The Hardness and Corrosion Properties of Trivalent Chromium Hard Chromium

The formulation of hard chromium plating from trivalent chromium electrolyte and its related process have been intensively studied in this work. Through optimized conditions, the coating hardness can achieve more than HV0.1900 without any treatment and HV0.11700 after heat treatment for five minutes at 300°C, and the thickness of hard chromium coating was about 100 μm. The hard chromium coatings show good adhesion on the carbon steel and low alloy structural steel. The corrosion resistance of hard chromium coatings was enhanced by the adding nanometer materials into trivalent chromium plating coatings. More than 120 hours salt spray corrosion resistance can be achieved with 40 to 50 microns thickness of trivalent chromium plating coatings.

Devise of a W serpentine shape tube heat exchanger in a hard chromium electroplating process

In a hard chromium electroplating process, a heat exchanger is employed to remove the heat produced from the high current intensity in an electroplating bath.Normally, a conventional U shape heat exchanger is installed in the bath, but it provides low heat removal.Thus, this study designs a novel W serpentine shape heat exchanger with identical heat transfer area to the conventional one for increasing heat removal performance.The performance of the heat exchange is tested with various flow velocities in a cross-section in range of 1.6 to 2.4 m·s^(-1).Mathematical models of this process have been formulated in order to simulate and evaluate the heat exchanger performance.The results show that the developed models give a good prediction of the plating solution and cooling water temperature, and the novel heat exchanger provides better results at any flow velocity.In addition, the W serpentine shape heat exchanger has been implemented in a real hard chromium electroplating plant.Actual data collected have shown that the new design gives higher heat removal performance compared with the U shape heat exchanger with identical heat transfer area; it removes more heat out of the process than the conventional one of about 23%.

润滑油添加剂羟基硅酸镁/二硫化钼含量对镀铬钢球-灰铸铁摩擦副摩擦学行为的影响

[目的]内燃机活塞环服役环境恶劣,需要良好的润滑条件来改善其磨损情况。[方法]在2Cr13钢球上电镀硬铬,分析了硬铬镀层的微观形貌、显微硬度和厚度。以镀铬钢球和灰铸铁作为摩擦副进行摩擦磨损试验,以模拟活塞环的服役环境。研究了添加剂羟基硅酸镁/二硫化钼(MSH/MoS_(2))含量不同的润滑油中镀铬层与灰铸铁之间的摩擦学行为。[结果]镀铬层具有微裂纹,显微硬度高达(1013.7±32.4)HV,平均厚度达(84.2±3.6)μm。润滑油中MSH/MoS_(2)纳米颗粒的质量分数为1.0%时,对镀铬钢球-灰铸铁摩擦副的减摩抗磨效果最显著,相较于采用纯润滑油时,镀铬钢球的平均摩擦因数和磨斑直径分别下降了28.2%和24.2%,灰铸铁的磨损率也下降了23.1%。[结论]润滑油中添加适量MSH/MoS_(2)纳米颗粒对镀铬钢球-灰铸铁摩擦副起到很好的减摩抗磨效果。

Thermal Fatigue Behaviour of a Chromium Electroplated 32NiCrMo145 Steel

Thermal fatigue behavior of hard chromium electroplated steel in three different crack intensities of high contraction(HC), medium contraction (MC) and low contraction (LC) was studied. Maximum and minimum temperaturesduring thermal cycle were 800 and 100℃, respectively. The topography and cross sections of the samples exposedto 50, 100 and 200 thermal cycles were studied. The thermal fatigue behavior was analyzed using the data obtainedfrom surface roughness, crack networks and stress induced during cycles. Although the as-coated sample with LCchromium contained no crack, it appeared to have a high crack density after only 50 cycles. The crack depth andwidth in cyclically oxidized LC coating were much less than those in MC and HC coatings. It was concluded that theLC coating protected the substrate from having cracks or subsurface oxidation during thermal fatigue. The cracksin the HC and MC coatings increased in density as well as in depth by thermal cycles. Moreover, the opening of thecracks to the substrate resulted in sub-surface oxidation.

Effect of vibration frequency on microstructure and performance of high chromium cast iron prepared by lost foam casting

In the present research, high chromium cast irons(HCCIs) were prepared using the lost foam casting(LFC) process. To improve the wear resistance of the high chromium cast irons(HCCIs), mechanical vibration was employed during the solidification of the HCCIs. The effects of vibration frequency on the microstructure and performance of the HCCIs under as-cast, as-quenched and as-tempered conditions were investigated. The results indicated that the microstructures of the LFC-produced HCCIs were refined due to the introduction of mechanical vibration, and the hardness was improved compared to that of the alloy without vibration. However, only a slight improvement in hardness was found in spite of the increase of vibration frequency. In contrast, the impact toughness of the as-tempered HCCIs increased with an increase in the vibration frequency. In addition, the wear resistance of the HCCIs was improved as a result of the introduction of vibration and increased with an increase in the vibration frequency.

Microstructure and wear resistance of highchromium cast iron containing niobium

In the paper, the effect of niobium addition on the microstructure, mechanical properties and wear resistance of high chromium cast iron has been studied. The results show that the microstructure of the heattreated alloys is composed of M7C3 and M23C6 types primary carbide, eutectic carbide, secondary carbide and a matrix of martensite and retained austenite. NbC particles appear both inside and on the edge of the primary carbides. The hardness of the studied alloys maintains around 66 HRC, not significantly affected by the Nb content within the selected range of 0.48%-0.74%. The impact toughness of the alloys increases with increasing niobium content. The wear resistance of the specimens presents little variation in spite of the increase of Nb content under a light load of 40 N. However, when heavier loads of 70 and 100 N are applied, the wear resistance increases with increasing Nb content.

Effects of Heat Treatment on Hardness and Dry Wear Properties of a Semi-Solid Processed Fe-27 wt pct Cr-2.9 wt pct C Cast Iron

EfFects of heat treatments on hardness and dry wear properties of a semi-solid processed Fe-26.96 wt pct Cr- 2.91 wt pct C cast iron were studied. Heat treatments included tempering at 500℃, destabilisation at 1075℃ and destabilisation at 1075℃ plus tempering at 500℃, all followed by air cooling. Electron microscopy revealed that, in the as-cast condition, the primary proeutectic austenite was round in shape while the eutectic M7C3 carbide was found as radiating clusters mixed with directional clusters. Tempering did not change the microstructure significantly when observed by scanning or transmission electron microscopy. Destabilisation followed by air cooling led to a precipitation of secondary M23C6 carbide and a transformation of the primary austenite to martensite. Precipitation behaviour is comparable to that observed in the conventionally cast iron. Tempering after destabilisation resulted in a higher amount of secondary carbide precipitation within the tempered martensite in the eutectic structure. Vickers macrohardness and microhardness in the proeutectic zones were measured. Dry wear properties were tested by using a pin-on-disc method. The maximum hardness and the lowest dry wear rate were obtained from the destabilisation-plus-tempering heat treatment due to the precipitation of secondary carbides within the martensite matrix and a possible reduction in the retained austenite.

提高内燃机气门杆部镀硬铬附着力的工艺方法研究

内燃机气门杆部镀硬铬后必须进行铬层附着力检查。气门杆铬层附着力行业标准是气门杆部弯曲试验或打硬度点后,在10倍~20倍放大镜或体视镜下无剥落。目前,附着力差的问题始终困扰与制约着气门杆部镀硬铬工序。本论文通过对附着力差的气门外观、金相等进行分析与研究,指出了目前气门杆部镀铬中存在的问题,并通过作业现场调查与产品检验确定了系列工艺试验方案。工艺试验采用万用表、ZEISS VERT.A1金相显微镜、KEYENCE VK-X1000激光显微镜、EV010电子扫描显微镜等仪器进行检测,确定造成附着力差的因素与环节,并给出应对措施。这些措施经小批与批量生产作业验证有效,彻底解决了气门杆部镀硬铬附着力差的难题;同时,根据实际情况提出了铬层附着力可接受标准,对于气门镀铬行业具有重要的参考价值与推广意义。

RESEARCH AND APPLICATION OF AS-CAST WEAR RESISTANCE HIGH CHROMIUM CAST IRON

The influence of alloy elements, such as boron and silicon, on the microstructure and properties of as cast high chromium cast iron is studied. The results show that boron and silicon have a great effect on the mechanical properties and the wear resistance. Through proper addition of boron and silicon, the properties of as cast high chromium cast iron can be improved effectively. Through analyzing the distribution of elements by scanning electron microscope, it has been shown that the addition of boron and silicon lowers the mass fraction of chromium saturated in as cast austenite, and makes it unstable and liable to be transformed into martensite. The as cast high chromium cast iron with proper content of boron and silicon is suitable for the manufacture of lining for asphalt concrete mixer and its wear resistance is 14 times that of lining made of low alloy white cast iron.

Refractory Hard Alloys Elaborated by Casting of Ternary (Co, Ni Fe)-30Cr-2.5 to 5 wt% C Compositions

Three series of ternary alloys of the {M-30Cr-xC}-type with M = Co, Ni or Fe and x ranging from 2.5 to 5 wt% were elaborated by casting. Their microstructure characterizations by XRD and SEM show that very high volume fractions in chromium carbides (even more than 50%) may be obtained in a metallic matrix by this way. However graphite may also appear in very low quantities in the carbon-richest alloys. The hardness increases with the carbon content (up to 1000 Hv30kg) but it may be a little lowered when graphite is also present. The results show that very hard alloys may be simply obtained by casting of rather cheap elements.

Chromium Electroplating of Aluminium Alloys Using Electroless Nickel as Underlayer

The growing demand for chromium coated aluminium components especially for the automotive industry is due to their favourable physical properties (density, strength to weight ratio etc.). However, their frequent use under harsh environmental conditions renders them corrosion sensitive and consequently they need to be protected. An approach that has been applied in industry is to directly electroplate nickel onto aluminium substrate prior to a top metallic finish;however, in components with complex geometry, certain areas could become exposed to corrosion attack due to poor surface coverage during plating. In this study, a modified electroless nickel undercoat was applied to pre-treated aluminium alloys prior to duplex nickel and chromium plating with a view to enhance corrosion resistance, improve coating adherence and durability, and overall, to achieve substrate protection. Hexavalent and trivalent chromium were applied to pre-treated Al 1050 and Al 6061 following electroless nickel deposition, and plating performance was assessed by surface and corrosion techniques, while durability was measured by scratch, adhesion and hardness tests. Overall, while chromium plating with an electroless nickel undercoat did not improve corrosion resistance or hardness of the materials, it provided an additional protective layer for the substrate with a potential for longer term durability.

碳氮共渗GCr15钢的组织及性能

对高碳铬轴承钢GCr15进行碳氮共渗,从显微组织、硬度、残余奥氏体、应力状态等方面研究其组织和性能,研究表明:碳氮共渗后,GCr15钢制内圈表面可获得深度约为0.40 mm的碳氮共渗层,内圈表面组织为弥散分布的碳氮化合物组织,显微组织(晶粒度)为8级;内圈表面层存在含量大于20%的残余奥氏体,其随回火温度的升高而降低;表面层呈现压应力状态,成品内圈表面可获得一定深度的压应力层。

9Cr18不锈钢表面不同耐磨镀层的微观结构及耐磨性

针对9Cr18不锈钢的耐磨需求,选用硬铬镀层、Ni-P化学镀层、Ni-cBN/h BN复合镀层等3种镀层,通过扫描电镜、划痕法、球盘磨损试验等研究了其在微观结构、结合力、常温及高温耐磨性等方面的差异。结果表明,3种镀层的硬度均可达800 HV以上,但Ni-cBN/hBN复合镀层的硬度略高;经过预镀镍处理后Ni-cBN/hBN复合镀层与基体之间的结合强度高达68 MPa,但硬铬镀层与基体的结合力较差;Ni-P化学镀层和Ni-cBN/hBN复合镀层在常温下的耐磨性相当,但Ni-cBN/hBN复合镀层在200℃下的耐磨性略优;硬铬镀层在摩擦应力作用下涂层出现明显剥落、黏着磨损严重,耐磨性较差。Ni-cBN/hBN复合镀层更宜选作9Cr18不锈钢表面的耐磨镀层。

液态模锻高铬铸铁亚温淬火工艺研究

对比压128 MPa液态模锻工艺制备的KmTBCr20Mo合金进行亚温淬火热处理工艺研究。结果表明,亚温热处理工艺能改变液态模锻高铬铸铁组织的形貌尺寸与数量,改变其洛氏硬度与冲击韧性。500℃亚温淬火相比于无热处理的对照组马氏体基体增多,基体析出小颗粒二次碳化物,同时生成了较多形状规则、断续块状分布的M_(7)C_(3)型碳化物,硬度和韧性均有明显提高,此温度为最佳亚温淬火温度。当淬火温度为530℃和550℃时,共晶团与晶界的碳化物存在微裂纹,形状粗大且不规则,洛氏硬度较高但韧性显著降低。当淬火温度为580℃和630℃时,马氏体基体形状粗大,碳化物呈针状与小块状分布,容易割裂基体,洛氏硬度下降,韧性显著降低。

提高电镀硬铬镀层与基体金属结合力的方法

本文通过在电镀硬铬生产实践中经常出现硬铬镀层与基体金属结合力的问题,研究了影响硬铬镀层与基体金属结合力的因素。优化了电镀硬铬的操作工艺和增加了电镀硬铬特殊操作方法。结果表明,通过优化操作工艺和增加了电镀硬铬特殊操作方法,硬铬镀层的各项指标达到了一个最佳的数值范围,使电镀硬铬镀层与基体金属结合力的合格率达到了96%以上。

高铬铸铁轧辊材质的氧化行为研究

将高铬铸铁轧辊材质试样分别在450℃、500℃、550℃下进行氧化,采用激光共聚焦显微镜、金相显微镜、扫描电镜观察氧化膜形貌、微区成分,硬度计检测硬度。结果表明:随氧化温度的升高、高铬铸铁轧辊中各相的氧化程度以及整体氧化膜的致密度均有明显差异,试样的硬度也有明显不同。

活塞杆零件局部镀硬铬技术研究

针对活塞杆零件局部镀硬铬在实际生产中存在的镀铬工序复杂和铬层质量较差的问题提出了解决办法。采用零件专用螺纹头夹具和热塑管对活塞杆进行装挂和绝缘,可以将镀铬工序优化为:绝缘保护→装挂→镀硬铬,减少了退铬工序;加强镀铬槽液的维护和镀铬过程的控制,配合使用绝缘保护套和阴极保护圈,得到的铬层厚度均匀,且镀铬区域与非镀铬区域界线清晰。

基于响应面法的矿用高铬磨球热处理参数优化设计

为实现矿用磨球强韧性的进一步提升,本文采用Box-Behnken设计-响应面法(BBD-RSM),选择奥氏体化温度、奥氏体化保温时间、回火温度、回火保温时间为自变量影响因子,磨球的洛氏硬度和冲击韧性作为响应目标值,构建了多项式回归方程模型,同时利用OM、SEM、XRD等分析手段,研究了不同热处理条件下磨球的显微组织形貌及物相特征。结果表明,热处理参数对磨球洛氏硬度的显著性影响排序为回火温度>奥氏体化温度>奥氏体化保温时间>回火保温时间,对磨球冲击韧性的显著性影响排序为回火温度>回火保温时间>奥氏体化温度>奥氏体化保温时间。通过优化获得最佳热处理参数为奥氏体化温度885℃,奥氏体化保温时间4.8 h,回火温度400℃,回火保温时间3.5 h,其洛氏硬度为59.84HRC,冲击韧性为6.16 J,验证实验相对误差<5%,证实了响应面法优化磨球热处理参数的精确性和科学性。奥氏体中的合金元素含量,碳化物尺寸、形态和分布情况,残余奥氏体的转变行为及占比的共同作用,是磨球的洛氏硬度和冲击功呈现规律性变化的主要原因。

不同碳含量高硬度共晶高铬铸铁的微观组织与力学性能

通过控制不同元素含量制备出含有2.9%碳和3.1%碳(质量百分比)的两种共晶高铬铸铁,并讨论了碳元素对共晶高铬铸铁微观组织与力学性能的影响。研究结果表明,两种高铬铸铁微观组织和力学性能存在显著差异。Ni、Mo、Mn、Cu和稀土元素的复合合金化以及优化热处理工艺可以控制碳化物的分布和数量,从而进一步提高样品硬度。此外通过弯曲和冲击测试,证实了两种不同碳含量的共晶高铬铸铁合金都具有优秀的硬度(65HRC)、抗弯强度(≥1160 MPa)和冲击韧性(≥2.88 J)。3.1%的较高碳含量导致铸态样品具有更高硬度,但抗弯强度明显降低。

时效处理工艺对铬锆铜合金性能的影响

铬锆铜合金具有良好的导电导热性,且硬度较高,广泛用作电阻焊电极材料。文章通过进行不同的温度、时间和出炉温度等时效处理工艺参数实验,检测铬锆铜合金的硬度和导电率,观察显微组织,研究时效处理工艺对铬锆铜合金性能的影响。结果表明:采用430℃温度、时间1~2 h时效处理工艺,铬锆铜合金的综合性能良好。