真空烧结—热锻高碳高钒模具钢CPM1OV抗弯断口的形貌特征

用扫描电镜观察了由相对密度为81％、85％、93％、98％的4种CPM10V烧结体热锻而成的材料的抗弯试样经淬火、回大后的断口形貌。结果表明：相对密度为93％、98％的烧结体锻材的抗弯断口形貌为准解理小平面上分布着许多小凹坑和凸起的小粒子；相对密度为81％、85％的烧结体锻材的抗弯断口形貌除上述特征外，还发现在局部区域有很大的凸出物和凹坑，这些区域具有光滑的曲面，无准解理平面。     

真空热压铍材工业实践中性能影响因素浅析

铍是一种低密度脆性材料,具有优良的比强度、比刚度、热性能和核性能,广泛用于航空、航天、舰船及核工业领域。由于历史原因和装备能力所限,国内铍材等静压成型技术发展较快,而真空热压成型的进展较落后。热压铍材通常采用粉末冶金真空模压方式生产,本文从铍粉末脱气工艺、模具装配和坯料径高比等方面进行了研究。简单揭示了在工业生产实践中影响真空热压铍材性能的几个因素。     

粉末热等静压9.75％钒成分冷作模具钢组织与力学性能的研究

通过气雾化制粉-热等静压工艺成功制备了含钒9.75％冷作模具钢.借助X射线衍射仪、扫描电镜、电子能谱分析仪、透射电镜等研究了该成分钢种不同热处理状态的相组成、组织形貌.研究表明:退火态相组成为铁素体和MC型碳化物及少量M7C3型碳化物,碳化物呈近球形颗粒状、粒径大多在2μm以下,分布均匀;1 120℃真空淬火条件下,随...     

高碳铬轴承钢碳化物带状评定方法探究

随着高碳铬轴承钢高温扩散时间的延长,碳化物带状的宽度会随之增加,碳化物颗粒变得细小。但按现有的SEP 1520-1998、GB/T 18254-2016及ISO 5949-1983标准图谱进行评级时,存在高温扩散时间越长,带状评级越高的情况,与改善工艺执行的效果相悖。本文采用一种新的碳化物带状评定方法,以带状内碳化物颗粒的尺寸为依据,完成碳化物带状评级,评定结果显示,高温扩散时间越长,所对应的碳化物带状级别越低,说明该方法可更清晰、直观及科学的回归反馈高温扩散改善带来的碳化物颗粒细化及分布均匀性的改善。     

高碳铬不锈轴承钢孪晶碳化物研究

研究了高碳铬不锈轴承钢“孪晶碳化物”（直线状和链状碳化物）的影响因素及形成原因,结果表明：加热温度达到1140℃,退火后开始出现沿晶界分布的链状碳化物;加热温度≥1160℃,退火后出现大量直线状和链状两种形态的碳化物。材料从高温直接冷却时,温度≥1080℃并且冷却速度≤80℃／h可能析出链状碳化物,并且温度越高冷却速度越慢析出的可能性就越大。直线状碳化物形成原因为：材料加热温度过高．晶粒长大的过程中晶界迁移时偶然发生堆垛错误形成了生长孪晶,在随后的退火过程中碳化物向奥氏体挛晶界面沉淀而形成,是真正意义上的孪晶碳化物。链状碳化物是由于材料过热或者局部过热,在随后冷却过程中碳化物沿奥氏体晶界析出而形成的,本质上是一种网状碳化物。     

真空热压技术在制备CuCr合金中的应用研究

采用真空热压新技术制造了高密度CuCr50合金，并与冷压成型技术进行了比较，分析了两种工艺合金的相对密度变化及显微组织，研究了真空热压工艺的致密化机理。     

真空热压烧结炉的研制

介绍了真空热压烧结炉的结构特点 ,包括热压合装置下压杆的动密封采用双向密封的优点 ,输电装置中引入电极的绝缘和耐高温性能 ,发热区获得 2 30 0℃高温的保温措施和保温桶的设计。     

真空热压结炉的研制

介绍了真空热压烧结炉的结构特点，包括热压合装置下压轩的动密封采用双向密封的优点，输电装置中引入电极的绝缘和耐高温性能，发热区获得2300℃高温的保温措施和保温桶的设计。     

真空热压制备W-50%Cu复合材料

采用真空热压制备了W-50%Cu复合材料,对其性能进行了测试,并利用SEM对其微观组织和断口形貌进行了观察与分析.结果表明:在30MPa压力下进行950℃×2h烧结,获得了相对密度达99.6%的W-50%Cu复合材料,其显微硬度、电导率和抗弯强度分别达到133HV、68.9%IACS和285MPa;W-50%Cu复合材料的抗弯断裂表现出塑性断裂特征,其断裂方式主要为沿晶断裂,并伴随少量的穿晶断裂.     

烧结法制备粉末冶金高碳铬钒工具钢的研究

用水雾化+真空烧结法制备了名义成分为C2.5Cr17Co2Mn2V3Fe的粉末冶金高碳铬钒工具钢,研究了配碳量和烧结温度对烧结行为的影响.结果表明,根据配碳量和烧结温度不同,存在固相烧结、超固相线液相烧结、液相烧结三种烧结方式,其碳化物尺寸分别为5μm、10μm、15μm左右;固相烧结试样相对密度和硬度只有90%和50HRC左右,而两种液相烧结试样的相对密度和硬度均可达99%和60HRC以上.XRD结果表明:烧结和淬火样品均由γ-Fe、α-Fe和Cr7C3组成;回火样品主要由α-Fe、Cr7C3组成,回火共析反应可能为γ-(Fe,Cr,Co,Mn,C)→α-(Fe,Cr,Co,Mn,C)+Cr7C3.     

Pearlite in ultrahigh carbon steels: Heat treatments and mechanical properties

Two ultrahigh carbon steel (UHCS) alloys containing 1.5 and 1.8 wt pct carbon, respectively, were studied. These materials were processed into fully spheroidized microstructures and were then given heat treatments to form pearlite. The mechanical properties of the heat-treated materials were evaluated by tension tests at room temperature. Use of the hypereutectoid austenite-cementite to pearlite transformation enabled achievement of pearlitic microstructures with various interlamellar spacings. The yield strengths of the pearlitic steels are found to correlate with a predictive relation based on interlamellar spacing and pearlite colony size. Decreasing the pearlite interlamellar spacing increases the yield strength and the ultimate strength and decreases the tensile ductility. It is shown that solid solution alloying strongly influences the strength of pearlitic steels.     

Mechanical behavior of superplastic ultrahigh carbon steels at elevated temperature

Ultrahigh carbon (UHC) steels have been investigated for their strength and ductility characteristics from 600 to 850°C. It has been shown that such UHC steels, in the carbon range 1.3 to 1.9 pct C, are superplastic when the microstructure consisted of fine equiaxed ferrite or austenite grains (∼1 μm) stabilized by fine spheroidized cementite particles. The flow stress-strain-rate relations obtained at various temperatures can be quantitatively described by the additive contributions of grain boundary (superplastic) creep and slip (lattice diffusion controlled) creep. It is predicted that superplastic characteristics should be observed at normal forming rates for the UHC steels if the grain size can be stabilized at 0.4 μm. The UHC steels were found to be readily rolled or forged at high strain-rates in the warm and hot range of temperatures even in the as-cast, coarse grained, condition. BRUNO WALSER, formerly with Department of Materials Science and Engineering, Stanford University     

Liquid phase sintering,heat treatment and properties of ultrahigh carbon steels

Abstract

Thermo-Calc modelling was employed to predict liquid phase amounts for Fe–0·85Mo–(0·4–0·6)Si–(1·2–1·4)C in the temperature range of 1285–1300°C and such powder mixes were pressed and liquid phase sintered. In high C steels, carbide networks form at the prior particle boundaries, leading to brittleness, unless the steel is heat treated. To assist the break-up of these continuous carbide networks, 0·4–0·6% silicon, in the form of silicon carbide, was added. After solution of processing problems associated with the formation of CO gas in the early part of the sintering cycle, and hence large porosity, densities in excess of 7·75 g cc^?1 were attained. A spheroidising treatment resulted in microstructures having the potential of producing components, which are both tough and suitable for sizing to improve dimensional tolerance. Yield strengths up to 410 MPa, fracture strengths up to 950 MPa and strains up to 16% were attained.     

The effect of chromium in high carbon bearing steels

Chromium is present in the 52100 bearing steel composition in the range 1.30 to 1.60 wt pct. Chromium has a significant influence on the spheroidization of cementite, finer carbides being formed due to chromium additions. The ferrite to austenite transformation temperatures are increased due to chromium. The microchemistry of the cementite in 52100 changes during heat treatment; the chromium content of secondary carbides is generally lower than that in the spheroidal (FeCr)₃C produced by soft annealing. The rate of carbide dissolution is controlled by the rate of chromium diffusion from the carbide-matrix interface. Also, the chromium content of the residual, spheroidal (FeCr)₃C increases during austenitization. The effect of substitution of chromium in bearing steel compositions is discussed. In view of the beneficial effect of chromium, only substitution by similar strong carbide forming elements should be considered for bearing steels.     

Reactions of chromium diboride with carbon steels under glow-discharge conditions. Part II

Conclusions A study was made of the zones of diffusional reaction of chromium diboride with carbon steels, cast iron, and Armco iron, forming under glow-discharge conditions. An attempt was made to discover the laws governing the formation of diffusion layers in these systems. It was established that with rise in carbon concentration in the steel the width of the diffusional reaction zone grows, attaining a maximum for a steel with a carbon content of 0.8%. At a carbon concentration in the steel of 1.6% or more, the width of the diffusion zone sharply decreases. In a CrB₂-steel system a strong inhibiting influence on diffusion is exerted by the higher chromium carbide Cr₃C₂.For Part I, see Poroshkovaya Metallurgiya, No. 10, 29–32 (1980).Translated from Poroshkovaya Metallurgiya, No. 1(217), pp. 42–47, January 1981.     

Surface alloying of carbon tool steels using laser heating

The problems of surface hardening of high-carbon steels by alloying using laser radiation are considered. The effect of the laser treatment parameters on the thickness, the structure, the phase composition, the microhardness, and the residual stresses of the surface layer is studied, and the influence of alloying elements on the strength of the surface layer in carbon steels and their wear resistance is investigated.     

Microalloyed,vacuum degassed high-strength steels with special emphasis on IF steels

In comparison with other high-strength concepts, high-strength IF steel has a particularly high forming capacity with increased strength, while the sheet thickness reduction through forming is, on the whole, smallest with high-strength IF steel. Solid-solution hardening through Si, Mn and P is particularly suitable as a mechanism for increasing strength, as this leads to comparatively low formability losses with increased strength values. An additional increase in strength is possible using the bake-hardening effect. This can be achieved with an incomplete C and N binding through Ti and/or Nb, or through stoichiometric microalloying with V. The effect is basically caused by the relatively low thermodynamic stability of VC. V-alloyed, vacuum degassed steel combines in this way good forming behaviour with an increase in strength through bake-hardening. Through an increasing segregation of P at grain boundaries, solid solution hardening with this element can lead to unfavourable embrittlement in higher strength IF steel and to intercrystalline fracture. B-addition to the amount of 0.002% (mass content) greatly reduces the tendency to become brittle without leading to any remarkable losses with regard to formability. Examinations concerning the precipitation behaviour of Ti-IF steel with P show that a formation of iron titanium phosphate (FeTiP) in the hot strip only occurs where there is an excess of Ti and high coiling temperatures are used. For a P-alloyed IF steel with stoichlometrical Ti-content no precipitation of FeTiP takes place in hot band, nor is the thermal activation in continuous annealing simulation sufficient to achieve a transformation of existing Ti-precipitates into FeTiP, which might occur according to literature.