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 研究了950~1300℃固溶处理对00Cr25Ni7Mo4N超级双相不锈钢组织的影响。结果表明,≤1000℃固溶处理时,钢中有σ相析出,要消除热轧态的σ相,固溶温度应大于1050℃;随着固溶温度升高,铁素体相含量增加,奥氏体相含量下降。最佳固溶处理温度在1050℃~1100℃之间,此时两相比例接近1：1;随着固溶温度的提高,两相的晶粒尺寸在逐渐增大,到了1250℃晶粒明显长大。     

双相不锈钢的研究与发展

简要介绍了双相不锈钢发展史和近期的发展状况;综述了国内外双相不锈钢组织特征转变(铁素体／奥氏体转变和σ相的形成长大)机制、变形机制,以及合金元素含量对其拉伸性能影响规律的研究;展望双相不锈钢有光明的发展前景,可为社会创造更多的经济效益.     

Microstructure Evolution and Strain-Dependent Constitutive Modeling to Predict the Flow Behavior of 20Cr–24Ni–6Mo Super-Austenitic Stainless Steel During Hot Deformation

Hot compression tests were carried out with specimens of 20 Cr–24 Ni–6 Mo super-austenitic stainless steel at strain rate from 0.01 to 10 s~(-1) in the temperature range from 950 to 1150 °C, and flow behavior was analyzed. Microstructure analysis indicated that dynamic recrystallization(DRX) behavior was more sensitive to the temperature than strain rate, and full DRX was obtained when the specimen deformed at 1150 °C. When the temperature reduced to 1050 °C, full DRX was completed at the highest strain rate 10 s~(-1) rather than at the lowest strain rate 0.01 s~(-1) because the adiabatic heating was pronounced at higher strain rate. In addition, flow behavior reflected in flow curves was inconsistent with the actual microstructural evolution during hot deformation, especially at higher strain rates and lower temperatures. Therefore, flow curves were revised in consideration of the effects of adiabatic heating and friction during hot deformation. The results showed that adiabatic heating became greater with the increase of strain level, strain rate and the decrease of temperature, while the frictional effect cannot be neglected at high strain level. Moreover, based on the revised flow curves, strain-dependent constitutive modeling was developed and verified by comparing the predicted data with the experimental data and the modified data. The result suggested that the developed constitutive modeling can more adequately predict the flow behavior reflected by corrected flow curves than that reflected by experimental flow curves, even though some difference existed at 950 °C and0.01 s~(-1). The main reason was that plenty of precipitates generated at this deformation condition and affected the DRX behavior and deformation behavior, eventually resulted in dramatic increase of deformation resistance.     

时效处理对20%冷变形15Cr-15Ni含Ti奥氏体不锈钢组织和高温力学性能的影响

针对钠冷快堆包壳管用15Cr-15Ni含Ti的奥氏体不锈钢,研究了550-750℃时效处理336h对20%冷变形合金组织和650℃拉伸性能的影响。结果表明：在550℃时效336h后,合金发生回复,组织中位错移动产生大量退火孪晶。当在650℃和750℃时效时,合金进一步回复,孪晶数量明显减少,且在组织中发现有Sigma相析出。随时效温度的升高,sigma相数量和尺寸增加。与20%冷变形合金650℃拉伸性能相比,550℃时效态样品拉伸时,合金屈服和抗拉强度略有增加;随着时效温度的升高,合金屈服和抗拉强度显著降低。与拉伸强度相比,时效态合金的延伸率变化趋势与之相反,时效温度升高,合金的延伸率提高。     

18.7Cr-1.0Ni-5.8Mn-0.2N节Ni型双相不锈钢的大变形热压缩软化行为

在1123~1423 K、0.1~10 s^-1条件下对18.7Cr-1.0Ni-5.8Mn-0.2N节Ni型双相不锈钢进行70%大变形量热压缩研究。利用OM、SEM和EBSD分析热变形组织。结果表明,铁素体动态再结晶(DRX)主要发生在1123 K较低变形温度,随应变速率增大,晶粒细化程度增加,晶粒不均匀程度减小。应变速率对铁素体DRX影响较大,而奥氏体DRX对变形温度更加敏感。在1223 K、10 s^-1条件下,铁素体相发生了以小角度晶界(LAGB)向大角度晶界(HAGB)转变的连续动态再结晶(CDRX),而在1323 K、0.1 s^-1条件下,奥氏体相以不连续动态再结晶(DDRX)为主。低应变速率条件下升高温度易诱发DDRX,而在高应变速率条件下易发生CDRX。在高温低应变条件下,奥氏体相晶粒取向主要为(001)和(111)再结晶织构,而铁素体相在(001)和(111)织构之间存在竞争关系。拟合获得临界应力(应变)并确定了其与峰值应力(应变)的关系。随着应变增加,热加工失稳区缩小,且稳定区逐渐向高温高应变速率方向移动,1323~1423 K、0.01~6.05 s^-1的热参数条件最适合热加工。     

00Cr25Ni6Mo3N双相不锈钢的力学性能

00Cr25Ni6Mo3N双相不锈钢可用于要求具有良好力学性能特别是低温冲击韧度的鼓风机叶轮等零件。某公司的00Cr25Ni6Mo3N双相不锈钢锻件低温冲击性能很不稳定。为此,对冲击性能不良的00Cr25Ni6Mo3N钢锻件进行了1050℃、1070℃、1100℃和1050℃保温1.5h水冷的固溶处理,随后测定了力学性能。结果表明:锻件的-40℃冲击吸收能量差异很大,有的达不到要求的27J。金相分析发现,00Cr25Ni6Mo3N钢锻件冲击韧度低的原因是锻造工艺不当析出了金属间相,而且热处理不能消除这种金属间相,严格控制锻造加热制度是解决该问题的唯一途径。     

室温形变对SAF2205双相不锈钢组织的影响

参照U型管制造工艺,在室温和同一形变速率下,对SAF2205双相不锈钢钢管进行不同半径的弯曲。通过定量显微组织观察,发现弯制最小半径的U型管没有发生相变,同时找出了室温形变后使组织发生改变的最小弯曲半径：并对发生改变的组织进行1050℃同溶处理。结果表明：在受压一侧的组织恢复到原始供货状态．而在受拉一侧的组织比例没有恢复到形变以前的状态。     

固溶处理温度对氮强化高锰奥氏体不锈钢组织和性能的影响

研究了固溶处理温度对２２Ｍｎ－１３Ｃｒ－５Ｎｉ－０．２５Ｎ奥氏体不锈钢组织和性能的影响。结果表明，随固溶处理温度提高，奥氏体晶粒尺寸增大，强度降低，延伸率和断面收缩率变化不大。在拉伸变形过程中沿，面产生形变孪晶，先形成的形变孪晶阻碍位错运动，使强度进一步增加。     

Experimental Investigation on Friction Welding of UNS S32205 Duplex Stainless Steel

UNS S 32205 duplex stainless steel specimens were joined by continuous drive friction welding process. The experiments were conducted as per the Taguchi（L16 orthogonal array） method. The friction welding process parameters such as heating pressure, heating time, upsetting pressure, upsetting time, and speed of rotation were fixed with low,medium, and high levels of range based on the machine capacity, and the required knowledge was acquired from the preliminary experiments. The joint characterization studies included micro structural examination and evaluation of mechanical properties of the joints. Microhardness variation, impact toughness, and tensile strength of the joints were evaluated. Neither a crack nor an incomplete bonding zone was observed. The tensile strength of the joints was higher than the strength of the base material, and the friction and upsetting pressures were found to influence the joint strength. The tensile strength of all the welds was observed to be increasing with an increase in the rotational speed. The toughness of the friction welds was evaluated at room temperature and also at subzero（cryo） temperature conditions. The toughness for friction welds was found to be superior to the fusion welds of duplex stainless steel at room temperature and cryo conditions. Weldments exhibited better corrosion resistance than the parent material.     

时效对2205双相不锈钢组织和性能的影响

研究了时效处理对2205双相不锈钢性能的影响.结果表明:2205双相不锈钢在475℃进行时效处理会发生严重脆化现象:其原因是由于在时效处理过程中,δ-铁素体相的微观结构发生了剧烈的转变,从而造成了严重的时效硬化.     

Characterization of Microstructure,Strength, and Toughness of Dissimilar Weldments of Inconel 625 and Duplex Stainless Steel SAF 2205

The dissimilar combinations of Inconel 625 and duplex stainless steel SAF 2205 obtained from manual GTA welding process employing ER2209 and ERNi CrMo-3 filler metals have been investigated. Formation of secondary phases at the HAZ of Inconel 625 and grain coarsening at the HAZ of SAF 2205 were witnessed while using these filler wires. The average hardness of ER2209 weldments was found to be greater than ERNi CrMo-3 weld. Tensile fracture was observed at the weld zones for both the fillers. Impact test trials showed brittle mode of fracture on employing ER2209 filler and mixed(ductile–brittle) mode of fracture while using ERNi CrMo-3 filler. Further optical microscopy and SEM/EDS analysis were carried out across the weldments to investigate the structure–property relationships.     

高韧性不锈钢FV520(B)的析出硬化行为研究

研究了350、420、470、520、560、600、630℃时效温度下沉淀硬化不锈钢FV520(B)的TEM组织、硬度和示波冲击韧度。结果表明:时效过程中,FV520(B)钢主要以富铜相-εCu析出为主。硬度在420℃时效出现峰值,而韧性最差,主要与组织中细小富铜相共格析出有关。随着时效温度增加,富铜相逐步脱溶长大,基体再结晶,硬化程度逐步降低。FV520(B)钢的韧性主要决定于冲击裂纹扩展功。时效组织对FV520(B)钢冲击裂纹萌生功影响较小,对裂纹扩展功有着较大的影响。     

Hot Deformation Behavior and Processing Maps of 0.3C-15Cr-1Mo-0.5N High Nitrogen Martensitic Stainless Steel

Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS) was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s~(-1) using a Gleeble 3500 thermal-mechanical simulator.The true stress-strain curves of the studied HNMSS were measured and corrected to eliminate the effect of friction on the flow stress.The relationship between the flow stress and Zener-Hollomon parameter for the studied HNMSS wsa analyzed in the Arrhenius hyperbolic sine constitutive model by the law of Z=3.76×10~(15) sinh(0.004979σ_p)~(7.5022).The processing maps at different strains of the studied HNMSS were plotted,and its flow instability regions in hot working were also confirmed in combination with the microstructure examination.Moreover,the optimal hot deformation parameters of the studied HNMSS could be suggested at T=1303-1423 K and ε=5-10 s~(-1) or T=1273-1473 K and ε=0.005-0.04 s~(-1).     

Influence of Aging Time on Microstructure and Corrosion Behavior of a Cu-Bearing 17Cr-1Si-0.5Nb Ferritic Heat-Resistant Stainless Steel

17Cr-1Si-0.5Nb-1.2Cu ferritic heat-resistant stainless steel was aged at 750 °C from 10 min to 30 h to simulate time aging and study the microstructural evolution and its effect on corrosion behavior by using optical microscopy, scanning electron microscopy, transmission electron microscopy, potentiodynamic polarization, electrochemical impedance spectroscopy, and the Mott-Schottky approach. Four types of precipitates were discovered, including ε-Cu, NbC, Fe₃Nb₃C, and Fe₂Nb-type Laves phase. The nano-sized ε-Cu phase forms first, and its fraction follows the parabolic law change and is the largest. Compared to NbC and Fe₃Nb₃C particles, the coarsening of the Laves phase is the most pronounced. The aging process is divided into three parts: early-aged (0-5 h), peak-aged (5 h), and over-aged (5-30 h). However, the corrosion resistance is reduced in the early-aged stage of 0-2 h. Further extending the aging time to 30 h, the corrosion resistance is gradually improved. This change may be related to the competitive relationship between the beneficial effects of the Cu-rich phase and the harmful effects of Nb-containing particles. The dissolved Cu on the surface becomes more effective for the suppression of the anodic dissolution by the formation of ionic compounds of chlorine, thereby reducing the deterioration of corrosion resistance caused by Nb-rich precipitation.     

固溶温度对铸造双相不锈钢微观组织及力学性能的影响

研究了不同固溶温度对00Cr22Ni5Mo3N铸造双相不锈钢微观组织和力学性能的影响.结果表明:在1 120～1 200℃温度区内固溶处理后,合金中的铁素体相比例随着固溶温度的升高而升高;冲击性能随着固溶温度的升高而降低;合金的拉伸强度和断面伸长率随固溶温度的升高变化不大;屈服强度在1 120～1 140℃温度阶段有所升高,在1 160～1 200℃屈服强度变化不大.     

Characterization of Impact Deformation Behavior of a Thermally Aged Duplex Stainless Steel by EBSD

The effect of thermal aging on phase transformation and impact toughness of an as-cast duplex stainless steel was investigated at room temperature. After long-term thermal aging, the impact toughness decreases significantly and the cracks initiate and propagate more easily. The plastic deformation ability of the ferrite phase decreases after thermal aging,which leads to the degradation of impact toughness. High stress concentration occurs on the grain boundaries of the austenite phase in the aged materials. Meanwhile, high-stress concentration areas are also observed in the austenite phase near the grain boundaries. After long-term thermal aging, pinned dislocations in ferrite and along phase boundaries lead to the high stress concentration. Micro-cracks preferentially initiate in the ferrite phase and propagate via separation of phase boundaries. The blocking influences of spinodal decomposition precipitates and G-phase precipitates are stronger than the effect of grain boundaries and phase boundaries on the dislocation movement.     

Precipitation Behavior and Mechanical Properties of a 16Cr-25Ni Superaustenitic Stainless Steel Weld Metal During Post-weld Heat Treatment

A 16Cr-25Ni superaustenitic stainless steel weld metal for austenitic stainless steel/ferrite heat-resistance steel dissimilar metal weld was designed and prepared through tungsten inert-gas welding. The precipitate evolution and its correlation with mechanical properties were investigated during post-weld heat treatment (PWHT) at 690 °C for up to 12 h. The primary precipitates in the as-welded weld metal were identified as Mo-rich M₆C carbides in the interdendritic region and semicontinuous fine-sized M₂₃C₆ carbides along grain boundary. After PWHT, three types of precipitates coexisted in the interdendritic region: primary M₆C carbides, newly precipitated Mo-rich M₂X carbonitrides and some of the secondary M₂₃C₆ carbides. Additionally, mass secondary M₂₃C₆ carbides formed and coarsened along grain boundary. No undesirable intermetallic phases formed during the whole period. The M₂X and interdendritic M₂₃C₆ improved the strength of the weld metal after PWHT, but the elongation and impact toughness degraded, which were mainly owing to the intergranular M₂₃C₆ carbides that changed the fracture mode from ductile transgranular mode to mixed mode of transgranular and intergranular fracture. Meanwhile, the coarsening of M₂X carbonitrides may lead to the elongation loss during 8 h to 12 h. Evolution of impact toughness was also related to the M₂X carbonitrides, which made the crack easier to propagate compared with austenitic matrix and contributed to the decline of impact toughness. However, due to the sluggish precipitation of M₂X carbonitrides with longer holding time, the decreasing trend became slow from 4 to 12 h. The results showed that PWHT should be controlled within 8 h to obtain better combination of strength and ductility.     

固溶温度对铸造双相不锈钢组织和力学性能的影响

采用POLYVAR MET型金相显微镜、X-650扫描电镜、SIMENS-500X型X射线衍射方法及CSS万能电子试验机研究了固溶温度对一种新型铸造双相不锈钢组织及力学性能的影响，并对其在不同固溶温度下的断口形貌进行了分析。结果表明，在950-1050℃固溶处理后，均能获得α/γ双相组织，合金的强度随固溶温度的提高而增大：随着固溶温度的升高，试验钢的断口形貌从解理断裂变为准解理断裂。     

固溶处理对S32750双相不锈钢焊缝组织和性能的影响

采用金相、X射线衍射、极化曲线测试、力学性能测试等方法研究了固溶处理对S32750双相不锈钢焊接钢管焊缝性能、组织的影响。结果表明,固溶处理能显著改善焊缝的低温冲击韧度和耐腐蚀性能;固溶处理前后焊缝各区域的相结构相同,但铁素体和奥氏体含量有差异,这种差异对焊缝耐蚀性的影响不大。     

Effect of Short-Time Aging on the Pitting Corrosion Behavior of a Novel Lean Duplex Stainless Steel 2002

The effect of short-time aging in the temperature range between 400 and 1000 °C on the pitting corrosion behavior and mechanical property of a novel lean duplex stainless steel(LDSS) 2002 was investigated through the potentiostatic critical pitting temperature(CPT) tests and the Charpy impact tests. Both the pitting corrosion resistance and the toughness of aged specimens degraded due to the precipitation of detrimental secondary phases and the most significant reduction of CPT and impact energy emerged at 650 °C concurrently. The CPT of LDSS 2002 specimen aged at 650 °C decreased by 28 °C, and the impact energy dropped from 69 to 29 J/cm~2 compared with the solution-annealed sample. Transmission electron microscopy characterization showed that the main precipitates in LDSS 2002 were Cr_2N and M_(23)C_6 along the ferrite–austenite grain boundaries.