AerMet100超高强度钢热变形行为

在热模拟机上对AerMet100超高强度钢进行了恒温和恒应变速率的热压缩实验,温度范围是900℃～1100℃,应变速率范围是0.01s-1～10s-1。实测了高温下应力-应变关系曲线,观察了变形后的显微组织,计算了材料的激活能,并建立了峰值应力与变形温度和应变速率的关系。结果表明,材料的流动应力随着变形温度的升高而降低,随应变速率的增大而增大;材料在不同变形条件下其软化机制分别受动态回复和动态再结晶控制;在实验条件范围内,AerMet100超高强度钢的再结晶温度在1000℃～1050℃之间,材料的热变形激活能为261.2kJ/mol。     

回火工艺对AerMet100超高强钢组织与力学性能的影响

采用OM、万能试验机、摆锤冲击试验机、维氏硬度计等研究了AerMet100超高强度钢不同温度回火后的组织与力学性能。结果表明:经过880℃×1 h油淬+(450～510)℃×5 h的回火后,AerMet100试验钢的显微组织为板条马氏体。随着回火温度的升高,板条马氏体板条尺寸先减小后增大,480℃回火的试验钢马氏体板条最为细小。随着回火温度的升高,试验钢的硬度、抗拉强度先升高后降低。480℃回火试验钢的硬度、抗拉强度均达到最大值,分别为604.2 HV和1965.5 MPa,其伸长率、冲击功分别为12.4%和73.4 J。     

AerMet100钢热挤压变形过程数值模拟

建立了AerMet100钢热挤压过程的瞬态温度场和应力场三维限元数学模型，在热力耦合与刚粘塑性有限元分析基础上采用DEFORM软件模拟了AerMet100钢的热挤压变形过程，得出了热挤压过程中坯料心部温度先升高后下降，心部最高，与模具接触区温度下降较快；坯料应力不断增大，且外侧比心部增长快；坯料在工作带处应力较大。     

AerMet100二次硬化过程组织和性能的研究

研究了超高强度钢AerMet100经复合形变处理后的试样,二次硬化保温时间对显微组织和力学性能的影响.TEM结果表明,经高温固溶复合形变处理,使供货态组织中未熔的碳化物全部回溶,晶粒细化;随着二次硬化保温时间的延长,析出相形态发生了根本改变.力学性能测量结果表明,60 min时抗拉强度和塑性指标满足标准要求,σb为1965 Mpa,δ为19%.     

AerMet100钢热压缩过程流变应力的神经网络预报

本文研究了变形温度、应变速率和应变量对固溶和轧制态的AerMet100钢热压缩变形过程流变应力的影响规律.结果表明:变形温度、应变速率和应变量对流变应力有显著影响,预处理方式对流变应力的影响不大.基于人工神经网络原理,建立了流变应力与变形温度、应变速率和应变量的数学模型,由此预报的AerMet100钢热压缩过程流变应力与实测结果相吻合.     

激光直接沉积成形 AerMet100 高强钢的显微组织和力学性能

采用正交试验制备了激光直接沉积成形(laser metal deposition, LMD)AerMet100高强钢,借助光学显微镜、扫描电子显微镜、电子探针、显微硬度仪、室温拉伸及冲击试验对制备的合金显微组织和力学性能进行了研究. 结果表明,激光沉积成形AerMet100高强钢的优化热输入区间为170 ~ 250 J/mm;沉积组织为沿凝固方向的由板条状马氏体与胞状枝晶边界的残余奥氏体组成的柱状胞晶,板条状马氏体由奥氏体在激光成形过程的快速冷却形成,而残余奥氏体主要由于凝固过程中奥氏体稳定化元素Cr、Mo、Ni元素偏析形成;沉积态硬度与基材硬度相当,但由于沉积过程中的热量累积促使基体中的回火马氏体发生高温回火,使得在沉积方向上存在明显的热影响区(heat affected zone, HAZ)软化;通过工艺优化激光沉积成形AerMet100高强钢在P = 1700 W,v_s = 10 mm/s时获得较优异的综合力学性能,抗拉强度、屈服强度分别达1865.3、1585.5 MPa,断后伸长率达12.4%. 通过断口形貌分析,随着热输入密度的降低,拉伸断口剪切唇消失,韧窝深度变浅;冲击断口解理面增大,由韧性断裂转变为脆性断裂.     

AerMet100超高强度钢激光相变硬化研究

对AerMet100超高强度钢进行了激光相变硬化试验,并对淬硬层的显微硬度分布及其物相变化进行了测试与分析.结果表明,激光相变硬化后淬硬层的硬度得到提高,比基体提高了约200 HV0.2;在同样的激光处理工艺条件下,经激光相变硬化后原始状态为淬火态试样的淬硬层的硬度和深度比退火态试样的要高和深;相变硬化后,随着回火时间的延长,逆转变奥氏体含量增多,硬化层硬度降低.     

热加工过程AISI1215钢动态再结晶临界条件

根据AISI1215钢热模拟压缩实验的结果,采用Poliak和Jonas提出的计算动态再结晶临界应变(εc)和临界应力(σc)方法,研究了形变温度和应变速率对εc和σc的影响规律。结果表明,在应变速度较低时(小于30 s-1),采用指数函数形式可以较好描述热加工参数Z(Zener-Hollomon参数)与εc,σc,εP(峰值应变)和σP(峰值应力)间的关系,实验分析的结果表明,峰值应变(临界应变)与Z参数之间表现为正比关系,Z参数增大(形变温度降低或应变速度增加),材料发生动态再结晶的临界应变增加,应力应变曲线上表现出的表观峰值应变增加。根据模型计算的结果,在实验数据的范围内,动态再结晶临界应变与应力应变曲线的峰值应变之间的比值约为0.4~0.5之间,明显小于一般工程应用中估计的0.7。根据模型的计算的结果,用中断淬火试验进行了验证,结果表明与模型计算值吻合良好。     

超高强DP980钢的动态再结晶模型

采用Gleeble-3500热模拟试验机对超高强DP980钢进行热压缩试验,研究其在变形温度为900~1 200℃、应变速率为0.05~30s~(-1)条件下的动态再结晶行为,分析了变形温度和应变速率对真应力-真应变曲线的影响。结果表明:超高强DP980钢在变形过程中,存在动态再结晶和动态回复两种软化机制,且随着温度的升高和应变速率的降低,临界应变越小,动态再结晶越容易发生;同时,得到了发生动态再结晶时的形变激活能,建立了峰值应变模型、动态再结晶临界应力模型和动态再结晶动力学模型。     

微合金化钢的动态再结晶及其显微组织的研究

应用Ｇｌｅｅｂｌｅ－１５００热模拟试验机测定了合金化钢在不轧温度下的真应力－真应变曲线,研究了终轧温度及微合金元素含量对动态再结晶的影响。研究结果表明,Ｖ、Ｎｂ可显著抑制微合金化钢轧制过程中形变奥氏体的动态再结晶,因此,在较高的终轧温度下,仍能得到细小而均匀的显微组织。     

涡轮盘用GH4742合金动态再结晶行为

采用单道次等温压缩实验获得了GH4742合金在变形温度为980～1100℃,应变速率为0.005～5 s-1条件下的应力-应变曲线.以实验数据为基础,运用KM模型、Poliak-Jonas准则、Avrami模型较为系统地描述了该合金动态再结晶过程的流变应力、临界应变量、组织演化动力学等特征.并在Prasad功率耗散率模...     

Hot Deformation and Dynamic Recrystallization Behavior of Austenite-Based Low-Density Fe–Mn–Al–C Steel

The hot deformation and dynamic recrystallization(DRX) behavior of austenite-based Fe–27Mn–11.5Al–0.95 C steel with a density of 6.55 g cm-3were investigated by compressive deformation at the temperature range of900–1150 °C and strain rate of 0.01–10 s-1. Typical DRX behavior was observed under chosen deformation conditions and yield-point-elongation-like effect caused by DRX of d-ferrite. The flow stress characteristics were determined by DRX of the d-ferrite at early stage and the austenite at later stage, respectively. On the basis of hyperbolic sine function and linear fitting, the calculated thermal activation energy for the experimental steel was 294.204 k J mol-1. The occurrence of DRX for both the austenite and the d-ferrite was estimated and plotted by related Zener–Hollomon equations. A DRX kinetic model of the steel was established by flow stress and peak strain without considering dynamic recovery and d-ferrite DRX. The effects of deformation temperature and strain rate on DRX volume fraction were discussed in detail. Increasing deformation temperature or strain rate contributes to DRX of both the austenite and the d-ferrite, whereas a lower strain rate leads to the austenite grains growth and the d-ferrite evolution, from banded to island-like structure.     

Incoloy825合金热变形为与组织演变

通过热压缩实验,研究了Incoloy825合金在变形量为60％,温度为950~1150℃和应变速率0.001~1s-1范围内热变形行为。基于Arrhenius方程和Zener-Hollomon参数模型,建立该合金的本构方程模型。采用金相显微镜（OM）和电子背散射衍射（EBSD）技术研究了合金的组织演变规律。结果表明,随着变形温度的升高或应变速率的降低,DRX的百分含量增加。热变形过程中DRX既包括晶界弓起形核机制的不连续动态再结晶（DDRX）也包括渐进式亚晶旋转形核机制的连续动态再结晶（CDRX）。随着变形温度的升高或应变速率的降低DDRX增强而CDRX减弱。此外随着温度的升高或应变速率的降低,低角度晶界逐渐向高角度晶界转化。同时随机分布的Σ3孪晶界趋于均匀化,且对动态再结晶起促进作用。     

Influence of Microstructural Evolution on the Hot Deformation Behavior of an Fe–Mn–Al Duplex Lightweight Steel

The hot deformation behavior of Fe–26 Mn–6.2 Al–0.05 C steel was studied by experimental hot compression tests in the temperature range of 800–1050 °C and strain rate range of 0.01–30 s21 on a Gleeble-3500 thermal simulation machine. The microstructural evolution during the corresponding thermal process was observed in situ by confocal laser scanning microscopy. Electron backscattered diffraction and transmission electron microscopy analyses were carried out to observe the microstructural morphology before and after the hot deformation. Furthermore, interrupted compression tests were conducted to correlate the microstructural characteristics and softening mechanisms at different deformation stages.The results showed that hot compression tests of this steel were all carried out on a duplex matrix composed of austenite and d-ferrite. As the deformation temperature increased from 800 to 1050 °C, the volume fraction of austenite decreased from 70.9% to 44.0%, while that of d-ferrite increased from 29.1% to 56.0%. Due to the different stress exponents(n) and apparent activation energies(Q), the generated strain was mostly accommodated by d-ferrite at the commencement of deformation, and then both dynamic recovery and dynamic recrystallization occurred earlier in d-ferrite than in austenite.This interaction of strain partitioning and unsynchronized softening behavior caused an abnormal hot deformation behavior profile in the Fe–Mn–Al duplex steel, such as yield-like behavior, peculiar work-hardening behavior, and dynamic softening behavior, which are influenced by not only temperature and strain rate but also by microstructural evolution.