表面机械研磨诱导AISI 304不锈钢表层纳米化 Ⅰ.组织与性能

采用表面机械研磨处理(SMAT)在AISI 304不锈钢上制备出纳米结构表层,研究纳米化行为及其对硬度的影响。结果表明:经过SMAT后,样品表面形成了厚度约为30μm的纳米晶层,显微组织由平均晶粒尺寸约为10nm的单一马氏体相演变为尺寸稍大的双相组织;在距表面30—300μm的范围内,显微组织由以亚微米级的奥氏体多系孪晶为主逐渐演变为单系孪晶,表面纳米化是晶粒碎化与纳米尺度新相形成共同作用的结果,与心部相比,表面硬度显著提高。

表面机械研磨诱导AISI 304不锈钢表层纳米化 Ⅱ.晶粒细化机理

采用表面机械研磨处理(SMAT)在AISI 304不锈钢上制备出纳米结构表层,用透射电镜(TEM)研究组织演变过程,晶粒细化机理可归纳如下:位错在{111}面上滑移并相互交割形成网格结构;单系孪晶形成并逐渐过渡到多系孪晶;多系孪晶相互交割使晶粒尺寸不断减小,并在孪晶交叉处形成了马氏体相;孪晶系增多与孪晶重复交割强度加大使得细化晶粒的尺寸进一步减小;最终在大应变量、高应变速率和多方向重复载荷的作用下,形成等轴状、取向呈随机分布的马氏体相纳米晶组织。

AISI 304不锈钢表面Fe_3Si型硅化物渗层的制备及渗硅机理

以n(NaCl):n(KCl):n(NaF)=2:2:1碱金属卤化物混合体系做载体,采用不同摩尔比的Na2SiF6和Si粉作渗硅剂,在800℃下利用熔融盐法分别对AISI 304不锈钢进行渗硅处理。采用X射线衍射仪(XRD)分析渗硅层的物相组成,用附带能量色散谱仪(EDS)附件的扫描电子显微镜(SEM)研究渗层截面的形貌和成分,分析熔盐法渗硅层的形成机理。结果表明:融盐中SiF62-的浓度决定渗层中Si元素的含量,由于SiO2在融盐体系中的溶解,融盐中SiF62-得到补充,渗层中Si元素的含量进一步提高。

AISI 304表面硅化物渗层的制备及其900℃循环氧化性能研究

采用NaCl∶KCl∶NaF=2∶2∶1(摩尔比)的中性熔融盐作为载体,Na2SiF6∶Si=8∶2粉末做为渗硅剂,以SiO2为助渗剂,800℃下渗硅5h可实现在AISI 304不锈钢表面形成厚约600μm的富含Cr、Ni合金元素的Fe3Si型硅化物渗层,研究了渗层在900℃下的循环氧化行为。采用X射线衍射仪分析了渗层和氧化膜的物相组成,用附带能量色散谱仪附件的扫描电子显微镜研究了渗层和氧化膜截面的形貌和成分。结果表明,渗层为以Fe3Si相为主,Cr在渗层中含量低于其在304不锈钢基体中含量,而Fe和Ni在基体和渗层中的含量大致相当。氧化动力学遵从二次抛物线规律;Cr和Si元素发生上坡扩散形成以SiO2和Cr2O3为主的内层氧化膜,外层氧化膜以Fe2O3为主,这种复合氧化膜是渗层具有优异抗氧化性能的原因。

冷轧AISI 304不锈钢微观组织及力学性能的变化

采用金相显微镜、铁素体测量仪、硬度计及力学分析等手段,研究了AISI 304不锈钢的微观组织和力学性能在冷轧过程中的演变规律.试验结果表明:冷轧变形可使AISI 304不锈钢产生形变诱发马氏体相变,试样中金属晶粒沿着轧制方向被拉扁拉长;在冷轧压下量较小时,仅有少量的奥氏体相转变为马氏体相,并且马氏体组织以板条状出现;冷轧压下量较大时,金属晶粒逐渐被拉长为纤维状;随着冷轧压下量的增大,马氏体体积分数、硬度和抗拉强度均随之增大,但延伸率逐步下降.

等离子体源渗氮AISI 304不锈钢在3.5%NaCl溶液中钝化膜的稳定性

采用等离子体源渗氮技术对AISI 304奥氏体不锈钢进行表面渗氮处理.利用X射线衍射(XRD)、扫描电子显微镜(SEM)和电子探针显微分析(EPMA)技术,并结合电化学交流阻抗(EIS)测试技术和Zsimp Win软件拟合技术研究改性前后AISI 304奥氏体不锈钢的表面组成结构及在3.5%NaCl溶液中钝化膜的稳定性.研究结果表明,等离子体源渗氮AISI 304奥氏体不锈钢表面形成了氮浓度峰值为23.0%、厚度约为17μm的相改性层.改性前后AISI 304不锈钢在3.5%NaCl溶液中浸泡不同时间形成的钝化膜电极过程的等效电路为R(QR);浸泡时间为10 h时,与AISI 304不锈钢相比,γN改性层的钝化膜电阻R_p从3.615×10~4Ω·cm^2增加至3.765×105Ω·cm^2,增大了1个数量级,具有更好的耐点蚀性能.随着浸泡时间增加至48 h,γN相改性层的钝化膜电阻始终高于AISI 304不锈钢1个数量级,保持在105Ω量级,具有良好的稳定性.

Experimental determination of mechanical properties and short-time creep of AISI 304 stainless steel at elevated temperatures

The high temperature properties of AISI 304 stainless steel were studied. Basic data about the employed experimental equipment, testing procedures, and specimen geometry were given. The experimental setup was used to obtain stress-strain diagrams from tensile tests at room temperature as well as several elevated temperatures. Furthermore, the specimens were subjected to short-time creep tests at various temperatures. Stress levels for creep testing were established as a percentage of yield stress. The results indicate that at lowered temperatures and lower stress levels, AISI 304 stainless steel can be used as a sufficiently creep resistant material.

AISI 304不锈钢的车削加工

针对AISI 304奥氏体不锈钢的特点,分析了AISI 304不锈钢材料的物理性能和切削加工性能,从刀具材料、切削用量和冷却液的选择等方面研究了AISI 304不锈钢车削加工的影响因素,通过合理选择和优化相关参数等方法有效解决了AISI 304不锈钢的加工难题,获得了较好的车削加工效果,提高了生产效率。

高覆盖率下超声冲击处理改善AISI 304力学性能研究

以AISI304材料为例,实验研究了在高覆盖率下超声冲击处理后GNG/CG(Gradient nano-grained on the coarse-grained substrate)材料的力学性能,分析了覆盖率、应力状态、应变率对力学性能的影响。结果表明,随着覆盖率的增加,GNG/CG304不锈钢的屈服强度逐步提高,塑性降低,应变率敏感系数提高,双轴应力状态下变形能力提高。高覆盖率冲击处理得到的GNG/CG结构能够有效抑制NG层的局部塑性应变,从而在提高材料强度的同时,保持良好的塑性。

Deformation Behavior and Formability of Gradient Nano-grained AISI 304 Stainless Steel Processed by Ultrasonic Impact Treatment

The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.

AISI 304不锈钢铣削加工刀具磨损实验研究

AISI 304不锈钢具有低导热性和高韧性等特性,切削加工性较差。研究采用复合涂层硬质合金铣刀,对AISI 304不锈钢进行了端铣实验研究,考察后刀面磨损情况。实验表明,进给率对磨损的影响大于切削速度。针对刀具后刀面磨损,给出了相对较好的切削条件组合。

1-Hydroxyethylidene-1,1-diphosphonic Acid (HEDP) as a Corrosion Inhibitor of AISI 304 Stainless Steel in a Medium Containing Chloride and Sulfide Ions in the Presence of Different Metallic Cations

The novelty of this paper is the analysis in a medium containing sulfide ion due to the generation of this ion in petroleum industries, in the refining stage (the sulfide ion is also present on the produced water). The performance of 1-hydroxyethylidene-1,1-diphosphonic acid inhibitor (HEDP) was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and weight loss measurements in a dissolution of AISI 304 stainless steel immersed in a solution containing chloride and sulfide ions. The protection of the stainless was increased with the addition of divalent cations (Ca2+, Zn2+, and Mg2+). Potentiodynamic polarization studies have shown that the inhibitor alone has anodic protection, but the addition of Ca2+ (10 mg·L-1) favors the cathodic protection, and the addition of Zn2+ (20 mg·L-1) and Mg2+ (10 mg·L-1) mixed-type is observed. Electrochemical impedance spectroscopy was performed at three distinct potentials: -0.3 [V vs. SCE], Ecorr [V vs. SCE], and 0.1 [V vs. SCE]. This revealed that calcium is responsible for favoring the formation of the film and the other elements (zinc and magnesium) favor the stabilization of the protective film. Scanning electron microscopy analysis revealed that the addition of cations provided the adsorption of HEDP on the metal surface. Weight loss results showed that the presence of zinc in a solution containing HEDP favored greater inhibitor efficiency (Zn2+ ηm = 85.2% and for Mg2+ ηm = 70.4%).

AISI 304不锈钢中δ→γ相变的原位观察

利用共焦激光扫描显微镜原位观察了AISI304不锈钢冷却过程中高温铁素体(δ)→奥氏体(→)相变的过程及其特征．结果表明,γ相优先在δ晶界处形成；冷却速率影响γ相的生长形态,典型形态分为块状、圆形、树枝状等；“游离”γ枝晶发生粗化,并和周围的γ枝晶聚合；相同冷却条件下,δ晶界处的γ枝晶聚合程度明显高于δ晶粒内部；二次枝晶在冷却过程中粗化,并竞争生长．利用ThermoCalc计算C元素在δ→γ相变过程中的偏析系数,以此求解δ→γ相变数学模型．

AISI 304不锈钢车削加工切削速度对加工性能影响的实验研究

利用硬质合金刀具,对奥氏体不锈钢AISI 304进行了车削加工实验研究.讨论了车削速度对切屑形态、刀具磨损及工件表面粗糙度的影响.试验结果表明,随着切削速度的增大,切削热对切屑形态的影响降低,刀具后刀面磨损及工件表面粗糙度均减小.给出了不同切削速度下的切屑形态以及切削速度与刀具磨损、切削速度与表面粗糙度的关系曲线.

AISI 304钢-铌异种金属激光焊温度场及残余应力研究

采用SYSWELD软件,对AISI 304钢–铌异种金属激光焊接过程进行动态模拟,在研究了AISI 304钢–铌异种金属激光焊接接头温度场的基础上,分析了焊后薄板的残余应力分布。结果表明:异种金属焊接温度场呈不对称分布,铌侧高温区域比不锈钢侧要宽;沿焊接方向上,无论是横向残余应力还是纵向残余应力,焊缝中部区域都存在最大残余拉应力;而垂直于焊缝方向上,横向残余应力和纵向残余应力在焊缝及焊缝附近区域应力梯度都比较大,分布形态都呈“M”状,纵向残余应力在焊缝区表现为残余拉应力,而横向残余应力在焊缝中心处出现了压应力。

Optimization of gas tungsten arc welding parameters for the dissimilar welding between AISI 304 and AISI 201 stainless steels

This present study applied gas tungsten arc welding in order to join AISI 304 and AISI 201 stainless steels.The objective was to find the optimum welding condition that gave a weld bead in accordance with DIN EN ISO 25817 quality level B, pitting corrosion potential of the weld metal of not less than that of the AISI304 base metal and a ratio of delta-ferrite in austenite matrix of the weld metal of not lower than 3%.Such a ratio is a criterion widely accepted to protect the weld metal from solidification cracking. At the welding current of 75 A and by using pure argon as a shielding gas 0 to 8 vol.% and applying a welding speed in the range of 2-3.5 mm·s^(-1) was found to give a complete weld bead with an increased depthper-width ratio(promote weldability). For welding speed in the range of 3 and 3.5 mm·s^(-1)(promote corrosion resistance). Increasing the welding speed in such a range decreased the amount of delta-ferrite in the austenite matrix, and increased the pitting corrosion potential of the weld metal to be 302 mV_(SCE).This value was still lower than the pitting corrosion potential of the AISI 304 base metal. Mixing nitrogen in argon shielding gas increased the nitrogen content in the weld. The optimum condition was found when using a welding speed of 3 mm· s^(-1) and mixing 1 vol.% of nitrogen in the argon shielding gas(promote weldability and corrosion resistance). Pitted areas after potentiodynamic test were observed in the austenite in which its Cr content was relatively low.

低温冷却对AISI 304不锈钢铣削加工的影响(英文)

研究低温冷却对AISI304不锈钢铣削加工的影响。用内径为1mm的管子来喷淋液氮到铣刀、削口和材料界面起到低温冷却的作用。液氮的流量为5.2L/min;采用顺铣和逆铣2个铣削方向、干铣和低温冷却2种方式和80、120、160和200m/min 4种铣削速度。结果表明:低温冷却和铣削速度对切削力有影响;低温冷却过程中的切削力和扭矩比干铣过程中的高;切削力随着铣削速度的加快而增大。进入铣刀半径范围内的削屑影响低速顺铣的效果。

AISI 304不锈钢高速铣孔测温实验研究

为揭示立铣刀磨损、破损机理,本文采用课题组自主研发的嵌入式刀柄系统,对难加工金属AISI 304不锈钢进行了不同冷却方式、铣刀转速和铣刀直径等变切削参数的测温实验研究,结果表明:主轴转速10 000 r/min时,由干式切削变为湿式切削最高切削温度可下降246℃;在相同刀孔比(1∶1.5)干式铣削时,?12 mm铣刀比?20 mm铣刀测温点最高温度高500℃;湿式切削加工质量较高,圆柱度均小于0.02 mm,尤其是在深孔铣削加工时,内冷铣削优势更趋明显,为高速内冷铣削方式的推广应用提供参考。

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AISI30 4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AISI30 4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AISI30 4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。

塑性变形对AISI304不锈钢组织及耐蚀性的影响

AISI30 4不锈钢分别在加热 180℃和低温 - 70℃条件下进行拉伸变形。采用透射电镜观测位错分布 ,利用铁素体测量仪测定马氏体相 (铁磁相 )含量 ,并通过电化学滞后技术分别研究它们在 5 0℃条件下 0 5mol·L-1MgCl2 水溶液中的腐蚀行为 .结果表明 :加热 180℃和低温 - 70℃条件下塑性变形均使AISI30 4不锈钢中位错密度随变形量增大而增加 ,AISI30 4不锈钢在 - 70℃条件下塑性变形时部分奥氏体相转变为马氏体相 ,而在180℃条件下塑性变形时不发生马氏体相变 ;位错密度的增加使AISI30 4不锈钢钝化膜的击穿电位略微正移 ,而马氏体相的增加使击穿电位呈负移趋势 ,材料耐孔蚀性能降低 .