6061铝合金淬火冷却过程中的表面换热系数

通过6061铝合金末端淬火测得的冷却曲线,结合有限差分法和反传热求解法,研究了6061合金固溶处理在不同冷却方式下的冷速及表面换热系数与温度的变化规律。结果表明,6061铝合金在水雾冷和喷水冷却过程中,端面冷速先增大后减小,在400℃左右达到峰值,峰值冷速约为30℃/s。6061铝合金的表面换热系数与温度呈非线性关系,其大小随着温度的降低先逐渐增大,在150～100℃范围内达最大值,然后下降;在风冷过程中,表面换热系数值先急剧增大,当温度下降到500℃后增速明显减慢。     

Calculation of thermal stress field with non-linear surface heat-transfer coefficient during quenching

The heat conduction equation in a coupled thermo-inelastic body, was derived by means of the irreversible thermodynamics and the measured data of the inner dissipation for metal. The coupled coefficients, which are dependent on temperature and inelastic strain rate, can be determined by the measured data of inner dissipation for metal. The functional of a coupled thermal inelastic problem was derived by means of nonlinear functional analysis theory. Finally, it is proved that the critical points of the functional are the solutions of coupled thermal inelastic equations.     

常用钢淬火表面换热系数耦合相变的反传热分析

根据反传热方法和实测的每种钢探头在多种介质中淬火时的冷却曲线,建立了耦合相变的轴对称有限差分模型,结合编写的FORTRAN程序计算每种钢探头淬火过程的表面换热系数。结果表明,相变对计算有影响,考虑相变时的计算值是合理的。同时发现,淬火过程的换热系数与淬火介质及探头材料均相关,相同的钢探头在不同介质中淬火时的换热系数不同,而不同材料的钢探头在同种介质中淬火时的换热系数也不同。     

Dependence of heat transfer coefficient at quenching on diameter of cylindrical workpieces

Abstract

For computer simulation of a quenching process, the fundamental prerequisite is to have the relevant heat transfer coefficient (HTC) calculated as a function of the workpiece’s surface temperature and time respectively. In order to calculate the HTC experimental measurement of the temperature–time history (cooling curve) near the workpiece surface is necessary. In this investigation, cylindrical probes with diameters of 20, 50 and 80 mm are used. The cooling curve was always measured 1 mm below the surface of the probe. Special care has been taken to keep all other factors (e.g. design of the probes, temperature measurement, quenching conditions and calculation procedure), which can influence the calculated HTC, constant, in order to ensure that the only variable is the diameter of the probe. Assuming a radially symmetrical heat flow at the half length of the probe, the HTC was calculated using one-dimensional inverse heat conduction method. The unexpected striking result of this investigation is the fact that for the probe diameter (80 mm) the calculated HTC as a function of surface temperature does not show the film boiling phase. A plausible explanation for this effect is given, based on the critical heat flux density. The possibility of establishing a simple fixed relation (a correction factor) between the HTC and the diameter of cylinders is discussed.     

高强度钢板热成形界面换热系数估算

为评估高强度钢板热冲压成形过程中的传热强度,本文根据实验采集的温度曲线,利用热平衡的数值积分形式得到了不同压强下随温度连续变化的换热系数,求解过程中通过等效热容的方式引入了马氏体相变的影响.结果表明,换热系数的大小不仅与压强相关,而且随着材料温度变化.最后求得的换热系数被带入Abaqus仿真计算,仿真结果能和实验数据较好的吻合,从而对实验及估算方法的有效性进行了验证.     

Computation of synthetic surface heat transfer coefficient of 7B50 ultra-high-strength aluminum alloy during spray quenching

According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient (SSHTC) of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the ProCAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7B50 alloy calculated using the JMatPro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420–230 °C (quench sensitive temperature range) is 45.78 °C/s. The peak-value of the SSHTC is 69 kW/(m²·K) obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 °C. In the initial stage of spray quenching, the phenomenon called “temperature plateau” appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160–170 °C with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.     

Spatial interfacial heat transfer and surface characteristics during gravity casting of A356 alloy

As one of the key boundary conditions during casting solidification process, the interfacial heat transfer coefficient (IHTC) affects the temperature variation and distribution. Based on the improved nonlinear estimation method (NEM), thermal measurements near both bottom and lateral metal-mold interfaces throughout A356 gravity casting process were carried out and applied to solving the inverse heat conduction problem (IHCP). Finite element method (FEM) is employed for modeling transient thermal fields implementing a developed NEM interface program to quantify transient IHTCs. It is found that IHTCs at the lateral interface become stable after the volumetric shrinkage of casting while those of the bottom interface reach the steady period once a surface layer has solidified. The stable value of bottom IHTCs is 750 W/(m²·°C), which is approximately 3 times that at the lateral interface. Further analysis of the interplay between spatial IHTCs and observed surface morphology reveals that spatial heat transfer across casting-mold interfaces is the direct result of different interface evolution during solidification process.     

传热反问题方法在漏钢预报中的应用

基于漏钢预报中实时监测结晶器铜板受热状态的需要,建立了二维稳态热传导模型,在Vc＋＋6.0平台下编制了传热反问题计算程序（IHCP_2D）,该程序能通过结晶器铜板中有限个热电偶的测量值,快速反算出铜板受热面上的热流密度和温度分布.通过对一组实测数据的分析,验证了程序的可靠性.     

单圆孔气体冲击射流冷却高温钢板瞬态传热特性

采用单点测温试验方法,结合导热反问题计算,研究了钢板表面温度从800 ℃降至100 ℃、喷嘴出口Re数为27000、出口距钢板垂直冲击距离Z/D为4情况下钢板表面瞬态传热特性。结果表明,冷却初始阶段局部Nu数沿冲击中心径向呈钟形分布,随冷却过程进行在r/D=2处出现第二峰值。冷却初始阶段平均努塞尔数与经典Hofmann公式及Martin公式基本一致,随冷却过程进行明显下降,但当r/D>10时这一趋势并不明显。     

Dissimilar spot welding of dual phase steel/ferritic stainless steel: phase transformations

Phase transformations in dissimilar resistance spot welds of dual phase steel and ferritic stainless steel are analysed. In contrast to a full martensitic microstructure predicted by the Schaeffler and Balmforth diagrams, a ferrite–martensite microstructure was observed in the fusion zone. The formation of ferrite phase in the fusion zone can be attributed to the rapid cooling rate of resistance spot welding, which suppresses the post-solidification ferrite–austenite transformation. The grain growth and martensite formation were main metallurgical features of the heat affected zone of ferritic stainless steel side. Microstructure gradient of heat affected zone in dual phase steel side was dictated by martensitic transformation. The effect of weld thermal cycle on the mechanical performance of the joint is discussed.     

The application of rational approximation in the calculation of a temperature field with a non-linear surface heat-transfer coefficient during quenching for 42CrMo steel cylinder

The calculation of a temperature field has a great influence upon the analysis of thermal stresses and stains during quenching. In this paper, a 42CrMo steel cylinder was used an example for investigation. From the TTT diagram of the 42CrMo steel, the CCT diagram was simulated by mathematical transformation, and the volume fraction of phase constituents was calculated. The thermal physical properties were treated as functions of temperature and the volume fraction of phase constituents. The rational approximation was applied to the finite element method. The temperature field with phase transformation and non-linear surface heat-transfer coefficients was calculated using this technique, which can effectively avoid oscillationin the numerical solution for a small time step. The experimental results of the temperature field calculation coincide with the numerical solutions.     

热成形淬火过程模具/板料界面接触热阻的测量计算方法概述

分析了固体界面接触热阻的形成机理和影响接触热阻数值的诸多因素,并根据热成形淬火过程模具/板料界面的传热模型,基于傅里叶定律对其界面传热情况进行分析,利用热阻的思想推导出界面接触热阻的表示方法。对已有的测量、计算热成形模具/板料界面接触热阻的方法进行概述:逆热传导法基于导热微分方程和傅里叶定律,通过测得的热流密度计算得到接触热阻;间接法依据接触电阻和接触热阻有相同的产生原因,通过特定装置测定接触电阻再根据接触电阻和接触热阻的关系计算得到接触热阻。最后从测量装置、测量计算原理和测量计算的过程等方面对两种方法进行了比较,并分析了界面接触热阻对热成形模具以及新型材料研发的重要性。     

大功率发光二极管相变热沉的制造及测试(英文)

制造一种新型大功率发光二极管(LED)相变热沉作为封装级散热元件,采用犁切?挤压成形的周向螺旋状微沟槽和采用冲压成形的放射状径向沟槽组成的三维结构作为蒸发面强化沸腾结构,内壁采用铜粉颗粒烧结而成的毛细芯结构为工质提供循环动力。测试了相变热沉在不同输入功率和工质条件下的运行特性。结果表明,相变热沉具有良好的传热能力,在环境温度为20°C,输入功率为10W的条件下,相变热沉最高温度为86.8°C,可满足功率为10W的LED封装散热需求。     

相变对22CrMo钢淬火应力影响的数值模拟

利用有限元法和热弹塑性理论,结合马氏体相变动力学方程,对22CrMo钢圆柱体试样在淬火过程中的温度场、组织场和应力场进行数值模拟分析,重点模拟分析了试样表面和心部在淬火过程中应力的变化及马氏体相变对淬火应力的影响。模拟发现,相变对淬火应力影响比较明显。在一定条件下,在油中淬火,组织应力对淬火应力分布的影响要远大于热应力的影响,最终试样的淬火残余应力将以表层为拉应力而心部为压应力的组织应力形式存在。通过对残余应力的测量结果表明,计算结果与实测值相吻合。     

Inverse optimal design of the radiant heating in materials processing and manufacturing

Combined convective, conductive, and radiative heat transfer is analyzed during heating of a continuously moving load in the industrial radiant oven. A transient, quasi-three-dimensional model of heat transfer between a continuous load of parts moving inside an oven on a conveyor belt at a constant speed and an array of radiant heaters/burners placed inside the furnace enclosure is developed. The model accounts for radiative exchange between the heaters and the load, heat conduction in the load, and convective heat transfer between the moving load and oven environment. The thermal model developed has been used to construct a general framework for an inverse optimal design of an industrial oven as an example. In particular, the procedure based on the Levenberg-Marquardt nonlinear least squares optimization algorithm has been developed to obtain the optimal temperatures of the heaters/burners that need to be specified to achieve a prescribed temperature distribution of the surface of a load. The results of calculations for several sample cases are reported to illustrate the capabilities of the procedure developed for the optimal inverse design of an industrial radiant oven.     

以BNi2非晶为中间层的CB2耐热钢瞬时液相扩散连接的接头组织和性能研究

本文主要研究采用BNi2非晶态中间层的CB2耐热钢瞬时液相扩散连接接头组织和性能,及焊后热处理对接头组织和性能的影响。富Cr硼化物(CrB, CrB2, Cr2B3, Cr3B4 and Cr5B3)和Cr-Mo硼化物出现在接头的过渡区和扩散影响区,其尺寸和数量在等温凝固完成时达到最大值。随着连接温度和时间的增加,富Cr的硼化物和Cr-Mo硼化物逐渐减少,而BN相逐渐增加。经过焊后热处理后,接头的富Cr硼化物几乎全部消失,而BN相的尺寸和数量增加。在热处理之前,焊接温度为1150°C ,保温时间1800s的接头有最大的拉伸强度为934 MPa,延伸率为5.3%。通过焊后热处理,断裂发生在母材,延伸率提升到20%,而拉伸强度降低到720 MPa。     

高速线材风冷段温度及相变藕合模型开发

研究开发成功了高速线材斯太尔摩冷却线风冷段温度及性能预报综合新模型,对该模型的相变模拟的基本原理进行介绍.该模型在重钢高线厂得到应用,现场实测的温度数据证明了模型的可靠性,预测温度与实测温度的偏差不超过20℃,模型预测了φ8mm 70钢线材在三台风机全开条件下相变在第二台风机附近发生,相变持续了约6s.基于开发的新模型,分析表明不同工艺参数如线材的直径和辊道速度对风冷段线材的冷却速度和相变区间有直接的影响.     

Intermetallics and phase transformations of the Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr alloy

Intermetallics and phase transformations of the zirconium-based alloy,Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr,were investigated by conventional X-ray diffraction (XRD),differential scanning calorimetry (DSC),and dilation measurement.Three types of precipitates,namely,(ZrNb)2Fe,Zr(CrFe)2,and Zr3Fe,were detected by XRD.The cubic Ti2Ni-type (ZrNb)2Fe was found to be the main precipitate in the alloy,and it was proposed to dissolve at 861℃,whereas Zr3Fe dissolved at 780℃ and Zr(CrFe)2 at 814℃.No precipitates were observed at a temperature higher than 900℃.The transformation-start temperature of α-Zr →β-Zr was reconfirmed to be 780℃,and the end temperature of α-Zr→β-Zr was determined to be 955℃.The dilation result also revealed that the martensitic transformation-start temperature,Mr,and the finish temperature,Mr,of this alloy were 741℃ and 645℃,respectively.     

大线能量低焊接裂纹敏感性钢的显微组织

简要叙述了新研制的大线能量焊接低焊接裂纹敏感性调质高强度钢的特点.研制的新钢种属低碳低合金高强钢,集高强度(σs≥490 MPa、σb≥610 MPa)、高韧性(-20℃时横向Akv≥47 J)、优异的焊接性能(厚度≤50 mm钢板焊前不需预热或稍加预热而不产生冷裂纹)于一体,并能承受大线能量(≥50 kJ/cm)焊接.研究了模拟焊接热影响粗晶区(CGHAZ)的微观组织结构特征及其与力学性能的关系.结果表明:CGHAZ中复合夹杂物可促进针状铁素体的形成,针状铁素体的数量与输入线能量有关并显著影响CGHAZ的力学性能.     

Calculation of phase transformation latent heat based on cooling curves in end-quench test and its application in nickel-based superalloy

To obtain the phase transformation latent heat corresponding to different cooling rates with low test workload and cost, the Newton thermal analysis method and the improved Newtonian thermal analysis method were discussed based on the cooling curve obtained in the end-quench test. The validity of two methods was given by the latent heat calculation of 45^# steel. The results show that the relative error of latent heat is 5.20% through the improved Newtonian thermal analysis method, which is more accurate than the Newtonian thermal analysis method. Furthermore, the latent heat release of phase transformation of the self-designed CSU-A1 powder metallurgy nickel-based superalloy increases from 4.3 to 12.29 J/g when the cooling rate decreases from 50.15 to 33.40 °C/min, because there is more sufficient time for the alloy microstructure to complete the phase transformation process when the cooling rate is smaller.