等温温度对低合金复相钢力学性能的影响

研究了质量分数为0．4％C、1．5％Si、1．5％Mn、0．95％Cr、添加微量稀土的试验钢的力学性能，试验钢由真空感应炉熔炼，经扩散退火、等温淬火处理后，利用扫描电子显微镜进行组织观察分析和XRD定量分析。结果表明，试验铸钢经适当的等温淬火处理后，可获得无碳化物析出的奥氏体-贝氏体复相组织，该复相钢残余奥氏体含量约为8％，具有良好力学性能，硬度值为46．5HRC，冲击韧度值αk=162．843J／cm^2。     

等温淬火工艺对奥-贝铸钢组织和性能的影响

研究等温淬火工艺因素(奥氏体化温度、等温淬火温度、等温淬火时间等)对奥氏体 贝氏体铸钢显微组织和力学性能的影响的试验结果表明,选定成分的高碳(0 75%)高硅(2 4%)铸钢,在280～360℃范围内经等温淬火处理后,可以获得无碳化物析出的奥氏体-贝氏体组织,且随着等温淬火温度的升高,贝氏体形貌由针状下贝氏体逐渐向羽毛状上贝氏体转变。试验结果还表明,等温淬火工艺对力学性能的影响较复杂,奥氏体化温度和时间为900℃×120min、等温淬火温度和时间为320℃、120min时,可以获得较佳的综合力学性能。     

75Si2Mn1.5CrB等温淬火工艺及性能研究

研究了新型的高碳合金75Si2Mn1.5CrB在250℃等温淬火工艺下的组织和力学性能。结果表明,75Si2Mn1.5CrB铸钢经920℃奥氏体化后进行250℃保温不同时间的淬火处理后,组织均为带有奥氏体薄膜的贝氏体铁素体+马氏体+残余奥氏体。75Si2Mn1.5CrB经250℃保温1 h处理,其硬度和耐磨性最佳。     

等温淬火对中碳低合金高硅铸钢力学性能的影响

研究了等温淬火工艺参数对化学成分(质量分数)为0.42%C,2.1%Si,1.64%Mn,0.9%Cr中低碳低合金铸钢力学性能的影响.光学显微组织、透射电镜组织以及XRD物相分析结果表明,试样在340～380℃范围内经等温淬火处理后,可以获得无碳化物析出的奥氏体-贝氏体组织,且随着等温淬火温度的升高,贝氏体形貌由板条状下贝氏体逐渐向上贝氏体转变,试样的硬度≥HRC 40,冲击韧性ak≥120 J/cm2.     

化学成分对奥氏体-贝氏体铸钢组织与性能的影响

系统地研究了碳、硅成分对奥氏体－贝氏体铸钢显微组织和力学性能的影响。试验结果表明，设定成分的铸钢，在合理等温淬火工艺条件下，可以获得无碳化物析出的奥氏体－贝氏体组织，含有该组织的铸钢具有良好的综合力学性能。     

Si、Mn复相耐磨铸钢复相热处理组织与性能研究

测定了以Ｓｉ、Ｍｎ为主合金化元素的耐铸钢的ＴＴＴ曲线,曲线存在明显的海湾,贝氏体转变区域较宽;根据ＴＴＴ曲线,研究分析了这种耐磨铸钢在不同工艺条件下等温淬火复相热处理后组织、性能;结果表明,等温淬火复相蝗所得 组织为板条状贝氏体铁素体和奥氏体、贝氏体铁素体间距随等温的升高而变宽,奥氏体量增我,其强度,硬度下降,塑韧性提高。     

ZG75Si2Mn1CrB钢的等温淬火工艺

利用光学显微镜、洛氏硬度计和摆锤式冲击试验机对新型的高碳低合金钢ZG75Si2Mn1 CrB进行了低温条件下等温淬火工艺和组织力学性能的研究.结果表明,ZG75Si2Mn1 CrB钢经200℃等温淬火,能够获得贝氏体铁素体与奥氏体、马氏体和残留奥氏体的混合组织.该钢种理想的等温淬火工艺为920℃奥氏体化,200℃等温22 h,其硬度为49.16 HRC,冲击吸收能量为28 J.低温等温淬火不但使组织细化,且能提高耐磨性降低生产成本.综合力学性能也有改善.     

75Si2Mn1.5CrB铸钢等温淬火组织及力学性能

对新型的高碳低合金75Si2Mn1.5CrB钢进行了在200℃等温淬火工艺组织和力学性能的研究。利用激光显微镜、透射电子显微镜(TEM)和X射线衍射仪(XRD)对等温淬火处理的试验用钢进行了观察和分析。结果表明,75Si2Mn1.5CrB钢经920℃奥氏体化快冷至200℃等温处理后,组织为带有奥氏体薄膜的贝氏体铁素体、马氏体和残留奥氏体。75Si2Mn1.5CrB钢在200℃等温22 h时,其综合力学性能良好。     

中碳低合金贝氏体钢力学性能研究

本文主要通过实验研究了铸态空冷贝氏体钢的热处理工艺和综合性能。根据合金元素的作用通过正交分析设计一种中碳合金钢,以Cr,Mn,Si为主要合金元素,辅以少量的Cu,Mo,经铸造成型及奥氏体化处理后直接空冷获得贝氏体组织。采用冲击实验机和洛氏硬度计对获得的贝氏体钢进行力学性能测试;利用金相显微镜和扫描电镜对其微观组织和形貌进行分析。结果表明:该合金在920℃淬火下具有很好的强韧配合(硬度≥53 HRC;αK≥23 J/cm2).因此,该铸钢是一种生产工艺简便,成本低,具有很好的强韧匹配和较高的中碳低合金贝氏体钢。     

淬火合金钢中的奥氏体稳定化

研究了马氏体(M)和贝氏体(B)两相温度区等温淬火组织中的奥氏体稳定化．在一定等温时间内，奥氏体稳定化程度，即残余奥氏体量与等温温度间的关系呈马鞍型曲线．在实验钢中，其谷底值低于用同冷却介质淬火组织中的AR，表明在一定条件下等温停留并不引起残余奥氏体量增多．可利用马鞍型曲线调整AR与M及B的含量配比，获得无变形或强韧性配合最佳的准贝氏体等温淬火工艺．奥氏体稳定化为热稳定化、化学稳定化、相致稳定化和宏观热应力稳定化诸机制的综合作用．马氏体临界点Mc点无特殊物理意义。     

均热温度对不同成分980 MPa级高强钢组织和性能的影响

采用Gleeble-3500热模拟试验机对两种不同成分的1.4 mm厚冷硬带钢进行退火热模拟试验,并利用万能拉伸试验机、光学显微镜、扫描电镜、EDS对所得热模拟退火试样进行力学性能和组织分析。结果表明,其他退火参数相同,低C高Mn成分前提下,添加合金元素Cr、Mo及高Si含量的C-Mn-Si(高)+Cr+Mo钢和不添加合金元素Cr、Mo且低Si含量的C-Mn-Si(低)钢经760、780 ℃均热退火可得到力学性能满足要求的980 MPa级双相钢。不同均热温度下,C-Mn-Si(高)+Cr+Mo钢组织均为铁素体、岛状马氏体和少量贝氏体,区别在于均热温度高的铁素体晶粒细小且数量较多,呈凹凸不平形貌,马氏体含量少一些,贝氏体呈针状或团簇状;C-Mn-Si(低)钢组织则由铁素体、马氏体、少量的贝氏体和残留奥氏体组成,区别在于均热温度高,铁素体晶粒细化,轧制特征不明显,马氏体含量少,贝氏体呈粒状且量较少。残留奥氏体呈亮白色条状,这种亮白色的特征主要是因为Mn的局部富集。两种试验钢组织差异本质上是Cr、Mo和Si 3种合金元素的含量差异影响过冷奥氏体稳定性引起的。     

Macro and microstructural characterisation of high Si cast steels – Study of microsegregation patterns

In this study the as-cast macro and microstructures of medium C – high Si cast steels of three different levels of alloying are characterised. The application of a colour-etching reagent sensitive to Si segregation effectively revealed the solidification macrostructure, showing that the patterns of macrostructure and microsegregation are governed by the initial precipitation of δ-ferrite dendrites. A study of microsegregation carried out using advanced EDS techniques showed that, for the studied chemical compositions, Si, Mn, Cr, Ni, Mo and Al tend to concentrate at the last liquid to solidify. Accordingly, effective partition coefficients of values below unity were calculated for all alloying elements tested. It was verified that the minimum local Si contents measured on the steels investigated were greater than 1.7%, value above the minimum value (1.5%) necessary to obtain carbide-free bainite after austempering.     

Microstructure and pitting corrosion of similar and dissimilar stainless steel welds

Abstract

Pitting Corrosion behaviour of similar and dissimilar metal welds of three classes of stainless steels, namely, austenitic stainless steel (AISI 304), ferritic stainless steel (AISI 430) and duplex stainless steel (AISI 2205), has been studied. Three regions of the weldment, i.e. fusion zone, heat affected zone and unaffected parent metal, were subjected to corrosion studies. Electron beam and friction welds have been compared. Optical, scanning electron microscopy and electron probe analysis were carried out to determine the mechanism of corrosion behaviour. Dissimilar metal electron beam welds of austenitic–ferritic (A–F), ferritic–duplex (F–D) and austenitic–duplex stainless steel (A–D) welds contained coarse grains which are predominantly equiaxed on austenitic and duplex stainless steel side while they were columnar on the ferritic stainless steel side. Microstructural features in the central region of dissimilar stainless steel friction welds exhibit fine equiaxed grains due to dynamic recrystallisation as a result of thermomechanical working during welding and is confined to ferritic stainless steel side in the case of A–F, D–F welds and duplex stainless steel side in the case of D–A welds. Beside this region bent and elongated grains were observed on ferritic stainless steel side in the case of A–F, D–F welds and duplex stainless steel side in the case of D–A welds. Interdiffusion of elements was significant in electron beam welding and insignificant in friction welds. Pitting corrosion has been observed to be predominantly confined to heat affected zone (HAZ) close to fusion boundary of ferritic stainless steel interface of A–F electron beam and D–F electron beam and friction weldments. The pitting resistance of stainless steel electron beam weldments was found to be lower than that of parent metal as a result of segregation and partitioning of alloying elements. In general, friction weldments exhibited better pitting corrosion resistance due to lower incidence of carbides in the microstructure.     

冷轧对M50钢马氏体/贝氏体复相组织与力学性能的影响

利用X射线衍射仪(XRD) 、扫描电镜(SEM) 、透射电镜(TEM)、室温拉伸和冲击性能测试研究了冷轧对M50钢马氏体/贝氏体(M/B)复相组织和性能的影响。结果表明:20%冷轧变形量的试样经等温淬火后具有最佳的抗拉强度(2535.7 MPa)和冲击性能(96.93 J),相比变形量为0%的试样,冲击吸收能量提高了约21%,抗拉强度提高了约5%。当变形量小于20%时,随着变形量的增加,M/B复相组织逐渐细化且在20%的冷轧变形量下组织最细;当变形量大于20%时,随着变形量的增加,贝氏体束减少,其对马氏体板条的分割作用减弱,导致组织呈现一定的粗化。     

Effect of annealing temperature on the corrosion behavior of duplex stainless steel studied by in situ techniques

The effects of the annealing temperature on the microstructure and the corrosion behavior of duplex stainless steel 2507 were investigated by means of magnetic force microscopy (MFM), scanning Kelvin probe force microscopy (SKPFM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The SEM results indicated that the volume fraction of the austenite phase decreased with the increased annealing temperature. SKPFM/MFM measurements conducted in air at the room temperature and an ambient relative humidity of about 25% showed a higher Volta potential of the paramagnetic austenite than that of the ferromagnetic ferrite. The in situ AFM observation in a hydrochloric acid solution provided solid evidence that corrosion preferentially occurred in the ferrite phase. The sample annealed at 1100 °C exhibited a greater Volta potential difference between the ferrite and austenite and a higher corrosion rate in the ferrite, while that annealed at 1150 °C had a smaller Volta potential difference and a lower corrosion rate. The relative nobility and microstructure change of two phases, as well as their corrosion behavior, can be explained by the effect of the composition of alloying elements.     

Study of austempering kinetics of high silicon bainitic cast steels

This study investigates the effect of chemical composition and microsegregation on the bainitic transformation of high Si cast steels at two different austempering temperatures. The advance of the bainite precipitation as a function of time and temperature was monitored through measurements of the amount of retained austenite by X-ray diffraction, the evolution of hardness and microstructural characterization. The results showed that the bainitic transformation starts preferentially at zones with lower contents of alloying elements but later covers the entire matrix. The austempering heat treatments resulted in an apparently homogeneous bainitic microstructure throughout the entire matrix after a short period of time. The results encourage the continuation of the development of high Si steels suitable to produce carbide-free austempered cast parts.     

Selektive Korrosion von Duplexstahl. Teil 2: Lokale Korrosionserscheinungen an Duplexstahl X2CrNiMoN22‐5‐3 unter Einwirkung von Chloriden und mechanisches Verhalten in Abhängigkeit vom Gefügezustand

Selective corrosion of duplex stainless steel. Part 2: Localized corrosion manifestations under exposure of chlorides on duplex stainless steel X2CrNiMoN22‐5‐3 and mechanical behavior in dependence of the microstructure In completion to part 1 of this paper this part deals with interrelations between localized corrosion manifestations, mechanical properties and the microstructure of duplex stainless steel X2CrNiMoN22‐5‐3. The pit formation on duplex stainless steels is substantially determined by the distribution of the alloying elements within single phases and by defects in the oxide layer. The positive properties of molybdenum become ineffective at thicker oxide layers due to the fact, that molybdate, which is responsible for inhibition of pitting, can not be formed. Depletion areas caused by precipitations are preferential attack places for corrosion. The influence of chlorides for duplex stainless steels in rolled and welded conditions is characterized by a logarithmic dependence.     

碳含量及合金元素对低温盐浴渗铬层的影响

以45钢、T10钢及3Cr2W8V钢为例,使用OM、SEM等方法,研究了碳以及合金元素含量对低温盐浴渗铬层的影响.结果表明,钢的碳含量在低温盐浴渗铬过程中起到了促进作用,能增加渗铬层的深度,提高渗层的显微硬度和铬浓度,T10钢表面铬浓度为85.4％,45钢为81.3％,T10钢表面硬度为1 380 HV,45钢为1 290 HV;而合金元素则起到了阻碍作用,减少了渗铬层的深度,渗层的显微硬度和铬浓度均有所下降,3Cr2W8V钢表面硬度为1 280 HV,表面铬浓度为76.3％.     

Assessment of the microstructure evolution of an austempered ductile iron during austempering process through strain hardening analysis

The aim of this investigation was to determine a procedure based on tensile testing to assess the critical range of austempering times for having the best ausferrite produced through austempering. The austempered ductile iron (ADI) 1050 was quenched at different times during austempering and the quenched samples were tested in tension. The dislocation-density-related constitutive equation proposed by Estrin for materials having high density of geometrical obstacles to dislocation motion, was used to model the flow curves of the tensile tested samples. On the basis of strain hardening theory, the equation parameters were related to the microstructure of the quenched samples and were used to assess the ADI microstructure evolution during austempering. The microstructure evolution was also analysed through conventional optical microscopy, electron back-scattered diffraction technique and transmission electron microscopy. The microstructure observations resulted to be consistent with the assessment based on tensile testing, so the dislocation-density-related constitutive equation was found to be a powerful tool to characterise the evolution of the solid state transformations of austempering.