Development and application of a new hot-work die steel for hot stamping

A new hot-work die steel for hot stamping was developed, and used the die for mass production. The produced die showed good performance owing to its high heat conductivity and wear-resistant characteristics. Two different benchmarking hot-work die steels were investigated, and then compared in terms of their impact ductility, temper characteristics ,heat conductivity, and thermal stability. The result of the high-temperature friction wear test indicated that oxidative wear was the main mode in high temperature. On the basis of the comparison and test results, the alloying composition of the new hot-work die steel was especially designed. The new die steel showed good performance with good wear-resistant quality, as well as temper hardness and heat conductivity of HRC 50 and 34.3 W/（ m ~ K）, respectively. Furthermore, without surface plasma nitriding, the die made of the new steel had no obvious galling with 6 142 strokes. After surface plasma nitriding, the die completed 40 000 strokes with good surface. The die life is expected to exceed 200 000 strokes.

NUMERICAL SIMULATION METHODS AND THEIR APPLICATION IN MATERIAL HOT-WORKING

With the development of modern science and technology, especially computer science, the numerical simulation method has been widely used in material hot-working. Mary achievements have been made in this field by using the numerical simulation method. The numerical simulation method, especially finite element method fully described in this paper.Applications of the numerical simulation method in material hot-working are also discussed. Finally, the future of the numerical simulation method is outlined.

Effect of Rare Earth Composite Modification on Microstructure and Properties of a New Cast Hot-Work Die Steel

The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly-distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02%, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.

APPLICATION OF RARE EARTH IN SURFACE HEAT TREATMENT OF HOT-WORKING DIE STEELS

This paper studies a compound treatment. i. e. liquid S , N,C co-diffusing with rare earth (RE) and then oxidization , for hot-working die steels , and the effect of RE on thermal fatigue behavior of the diffused layer. XRD and SEM energy spectrum prove that trace RE element actually penetrates into the surface layer of steels. The result shows that RE can reduce the gradient of change of hardness in diffused layer, improve the morphology and distribution of compounds , and reduce the degree of surface alligator crack for thermal fatigue. The behavior of thermal fatigue of hot-working die steels is raised by 70% or so after the application of RE. The effect of RE is analysed according to the theory.

CYCLIC SOFTENING IN HOT-WORKING DIE STEELS DURING LOW-CYCLE FATIGUE

The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening is featured in both steels hardened in different conditions under the strain controlled amplitude range of Δε_t/2=0.6-1.8×10^(-2).The softening effect mainly occurs in some initial cycles and the stress amplitude varies slightly in the sequential cycles,i.e.the softening effect is minified.No obvious stress saturation phenomenon was ob- served during the whole cyclic deformation.The TEM analysis shows that the cyclic softening is related to heterogenity of plastic deformation.The softening of the tested steels is caused by the formation of the dislocation cell structure with low density and low internal stress,and by the fragmentation and redissolution of fine carbides into matrix.

18CrNiMo7-6齿轮钢的热压缩变形行为及显微组织演变

采用热模拟方法研究了18CrNiMo7-6齿轮钢在变形温度900~1150℃、应变速率0.01~5 s-1条件下的热压缩变形行为;建立了基于Arrhenius模型的全应变本构方程,采用该方程对流变应力曲线进行预测;根据动态材料模型绘制热加工图,并结合热加工图系统地研究显微组织演变特征。结果表明:试验钢的峰值应力随应变速率的增加或变形温度的降低而增大,动态回复和动态再结晶是热变形过程中的主要软化机制;采用建立的全应变本构方程预测得到流变应力曲线与试验结果基本吻合,预测真应力与试验结果的相对误差小于4.715%,说明该模型可以精确地模拟18CrNiMo7-6齿轮钢的热压缩变形行为。试验钢的适合热加工工艺参数为变形温度1050~1150℃、应变速率0.1~1 s^(-1),此时组织为均匀细小的再结晶晶粒,晶粒尺寸在5~15μm。随着变形温度的升高或应变速率的降低,原始奥氏体晶粒不断被动态再结晶晶粒取代,且动态再结晶程度和再结晶晶粒尺寸增大。

热作模具钢磨损性能的研究现状

磨损是热作模具的主要失效形式之一,了解材料磨损机理和开发改善材料磨损性能的方法对提高模具寿命具有重要意义。本文对热作模具钢磨损性能的研究现状进行了阐述,对影响磨损性能的因素和改善磨损性能的方法进行了探讨和总结,并对热作模具钢磨损性能的研究趋势进行了展望。

热加工过程中M50轴承钢一次碳化物的形成与演化

针对M50轴承套圈生产过程中的真空感应熔炼、真空自耗重熔、锻造、轧制、辗环五个环节,利用OM、SEM、EDS及X射线三维成像技术分析了一次碳化物在整个生产流程中的演化。结果表明:真空感应熔炼后粗大的一次碳化物M2C和MC沿晶间呈网状析出,真空自耗重熔可减少一次碳化物的析出,自耗锭边缘处析出的一次碳化物尺寸较小,体积分数最少,为2.614%。锻造过程中网状一次碳化物被部分破碎,轧制和辗环可进一步破碎一次碳化物并使其沿加工流线分布,但并不能完全改变一次碳化物分布不均匀的情况。热变形在破碎细化碳化物的同时也会在一次碳化物内部及周围形成孔洞。

新型Cr-Mo-V型热作模具钢高温流变应力模型

通过热压缩实验,获得实验钢在变形温度为950~1200℃、应变速率为0.001~5 s^(-1)和最大真应变为0.916条件下的真应力-真应变曲线。结果表明:在本实验选取的变形条件下,新型Cr-Mo-V钢呈现出典型的动态再结晶特征,变形温度高于1050℃且应变速率低于0.1 s^(-1)时,动态再结晶特征更明显;同一变形温度下,峰值应力和峰值应变随应变速率的提高呈增大趋势;同一应变速率下,峰值应力和稳态应力随变形温度的升高逐渐降低。采用多元线性回归法获得与峰值应力对应的Arrhenius方程模型参数,基于此建立了实验钢的高温流变应力本构模型。利用创建的不同应变下本构方程材料常数的八次多项式对实验钢的流变应力进行计算,应变补偿相关系数R和平均绝对相对误差e AARE分别为0.98902和3.21%,计算数据与实验数据吻合良好。

GH4738高温合金高通量双锥试样设计及晶粒组织演变

在高温合金领域,双锥试样被广泛用于高通量研究热加工工艺与组织关系。针对GH4738高温合金,本文通过有限元分析,设计了一种在压缩过程中具有较小等效应变速率波动的双锥试样,并研究了其对晶粒尺寸的影响及其温度依赖性,进而研究了在变形温度为1000~1160℃、应变速率为2 s^(-1)和14 s^(-1)、工程应变为30%、50%、70%的条件下合金的晶粒演变。结果表明:等效应变速率的波动会影响变形后合金的晶粒尺寸,并且具有变形温度依赖性。所设计的双锥试样有利于精确研究等效应变与晶粒组织关系。热压缩实验表明,合金的软化以非连续动态再结晶为主,热加工窗口为变形温度1030~1080℃、应变速率14 s^(-1)、工程应变50%~70%。

便携式锂钾分析仪现场测定热泉水中的锂

锂是绿色能源和轻质合金的理想原料,作为一种重要的战略性资源而备受各国重视。热泉水中富含锂,储量可观,然而热泉水主要分布在西藏、云南等偏远地区,样品运输与实验室测试成本高、效率低,锂资源勘查急需现场分析技术的支持。热泉水一般含有较高浓度的钠、钾等元素,基体效应显著。本文利用自主研发的便携式锂钾分析仪,搭配负性滤光片,选择锂的分析谱线波长670.78nm,通过优化测量条件,建立了标准曲线法与标准加入法现场测定热泉水中锂元素的分析方法。实验结果表明,当电解质是体积分数为1.5%的盐酸,工作电流为70mA,进样流速为3.0mL/min时,锂检出限为4.07μg/L,相对标准偏差(RSD)为1.03%。对热泉水样品进行加标测试,加标回收率为81.6%~115.9%。当热泉水样品基体组成较简单时,直接采用标准曲线法即可获得较准确的分析结果;当样品基体组成较复杂或者基体浓度高时,采用标准加入法可有效地减小基体效应,获得的分析结果相对更准确。本方法适用于不同类型基体的热泉水中锂含量的分析测试。

喷丸对4Cr5Mo2V钢高温摩擦磨损性能的影响

对4Cr5Mo2V钢试样进行3道次复合喷丸,通过与未喷丸试样对比,研究了喷丸对试验钢表面形貌、显微组织、硬度、残余应力以及高温(100,300,500℃)摩擦磨损性能和机制的影响。结果表明:喷丸处理显著提高了试验钢表面粗糙度,使试验钢表面形成了明显的塑性变形层、硬化层与残余压应力层;在100,300,500℃下,与喷丸前相比,喷丸后试验钢的磨损率分别降低了41.8%,17.1%,63.3%,耐磨性能的提高与喷丸产生的硬化层和残余压应力层有关。在100,300℃下,喷丸前后试验钢的磨损机制均主要为黏着磨损和磨粒磨损,而当温度升高至500℃时,磨损机制为氧化磨损,喷丸试验钢仍能保持较高的硬度与残余压应力,同时表面氧化层更致密稳定,仅发生轻微氧化磨损。

Microstructural evolution and mechanical properties of 55NiCrMoV7 hot-work die steel during quenching and tempering treatments

55NiCrMoV7 hot-work die steel is mainly used to manufacture heavy forgings in the fields of aerospace and automobile.This study aims to clarify the effects of heat treatment on the microstructural evolution and mechanical properties of the steel,in order to find out an optimal heat treatment scheme to obtain an excellent balance of strength,ductility and toughness.The steel was quenched at temperature from 790℃ to 910℃ followed by tempering treatments of 100–650℃ for 5 h.The mechanical property tests were carried out by tensile,impact toughness and hardness.Optical microscope(OM),scanning electron microscope(SEM)and transmission electron microscope(TEM)were used to observe the austenite grains,lath martensite,carbides and fracture morphology.The results show that the quenching temperature mainly influences the austenite grain size and the volume fraction of undissolved carbides(UCs),while the tempering temperature mainly influences the size and morphology of the martensite with a body centered cubic(BCC)and the carbides with a face centered cubic(FCC).The mechanical properties of the steel,including yield and tensile strength,ductility,impact toughness and hardness,get an excellent balance at a quenching range of 850–870C.As the tempering temperature increases,the yield and tensile strength and hardness decrease,while the ductility and impact toughness increase.These variation trends can be further verified by fracture SEM observation and analysis.Combined with a macro-micro coupled finite element(MMFE)modeling technique,the cooling rate,microstructural evolution and yield strength of the steel were predicted and compared with the tested data.

炼油装置检修工程高危区域首次动火作业工艺

某炼油厂大检修需在油品车间装卸车单元增加7台切断阀,动火位置特殊,动火作业处管道取样困难,并且为首次动火,工期也很紧张。鉴于此,制定了首次动火施工工艺和钻孔取样方案。详细介绍了施工前的准备工作、具体安全防护措施、钻孔取样分析工艺及作业程序。按制定的工艺实施首次动火作业,安全、高效地完成了7台切断阀的安装,解决了检修工程中高危区域内首次动火作业的难题,并且作业过程中质量、安全等得到有效控制。

热加工对铝合金组织和性能影响的研究现状

铝合金热加工变形是制备铝合金产品重要的工序之一。合金的组织决定了合金的性能。综述了热轧制加工、热挤压及热锻造等常规的热加工变形方式对铝合金组织和性能的影响。针对目前热加工技术存在的问题及与国外先进技术的差距,提出了今后的发展方向。

氯碱化工系统消缺期间动火作业安全管控实践

从两起典型事故案例入手,从系统置换隔离、风险分析、作业过程管控及联动作业管理等方面,阐述了系统消缺期间动火作业管控关键点及相关最佳实践。

航空金属材料热加工仿真研究现状

目前,双碳目标日益成为我国经济高质量发展的绿色引擎,而热加工作为改善金属材料使用性能的重要基础工艺,存在着影响因素众多、研发周期长的问题。因此,开展模拟工艺参数优化设定、多场耦合实体仿真以及精细化控制工艺,进行材料组织-变形-性能协同调控方法的研究是十分必要的。介绍了近年来国内外热加工数值模拟方法,并对典型航空金属材料热加工数值模拟研究进展进行了介绍,最后对未来发展方向进行了展望。

氯碱企业动火作业爆炸事故暴露的安全问题与预防措施探究

动火作业在工业生产中扮演着不可或缺的角色,然而,爆炸事故时有发生,不仅对人员安全构成威胁,同时也可能导致环境破坏和财产损失。爆炸事故的发生往往暴露出动火作业中存在的潜在安全问题,如何有效应对这些问题成为当前安全管理的紧迫任务。本文探讨动火作业爆炸事故中暴露的安全问题,并提出相应的防范措施,以期为动火作业的安全管理提供有效的指导。

高强无磁不锈钢Cr21Ni13Mn5Mo2N的热加工特性

利用Gleeble 3800热模拟机对奥氏体不锈钢Cr21Ni13Mn5Mo2N进行热压缩实验,研究该钢种的高温变形与应变速率以及温度的关系,建立了双曲正弦本构方程,最终得到其热激活能为679.58 kJ/mol,应变速率因子Z=εexp(679580/R T)。实验结果表明,在950~1200℃,0.01~10 s^(-1)条件内,材料变形过程均发生动态再结晶,在950℃,应变速率为0.1 s^(-1)条件下,再结晶开始的变形量为10%。流变应力随温度升高及应变速率降低呈现明显下降趋势,由950℃、10 s^(-1)时的326 MPa降低至1200℃、0.01 s^(-1)时的75 MPa。结合微观组织分析及锻造试验,对压缩试样开裂问题进行深入探究,结果表明晶界处碳、氧化物的聚集恶化晶界塑性,导致热变形过程中在该处形成裂纹源并逐步扩展。通过热处理和热变形试验,确定Cr21Ni13Mn5Mo2N电渣锭在1170℃固溶6 h后晶界碳、氧化物消除,电渣锭晶界处结合力明显提升,成功消除锻造开裂问题,实现锻造成材率大幅提升。

新型引流线搭接工具的研制与应用

供电过程中配电设备的损坏及检修过程中局部供电中断,使得人们生活中用电间断。为尽快恢复正常供电,更安全便捷地进行检修,设计了一种可伸缩、防电弧、一体化绝缘、适用性强、实时动态电流检测的新型绝缘引流线搭接工具。新型引流线的消弧功能利用张力弹簧实现快速接通和断开,根据绝缘罩利用空气快速灭弧原理,引流线金属夹具的自动绝缘防护能有效提升作业效率和作业安全。通过现场作业进行验证,证明新型装置能够满足作业时的要求和规范,提高了带电搭接引流线作业项目的质量和效率,相比传统引流线作业,效率可提高50%。