喷射成形CPM9V高速钢组织性能研究

为了提高CPM9V高速钢组织均匀性,采用喷射成形方法制备CPM9V高速钢,研究了喷射成形CPM9V高速钢热处理前后的微观组织.结果表明:喷射成形制备的CPM9V高速钢沉积坯晶粒细小,组织致密,无宏观偏析,沉积坯平均体密度为7.306 g/cm3,达到理论密度的98.1%;CPM9V高速钢沉积坯经热处理后组织为回火马氏体、铁素体和碳化物,二次回火硬度为52HRC,与粉末冶金CPM9V高速钢相当;组织中绝大部分为小于15μm的等轴晶,分布在晶界的碳化物主要为MC型碳化钒,分布在晶内的碳化物为VC和Mo的复合碳化物.     

Microstructure and elevated temperature mechanical properties of Al–8Fe–4RE alloy fabricated by spray forming

Al–8Fe–4Ce alloy is currently manufactured by consolidating the atomized powders. With the aim to reduce the cost, spray forming process was applied in manufacturing with misch metal as raw materials. Spray forming (SF) as well as casting were employed to prepare Al–8Fe–4RE alloy, followed by hot‐press to compact the samples. The mechanical properties of SFed and cast Al–8Fe–4RE alloys are characterized at a temperature of 350 °C. The results show that the Al₃Fe phases contained in SF alloy is comparatively refined, forming needle‐shaped phases embedded in the Al matrix, and the SF alloy also showed lower degree of preferred orientation in (111) plane. Although both factors might explain the superior performance of the SF sample, the fracture appearance after tensile test at 350 °C shows that the contribution from crystallographic feature might be predominant. Spray forming is proved to be a very promising technique for manufacture of Al–Fe–Ce alloys of high strength at an elevated temperature.     

Analysis of spray formed tool steels

The technique of atomising liquid metal and compacting the micro‐droplets to a billet on a rotating support combines advantages from cast, wrought and powder metallurgical materials. A production rate of several tons per hour requires precisely controlled processing routines. Important process parameters based on processing, manufacturing and application of spray formed material are now developed by fundamental investigations established in projects focused in a special co‐operative research program (SFB 372) at the University of Bremen which is funded by the Deutsche Forschungsgemeinschaft (DFG). By this method advanced alloys of high hardness can be formed without inhomogeneities like segregations and pores in the center of the ingot. By example of tool steels the influence of spray forming on microstructure and homogeneity of the elemental distribution is shown.     

Spray formed and rolled aluminium‐magnesium‐scandium alloys with high scandium content

Aluminium‐magnesium‐scandium alloys offer good weldability, high corrosion resistance, high thermal stability and the potential for high strength by precipitation hardening. A problem of aluminium‐scandium alloys is the low solubility of about 0.3 mass‐% scandium when using conventional casting methods. The solution of scandium can be raised by higher cooling rates during solidification. This was realised by spray forming of Al‐4.5Mg‐0.7Sc alloys as flat deposits. Further cooling rates after solidification should also be high to prevent coarse precipitation of secondary Al₃Sc. Therefore a cooling device was designed for the spray formed flat deposits. The flat deposits were rolled at elevated temperatures to close the porosity from spray forming. Microstructures, aging behaviour and tensile properties of the rolled sheets were investigated. Strength enhancements of about 100 MPa compared to conventional Al‐Mg‐Sc alloys were achieved.     

Materials characterization and mechanical properties of graded tool steels processed by a new co‐spray forming technique

In order to meet the requirements of micro cold forming tools, a new co‐spray forming process has been applied to produce graded materials from two different tool steels in this study. The two steel melts were atomized and co‐sprayed simultaneously onto a flat substrate, resulting in a flat graded deposit when the two sprays were overlapped. To eliminate porosity and break up carbide network, the graded deposits were further hot rolled. The resultant graded tool steels were investigated with respect to porosity, element distribution, microstructure, hardness, strength, and toughness. The degree of overlapping of the two sprays determined the concentration gradient of the chemical elements in the deposits. The overlapping of the spray cones also contributed to low porosity in the gradient zone of the deposits. The porosity in the graded deposits could be essentially eliminated by means of hot rolling. The carbides and grain structures of the hot rolled tool steels were fine and homogeneous. By means of combining different tool steels in a single deposit, different microstructures and properties were combined.     

Effect of tempering temperature on microstructure and properties of aluminium-bearing high boron high speed steel

Heat treatment is of great significance to the performance improvement of high speed steel. Via heat treatment, the microstructure of high speed steel can be improved, thus greatly improving the material performance. The effect of tempering temperature on the microstructure of aluminium-bearing high boron high speed steel (AB-HSS) was investigated by optical microscope (OM), scanning electron microscope (SEM) and x-ray diffraction (XRD). The hardness and wear resistance of the alloy at different tempering temperatures were tested by Rockwell hardness tester, micro-hardness tester and wear tester. The experimental results indicate that the tempering microstructure of aluminium-bearing high boron high speed steel consists of α-Fe, M₂B and a few of M₂₃(C, B)₆. Tempering temperature could greatly affect the wear resistance of materials. With the increase of tempering temperature, the wear resistance of aluminium-bearing high boron high speed steel firstly increase and then decrease. The alloy tempered at 450 °C has the best wear resistance and minimum wear weight loss. This study provides a reference for the formulation of heat treatment process of aluminium-bearing high boron high speed steel.     

Bulk synthesis of amorphous and nano‐crystalline materials by spray forming

Bulk amorphous and nano‐crystalline metallic materials have been observed to possess excellent mechanical and physical properties. The conventional process routes, to synthesize such materials, are restricted by their ability to achieve rapid solidification, which limits the dimensions of the materials produced. In the last 10–12 years, spray forming has been employed to avoid these limitations by using its capability of layer by layer deposition of undercooled droplets. The current literature indicates that the opportunities provided by this process can be effectively utilized to produce bulk materials in a single step. In this paper, an attempt has been made to bring out the developments in the synthesis of bulk amorphous and/or nano‐crystalline materials by spray forming. The effect of process parameters, droplet size distribution in the atomized spray, the thermal conditions of droplets prior to deposition and the deposition surface conditions have been discussed. It has been demonstrate that a layer by layer deposition of undercooled droplets of glass forming alloys on a relatively cold deposition surface is the suitable condition to achieve bulk amorphous/nano‐crystalline materials.     

The influence of the temperature on the stress‐strain curves of a bearing steel and a case hardening steel

In the present paper the influence of the temperature and strain rate on the stress strain behaviour of two different steels were investigated. Two microstructures were considered: pearlitic and austenitic. Tensile tests with the bearing steel 100Cr6 and the case hardening steel 20MnCr5 were accomplished at various temperatures. For this purpose the Ludwik equation was used to describe the stress‐strain curve. The parameter of the constitutive equation was determined for each steel and microstructure. Especially for the austenitic state the parameters of the used material law were described as a function of the temperature.     

结构材料喷射成形技术与雾化沉积高温合金

喷射成形是利用快速凝固方法直接制备金属材料坯料或半成品的先进材料制造技术 ,喷射沉积高温结构材料的冶金性能好、生产效率高、成本低 ,因而在近几年得到了迅速发展 .本项研究的主要目的是要通过喷射成形工艺参数的调整、最大限度地直接减少喷射成形坯中的孔隙度 ,进而得到优质坯料 .利用优化的雾化喷射沉积技术制备了多种高温合金沉积坯 ,沉积坯整体致密、晶粒细小、组织均匀、无宏观偏析、含气量低、力学性能提高 .还简要地比较了喷射成形高温合金与用常规铸锭冶金工艺和粉末冶金工艺制备高温合金的异同 ;总结了航空材料研究院喷射成形高温材料近年来的研究状况 ,包括专用高温材料喷射成形装置和技术及其应用 .     

M2高速钢的影响表面复合强化的研究

对比了分别经可控渗氮、离子注入形成TiN及可控渗氮 +离子注入Ti2 +后 ,M2高速钢零件(精冲模 )的寿命实验 .结果表明 ,采用可控渗氮 +离子注入Ti2 +的复合处理工艺 ,可使零件的使用寿命获得明显提高 .断口分析、表面硬度测试、金相分析、XRD和AES分析表明 ,寿命的提高是由于 :①用Jonsson经验公式测得的该TiN注入层的真实硬度为HV3 0 0 0 ,TiN的超高硬度是寿命提高的根本原因 .②该复合工艺可使M2高速钢表面TiN注入层获得较厚较硬的氮化过度层 ,增强了膜基间的结合力 ,从而提高了零件的抗磨损和抗冲击性能 .③渗氮层增加了钛离子的注入深度 ,获得了更宽的TiN改性层 ,用JT -PRII所得到的模拟计算结果与此吻合得很好 .     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Microstructures and mechanical properties of as‐cast titanium–zirconium–molybdenum ternary alloys

In this study titanium–zirconium–molybdenum alloys (Ti₅₀Zr₅₀)_100‐xMo_x (xMo; x = 0 at.%, 1 at.%, 3 at.%, 5 at.% or 7 at.%) were investigated, focusing on the effect of molybdenum addition on their microstructures and mechanical properties. Transmission electron microscopy observations revealed that the binary Ti₅₀Zr₅₀ alloy was composed entirely of an acicular hexagonal structure of the α’ phase. When the molybdenum content was 1 at.%, the alloy was composed of β and ω phases. However, when 3 at.% or more molybdenum was added, only the equiaxed, retained β phase was observed. Tensile tests at room temperature indicated that the mechanical properties of the 1Mo alloy were inferior owing to the embrittlement effects of the ω phase and the difficulty of dislocation motion through the ω phase. Our research suggested that the 5Mo alloy had excellent ductility (16.5 %) as well as adequate strength (780 MPa). The improved mechanical properties were attributed to the enhanced stability of the β phase and the disappearance of the ω phase.     

High yield spray forming of small diameter tubes using pressure‐gas‐atomization

The economy of the spray forming process is restricted by the generation of overspray, which in many cases cannot be re‐introduced into the process by re‐melting or co‐injection. Especially for small deposits, such as small diameter tubes (diameter <100 mm), the amount of overspray can become large in conventional spray‐forming processes. In this work, an alternative process with a pressure‐gas‐atomizer operating at low melt flows is presented. Tubes with diameters of 50 mm and 90 mm were spray‐formed and analyzed regarding yield and porosity. It was found that yields up to 96% can be achieved with porosities below 1% if proper process parameters are identified and used. An evaluation of the yield and the corresponding achievable porosity is conducted to identify resource‐efficient sets of parameters.     

Microstructure and wear resistance of spray formed and conventionally cast high‐chromium white iron

A billet of hypoeutectic high‐chromium white iron (19% Cr, 2.5% C) was spray formed using Gas‐to‐Metal Ratios (GMR) of 0.9, 1.0, and 1.1. Microstructural studies and dry sand rubber wheel abrasion tests were carried out, on the one hand, to compare between the spray formed and conventionally cast material and, on the other hand, to investigate the relationship between gas‐to‐metal‐ratio, eutectic carbide morphology and abrasion resistance. The spray formed material was characterized by a considerably finer carbide morphology (max. ?30 μm) than the conventionally cast material (max. 100–200 μm). The coarser carbide morphology is believed to be responsible for the superior abrasion resistance of the conventionally cast material. Although the carbide morphology of the spray formed material was only moderately influenced by the changes in the gas‐to‐metal‐ratio, there was a clear improvement in the abrasion resistance with decreasing gas‐to‐metal‐ratio. The improvement correlated with a decrease in the fraction of very fine (<1.5 μm) carbides, rather than with an increase in the mean carbide size.     

Effect of electromagnetic centrifugal casting on solidification microstructure of cast high speed steel roll

Using self‐made electromagnetic centrifugal casting machine, optical microscopy (OM) and D/max2200pc X‐ray diffraction, the solidification microstructure and phases of as‐cast high speed steel(HSS) roll made by sand casting, centrifugal casting and electromagnetic centrifugal casting were investigated. The experiment results show that the phases of as‐cast high speed steel (HSS) roll are alloy carbide (such as W₂C, VC, Cr₇C₃), martensite and austenite. The centrifugal casting and electromagnetic centrifugal casting can apparently improve the solidification structure of HSS roll. With the increase of electromagnetic field intensity (B), the volume fraction of austenite in the HSS solidification structure increased obviously and eutectic ledeburite decreased, the secondary carbide precipitated from the austenite is more fine and distribution of secondary carbide is more even.     

Microstructures and corrosion resistance of as‐cast aluminum‐10 wt.% silicon and aluminum‐20 wt.% silicon alloys

The microstructures and corrosion resistance of two as‐cast alloys, aluminum‐10 wt.% silicon hypoeutectic alloy and aluminum‐20 wt.% silicon (weight percent) hypereutectic alloy are investigated by conventional casting, the scanning electron microscope equipped with oxford X‐ray energy dispersive spectroscopy system and transmission electron microscope are applied for analysis. The results show that the microstructures change from the strip‐like into lump shape with the increase of silicon content from 10 % to 20 %. The electrochemical polarization curves prove that the aluminum‐20 wt.% hypereutectic silicon alloy had the better resistance with the corrosion potential of ?1.414 V and corrosion current density of 5.41 ? 10^?5 ampere compared with the aluminum‐10 wt.% silicon hypoeutectic alloy.     

Development of low‐melting‐point filler materials for laser beam brazing of aluminum alloys

In order to develop low‐melting‐point filler materials for laser beam brazing of aluminum alloys, Al–Si–Cu based alloys and Al–Si–Zn based alloys were produced via spray forming and associated deformation processes. The selected alloys were spray formed in the form of billet with a diameter around 160 mm and hot extruded into wire rods with a diameter of 8 mm. The extrusions were further cold worked into thin wires with a diameter of 1.2 mm via rotary swaging. Finally, the filler wires were applied in the laser beam brazing of AA6082 structures. It showed that the newly developed filler materials could meet the requirements of the laser beam brazing of aluminum alloys. Particularly, the laser beam brazing process using the spray‐formed filler materials required a significantly lower energy input and allowed for higher brazing speed as compared to the conventional AlSi12 filler material.     

精密喷射成形HM1钢摩擦磨损性能研究

为了探索提高HM1钢耐磨性能的制备新途径,采用往复式滑动干摩擦实验研究了精密喷射成形HM1钢摩擦磨损性能并对其磨损机制进行了分析,同时还与铸态材料进行了对比.结果表明:不同载荷下,喷射态和喷射回火态HM1钢摩擦系数均低于铸态;当载荷为100 N时,与铸态相比,喷射态磨损量比其低约34%,喷射回火态磨损量比其减少约48%.对磨痕形貌分析表明,当载荷为40 N时,铸态试样以粘着磨损为主,当载荷为100 N时,转换为粘着磨损与磨粒磨损共存,并伴随严重的氧化磨损;对于喷射态和喷射回火态试样,则以磨粒磨损为主,氧化磨损减轻.     

A study of casting high‐boron high‐speed steel roll materials

In this paper, we design and prepare five kinds of high‐boron high‐speed steel roll materials. The microstructure, mechanical property and wear resistance of high‐boron high‐speed steel roll materials were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X‐ray diffraction (XRD) and hardness measurement, impact test and abrasion test. The results show that as‐cast microstructure of high‐boron high‐speed steel consists of martensite, retained austenite and borocarbide. Hardness of as‐cast high‐boron high‐speed steel excels 64 HRC. In unmodified high‐boron high‐speed steel, eutectic borocarbide is distributed in a network along the grain boundary. With the addition of RE‐Mg‐Ti compound modifier, the networks of borocarbide is broken. The hardness of high‐boron high‐speed steel gradually decreased with the increase of tempering temperature. Under the same conditions, the impact toughness of unmodified high‐boron high‐speed steel roll material is slightly lower than that of modified steel. The wear resistance of modified high‐boron high‐speed steel roll material is greater than that of high‐carbon high‐vanadium high‐speed steel roll.     

A study of heat treatment of high‐boron high‐speed steel roll

High‐boron high‐speed steel (HSS) is a cheap roll material. In the paper, the authors research the effect of heat treatment on the microstructure and properties of high‐boron high‐speed steel HSS roll containing 0.54% C, 1.96% B, 3.82% W, 7.06% Mo, 5.23% Cr and 2.62% Al by means of the optical microscopy (OM), the scanning electron microscopy (SEM), X‐ray diffraction (XRD) and hardness test. The results showed that as‐cast structure of boron‐bearing high‐speed steel HSS consisted of martensite, pearlite, M₂(B, C), M₃(B, C) and M₂₃(B, C)₆ type borocarbides. After quenching, the matrix transformed into the lath martensite, and M₃(B, C) dissolved into the matrix. When quenching temperature is lower than 1050°C, the hardness is increased with the increase of quenching temperature under oil cooling, while quenching temperature excels 1100°C, the hardness will decrease with the increase of quenching temperature. Under the condition of salt bath and air cooling, the effect of quenching temperature on the hardness is similar to the above law, but the quenching temperature obtaining the highest hardness is higher than that of oil cooling. The highest hardness is obtained while tempering at 525°C. The hardness of high‐boron high‐speed steel HSS roll is 66.5 HRC, and its impact toughness excels 13.1 J/cm². Using in pre‐finishing stands of high‐speed hot wire‐rod rolling mill, the wear rate of high‐boron HSS rolls is 0.26 mm/one thousand tons steel. However the manufacturing cost of high‐boron HSS rolls is obviously lower than that of powder metallurgy hard alloy rolls, it is only 28% of that of powder metallurgy (PM) hard alloy rolls.