激光表面相变硬化对T10微观组织与性能的影响

采用激光相变硬化方法对T10钢进行表面处理,研究了不同激光功率、扫描速度、光斑直径等参数对T10钢的微观组织、划痕硬度及其力学性能的影响,并采用XRD和SEM/DES分析了T10钢的相组成、微观结构。结果表明:激光相变硬化是对T10钢进行相变处理的有效方法,选用合理的加工参数,可以获得组织均匀致密的硬化层,随着距表面距离的增加,马氏体数量逐渐增多,硬度也逐渐增加,当激光功率P=1.2 kW,扫描速度v=20 mm/s,光斑直径d=5 mm时,其平均划痕硬度可达到896,较原始试样的平均划痕硬度提高了43.36%。     

激光扫描速度对 45 钢组织影响及耐磨性研究

激光表面硬化是利用激光将材料表面加热到相变点以上,随着材料自身冷却,可使原奥氏体组织转变为马氏体组织,从而使材料表面硬化的淬火技术。本文研究了不同激光扫描速度下,45钢激光表面硬化的组织变化及耐磨性能。结果表明,在激光功率1600W、扫描速度600mm/min条件下,获得的45钢表面组织主要为马氏体,硬化后硬度高达50.4(HRC),相比处理前提高1倍,耐磨性能优异。     

斜角度入射激光相变硬化的组织与性能研究

利用无氦横流CO2激光加工机对40Cr表面进行激光相变硬化处理,采用扫描电子显微镜(SEM)、立式金相显微镜(OM)、努氏显微硬度计、滑动摩擦磨损试验机和恒电位仪等设备对不同入射角相变硬化层的显微组织及性能进行研究。结果表明:相变硬化区的组织为隐晶马氏体+残余奥氏体,过渡区的组织为马氏体+残余奥氏体+铁素体+碳化物;激光入射角度增大,硬化层的深度减小。当入射角度为10°时,硬化层深度最大,为839μm。其硬化层的硬度比基体提高约4倍,耐磨性提高8倍,耐蚀性也显著提高。     

75CrMnMo铸钢轧辊激光熔凝强化的组织及性能分析

应用5kW连续CO2激光器对铸钢轧辊进行激光熔凝强化处理并进行显微组织分析和硬度测试。结果表明，其试样剖面组织区域分为激光熔凝强化区(细小马氏体 残余奥氏体 碳化物)，激光相变强化区(马氏体 残余奥氏体 碳化物)，过渡区和母材4个区域。激光处理后可达70～85 HSD。熔凝区和相变硬化区的淬硬深度依工艺参数不同，可达1～2mm。此工艺可以作为提高轧辊过钢量的一种途径。     

H13铝材挤压模具工作带激光相变强化工业化应用研究

以H13钢模具为研究对象,结合激光相变强化机理,利用激光技术对铝材挤压模具工作带进行相变强化处理,分析激光相变强化对铝材挤压模具工作带的表面硬度、硬化层深、表面粗糙度的影响.结果表明,激光相变强化技术通过改变H13钢模具工作带浅层晶格排列达到了硬化效果,硬度达到60～65 HRC,硬化层深度可达200～1000μm,工...     

40CrMo齿轮钢表面激光熔覆0.60C-15.25Cr-1.85Mo粉末工艺及其组织和性能

基于"光束中空,光内送粉"技术对40CrMo钢(/%:0.40C,1.20Cr,0.25Mo)进行表面激光熔覆铁基合金粉末(/%:0.60C,15.25Cr,1.11Si,1.85Mo)以提高硬度,获得更加理想的耐磨性能。40CrMo钢硬度HV_(0.2)值为250,激光熔覆后表面硬度HV_(0.2)值为500。对基体的进行200℃预热处理有利于获得更加良好的冶金结合,其基体的热影响区和结合区也相对较小。由于较大的温度梯度造成的快速冷却和合金化共同影响的结果,试样结合区硬度高于激光熔覆层其他区域。     

激光熔覆铁基合金粉末修复高速列车车轮磨损研究

针对高速列车车轮踏面磨耗问题,利用5 kW横流CO2激光器,采用预置铁基合金粉末法,对车轮钢表面进行激光熔覆修复研究。通过选择合适水平的正交试验,确定了高速列车车轮钢表面激光熔覆铁基合金粉末的最优工艺激光功率、离焦量、扫描速度分别为:2.5 kW、20 mm和5 mm·s-1;采用扫描电镜(SEM)、自动转塔数显显微硬度计、摩擦磨损试验机、微机控制电子万能试验机对合金化涂层的显微组织、性能及界面结合强度进行性能测试。结果表明,通过激光熔覆制备的合金化涂层与车轮钢基体形成冶金结合、组织均匀致密,合金化涂层硬度从车轮钢基体到表面呈梯度分布,由基材的246 HV提高到326.5 HV,相对耐磨性为1.33,界面结合强度达到163.91 MPa。     

轧机衬板激光淬火工艺优化及变形的消除

激光表面淬火是激光表面改性领域中最先进的技术，它利用金属良好的导热性，将高能激光束照射到工件表面，使表层温度迅速升高至相变点之上(低于熔点),当激光束移开后，工件快速地自然冷却，实现材料的相变硬化。介绍了轧机衬板激光淬火的工艺特点，研究了激光表面淬火工艺参数对工件组织及性能的影响，确定了满足轧机衬板硬度和安装精度的工艺参数：激光功率1 600～1 700 W,扫描速度8～10 mm/s,光斑宽度15～17 mm。通过分析淬火后工件变形的原因，提出可利用专用加热设备使工件产生反向预变形，消除因激光淬火残余压应力产生的平面度变形。     

球墨铸铁表面激光熔覆钴基合金涂层的组织与性能

为了研究球墨铸铁QT600-3表面激光熔覆钴基合金的组织和性能,本试验采用预置送粉法,利用6 kW CO_2激光器将粒度为46~106μm的CoCrW合金粉末激光熔覆到QT600-3基材表面,激光熔覆工艺参数为:激光功率P=3.0 kW、扫描速度V=350 mm·min~(-1)、光斑直径2 mm、搭接率1.5,三道次熔覆,熔覆层厚度约为3 mm,在熔覆过程中采用热量补偿方法对试样温度场进行调控。通过Olympus金相显微镜(OM)、Zeiss-Sigma扫描电镜(SEM)、X'Pert MPD Pro型X射线衍射仪(XRD)、MHV2000数显显微硬度计,分析了熔覆层横截面的显微组织、物相及硬度的变化规律。结果表明:熔覆层表面成形良好,无裂纹、气孔等缺陷;熔覆层分为熔化区、结合区和热影响区,熔覆层与基体冶金结合良好,主要由γ-Co(面心立方)过饱和固溶体以及碳化物CoC_x,Cr_7C_3等组成;熔化区由表层的树枝晶和内部的胞状晶组成,在热影响区发生了组织转变,形成了马氏体并且球状石墨部分溶解,直径变小。熔覆层硬度随着与球墨铸铁基体表面距离增加,呈现先快速增大,后平缓增加,最后在表层区域又快速增大,熔覆层的最高硬度达到HV0.21077,较球墨铸铁基体的硬度提高了4倍以上。     

60CrMnMo激光表面处理的组织与性能

应用3kW连续CO2激光器对60CrMnMo轧辊钢在涂敷不同合金粉时进行表面激光熔凝处理,处理后对组织、硬度、脆性进行观察与测试.结果表明,处理后可获得熔凝层、硬化层、过渡层及基体四层组织;涂敷黑涂料时能得到最高的熔凝层与硬化层硬度,表面熔凝层硬度最高可达880 HV0.1,硬化层硬度最高可达997 HV0.1,涂敷Ni60合金粉对改善处理层的脆性有较好效果.     

Laser transformation hardening of iron-carbon and iron- carbon- chromium steels

The laser transformation hardening response of Fe-0.5C-0.8Mn and Fe-0.5C-0.8Mn-0.8Cr steels was examined. A 2 kW CO₂ laser was used to scan the steel surfaces at various rates. Complete transformation of pearlite to austenite, and hence to martensite, occurred in the laser heated surface layer of the Fe-C-Mn steel. During equivalent heat treatment of the Fe-C-Mn-Cr steel, incomplete austenitization of the pearlite colonies left the cementite plates largely undissolved. However, the maximum surface hardness was approximately the same for both alloys. Comparison of calculated and measured hardened depths yielded values of the effective coupling coefficient of the laser beam to the steel which varied as a function of beam interaction time. Modeling the process allowed a dis-tinction to be made between the effects of alloying elements and of pearlite spacing upon the depth of complete austenitization. In this case, the effect of the difference in pearlite spacing between the two steels was negligible. In the alloy steel, Cr and Mn were strongly partitioned to the cementite before heat treatment, and remained so after laser processing. Incomplete austenitization of that steel is attributed to partitioning of alloying elements to the cementite and their retarding influence on the diffusion controlled dissolution kinetics of the alloyed carbide.     

Laser-beam surface transformation hardening of hypoeutectoid Ck-60 steel

A carbon dioxide laser with a power of 1.5 KW was employed for surface hardening of a hypoeutectoid Ck-60 steel. The microstructures and hardness profiles were determined as a function of power density and laser beam travel speed. The microstructure in the laser-beam hardened zone depended on power density and consisted of plate martensite (for high power density) or autotempered martensite (for low power density). In the transition zone of the laser-beam treated specimens, martensite and ferrite were observed. Case depth and maximum hardness were found to depend on power density and travel speed. A simple one-dimensional heat flow model has been used for the selection of process parameters and for the prediction of case depth. Calculated and experimentally determined case depths are in good agreement for medium values of power density.     

Laser transformation hardening of tempered 4340 steel

A CO₂ laser with a fixed laser power of 1.8 KW was employed to harden the surface of some AISI 4340 steel specimens, with a scan rate from 5 to 10 mm/s. The influence of scan rates and tempering treatments of the alloy on the hardness profile and microstructure of the laserhardened zone was analyzed. Microstructures in the hardened zone consisted of mainly lath and twinned martensites. However, depending on the scan rate, autotempered martensite has also been found. In the transition zone of laser-treated specimens, partially dissolved carbides with austenite envelopes and/or austenite islands in a matrix of martensite were observed. The time required for complete carbide dissolution into austenite during laser treatment depended on the tempering conditions. A lower tempering temperature of the alloy produced a deeper hardened zone and a narrower transition zone in the hardness profile. A simple mathematical estimation of the hardness profile, based on the carbon diffusion distance in austenite, was performed. The calculated results are in reasonably good agreement with the measured hardness profiles and the microstructural observations in the laser transformation hardening process. Formerly Graduate Research Assistant, Institute of Materials Science and Engineering, National Taiwan University     

A Fundamental Study of Laser Transformation Hardening

A theoretical and experimental study of heat flow and solid-state phase transformations during the laser surface hardening of 1018 steel was conducted. In the theoretical part of the study, a three-dimensional heat flow model was developed using the finite difference method. The surface heat loss, the temperature dependence of the surface absorptivity, and the temperature dependence of thermal properties were considered. This heat flow model was verified with the analytical solution of Jaeger and was used to provide general heat flow information, based on the assumptions of no surface heat loss, constant surface absorptivity, and constant thermal properties. The validity of each of these three assumptions was evaluated with the help of this heat flow model. In the experimental part of the study, on the other hand, a continuous-wave CO₂ laser of 15 kW capacity was used in conjunction with a beam integrator to surface harden 1018 steel plates. The beam power and the travel speed of the workpiece were varied, and the onset of surface melting was determined. The configurations of the heat-affected zone observed were compared with those calculated using the heat flow model. The microstructure of the heat-affected zone was explained with the help of the calculated peak temperature, heating, and cooling rates.     

Laser melt injection of austenitic cast iron Ch16D7GKh with titanium

The results of studying the microstructure and microhardness of Ni-resist cast iron ChN16D7GKh after laser melt injection by means of introducing titanium particles into the melt are presented. The treatment was performed using a fiber laser with a beam focused into a spot 0.2 mm in diameter with a radiation power of 1 kW and the motion velocity of the laser beam of 10–40 mm/s. Titanium is dissolved in the cast-iron melt, and TiC particles are formed in the structure upon cooling. The coefficient of using the titanium powder increases as the fusion zone size increases and reaches 50% in the best case. A modified layer has a composite structure with a metallic matrix and a comparatively uniform distribution of titanium carbide particles. The microhardness of the modified zone is 600–700 HV. Its further growth is suppressed by the partial removal of carbon from the melt zone in the composition of red fume evolved in the process. Therefore, the Laves phase (TiFe₂) is formed instead of an increase in the TiC content upon increasing the titanium supply. The experimental data on the regularities of the weight loss caused by the substance removal from the melt zone depending on laser melting parameters are presented.     

利用激光相变硬化技术对合金压片模进行国产化替代研究

采用3千瓦横流CO2激光器及激光相变硬化技术，对40Cr锻件进行激光扫描，利用金相分析及测定显徽硬度的方法，对激光工艺进行优化筛选，利用优化出来的参数进行实际加工，与对照组进行同时上机实用。结果表明：用激光相变技术处理的40Ct材质压片模，完全达到生产实用要求，能够替代贵重材质的、价格昂贵的进口品。     

40Cr钢方坯表面淬火工艺及组织转变规律

热送裂纹限制了热送技术的推广应用,而表面淬火技术可以有效改善热送裂纹的质量问题.以某钢厂180 mm×180mm断面小方坯连铸机为对象,40Cr钢为淬火试验钢种,通过开展现场离线淬火试验研究,并利用光学显微镜(OM)及数值仿真技术,进行显微组织分析与淬火-自回火过程传热分析,研究了表面淬火对铸坯表层组织转变的影响规律....     

Heat flow during the laser transformation hardening of cylindrical bodies

A heat flow model was developed for the laser transformation hardening of cylindrical bodies. Three different cases of surface hardening were considered,i.e., the surface of a solid cylinder, the outer surface of a hollow cylinder, and the inner surface of a hollow cylinder. The thermal responses of the workpiece in these three different cases were compared and discussed. The validity of the model was verified with experimental results obtained on 4140 steel. The effects of operating conditions on heat flow and the surface hardening of the workpiece were discussed. These operating conditions are the travel speed of the workpiece, the power input, the width of the laser beam on the surface of the workpiece, and the cooling of the workpiece. In order to provide general heat flow information, calculated results based on dimensionless variables were presented.     

热回复过程高强耐候钢Q450NQR1的高温力学性能

在热回复条件下,采用Gleeble-1500D热/力模拟实验机,研究测试了高强耐候钢Q450NQR1(/%:0.05～0.10C、0.30～0.50Si、0.80～1.00Mn、≤0.020P、≤0.008S、0.20～0.40Cu、0.15～0.35Ni、0.40～0.60Cr)200mm×1 350 mm铸坯试样在700～1 000℃,热拉伸应变率5×10^-3 s^-1时的强度、塑性模量和断面收缩率。结果表明,随温度下降铸坯塑性模量(硬化系数)和强度增加,800℃时铸坯的强度随温度的变化速率出现明显转变;925～700℃时铸坯断面收缩率≤60%;为保证铸坯质量,在矫直过程铸坯表面温度应≥950℃。     

The prediction of case depth in laser transformation hardening

An approximate heat flow model is developed to predict the case depth in laser transformation hardening of steel surfaces. The model exploits the dimensional relationships between the process variables to give master diagrams for the hardened depth using Gaussian and uniform, rectangular sources. Critical values of dimensionless parameters are identified which predict the conditions for first hardening and the onset of surface melting. Good agreement is demonstrated with a wide range of experimental data, and comparisons are made with previous modeling methods and process diagrams.