AISI304不锈钢在冷加工过程中的微观组织变化

在不同温度下对AISI304不锈钢进行不同方式、不同程度冷加工,用铁素体测量仪测定马氏体相变量,研究了冷加工与马氏体相变的关系;将AISI304不锈钢在低温(液氮,-70#℃)条件下进行不同程度拉伸,采用透射电镜观测位错分布,研究了冷加工与位错密度的关系.结果表明:冷加工在一定条件下可以产生形变诱发马氏体,其含量随冷加工变形量的增大而增加;同时,冷加工导致AISI304不锈钢中金属晶粒拉长,其位错密度随冷加工变形量的增加而增大.     

Preparation of high-performance ultrafine-grained AISI 304L stainless steel under high temperature and pressure

Bulk ultra-fine grained (UFG) AISI 304L stainless steel with excellent mechanical properties was prepared by a high-temperature and high-pressure (HTHP) method using nanocrystalline AISI 304L stainless steel powders obtained from ball milling. Samples were sintered in high-pressure conditions using the highest martensite content of AISI 304L stainless steel powders milled for 25 h. Analyses of phase composition and grain size were accomplished by X-ray diffraction and Rietveld refinement. By comparing the reverse martensite transformation under vacuum and HTHP treat, we consider that pressure can effectively promote the change in the process of transformation. Compared with the solid-solution-treated 304L, the hardness and yield strength of the samples sintered under HTHP are considerably higher. This method of preparation of UFG bulk stainless steel may be widely popularised and used to obtain UFG metallic materials with good comprehensive performance.     

AISI304/低碳钢真空扩散焊接头组织和性能

采用真空扩散焊接方法连接AISI304奥氏体不锈钢和低碳钢异种材料.在焊接温度和焊接压力恒定的条件下,研究焊接时间对ASTM304/低碳钢异种材料扩散焊接头组织和性能的影响.研究结果表明:在焊接温度850℃,焊接压力10 MPa,焊接时间60 min条件下AISI304奥氏体不锈钢/低碳钢异种材料实现了良好的扩散结合,其强度和韧性均超过低碳钢母材水平.接头抗拉强度达到440 MPa,拉伸断裂发生在低碳钢一侧.在扩散焊高温环境下,界面附近有碳化物偏析现象,析出相为脆硬的Cr23C6,脆硬相的出现导致界面韧性下降,延长焊接时间可有效避免有害化合物Cr23C6的析出,冲击韧性达到120.5 J/cm2,冲击断口在低碳钢一侧.     

应用方波电位脉冲方法检测304L奥氏体不锈钢晶间腐蚀敏感性

用方波电位脉冲法，对ＡＩＳＩ３０４Ｌ不锈钢主要由晶界贫铬引起的晶间腐蚀敏感性随敏化时间的变化规律进行了研究。通过比较发现方波电位脉冲实验与ＥＰＲ方法、１０％草酸电解实验以及Ｈ２ＳＯ４－ＣｕＳＯ（４－）钢屑实验之间存在着较好的对应关系。方波电位脉冲法可以精确地定量反映３０４Ｌ不锈钢的晶间腐蚀敏感性，对应第１０个脉冲的再活化电流密度峰值ｉ（ｒ１０）可作为反映晶间腐蚀敏感性的特征参数。     

Production of 316L stainless steel implant materials by powder metallurgy and investigation of their wear properties

In this study,the mechanical and wear properties of AISI 316L stainless steel implant materials,produced by powder metallurgy(P/M),were investigated.AISI 316L stainless steel powder was cold-pressed with 800 MPa of pressure and then sintered at 1200,1250 and 1300°C for 30 min as three sample groups.The microstructure,and mechanical and wear properties of the resulting steels were investigated.Light optical and scanning electron microscopiese were used to characterize the microstructure of the steels.Room temperature mechanical properties of the steels were determined by hardness measurements and impact tests.Wear was determined using the pin-on-disc wear test,and the results were evaluated according to weight loss.The results indicate that the sintering temperature,time and atmosphere are important parameters that affect the porous ratio of materials produced by P/M.Sintering at high temperature can eliminate small pores and make the residual pores spherical.The wear tests showed that the wear of the AISI 316L stainless steel implants changed depending on the sintering temperature and load.Spherical pores in the samples increase the wear resistance.Moreover,decreasing the porosity ratio of these materials improves all of their mechanical properties.     

Martensite transformation induced by deformation and its phase electrochemical behavior for stainless steels AISI 304 and 316L

The martensite transformation induced by tensile elongation and its effect on the behavior of phase electrochemistry of AISI 304 and 316L in 3.5% NaCl solution were studied. The results show that the content of α'-martensite in stainless steel 304 increases with the true strain. As α'-martensite content increased, free corrosion potential and pitting potential of stainless steel 304 in 3.5% NaCl solution appeared the change trend of a minimum. It was also found that pitting nucleated preferentially at the phase interfaces between martensite and austenite. There existed apparent difference between electrochemical properties of austenite and of martensite for stainless steel 304 and 316L in 3.5% NaCl solution.     

晶界特征分布对304不锈钢应力腐蚀开裂的影响

通过5%的冷轧变形及在1 100 ℃退火5 min,使304不锈钢中的低ΣCSL晶界比例从固溶处理后的49%提高到75%（Palumbo-Aust标准）.采用C型环样品恒定加载方法,在pH值为1.5的沸腾25%NaCl酸化溶液中进行应力腐蚀实验,低ΣCSL晶界比例为75%的样品在浸泡120 h内没有发生应力腐蚀开裂,而低ΣCSL晶界比例为47%的试样在浸泡24 h后就产生了应力腐蚀裂纹.由断口形貌观察及电子背散射衍射(EBSD)分析表明,开始发生的晶间腐蚀会成为后来应力腐蚀开裂的裂纹源,应力腐蚀开裂由最初的沿晶转变为穿晶形式.低ΣCSL晶界比例提高后的试样因其抗晶间腐蚀性能较好,抑制了在Cl^-环境下应力腐蚀裂纹的萌生,因而提高了抗应力腐蚀性能.     

高强度Q460钢高温蠕变性能

为了研究高强度Q460钢的高温蠕变对钢结构抗火性能的影响,采用高温蠕变试验装置测试了高温下高强度Q460钢材在不同应力水平下的蠕变应变随时间的变化曲线.根据试验数据,在现有蠕变模型的基础上拟合了高强度Q460钢材的高温蠕变模型.在有限元结构分析中引入钢材高温材料力学性能和蠕变参数,分析了考虑高温蠕变后轴心受力Q460钢柱的抗火性能.研究表明,高强度Q460钢材在高温和应力作用下具有明显的蠕变变形,在同一温度和时间下,蠕变应变随应力水平的提高明显增加;考虑蠕变效应后,在标准(ISO-834)的升温条件下,钢柱的耐火极限明显降低;在恒定温度下,钢柱的极限承载力随着时间的增加急剧降低,因而结构的抗火承载力设计需要考虑受火时间的影响.     

不同生物炭进入土壤后对304不锈钢腐蚀的影响

生物炭在土壤应用过程,不可避免地会对与土壤之间接触的机械设备部分产生腐蚀作用。为探究生物炭应用于农业生产中对机械设备以及金属工具损耗的影响,采用分别在700、400和100℃温度下裂解制备的小麦秸秆生物炭(WB)、水稻秸秆生物炭(RB)和松木生物炭(PB)的生物炭对304不锈钢板材进行腐蚀处理,并测量其极化曲线和电化学阻抗谱和腐蚀表现。结果表明:与空白组(CK)对比,相较于304不锈钢的腐蚀速率,在施入WB的土壤中,腐蚀速率会随着WB裂解温度的增大而增大;而加入RB的土壤会加剧不锈钢的腐蚀,其中在加入400℃RB的土壤中腐蚀速率达到最大;这是因为WB和RB的加入会提升土壤中的Cl~-含量至足以达到点蚀效应的程度加速了不锈钢板材的腐蚀。与此同时,发现100℃制备的PB生物炭可以抑制不锈钢的腐蚀。总而言之,不同生物质和制备温度的生物炭在土壤实际应用中表现出不同的腐蚀和抗腐蚀特性,因此深入研究这些方面将为其农业应用具有深远影响。     

汽车弹簧与螺栓用钢微塑性服役行为的研究

为研究汽车用弹簧钢与高强度螺栓钢的微生服役行为,在MTS材料试验系统上进行了不同钢种在不同强度水平和不同循环应力条件下的室温蠕变试验,结果表明,较低含碳量弹簧钢和螺栓钢的循环蠕变经历快速蠕变,稳定蠕变和失稳蠕变三阶段,而较高含碳量的钢,则只有后两个阶段,循环蠕变规律可用经验公式Δε=εoN^c描述,钢的化学成分,强度,服役应力和预应变处理显著影响其微塑性服役行为。     

不同送进量对皮尔格轧制成形的影响及验证

皮尔格冷轧无缝钢管过程中为了获得性能较好的成品需要选择合理的送进量数值,本文以冷轧304不锈钢为研究对象,借助有限元模拟软件对不同送进量下的皮尔格冷轧过程进行了完整的仿真,对比分析了送进量对金属流动速度、轧制力、等效应力、残余应力及管材回弹的影响规律.结果表明轧制过程中孔型背脊和与轧辊接触的孔型侧壁处管材金属流动速度随送进量增加而增加,轧制力、等效应力及残余应力均随送进量的增加而增大,并且送进量的增大还会显著增加管材的回弹量.借助试验轧机对不同送进量下皮尔格冷轧管进行轧制试验,对试验得到的管材进行尺寸和残余应力测量,测量结果与有限元仿真结果基本一致,为皮尔格轧制过程不同送进量的选择提供依据.     

研究金属材料高温动态拉伸性能新方法

采用自行设计带有小型加温装置的改进的分离式Hopkinson拉杆装置测试了金属材料在高温条件下的动态拉伸性能,并用修正的Johnson-Cook模型作为材料的本构关系,提出了一种拟合金属材料在弹性及塑性阶段应变率及温度相关的损伤模型,并拟合出参数.结果表明:改进装置能够精确控制加温速率及温度,减小杆端软化的影响,测试结果相对误差小于1.5%;金属材料304不锈钢的屈服应力及断裂应变具有明显的正应变率效应的温度软化效应,但材料弹性模量具有负应变率效应和负温度效应;在293—625K之间计算结果和试验结果吻合较好,表明可用这种方法测试及估算材料高温动态力学性能,并用于工程分析.     

脉冲等离子渗氮预处理后对AISI304奥氏体不锈钢疲劳行为的综合分析

This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions. The pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless steel at different temperatures and durations. Results reveal that nitriding depth increased as process temperature and duration increase. The nitriding depth remarkably increased at 475°C for 8 h and at 550°C for 4 h. An austenite structure was transformed into a metastable nitrogen-oversaturated body-centered tetragonal expanded austenite (S-phase) during low-temperature plasma nitriding. The S-phase was converted to CrN precipitation at 475°C for 8 h and at 550°C for 4 h. Surface hardness and fatigue limit increased through plasma nitriding regardless of process conditions. The best surface hardness and fatigue limit were obtained at 550°C for 4 h because of the occurrence of CrN precipitation.     

Electrochemical behavior of 304 stainless steel with electrodeposited niobium as PEMFC bipolar plates

In order to enhance the corrosion resistance of 304 stainless steel, niobium was electrodeposited on its surface in air- and water-stable ionic liquids. The electrochemical behaviors of bare and niobium-coated 304 stainless steel were evaluated by electrochemical tests in a simulated proton exchange membrane fuel cell (PEMFC) environment. The results showed that niobium could be electrodeposited on the surface of 304 stainless steel from ionic liquids, and a smooth and strong chemical inert compound film was obtained on the surface of 304 stainless steel, which was mainly composed of NbO and Nb₂O₅. The thin composite film acted as a barrier and remarkably improved the corrosion resistance of 304 stainless steel in the PEMFC environment.     

Hot compression deformation behavior of AISI 321 austenitic stainless steel

The hot compression behavior of AISI 321 austenitic stainless steel was studied at the temperatures of 950–1100℃ and the strain rates of 0.01–1 s?1 using a Baehr DIL-805 deformation dilatometer. The hot deformation equations and the relationship between hot deformation parameters were obtained. It is found that strain rate and deformation temperature significantly influence the flow stress behavior of the steel. The work hardening rate and the peak value of flow stress increase with the decrease of deformation temperature and the increase of strain rate. In addition, the activation energy of deformation (Q) is calculated as 433.343 kJ/mol. The microstructural evolution during deformation indicates that, at the temperature of 950℃ and the strain rate of 0.01 s?1, small circle-like precipitates form along grain boundaries; but at the temperatures above 950℃, the dissolution of such precipitates occurs. Energy-dispersive X-ray analyses indicate that the precipitates are complex carbides of Cr, Fe, Mn, Ni, and Ti.     

Effect of cryogenic rolling and annealing on the microstructure evolution and mechanical properties of 304 stainless steel

Metastable 304 austenitic stainless steel was subjected to rolling at cryogenic and room temperatures, followed by annealing at different temperatures from 500 to 950℃. Phase transition during annealing was studied using X-ray diffractometry. Transmission electron microscopy and electron backscattered diffraction were used to characterize the martensite transformation and the distribution of austenite grain size after annealing. The recrystallization mechanism during cryogenic rolling was a reversal of martensite into austenite and austenite growth. Cryogenic rolling followed by annealing refined grains to 4.7 μm compared with 8.7 μm achieved under room-temperature rolling, as shown by the electron backscattered diffraction images. Tensile tests showed significantly improved mechanical properties after cryogenic rolling as the yield strength was enhanced by 47% compared with room-temperature rolling.     

动态应变时效对18-8型奥氏体不锈钢持久强度的影响

１８－８型奥氏体不锈钢试样经冷变形和不同工艺的动态应变时效预处理后，在８７３Ｋ温度下进行不同应力水平的持久性能试验．结果表明，动态应变时效预处理提高了材料的高温持久强度，且比冷变形处理具有更好的强化效果。微观组织观测结果很好地解释了其强化作用。     

304不锈钢超高周疲劳试验裂尖马氏体相变

采用超声疲劳试验技术对304不锈钢进行了超高周疲劳试验,并用扫描电镜对疲劳断口进行了分析。结果显示304不锈钢在Nf=8.60×108,σα=±206MPa的疲劳断口SEM形貌中的第一裂纹扩展区高倍放大像出现羽毛状片层结构,通过X射线衍射发现在奥氏体峰旁有铁素体峰出现。通过分析推测,304不锈钢超高周疲劳试验形变诱发马氏体相变。     

316L不锈钢动态再结晶行为

在Gleeble-1500热模拟试验机上, 通过高温压缩实验对316L不锈钢的动态再结晶行为进行了系统研究. 结果表明:316L不锈钢热变形加工硬化倾向性较大, 在真应力应变曲线上没有出现明显的应力峰值σ_p;316L不锈钢在热变形过程中发生了动态再结晶, 但只是在局部区域观察到了动态再结晶晶粒. 对动态再结晶的实验数据进行拟合, 得到316L不锈钢的热激活能和热变形方程, 并给出了发生动态再结晶的临界应变和临界应力以及Zener-Hollomon参数和稳态应力的关系.     

玻璃纤维增强塑料低温收缩率的测量

以二级G-M制冷机为冷源建立了15~293K温区的应变测量系统.采用应变片法测量了材料低温收缩率,分析并修正了低温下卡玛箔应变片电阻和灵敏系数变化对测量结果的影响.通过测量304不锈钢收缩率并与标准值比较,验证了系统测量的准确性且得出灵敏系数的修正系数随温度的变化关系.随后测量Al6061-T6的收缩率并与标准值对比,两者最大偏差为-4.8%,验证了修正系数的合理性.最后测量了玻璃纤维质量分数为70%的玻璃纤维增强塑料(GFRP)横向和纵向的收缩率.结果表明:同一温度范围内GFRP横向应变值为纵向应变值的1.12倍.