变形速率对2205双相不锈钢形变诱导相变的影响

通过单道次压缩热模拟试验,研究了2205双相不锈钢在热变形过程中组织组成相奥氏体相(γ)和铁素体相(δ)所占比例的变化情况.分析得到:2205双相不锈钢在热变形过程中存在奥氏体相和铁素体相之间的相互转变,且热变形过程中发生的两相之间的相互转变也是2205双相不锈钢热变形过程中的一种动态软化机制.变形速率对2205双相不锈钢热变形过程中发生的相转变的影响规律为:变形速率很小时,δ→γ的转变占较大比重;随着变形速率的升高,γ→δ所占比例增加.     

双相不锈钢热变形行为研究

采用高温压缩实验方法研究了两种不同氮含量双相不锈钢00Cr22Ni5Mo3N和00Cr22Ni1Mo0.7N在1 000~1 200℃温度范围内、应变速率为0.01~30 s-1条件下的热变形行为.根据实验数据构建了两种双相不锈钢的热变形方程,两种双相不锈钢的形变激活能分别为534 kJ/mol和482 kJ/mol.通过对微观组织的观察和分析,确定了较高温度且较低应变速率区域为优化的热加工区域.在该优化的热加工区域进行变形时,奥氏体和铁素体发生充分的动态再结晶和动态回复;而在较低温度、较高应变速率区域进行变形时,微观组织呈现强烈的局部流变,甚至可以观察到裂纹.     

双相不锈钢超塑性变形机理

从材料的晶体结构出发,研究了双相不锈钢超塑性变形的机理.利用背散射电子衍射花样分析系统(EBSD),获得了双相不锈钢变形过程中的ODF图、极图和取向与转轴分布等晶体取向分布规律.结合透射电镜对微观组织的观察结果进行了综合分析.研究表明,双相不锈钢超塑性变形的机理为形变诱导析出和动态再结晶、晶界滑移以及变形中的晶粒转动.     

Cr21节约型双相不锈钢的高温塑性

通过高温拉伸和高温压缩试验研究了两种Cr21节约型双相不锈钢在950～1150℃温度范围内的高温塑性,结果表明两种材料的高温塑性差异很大.通过温度、应变速率、相比例和显微组织4个方面的分析发现,适当增加稳定铁素体相元素和升高变形温度有利于提高Cr21节约型双相不锈钢的高温塑性.在较低温度较高应变速率热变形时,裂纹容易在被拉长的奥氏体和铁素体相界处形核并沿着相界在铁素体内进行扩展.     

Zeron100双相不锈钢材料组织结构的EBSD分析

利用电子背散射衍射(EBSD)技术对Zeron100双相不锈钢的微观结构进行了研究。在利用EBSD对Zeron100双相不锈钢热处理进行快速相鉴别和相分布的分析中发现,随着热暴露时间的延长(热暴露温度为850℃),材料的铁素体相含量减少而脆性金属间化合物增多,从而使材料的脆性提高而抗蚀性能降低。在利用EBSD对Zeron100双相不锈钢的奥氏体和铁素体的取向关系的分析表明两相符合Kurdjumov-Sachs(K-S)取向关系。偏离理想取向关系的角度分布在0°～4°,大多数集中在1°～2°,这个分析结果与理论计算的结果符合较好。     

不同应变速率热变形双相不锈钢的取向特征

在MMS-200热模拟实验机上,对S32750超级双相不锈钢在1 000℃,应变速率为0.01～10 s-1的条件下进行了高温压缩实验,利用电子背散射衍射(EBSD)技术对其晶体取向和晶界特征进行了分析.研究结果表明:在低应变速率时,铁素体晶粒出现〈111〉∥压缩轴织构;在高应变速率时,〈001〉织构又明显增加.铁素体晶粒随着应变速率的增加变得细小,而小角度晶界数量增加;在应变速率为10 s-1时,形变后奥氏体晶粒得到了〈110〉织构.应变速率的增加使奥氏体晶粒变大,小角度晶界数量增加.奥氏体相在小应变速率条件下变形可以获得更多的Σ3孪晶界.     

高纯Cr17铁素体不锈钢的热变形行为

采用MMS200热/力模拟机及Thermo-Calc热力学计算方法,研究了高纯Cr17铁素体不锈钢在变形温度为600～1 100℃、应变速率为1～10 s-1条件下的热变形规律.结果表明,在热变形过程中,高纯Cr17铁素体不锈钢的组织均以铁素体为主,不存在γ/α相变且仅仅发生较快的动态回复软化;高纯Cr17铁素体不锈钢热的变形激活能为384.985 kJ/mol.在此基础上,确定了Z参数,并得到了高纯Cr17铁素体不锈钢的峰值应力σp与Z参数间的关系.     

双相钢不锈钢药芯焊丝堆焊试验

双相不锈钢在室温下固溶体中奥氏体和铁素体约各占半且兼有两相组织特征。它保留了铁素体不锈钢导热系数大、线膨胀系数小、耐点蚀,缝蚀及氯化物应力腐蚀性能的特点;又具备奥氏体钢不锈钢韧性好、脆性转变温度较低、抗晶间腐蚀、力学性能和焊接性能好的优点,双相不锈钢堆焊层的力学性能和耐蚀性取决于接头能否保持适当的相比例,正确选用焊接材料、严格控制焊接热输入量以及制定合理的焊接工艺是是双相不锈钢焊接的关键,本文进行了双相不锈钢药芯焊丝堆焊工艺试验、焊接工艺评定及产品的施焊,各项技术指标均满足要求,证明所选用的焊接方法、焊接材料、焊接工艺规范正确合理。     

铁素体/贝氏体双相X80管线钢疲劳性能研究

采用MTS Landmark 370型万能机研究了全壁厚铁素体/贝氏体双相X80管线钢的疲劳性能,并通过SEM方法对钢的组织及断口进行了分析。结果表明,铁素体/贝氏体双相钢中的铁素体有大角度晶界,而贝氏体由小角度晶界的贝氏体铁素体及细小的马氏体/奥氏体(M/A)岛构成。疲劳裂纹主要在钢板表面凹坑处萌生;疲劳强度S与寿命N的关系为S=2 973×N-0.14;在裂纹扩展过程中,铁素体晶界、贝氏体及贝氏体组织中的M/A岛对疲劳裂纹扩展有抑制作用。     

含稀土的23Cr型双相不锈钢的高温变形行为

利用Gleeble-3500热力模拟试验机在950~1200℃,应变速率为0.1~10s-1条件下进行了含稀土的23Cr型双相不锈钢的热压缩变形,获得了流变曲线,建立了热变形方程,分析了变形组织。结果表明:在流变曲线上既存在峰值应力也有稳态应力;在高温低应变速率条件下,峰值应变减小。上述变形条件下,试验钢的热变形激活能Q=436kJ/mol,表观应力指数n=3.91,热变形方程为:ε=2.41×1016[sinh(0.012σs)]3.91exp (-436000/RT)。奥氏体的动态再结晶在试验钢的动态软化机制中起主导作用且随着温度的升高和应变速率的降低越来越充分;而大应变下,铁素体的软化主要表现为较充分的动态回复。稀土元素影响了热变形时两相中Mo元素的再分配是稀土改善双相不锈钢高温塑性的重要原因之一。稀土使Mo在铁素体中浓度较低温度下降低,高温下升高;而奥氏体相中,使得Mo浓度在较低温度下升高而高温下降低。     

Mechanism of hot-rolling crack formation in lean duplex stainless steel 2101

The thermoplasticity of duplex stainless steel 2205 (DSS2205) is better than that of lean duplex steel 2101 (LDX2101), which undergoes severe cracking during hot rolling. The microstructure, microhardness, phase ratio, and recrystallization dependence of the deformation compatibility of LDX2101 and DSS2205 were investigated using optical microscopy (OM), electron backscatter diffraction (EBSD), Thermo-Calc software, and transmission electron microscopy (TEM). The results showed that the phase-ratio transformations of LDX2101 and DSS2205 were almost equal under the condition of increasing solution temperature. Thus, the phase transformation was not the main cause for the hot plasticity difference of these two steels. The grain size of LDX2101 was substantially greater than that of DSS2205, and the microhardness difference of LDX2101 was larger than that of DSS2205. This difference hinders the transfer of strain from ferrite to austenite. In the rolling process, the ferrite grains of LDX2101 underwent continuous softening and were substantially refined. However, although little recrystallization occurred at the boundaries of austenite, serious deformation accumulated in the interior of austenite, leading to a substantial increase in hardness. The main cause of crack formation is the microhardness difference between ferrite and austenite.     

Effect of superplastic deformation on precipitation behavior of sigma phase in 3207 duplex stainless steel

Owing to excellent strength, toughness and corrosion resistance, duplex stainless steels(DSS) are widely used in constructional and petrochemical applications. Sigma phase, which has detrimental impact on the properties, is readily precipitated during hot working of DSS. However, precipitation behavior of sigma phase during superplastic deformation, which is the most significant processing method of DSS, is still unclear. In the current study,the effect of superplastic deformation on the precipitation behavior of sigma phase was investigated in 3207 duplex stainless steel. The result shows that superplastic deformation could prevent sigma phase precipitation generally by increasing mobility of grain boundaries and decreasing misorientation of the sigma phase boundaries, resulting in some sigma phase precipitated on the twin boundaries. Most of the sigma phase precipitated on ferrite-austenite interface with misorientation of 20–25°, while it precipitated in ferrite or austenite with the misorientation of 40°–45°. The orientation relationship between sigma phase and matrix matched well in austenite and on the ferrite/austenite interfaces, while it showed a small misfit in ferrite. The prevention effect of the superplastic deformation on the sigma phase precipitation was beneficial to quasi stable deformation stage,resulting in longer elongation.     

碳、锰含量对低碳(锰)钢过冷奥氏体形变过程中铁素体形核率的影响

研究了碳、锰含量对低碳(锰)钢形变强化铁素体晶粒数目变化的影响.结果表明,形变使低碳(锰)钢过冷奥氏体内部形核位置增加,铁素体形核率显著提高,晶粒大大细化.碳、锰含量提高有利于钢中过冷奥氏体累积变形的增加,形变强化相变晶粒细化能力增强,而碳的促进作用尤为显著.     

Mechanical properties and kinetics of thermally aged Z3CN20.09M cast duplex stainless steel

Cast stainless steels used in nuclear power plants suffer from fracture toughness losses owing to thermal aging after long-term service at temperatures ranging from 280-320℃. To study the thermal aging embrittlement of Z3CN20.09M duplex stainless steel produced in China, accelerated thermal aging experiments were carried out at 350, 380, and 400℃ for up to 10000 h. Microhardness and Charpy impact energies were measured at different aging times. The microhardness of ferrite increased drastically over the initial aging time of 2000 h at 380 and 400℃ and then slowly reached HV_0.01 560. In contrast to this observed change in microhardness, Charpy impact energies sharply decreased after initial aging and then gradually reached a minimum value. Taking the microhardness of the ferrite phase as the parameter describing the thermal kinetics of the stainless steel samples, the activation energy of thermal aging was calculated to be 51 kJ/mol. Correlations between the thermal aging parameter, P, and ferrite microhardness and between P and Charpy impact energy were also analyzed. The results showed that the activation energy calculated from the ferrite microhardness is much more reasonable than that obtained using other parameters, such as chemical composition and impact energy.     

奥氏体变形及冷却速率对低碳贝氏体组织中大角晶界分布的影响

使用电子背散射衍射技术研究了低C高Mn高Nb成分设计下,非再结晶奥氏体变形及加速冷却速率对低碳贝氏体组织取向差特征和大角晶界分布的影响.结果表明,与原奥氏体晶粒内部的相变组织相比,原奥氏体晶界附近具有更高的大角晶界密度,非再结晶区奥氏体变形及快速冷却都有利于提高共格相变的驱动力、弱化变体选择以及有效增加大角晶界密度.此外,非再结晶区的大变形除了可充分压扁奥氏体晶粒和增加单位面积的奥氏体晶界密度外,还导致奥氏体晶界上细小的非共格转变铁素体晶粒生成,且这些铁素体晶粒与相邻组织表现出大取向差.     

时效处理对2205 DSS组织及力学性能的影响

首先对2205 DSS进行了1 100℃固溶处理,随后将试样分别在650,700,750,800,850和900℃下进行不同时间的时效处理,探究2205 DSS中σ相的析出规律及其对材料组织和力学性能的影响.研究结果表明:2205 DSS中σ相的析出分为有碳化物伴随和无碳化物伴随两种方式,前者发生在α-γ相界上,后者则主要发生在α相的晶内和晶界;2205 DSS在850℃时效时σ相的析出行为最严重;在析出σ相后,合金元素Cr和Mo在各相中会发生不同程度的偏聚;2205 DSS中析出少量的σ相对材料的塑性影响不大,但会显著降低材料的冲击韧性,而σ相的大量析出则会使两者均发生严重恶化;σ相的析出对材料的屈服强度影响不大,对材料的抗拉强度有略微的提高作用.