T91铁素体耐热钢过冷奥氏体转变过程中临界冷却速度的研究

利用DIL805A/D高精度差分膨胀仪,通过线膨胀行为测量与微观组织分析,获得T91铁素体耐热钢连续冷却转变过程中相关动力学信息,结合冷却后T91钢组织特征,确定了T91钢过冷奥氏体转变过程中的临界冷却速度.研究表明:T91钢过冷奥氏体连续冷却过程中只存在铁素体和马氏体转变区,而不出现贝氏体和珠光体转变.在冷却速度为10K/min时该钢获得完全板条马氏体组织,9K/min时组织中开始出现铁素体,即10K/min可以定为T91钢奥氏体向马氏体转变的上临界冷却速度;当冷却速度介于3～9K/min时为马氏体和铁素体的混合组织,冷却速度为2K/min时T91钢中不存在马氏体转变,室温组织为铁素体,即2K/min可以定为T91钢奥氏体向马氏体转变的下临界冷却速度.     

环境温度对Fe-14Mn-0.22C合金阻尼性能的影响

为了了解Fe-Mn基阻尼合金的高温阻尼性能,用真空感应电炉的方法制备了Fe-14.04Mn-0.22C合金.用倒扭摆内耗仪测试了环境温度在23～400℃变化时合金阻尼性能的变化规律,并用热机械分析仪和光学显微镜分析了合金的组织结构及其相变特点.研究结果表明,在常温条件下合金的阻尼性能随扭转应变的增加而呈线性方式增加,扭转应变在1×10-4时,对数衰减率达0.1,且没有出现峰值;随着环境温度的变化,对数衰减曲线与应变的线性关系没有发生改变,但是曲线发生了整体的上下平移;当环境温度低于200℃时,合金的阻尼性能随温度的升高而增加,但当温度达到或超过200℃后,合金的阻尼性能迅速下降,其原因在于合金发生了奥氏体转变(As为270℃),马氏体的百分含量降低,阻尼源减少.     

奥氏体不锈钢显微组织状况对使用性能的影响

通过对奥氏体不锈钢非正常显微组织的分析研究，发现导致奥氏体不锈钢钢管失效的一个主要原因是钢管加工工艺在执行的过程中存在偏差，造成其显微组织不均匀，从而使得其耐腐蚀的能力和力学性能迅速下降，降低了管材的使用性能。     

Modeling of microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite

The aim of the current study was to investigate the microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite in thin slab direct rolling （TSDR） processing. A model was developed to predict the change of the austenite grain size during the dynamic recrystallization, by using the law of mixtures. The equations initially developed for partial static recrystallization were used for partial dynamic recrystallization, by adjusting the value of the constant. The results show that the change of the austenite grain size can be reasonably described by using the equations developed according to the law of mixtures.     

含铜奥氏体抗菌不锈钢抗菌性能和机理初步研究

考察了含铜奥氏体抗菌不锈钢的抗菌性能，并对其抗菌机理进行了初步探讨。方法：覆膜法测定杀菌率；透射电镜观察E．coli细胞形态；考马斯亮蓝法测定细胞漏出液中可溶性蛋白含量；琼脂糖凝胶电泳检测菌体基因组DNA考察抗菌不锈钢对DNA的剪切作用。结果：除产气肠杆菌外，奥氏体抗菌不锈钢对其它供试的16种常见微生物均显示较强的抗菌活性，具有广谱抗菌性．在作用9h时可将1×10^7cfu／ml的E．coli全部杀灭，对浓度≤1×10^7cfu／ml的E．coli液在24h内杀灭率达到99．5％。透射电镜结果显示，与奥氏体抗菌不锈钢作用后的E．coli细胞壁和细胞膜破裂，核区不明显；作用后的菌液中可溶性蛋白质含量增加；实验中未检测到有明显的菌体DNA断裂现象．结论：奥氏体抗菌不锈钢具较强的抗菌性能和广谱抗菌性。其作用机理可能为使菌体细胞壁和细胞膜因氧化而破裂，胞内可溶性蛋白漏出，最终导致菌死亡。     

Increasing the wear resistance of stainless steels

The wear resistance of martensitic, austenitic and duplex stainless steels is increased by carbon and nitrogen in solid solution and in addition by carbides and nitrides, which are formed during conventional ingot metallurgy or by powder metallurgical processing. High temperature and low temperature nitriding provide a hard surface zone. Characteristic alloys and applications are discussed, which try to optimize the resistance to wear and corrosion.     

Microstructures and Mechanical Properties of Si-Al-Mn TRIP Steel with Niobium

Microstructure consisting of ferrite, bainite and retained austenite can be obtained through intercritical annealing and isothermal treatment in bainite transformation region for low silicon TRIP (transformation induced plasticity) steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that as strain rate ranges from 10-2 to 10-4 s-1, the volume fraction of transformed martensite from retained austenite,as well as tensile strength, elongation rate and strength-ductility product, increases. When Nb is added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. While Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility. Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400℃. The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.     

Effect of austenitization heat treatment on the magnetic properties of Fe-40wt % Ni-2wt % Mn alloy

The effect of austenitization heat treatment on magnetic properties was examined by means of M6ssbauer spectroscopy on an Fe-40wt%Ni-2wt%Mn alloy. The morphology of the alloy was obtained by using scanning electron microscopy （SEM） under different heat treatment conditions. The magnetic behavior of the non heat-treated alloy is ferromagnetic. A mixed magnetic structure including both paramagnetic and ferromagnetic states was obtained at 800℃ after 6 and 12 h heat treatments. In addition, the magnetic structure of the heat-treated alloy at 1150~C for 12 h was ferromagnetic. With the volume fraction changing, the effective hyperfine field of the ferromagnetic austenite phase and isomery shift values were also determined by Mtssbauer spectroscopy.     

Contactless Electrical Conductivity Measurement of Electromagnetically Levitated Metallic Melts

A facility for noninvasive measurements of the electrical conductivity of liquid metals above and below the melting temperature is presented. It combines the containerless positioning method of electromagnetic levitation with the contact-less technique of inductive conductivity measurement. Contrary to the conventional measurement method, the sample is freely suspended within the measuring field and, thus, has no exactly predefined shape. This made a new theoretical basis necessary with implications on the measurement and levitation fields. Furthermore, the problem of the mutual inductive interactions between the levitation and the measuring coils had to be solved.     

Improving the composition of the flux for surfacing chromium-manganese steels

The results of investigation of the effect of the chemical composition of the flux used in surfacing with flux-cored wires are presented and the formation of metastable austenite in the deposited metal is described.