Laser Surface Hardening of 9CrSi Steel

The effects of laser hardening parameters such as beam power,beam diameter and scanning rate on microstructure and mardness of 9CrSi steel were investigated.The microstructure of the surface layer of 9CiSi steel was changed from pearlite to martensite,retained austenite and carbide by laser hardening .The depth of the hardened layer increased with increasing laser energy density and the surface hardeness increased by 3-5times as high as the untreated steel.The laser hardened surface had good wear resistance due to martensite and carbide in the surface layer.The wear mode at low speed was abrasive,while the wear mode at high speed was adhesive.     

A study of local deformation and damage of dual phase steel

Deformation and fracture behavior of Dual Phase (DP) high strength steel were investigated by means of a microstructure based Finite Element (FE) modeling. Representative Volume Elements (RVEs) were applied to consider effects of various microstructure constituents and characteristics. Individual stress–strain curves were provided for ferrite, martensite as well as transformation induced Geometrically Necessary Dislocations (GNDs) taking into account in the RVEs. Principally, the GNDs occurred around phase boundaries during quenching process due to the austenite–martensite transformation. Flow behaviors of individual phases were defined on the basis of dislocation theory and partitioning of local chemical composition. Then, flow curves of the examined DP steel were predicted. Furthermore, the Gurson–Tvergaard–Needleman (GTN) model was used to represent ductile damage evolution in the microstructure. Occurrences of void initiation were characterized and damage parameters for RVE simulations were hence identified. Finally, influences of the GNDs, local stress and strain distributions and interactions between phases on predicted crack initiation in the DP microstructure were discussed and correlated with experimental results.     

The role of Cu and Al addition on the microstructure and fracture characteristics in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels with superior toughness

The effects of Cu and Al addition on the microstructure and fracture in the coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels with superior toughness were studied and compared with the X70 pipeline base steel counterpart. The microstructure in base steel was dominated by a small fraction of acicular ferrite and predominantly bainite. However, acicular ferrite microstructure was obtained in Cu-bearing steel, which nucleated on complex oxide with outer layer of MnS and CuS because of Cu addition. The microstructure in Al-bearing steel consisted of bainite with ultrafine martensite–austenite constituent, which was refined by Al addition. CGHAZ in Cu-bearing and Al-bearing steels had superior impact toughness and ductile fracture, which were attributed to acicular ferrite and ultrafine martensite–austenite constituent, respectively.     

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。     

Real microstructure based micromechanical model to simulate microstructural level deformation behavior and failure initiation in DP 590 steel

Dual phase (DP) steels having a microstructure consists of a ferrite matrix, in which particles of martensite are dispersed, have received a great deal of attention due to their useful combination of high strength, high work hardening rate and ductility. In the present work, a microstructure based micromechanical model is developed to capture the deformation behavior, plastic strain localization and plastic instability of DP 590 steel. A microstructure based approach by means of representative volume element (RVE) is employed for this purpose. Dislocation based model is implemented to predict the flow behavior of the single phases. Plastic strain localization which arises due to incompatible deformation between the hard martensite and soft ferrite phases is predicted for DP 590 steel. Different failure modes arise from plastic strain localization in DP 590 steel are investigated on the actual microstructure by finite element method.     

Microstructure and wear resistance enhancement of cast steel rolls by laser surface alloying NiCr–Cr3C2

The laser surface alloying technique was used to form wear resistant layers on 70MnV cast steel rolls with NiCr–Cr₃C₂ powders. The objective was to investigate the effects of the scanning speed on microstructure, phases, microhardness and wear resistance. Results indicate that the alloyed layers had dense, pore and crack free and homogeneous structures, as well as a metallurgical bonding with the substrates. With the increase of scanning speed, volume of retained austenite in the alloyed layer increased, microhardness and wear resistance increased and the microstructure refined. Wear results indicated that the wear resistance of the alloyed layer was enhanced by 7.8 times compared with that of the cast steel substrate. The improvement in wear resistance was attributed to the combined results of the grain refining effect, the solution strengthening effect, the tough γ-Fe matrix of the layer, the distribution of the hard Cr₇C₃, Fe₃C and martensite phases, and the good bonding between these hard phases and the matrix.     

45 钢表面激光相变硬化改性组织及耐蚀性能

目的为了改善45钢表面状态,提高其表面性能,采用CO2激光器对其表面进行激光相变硬化处理。方法利用带有能谱的扫描电子显微镜(SEM/EDS)、盐雾试验机等,对激光相变硬化层组织及耐蚀性能进行了观察和分析。结果激光相变硬化层由熔化区、相变硬化区和热影响区三部分组成,其组织依次为:混合马氏体+未溶碳化物、针状马氏体、残余奥氏体。随扫描速度增加,耐蚀性先变好而后变差。结论激光相变硬化处理可改善45钢的表面性能,显著提高其耐蚀性能。     

模具钢表面激光沉积316L不锈钢的组织转变及差异性

为了揭示Cr系注塑模具钢表面采用异种材料沉积过程的组织演变机制,在两种模具钢表面沉积316L不锈钢,利用扫描电镜、电子探针、X射线衍射仪等表征微观组织及硬度特征,并结合熔凝动态过程及Schaeffler相图分析界面及沉积层区组织转变机理。结果表明:由于基体元素组成及组成相分布的差异,导致在沉积层界面的组织转变呈现明显差异性。高Cr莱氏体钢组织过渡区厚度为200μm,过渡区组织形态和组成相明显区别于沉积层其他区域,碳化物在过渡区经历了先局部聚集性长大、之后枝晶间均匀分布等复杂变化;而P20钢沉积层的组织过渡区厚度小于20μm,组织以枝晶方式生长且与沉积层非过渡区连通,同时枝晶内发现了弥散分布的颗粒状碳化物。在熔池中C,Cr,Ni等元素的动态变化作用下,两种钢沉积层的非过渡区组成相也呈现明显差异,高Cr莱氏体钢和P20钢沉积层的基体相分别为奥氏体相与马氏体相,由此导致其硬度值变化范围分别为295~325HV_0.2和500~575HV_0.2。     

低碳双相钢丝热处理与冷拉拨变形的组织观察

对２０双相钢线热处理与拉拨变形的组织进行了观察，结果表明，随亚温淬火温度的升高，双相组织中马氏体的亚结构由孪晶型变成位错型，两相的变形能力和拉拨性能都得到改善，变形量是影响位错数量及在双相组织中形成错胞的主要因素。     

激光熔敷Ni基合金涂层的结构与性能

观测了激光熔敷NiCrBSi合金涂层的显微结构，研究了涂层与不锈钢基体的结合方式和时效处理对其组织结构和显微硬度的影响．用5kW连续二氧化碳激光器对不锈钢上等离子喷涂NiCrBSi合金层进行重熔．涂层的显微结构为细化树枝晶，由γ基体与γ／γ'和NiB的共晶组成．面心立方γ基体品格常数是0．3572nm．时效处理后的合金层由析出γ’沉淀强化相的针状和羽毛状马氏体组成，时效使显微硬度值显著提高．     

激光表面重熔对高速钢显微组织的影响

采用CO_2连续波激光对W18Cr4V高速钢进行表面重熔处理。分析结果表明,经激光重熔后高速钢的显微组织明显细化,重熔层内的相构成为马氏体、奥氏体,过剩的δ铁素体和M_6C、M_(23)C_6型碳化物。枝晶内为孪晶马氏体和部分板条马氏体。枝晶间为富合金元素的奥氏体和M_6C碳化物,孪晶马氏体上沿孪晶面有M_(23)C_6碳化物共格析出。激光扫描速度增加、δ铁素体量增多,重熔层显微硬度下降。     

40Cr激光熔凝硬化组织形态及硬度研究

利用CO2轴流激光加工机对40Cr钢表面进行激光熔凝硬化处理。利用扫描电子显微镜、金相显微镜和显微硬度计研究了不同工艺下熔凝硬化层及基体的显微组织和硬度分布特征。实验表明：熔凝硬化层由熔化区、相变硬化区和热影响区组成;由表及里组织分别为极细隐晶马氏体＋少量残余奥氏体、隐晶马氏体＋碳化物＋残余奥氏体、马氏体＋回火屈氏体＋铁素体。硬化层最高硬度约是基体的3倍;随着扫描速度的增加表层硬度先增加后减小,当扫描速度为2.5m·min^-1时,表层硬度最大,为1097.9HK。     

Investigation of electrochemical corrosion behavior in a 3.5 wt.% NaCl solution of boronized dual-phase steel

In this study, corrosion behaviors of boronized and non-boronized dual-phase steel were investigated with Tafel extrapolation and linear polarization methods in a 3.5 wt.% NaCl solution. Microstructure analyses show that the boride layer on the dual-phase steel surface had a flat and saw smooth morphology. It was detected by X-ray diffraction (XRD) analysis that the boride layer contained FeB and Fe₂B phases. The amount of martensite increases with an increase in the intercritical annealing temperature. Both the amount of martensite and the morphology of the phase constituents have an influence on the corrosion behavior of dual-phase steel. A higher corrosion tendency was observed with an increased amount of martensite. The corrosion resistance of boronized dual-phase steel is higher compared with that of dual-phase steel.     

Q&P980镀锌高强钢电阻点焊工艺及液态金属脆化裂纹分布EI北大核心

通过设计电阻点焊工艺的正交实验,确定了Q&P980镀锌高强钢的点焊工艺参数范围,并对其焊接接头进行显微组织表征和力学性能分析。结果表明:熔核区组织以交错分布的板条马氏体为主;热影响区组织由板条马氏体、残余奥氏体和铁素体组成,马氏体板条平均宽度在不完全淬火区最大为4.86μm。显微硬度测试发现,焊接接头硬度值呈“W”形对称分布,硬度峰值出现在细晶区,达到559HV,硬度最低值出现在不完全淬火区,为338HV,呈现明显的软化现象。对焊接接头进行室温拉伸,最大拉剪载荷的峰值为27.92 kN,其断口形貌呈现典型的韧窝状,属于韧性断裂。由于Zn的熔点较钢基体低,镀锌高强钢点焊时易发生Zn层优先熔化并沿晶界向基体渗透,在焊接接头处可观察到明显的液态金属脆化裂纹。     

Microstructure—Properties Correlation of Dual Phase Steels Produced by Controlled Rolling Process

The purpose of this research is to quantify the effects of compositional and processing parameters on the microstructure and properties of dual phase steel produced directly by hot rolling and rapid cooling.Steels with the base composition of 0.1%C,1.4%Si,and 1.0%Mn with additions of 0.5%Cr to influence hardenability,0.04%Nb to retard recrystallization in the latter stages of rolling,or 0.02% Ti to inhibit grain growth during and after reheating were investigated.Investigation was made to predict microstructure evolution and to correlate microstructure with processing parameters.The effects of the important microstructure parameters such as ferrite grain size,martensite volume fraction (VM) and morphology (polygonal or fibrous) on the tensile and impact properties are discussed.Multiple linear regression analysis of the ultimate tensile strength has shown that,increasing VM and martensite microhardness and grain refinement of ferrite are the major contributions to increase the strength of the steel.It was found that the dual-phase steel produced by controlled rolling process,with a microstructure which consisted of fine grained ferrite(4μm) and 35%-40% fibrous martensite,presented optimum tensile and impact properties because of enhanced resistance to crack propagation.     

塑料模具标准件顶杆用65MnV钢的组织分析

对新型塑料模具标准件顶杆用钢６５ＭｎＶ在淬火和氏温回火过程组织的变化进行了系统的研究。结果表明,６５ＭｎＶ钢的低温淬火组织为位错马氏体组织,随淬火温度的升高,淬火组织逐渐由针状与板条状马氏体的混合组织变成针状马氏体组织,马氏体组织的亚结构由位错型马氏体向孪晶马多体转变。钢在低温回火时析出与基体共格的弥散分布的须状ε碳化物,ε碳化物随回火温度的升高而发生转变,形成非共格的棒状渗碳体组织。     

60Si2Mn钢摩擦焊后热处理工艺的改进

对60Si2Mn钢摩擦焊焊接接头热处理后的组织和性能进行了研究,通过显微镜(OM)观察焊缝的界面层显微组织形貌特征,分析了热处理工艺对焊接接头性能的影响.结果表明:该钢摩擦焊焊接接头为珠光体+铁素体+马氏体组织,组织不均匀.经正火预处理后,焊接接头为细小粒状珠光体,再进行淬火加回火处理,组织均匀,为回火索氏体,焊缝下屈...     

Evaluation of properties and microstructure as a function of tempering time at intercritical temperatures in HY-80 steel castings

Prior work on a failed HY-80 Bridge Access Trunk (BAT) casting indicated the cause of failure to be improper processing techniques. As-received HY-80 casting material showed a non-homogenous microstructure with two distinct microconstituents present: undertempered martensite and a layered martensite–ferrite structure. Heat treatment temperatures from in the intercritical range (721–799 °C) produced microstructures that differ from the desired uniform microstructure of tempered martensite and were similar to those found in the failed casting. In order to further examine the relationship between processing and microstructure, it was decided to vary the time for which the steel was held in the intercritical temperature range. This additional work was warranted by the medium intercritical heat treatment results in the previous study [Holthaus JE, Koul MG, Moran AL. Property and microstructure evaluation as a function of processing parameters: large hy-80 steel casting for a US navy submarine. Eng Fail Anal 2006;13(1):1397–409] and its similarity to the failed casting microstructures. An important finding of this study is that, contrary to normal behavior during tempering, HY-80 steel tempered in the intercritical range demonstrates a severe loss of toughness; which can be exaggerated for longer hold times and higher temperatures. To confirm the hypothesis that the presence of brittle martensite formed by improper heat treatment was the cause of failure, SEM section fractography was employed to directly examine the microstructure underlying the fracture surface and to identify a correlation between microstructure and fracture mode.     

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。     

Fatigue life studies in carbon dual-phase steels

An investigation has been conducted to examine the morphological influence on fatigue life of low carbon steel with dual phase microstructure. The results showed that dual-phase microstructure, composed by ferrite and martensite had superior symmetrical bending fatigue strength when compared with ferrite-pearlite steel. Through those tests, evidences of different mechanisms were verified (such as ferrite cyclic hardening, slip band formation and beginning of crack nucleation and propagation). Based on the fatigue tests results, various mechanisms stages were discussed associated with different microstructure morphology.