To study the influence of different deformation parameters of the hot working process on the microstructure of 20Cr2Ni4A gear steel during the plastic forming process, the heat deformation experiment of 20Cr2Ni4A gear steel was carried out using the Gleeble-3500 Thermal Machanical Simulator, and the heat deformation behavior of hot 20Cr2Ni4A gear steel under different deformation conditions was investigated. Through the dislocation density model, recrystallization nucleation and grain growth model, we innovatively wrote the cellular automaton program to simulate the dynamic recrystallization behavior during the heat deformation process. The simulation results were verified through EBSD and metallographic diagrams.
This paper studied the high-temperature stability of dissimilar steel welded joints between G115 and Sanicro25 steel. The joints were exposed to 700 C-degrees for time up to 2000h. The microstructure evolution of base metal (BM) and fine-grain heat-affected zone (FGHAZ) were analyzed. Tensile, microhardness, and impact experiments were conducted on the joints, and the explanations for the changes in mechanical performance are derived from the microstructure. The results showed that the Laves phase were precipitated after aging for 100 h, which has two nucleation methods. Nucleation adjacent to M23C6 is the main way in this research. Laves phase mainly grows up to consume M23C6. The microstructure in BM and FGHAZ is obviously different after aging. After aging for 1000 h, mechanical properties such as tensile strength, Vickers hardness, impact energy, elongation and area reduction are reduced, except for the yield strength. The softening caused by the microstructure evolution of FGHAZ is the main reason for the joint fracture in FGHAZ.
Effect of aging rolling on the microstructure,texture and magnetic properties of the low-temperature oriented silicon steel was studied by conducting aging rolling tests at 250 ℃ for different time using a single cold rolling method.The results indicate that the aging rolling has no significant effect on the cold rolling and primary recrystallization microstructure of low-temperature oriented silicon steel,but it can significantly improve the primary recrystallization texture.The contents of favorable Goss and { 111 }<112>textures in the primary recrystallization microstructure increase first and then decrease with the increase of aging rolling time,reaching the maximum value at 5 min.An increase in favorable texture content can improve the secondary recrystallization microstructure and enhance the magnetic properties of the final sheet.The magnetic induction intensity of the final sheet increases first and then decreases with the prolongation of aging rolling time,and the iron loss shows the opposite trend.When the aging rolling time is 3-7 min,the final sheet has excellent magnetic properties.
The reutilization of granite sludge generated in granite cutting and processing possesses economic and ecological benefits. In this study, high-strength glazed glass-ceramics were prepared entirely from granite powder using dense sintering and instantaneous glaze firing. The densification and glaze formation are clarified in terms of phase evolution to study their effects on the flexural strength and surface glossiness of the glass-ceramics. The milling process promotes particle refinement and the removal of colored minerals, thus increasing the powder whiteness and sinterability. After dense sintering at 1100 degrees C, instantaneous glaze firing at high temperatures decreases the flexural strength while greatly increases the surface glossiness of the glass-ceramics due to the dissolution of quartz and feldspars in the liquid phase. After the acid-leached powder was densely sintered and fired with a rapid heating of 50 degrees C/min to 1300 degrees C, the pinhole-free glazed glass-ceramic has a flexural strength of 112.5 MPa and a surface glossiness of 54.7 GU (glossiness unit), meeting the quality requirements of the bright glazed tiles in the market. The stepwise sintering process provides a simple processing route for recycling granite sludge into decorative construction tiles and high-temperature glazes, promising the scalable and value-added utilization of granite sludge.
The effects of Sc and/or excess Mg on the microstructure characteristics, tensile properties, and fracture behavior of a hypoeutectic Al-10Mg2Si alloy were systematically studied. The results showed that adding 0.25
利用放电等离子烧结(Spark plasma sintering,简称SPS)技术并配合机械加工的方式制备了 3种相对摩擦工作面石墨取向为0°、45°和90°的铜基粉末冶金摩擦材料.采用MM1000-Ⅱ型惯性制动试验台测试了 3种材料的制动摩擦磨损性能,并对其试验后的摩擦表面三维形貌特征、近摩擦面区域特征、磨屑特征和摩擦表面物相进行分析,研究了石墨排列取向对不同制动条件下铜基粉末冶金材料摩擦磨损性能的影响.结果表明:与石墨取向为0°比,石墨取向为45°和90°均摩擦系数均呈现先上升后下降的趋势;在相同的制动条件下,石墨取向为45°的平均摩擦系数与石墨取向为0°的材料相差不大,但磨损率较低,特别是0.8 MPa、250 km/h条件下石墨取向为90°的材料的磨损率仅为石墨取向为0°的材料的31.8％.提高制动初速度均能够促进3种材料摩擦表面形成氧化膜,对于石墨取向为0°的材料,表面形成以Fe3O4为主的氧化膜,而对于石墨取向为90°的材料,则形成以Fe2O3为主的氧化膜.
The recrystallization and inhibitor precipitation behaviors of rare earths under water cooling after holding for different times of oriented silicon steel hot rolled at 1200°C in the ferrite zone with 30% deformation were analyzed using Gleeble 1500D, SEM,TEM and ICP. The results showed that: during the hot rolling of oriented silicon steel in the high temperature ferrite zone, only dynamic reversion occurred, no dynamic recrystallization occurred, and the amount of precipitates did not increase significantly; after deformation at 1200°C, static recrystallization occurred after holding for about 20s, and the inhibitor started to precipitate and grow. The higher the recrystallization rate, the faster the volume fraction of precipitates. After the deformation, the amount of Cu 2 S and MnS in the precipitates was similar. At 64% recrystallization rate, MnS increased by about 8% and Cu 2 S increased by about 23%. At the same time, most of the precipitates were precipitated in the crystal, and gradually nucleated and grew at the grain boundary when the holding time was extended. After rare earth lanthanum and cerium were added, the precipitation amount of inhibitor was reduced. The higher the degree of static recrystallization, the more obvious the effect of rare earth on the precipitation of inhibitor.
通过等温热压缩试验研究了新型亚稳β钛合金Ti-1500在750～910℃、0.001～10 s-1条件下的热变形行为.建立了耦合应变的双曲正弦型Arrhenius本构方程,基于动态材料模型及Prasad流变失稳准则构建了热加工图,分析了变形后的显微组织.结果表明,随着变形温度升高、应变速率降低,合金的流变应力降低,相同条件下合金的峰值流变应力略高于Ti55531合金,低于M28合金.合金在两相区的平均热变形激活能为291.36 kJ/mol,远高于纯钛的自扩散激活能,β单相区为153.96 kJ/mol,与纯钛的自扩散激活能接近.两相区能量耗散效率峰值位于低应变速率(0.001 s-1);单相区能量耗散效率峰值位于中低应变速率(0.01～0.1 s-1);所有试验温度下,应变速率高于1 s-1时发生变形失稳.结合显微组织分析可以将变形分为3个区域,即低温低应变速率下的β→α相变区、中高温低应变速率下的β再结晶区以及高应变速率下变形不均匀的失稳区.
采用扫描电镜(SEM)、电子背散射衍射(EBSD)技术和室温拉伸测试等研究了 Nb、V、Ti微合金化元素对20MnSi钢显微组织和力学性能的影响.结果表明:Nb、V、Ti微合金化及其所形成的第二相粒子可以阻碍试验钢的晶界迁移、细化晶粒尺寸,经热轧-空冷后晶粒明显细化,晶粒尺寸可达12级,综合力学性能明显优于20MnSi穿水钢筋,并达到新国标中400 MPa级钢筋所要求的性能指标.根据理论模型计算,晶界强化、固溶强化和位错强化增量分别约占屈服强度的54％、22％和17％,而由于微合金化元素含量较低且所形成的第二相粒子体积分数较低,析出强化增量在试验钢屈服强度中的占比仅约7％,表明Nb、V、Ti微合金化设计而导致的晶粒细化对试验钢力学性能提升所产生的贡献十分显著.
采用光学显微镜(OM)、透射电镜(TEM)及有限元分析(FEA)等研究了轧制工艺对Fe-0.2C-1.45Mn-Nb-V-Ti钢板厚方向的组织和力学性能均匀性的影响.结果表明:在压缩比受限的条件下,利用奥氏体晶界促进形核的机制(即边界诱导相变机制,BIT机制)可以达到细化晶粒的目的,试验钢的平均晶粒尺寸均小于10 μm;结合温度与累计应变的反向分布特点和轧制工艺的优化,轧制63 mm厚的试样表面和中心晶粒尺寸偏差小于2μm,有效改善了晶粒尺寸沿板厚方向的偏差.在本文的轧制工艺下,提高了厚板沿厚度方向的组织均匀性,获得了优异的力学性能.
Effect of Mg and Si addition on aging precipitation behavior and microstructure of AlCuMnZr alloy was studied by microhardness tester and transmission electron microscopy. The results show that the Mg and Si addition can significantly improve the aging hardness of the alloy and ensure good thermal stability. The peak hardness of the Al5.5Cu0.25Mg0.3Mn0.2Zr0.15Si alloy can reach 156.3 HV0.2 after solution treatment at 540 ℃ for 7 h and aging at 175 ℃ for 24 h. The addition of Mg refines the size of the θ′ phase in the AlCuMnZr alloy and increases the number density of the θ′ phase, makes its distribution more disperse and uniform. However, after the addition of Si, due to the precipitation of σ phase and Q phase and the segregation of Si around the θ′ phase, the size and the coarsening speed of the θ′ phase precipitates are reduced. However, after a long time of thermal exposure at 225 ℃, due to the disappearance of Si segregation, part of the θ′ phases will be coarsened and the thermal stability of the alloy will be reduced.
利用Gleeble-3500热模拟试验机研究了 40Cr10Si2Mo钢在不同冷却速度下的连续冷却相变行为,建立了试验钢的动态连续冷却转变(CCT)曲线和连续冷却相变动力学模型,通过表征不同冷速下的微观组织,分析和讨论了不同冷速对相转变以及合金元素析出的影响.发现在冷速为0.1～0.3 ℃/s时,组织为铁素体基体上分布着大量碳化物颗粒.碳化物中Cr和Mo的含量随着冷却速度的升高而减少.冷速为0.5～0.8℃/s时,组织为铁素体+片层珠光体+少量马氏体+网状碳化物.当冷速大于3℃/s时,组织完全转变为马氏体.分别建立了扩散型Johnson-Mehl-Avrami(JMA)模型和非扩散型Koistinen-Marburger(K-M)相变模型,结果表明,试验值与模型拟合曲线吻合度良好.
探究了烘烤硬化钢(HC180B)烘烤硬化过程析出行为对力学性能的影响.利用光学显微镜(OM)、透射电镜(TEM)和三维原子探针(3DAP)研究了位错、析出物以及C、N等原子在晶界处的偏析行为.结果表明,2％预拉伸形变及其烘烤后的屈服强度相比冷轧退火板分别提高了 2 MPa及73 MPa.3DAP及TEM表明,退火冷轧板中仅有C原子在晶界处轻微偏聚,N、Ti和Nb均匀分布在晶粒中;而2％预拉伸形变后,C、Ti和Nb在晶界处有不同程度的偏聚现象,根据二者吉布斯自由能和晶界处原子浓度差异得出,TiC多呈矩形状在晶界处优先大量析出,NbC微量析出;2％预拉伸形变烘烤后,C、Ti和Nb在品界处偏聚更明显,NbC呈椭球形在晶界处大量析出,TiC微量析出,不同状态下的N原子分布都较为均匀,而Ti、Nb碳化物则以复合析出的形式出现.
利用同步差热分析仪对SK85钢冷轧板进行球化退火工艺模拟.采用光学显微镜、扫描电镜、硬度计等研究变形珠光体和粒状珠光体形态对球化组织与性能的影响.结果表明,随着退火温度的升高,两种形态珠光体试样的球化硬度先降低后升高,在740～750℃时为最小值.当退火温度低于740℃时,球化组织为粒状珠光体,变形珠光体的球化速度大于粒状珠光体,退火硬度大于粒状珠光体试样.当退火温度高于750 ℃时,球化组织均为片层珠光体和粒状珠光体,两者硬度变化趋于一致.粒状珠光体球化后获得的碳化物颗粒尺寸大于变形珠光体,是粒状珠光体球化硬度小于变形珠光体的原因.通过软化退火工艺设计调节碳化物弥散度可以进一步降低SK85钢冷轧板的硬度,满足冷冲压行业要求.
针对多股绞丝焊接的S32205双相不锈钢焊接接头,进行1080 ℃固溶处理.采用电子背散射衍射、扫描电镜、电子万能试验机以及电化学试验等手段,对比分析了固溶处理对焊接接头显微组织、力学性能以及耐点蚀性能的影响.结果表明,经过1080 ℃固溶处理,焊接接头主要合金元素得到充分扩散,组织更均匀,焊缝奥氏体体积分数增加11.2％,两相比例更均衡;焊接接头的平均抗拉强度提高了 32.7 MPa,塑性略有改善,同时焊接接头的耐点蚀性能也有明显的提高.
利用JMatPro7.0软件模拟预测20Mn23AlV无磁钢的平衡相组成、析出相元素成分、奥氏体化元素含量对无磁钢组织的影响、淬透性、力学性能及热物理性能参数.将模拟参数与部分试验所得数据进行对比分析.计算结果表明,该无磁钢奥氏体占比高达99.89％,其余为第二相强化作用的弥散相,弥散相中占比最多的为金属钒的碳氮化物.该无磁钢在不同冷速下并不会引起组织转变,均为奥氏体相.Mn和Al含量要控制在一定的范围内才能使奥氏体占比最大化.预测和实测力学性能差异不大.随温度的降低,线膨胀系数、比热容、泊松比和导热系数均减小,密度、剪切模量、电导率和杨氏模量均随温度降低而增大.
利用光学显微镜、扫描电镜、硬度计和电子万能试验机研究了温成形温度对38Si7弹簧钢变形抗力和显微组织的影响,并探讨了原始组织对淬火+回火处理后38Si7弹簧钢组织性能的影响,同时,研究了淬火+回火处理工艺参数对弹簧钢组织性能的影响.结果表明,温成形温度为720～800 ℃时,38Si7弹簧钢的变形抗力较高,为225.6～242.2 MPa.温成形温度选择800 ℃,该条件下38Si7弹簧钢的组织均匀性较好.淬火温度的控制是调控残留铁素体的含量和形貌的主要因素,淬火温度≥880 ℃,可大大减少38Si7弹簧钢中铁素体的含量.随着淬火温度的升高,38Si7弹簧钢的强度和硬度不断增大,断后伸长率呈先减小后增大的特征.淬火温度为900 ℃时,38Si7弹簧钢的综合力学性能最好,抗拉强度、硬度和断后伸长率分别为1396.8 MPa、40 HRC和12.5％,屈强比为0.9.油淬会导致网状铁素体的形成,对力学性能不利.回火温度为410～430℃时,回火温度的变化对试样的组织性能无明显影响,而回火温度为450 ℃时,强度和硬度明显降低,塑性提高.38Si7弹簧钢最佳的热处理工艺为900 ℃ ×30 min,水淬+430 ℃×60 min,空冷.
通过OM、SEM、DSC、XRD等分析技术及拉伸、导电率检测手段,对不同单级固溶过程中Al-Zn-Mg-Cu合金微观组织及性能进行表征,研究了不同固溶工艺对合金组织及性能的影响.结果表明,合金在475～482 ℃范围内进行固溶处理,7055铝合金板材中的第二相发生回溶,基体中残留的第二相含量逐渐减少,合金的导电率显著下降,强度呈先上升后下降趋势,且当固溶温度为479 ℃,保温时间为1 h时,合金的综合力学性能最优,屈服强度与抗拉强度分别达到377、544 MPa.
以17Cr2Ni2Mo和20CrNi2Mo合金钢为例,在前人扩散系数计算模型D(T,C)的基础上添加合金因子Q,提出了一种新的扩散系数的计算模型D(T,C,Q),同时与另一扩散系数模型D(T,C,M)进行比较,利用DEFORM软件对两种合金钢的渗碳过程进行了模拟分析,再通过剥层试验对模拟结果进行验证.结果表明,考虑合金元素影响的D(T,C,Q)与D(T,C,M)模型要比D(T,C)模型模拟精度高.17Cr2Ni2Mo钢的D(T,C,Q)模型的模拟精度要高于D(T,C,M)模型,20CrNi2Mo钢的D(T,C,M)模型的模拟精度要稍高于D(T,C,Q)模型,说明D(T,C,Q)模型在计算扩散系数时具有较高的准确性.
