QPQ处理对45钢组织与性能的影响

对用于制作高压开关构件的45钢进行了3 h盐浴渗氮,抛光后再进行400 ℃×30 min氧化的QPQ处理。通过观察渗层表面形貌,测量渗层表面硬度及耐磨性,分析了渗层性能与QPQ工艺之间关系。研究结果表明,45号钢在不同QPQ渗氮温度下得到了不同厚度的化合物层,具有很高的硬度和耐磨性。当620 ℃渗氮时,渗氮层的综合性能最佳。     

Corrosion of type 316L stainless steel in molten LiCl–KCl salt

Pyrochemical reprocessing in molten chloride salt medium has been considered as one of the best options for the reprocessing of spent metallic fuels. The AISI 316L stainless steel (SS) is envisaged as a candidate material for the fabrication of components for various unit operations like salt preparation vessel, electro‐refiner and cathode processor, on which ceramic coatings with metallic bond coat will be applied by the thermal plasma spraying. The unit operation like electro‐refining is carried out in the molten lithium chloride–potassium chloride (LiCl–KCl) eutectic salt at 773 K in argon atmosphere. The corrosion behaviour of the container vessel in molten chloride salts is therefore important, hence corrosion tests were carried out in a molten salt test assembly under argon gas atmosphere. The present paper discusses the corrosion behaviour of 316L SS in the molten LiCl–KCl eutectic salt at 873 K. The 316L SS samples were immersed in the molten LiCl–KCl eutectic for 25, 100 and 250 h, while 316L SS with yttria stabilized zirconia coating was exposed for 1000 h. The exposed samples were examined by optical and scanning electron microscope for corrosion attack. The X‐ray mappings of the cross‐section of the degraded layer onto the 316L SS indicated that the mechanism of corrosion corresponds to the selective diffusion of Cr to the surface with the formation of voids below, and the formation of chromium compounds at the surface. The results of the present study indicated that the yttria stabilized zirconia coating onto the 316L SS exhibits a better corrosion resistance in molten chloride salt than with uncoated 316L SS.     

Influence of time on the microstructure of AISI 321 austenitic stainless steel in salt bath nitriding

Influence of nitriding time on the microstructure and microhardness of AISI 321 austenite stainless steel was investigated, using a complex salt bath heat-treatment at low temperature, 430 °C. Experimental results revealed that after salt bath nitriding, a modified layer was formed on the surface of substrate with the thickness ranging from 2 μm to 30 μm with changing treating time. The nitrided layer depth thickened extensively with increasing nitriding time. The growth of the nitrided layer takes place mainly by nitrogen diffusion according to the expected parabolic rate law. Scanning electron microscopy and X-ray diffraction showed that in 321 stainless steel subjected to complex salt bathing nitrided at such temperature for less than 8 hours, the main phase of the nitrided layer was expanded austenite (S phase) by large. When the treatment time is prolonged up to 8 hours and more, S phase is formed and subsequently transforms partially into CrN, and then the secondary CrN phase precipitated. With treating time prolonged, more CrN precipitates formed along the grain boundaries in the outer part. In the inside part between the some CrN and the substrate, there is still a broad single S phase layer. All treatments can effectively improve the surface hardness.     

304奥氏体不锈钢低温盐浴渗氮处理

采用430℃低温盐浴对304奥氏体不锈钢进行渗氮处理,研究了渗氮时间对渗氮层组织和性能的影响。利用XRD衍射仪、光学显微镜、表面显微硬度计和带能谱仪(EDS)的扫描电镜(SEM)分别分析渗氮层的相组成、厚度、表面硬度和显微组织。结果表明:304奥氏体不锈钢在430℃渗氮不同时间后,渗氮层厚度和表面硬度都随着时间的延长而增加。渗氮时间为1 h时,渗氮层仅为单一的S相,随着渗氮时间的增加,渗氮8 h时开始有少量CrN生成,渗氮16 h时,渗氮层由大量CrN+S相两相混合。用电化学极化的方法评价耐蚀性能的结果表明:盐浴渗氮处理后耐Cl-点蚀性能得到了一定的改善,在430℃渗氮4 h,其耐蚀性能是最好的,优于没经过渗氮的试样,而在所有的渗氮试样中,渗氮8 h、16 h的试样耐点蚀性能较差。     

化学成分对316L奥氏体不锈钢组织及变形行为的影响

利用万能试验机对不同镍当量(Nieq)的316L不锈钢热轧钢板进行常温单轴拉伸试验,借助扫描电镜(SEM)和透射电镜(TEM)对其拉伸变形前后的微观组织进行观察,探索镍当量对316L不锈钢微观组织及性能的影响规律。结果表明,固溶态试验钢的组织均为奥氏体组织及少量高温δ相,强度随Nieq的升高而降低,塑性和韧性随Nieq升高而增加;拉伸断口均呈韧性断裂特征,且随Nieq的提高,韧窝的数量减少,韧窝尺寸增加;TEM显示,变形后的试验钢均未发生马氏体相变,Nieq较低时,变形量大的地方位错密度高,发生位错交互作用,局部有形变孪晶生成,且随着Nieq的增加,形变孪晶密度增大,出现相互交叉、阻滞。     

How different steel grades react to a salt bath nitrocarburizing and post-oxidation process: Influence of alloying elements

Two different grades of steel, DC 04 (non alloyed steel) and 15 CrMoV 6 (alloyed steel) were studied; both of them were salt bath nitrided with QPQ process. They were subjected to different durations of nitriding sequences, 2 h, 3 h and 8 h while the duration for the last sequence, i.e. oxidation remained the same. Microhardness measurements showed that the alloying elements had a strong influence on the profile and on the surface hardness value. For each grade, the maximum surface hardness value was already obtained after a 2 h treatment. The surface constitution was observed by XRD; the presence of Fe₃O₄was noticed above the compound layers made up of ε and γ′ nitrides. Cross sectional observations by SEM revealed that the growth kinetics of compound layers follows a parabolic law. The layers' thickness and constitution have also been confirmed by EDS analysis. On increasing nitriding duration, γ′ nitride content decreases while ε nitride content increases. For longer nitriding durations, mostly ε nitride and Fe₃O₄ are observed on the surface of both grades. It seems that for long nitriding sequences, additional elements are not essential for compound layers' nature.     

激光选区熔化316L奥氏体不锈钢微观组织和冲击韧性的各向异性研究

利用光学显微镜（OM）、X射线衍射(XRD)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和金属摆锤试验机等观察和分析激光选区熔化316L不锈钢的物相、织构、微观组织及冲击韧性各向异性。结果表明：激光选区熔化成形316L不锈钢的组织和冲击韧性存在着明显的各向异性。垂直和平行于构建方向试样的物相均为γ-Fe相,垂直于构建方向的组织呈“棋盘状”形貌,晶粒大多数为等轴晶且晶粒得到了细化(dmean=9.177μm),尤其熔池搭接区域晶粒更加细小(6μm以下),平行于构建方向上小角度晶界数目较多,而平行于构建方向为“鱼鳞状”形貌,大多数为柱状晶,晶粒直径较大(dmean=21.247μm)。同时垂直于构建方向织构为强纤维织构< 110 >//RD（强度为7.83）和弱板织构{112}<110>,而平行于构建方向为强纤维织构< 110 >//RD（强度为12.23）。在致密度相同条件下,横向、纵向的冲击韧性分别为62.8±3.2,38.6±4.5,横向明显优于纵向且提高了62.69%。此外晶粒大小、大小角度晶界和织构类型对冲击韧性各向异性有着显著影响,垂直于构建方向的晶粒得到了细化,大角度晶界数目多,韧性较好;纤维织构< 110 >//RD对冲击韧性不利,而板织构{112}<110>有利于韧性,垂直于构建方向的{112}<110>织构强度低且存在弱{112}<110>织构,横向韧性较好。     

Fatigue behaviour of low temperature carburised AISI 316L austenitic stainless steel

Low temperature carburising (LTC) was applied to AISI316L austenitic stainless steel and its effect on microstructure and fatigue behaviour was investigated. LTC treatment enhances surface hardness and wear resistance of the steel without reducing its corrosion resistance. Surface hardness up to 1150 Vickers was achieved in the carburised layer, thanks to the formation of the so-called “S-phase”, a carbon-supersaturated austenite phase. The XRD evaluation of treated material verified expanded austenite with no evidence of carbide precipitation. Rotating bending fatigue tests showed that the low temperature carburising treatment enhances the fatigue strength of the 316L steel by 40% with respect to the untreated material due to the high residual stresses present in the treated layer. A major temperature increase was found testing the LTC specimens, with a peak value at the end of the test up to 600 °C. By air cooling the LTC specimens during the tests, a further increase of fatigue strength up to 70% was achieved with respect to the untreated material. Fatigue cracks in the surface-treated specimens always nucleated near the boundary between the carburised case and the core.     

Effect of DC plasma nitriding temperature on microstructure and dry-sliding wear properties of 316L stainless steel

A wear resistant nitrided layer was formed on 316L austenitic stainless steel substrate by DC plasma nitriding (DCPN). The structural phases, micro-hardness and dry-sliding wear behavior of the nitrided layer were investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), micro-hardness tester and ring-on-block wear tester. The results show that a single expanded austenite layer (S-phase) and a single CrN nitride layer were formed at 400 °C and 480 °C, respectively. In addition, the S-phase layers formed on the samples exhibited the best dry-sliding wear resistance under ring-on-block contact configuration test. Wear of the untreated 316L was sever and characterized by strong adhesion, abrasion and oxidation mechanism, whilst wear of the DCPN-treated 316L was mild and dominated by plastic deformation, slight abrasion and frictional polishing.     

Strength and ductility of 316L austenitic stainless steel strengthened by nano-scale twin bundles

By means of dynamic plastic deformation (DPD) with high strain rates, a bulk nanostructured 316L austenitic stainless steel consisting of nano-sized grains embedded with bundles of nanometer-thick deformation twins was synthesized. The average transverse grain size is ∼33 nm and the twin/matrix lamellar thickness is ∼20 nm. The nano-twin bundles constitute ∼24% in volume. The nanostructured samples exhibit a high tensile strength of ∼1400 MPa but a limited ductility with a uniform elongation of ∼2%. Subsequent thermal annealing of the as-DPD samples in a temperature range of 730-800 °C led to a single-phased austenite structure consisting of static recrystallized (SRX) micro-sized grains embedded with remaining nano-twin bundles and nano-grains. The annealed DPD samples exhibit an enhanced strength-ductility synergy and much more enhanced work-hardening rates than the as-deformed samples. Work-hardening rates of the annealed DPD samples can be even higher than that of the original CG sample. Tensile ductility was found to increase almost linearly with the volume fraction of SRX grains. A combination of 1.0 GPa tensile strength with an elongation-to-failure of ∼27% is achieved in the annealed DPD 316L stainless steel samples.     

Intensified plasma-assisted nitriding of AISI 316L stainless steel

In the present study, processing of AISI 316L stainless steel (316ss) has been conducted by intensified plasma-assisted processing (IPAP). The processing parameters (bias voltage, current density, chamber pressure and substrate temperature) of IPAP have been varied in an effort to determine which conditions lead to the formation of a single-phase structure, ‘m’ phase, and evaluate the properties of this phase. The structural characteristics of the nitrided layers produced by IPAP have been investigated by X-ray diffraction analysis. Nanoindentation experiments have been performed over cross-section to determine hardness and elastic modulus profiles. Dry sliding wear and potentiodynamic aqueous corrosion experiments have been conducted to characterize 316ss nitrided by IPAP. IPAP has been successful in producing single-phase m with high hardness and in shorter processing time compared to diode plasma nitriding. The IPAP produced single-phase nitrided layer was found to possess higher hardness (fourfold increase over the unprocessed alloy), excellent wear and corrosion resistance.     

奥氏体不锈钢316L在ECAP过程中的组织演化及力学性能

对奥氏体不锈钢316L进行等效应变为1.02的6道次室温等通道挤压(ECAP)试验。结果表明,在ECAP挤压过程中316L发生了剪切滑移变形和孪生变形及晶粒碎化,经过4和6道次挤压后分别得到平均晶粒尺寸约80 nm和约61 nm的均匀分布的等轴晶粒。在1道次ECAP挤压后316L的抗拉强度由674 MPa增加到984 MPa, 规定塑性延伸强度则由594 MPa增加到922 MPa,维氏显微硬度由116.33 HV增加到328.31 HV,但是塑性下降严重,可以通过600 ℃后续退火处理进行改善。     

生物医用316L奥氏体不锈钢的形变组织

借助扫描电镜、电子背散射衍射和透射电镜组织观察,对生物医用奥氏体不锈钢316L的形变组织进行了多尺度深入研究,其工程应变量范围为2%~40%。结果表明,当应变>20%时,316L奥氏体不锈钢中的<001>和<111>取向平行于拉伸方向,即出现了大量的变形孪晶和马氏体。从微米尺度和纳米尺度对孪晶和马氏体相变做详细分析发现,形变首先诱发形成变形孪晶,由于孪晶界减小了位错平均自由程而引起位错塞积,进一步诱发马氏体的转变。随着变形量的增加出现了更多的孪晶和α-马氏体,马氏体相变的过程只有γ→α转变,α马氏体主要分布在孪晶界附近,特别是孪晶交叉的位置。其中,奥氏体基体和α-马氏体之间的取向关系为:[011]_γ//[011]_α,(420)_γ//(123)_α。     

Surface modification of 316L stainless steel with high-intensity pulsed ion beams

The surface of 316L stainless steel was irradiated by high-intensity pulsed ion beams (HIPIB) at ion current density of 100, 200 and 300 A/cm² with 10 shots. The surface morphology and the phase structure in the near surface region of original and treated samples were analyzed with scanning electron microscope (SEM) and X-ray diffraction (XRD). Electron probe microanalysis (EPMA) was used to study the distribution of elements on the irradiated surfaces. It is found that the HIPIB irradiation can smooth the surface of the targets, and a preferred orientation presents in the surface layer of the treated samples. Otherwise, selective ablation of impurities occurs during the interaction between HIPIB and the targets. Due to the compress stress wave induced by the bombardment, the microhardness is increased significantly in a depth range of up to 200 μm, which reduces the friction coefficient of the treated surfaces and improves the wear resistance of them. Because the grain size reduces and the impurities content decreases in the irradiated surface layer, the electrochemical corrosion resistance is enhanced. In addition, HIPIB irradiation prolongates the fatigue life of 316L at room temperature due to a combination of the smooth surface and the high dislocation density in the surface layer of the treated samples.     

Oxidation behavior of sintered 316L austenitic stainless steel-yttria composites with various additions

The oxidation behavior of sintered 316L austenitic stainless steel-Y₂O₃ composites and the effect of various additions, such as copper (up to 3 wt.%), bronze (up to 3 wt.%), phosphorus (up to 2 wt.%), and silicon (up to 5 wt.%) have been studied at 550°C inflowing oxygen at one atmosphere pressure for a maximum period of 9 hr. Among all the alloys studied, 316L-1% P showed excellent oxidation resistance. Under the general conditions, Cr₂O₃ is always the preferred protective scale. In general, Y₂O₃-containing composites showed greater oxidation as compared to 316L with other additions.     

离子扩渗工艺对316L不锈钢表层组织及磁性能的影响

采用离子渗氮(PN)、离子渗碳(PC)及离子氮碳共渗(PNC)工艺对316L不锈钢进行表面硬化处理。利用光学显微镜(OM)、X射线衍射仪(XRD)、电子探针(EPMA)、显微硬度仪和振动样品磁强计(VSM)等分析手段对处理后的试验钢组织、显微硬度及磁性能进行表征。结果表明,采用PC、PNC、PN这3种工艺处理的试验钢均可获得膨胀奥氏体相,但是间隙原子含量逐渐增大,晶格膨胀程度逐渐加剧,分别为1.7%、4.1％和5.5％。PNC与PN处理的试样可获得更厚的渗层厚度和更高的表面硬度,表面硬度约为基体的4.5倍。此外,PN处理的试样具有铁磁性,PC和PNC处理的试样则呈现出与原始奥氏体不锈钢一致的弱磁性。与PNC工艺相比,PN处理的试样表现出更弱的Cr与N间相互作用及略大的晶格膨胀,铁磁性却显著增强。在316L不锈钢离子扩渗处理中,诱发顺磁到铁磁转变的首要因素为晶格膨胀,晶格膨胀增大了Fe-Fe原子间距,减少了3d轨道的重叠,从而增大了Fe原子磁矩,使铁磁性显著增强,磁相变的临界晶格膨胀处于4.1%~5.5%之间;次要因素为Cr与N之间的相互作用。316L不锈钢的无磁强化最佳工艺为PNC工艺,具体为温度420 ℃、阴极电压600 V、气压200 Pa、气氛N₂∶H₂∶CH₄=20∶77∶3、处理时间6 h。采用此工艺对316L不锈钢进行表面强化,可在其表面获得厚度大、硬度高、磁性弱的强化层。     

Corrosion behaviour of 316L stainless steel manufactured by selective laser melting

This work investigates the electrochemical behaviour of an AISI 316L stainless steel produced by selective laser melting (SLM) and compares its behaviour with that of wrought stainless steel with similar chemical composition. The SLM stainless steel specimens are tested in the as‐produced condition without stress relief or recrystallization heat treatments. The electrochemical tests are carried out in two electrolytes: 3.5 wt% NaCl solution with neutral pH and with pH of 1.8. At the macroscale, the microstructure of the SLM specimens is determined by the laser scanning pattern and displays an overlapping network of melt pools. At the microscale, the SLM specimens exhibit a cellular/columnar dendritic structure with submicrometric cell size. Electrochemical measurements highlight a more extended passive range for SLM stainless steel in both neutral and acid electrolytes indicating higher protective properties of the oxide film on SLM specimens. In contrast to the wrought material, the refined microstructure of the SLM specimens promotes a very shallow morphology of attack without deep penetration in the bulk.     

热处理对增材制造316L不锈钢组织各向异性的影响

以选区激光熔化(SLM)制备的316L不锈钢为研究对象。首先对打印件的孔隙率、微观组织进行了表征,然后探究了热处理对组织各向异性及硬度的影响规律。结果表明,打印件的体积孔隙率和面孔隙率均较低,均在1%以下,二者之间没有明显差别;对于垂直打印方向的XY面,主要由互成67°交叉的条状微熔池组成,条状微熔池中包含柱状和胞状两种组织,前者主要位于熔池边界,长约几十微米、宽约400 nm,后者主要位于熔池中心位置,尺寸约400 nm;对于平行于打印方向的YZ面,熔池主要呈扇状,扇状熔池内部也包含柱状和胞状两种组织,但分布更加复杂,其中柱状组织贯穿多层熔池生长,XY面与YZ面在微观组织上存在着明显的各向异性。适当的热处理工艺可有效改善组织的各向异性, XY面在800 ℃×2 h热处理后基本可以实现均匀化,而YZ面在900 ℃×2 h处理后才达到均匀化。拥有微纳尺寸结构的增材制造件拥有比传统零件更高的硬度。此外,热处理可使不同方向上的硬度下降,但垂直打印方向上的硬度下降幅度更大。     

阀门球芯316L不锈钢小空间TIG焊接工艺

采用填丝的TIG焊接方法对不锈钢球芯流道口进行小空间全位置自动焊接。通过设计可进行小空间作业的TIG焊枪,配合送丝机气保托罩紫铜散热夹与小车行走装置,搭建自动化焊接平台。在阀门球芯的小空间内多重氩气保护下,开展不锈钢球芯流道口V形焊缝的焊接。焊前清理焊缝及周围区域的杂质油污,焊接时使用高纯氩进行严格的惰性气氛保护,获得各项性能均符合技术要求的焊缝。焊后对焊缝区域进行微观组织和力学性能的测试评定,分析缺陷的产生及原因,并改善焊接工艺参数。测试焊缝、热影响区附近及母材位置的硬度,绘制相应的工艺曲线,获得最佳的工艺参数组合。     

Electropolishing of 316L stainless steel for anticorrosion passivation

316L stainless steel is deemed an indispensable material in the semiconductor industry. In many instances, the surface of the production equipment needs to be treated for low-corrosion passivation, good finish, weldability, and cleanliness. The process characteristics of electropolishing meet these requirements well. The current study investigates the effects of the major processing parameters on the anticorrosion performance and the surface roughness. The electrolyte with 10% water content and a ratio between H₂SO₄ and H₃PO₄ of 4 and 6 has been proven to be successful, showing no corrosion pitting points on the specimen surface. The electrolyte temperature of 85±10 °C and the electrical current density of 0.5 to 1.0 A/cm² are found to be optimal. The processing time beyond 3 to 5 min produces no further improvement. The addition of 10% glycerin provides a very fine surface (maximum roughness of 0.05 μm), while the anticorrosion performance is deteriorated. The results obtained are useful for the manufacture of the semiconductor equipment.