Martensitic stainless steel modified by plasma nitrocarburizing at conventional temperature with and without rare earths addition

17-4PH Martensitic stainless steel was plasma nitrocarburized at conventional temperature (560 °C) with and without rare earths (RE) addition. The surface treated layers were characterized by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction and microhardness test. The wear and corrosion behavior of the modified specimens was studied respectively using pin-on-disc tribometer and anodic polarization tests. The results show that rare earths atoms can diffuse into the surface of the stainless steel. The microstructures of all modified layers are characterized by a compound layer containing three distinct zones but without an evident diffusion zone. The phases on all modified surface layers are mainly of θ-Fe₃C and CrN. It is exciting that the hardness profile of the modified layer is decreased gradually, which is rarely found in plasma nitriding of the stainless steel. The friction coefficient of a specimen can be dramatically decreased by plasma RE nitrocarburizing, whereas the corrosion resistance is deteriorated. In contrast, the corrosion resistance of a plasma nitrocarburized specimen is enhanced but the friction coefficient is not improved as much as that of a plasma RE nitrocarburized one.     

17-4PH钢脉冲等离子体稀土氮碳共渗研究

基于XRD、OM、STM、TEM分析与显微硬度和磨损测试研究了17-4PH钢在500℃有无稀土添加时脉冲等离子体氮碳共渗动力学、渗层的组织结构和性能。结果表明,添加稀土不改变共渗层的表面相结构,但提高了渗层中γ-Fe4N相的比例,使表面氮浓度提高7％,渗层深度最大可增加55％,表层显微硬度提高100～200HV;无稀土添加共渗层在抛光研磨过程中发生了粘着磨损;此外,在渗层中观察到了位错、层错等晶体缺陷。     

Layer growth kinetics and wear resistance of martensitic precipitation hardening stainless steel plasma nitrocarburized at 460°C with rare earth addition

To study the effect of rare earth (RE) addition on low temperature plasma nitrocarburizing of martensitic precipitation hardening stainless steel, 17-4PH stainless steel was plasma nitrocarburized at 460 °C for different times with RE addition. The modified layers were tested by optical microscope, scanning electron microscope, X-ray diffraction, microhardness tester and pin-on-disc tribometer. The experimental results show that the layer depth of plasma RE nitrocarburized layer can be increased up to 56% compared with plasma nitrocarburizing without RE addition. Incorporation of RE element is beneficial to the formation of nitrogen and carbon expanded martensite (α′_N). The surface microhardness of plasma RE nitrocarburized layer can be increased to 1286 HV and higher up to 80 HV than that obtained from the conventional treated one. The friction coefficient of martensitic stainless steel can be dramatically decreased by low temperature plasma nitrocarburizing with RE addition, and the friction coefficient of the modified specimens decrease gradually with increasing process time in the present test condition.     

The microstructure and properties of 17-4PH martensitic precipitation hardening stainless steel modified by plasma nitrocarburizing

17-4PH martensitic precipitation hardening stainless steel was plasma nitrocarburized at 430 °C and 460 °C for 8 h. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope, X-ray diffractometer, microhardness tests, pin-on-disc tribometer and the anodic polarization method in a 3.5% NaCl solution. The results show that the microstructure of plasma nitrocarburized layer is characterized by a compound layer with no evident diffusion zone. The phases in the 430 °C treated layer are mainly of γ′-Fe₄N, nitrogen and carbon expanded martensite (α′_N), and some incipient CrN phases. When the temperature increases up to 460 °C, there is no evidence of α′_N phase. The processes of bulk precipitation hardening and surface treatment by plasma nitrocarburizing can be successfully combined in a single-step process on this steel. The hardness of modified layer can reach up to 1186HV, which is 3 times higher than that of untreated steel. The wear and corrosion resistance of the specimens can be apparently improved by plasma nitrocarburizing. The 460 °C/8 h treated specimen has the best wear and corrosion resistance in the present test conditions.     

304 不锈钢低温离子渗氮及氮碳共渗处理

目的研究304不锈钢离子渗氮层和氮碳共渗层的组织、硬度及耐磨、耐蚀性能,并考察渗层的磨损机理。方法利用离子渗氮及氮碳共渗工艺在304不锈钢表面获得硬化层,利用XRD,OM及共聚焦显微镜、显微硬度仪、电化学测试仪,分析处理前后渗层的组织、相结构及渗层的硬度及耐磨耐蚀性能。结果 304不锈钢氮碳共渗和渗氮层主要为S相层,在相同工艺条件下,氮碳共渗工艺获得的渗层为γN+γC的复合渗层,且厚度大于单一渗氮层。渗氮层和氮碳共渗层硬度约为基体硬度的3.5倍。在干滑动摩擦条件下,氮碳共渗层比渗氮层具有更好的耐磨性能;渗氮层的磨损机理为磨粒磨损的犁沟效应和断裂,氮碳共渗层的磨损机理为磨粒磨损的犁沟和微切削。电化学测试表明,渗氮层和氮碳共渗层的耐蚀性能均优于基体。结论 304不锈钢在420℃进行离子渗氮和氮碳共渗处理后,硬度和耐磨性能可大幅提高,且氮碳共渗处理效果更佳。     

低温低压等离子弧辅助离子渗316L不锈钢的耐磨耐蚀性能

目的提高316L不锈钢的硬度、耐磨性。方法在400℃、2 Pa下,利用空心阴极直流弧辅助,进行了316L奥氏体不锈钢离子渗氮(PN)、离子氮碳共渗(PNC)及离子氮碳共渗加离子渗氮复合(PNC+PN)处理。针对处理后的样品,用莱卡显微镜、扫描电镜(SEM)、X射线衍射仪(XRD)、维氏硬度仪、3D形貌仪、球盘式摩擦磨损仪及电化学工作站等对组织、形貌、物相、机械性能及耐蚀性能进行表征。采用显微硬度计、微纳米综合力学系统测试分析处理后样品的力学性能。结果在空心阴极直流弧辅助下,三种工艺可获得超过3 mm/h的渗层生长速度。同316L不锈钢基体相比,PNC+PN复合处理样品的表面硬度提高3倍以上,在3.5%Na Cl中性电解质中的耐蚀电流密度降低约50%。结论 PNC处理和PNC+PN复合处理可获得更大的渗层厚度和更高的表面硬度,渗层中C、N含量越高,渗层组成相的晶格参数越大,渗层中产生的滑移带密度越大。低温低压等离子弧辅助离子渗不仅能有效提高316L不锈钢的表面硬度,还能提高不锈钢的耐蚀能力。     

低温离子氮碳共渗温度对AerMet100钢摩擦学性能的影响

研究了不同温度对AerMet100钢渗氮层和氮碳共渗层的显微组织、表面硬度、渗层截面硬度梯度以及耐磨性的影响,并考察了渗层的磨损机理。结果表明,氮碳共渗层相较于渗氮层表面生成的化合物更加细小,表面更加平整光滑;离子渗氮、离子氮碳共渗处理都可显著提高AerMet100钢的表面硬度;随着温度的增加,共渗层厚度也明显增加;氮碳共渗层比渗氮层具有更低的摩擦因数,在共渗温度为480 ℃时氮碳共渗试样具有最低摩擦因数和磨损率,表现出最佳的耐磨性。渗氮层的磨损机理为氧化磨损和表面疲劳磨损,氮碳共渗层的磨损机理为氧化磨损、磨粒磨损以及表面疲劳磨损。     

FORMATION OF GRADIENT COATING OF Fe-BASED ALLOY WITH RARE EARTHS BY PLASMA SURFACING

A gradient coating of Fe-based alloy was manufactured with rare earths (RE) by plasma surfacing on Q235 steel substrate. The coatings were studied by using X-ray diffraction (XRD), scanning electron microscope (SEM), differential thermal analyzer (DTA), and electron probe micro-analyzer (EPMA). The results show that the phases of the two kinds of coatings(with and without RE) both include α-Fe, Fe7C3， Fe3C, Cr2B, Fe2B and FeB. The microstructure of F314 coating is mainly hypereutectic, the pro-phases Cr7C3 and Cr2B are loose, crassi, spiculate and contain microcracks. The brittleness of the coating is high, and the average hardness is 787 HV. When 0.8wt% RE was added into the F314 alloy, the microstructure varied from hypoeutectic to hypereutectic continuously, The hardness appears as gradient distribution with the highest value of 773 HV, meanwhile, the brittleness decreases significantly. The formation of gradient structure depends on the fallowing factors: (i) the conversion of RE. The addition of RE lowers the elements point and Fe-C eutectic temperature, thus the base metal melting acutely. (ii) the heating of plasma arc.Graded temperature results in directional solidification, thus the gradient structure forms easily. The main reasons for the hardness decrease with RE addition in the alloy are the ratio of hard phase lowering and the hardness of the hard phase decreasing.     

稀土对42CrMo钢等离子体氮碳共渗组织及性能的影响

在渗剂中添加稀土,在42CrMo钢表面进行了等离子体氮碳共渗试验,并对渗层的组织形貌、显微硬度及接触疲劳强度进行了测试和分析,研究了稀土对等离子体氮碳共渗层的影响.结果表明,稀土在短时间内的催渗效果优于长时间,本次试验以低于8 h的效果最为明显;稀土有细化晶粒,使渗层组织结合得更加致密的效果,还可提高次表层的显微硬度和接触疲劳强度.     

The corrosion and corrosion-wear behaviour of plasma nitrided 17-4PH precipitation hardening stainless steel

Plasma surface nitriding of 17-4 PH martensitic precipitation hardening stainless steels was conducted at 350 °C, 420 °C and 500 °C for 10 h using a DC plasma nitriding unit, and the surface properties of the plasma surface engineered samples were systematically evaluated. Experimental results have shown that the surface properties of the plasma nitrided layers in terms of hardness, wear resistance, corrosion behaviour and corrosion-wear resistance are highly process condition dependent, and it is feasible to provide considerable improvement in wear, corrosion and corrosion-wear resistance of 17-4PH steel using optimised plasma treatment conditions. All three treatments can effectively improve the surface hardness and the sliding wear resistance under unlubricated conditions; high temperature (420 °C and 500 °C) treated materials revealed improved corrosion and corrosion-wear properties due to the formation of surface compound layers.     

17-4PH不锈钢激光气体渗氮层显微组织与摩擦学性能

目的 提高17-4PH马氏体沉淀硬化不锈钢的表面硬度及耐磨性。方法 采用光纤激光器对17-4PH不锈钢进行激光气体氮化,采用不同激光功率在其表面制备渗氮层。利用光学显微镜(OM)、电子扫描显微镜(SEM)和X射线衍射仪(XRD)等设备分析渗氮层的显微组织和相组成;借助显微硬度仪测试渗氮层截面深度方向的硬度;采用多功能摩擦磨损试验机测试基体、渗氮层的摩擦学性能,并通过SEM分析磨痕形貌,揭示基体与渗氮层的磨损机制。结果 在渗氮前样品组织为回火马氏体,经激光渗氮后样品表面形成了由板条马氏体组成的熔化区和回火马氏体组成的热影响区构成的渗氮层。经渗氮后,样品的硬度均得到提高。在激光功率3 000 W下,渗氮层的表面硬度最高,达到了415HV0.2,约是基体硬度的1.2倍,渗氮层的硬度随着深度的增加呈下降趋势,在深度为2.6 mm处其硬度与基体一致。在回火马氏体向板条马氏体转变的相变强化,以及氮原子(以固溶方式进入基体)的固溶强化作用下,提高了渗氮层的硬度。经渗氮后,样品的摩擦因数均高于基体,但渗氮后其磨损量相较于基体有所减少,在激光功率3 000 W下,其磨损体积最小,相较于基体减少了62%。在激光功率2 500 W下马氏体转变不完全,在激光功率3 500 W下渗氮层出现了裂纹,都降低了渗氮层的硬度,其耐磨性也随之减小,且都略低于在3 000 W下。磨损机制由渗氮前的以黏着磨损为主,转变为渗氮后的以磨粒磨损为主。结论 在17-4PH马氏体沉淀硬化不锈钢表面进行激光渗氮后,其表面硬度和耐磨性均得到提高,在激光功率3 000 W下制备的渗氮层具有较高的表面硬度和优异的耐磨性。     

纳米化3J33钢稀土氮碳共渗生成相第一性原理表征

通过稀土化学热处理和第一性原理计算方法研究了纳米化3J33钢在500℃脉冲等离子体稀土氮碳共渗4h时共渗层的相结构和硬度分布以及共渗相的性质.结果表明,共渗层由厚度约5μm的化合物层和90μm的扩散层组成;共渗相主要由γ′-Fe4N和含碳氮的α′-Fe相组成;与纳米化的3J33钢相比,渗层表面硬度提高约1倍,基体时效后硬度也有所提高.计算结果表明,在共渗过程中γ′-Fe4N相较α′-Fe相更容易形成,但α′-Fe相更加稳定;γ′-Fe4N相的硬度高于α′-Fe相的硬度的主要原因是γ′-Fe4N相的N-Fe键较α′-Fe相的C-Fe键更强;此外,γ′-Fe4N相的体模量与剪切模量的比值大于1.75,因此该相具有延性.     

AISI316L不锈钢等离子氮碳共渗层的表征

奥氏体不锈钢通过等离子氮碳共渗可显著提高其表面硬度,从而提高耐磨性而又不损害其抗腐蚀性能。本文采用光学显微镜、显微硬度和微磨损试验对经于450℃等离子氮碳共渗的AISI316L不锈钢和所获得的渗层进行了表征。结果证明,等离子氮碳共渗层由氮化铬析出相和富氮奥氏体基体组成,其硬度约850HV;渗层总深度平均约为45μm,且很均匀;渗层的耐磨性大大高于基体。     

硼对等离子熔覆高硼铁基合金组织和性能的影响

采用等离子弧熔覆技术在20g钢表面堆焊Fe-Cr-B-C系的铁基复合材料,利用X射线衍射（XRD）,光学显微镜（OM）,扫描电镜（SEM）,洛氏硬度计及湿砂磨损试验机等试验设备进行检测、试验,研究不同硼加入量对熔覆层显微组织与性能的影响规律.结果表明,熔覆层显微组织由过饱和α-Fe枝晶固溶体、枝晶间硼化物共晶组织以及碳化物等组成;熔覆层中硬质相主要有Cr2B,CrB2,Fe2B,Cr7C3,B4C等;随着硼含量的增加,硼化物明显增多,当硼添加量为5%时熔覆层的硬度及耐磨性达到最佳,其硬度值为66.1 HRC,磨损量仅为0.383 g;继续增加硼的添加量,熔覆层的耐磨性能降低.     

Y2O3对Fe-Al-Si-B等离子熔覆层组织与性能的影响

采用等离子弧熔覆技术,在Q235基体钢板表面熔覆了一层Fe-Al-Si-B原位复合涂层,并通过在熔覆粉末中添加稀土氧化物Y2O3改善熔覆层的组织与性能。利用光学显微镜(OM) 、扫描电镜( SEM) 、X射线衍射仪( XRD)、显微硬度仪、摩擦磨损试验机对熔覆层的组织、相组成、显微硬度及磨损性能进行了分析。结果表明：Y2O3的加入净化了晶界,使得晶界处夹杂物均匀化,明显改善了晶界处夹杂物的形态,形成了致密均匀、无缺陷且显著细化的熔覆层组织。当稀土氧化物Y2O3含量为0.9%时,熔覆层的硬度达到510HV,耐磨性能达到最佳。     

稀土对模具钢QPQ渗层组织和性能的影响

研究了5CrNiMo模具钢经不同浓度稀土QPQ处理后的组织和性能,在QPQ处理过程中加入适量稀土化合物LaCO3对5CrNiMo钢进行表面改性处理。利用扫描电镜(SEM)分析了5CrNiMo处理后的表面金相显微组织和表面形貌、氮化层深度,采用401MVA型显微维氏硬度计测量试样显微硬度,在M-2000型磨损试验机上进行滑动磨损试验。结果表明,QPQ处理加入适量的稀土不仅有明显的催渗作用,而且能提高5CrNiMo钢的硬度及耐磨性。     

Improvement of corrosion and wear resistances of AISI 420 martensitic stainless steel using plasma nitriding at low temperature

The influence of low temperature plasma nitriding on the wear and corrosion resistance of AISI 420 martensitic stainless steel was investigated. Plasma nitriding experiments were carried out with DC-pulsed plasma in 25% N₂ + 75% H₂ atmosphere at 350 °C, 450 °C and 550 °C for 15 h. The composition, microstructure and hardness of the nitrided samples were examined. The wear resistances of plasma nitrided samples were determined with a ball-on-disc wear tester. The corrosion behaviors of plasma nitrided AISI420 stainless steel were evaluated using anodic polarization tests and salt fog spray tests in the simulated industrial environment.The results show that plasma nitriding produces a relatively thick nitrided layer consisting of a compound layer and an adjacent nitrogen diffusion layer on the AISI 420 stainless steel surface. Plasma nitriding not only increases the surface hardness but also improves the wear resistance of the martensitic stainless steel. Furthermore, the anti-wear property of the steel nitrided at 350 °C is much more excellent than that at 550 °C. In addition, the corrosion resistance of AISI420 martensitic stainless steel is considerably improved by 350 °C low temperature plasma nitriding. The improved corrosion resistance is considered to be related to the combined effect of the solid solution of Cr and the high chemical stable phases of ?-Fe₃N and α_N formed on the martensitic stainless steel surface during 350 °C low temperature plasma nitriding. However, plasma nitriding carried out at 450 °C or 550 °C reduces the corrosion resistance of samples, because of the formation of CrN and leading to the depletion of Cr in the solid solution phase of the nitrided layer.     

Microstructure Characterization and Corrosion Properties of Nitrocarburized AISI 4140 Low Alloy Steel

Plasma nitrocarburizing treatments of AISI 4140 low alloy steel have been carried out in a gas mixture of 85% N₂-12% H₂-3% CO₂. All treatments were performed for 5 h at a chamber pressure of 4 mbar. Different treatment temperatures varying from 520 to 620 °C have been used to investigate the effect of treatment temperature on the corrosion and hardness properties and also microstructure of the plasma nitrocarburized steel. Scanning electron and optical microscopy, x-ray diffraction, microhardness measurement, and potentiodynamic polarization technique in 3.5% NaCl solution were used to study the treated surfaces. The results revealed that plasma nitrocarburizing at temperatures below 570 °C can readily produce a monophase ε compound layer. The compound layer formed at 620 °C is composed of two sub-layers and is supported by an austenite zone followed by the diffusion layer. The thickest diffusion layer was related to the sample treated at 620 °C. Microhardness results showed a reduction of surface hardness with increasing the treatment temperature from 520 to 620 °C. It has also been found that with increasing treatment temperature from 520 to 545 °C the corrosion resistance increases up to a maximum and then decreases with further increasing treatment temperature from 545 to 620 °C.     

一种复合催渗剂用于氮碳共渗的研究

采用一种由氯化铵、海绵钛、稀土和固态铬酸盐组成的复合催渗剂,对Cr12、3Cr2W8V和35CrMo钢进行了氮碳共渗.测定了渗层的硬度、深度、组织和相结构,并与采用纯稀土催渗剂的效果作了比较.试验结果表明,复合催渗剂对氮碳共渗有明显的催渗效果,并优于纯稀土催渗剂.     

中温时效对17-4PH不锈钢液体氮化后组织性能的影响

目的研究低温盐浴氮化17-4PH不锈钢经中温时效处理后氮化层组织性能的变化情况。方法采用光学显微镜(OM)分析氮化层的厚度和显微组织,利用X射线衍射仪(XRD)检测渗氮层的相组成,利用显微硬度计测定渗层的硬度,利用冲刷腐蚀实验评价渗层的耐腐蚀性能。结果 17-4PH不锈钢氮化后在425~475℃时效保温处理,其渗层厚度随时效时间的延长而增加。时效处理使渗层中N原子的浓度发生改变,过饱和扩展奥氏体发生分解,析出与其结构同为面心立方结构的Fe4N、Fe2N和Cr N。时效温度的升高能加速扩展奥氏体的分解,促进Cr N析出及氧化物的生成。经过渗氮时效后,渗层深度可达27.4μm。根据热力学公式计算出N原子在时效过程中的扩散激活能为216.2 k J/mol,表面显微硬度在初期显著升高,达到了近1150HV0.1,随后逐渐降低。在475℃、50 d的时效条件下,冲刷腐蚀中的失重率达到最大值30.3 mg/(h·dm~2)。结论不锈钢氮化后在一定的温度和时间内时效处理会达到最大表面硬度,在随后的保温过程中硬度开始下降。时效处理后17-4PH不锈钢的耐冲刷腐蚀性能下降。