780 MPa级热镀锌双相钢微观裂纹成因及改进措施

780MPa级热镀锌双相钢表面块状色差缺陷的原因为基板表面大量开口微观裂纹。微裂纹开口导致Fe2Al5抑制层形成异常,宏观表现为块状色差。微裂纹主要分布在带钢中部板面中间等热轧卷散热较慢位置,裂纹处珠光体晶粒较粗大。通过分析此带钢全流程氧化特性,带钢表层在加热炉中形成锚状氧化铁皮,附着在带钢基体上不易去除;在热轧工序中Si、Cr元素向表面富集形成硬质氧化圆点,附着在带钢近基体上。Si、Cr氧化圆点与粗大珠光体在冷轧过程中形成微裂纹。带钢在镀锌工序退火过程中,表面微裂纹在大张力作用下成为开口状态。微裂纹开口增加了基板与锌液接触面积,增加了锌液与铁的反应速度;同时裂纹开口导致带钢表面破碎,Fe2Al5抑制层无法良好结晶,这两点因素导致Fe_2Al_5抑制层无法良好形成。降低板坯加热炉温度,减少"锚状"氧化铁皮的生成。提高粗轧出口温度,形成疏松铁皮,在冷轧酸洗过程中带走Si、Cr氧化圆点。降低热轧卷取温度,使热卷带板中位置形成细小珠光体,提高开裂抗力。降低镀锌工序退火炉张力,减小微裂纹开口几率。通过以上措施,可有效改善780MPa级热镀锌双相钢表面微裂纹,消除色差。     

电镀锌表面条纹缺陷成因分析

运用扫描电子显微镜和电子背散射衍射(EBSD)技术对电镀锌板表面暗条纹及冷轧基板对应缺陷进行了失效分析。结果表明电镀锌耐指纹板表面暗条纹缺陷形成有三种原因:1)钢板次表面的冶炼缺陷经后续轧制露头后引起后续电镀锌层异常,形成黑色条带缺陷;2)热轧基板表面点状夹杂物露头(或热轧轧辊剥落物、富Cr的氧化铁皮压入),周边区域酸洗不完全,形成锈蚀产物后在后续轧制工序被轧入表面,引起电镀锌层异常形成条纹缺陷;3)热轧时表面局部温度偏低,在二相区轧制形成的高斯织构遗传到冷轧板,电镀锌时形成丝状斑迹缺陷。     

EPS处理对热浸镀锌高强钢表面质量的影响

目的 研究湿法抛丸（EPS）处理对800 MPa级高强钢表面质量及热浸镀锌效果的影响。方法 采用金相显微镜、扫描电镜和辉光光谱仪，对EPS处理及盐酸酸洗、冷轧和热浸镀锌各生产工序中的800 MPa级高强钢表面形貌和表层成分分布进行研究。结果 EPS处理卷表面凹凸不平，而盐酸酸洗态表面平整，EPS处理卷表面粗糙度Ra值为2.645 μm，约为盐酸酸洗卷的2倍，残留的表面氧化铁皮厚度为0.93 μm，比盐酸酸洗试样厚45%。冷轧状态下，EPS处理卷表面凸起被轧平，表面基体“露白”比例约为63.5%，比盐酸酸洗低20.1%，残留的表面氧化铁皮厚度为0.36 μm，比盐酸酸洗试样厚57%。热浸镀锌态下，EPS处理卷锌晶界存在尺寸3~5 μm的孔隙，表面易出现尺寸约1 cm的漏镀缺陷。去除表面锌层后发现，EPS处理卷基板表面存在“翘皮”，微观观察抑制层形貌发现，界面处Fe-Al抑制层颗粒未充分形成，甚至未形成。GDS分析表明，抑制层处Al峰值较盐酸酸洗卷低17%。结论 EPS处理后表面凹凸不平，冷轧时易“折叠”分层，去锌层基板表面有“翘皮”，易造成锌层厚薄不均，同时EPS处理的残留氧化层较厚，且易造成氧化铁皮嵌入基体，导致锌层与基板界面Fe-Al抑制层稀疏，锌层粘附性低，甚至漏镀。     

不同热连轧工艺参数条件下三次氧化铁皮的分析

采用热模拟实验机研究了不同的精轧开轧温度、终轧温度和卷取温度对钢板表面三次氧化铁皮的结构和厚度的影响规律。试验结果表明:随着精轧开轧温度和终轧温度的升高,Fe2O3和Fe3O4在整个铁皮层中的百分量逐渐降低,而FeO层的增长速率较快。氧化铁皮的共析转变普遍存在"迟滞现象",其中350~500℃是该试验用钢共析转变鼻温区。从高温区快速降温到鼻温区,而后缓慢冷却到室温是避免发生先共析反应、促进共析反应的有效方法之一。在鼻温区以上温度卷取,可获得含有FeO较多的减酸洗钢,此种氧化铁皮有利于酸洗。在鼻温区卷取可获得含有Fe3O4较多的免酸洗钢。这是热连轧钢板表面氧化铁皮的主要两个控制思路。     

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 要: 采用热模拟实验机研究了不同的精轧开轧温度、终轧温度和卷取温度对钢板表面三次氧化铁皮的结构和厚度的影响规律。实验结果表明：随着精轧开轧温度和终轧温度的升高，Fe2O3和Fe3O4在整个铁皮层中的百分量逐渐降低，而FeO层的增长速率较快。氧化铁皮的共析转变普遍存在“迟滞现象”，其中350-500℃是该实验用钢共析转变鼻温区。从高温区快速降温到鼻温区，而后缓慢冷却到室温是避免发生先共析反应、促进共析反应的有效方法之一。在鼻温区以上温度卷取，可获得含有FeO较多的减酸洗钢，此种氧化铁皮有利于酸洗。在鼻温区卷取可获得含有Fe3O4较多的免酸洗钢。这是热连轧钢板表面氧化铁皮的主要两个控制思路。     

卷取温度和随后的冷却方式对65Mn钢板表面质量的影响

热轧65Mn钢板表面常存在粉化的氧化皮，导致酸洗后钢板表面有色差。为解决这一问题，研究了热轧后在不同温度卷取随后以不同方式冷却的65Mn钢板发生表面氧化的原因。结果表明：热轧后在700～730℃卷取随后坑冷的65Mn钢板表面氧化皮粉化最严重，而热轧后在600～620℃卷取随后空冷的65Mn钢板表面氧化铁皮粉化最轻微，这是因为较高的卷取温度使钢板表面发生了较严重的脱碳和晶间氧化，晶界耐蚀性降低，酸洗过程中产生色差；热轧后在600～620℃卷取随后空冷的65Mn钢板表面晶间氧化深度从20μm下降至小于5μm,脱碳程度明显减轻，晶界耐蚀性提高，酸洗后色差减少。     

不同热轧工艺条件下镀锡板表面氧化铁皮分析

对不同热轧生产工艺条件的镀锡板表面氧化铁皮进行了对比试验.结果表明:由于热轧装备条件的改善,所生产的热轧镀锡板,其表面氧化铁皮厚度由原来的6～13 μm减薄至4～7μm,酸洗性能也明显提高;与MR-2相比,由于MR-3在CT 680℃高温卷取,MR-3氧化铁皮厚度较厚,氧化铁皮相变反应析出更强烈,析出的Fe3O4-Fe共晶组织明显增多;粗轧出口温度RT 1010～969℃,进行较低温度轧制时,随着轧制温度的降低,氧化铁皮厚度略有减薄.     

热基热镀锌板锌层粘附性控制机理

通过金相、扫描、能谱和辉光等方法研究了酸洗板表层以及热基镀锌板锌层中的元素分布规律,锌层组织特点及粘附性控制机理。结果表明:酸洗板存放时间长,表层C、O元素含量高,Si、Mn元素易在酸洗板表面富集,基板入锌锅前易带入杂物,退火过程中表面还原不充分,锌液中Al元素与带钢表面氧反应不充分导致基板与锌层间存在过量氧化物,造成锌层粘附不良。钢板入锌锅温度460℃时,锌层中易于形成ζ、δ1和Г等脆性相的合金化层,造成冲压脱锌;钢板入锌锅温度440℃时,Al Fe3抑制层更靠近锌层,更能有效抑制Fe向锌层扩散,减小合金层的厚度。     

低碳钢表面氧化铁皮在连续冷却过程中的组织转变

实验室条件下研究了低碳钢表面氧化铁皮在连续冷却过程中的组织转变,分析了卷取温度和冷却速率对Fe1-yO相变的影响。在不同连续冷却条件下,最终的氧化铁皮结构可分为两类,第一类氧化铁皮只包含先共析Fe3O4和残余Fe1-yO;第二类氧化铁皮由共析组织、先共析Fe3O4和少量残余Fe1-yO组成。结果表明,低冷却速率有利于共析反应的发生。在400~500℃,Fe1-yO最不稳定,在该温度区间卷取,最终氧化铁皮中将出现大量的共析组织。当卷取温度远高于570℃,Fe2+在Fe1-yO中扩散,使Fe1-yO的阳离子空位浓度降低,稳定性提高,这种Fe1-yO的共析转变需要更长时间,最终的氧化铁皮中共析组织含量较低。     

终轧温度和卷取温度对汽车大梁钢氧化铁皮特征的影响

通过SEM(扫描电镜)和IPP软件研究了不同终轧温度和卷取温度下汽车大梁钢的氧化铁皮厚度、微观结构。结果表明,终轧温度为800～920℃时,汽车大梁钢的氧化铁皮微观结构均为残余FeO+先共析Fe_3O_4,随着终轧温度的升高,氧化铁皮平均厚度增加,Fe O比例增加,先共析Fe_3O_4比例降低。卷取温度为530～650℃时,氧化铁皮组织中存在共析组织(Fe_3O_4+Fe),随着卷取温度的升高,汽车大梁钢的氧化铁皮平均厚度增加,FeO比例增加,先共析Fe_3O_4比例增加,共析(Fe_3O_4+Fe)比例降低。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.