准贝氏体组织及新型系列准贝氏体钢

新型钢中的准贝氏体由贝氏体铁素体和分布其上的残余奥氏体膜组成,处于贝氏体转变的初期阶段。新型准贝氏体钢具有优异的综合力学性能和简单易行的工艺性能,应用前景广阔。     

中碳低合金铸钢贝氏体中脊特征研究

利用光学显微镜，ＳＥＭ，ＴＥＭ研究了中碳低合金铸钢态下具有中脊的贝氏体形态和中脊特征，并探讨了带中脊贝氏体的相变机制，研究表明，中脊存在于不同形态的贝氏体中；中脊先天贝氏体铁素体基体核与长大，是与基体贝氏体衬度不同的单相氏体铁素体，类似片状马氏切变形核与长大，第一片贝氏体中脊可贯穿整个晶粒。     

GD钢下贝氏体相变研究

利用ＴＥＭ研究了ＧＤ钢下贝氏体的组织形态，并探讨了贝氏体的相变机制。ＧＤ钢中下贝氏体是由一束贝氏体铁素体片条组成的，而每一片条又是由多个贝氏体相变基元组成，下贝氏体中普遍存在中脊。ＧＤ钢中存在一种类马氏体形貌贝氏体，研究表明，下贝氏体相变过程中必定存在切变。     

低碳贝氏体钢连续冷却相变规律研究

利用Gleeble1500热/力模拟实验机,研究了抗拉强度为700 MPa级的低碳贝氏体钢的相变规律,分析了不同冷却速率对钢组织及性能的影响。结果表明：轧后试样在1℃/s～30℃/s较宽的冷却速度范围内均可得到贝氏体组织,并随着冷却速度的增加,显微组织以粒状贝氏体为主转变为以性能优良的板条贝氏体和马氏体为主,在不降低韧性指标的前提下,提高了强度,为700 MPa级的低碳贝氏体钢工艺制度的制订提供了依据。     

含硅钢中的贝氏体中脊

用透射电镜详细地研究了60Si2Mn和9SiCr两种含硅钢的中温贝氏体相变,观察到在360℃以下等温形成的贝氏体片中普遍地存在中脊。研究结果表明,中脊实质上是无碳化物的贝氏体铁素体。中脊附近的贝氏体铁素体和母相奥氏体之间呈西山关系。作者认为中脊是贝氏休铁素体的切变核。     

应力作用下的贝氏体相变动力学模型研究

贝氏体相变动力学及其模型构建一直是学者们研究的热点。以一种中碳超细晶贝氏体钢为对象,对应力作用下贝氏体相变动力学模型开展详细研究。首先采用van Bohemen和Sietsma提出的贝氏体相变动力学模型对实验数据进行拟合,发现拟合得到的自催化系数小于0,不符合物理规律。主要原因是塑性变形带来了额外形核点,这些形核点作为有利位置被优先消耗,导致形核率随时间延长而降低。基于该机制,对van Bohemen和Sietsma模型进行了修正,在贝氏体形核的原始模型中添加了描述形核率降低的函数g(t),并采用幂函数和指数函数2种形式来定义g(t),最终获得了改进后的贝氏体相变动力学模型。改进后的贝氏体相变动力学模型拟合获得的自催化系数大于0,符合物理规律。此外,g(t)为幂函数时,计算精度更高,模型形式更简洁。     

准贝氏体高强耐磨钢的开发和工艺研究

研究在典型贝氏体钢的成分基础上加入阻止碳化物析出的元素S i,开发出以贝氏体铁素体(BF)和残余奥氏体(AR)组成的准贝氏体组织的高强耐磨钢,在适当的工艺下钢板可获得最佳的综合性能,具有良好的强韧性、耐磨性和焊接性。     

稀土对低合金钢贝氏体相变动力学的影响

本文通过测量不同温度下贝氏体等温相变的动力学曲线和扫描电镜的成分分析，研究了添加稀土对０．２７Ｃ－１Ｃｒ钢相变动力学的影响。结果表明，稀土使奥氏体晶粒细化，提高了初期贝氏体相变速率，降低了淬透性，而稀土偏聚于铁素体／小岛相界面和稀土减慢碳的扩菜所产生的拖曳作用是减慢后期贝氏体相主速率，延长相变完成时间的原因。     

Cu-Zn-Al合金中贝氏体相变的机制及应用

对以往Cu-Zn-Al合金贝氏体相变机制的工作加以评述。相变驱动力计算的结果表明,Cu-Zn-Al合金中贝氏体相变在热力学上不可能按切变机制发生,只能以扩散过程:B′→B_1′+α进行;形成无序的贝氏体可能有序化。综合贝氏体相变热力学、晶体学、动力学、成分变化和内耗研究以及贝氏体的有序性,提出Cu-Zn-Al合金中贝氏体由扩散机制形成,虽然其晶体学在表面上符合马氏体相变晶体学的表象理论。简介Cu-Zn-Al贝氏体相变中出现可供工业应用的逆形状记忆效应。     

42CrMo钢的贝氏体组织相变

采用金相法研究了经950℃奥氏体化的0．41C-1．OCr-0．23Mo(42rMo)钢在550～380℃盐浴等温处理时贝氏体组织转变。观察结果表明,42CrMo钢550～510。c等温处理的组织为无碳贝氏体(粗大条片状贝氏体铁素体 残留奥氏体组成的整合组织) 马氏体,470℃等温处理为羽毛状上贝氏体 黑色针状下贝氏体 马氏体组织,380℃为黑色针状下贝氏体 马氏体组织;上贝氏体在奥氏体晶界形核,随等温处理的温度降低,下贝氏体在奥氏体晶内形核。     

下贝氏体碳化物形态及来源

用ＴＥＭ观察了Ｆｅ－１．０８Ｃ－３．９５Ｃｒ合金一贝氏体碳化物（θ）的形态，发现θ呈棒状或楔状。实测碳化物的主轴方向近似与「１００」或「０１０」平行，楔根源于贝氏体铁互体－奥氏体界面，或部分深入铁素体内部而形成在相界面钉扎的特殊形态。提出铁素体（α）可能按激发形核－扩散台阶（ＳＮＬＧ）机制长大，θ和α竞争长大，α的形成过程决定了θ的形态及分布。     

Fine Microstructure of Bainitic Ferrite in Bainitic Steel

Asbainiticsteelspossesshighhardness ,highstrength toughness ,highwearresistanceandhighhardenability ,theacademicandengineeringcircleshavepaidcloseattentiontotheinvestigationoffinemicrostructure[1,2 ] .However ,thefinemicrostruc tureofbainiticsteelsisnotdeterminedyet .Thefinemicrostructuresofmediumandmedium highcarbonbainiticsteelswereobservedandanalyzedbyhighresolutionelectronmicroscope (HREM ) ,andthere sultsshowthatthereareretainedausteniticfilmsatdifferentlevelstructureunitboundaries .The…     

贝氏体型非调质钢热变形奥氏体的连续冷却转变

研究了一种Ｍｎ－Ｂ系低碳贝氏体型非调质钢热变形奥氏体的连续冷却转变,得到了实验用钢热变形奥氏体的连续冷却转变曲线。结果表明,本实验用钢热变形奥氏体不发生先共析铁素体析出的临界冷却速度为１．５ ℃／ｓ;冷却速度在１．５～７ ℃／ｓ范围内可全部得到贝氏体组织;当冷却速度大于７ ℃／ｓ时,不再生成贝氏体,室温组织为马氏体和残余奥氏体。     

Factors Affecting the Mechanical Properties of Ultra-high-strength Bainitic Steel Containing W and 0.33 mass％ C

A novel ultra-high-strength bainitic steel was designed.The analysis of its mechanical properties by quasistatic testing showed that upper bainitic steel exhibited an ultimate tensile strength of 2 260 MPa(engineering stress)and an ultimate compressive strength of more than 2 700MPa(true stress).The ultra-high strength of upper bainitic steel was mainly attributed to untempered martensite and upper bainite with a feather-like microstructure.Moreover,lower bainitic steel demonstrated an ultimate tensile strength of 1 922 MPa(engineering stress)and an ultimate compressive strength of 2 500MPa(true stress).The ultra-high strength of lower bainitic steel was primarily due to untempered martensite and lower bainite with an acicular microstructure.The untempered martensite in the two kinds of bainitic steels was produced in different ways.The dynamic test results showed that the ultimate compressive strengths of the two bainitic steels were maintained at 1 600MPa(true stress)under high strain rates(1 100and2 200s-1)at 600℃,because of the added tungsten,confirming the satisfactory hot hardness property of the steel.Furthermore,lower bainitic steel showed better comprehensive mechanical properties than upper bainitic steel.     

Impact Toughness of an NM400 Wear-Resistant Steel

An NM400 wear-resistant steel was hot rolled and then the plates were heat-treated by direct quenching and tempering (DQT) and reheat quenching and tempering (RQT) techniques, respectively. The Charpy impact test was carried out with an instrumented Charpy impact tester. The microstructure and fracture surface were investigated by a combination of optical microscopy, transmission electron microscopy and scanning electron microscopy methods. It was found that the impact toughness of DQT specimen was much higher than that of RQT specimen. The microstructure of both DQT and RQT specimens was characterized by a mixture of tempered lath martensite and lower bainite. The lower bainite in DQT specimen extended into prior austenite grains and the content was higher than that in RQT specimen. The lower bainite in DQT specimen improved the impact toughness by increasing the proportion of large-angle boundaries and relieving the stress concentration at the crack tip. A number of fine and dispersed carbides in DQT specimen also contributed to the improvement of the impact toughness.     

Recent Development of Air-Cooled Bainitic Steels Containing Manganese

The superiorities of air-cooled bainitic steels were described. A series of air-cooled bainitic steels containing manganese were developed and presented, which include low carbon granular bainitic steels, low carbon grain-boundary allotriomorphic ferrite/granular bainite dual phase steels, medium and medium high carbon bainite/martensite dual phase steel, low carbon carbide free bainite/martensite dual phase steels and casting bainitic steels.The development of ultra-low carbon bainitic steels in China was also introduced.     

Creation of Air-Cooled Mn Series Bainitic Steels

The development and mechanical performances of new type air-cooled Mn series bainitic steels including granular bainitic steels, FGBA/BG duplex steels, CFB/M duplex steels, medium carbon bainite/martensite steels, cast bainitic steels invented by the authors are summarized. The novel series of bainitic steels are alloyed with Mn, and several series bainitic duplex microstructures can be easily obtained under the condition of air cooling through unique composition design. The invented idea, the principle of alloying design, the strengthening mechanism, and the evolution of the microstructure of new type air cooled Mn series bainitic steels are presented. Furthermore, the applications in different fields of these Mn series air cooled bainitic steels with different strength level are also introduced. It is suggested that the significance of the development of the air cooled Mn series bainitic steel can be summarized as follows： reducing costs of both raw materials and production; good combination of strength and toughness; self-hardening with high bainitic hardenahility by air cooling from hot working without additional quenching-tempering treatment or quenching procedure; large savings in energy resources; and reduced environmental pollution.     

Effect of Cerium on Structure and Properties of Granular Bainitic Steel

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低碳贝氏体非调质钢的试验研究

以开发与研究高品质低碳贝氏体非调质汽车用钢为目标,设计了适应要求的低成本的合金成分;采用锻造和空冷工艺使材料的组织和性能基本接近开发目标;利用SEM和EDS对钢中夹杂物进行观察分析,进一步提高钢的洁净度,开发钢完全满足汽车用钢的要求。