Microstructure,Properties and Crack Suppression Mechanism of High-speed Steel Fabricated by Selective Laser Melting at Different Process Parameters

To enrich material types applied to additive manufacturing and enlarge application scope of additive manufacturing in conformal cooling tools,M2 high-speed steel specimens were fabricated by selective laser melting(SLM).Effects of SLM parameters on the microstructure and mechanical properties of M2 high-speed steel were investigated.The results showed that substrate temperature and energy density had significant influence on the densification process of materials and defects control.Models to evaluate the effect of substrate temperature and energy density on hardness were studied.The optimized process parameters,laser power,scan speed,scan distance,and substrate temperature,for fabricated M2 are 220 W,960 mm/s,0.06 mm,and 200℃,respectively.Based on this,the hardness and tensile strength reached 60 HRC and 1000 MPa,respectively.Interlaminar crack formation and suppression mechanism and the relationship between temperature gradient and thermal stress were illustrated.The inhibition effect of substrate temperature on the cracks generated by residual stresses was also explained.AM showed great application potential in the field of special conformal cooling cutting tool preparation.

Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Cast High-Speed Steel Rolls

The influence of rare earth （RE） elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry （DSC） and scanning electron microscopy energy dispersive spectrometry （SEM-EDS）. The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing longpole M C carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.

The Effect of Intensity Pulsed Ion Beam Irradiation on Wear Resistance of High-speed Steel

The structural and phase transformations occurring in the near-surface layers of pre-quenched W6Mo5Cr4V2 high-speed steel (HSS) subjected to intensity pulsed ion beam (IPIB) melting have been investigated. The effect of IPIB irradiation on wear resistance of the HSS has also been studied. The IPIB consists mainly of Cn+(30%)^0 H+(70%), with a high beam current density of 80A/cm2, acceleration voltage of 250kV, pulse duration of 70 ns. Samples were bombarded with 1, 3, 5 pulses respectively. It has been revealed that after IPIB irradiation the initial martensite in the near-surface layer of HSS changed into austenite and produced residual stresses by using electron microscopy and X-ray diffraction. Redistribution and interlace of dislocations in the irradiated samples were generated under the impact of shock wave. With increasing pulse times gradual liquid-phase dissolution of M6C carbide particles occurs in the near-surface layer and produces nanocrystalline MC. This process results in the decrease of martensite crystal (a-phase) and increase of austenite (y-phase) content and the dispersed carbide. Wear resistance of the HSS is improved by a factor of 2, which is explained by the formation of metastable phases such nanocrystal and residual stresses and the redistribution and interlace of dislocations.

Precipitation and decomposition behaviors of carbides in AISI M2 high-speed steel with nitrogen and mischmetal

The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experimental steel consists of dendrites of iron matrix, networks of eutectic carbides and secondary carbides. The average distance between networks is about 34 μm. The carbides mainly include M_2C, M(C,N) and M_6C, and their relative contents are 58.5%, 30.3% and 11.2%, respectively. The average spacing between the M_2C fibers is 1.5 μm. The decomposition of M_2C occurs from 897.2 to 1221.5 ℃(heating rate of 200 ℃/h). Some precipitated carbide particles occur in the M_2C matrix after holding for 15 min at 1100 ℃. With increasing holding time, the carbide fibers neck down more and more obviously until they are broken down. The spectral peaks of M_2C almost disappear after holding for 60 min. The spectral peaks of M_6C gradually strengthen with the holding time, and the relative content of M_6C increases to 79.8% after holding for 60 min. After holding for 180 min, the carbide fibers disappear, and the decomposition products consist of fine carbide particles(about 300 nm) and short rod-like carbides(about 3.5 μm).

Effect of melting rate on microsegregation and primary MC carbides in M2 high-speed steel during electroslag remelting

Large-size primary MC carbides can significantly reduce the performance of M2 high-speed steel.To better control the morphology and size of primary MC carbides,the effect of melting rate on microsegregation and primary MC carbides of M2 steel during electroslag remelting was investigated.When the melting rate is decreased from 2 kg·min^(-1) to 0.8 kg·min^(-1),the columnar dendrites are gradually coarsened,and the extent of segregation of Mo and V is alleviated,while the segregation of Cr becomes severe.At 2 kg·min^(-1),the number of primary MC carbides per unit area with the sizes in the range of 2 μm to 6 μm accounts for about 75% of all MC carbides,while the carbides are mainly concentrated on the size larger than 8 μm at 0.8 kg·min^(-1).Thermodynamic calculations based on the Clyne-Kurz (simplified to C-K) model shows that MC carbide can be precipitated in the final solidification stage and a smaller secondary dendrite arm spacing caused by higher melting rate (2 kg·min^(-1) in this experiment) facilitates the refinement of primary MC carbides.

PREDICTION OF FLOW STRESS OF HIGH-SPEED STEEL DURING HOT DEFORMATION BY USING BP ARTIFICIAL NEURAL NETWORK

The hot deformation behavior of TI (18W-4Cr-1V) high-speed steel was investigated by means of continuous compression tests performed on Gleeble 1500 thermomechan- ical simulator in a wide range of tempemtures (950℃-1150℃) with strain rotes of 0.001s-1-10s-1 and true strains of 0-0. 7. The flow stress at the above hot defor- mation conditions is predicted by using BP artificial neural network. The architecture of network includes there are three input parameters:strain rate,temperature T and true strain , and just one output parameter, the flow stress ,2 hidden layers are adopted, the first hidden layer includes 9 neurons and second 10 negroes. It has been verified that BP artificial neural network with 3-9-10-1 architecture can predict flow stress of high-speed steel during hot deformation very well. Compared with the prediction method of flow stress by using Zaped-Holloman parumeter and hyperbolic sine stress function, the prediction method by using BP artificial neurul network has higher efficiency and accuracy.

Microstructure simulation of rapidly solidified ASP30 high-speed steel particles by gas atomization

In this study, the microstructure evolution of rapidly solidified ASP30 high-speed steel particles was predicted using a simulation method based on the cellular automaton-finite element （CAFE） model. The dendritic growth kinetics, in view of the characteristics of ASP30 steel, were calculated and combined with macro heat transfer calculations by user-defined functions （UDFs） to simulate the microstructure of gas-atomized particles. The relationship among particle diameter, undercooling, and the convection heat transfer coefficient was also inves- tigated to provide cooling conditions for simulations. The simulated results indicated that a columnar grain microstructure was observed in small particles, whereas an equiaxed microstructure was observed in large particles. In addition, the morphologies and microstructures of gas-atomized ASP30 steel particles were also investigated experimentally using scanning electron microscopy （SEM）. The experimental re- suits showed that four major types ofmicrostructures were formed： dendritic, equiaxed, mixed, and multi-droplet microstructures. The simu- lated results and the available experimental data are in good agreement.

Installation position determination of wind speed sensors on steel pole along a high-speed railway

In order to consider the influence of steel pole on the measurement of wind speed sensors and determinate the installation position of wind speed sensors, the flow field around wind speed sensors was investigated. Based on the three-dimensional steady Reynolds-averaged Navier-Stokes equations and k-ε double equations turbulent model, the field flow around the wind speed sensor and the steel pole along a high-speed railway was simulated on an unstructured grid. The grid-independent validation was conducted and the accuracy of the present numerical simulation method was validated by experiments and simulations carried out by previous researchers. Results show that the steel pole has a significant influence on the measurement results of wind speed sensors. As the distance between two wind speed sensors is varied from 0.3 to 1.0 m, the impact angles are less than ±20°, it is proposed that the distance between two wind speed sensors is 0.8 m at least, and the interval between wind speed sensors and the steel pole is more than 1.0 m with the sensors located on the upstream side.

Microstructure and cutting performance of CrTiAlN coating for high-speed dry milling

Using a closed field unbalanced magnetron sputtering system,the cemented carbide end mills were coated with a CrTiAlN hard coating,which consisted of a Cr adhesive layer,a CrN interlayer and a CrTiAlN top layer.The microstructure and mechanical properties of the coating were investigated by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,micro indentation and scratch test.The cutting performance of the coated end mills were conducted by high-speed dry milling hardened steel（P20,HRC 45）.The results indicates that the coating is composed of（Cr,Ti,Al）N columnar grains with nanolayers.The coating exhibits good adhesion to cemented carbide substrate and high microhardness of around 30 GPa.The coated end mills show significant improvement on tool life and much lower cutting force as compared to the uncoated ones.And the related mechanisms were discussed.

激光熔覆HSS涂层滚滑动摩擦磨损及热疲劳损伤研究

针对再制造轧辊使用过程中受高压高温作用,轧件易发生复杂的失效行为,文章采用激光熔覆技术在球墨铸铁芯材上制备M4高速钢(high-speed steel,HSS)涂层,利用高温滚滑动摩擦磨损与热疲劳试验机研究HSS涂层的摩擦磨损及热疲劳性能。结果表明:HSS涂层显微组织主要为马氏体、少量残留奥氏体和合金碳化物,涂层维氏硬度为823 HV 0.5,具有良好的耐磨性、耐热性。在滚滑动摩擦磨损形式下,随着表面接触温度的升高,涂层磨损机制发生改变,磨损量逐渐降低。440℃时表现为疲劳磨损和轻微氧化磨损,525℃时表现为氧化磨损和疲劳磨损,580℃时以氧化磨损为主。

Computer simulation on the controlled cooling of 82B high-speed rod

A modified temperature-phase transformation field coupled nonlinear mathematical model was made and used in computer simulation on the controlled cooling of 82B high-speed rods. The surface temperature history and volume fraction of pearlite as well as the phase transformation history were simulated by using the finite element software Marc/Mentat. The simulated results were compared with the actual measurement and the agreement is good which can validate the presented computational models.

Test study on the fatigue performance of HSS for steel wheels

High-strength steel is currently one of the main material choices for creating lightw eight automobiles. To realize lighter wheels that can comply with harsh fatigue requirements,sufficient know ledge of the relevant material fatigue properties is required. Fatigue tests were conducted on Baosteel＇s 600 M Pa level dual-phase steel DP600,which is a typical high-strength hot-rolled steel for steel wheel,and on 550 M Pa level HR60. Whler（ S-N） fatigue curves were obtained for both steels,and the measured stress fatigue limits were 414 and 329 M Pa for the HR60 and the DP600,respectively.

湖中基坑-双排钢管桩围堰受力变形分析

为便于施工,位于水域中的基坑工程通常需要施作围堰来保证施工场地干燥,但目前对围堰变形的研究尚不完善。以南昌艾溪湖隧道工程为研究背景,利用Midas GTS NX有限元软件,研究围堰宽度、拉杆位置对双排钢管桩围堰变形规律的影响,并通过将模拟计算结果与实测数据进行对比,验证了模型的合理性。研究结果表明:围堰宽度有一个合适的范围,过小过大均会造成围堰变形过大。在本工程中,围堰合理宽度范围为3.5~4.5 m,围堰宽度的改变对围堰内基坑开挖变形影响较小;综合两侧钢管桩变形来看,拉杆设置在围堰顶部0.8 m处时两侧钢管桩变形较小。

M2(HSS)热处理工艺的神经网络优化研究

采用3×12×2三层拓扑结构,以退火温度、淬火温度、回火温度作为输入层参数,以抗弯强度和磨损体积为输出层参数,构建了M2高速钢(HSS)热处理工艺的神经网络优化模型。并对模型进行了训练、预测验证与现场应用。结果表明:该神经网络优化模型有高的预测能力和预测精度,输出的抗拉强度和磨损体积的平均预测相对误差分别为1.93%、1.89%。与原结果相比,使用神经网络优化工艺参数热处理的M2高速钢的抗弯强度增加35%、磨损体积减小41%。M2高速钢的最佳退火、淬火和回火温度分别为:(810±10)、(1230±10)、(520±10)℃。

Effect of Fe content on type and distribution of carbides in medium-entropy high-speed steels

The effect of iron content on the type and distribution of carbides in the vacuum arc melted Fex(AlCoCrCuNiV)_(88.05-x)Mo_(5)W_(6)-C_(0.95)(x=69,76,83 wt%,respectively) medium-entropy high-speed steels(ME-HSSs) was studied.The homogeneous distribution of granular MC carbides(M refers to the carbides forming transition metal elements,such as W,Mo and V),both at the grain boundary and in the martensitic matrix,was obtained in the Fe_(76)(AlCoCrCuNiV)_(12.05)Mo_(5)W_(6)-C_(0.95)ME-HSS,after quenching at 1210 ℃ followed by triple tempering at 530 ℃.A maximum hardness of about 841 HV_(0.5) was achieved,even higher than the maximum hardness of the commercially available M_(2)(W_(6)Mo_(5)Cr_(4)V_(2)) HSS,826 HV_(0.5).The medium-entropy effect was shown to be beneficial to transform the solidified primary carbide network into finely dispersed granular MC.However,when the iron content was further reduced to 69 wt%,the enhanced entropy effect promoted the dispersion of carbides but at the same time led to a decrease in the carbide content,so that the maximum hardness(816 HV_(0.5)) was slightly lower than the maximum hardness of M2-HSS.The results provide a novel alloy system together with a simple heat treatment method to obtain hard HSSs,and more importantly to eliminate the primary carbide network which is harmful to the toughness of traditional HSS.

HSS圆锯片锯齿参数自动检测装置及算法研究

将计算机视觉技术应用于HSS锯齿边缘检测中时,无法依靠锯齿边缘来检测锯齿的参数,为此,提出了一种基于图像处理的自动检测装置,以及提高其检测精度的检测算法。首先,对检测装置的硬件结构进行了设计(操作步骤由锯齿拍摄、锯片夹持、锯片旋转、锯片水平检测、锯片水平调整等5部分组成);然后,对检测装置的算法流程进行了设计(由图像预处理、锯齿边缘检测、锯齿参数计算3个步骤组成);针对高速钢锯齿表面灰度值噪点导致的锯齿参数识别误差大的问题,引入了最大类间与类内方差比法,自适应调整灰度最优阀值,准确检测锯齿边缘,进而准确计算了锯齿齿形参数;最后,搭建了锯齿参数测量装置,通过实验的方法,对锯齿参数测量装置的可行性及检测算法的正确性进行了验证。研究结果表明:该检测装置对锯齿齿形参数的检测精度为3%,与三坐标等其他设备的检测结果接近;该装置可作为高速钢圆锯片选型、锯片修磨检测的基础工具。

Scratch behavior of high speed steels for hot rolls

The scratch behaviors of two high speed steels （HSS） for hot rolls were studied by a Micro-combi Tester, and the emphasis was placed on researching the relations between the microstructure and the scratch resistance property of different HSS. The experimental results indicate that during the scratch process, the carbides are embedded into the matrix, the penetration depth of different HSS is closely related with the matrix hardness, i.e., the higher the matrix hardness, the better the scratch resistance property; and in the matrix, the fine, dispersive carbides are beneficial to form steady friction between the indenter and the scratched materials, but the coarser carbides are easier to fall into pieces.

Centrifugal Casting of High Speed Steel/Nodular Cast Iron Compound Roll Collar

The centrifugal casting of compound HSS/nodular cast iron roll collar was studied,and the factors affecting transition zone quality were analyzed.The pouring temperature and interval in pouring are the main factors affecting transition zone quality.By controlling process parameter and flux adding during casting,high quality roll collar was obtained.The cause,why in the casting of HSS part,segregation appears easily,was analyzed and the countermeasure eliminating segregation was put forward,the measure eliminating heat treatment crackling was also put forward.

Effect of Quenching Parameters on Mechanical Property of Ultra High Strength Steel BR1500HS Based on Response Surface Methodology

Hot stamping of high strength steels is defined as a process in which blank is heated to the temperature of the austenite stabilization region for a definite time and then formed and quenched simultaneously in a mold with cooling channels. During this process,the processing parameters of austenite temperature and soaking time have strong effects on the mechanical properties such as quenching hardness,tensile strength and elongation. Hence,it is necessary to investigate the relationship between the mechanical properties and the two processing parameters. In this paper,the orthogonal experiment with two factors and five levels was applied, and the experimental data based on the orthogonal experiment was acquired. Based on the data,regression models were set up and the results of the analysis of variance( ANOVA) showed that it is reliable to predict the quenching hardness,tensile strength and elongation by the regression models. Besides,the optimal results of each single object were obtained based on response surface methodology( RSM),and global optimums was gained by employing ideal point method in which the quenching hardness,and tensile strength and elongation were considered simultaneously.

Effect of Cryogenic and QPQ Compound Treatment on the Microstructures and Performance of High Speed Steel

China’s High-speed steel cutting tools hold a considerable share in the global market. However, the overproduction of low-end HSS tools causes serious resource waste and low efficiency, which has become one of the major problems in the tool industry in China. So a new Surface Modification technology is developed, which can make the low-end HSS tools into the high-end ones. On the analysis of the mechanism of cryogenic and quenching-polish-quenching(QPQ), the cryogenic and QPQ compound treatment are studied by using ?8 HSS(M2) drills. The nitriding layer and the base of the drill bit are Studied and analyzed, and the mechanism of compound treatment is discussed by the technological parameters adjustment and the combination test of cryogenic, nitrogen, tempering procedures, and several analysis methods such as the optics metallographic microscope, the scanning electronic microscope (SEM), X-ray diffraction and micro hardness. The cutting test is done on the drills by cryogenic treatment, QPQ treatment and cryogenic and QPQ compound treatment separately. The results indicates that the cutting life of HSS (M2) drill can be increased dramatically by cryogenic and QPQ compound treatment.