BEHAVIOUR OF BUFFER LAYER IN JOINING OF SIALON CERAMICS TO STEEL 40Cr

The buffer layer material itself may be influential to the bond strength between active brazing filler and ceramics.For Ag_(57)Cu_(38)Ti_5 filler metal,Cu or Ta is excellent buffer layer material, but Kovar or Ni-15Cr-15Co is worse.It was important to design a layer of soft buffer,such as Cu,to relax interfacial stress rather than hard buffer layer,such as Mo,to avoid stress. There is an optimum thickness range of soft buffer layer,saying h/L=0.02—0.1. It was a good solution to the interfacial stress problem to use soft/hard buffer layer to increase metal/ceramics joint strength.Finally,an idea of designing gradual materials as buffer layer between metal and ceramics was suggested.

40Cr钢棒材剪切开裂原因

某公司生产的40Cr钢棒材在冷剪切下料过程中发生开裂。采用宏观观察、化学成分分析、扫描电镜分析、金相检验等方法分析了该棒材开裂的原因。结果表明:棒材表面局部存在加工硬化层,导致棒材发生了剪切开裂;加工硬化层的产生原因是棒材在精整过程中,矫直及砂轮扒皮工艺不当。

40Cr圆钢热顶锻开裂原因

某40Cr圆钢热顶锻发生开裂现象,采用宏观观察、化学成分分析、扫描电镜分析、金相检验等方法对材料开裂原因进行分析。结果表明:40Cr圆钢裂纹缺陷处显微组织正常,组织中的非金属夹杂物成分含量符合产品标准要求;顶锻母材上的缺陷是由圆钢在轧制过程中出现的表面划伤导致的。最后提出了改进方法,以避免该类问题再次发生。

CONSTITUTE EQUATIONS OF 40Cr STEEL UNDER SUPERPLASTIC COMPRESSIVE DEFORMATION

The microstructure of 40Cr steel sample and its surface is ultra-fined through salt-bath cyclic quenching and high frequency hardening, then the superplasticity is studied under isothermal superplastic compressive deformation condition. The experimental results indicate that the stress-strain curves are shown to take place obvious superplastic flow characteristic at the temperature of 750-770℃ and at the initial strain rate of (1.7-5.0)×10-4 s-1. Its strain rate sensitivity is 0.30-0.38, the steady superplastic flow stress is 60-70MPa, the superplastic flow activation energy is 198-217kJ/mol, and it is close to α-Fe grain boundary self-diffusion activation energy. The super-plastic compressive constitute equations of this steel are correspondingly set up. Due to the finer microstructure of high frequency hardening, it appears bigger strain rate sensitivity value, smaller the steady superplastic flow stress and the superplastic flow activation energy, so it has better superplastic deformation capability.

40Cr钢热变形行为及热加工图

为研究40Cr钢的热变形行为和热加工性能,在Gleeble1500型热模拟试验机上对40Cr钢进行了不同参数下的等温热压缩试验,建立了包含再结晶特征的40Cr钢高温流变应力模型,并绘制了其热加工图。结果表明,所建立的流动应力模型能够很好地预测40Cr钢不同热变形条件下的应力-应变曲线。观察了不同变形条件下热压缩试样的微观组织,发现失稳区域为不完全动态再结晶的“项链”组织,非失稳区域中耗散值较小区域和较大区域分别为平均晶粒尺寸为128.2和20.4μm的动态再结晶组织,验证了热加工图的可靠性。结合微观组织观察和热加工图分析,可以确定40Cr钢的最佳热加工区域为温度1050~1150℃、应变速率1~10 s^(-1)。

Influence of load on sliding tribology of C/C composite with 40Cr steel couple coated by Cr

With the 40Cr steel couple coated by Cr, the sliding tribology behavior of two kinds of C/C composites with different matrix was tested using a M2000 wear tester. The results show that with the increasing of load, the friction coefficients of the composite with resin carbon matrix(RC) decrease quickly from 0.156 under 60 N to 0.123 under 150 N, while those of the composite with rough lamination/smooth lamination /resin carbon (RL/SL/RC) change only between 0.122 and 0.101. The wear volume loss of the two composites increases except for under 100 N. The SEM morphology shows that with the increasing of load, the worn surface of the composite with RC becomes more and more integrated while the size of the debris becomes less and less. The Raman spectrum shows that the graphitization on the worn surface of the fibers draws down after 100 N, the graphitization of the boundary between the fiber and the matrix carbon rises up to 150 N, but the graphitization of the matrix carbon draws down all the while. With the increasing of load, the graphitization on the worn surface of all the worn areas becomes closer and closer, which indicates the worn surface of the different component has the similar friction ability. The composites with RL/SL/RC have better tribological characteristic than the composite with RC.

Vacuum brazing of TiAl to 40Cr steel with Ti-Zr-Cu-Ni-Sn amorphous foils

Vacuum brazing of TiAl alloy to 40Cr steel was carried out in a vacuum furnace using Ti40 Zr10 CU34. 95 Ni11. 2Sn3.85 , Ti51Zr8.7 Cu24. 5 Ni11.8 Sn4 and pure copper foils, and the mierostructure and microhardness of the resultant joints were investigated. The experimental results reveal that FeTi compounds formed in the brazing seam made with pure copper foil. However, the FeTi compounds were not detected when using Ti-Zr-Cu-Ni-Sn foils and the brazing seams were composed of two layers, one layer mixed Ti（ Ni, Cu）Al and Ti-Al compounds, and the other mixed the filler metal matrix with Ti-Sn and Ti （Ni, Cu ） compounds. The microhardness test results show that the brazing seams have higher microhardness values than the TiAl alloy and 40Cr steel base metals. Moreover, the microhardness in the brazing seam. made with Ti51 Zr8 7 Cu24 5N i11.8Sn4 is higher than those made with Ti 40 Zr , o Cu34. 95 Ni l12 Sn3 a5 and pure copper.

FEM simulation on residual stress distribution during diffusion bonding between Ti （ C, N） metallic ceramic/interlayer/40Cr steel

Based on ANSYS FEM software, the distribution of residual stress in the diffusion bonding joints between Ti（ C,N） metallic ceramic/interlayer/4OCr steel was calculated and experimentally ver^ed. The results showed that the trend on the distribution of residual stress field in the joints was not changed with the use of interlayer. The maximum residual stress was always located in metallic ceramic with area ranging from 1 mm to 4 mm to the interlayer. The maximum residual stress in the joints was also affected by diffusion temperature. The satellite pulse current during the initial stage on diffusion bonding can promote the formation of liquid film at the interface, by which diffusion temperature and loading pressure can be greatly decreased. The crack initiation was easily produced at the corner of Ti （ C, N） metallic ceramic close to the interlayer. If a higher residual stress produced in the joints, the crack was propagated into the whole ceramic.

Effect of Extrusion Temperatures on Friction-wear Behavior of Chain-wheel Fabricated by 40Cr Steel under Oil-lubrication Condition

A 40Cr steel was formed into a chain-wheel using a warm extrusion technology. The surface roughness and micro-structure, micro-hardness and phases of the extruded samples at different temperatures were analyzed using a three-dimensional optical microscope (OM), micro-hardness tester, and X-ray diffraction (XRD), respectively. The morphologies, chemical element distributions and phases of worn tracks at the extrusion temperatures of 550, 650 and 750 °C were analyzed using a scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), and XRD, respectively. The friction-wear behaviors of extruded samples under oil-lubrication condition were observed using a wear test. And the effects of extrusion temperatures on the wear mechanism were discussed. The results show that residual austenite and pearlite exist on the sample at the extrusion temperature of 550 °C with the corresponding grain size and surface micro-hardness of 32.7 nm and 370.33 HV, respectively. The average coefficient of friction (COF) of extruded sample at the temperature of 550 °C is 0.196 5, and the wear mechanism is fatigue and abrasive wear. While the acicular martensite exists on the extruded samples at the extrusion temperatures of 650 and 750 °C, the corresponding grain sizes are 30.0 and 29.1 nm, respectively. The average COF (coefficient of friction) of extruded sample at the temperatures of 650 and 750 °C are 0.187 4 and 0.163 6, respectively, and the wear mechanism is abrasive wear. As a result, the friction performance of extruded sample at the temperatures of 650 and 750 °C is better than that at the temperature of 550 °C.

SUPERPLASTICITY OF A WATER-QUENCHED AND TEMPERED 40Cr STEEL

The superplastic deformation characteristics, of commercial 40Cr (i.e., 5140) steel that was water-quenched only 1 times and subsequent high-temperature tempered, were investigated. The results showed that the 40Cr steel has a fine grain of 10-15μm at room temperature, and exhibits a tensile elongation of 304%, a true flow stress of 89.3MPa and a strain rate sensitivity m-value of 0.227 at the initial strain rate of 1.0×10-3s-1and at the temperature of 750°C. The final fracture is caused by the development of neck. The experimental result of elongation is in good agreement with the theoretically predicated value according to the analytical expression (where ef, m, f, nv and ε is respectively elongation, average strain rate sensitivity, initial geometric defect, average strain hardening sensitivity at constant deformation velocity and average true strain). The fracture surface is intergraular, and superplastic deformation induces an equiaxed and grown grain. Decreasing strain rate increases tensile elongation and strain rate sensitivity m-value. The primary superplastic deformation mechanism is thought to be atom-diffusion-controlled grain boundary sliding.

Effect of interlayer on the mechanical properties of YG8 hard carbide/40Cr steel brazed joints

The effects of Cu foil and Ni foil on the mechanical properties of YG8 hard carbide/4OCr steel brazed joints were investigated. The results show that both Cu foil and Ni foil were beneficial to decrease the residual stress and enhance the joint strength. Moreover, Ni foil exhibited the better impact on enhancing the joint strength relative to Cu foil. When Cu foil was used as interlayer material, the key factor to restrain the joint strength was the massive and quick dissolution of Cu. Therefore, in order to prevent the excessive dissolution of Cu foil, the process parameter should be controlled strictly in the brazing process.

Low Temperature Superplasticity of 40Cr Steel

The low temperature superplastic characteristics of commercial 40 Cr steel,which was subjected to water quenching three times and subsequent high temperature tempering,were investigated.The results show that the 40 Cr steel has a grain size of 5-10μm,and exhibits an elongation of 254 %,a flow stress of 108.1 MPa,a strain rate sensitivity m-value of 0.221 at the temperature of 650 ℃ and the initial strain rate of 3.16×10-4 s-1.

Vacuum Brazing of TiAl Based Alloy with 40Cr Steel

The vacuum brazing of TiAl based alloy with 40Cr steel was investigated using Ag-Cu-Ti filler metal. The experimental results show that the Ag, Cu, Ti atoms in the filler metal and the base metal inter-diffuse toward each other during brazing and react at the interface to form an inter-metallic AlCu 2Ti compound which joins two parts to produce a brazing joint with higher strength.

Electrochemical techniques for monitoring stress corrosion cracking of Type 40Cr steel in acidified chloride solution

Electrochemical impedance spectroscopy(EIS) and electrochemical noise(EN) techniques were used to detect stress corrosion cracking(SCC) on 40Cr steel specimens exposed to the acidified chloride solution at ambient. To test these two techniques,slow strain rate tensile(SSRT) tests were performed with 40Cr specimen in the identical corrosive solution at room temperature. In impedance measurements,phase shifts in frequency range from 1 to 1 000 Hz show a clear difference between the stressed and non-stressed specimens,suggesting that stress corrosion cracks are detected by the impedance measurements. EN signals in the process of SCC were recorded and then analyzed by standard deviation(STD). On the other hand,the mechanical properties,such as maximum tensile strength(MTS) and fracture strain(FS) measured by the SSRT,decrease significantly when the specimens are exposed to the corrosive solution relative to that in an inert medium. The SSRT results are consistent with fractography of the tested specimens by scanning electron microscopy(SEM). Analysis of the fracture surface clearly shows intergranular attack,suggesting that stress corrosion cracks are formed.

40Cr钢热变形行为研究

利用Gleeble-3500热模拟试验机在变形温度900~1200℃和应变速率0.01~10 s-1范围内,对40Cr钢试样进行压缩实验。研究了40Cr钢真应力-应变曲线特征,建立了峰值应力、应变速率和变形温度间的本构方程,并确定了40Cr钢热变形激活能为310.625 kJ/mol。研究结果显示:40Cr钢热变形时的流变软化机制为动态回复和动态再结晶;随着变形温度增加和应变速率减小,流变应力减小;试样的变形温度越高,应变速率越低,显微组织中的动态再结晶越完全,并且动态再结晶晶粒越容易长大。

40Cr钢油缸断裂原因

采用宏观观察、化学成分分析、金相检验、扫描电镜和能谱分析、显微硬度测试等方法分析了40Cr钢油缸断裂的原因。结果表明:油缸断裂主要与硫元素含量超标、硫化物聚集、表面凹坑缺陷及热处理不均匀有关;硫元素易产生“热脆”,聚集的条状夹杂物破坏了基体的连续性,使油缸产生微裂纹,在表面凹坑处产生应力集中,热处理不均匀使组织产生内应力,萌生的裂纹及表面凹坑在以上因素的作用下不断扩展,最终导致油缸断裂。

40Cr钢承重连接杆开裂原因

在对经调质处理的40Cr钢承重连接杆进行精加工时,发现其外表面发生横向开裂。采用宏观观察、化学成分分析、气体分析、金相检验及硬度测试等方法分析了该连接杆开裂的原因。结果表明:该连接杆开裂的原因是热处理工艺不当,导致组织未被淬透;在零件内槽变形处的加工精度不足,产生了应力集中,导致弧形裂纹延伸至表面。采用调整淬火工艺参数、将冷却介质改为水基淬火液、优化工件车削精度、将过渡区域改为圆角等方法可以提高产品的合格率。

退火和调质处理的40Cr钢的性能研究

对尺寸为Ф15 mm×20 mm的40Cr钢试样分别进行了840℃保温40 min炉冷退火、840℃保温50 min水淬和油淬以及淬火后540℃回火40 min空冷。检测了交货态棒材和热处理后试样的显微组织和硬度。采用JMatPro软件对40Cr钢的奥氏体化、马氏体转变和CCT曲线及淬火和回火过程进行了模拟。结果表明:交货态40Cr钢棒材的表面硬度为61 HRA;840℃退火后试样的硬度为49 HRA,组织为铁素体和珠光体;840℃水淬后试样的硬度为73 HRA,油淬后为71 HRA,组织均为板条马氏体;水淬和油淬随后540℃回火后试样的硬度均为66 HRA,组织主要为回火索氏体。

亚温淬火对40Cr钢渗氮层组织与性能的影响

对40Cr钢分别进行亚温处理(亚温淬火+高温回火)和常规调质预处理,研究不同热处理工艺对40Cr钢的显微组织、渗氮层厚度、表面硬度和硬度分布及渗氮后整体冲击韧性的影响。结果表明,与调质预处理相比,亚温处理后40Cr钢的渗氮层厚度增加,硬度分布更加平缓。亚温处理试样渗氮后的冲击功是调质预处理试样的2.37倍以上,表明亚温处理作为渗氮预处理可显著提高40Cr钢渗氮件的冲击韧性。

40Cr钢大断面工件的淬火工艺及淬火组织

设计了40Cr钢的端面淬火工艺,研究了φ110 mm工件断面从表层到心部淬火后的组织,并测试了从表层到心部的硬度分布。结果表明:40Cr最佳淬火工艺为淬火3 min后250℃回火;按照此淬火工艺,φ110 mm工件断面淬火后淬硬层硬度为53~55 HRC,半马氏体深度为5~10 mm。在距表面深度超过15 mm后,马氏体消失,显微组织主要为片层状珠光体+先共析铁素体,硬度下降到表面硬度的1/2。