深冷处理对低碳高合金马氏体轴承钢力学性能及组织的影响

利用洛氏硬度计、X射线衍射仪、扫描电子显微镜及透射电子显微镜等研究了低碳高合金马氏体轴承钢深冷处理后的硬度变化及组织演化。结果表明:深冷处理促使部分残留奥氏体转变为马氏体,导致深冷处理后实验钢的硬度较淬火态硬度有所升高。经深冷处理后实验钢在0~100 h回火过程中的硬度均比未深冷处理实验钢的硬度高。深冷处理促使钢中碳原子偏聚并在回火过程中以碳化物的形式析出,与未经深冷处理的实验钢相比,经深冷处理的实验钢回火后马氏体基体中的含碳量更低,表明实验钢经深冷处理后在回火过程中析出更多的碳化物。透射电镜分析表明,实验钢在回火过程中析出的大量弥散分布的纳米级M2C和M6C型碳化物是实验钢长时间回火后保持高硬度的主要原因。     

GCr15钢深冷条件下的组织转变

以GCr15钢轴承套圈为对象,采用深冷处理的方法对淬火后的零件进行处理以减少零件中的残余奥氏体含量。通过X射线衍射法检测残余奥氏体含量和扫描电子显微镜(scanning elec-tron m icroscopy,SEM)观察深冷处理后的零件组织,研究了深冷处理温度和时间对GCr15钢淬火后的残余奥氏体转变的影响。结果表明,深冷处理可以大幅降低淬火GCr15钢零件中的残余奥氏体,最多可使零件中71.6%的残余奥氏体可以转变为马氏体。     

深冷处理消除7A04长条构件残余应力的建模与仿真

建立了7A04铝合金长条构件深冷处理过程瞬态应力场的有限元模型,在构件瞬态温度场数值模拟的基础上,采用热-力顺序耦合方法对该构件深冷处理过程各阶段的瞬态应力场及残余应力场进行了数值模拟.数值模拟结果表明,该长条构件经深冷处理后其最大残余应力(Mises应力)从淬火状态的314.8 MPa降至152.6 MPa,残余应力幅度Δσ减小37.5%.     

T12高碳钢深冷处理之组织结构研究

采用ＴＥＭ和ＸＲＤ研究了Ｔ１２高碳钢深冷处理过程中组织结构的变化。结果表明,残余奥氏体部分墨迹为马氏体,微细碳化物将在马氏体挛晶带及们错线处析出,碳化物类型为η－Ｆｅ２Ｃｏ延长深冷处理时间将有利于碳化物的析出。     

7A04铝合金构件深冷处理过程瞬态温度场的数值模拟

建立了7A04铝合金构件深冷处理过程瞬态温度场的有限元模型,对7A04铝合金材料在低温状态下的若干物性参数进行了实验研究,并运用温度场反算法分别得到了铝合金试件与低温（热）介质之间的传热系数。运用ABAQUS6．5有限元软件,对7A04铝合金构件瞬态温度场的数值结果表明,在淬火、深冷与上坡淬火过程中,构件上端部位存在很陡峭的温度梯度。     

深冷处理对高碳高合金工具钢SDC99回火过程碳配分的影响

采用内耗和三维原子探针结合硬度测试研究了深冷处理对高碳高合金工具钢SDC99不同回火温度下组织和碳偏聚情况的影响。结果表明:深冷处理显著提高工具钢SDC99的硬度,深冷处理试样较淬火试样硬度提高2HRC,深冷处理并200℃回火试样比常规热处理试样硬度提高1.5HRC;深冷处理后碳原子与位错的相互作用增强,内耗的Snoek-Kê-K?ster(SKK)峰强度提高,位错密度增加;深冷处理后碳原子的偏聚程度加剧,淬火、深冷、淬火并200℃回火、深冷并200℃回火试样中富碳相的碳浓度峰值分别为2%、8%、8%和15%(原子分数)。     

球化退火后的深冷处理对9SiCr钢强韧性的影响

目的 针对9SiCr钢加热脱碳倾向大、加工性较差的问题,研究能够提高9SiCr钢的强韧度与耐磨性的热处理工艺。方法 设计一种球化退火后进行深冷处理的新热处理工艺路线来实现对9SiCr钢强度与耐磨性的改良。对比9SiCr钢的等温球化退火与循环球化退火后的组织与性能,确定最适合的球化退火工艺;对退火后的9SiCr钢进行淬火,之后按照淬火后是否进行深冷处理、深冷处理前是否进行预回火进行分组对照试验。结果 对于热轧态9SiCr钢,800～750℃往复循环球化退火的强化效果优于各温度下等温球化退火的强化效果;深冷处理12 h后,9SiCr钢循环退火组织中的马氏体基体析出了大量超微细碳化物,增强了9SiCr钢的耐磨性与刚性。并且,进行深冷处理前在160℃（9SiCr钢Ms点附近）下保温1 h可以增大碳化物的形核率,之后再进行深冷工艺,可以进一步促进碳化物析出,有利于改善9SiCr钢的退火组织,增强材料强度与韧性。结论 循环球化退火后预回火并进行深冷处理可以显著提高9SiCr钢的强韧性与耐磨性。     

深冷处理改善高速钢性能及其机理研究

深冷处理是一种有效的热处理工艺方法,通过深冷处理后,能够比较显著地改善材料的力学性能和较大幅度地提高工件的使用寿命。深冷处理工艺在金属材料领域的应用已经越来越广泛。研究表明,深冷处理不仅可以使残余奥氏体减少,而且还可以细化马氏体孪晶,促使纳米级碳化物的析出,并附着在马氏体孪晶带上。深冷处理不仅可以提高材料的硬度,也能够使材料的韧性略有增加。经过深冷处理,能够有效促使残留奥氏体向马氏体转变,并且析出超微细碳化物,可以获得比较好的综合力学性能,显著提高高速钢刀具的使用寿命。本文介绍了深冷处理工艺的特点和它的发展情况,阐述了深冷处理工艺对高速钢材料的影响,并展望了深冷处理工艺的发展前景。     

淬火温度对Ti-3Al-4.5V-5Mo钛合金形变诱发马氏体的影响

通过测试不同淬火温度下的拉伸应力应变曲线、750～790℃淬火拉伸断裂后均匀变形区域的X射线衍射谱研究了淬火温度对Ti-3Al-4.5V-5Mo钛合金形变诱发马氏体的影响.结果表明:该合金在750～790℃淬火后拉伸变形机制为亚稳定β相变形诱发马氏体转变,790℃淬火合金在6.5%的变形量下亚稳定β相基本完全转变为α″马氏体.790℃淬火后拉伸形成应力诱发马氏体,β立方→α″σ;750℃淬火后拉伸形成应变诱发马氏体,β立方→β正方→α″ε.形变诱发α″相在拉伸变形时发生晶格重新取向:[010] α″方向平行于拉伸轴线,[100]α″方向垂直于拉伸轴线.     

深冷处理降温速率对304LN焊接接头组织和热应力的影响

为探究深冷处理中降温速率对304LN焊接接头组织和热应力的影响,对304LN焊接钢板分别以2 K/min和5K/min 2种降温方式做深冷处理,并通过应变仪、温度传感器和光学显微镜等考察了深冷处理前后焊接接头组织及热应力的变化.试验结果表明:随着降温速率的增加,深冷处理过程中焊接接头的热应力在数值上增大,但其均小于材料的屈服强度;深冷处理后明显可观察到马氏体的生成和碳化物的析出,且随着降温速率的增加,碳化物数量更多且分布更加均匀;同时借助能谱仪(EDS)对焊接接头碳化物含量进行了测定,证实了降温速率的增加将促使碳化物析出的观点.由此建议对工件采取降温速率为5 K/min的深冷处理从而获得较为稳定的微观组织.     

Quantitative microstructural characterisation of Fe–30Ni alloy after martensitic transformations by means of stereological and magnetic methods

In the Fe–30Ni alloy investigated a martensitic transformation can occur both during quenching or plastic deformation. Martensite formed during plastic deformation, depending on the thermo-mechanical treatment applied, exhibits a different morphology from that achieved during quenching and forms the so-called composite-like structure. The morphology and volume fraction of martensite depends both on strain and temperature. In the present studies Fe–30Ni alloy was deformed by monotonic rolling in one path and perpendicular rolling in the temperature range M_D–M_S. The aim of the investigations was a determination of martensite volume fraction depending on the strain and temperature. To examine the influence of strain, the alloy was deformed by rolling in one path or perpendicular rolling at a temperature of − 30 °C, in the strain range of 10–30%. The dependence of temperature was investigated by rolling with 30% strain in a temperature range from − 30 °C to − 80 °C. The variants of thermo-mechanical treatment performed enabled us to achieve different martensite morphologies and volume fractions. Microstructural analysis was performed by means of light microscopy and transmission electron microscopy. The results of quantitative microstructural analysis of martensite and retained austenite volume fractions formed in different thermo-mechanical treatments were compared with those obtained by magnetic measurements. The fraction of deformation-induced martensite determined varied from 2% to 86%. The partial volume fractions V_V^MF of martensite formed in different deformation directions were also determined. It was found that the influence of the temperature on the martensite volume fraction is more pronounced than the influence of strain.     

A Role of α′ Martensite Introduced by Thermo‐Mechanical Treatment in Improving Shape Memory Effect of an Fe‐Mn‐Si‐Cr‐Ni Alloy

The evolution of α′ martensite with different thermo‐mechanical treatment and its effect on the shape memory effect were studied in an Fe‐14Mn‐5Si‐8Cr‐4Ni alloy. The α′ martensite was introduced by only 5% pre‐deformation, and its amount increased with increasing pre‐deformation up to 20%. The α′ martensite started to transform into austenite when the annealing temperature was 773 K. As the annealing temperature increased to 1 073 K, the α′ martensite almost transformed fully into austenite. The α′ martensite introduced by the thermo‐mechanical treatment could prevent collisions between different ε martensite bands during deformation. The intrusion of α′ martensite was another key reason that the stress‐induced ε martensite bands in Fe‐Mn‐Si based shape memory alloys formed in a domain‐specific manner in addition to that of uniformly distributed stacking faults after thermo‐mechanical treatment.     

Ti-49.6Ni合金在拉压对称循环载荷下的电阻-温度曲线

用电阻法测量了固溶后Ti-49.6Ni形状记忆合金的相变行为,马氏体逆相变具有明显的相变温度点;在降温过程中没有发生R相变。在该热处理制度下材料疲劳后,在升温过程中没有明显的逆相变温度点;在降温过程中出现R相变。电阻-温度曲线特征发生明显规律性变化,提出一种解释这一现象的微观机制。     

约束态相变中TiNi形状记忆合金的马氏体自拉伸过程

研究了约束态加热过程中产生的回复力对TiNi形状记忆合金剩余马氏体的影响．结果表明，产生的回复力使剩余马氏体发生了塑性变形，使逆相变温度升高，剩余马氏体分数和其逆相变温度之间存在特定的函数关系．但是，外部约束条件的变化对马氏体的自拉伸过程所造成的剩余马氏体分数与其逆相变温度之间的关系影响很小．     

奥氏体动态再结晶组织对马氏体相变的影响

采用电阻测量和Ｘ射线衍射分析方法，研究了Ｆｅ－３２Ｎｉ合金高温变形奥氏体动态再结晶组织对马氏体相变开始温度Ｍｓ点和一定深冷处理温度下马氏体生成量的影响。与静态再结晶组织相比，动态再结晶晶粒组织不均匀，其位错亚结构也不均匀。具有位错密度梯度分布的成长中的动态再结晶晶粒晶界附近含有少量的易移动位错，促进马氏体的形核，提高Ｍｓ点及其Ｍｓ点以下较高温度区域墨迹初期的马氏体生成量，但是对于较低温度区域转变后     

TiNi形状记忆合金在定应变约束下的马氏体相变

通过DSC及回复应变的测量,研究了定应变约束态加热-冷却过程对预应变TiNi形状记忆合金相变行为的影响。结果表明,在约束态相变中,逆相变温度区间拓宽;取向马氏体除向母相转变外,应变还要进一步增大;在正相变过程中,从母相生成的马氏体也具有变形结构。约束态不完全相变后,样品中存在两种马氏体;再变形马氏体和继承变形马氏体,在随后的无约束逆相变过程中,前者的相变温度高于后者,并且输出两段回复应变。     

Phase transformations during the decomposition of austenite below Ms in a low-carbon steel

The purpose of this study is to investigate and understand the phase transformations during the decomposition of austenite, which occurs during isothermal treatments below the martensite start temperature (M_s) in a low-carbon steel. Isothermal holding treatments after rapid cooling to various temperatures (forming a controlled volume fraction of initial martensite) were carried out in a dilatometer. Results obtained by dilatometry, microstructural characterization and hardness were analyzed. This combination of results shows that the microstructures formed below the M_s temperature are mainly bainitic, mixed with tempered martensite. The kinetics of isothermal bainite formation was described by a nucleation-based transformation model. The complex competition and interactions between their transformation mechanisms during the isothermal holding at different temperature regimes are discussed.     

30CrNi3MoV低合金超高强钢中的马氏体相变

通过对马氏体的显微组织进行分析,并结合线膨胀试验得到的相变动力学信息研究了30CrNi3MoV低合金超高强钢中的马氏体相变特征.结果表明:淬火冷却30CrNi3MoV钢的相变产物包括低碳板条状和高碳针状两种马氏体形态,两者的形成在动力学曲线中截然分开.板条马氏体形成于Ms以下的较高温(310℃～260℃),相变过程中发生了碳的重新分配,造成富碳奥氏体微区的形成;高碳针状马氏体形成于Ms以下的较低温(260℃～170℃),由富碳奥氏体微区转变而成.板条马氏体形成速率远高于针状马氏体.     

30MnSi管桩钢筋延迟脆断原因分析

针对30MnSi管桩钢筋（PC钢棒）延迟脆断的现象,从力学性能、化学成分、显微组织、表面质量、断口形貌以及后续热处理工艺等方面对延迟脆断的原因进行了分析。结果表明：该管桩钢筋发生延迟脆断主要是由于其热处理过程中回火温度不稳定,使钢筋表面局部形成异常马氏体组织,这种组织形式自身存在着组织应力,而内氢的存在增加了管桩钢筋的内应力;当受外力作用时,外力和管桩钢筋自身的内应力经过一段时间逐渐集中于表面马氏体区,形成断裂源,从而导致管桩钢筋静置数日后突然脆断。     

Transformations and Two Way Memory Effect Associated with Solution-treatment Temperature

Effect of solution treatment temperature on transformations and two way memory, effect in a Ti-55.2 wt-%Ni alloy was investigated. The results show that with increasing the solution treatmenttemperature (T_s), two way memory effect (TWME) decreases continuously and temperatures ofmartensite and reverse, martensite transformations (MR) rise, but the temperature of R start trans-formation (parent→R) does not change. The results of the internal friction measurements indicatethat when T_s=1073 K, internal friction peaks of MR and P→R transformations are larger thanthose of the specimens after solution-treatments at 973 and 1173 K. With increasing T_s, the de-crease of TWME can be attributed to that the defect stress field caused by the rolling fades out grad-ually and preferential martensite variants, which fit into the defect stress field, decrease. The changesof transformation temperatures and internal friction peaks with T_s are closely related to the changeof defect numbers.