钢的热处理组织分析：第四讲 钢的热处理组织分析实例（二）

5 40Cr球化退火组织 图6为40Cr球化退火组织。从显微观察可见,该组织由两部分组成:白亮块和分布着小颗粒的白亮块。40Cr钢球化退火后只能由铁素体与渗碳体两相组成。所以白色颗粒状物为渗碳体,白亮块及分布有渗碳体颗粒的白亮块(基体)均为铁素体。从形态看也可判断它是铁素体块及分布有渗碳体的铁素体。形成这种组织完全决定于退火工艺。球化前原始组织为大块状铁素体与珠光体的混合组织,经750℃加热时,组织为铁素体块+(奥氏体和少量的渗碳体);缓冷后,铁素体块不变,而奥氏体分解为球状珠光体,致使缓冷后组织中碳化物分布极不均匀,     

预奥氏体化对中Mn TRIP钢组织及力学性能的影响

为了提高钢的综合力学性能,用盐浴法对中Mn TRIP钢进行了热处理.采用SEM、TEM、XRD和拉伸测试研究了预奥氏体化处理对中Mn TRIP钢显微组织及力学性能的影响.实验结果表明:全马氏体冷轧态组织经两相区退火处理后,会析出大量渗碳体颗粒,随着退火时间延长,渗碳体颗粒逐渐溶解,马氏体组织逐渐转变为奥氏体和铁素体双相片层状组织;而在两相区退火处理前添加两相区预奥氏体化处理后,渗碳体析出被有效抑制,双相片层组织迅速形成;相比于常规两相区退火处理,预奥氏体化处理能够提高组织中残余奥氏体体积分数和综合力学性能.     

铸铁的热物性测定及其与显微组织的关系

用激光脉冲法和比较法测量了不同种类铸铁300-1300K的热物理参数(α,Cp,λ),并对铸铁热物性与显微组织的关系作了初步讨论。结果表明,片状石墨对铸铁导热、导温能力影响最大,蠕虫状石墨次之,球状石墨较小。石墨对铸铁的导热、导温能力的贡献最大,基体组织次之,而合金元素对热物性的影响大小则决定于其在基体中的存在形式;通常各种铸铁的导热、导温系数值按灰口铁、蠕虫铁、球铁、可锻铸铁、奥氏体铸铁和白口铸铁的顺序依次降低,且在810K以后开始趋于一致;除奥氏体铸铁和白口铸铁外大多数铸铁在1040K附近存在居里点,导温系数在该处出现最小值;除奥氏体铸铁外,多数铸铁在1040K附近比热容出现峰值,有些铸铁在490K附近存在渗碳体居里点,比热容在该处也出现峰值。     

奥氏体—贝氏体抗磨钢中共晶体的团球化

用扫描电镜、透射电镜和电子探针研究Ｍｇ－Ａｌ复合变质向－贝钢中共晶体的团球化。结果表明，团球状共晶体是由于Ｃ、Ｍｎ、Ｓｉ偏折、于凝固后期在奥氏体枝晶间形成的渗碳体和奥氏体伪共晶组织，共晶体结晶时的异质核心是ＭｇＳ。团球化是异质核心和变质元素影响共晶体的结晶方式。     

共晶碳化物团球化对铸铁激光熔敷层抗裂性的影响

为提高铸铁表面大面积激光熔敷层抗裂性问题，通过冶金因元素控制熔敷层组织形态在熔敷材料中加入碱金属元素钾，研究了在激光快速加热条件下钾对铸铁激光熔敷层组织团球化的影响，进而分析了该球状组织对熔敷层抗裂性的影响，结果表明随熔敷金属内钾含量增多熔敷层内共晶碳化物组织呈球状及孤岛状，这种组织明显提高了熔敷层抗裂性，此外大量的渗碳体组织确保了熔敷层具有较高的耐磨性；获得了无裂纹的大面积搭接熔敷层，其对应合金系统为Fe-C-Si-Ni-K。     

奥氏体─贝氏体抗磨钢中共晶体的团球化

用扫描电镜、透射电镜和电子探针研究Mg－Al复合变质奥─贝钢中共晶体的团球化结果表明，团球状共晶体是由于C、Mn、Si偏析，于凝固后期在奥氏体校晶间形成的渗碳体和奥氏体伪共晶组织，共晶体结晶时的异质核心是MgS．团球化是异质核心和变质元素影响共晶体的结晶方式     

球铁激光表面重熔组织热处理制备新型铁基耐磨材料

对球墨铸铁激光表面重熔／快速凝固组织进行处理，使亚稳相快速凝固共晶渗碳体部分转变为石墨，成功地制得了既含快速凝固共晶渗碳体又含弥散石墨的新型多相铁基耐磨材料。     

珠光体组织的等径弯曲通道变形

具有全珠光体组织的65Mn钢在650℃以C方式等径弯曲通道变形(ECAP)后,珠光体组织中的渗碳体片层以周期性的弯曲变形、周期性的剪切变形、剪切断裂等形式协调ECAP的强烈塑性变形.渗碳体表现出很强的塑性变形能力,在其内部导入了大量的晶体缺陷,为渗碳体的球化打下了能量基础.变形五道次后,片层状的珠光体组织演变成了超细的渗碳体颗粒均匀分布于铁素体基体的组织.铁素体基体为均匀的等轴晶,平均晶粒大小为～0.3 μm.渗碳体的球化可能以两种机制进行:破碎渗碳体片的非均匀长大(Ostwald熟化)和细小球状渗碳体颗粒的形核长大.     

合金元素Ni对铸铁短纤维烧结特性的影响

Ni 作为铁元素扩散的载体,显著加快了铸铁短纤维烧结体的致密化。当镍含量高于4.5%时,显微组织中发现了奥氏体,在奥氏体与珠光体边界析出断网状渗碳体,在奥氏体晶内析出魏氏碳化物及游离石墨,引起致密化速率下降,断裂方式由延性断裂转化为脆性断裂。     

过冷对共析钢动态相变和组织演变的影响

将共析钢在600-700℃的过冷奥氏体状态下进行单轴热压缩,获得了亚微米级别等轴铁素体 纳米级别弥散分布球化渗碳体的复相组织,其组织演变经历动态相变、片层渗碳体球化、铁素体动态再结晶和纳米级别渗碳体颗粒析出等过程.随着形变温度的降低,过冷度增加,相变动力学过程加快.片层渗碳体的球化程度由球化时间和球化速度控制,形变温度升高使渗碳体球化速度加快,但是相变开始时间及动力学延迟使得用于渗碳体球化和熟化的时间相应缩短,导致球化程度降低.铁素体再结晶和等轴化过程则主要受位错迁移、渗碳体颗粒钉扎的影响,形变温度升高导致较高的等轴化发展速度.     

Zr58Nb2.76Cu15.46Ni12.74Al10.34Y0.5非晶合金激光焊接接头微观结构及显微硬度表征

目的 探究激光焊接参数对非晶合金焊接接头的组织演变、焊缝成形、晶化程度等的影响规律,以及控制接头晶化的有效途径.方法 采用碟片激光器对Zr58Nb2.76Cu15.46Ni12.74Al10.34Y0.5非晶合金进行激光焊接,对比分析不同激光功率下,焊接速度对接头熔宽和晶化组织形成的影响规律,并对接头各区域微观组织特征...     

An Investigation on Vibration Welding of Amorphous and Semicrystalline Polymers

Vibration welding technique has been used to study the weld zone of thermoplastic polymers using ABS (amorphous), PC (amorphous), PMMA (amorphous), and PBT (semicrystalline). Polymers were welded using alike components and combinations of semicrystalline polymer with different amorphous polymers. Mechanical testing of welded polymers has proved that the tensile strength, elongation at break, and deformation was highest for PC–PC weld and least for ABS–ABS weld, when alike polymers were welded. However, welding of semicrystalline and amorphous polymer shows enormous reduction in its tensile strength as well as other tensile properties. Also, the tensile fracture of PBT with other amorphous polymers always occurred at weld zone which was not always in case of alike polymer welds. The weld strength of these polymers was observed to be dependent on the mechanical interlocking among the layers and not on interfacial bonding. This phenomenon may be due to the difference in glass transition temperatures of semicrystalline and amorphous polymers. XRD, FESEM, and AFM have been used in this study to observe the morphology of welded surfaces.     

Amorphous and nanograins in the bonding zone of explosive cladding

The amorphous and nanograins in the bonding zone of the titanium/titanium explosive cladding were investigated by means of transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The nanograins with perfect crystal structure range from 2 to 50 nm in diameter were in coherent with the matrix. While the amorphous were in the state of the long-range disorder and coexisted with the nanograins. The formation of the amorphous and the nanograins as well as their coexisting were due to the high cooling rate (range from 3.55 × 10⁶ to 7.8 × 10⁶ K/s at the amorphous transition temperature) within the bonding zone, and the high pressure as well as the high shear stress during the explosive cladding.     

TEM Observation of the Zrc/Zro2 Interface Formed by Oxidation of Zrc Single Crystals

Microstructure at the interface of ZrC and ZrO₂ formed by oxidation of a single crystal of ZrC with 100 faces at 600°C at an oxygen pressure of 2 kPa was observed by high-resolution transmission electron microscopy and scanning electron microscopy. The ZrO₂ scale was shown to consist of two subscales, zones 1 and 2. The interfacial area in zone 1 was composed of regular lattice fringes corresponding to the 111, 200, and 220 lattices of cubic ZrO₂ (c-ZrO₂) crystallites 2 to 10 nm in size and an amorphous phase. The growth of crystallites occurred in zone 2, which visualized the interface of zones 1 and 2. Black thin films reminiscent of zone 1 were successfully separated, which were composed of amorphous carbon in which c-ZrO₂ particles 2 to 20 nm in size were included.     

Surface crystallization of amorphous Fe-B-Si alloy annealed in a gas atmosphere containing organic vapour

The relationship between the annealing atmosphere and the magnetic properties of Fe_78.5B₁₃Si_8.5 amorphous alloy has been studied, showing that annealing in an inert gas atmosphere containing a borosiloxane resin significantly improves the core loss of the amorphous ribbon, and that annealing in an inert gas without any organic resins, gives much better results than annealing in an inert gas atmosphere containing cellulose and vinyl acetate resins. A boron-depletion zone was detected by Auger electron spectroscopy under the oxide film formed during annealing in the inert gas atmosphere containing cellulose and vinyl acetate resins. Annealing of the amorphous ribbon in the cellulose and vinyl acetate resins selectively oxidizes boron in the alloy to form a B₂O₃ film and a boron depletion zone; the alloy in this zone is then crystallized into -Fe. This surface crystalline layer induces out-of-plane magnetic anisotropy in the amorphous ribbon and thus deterioration of the core loss. On the other hand, annealing in the borosiloxane resin results in neither selective oxidation of boron nor surface crystallization of the amorphous ribbon     

基于工业合金激光熔覆制备Fe基非晶涂层

以FeCoCrMoCBY块体合金为熔覆材料,采用激光熔覆在低碳钢表面制备非晶涂层,探讨不同激光功率对涂层成形及组织的影响,通过显微硬度仪、电化学工作站测试涂层显微硬度及耐腐蚀性能。研究结果表明,其他参数不变,激光功率为17.6~20.8 W时,涂层成形良好,与基材呈典型冶金结合。随激光功率增加,涂层稀释率升高,裂纹倾向增大,非晶化程度降低。激光功率为17.6 W时,涂层主要由非晶组成,稀释率低于24.2%,结构致密,包括热影响区、熔合区和熔覆区;涂层平均显微硬度为1 330HV,约高于基材9倍,在3.5%NaCl溶液中的耐腐蚀性能明显优于316L不锈钢。     

钛板表面激光熔覆锆基合金涂层的组织结构

利用激光熔覆技术在Ti板上制备了非晶复合涂层,利用X射线衍射仪、能谱仪、扫描电镜和透射电子显微镜对熔覆层和结合区的组织结构进行了表征。研究发现,熔覆层组织主要由非晶、Zr的金属间化合物、氧化物及局部纳米晶组成。基体与熔覆层结合区由Ti的柱状晶和α(Ti/Zr)固溶体所构成,保证了基体与熔覆层之间有良好的冶金结合。     

Interface studies on crystallized alumina-silica fibre-reinforced Al-Si alloy composites

On applying heat treatments to the amorphous alumina-silica fibre (55% Al₂O₃, 45% SiO₂), the mullite crystal is separated out, and the crystallinity depends on the heat treatment parameters. The crystallized alumina-silica fibre shows higher hardness than amorphous alumina-silica fibre and a remarkable stability to chemical reaction with molten metal. The primary interfacial reaction zone product was found to be 2MgO · SiO₂.     

Effect of notching speed on dynamic fatigue behaviour of polyethylene terephthalate polymers

The influence of notching speed on the fatigue behaviour of crystalline and amorphous polyethylene terephthalate (PET) was investigated. A clear precrack adjacent to the notch tip was found after each crystalline sample was notched, and the precrack length increased when the samples were notched at higher speeds. The failure time, t _f, decreased significantly for samples with longer precrack lengths, and the decrease in t _f due to faster notching speeds was significantly lower for samples of high average molecule weight and calculated tie-molecule density. In contrast, a heart-shaped damaged structure surrounding the notch tip was observed after each amorphous sample was notched, and the size of the damaged zone, adjacent to the notch tip, increased significantly with the notching speed. Furthermore, the time to failure of each amorphous sample increased significantly as the notching speed increased. In fact, most of the increase in t _f is due to an increase in the initiation period, t _i. This significant increase in t _i is attributed to the larger damaged zone caused by higher notching speeds.     

The role of amorphous phase separation in crystal nucleation in splat cooled Li2O-SiO2 glasses

Amorphous phase separation and its influence on crystal nucleation in Li₂O-SiO₂ splat cooled glasses was studied. By means of small-angle X-ray scattering and optical reflection microscopy associated with stereological analysis it was shown that the crystal nucleation rate is increased during the early stages of primary and secondary phase separation. These observations emphasize the important role played by the diffusion zone around the amorphous droplets acting as nucleation sites. Some suggestions are advanced to explain why some authors found that the amorphous separation does not influence the crystal nucleation.