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 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.
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.
研究了性能热处理(Performance heat treatment,PHT)与模拟焊接热处理(Simulated welding heat treatment,SWHT)工艺对顶拔锻造工艺生产的P280GH钢超级管道管嘴力学性能的影响及作用机理.采用光学显微镜、扫描电镜以及能谱分析仪研究了不同热处理工艺对显微组织的影响,并开展了室温与300 ℃高温拉伸、0℃冲击、布氏硬度测试等力学试验.结果表明,PHT热处理后和PHT+SWHT热处理后管嘴的微观结构均主要由铁素体和珠光体两相组成,但经PHT后珠光体主要分布在铁素体晶界处,而经PHT+SWHT后珠光体有球化趋势,而且在铁素体内部亦有珠光体形成.经PHT后的管嘴试样拉伸性能与未经热处理的母材性能基本一致,平均冲击吸收能量高于母材约15 J;而PHT+SWHT热处理后管嘴室温拉伸性能比母材性能平均下降约18 MPa,平均冲击吸收能量下降了约20 J.研究表明,顶拔锻造工艺制造的管嘴显微组织中珠光体的分解与球化是不同热处理工艺试样力学性能变化的主要原因.
通过等离子转移弧焊技术在Q235钢基体上制备了无钴AlxCrFeMnNi高熵合金(HEA)涂层(x=0.2,0.4,0.6,0.8,1).研究了 Al的加入对HEA涂层的相组成、组织和力学性能的影响.结果表明,由于高熵效应,AlxCrFeMnNi HEA涂层主要由简单的BCC和FCC相以及少量碳化物相组成.此外,Al元素的加入抑制了 FCC相的形成.随着Al添加量的增加,枝晶间明显粗化.当Al添加量为0.8时,HEA涂层平均维氏硬度为386.5 HV0.2,平均摩擦因数为0.595,耐磨性能最稳定.
针对锆合金带材冲压成形时易破裂的问题,研究了再结晶退火对Zr-Sn-Nb-Fe-Si新锆合金薄板带材组织性能的影响.结果表明,随着退火温度的升高,新锆合金薄板带材的最大减薄率减小;第二相颗粒弥散分布于新锆合金品粒内部及品界,其形貌基本为球状,尺寸较大第二相为Zr(NbFe)2,较小为β-Nb;新锆合金带材具有<10(1)0>//RD和<11(2)0>//RD两类织构,其中<11(2)0>//RD取向的晶粒与形变基体的取向差为30°/<0001>.随着再结晶退火温度的升高,第二相颗粒产生的钉扎作用不能阻碍锆合金重合点阵Σ13晶界的快速迁移,导致<11(2)0>//RD取向的再结晶晶粒择优长大,吞并形变基体,小角度晶界占比降低,大角度晶界占比升高,造成再结晶织构由<10(1)0>//RD转变为<11(2)0>//RD,改善品粒变形的均匀性,提高带材冲压时塑性变形的均匀程度,因此再结晶退火有利于改善新锆合金薄板带材的冲压成形性能.
通过热力学计算并采用光镜、扫描电镜、X射线衍射仪、洛氏硬度计及冲击试验机等,研究了奥氏体化温度对1.2367热作模具钢显微组织及性能的影响.结果表明,1.2367钢的室温平衡组织为铁素体基体上分布着M23C6、M6C和MC型碳化物,而在1025～1080℃之间淬火时,随着奥氏体化温度的升高碳化物逐渐减少、残留奥氏体量逐渐增加,淬火态组织为马氏体+碳化物+残留奥氏体.在615℃保温2 h两次回火后的组织为回火马氏体+碳化物,随奥氏体化温度的升高,硬度逐渐增加,最高硬度达49.05 HRC,冲击吸收能量逐渐降低.1050℃淬火+615 ℃回火后,1.2367热作模具钢可获得最佳强韧性匹配.
利用拉伸试验机、扫描电镜和X射线衍射仪研究了临界区退火时间对0.21C-4.1Mn-1.85Si-0.05Nb-Fe冷轧中锰钢组织性能的影响.结果表明,随退火时间增加,铁素体比例降低,残留奥氏体含量先增加后降低,马氏体尺寸不断增加,试验钢的屈服强度先升高后逐渐降低,抗拉强度先降低后升高,伸长率和强塑积先增加后逐渐降低.退火10 min,工程应力-工程应变曲线表现为连续屈服,但加工硬化能力不足导致塑性最差.增加退火时间,工程应力-工程应变曲线出现屈服平台,但较大应变范围内不断出现的TRIP效应使得试验钢保持了持续的加工硬化能力,塑性提升.690℃退火60 min,试验钢的综合力学性能最佳,抗拉强度为1036.9 MPa,伸长率 25.6％,强塑积可达 26.5 GPa·％.
对不同Ce含量的H13钢进行1040℃油淬和580 ℃两次冋火处理后进行热疲劳循环试验,采用光学显微镜、扫描电镜及硬度计对不同热疲劳循环次数下试验钢的显微组织、裂纹形貌及硬度进行分析.结果表明,试验钢热疲劳循环后显微组织为回火索氏体,热疲劳裂纹优先在预先处理的缺口尖端处萌生,热疲劳循环过程中出现的氧化凹坑和夹杂物会促使裂纹生成,裂纹不断扩展,宽度增加.稀土 Ce对试验钢组织和晶粒尺寸有明显的细化作用,提升试验钢的抗软化能力,抑制热疲劳裂纹的生长,其中最佳稀土 Ce 含量为 0.026％.
