深冷处理对低碳高合金马氏体轴承钢力学性能及组织的影响

利用洛氏硬度计、X射线衍射仪、扫描电子显微镜及透射电子显微镜等研究了低碳高合金马氏体轴承钢深冷处理后的硬度变化及组织演化。结果表明:深冷处理促使部分残留奥氏体转变为马氏体,导致深冷处理后实验钢的硬度较淬火态硬度有所升高。经深冷处理后实验钢在0~100 h回火过程中的硬度均比未深冷处理实验钢的硬度高。深冷处理促使钢中碳原子偏聚并在回火过程中以碳化物的形式析出,与未经深冷处理的实验钢相比,经深冷处理的实验钢回火后马氏体基体中的含碳量更低,表明实验钢经深冷处理后在回火过程中析出更多的碳化物。透射电镜分析表明,实验钢在回火过程中析出的大量弥散分布的纳米级M2C和M6C型碳化物是实验钢长时间回火后保持高硬度的主要原因。     

深冷处理对碳钢表面Mo-Cr合金层摩擦性能的影响

介绍了一种在Q235钢表面进行等离子合金化及热处理工艺,获得表面高性能强化层的技术方法.通过该技术方法的处理,使Q235钢表面含有Mo,Cr,C合金元素,成分达到或接近冶金高速钢.该工艺技术的基本原理是在真空容器中,利用辉光放电的溅射现象,首先在Q235钢表面渗入合金元素Mo,Cr,表面含量分别达到12%(质量分数,下同)和4%左右,随后进行超饱和渗碳,使表面含碳量达到2.0%以上,合金化层成分接近钼系高速钢.合金层中的碳化物细小、均匀、弥散,无粗大的共晶莱氏体组织.Q235钢表面合金化后分别采用淬火 低温回火,淬火 2h深冷处理 低温回火两种工艺.结果发现,经深冷处理的试样表面硬度达到1600HV,明显高于未经过深冷处理试样的表面硬度.摩擦磨损实验表明,经深冷处理试样的滑动摩擦系数较未经深冷处理试样的要小,经深冷处理试样的耐磨性是未经深冷处理的1.6倍.     

纳米贝氏体/马氏体钢的热稳定性

将低温贝氏体相变前淬火得到由马氏体、贝氏体铁素体和残余奥氏体组成的纳米贝氏体钢,使用扫描电镜(SEM)、X射线衍射(XRD)和透射电镜(TEM)等手段观察在不同温度回火的纳米贝氏体钢的显微组织和硬度变化,研究了预相变马氏体对纳米贝氏体钢热稳定性的影响。结果表明:含有马氏体的纳米贝氏体钢在中低温(473~773 K)回火后其硬度比回火前的高,回火温度高于823 K其硬度迅速下降到266.2HV(923 K)。预形成的马氏体在473~573 K回火后向附近的残余奥氏体排碳,后者的碳含量提高到峰值1.52%,提高了残余奥氏体的热稳定性,延迟后者在高温时的分解,从而提高了纳米贝氏体钢的高温热稳定性;回火温度高于723 K则残余奥氏体分解成碳化物,贝氏体铁素体粗化、回复形成新的铁素体晶粒。     

准贝氏体钢渗碳特性及磨损性能研究

研究了准贝工体钢渗碳特性及渗层磨损性能。结果表明，准贝氏体钢渗碳后空冷，渗碳最外层为高碳马氏体和残留奥氏体组织，无碳化物及石相析出；心部为准贝氏体组织，渗层碳浓度及浓度梯度平缓，显示出准贝氏体渗碳特性。磨损试验表明，渗碳后不同温度回火，准贝氏体钢渗层耐磨性接近和超过１８Ｃｒ２Ｎｉ４ＷＡ渗碳钢水平，二体磨料磨损朵制以微切削机制为主，三体产磨损以应变疲劳为主，准贝氏体钢可作为渗碳钢代替含 高Ｃｒ、Ｎｉ     

航空齿轮钢16Cr3NiWMoVNbE的真空低压渗碳

对航空齿轮钢16Cr3NiWMoVNbE进行真空低压渗碳热处理,研究了真空渗碳、淬火、冰冷处理以及回火工艺对材料的组织和性能的影响。结果表明：实验钢经渗碳淬火处理后,从表面到心部的组织可分为碳化物区、碳化物与针状马氏体混合区、针状马氏体区和心部板条马氏体区。在碳化物区的晶界有大量的块状Cr碳化物析出,在析出位置Ni元素较少。在针状马氏体和板条马氏体基体中细小的析出物为Nb、V、Mo微合金元素的碳化物。从渗碳钢表面到心部,随着碳浓度的降低硬度曲线呈现先升高后降低的趋势,渗层深度为0.95 mm。冰冷处理使残余奥氏体进一步转化为马氏体,使实验钢的硬度大幅度提高。     

15CrNi4Mo钢渗碳及热处理工艺研究

研究了表面碳含量和热处理工艺对15CrNi4Mo钢渗碳层的影响,分析了渗层显微组织和硬度分布。结果表明:渗碳后表面碳含量为0.90%时,在805℃淬火310℃回火后,渗碳层组织为细针状回火马氏体、残余奥氏体和少量碳化物,心部组织为回火马氏体及少量铁素体,能够满足使用要求。     

具有合理硬度梯度和组织分布的渗碳钢23CrNi3Mo的热处理冷却行为

利用Gleeble-1500热模拟机、光学显微镜(OM)、扫描电镜(SEM)以及透射电镜(TEM)对渗碳钢23CrNi3Mo的连续冷却相变规律以及等温转变规律进行了研究,并基于此,设计了一种新的热处理冷却工艺。研究结果表明,渗碳后试样以0.05℃/s和0.1℃/s的冷速连续冷却时,表面渗碳层为高碳马氏体组织,过渡区为高碳马氏体+下贝氏体的混合组织,基体为下贝氏体组织;渗碳试样外表面在高温段以较低的冷速(0.05~3℃/s)连续冷却时,碳化物沿晶界析出形成网状碳化物;无渗碳的实验钢的贝氏体等温转变温度范围为375~450℃。新的热处理冷却工艺为:试样在880℃保温完成后,采用快速冷却工艺,以冷速大于等于5℃/s进入贝氏体转变温度区,直接入450℃的盐浴炉,入炉后均温5~10min,在低温转变区即贝氏体转变温度区间,采用慢速冷却工艺,冷速小于等于0.1℃/s。获得的试样渗碳层深度为1.4mm,国外的阿特拉斯钎头渗碳层深度为1.2mm,两者基本相同,但前者硬度分布更加平缓;两者表面显微组织均为高碳马氏体组织,过渡区均为马氏体加下贝氏体组织,基体均为贝氏体组织。通过设计新的热处理冷却工艺,获得了与国外钎头相同水平的试样。     

65Si2MnWA钢下贝氏体碳原子调幅分解及有序化的TEM研究

利用Ｓｉ元素阻碍碳化物析出的作用，对６５ＳｉＭｎＷＡ钢进行适当热处理，获得无碳化物析出的下贝氏体组织，通过透射电镜分析了贝氏体基体衍射花样特征，进而考察其碳含量，结果表明，该钢下贝氏体转变初期存在碳原子调幅分解及有序化过程，其碳原子行为与马氏体回火早期阶段碳原子行为相似，说明该钢下贝氏体基体含碳量是过饱和的。     

变形温度对贝氏体钢组织性能的影响

为合理制定Si-Mn-MO系无碳化物贝氏体钢的生产工艺,利用GLEEBLE-3800热模拟试验机,在真空条件下开展了变形温度对贝氏体钢组织性能影响的热模拟试验.利用光学显微镜、透射电镜等设备,采用力学性能测试、微观组织观察等技术分析手段,对热模拟试样进行了组织观察和硬度检测分析,绘制了Si-Mn-MO系无碳化物贝氏体钢不同变形温度的动态CCT曲线,得出了变形温度对其组织和硬度的影响规律.结果表明,变形温度越低,无碳化物贝氏体钢的相变温度越低,组织越细小,先析铁素体越易析出,越有利于提高贝氏体钢的强硬性和韧塑性.     

等离子渗铬及复合强化处理提高耐磨性能的研究EI

利用铬与-αFe无限互溶,含铬的共晶碳化物与二次碳化物形成机理不同,首先在Q235钢和45钢表面渗入合金元素铬,形成高铬合金扩散层,表面含铬量达到40%(质量分数,下同)以上,并在一定范围内使表面合金层铬含量呈梯度分布。利用铬是碳化物形成元素,进行等离子渗碳,因为碳化物形成温度低,在高铬合金层中固体形核长大,所形成的含铬碳化物弥散、细小、均匀。虽表面含碳量达2.8%以上,但是没有共晶碳化物。经淬火及回火处理,表面硬度在HV1800以上。磨损实验表明:与对磨淬火GCr15钢相比,耐磨性能提高7倍以上。     

Comparison of Electronic Speckle Laser Interferometry Hole-Drilling and X-ray Diffraction Techniques for Determination of Residual Stresses in the Heat Treated Steels

Carburizing is widely used to improve wear resistance and fatigue life of high duty machine parts. Fatigue performance of the carburized components is greatly dependent on the residual stress state in the surface layer. The aim of this paper is to measure the depth profiles of residual stresses in the carburized steels by electronic speckle laser interferometry (ESPI) assisted hole-drilling, and to compare the results with those measured by X-ray diffraction technique. To comprehend the differences in the residual stress state, the low-C steel components were carburized, and then, tempered in the range of 180–600 \(^{\circ }\)C. Microstructural investigations and hardness measurements were also conducted. The results obtained from both techniques gave identical results, and showed that the beneficial compressive residual stresses exist at the surface after carburizing, and their magnitudes decrease with increasing tempering temperature. It was concluded that ESPI assisted hole-drilling, with optimized drilling and stress calculation parameters, is suitable for determining the residual stress state of the carburized and tempered steels.     

Formation of nanocrystalline layers by surface severe plastic deformation and pulsed plasma electrolytic carburizing

Surfaces of various kinds of metallic materials spheres were treated by nanocrystalline surface severe plastic deformation and then pulsed nanocrystalline plasma electrolytic carburizing to study nanocrystalline substrate effect on formation and nano-hardness of hard nanocrystalline layer. The surface layers of the metallic materials developed by the nanocrystalline surface severe plastic deformation were characterized by means of high resolution scanning electron microscope. Nearly equiaxed nanocrystals with grain sizes ranging from 15 to 90 nm were observed in the near surface regions of all metallic materials, which are low carbon steel and commercially pure titanium. The effect of substrate nanocrystallization on growth kinetics and hardness of formed nanocrystalline carbide layer was studied with the means of figure analysis and nanohardness tests. Figure analysis show the length to diameter ratio and distribution curve of nanocrystals and it has been found that the achieved properties of hard layer (growth rate, nano-hardness, nanostructure...) are related to these factors. It was also clarified that these techniques and surface nanocrystallization can be easily achieved in most of metallic materials. Results indicate that the resultant hardened carburized layers exhibited excellent hardness profile. Investigation of the layer characteristics showed strong dependence followed from the treatment experimental parameters as well as the shape of nanocrystals.     

奥氏体不锈钢离子渗碳后的腐蚀行为

为了提高奥氏体不锈钢零件的使用寿命,利用低温离子渗碳技术对AISI 316L奥氏体不锈钢进行了表面渗碳处理.用X射线衍射仪和光学显微镜分析了渗碳层的微观组织结构,用显微硬度计测试了渗碳层的硬度分布,通过电化学极化曲线测试技术和化学腐蚀试验研究了离子渗碳AISI 316L不锈钢的腐蚀行为.渗碳层为单相碳过饱和奥氏体固溶体,由此明显提高了AISI 316L不锈钢的抗腐蚀性能,渗碳层硬度梯度平缓,表面显微硬度高达900 HV.结果表明,奥氏体不锈钢低温离子渗碳处理不仅提高了其表面硬度,而且提高了不锈钢表面的耐腐蚀性能,从而提高了其使用寿命.     

医用锻造CoCrMo合金高温渗碳性能研究

采用高温气体渗碳技术,对医用锻造钴铬钼合金进行表面渗碳处理.考察了高温渗碳行为对钴铬钼合金性能的影响.运用XRD、显微硬度计和光学动/静态接触角仪等分析手段对渗碳层的物相组成、表面硬度及润湿性能进行分析及测量;利用球-盘摩擦实验在Tyrode’s 溶液润滑条件下对渗碳层的摩擦磨损性能进行测试.结果表明：医用锻造钴铬钼合金经高温渗碳处理后,形成致密的硬质化合物相Cr3C2,合金硬度较未处理试样明显升高,最高可达560 HV.与未处理合金试样相比,渗碳合金的亲水性及耐磨损性得到明显改善,耐磨损性提高近3 倍.     

Surface hardness improvement of plasma-sprayed AISI 316L stainless steel coating by low-temperature plasma carburizing

Low-temperature carburizing below 773 K of austenite stainless steel can produce expanded austenite, known as S-phase, where surface hardness is improved while corrosion resistance is retained. Plasma-sprayed austenitic AISI 316L stainless steel coatings were carburized at low temperatures to enhance wear resistance. Because the sprayed AISI 316L coatings include oxide layers synthesized in the air during the plasma spraying process, the oxide layers may restrict carbon diffusion. We found that the carbon content of the sprayed AISI 316L coatings by low-temperature carburizing was less than that of the AISI 316L steel plates; however, there was little difference in the thickness of the carburized layers. The Vickers hardness of the carburized AISI 316L spray coating was above 1000 HV and the amount of specific wear by dry sliding wear was improved by two orders of magnitude. We conclude that low-temperature plasma carburizing enabling the sprayed coatings to enhance the wear resistance to the level of carburized AISI 316L stainless steel plates. As for corrosion resistance in a 3.5 mass% NaCl solution, the carburized AISI 316L spray coating was slightly inferior to the as-sprayed AISI 316L coating.     

Laser surface modification of carburized and borocarburized 15CrNi6 steel

The paper presents the results of laser heat treatment (LHT) of carburized and borocarburized 15CrNi6 low-carbon steel. Laser tracks were arranged by CO₂ laser beam as multiple tracks formed in the shape of a helical line. The microstructure and properties of these diffusion layers were compared with those obtained after through-hardening. The microstructure after carburizing and LHT consists of adjacent characteristic zones: re-melted zone (coarse-grained martensite), carburized layer with heat affected zone (fine acicular martensite), carburized layer without heat treatment and the substrate (ferrite and pearlite). The highest measured microhardness (about 820 HV) was observed in re-melted and heat affected zones. The increase of distance from the surface was accompanied by a gradual decrease of microhardness up to 400 HV beneath the HAZ and up to 250 HV in the core of steel. The carburized layer after LHT exhibited a higher resistance to frictional wear compared to a carburized layer after through-hardening. The microstructure after borocarburizing and LHT consists of the following characteristic zones: iron borides of laser-modified morphology (FeB and Fe₂B), carburized layer with heat affected zone (martensite and alloyed cementite), carburized layer without heat treatment and the substrate (ferrite and pearlite). The highest microhardness was obtained in the iron boride zone. The microhardness of FeB boride extended up to 2200 HV and for the Fe₂B boride up to about 1300–1600 HV. With increased distance from the surface, the microhardness gradually decreases to 800 HV in HAZ, 400–450 HV in the carburized layer without heat treatment and to 250 HV in low-carbon substrate. The iron borides after LHT assume a globular shape, which leads to a lower texture and porosity of the borided layers. The increased resistance to friction wear of the borocarburized layers is certified in comparison with the borided layer after conventional heat treatment (through-hardening).