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.     

离子渗碳温度对316L不锈钢渗层组织和性能的影响

利用低温离子渗碳技术.在不同温度下对AISI 316L奥氏体不锈钢进行渗碳处理.利用光学显微镜、显微硬度计、XRD以及电化学测试技术研究了渗碳温度对不锈钢表面显微组织和性能的影响.结果表明,渗碳温度显著影响AISI 316L奥氏体不锈钢渗碳层的组织结构与性能.渗碳温度在400～550℃之间时,可以获得无碳化物析出的、具有单一γ_c相结构的渗碳层;渗碳温度在550℃时,渗碳层为γ相+Cr_(23)C_6+Cr_7C_3+Fe_3C+Fe_2C的混合组织.渗碳层的厚度与硬度均随渗碳温度的升高而增加.550℃是AISI 316L奥氏体不锈钢中铬的碳化物析出的临界温度.为了避免铬的碳化物析出而降低不锈钢的耐蚀性能.奥氏体不锈钢渗碳必须在低于550℃的渗碳温度下进行.     

Hydrogen-assisted fatigue crack growth of AISI 316L stainless steel weld

The fatigue crack growth behaviors of AISI 316L stainless steel (SS) welds in air and gaseous hydrogen were evaluated, and further compared with the base plate. In air, the fatigue crack growth rate (FCGR) of the weld after heat-treatment at 1050 ^oC/1 h was similar to that of the base metal. Furthermore, all specimens became susceptible to hydrogen-accelerated crack growth. Mainly quasi-cleavage fracture related with the strain-induced martensite accounted for the accelerated crack growth in hydrogen. A smaller amount of martensite in the weld was responsible for the decreased susceptibility to hydrogen-enhanced fatigue crack growth relative to the base metal.     

离子渗氮对304L不锈钢组织及高温耐磨性能的影响

以焚烧炉用热电偶304L不锈钢套管为研究对象,开展了不同温度的离子渗氮试验研究。采用光学显微镜、扫描电镜、显微硬度计等分析了304L不锈钢离子渗氮前后的微观结构与力学性能,并研究了其在400 ℃的耐磨损性能。结果表明,304L不锈钢离子渗氮后,可形成硬度1300 HV以上的表面硬化层。随着渗氮温度的提高,表面硬度有所提升,同时硬化层厚度显著增加。离子渗氮可提高304L不锈钢的磨损性能及耐高温氧化性能。     

Super304H奥氏体不锈钢的高温抗氧化性能

对Super304H奥氏体不锈钢在550～800℃进行高温氧化试验,结合氧化动力学规律去研究Super304H奥氏体不锈钢的氧化机理。结果表明,Super304H奥氏体不锈钢在550～800℃氧化质量增加曲线遵循抛物线规律,在750～800℃时60 h以内氧化质量增加趋势最明显,100 h后质量增加高达0.005 mg·mm^-2。在550～750℃逐渐生成致密的氧化膜,主要由Cr₂O₃和Fe_3-xCr_xNiO₄混合氧化物和少量CuCrMnO₄构成。升高温度会促进Cr的选择性氧化,使得Cr₂O₃保护膜开裂,800℃时暴露出的Fe基体与氧原子反应生成瘤状Fe₃O₄,氧化膜厚重并伴有剥落现象。应变速率为3.2×10^-4 s^-1时,不锈钢的抗拉强度随氧化温度升高而降低,600℃的抗拉强度最大,达350 MPa; ...     

Surface modifications of oxide layer formed in isothermal high temperature conditions of AISI 304 stainless steel

Abstract

Chromia forming steels are excellent candidates to resist to high temperature oxidising atmospheres because they form protective oxide scales. To understand the oxidation mechanisms of the AISI 304 stainless steel in air at 800°C, in situ X-ray diffraction (XRD) has been used not only during high temperature oxidation, but also during and after cooling. The in situ XRD analyses carried out during high temperature AISI 304 steel oxidation in air at 800°C reveal the growth of iron containing oxides such as haematite Fe₂O₃ and iron chromite FeCr₂O₄, after 35 h of the oxidation test, whereas the initial nucleation of the oxide layer shows the single growth of chromia. Iron containing oxides develop over the initial layer and these oxides appear to be poorly adherent and spall off during cooling between 200 and 50°C. Protection against high temperature oxidation would be increased when the initial nucleation of manganese spinel compound is delayed in the oxide scale.     

316L不锈钢强流脉冲电子束表面钛合金化及其耐蚀性

利用强流脉冲电子束对不锈钢表面进行了快速钛合金化。将精细钛粉预涂在基体表面后采用强流脉冲电子束对其进行后处理。在电子束对表面的快速加热熔化、混合及增强扩散效应的作用下,部分钛熔入基体表层形成一层富钛层。由于钛的添加有利于形成α相,合金层由α相和γ相混合组成。在模拟体液中的动态极化测试表明,316L医用不锈钢经强流脉冲电子束表面钛合金化后,其在模拟体液中的耐腐蚀性能获得了显著的提高。     

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.     

P92钢焊接接头的高温抗氧化性研究

P92钢因优异的综合性能逐渐成为超超临界机组过热器、再热器等零部件的理想用钢,材料经焊接后,焊接接头在服役温度中的高温抗氧化性直接影响零部件的使用寿命。利用增重法研究P92钢焊接接头在650℃高温空气介质中的氧化动力学,采用OM、SEM观察和分析氧化层表面及截面形貌,利用XRD分析氧化物物相。结果表明:在一定温度下,P92钢焊接接头各区域氧化速率均是先增加后降低,然后趋于稳定值,符合抛物线规律;在650℃空气介质中氧化132 h后,焊接接头中距焊缝3 mm热影响区A部位、焊缝、母材各区域氧化层的厚度分别为45μm,30μm,27μm;焊接接头氧化后表面的主要氧化产物为Fe_2O_3。     

316L不锈钢等离子熔覆Ni基合金涂层的组织与性能

利用等离子熔覆工艺在316L不锈钢基体上熔覆Ni基合金粉末制备耐磨耐蚀涂层,借助于金相显微镜、扫描电镜、X射线衍射仪分析了涂层的组织,利用显微硬度计测试了涂层的显微硬度,采用线性极化法研究了涂层在3.5%NaCl溶液中的耐蚀性能.结果表明,Ni基合金涂层组织主要为固溶大量Cr和Si元素的枝晶γ-(Ni,Fe)及Cr23...     

低温离子硬化处理对AISI 420不锈钢组织与性能的影响

研究了低温离子渗氮、离子氮碳共渗和离子渗碳硬化处理对AISI 420马氏体不锈钢的显微组织、表面硬度、耐蚀性、耐磨性的影响。结果表明,离子渗氮、氮碳共渗和离子渗碳处理都可提高马氏体不锈钢的表面硬度;经不同工艺处理后的试样,除500 ℃×4 h渗氮工艺外,其他不锈钢试样表面的耐蚀性均未出现明显降低,当渗氮温度过高（500 ℃）时,由于CrN的析出使得渗氮层的耐蚀性显著下降;磨损试验的结果表明,离子渗碳处理后硬化层的耐磨性最佳。     

AISI 201奥氏体不锈钢低温离子渗碳

利用低温等离子体辉光放电技术对AISI 201奥氏体不锈钢进行低温离子渗碳(DCPC)处理,处理后的不锈钢表面可以形成一层无碳化铬析出的碳的过饱和固溶体(SC相)。由于渗入钢中的过饱和碳原子引起奥氏体晶格发生畸变,结果使渗层的硬度和耐蚀性都有较大幅度的提高。     

Tribocorrosion behaviour of low temperature plasma carburised 316L stainless steel in 0.5 M NaCl solution

Experiments have been carried out to study the tribocorrosion behaviour of low temperature plasma carburised 316L stainless steel under unidirectional sliding in 0.5 M NaCl solution, using a pin-on-disk tribometer integrated with a potentiostat for electrochemical control. It is found that the carburised layer exhibits much better resistance to material removal than the untreated specimen, particularly at anodic potentials. No corrosion pits are observed inside the wear track on the carburised specimen at anodic potentials as high as 750 mV (SCE). The results are discussed in terms of the relative contribution of wear and corrosion to overall material removal by tribocorrosion.     

Tribological behavior of AISI302 austenitic stainless steel modified by elevated temperature nitrogen plasma immersion ion implantation

AISI302 stainless steel samples were modified by elevated temperature nitrogen plasma immersion ion implantation at temperature ranging from 330 ℃ to 450 ℃. The tribological behaviors of the implanted layers of the samples were investigated. The samples were characterized by Auger electron spectroscopy (AES), glancing angle X-ray diffraction (GXRD), and nanoindentation. The results show that the implantation temperature plays an important rule on the microstructure and surface properties of the implanted layers. The thickness of the modified layer implanted at 390 ℃ is about 9 μm. It is improved about two orders compared with that of the implanted at room temperature. The surface nanohardness and the wear resistance of elevated temperature implanted layers increase significantly, and the friction coefficient decreases obviously in comparison with the unimplanted one. These data suggests that the improvement results from the formation of new phases such as ε-(Fe, Cr, Ni)2 xN, or noncrystal phase.     

Elevated temperature nitrogen plasma immersion ion implantation of AISI 302 austenitic stainless steel

AISI 302 steel was modified using elevated temperature nitrogen plasma immersion ion implantation. The thickness of the modified layers is improved significantly compared with that of the layer implanted at room temperature. The surface nanohardness of the treated sample is much higher. Both the friction coefficient and wear rate are dramatically reduced due to the formation of new phases such as (Cr, Fe)₂N_1−x, ε-(Fe, Cr, Ni)_2+xN, nitrogen expanded austenite (γ_N) or noncrystalline phase in the near surface.     

Corrosion behaviour of low temperature plasma carburised 316L stainless steel in chloride containing solutions

The electrochemical corrosion behaviour of the carburised (expanded austenite) layer on 316L austenitic stainless steel produced by low temperature plasma carburising has been studied in 0.5 M NaCl and 0.5 M HCl + 0.5 M NaCl solutions. The present work focuses on the variation of the corrosion behaviour of the carburised layer with depth from the surface and the effect of carbon concentration on electrochemical behaviour. The results show that the carburised layer has excellent resistance to localised corrosion. There exists a critical carbon concentration, above which the expanded austenite possesses excellent resistance to both metastable pit formation and pit growth.     

Effects of pH value on characteristics of oxide films on 316L stainless steel in Zn-injected borated and lithiated high temperature water

The effects of pH values from 6.9 to 7.4 on oxide films for 316L stainless steel in borated and lithiated high temperature water at 573.15 K without and with Zn injection were examined by in situ potentiodynamic polarization curves, electrochemical impedance spectra and ex situ X-ray photoelectron spectroscopy (XPS) analysis. The composition of oxide films appears slightly pH dependent: rich in chromites and ferrites at pH = 6.9 and pH = 7.4, respectively. The corrosion rate decreases significantly in the high pH value solution with Zn injection due to the formation of compact oxide films. The solubilities and structural model of oxides are proposed and discussed.     

Pulsed Nd:YAG laser seam welding of AISI 316L stainless steel thin foils

Experimental investigations were carried out using a pulsed neodymium:yttrium aluminum garnet laser weld to examine the influence of the pulse energy in the characteristics of the weld fillet. The pulse energy was varied from 1.0 to 2.25 J at increments of 0.25 J with a 4 ms pulse duration. The base material used for this study was AISI 316L stainless steel foil with 100 μm thickness. The welds were analyzed by optical microscopy, tensile shear tests and microhardness. The results indicate that pulse energy control is of considerable importance to thin foil weld quality because it can generate good mechanical properties and reduce discontinuities in weld joints. The ultimate tensile strength of the welded joints increased at first and then decreased as the pulse energy increased. The process appeared to be very sensitive to the gap between couples.