiC is realized by using coarse grain size grinding wheels, but serious grinding damage is inevitable. In this paper, monolayer nickel electroplated coarse grain size diamond grinding wheels with grain sizes of 46 μm, 91 μm, and 151 μm were applied to the grinding of RBSiC. An electrolytic in-process dressing（ELID） assisted conditioning technique was first developed by using cup shape copper bonded conditioning wheels with grain sizes of 15 μm and 91 μm to generate the conditioned coarse grain size wheels with minimized wheel run-out error within 2 μm, constant wheel peripheral envelop as well as top-flattened diamond grains. Then, the grinding experiments on RBSiC were carried out to investigate the grinding performance and material removal mechanism. The experimental results indicate that the developed conditioning technique is applicable and feasible to condition the coarse grain size diamond wheels under optimal conditioning parameters, and the material removal mechanism involved in RBSiC grinding is the combination of brittle fracture and ductile deformation to generate smooth ground surface. This research is significant for the high efficient and low-cost precision grinding of RBSiC with good ground surface quality.

Effect of titanium content on the refinement of coarse columnar austenite grains during the solidification of peritectic steel

The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs.Transmission electron microscope(TEM)and scanning electron microscope(SEM)were used to analyze the size and distribution of Ti(C,N)precipitates during solidification.Based on these results,the pinning pressure of Ti(C,N)precipitates on the growth of coarse columnar grains(CCGs)was studied.The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains(FCGs).Increasing the content of titanium reduces the region and the short axis of the CCGs.When the content of titanium is 0.09wt%,there is no CCG region.Dispersed microscale particles will firstly form in the liquid,which will decrease the transition temperature from FCGs to CCGs.The chain-like nanoscale Ti(C,N)will precipitate with the decrease of the transition temperature.Furthermore,calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N)precipitates.

Experimental study on permanent deformation characteristics of coarse-grained soil under repeated dynamic loading

Practical assessment of subgrade settlement induced by train operation requires developing suitable models capable of describing permanent deformation characteristics of subgrade filling under repeated dynamic loading.In this paper,repeated load triaxial tests were performed on coarse-grained soil(CGS),and the axial permanent strain of CGS under different confining pressures and dynamic stress amplitudes was analysed.Permanent deformation behaviors of CGS were categorized based on the variation trend of permanent strain rate with accumulated permanent strain and the shakedown theory.A prediction model of permanent deformation considering stress state and number of load cycles was established,and the ranges of parameters for different types of dynamic behaviors were also divided.The results indicated that the variational trend of permanent strain rate with accumulated permanent strain can be used as a basis for classifying dynamic behaviors of CGS.The stress state(confining pressure and dynamic stress amplitude)has significant effects on the permanent strain rate.The accumulative characteristics of permanent deformation of CGS with the number of load cycles can be described by a power function,and the model parameters can reflect the influence of confining pressure and dynamic stress amplitude.The study’s results could help deepen understanding of the permanent deformation characteristics of CGS.

MICROTHREAD BASED (MTB) COARSE GRAINED FAULT TOLERANCE SUPERSCALAR PROCESSOR ARCHITECTURE

Fault tolerance in microprocessor systems has become a popular topic of architecture research. Much work has been done at different levels to accomplish reliability against soft errors, and some fault tolerance architectures have been proposed. But little attention is paid to the thread level superscalar fault tolerance. This letter introduces microthread concept into superscalar processor fault tolerance domain, and puts forward a novel fault tolerance architecture, namely, MicroThread Based (MTB) coarse grained transient fault tolerance superscalar processor architecture, then discusses some detailed implementations.

Comparison of Coarse Graining DEM Models Based on Exact Scaling Laws

The simulation of a large number of particles requires unacceptable computational time that is the most criticalproblem existing in the industrial application of the DEM. Coarse graining is a promising approach to facilitatethe application of DEM to industrial problems. While the current coarse graining framework is often developedin an ad-hoc manner, leading to different formulations and different solution accuracy and efficiency. Therefore,in this paper, existing coarse graining techniques have been carefully analysed by the exact scaling law which canprovide the theory basis for the upscaling method. A proper scaling rule for the size of particles and samples as wellas interaction laws have been proposed. The scaling rule is applied to a series simulations of biaxial compressiontests with different scale factors to investigate the precision of the coarse graining system. The error between theoriginal system and the coarse system shows a growing tendency as the scale factor increases. It can be concludedthat the precision of the coarse graining system is accepted when applying scaling rules based on the exact scalinglaws.

Influence of different microstructural features on impact toughness and crack initiation behavior of coarse grain heat-affected zone in X80 pipeline steel

Coarse grain heat-affected zone samples of X80 pipeline steel under different heat inputs were obtained through thermal welding simulation experiments with Gleeble 3500.Charpy impact tests and a combination of multiscale characterizations were conducted to investigate the influence of various microstructural features on impact toughness and crack initiation behavior.The results prove that, as the heat input increases, the number of M/A components increases, thereby degrading toughness and increasing hardness.Meanwhile, more M/A constituents tend to aggregate on prior austenite grain boundaries(PAGBs),and the overall dimensions of M/A and the width and volume fraction of the lath martensite substructure inside M/A islands would increase as well.These changes make intersections between boundary M/As and PAGBs become one of the preferred sites for crack initiation.In addition, only large-sized grotesque inclusions can act as a direct inducement of crack initiation.

Coarse-Grained Molecular Dynamics Study based on TorchMD

The coarse grained(CG)model implements the molecular dynamics simulation by simplifying atom properties and interaction between them.Despite losing certain detailed information,the CG model is still the first-thought option to study the large molecule in long time scale with less computing resource.The deep learning model mainly mimics the human studying process to handle the network input as the image to achieve a good classification and regression result.In this work,the TorchMD,a MD framework combining the CG model and deep learning model,is applied to study the protein folding process.In 3D collective variable(CV)space,the modified find density peaks algorithm is applied to cluster the conformations from the TorchMD CG simulation.The center conformation in different states is searched.And the boundary conformations between clusters are assigned.The string algorithm is applied to study the path between two states,which are compared with the end conformations from all atoms simulations.The result shows that the main phenomenon of protein folding with TorchMD CG model is the same as the all-atom simulations,but with a less simulating time scale.The workflow in this work provides another option to study the protein folding and other relative processes with the deep learning CG model.

Comprehensive tests on rising height of capillary water for coarse grained soil

According to the comprehensive tests on the rising height of capillary water for seven kinds of differ- ent coarse grained soil by use of the method of standpipe, the relationship between the rising height of capillary water and time was obtained, and the influencing factors and rules were analyzed. The data of the steady rising height of capillary water were obtained, and the regression equation of coarse grained soil on steady height and physical indexes （effective grain dl0 and porosity n） was found. Compared with Hazen＇s and other expressions that could estimate the steady height of capillary water of coarse grained soil, the proposed method is satisfactory and the defects of the latter were pointed out.

Influence of the secondary welding thermal cycle on the microstructure and property of coarse grain heat-affected zone in an X100 pipeline steel

The influence of the secondary thermal cycle on the microstructure of coarse grain heat-affected zone in an XIO0 pipeline steel was investigated by means of a thermal simulation technique and microscopic analysis method. The property of coarse grain heat-affected zone was characterized by Charpy V-Notch impact properties testing. The results indicated that the experimental steel exhibited local brittleness of intercritically reheated coarse-grained heat-affected zone when the peak tempera- ture of secondary thermal cycle was in the range of two phases region （ ~ and 3/）. There were two main reasons for the local brittleness. The first was that the microstructures of intercritically reheated coarse-grained heat-affected zone were not fined although partial grain recrystallization occurred. The second was that M-A islands, which had the higher content, larger size and higher hardness, existed in intercritically reheated coarse-grained heat-affected zone.

Residual stress measurement of coarse-grain aluminum alloy using X-ray diffraction method

When measuring residual stress of coarse-grain aluminum alloy using X-ray diffraction method, the diffraction profile shows two peaks and position of measured 20 will be changed, which lead to an inaccurate measurement result. Hence, in this paper, some methods were employed to improve the measurement accuracy. During the measuring process, different parameters （diameter of irradiated area, Ψ-oscillation range and exposure time） were selected and profile peak shift method was utilized. Moreover, when the 20 of profiles was determined, different calculation methods were used to calculate the residual stress. The results show that diameter of irradiated area and Ψ-oscillation range have significant influence on the measuring result. For stress value calculated directly from the test equipment, cross correlation method is more accurate than the absolute peak. Furthermore, another two calculation methods of slope with 2θ- sin^2Ψ and ε- sin^2Ψwere used to calculate the stress based on parameters （2θ, ε） obtained from cross correlation method. It is concluded that 2θ - sin^2Ψ method can further improve the measurement accuracy.

EFFECT OF LOCAL HARD ZONE ONFRACTURE INITIATION OF WELD HAZ

The effect of the local hard zone (LHZ) distributed in the coarse grained HAZ (CGHAZ) has been analyzed by 2-dimensional FEM on a mechanical model of the weld CGHAZ. The existence of the LHZ elevates considerably the stress in LHZ and causes the discontinuity of strain at the boundary between the LHZ and the matrix. The stress distribution in the LHZ is strongly affected by the shape of the LHZ. In a slender LHZ almost the whole region in the LHZ is exposed to elevated stress, whereas in the massive LHZ only the edge region sustains high stress. The longer the LHZ becomes, the more the highly stressed area, and the peak stress in the LHZ grows even under the same volume fraction of the LHZ. These results indicate that the slender LHZ brings about unstable fracture at a lower load level than the blocky LHZ. This tendency was confirmed by CTOD test results on the weld CGHAZ of a high-strength steel. The CGHAZ with elongated M-A constituents fractures at apparently lower critical CTOD than the CGHAZ with massive M-A constituents. In conclusion, the control of the shape of the M-A constituent has a striking effect on the toughness improvement of CGHAZ.

A study on welded joint toughness of X-60 steel

Charpy impact test and COD test were performed on the specimens subjected to simulated welded thermal cycle and the specimens taken from welded joint. The optical microscope, TEM, SEM, EDAX and XRD analysis have been used to investigate the behaviors of second phase particles and the effects of microstructure on toughness separately. The results are as follows. The dispersed second phase particles can effectively retard the growth of austenite grain in the coarse grained HAZ (CGHAZ), and improve the toughness. When t 8/5 is different, the behaviors of the particles are also different in dissolving, coarsening and re precipitating. The ability of retarding the growth of austenite grain will be affected. When t 8/5 increases from 10 s to 70 s , the microstructure of CGHAZ will transform from upper bainite and granular bainite to granular bainite, and the size of austenite grain will grow a little, thus the toughness of the materials decreases slightly.

Effect of Heat Input on Microstructure and Toughness of Coarse Grain Heat Affected Zone in Nb Microalloyed HSLA Steels

The influence of Nb on microstructure, mechanical property and the transformation kinetics of the coarse grain heat affected zone （CGHAZ） in HSLA steels for different heat inputs, has been investigated. When welded at higher heat inputs （100-60 kJ/cm）, impact toughness values of the steel without Nb are much higher than those of the steel with Nb, and the lowest span is 153 J at 60 kJ/cm. But only a little higher values are observed at lower heat inputs （40-30 kJ/cm）, and the highest span is 68 J at 30 kJ/cm. Dilatation studies indicate that continuous cooling transformation starting temperatures （Ts） of CGHAZ for the steel with Nb are approximately 15-30℃ which are lower than those of the steel without Nb at all heat inputs. For higher heat inputs, Nb in solid solution suppresses ferrite transformation and promotes the formation of granular bainite which has detrimental effect on impact toughness. For lower heat inputs higher Charpy impact energy values in the steel with Nb are associated with the formation of low carbon self-tempered martensite.

Incipient motion of non-uniform coarse grain of bedload considering the impact of two-way exposure

The incipient motion of bedload is due to the interaction between the flow and sediment.It is stochastically correlated with the flow structure,the sediment gradation and the arrangement of grains on the bed surface.The random position of the sediment on bed can be represented by a hiding factor or an exposure degree.Based on the numerical simulation of the disturbed flow in the interstice of grains,the influence of the two-way exposure degree(the vertical exposure degree and the longitudinal exposure degree) on the coarse grain incipient motion was investigated in this work.Results show that the exposure degree varies with the position of the sediment on the bed,which influences the flow structure around the particle and the incipient motion.In this paper,the major research achievements on this phenomenon include:Firstly,a mathematical model is established for the rolling-pattern incipient motion of the coarse grain under a critical state of moment balance.The influence of the partial disturbed flow is considered.Secondly,the two-way relative-exposure-degree probability distribution functions are developed to reflect the influence of the disturbed flow and the random arrangement of sediments.Thirdly,a formula to calculate the incipient velocity is presented based on the above results,which considers the impact of the two-way exposure degree of sediment particles.

Formation mechanism and evolution of surface coarse grains on a ZK60 Mg profile extruded by a porthole die

Porthole die extrusion of Mg alloys was studied by means of experimental and numerical studies. Results indicated that an inhomogeneous microstructure formed on the cross-section of the extruded profile. On the profile surface, abnormal coarse grains with an orientation of <11-20> in parallel to ED(extrusion direction) appeared. In the profile center, the welding zone was composed of fine grains with an average size of 4.19 um and an orientation of <10-10> in parallel to ED, while the matrix zone exhibited a bimodal grain structure. Disk-like, near-spherical and rod-like precipitates were observed, and the number density of those features was lower on the profile surface than that in the profile center. Then, the formation and evolution of coarse grains on the profile surface were investigated, which were found to depend on the competition between static recrystallization and grain growth. The stored deformation energy was the factor dominating the surface structure through effective regulation over nucleation of the precipitates and recrystallization. A profile with a low stored deformation energy suppressed formation of precipitates and consequently facilitated grain growth rather than recrystallization, resulting in the formation of abnormal coarse grains. Finally, the surface coarse grains contributed detrimentally to hardness, tensile properties, and wear performance of the bulk structure.

Effects of process parameters on fragment and refinement of millimeter- grade coarse grains for 316LN steel during hot cogging

The heterogeneous mixed-grain microstructure is a common defect for the heavy forging of 316LN austenitie stainless steel. Isothermal compression experiments were performed on a Gleeble-3500 thermo-mechanical simulator to investigate the effect of process parameters on the fragment and re- finement of millimeter-grade coarse grains （MCGs） during hot cogging. The experimental results in- dicate that the stress of MCG specimens is much larger than that of fine grain （FG） ones at 1150 ℃, while the stress difference between MCG and FG samples became smaller at 1200 ℃. Moreover, the MCGs can be well fragmented and refined under the condition of temperature of 1200 ℃, strain rate of 0.01 s-1 , and reduction rate of 50%. Meanwhile, numerical simulations were conducted to study the influences of temperature, strain and strain rate on microstructure evolution. The results of ex- periments and simulations comprehensively demonstrate that the MCG results in the increase of de- formation resistance and incompatibility of deformation, and it can be fragmented and refined at 1200 ℃ so that the plastic deformation energy decreases remarkably with the increase of temperature from 1 150 to 1200 ℃.

Effect of granite gravel content on improved granular mixtures as railway subgrade fillings

The improved granular mixtures are widely used as the fillings of railway 8ubgrade, and in order to investigate the effect of coarse grain content on granular mixtures, a series of field tests were conducted. The experimental results indicate that the permeability coefficient increases significantly with the increment of granite gravel content, especially in the range of 60%-70%. Thcrc exists a coarse grain content limit defined as 53%-58.5% to reform the permeable granular skeleton. Beyond this limit, the permeable granular skeleton is efficiently formed, and the macro pores between the separate gravels are partially filled, which is the explanation lbr the permeability increase. The investigations indicate the subgrade resistance modulus （ks0, Ev2, and Evd） depends on the granite gravel content, and the resistance modulus increases significantly beyond granite gravel content of 50%. The skeletons of granitc gravel clayey sand mixture change in the long-term deformation objected to the train-induced dynamic load, which involves three main repeated and circular deformation stages. Generally, the long-time deformation is explained as the gravel crushing and filling the internal porous space with crushed gravel fragments. Through these investigations, the C40-G60 or C30-G70 is recommended as an optimum soil mixture for the good permeability and high resistance modulus.

Effects of arc-excited ultrasonic on microstructures and properties of weld

To control the solidification process of metal, a new method, arc ultrasonic, was developed. A high frequency exciting supply was electromagnetically coupled with conventional welding supply. An arc excited ultrasonic emission was induced successfully in arc combustion process. Some signals with different frequencies and currents were used in submerged arc welding and CO 2 gas shielded arc welding. The effects of arc ultrasonic on the structures and properties of the weld (including the fusion zone, coarse grain zone and heat affected zone) were studied. The results show that more acicular ferrites form in the fusion zone, the toughness is improved under the arc ultrasonic of different frequency, and the coarse microstructures in the partially melted zone is refined. [