纳米贝氏体钢相变加速技术开发进展

摘要：纳米贝氏体的成功开发使得常规条件下对钢铁材料组织的纳米级细化成为可能,然而奥氏体中低温转变的热动力学条件限制了纳米贝氏体的相变速率,阻碍了纳米贝氏体钢的合金范围拓展和大规模工程应用。梳理了近期国内外学者针对这一问题开发的纳米贝氏体相变加速技术,综述了化学成分、预相变、预变形、强磁场等条件下贝氏体相变加速方面的进展。综合分析表明,针对贝氏体相变需充分考虑贝氏体形核以及长大2个过程。纳米贝氏体合金和工艺的设计需充分考虑各因素对2个过程的不同影响,充分优化贝氏体相变动力学和微观组织。复合相变加速技术可以成为纳米贝氏体钢开发的新方向。     

有色合金的热弹性马氏体相变及其应用

综述本文作者及其合作者对有色合金的热弹性马氏体相变及其在形状记忆中应用的已发表的工作。在热力学研究、M_s 及 A_s 计算的基础上,本文提出材料中发生热弹性马氏体相变的必需条件。扼要总结我们对 Ni-Ti 及 Cu-Zn-Al 合金中的相变及形状记忆效应的工作。     

准下贝氏体相变研究

利用电镜研究了４０ＣｒＭｎ２Ｓｉ２Ｍｏ铸钢准下贝氏体中变态组织及精细结构，观察到交叉型，中脊型类马氏体形貌贝氏体，发现贝氏体中脊中有大量层错。贝氏体交叉的形成是变应力－应变诱发贝氏本转变引起，中脊是贝氏体相变初期切变机制快速形核与长大的结果，中脊中层错的存在，为贝氏体相变过程存在切变机制提供了依据。     

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。     

合金元素铜对ULCB钢相变及组织结构的影响

主要以ULCB钢的化学成分为基础，通过添加不同含量的合金元素Cu，着重分析研究了合金元素Cu对ULCB钢的相变、组织结构的影响，并对合金元素Cu的作用机理进行了探讨。研究结果表明，随着钢中w(Cu)的增加，相变点Ac1、Ac3及贝氏体转变温度均呈下降趋势，试验钢的奥氏体晶粒大小及在随后淬火冷却过程中形成的贝氏体的尺寸亦随钢中w(Cu)增加而呈下降趋势，当w(Cu)增加到1．0％以上时，这种趋势有所减缓。     

纳米贝氏体的热力学分析及强韧化研究

针对目前高碳高硅低温贝氏体(纳米结构贝氏体)相变速度缓慢的现状,采用贝氏体相变热力学理论分析主要合金元素对低温贝氏体相变驱动力的影响,设计了新型纳米结构贝氏体钢成分0.83C-2.44Si-0.43Mn-0.73Al.利用膨胀仪研究该成分贝氏体钢在不同温度下的相变整体动力学,综合使用扫描电子显微镜、X射线衍射、电子背散射衍射等方法研究热处理工艺对实验钢组织和力学性能的影响.结果表明,350℃等温转变贝氏体的抗拉强度为1401 MPa,延伸率为42.21%,强塑积可达59136 MPa·%,在室温拉伸过程中发生明显的相变诱导塑性效应;230℃等温转变组织中贝氏体铁素体片层厚度小于100 nm,抗拉强度达2169 MPa.      

低碳微合金贝氏体钢的转变动力学研究

以低碳微合金贝氏体钢为研究对象,用热膨胀法测定了奥氏体的连续冷却转变曲线,用光学显微镜观察了相变组织,发现相变温度区间较宽,且在1～30℃/s冷速范围内均可得到贝氏体组织,随冷速提高,相变温度降低,组织晶粒细化。     

NiAl合金的B2→L10（3R）马氏体相变晶体学研究

根据ＮｉＡｌ合金的三种Ｂ２→Ｌ１０（３Ｒ）马氏体相变表象理论模型，从原子迁动的晶体几何关系出发，讨论了Ｂ２→Ｌ１０（３Ｒ）马氏体相变晶体学及２４种马氏体变体间的位向关系。对分别由这三种相变机制形成的２４种马氏体变体之间的晶体学等价关系进行了详尽的说明     

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。     

硅含量对低碳贝氏体相变动力学和性能的影响

摘要：设计了3种不同Si含量的低碳贝氏体钢,进行了不同温度下等温淬火热处理热模拟实验、X-射线衍射和拉伸实验等,研究Si含量对贝氏体相变动力学和贝氏体钢性能的影响。结果表明,随Si含量增加,贝氏体相变量降低,动力学方程参数b减小,n增大。另外,随贝氏体相变温度增加,参数b减小,n增大。而且在较低相变温度下,因Si含量不同造成参数b和n的值的差异更大,说明低温下Si含量对贝氏体相变动力学的影响更大。此外,Si含量越低,因相变温度不同造成贝氏体相变孕育期和完成时间的差异逐渐增大,表明随Si含量的增加,Si对贝氏体相变动力学的影响降低。最后,随着Si含量的增加,试样抗拉强度和伸长率均逐渐增加。研究结果为优化低碳贝氏体钢成分设计、调控其力学性能提供了参考。     

Pre-bainitic Transformation in Fe-Ni Alloy

Ｔｈｅｐｒｅ－ｂａｉｎｉｔｉｃｐｈｅｎｏｍｅｎｏｎｉｓｏｎｅｏｆｔｈｅｉｍ－ｐｏｒｔａｎｔｓｕｂｊｅｃｔｓｏｆｂａｉｎｉｔｉｃｔｒａｎｓｆｏｒｍａｔｉｏｎｗｈｉｃｈｉｓｓｔｉｌｃｏｎｔｒｏｖｅｒｓｉａｌ．Ｏｎｅｖｉｅｗｉｓｔｈａｔｔｈｅｓｏｌｕｔｅａ...     

Effect of heat treatment on mechanical and stirring wear properties of low temperature bainite steels

One- step and two- step isothermal low temperature bainitic transformation were designed. The effects of heat treatments on the microstructures, mechanical properties and stirring wear resistance of low temperature bainite were discussed. The results show that the microstructures of samples under different heat treatments all consist of micro- and nano- scale bainite lath and austenite. The size of bainite lath decreases from 95 nm to 65 nm with the decrease of isothermal temperature from 300?? to 250?? under the one- step isothermal bainitic transformation. Moreover, the volume fraction of austenite likewise decreases from 28??1% to 19??9%. The unstable block austenite is apparently refined by the two- step isothermal bainitic transformation. The optimal balance between the tensile strength (1857MPa) and elongation (10??59%) is obtained in the sample treated by two- step isothermal bainitic transformation. Also, the V- notch impact absorbed energy of the sample treated by two- step isothermal bainitic transformation reaches 11J. Compared with the one- step isothermal bainitic transformation (300, 250??), the sample treated by two- step isothermal bainitic transformation shows the optimized wear resistance and increases by 11??8% and 31??4%, respectively, which is attributed to the better ductility and toughness.     

不同硼含量微合金钢的连续冷却相变行为

 利用热模拟试验技术对实验室制备的含硼微合金钢连续冷却转变形为进行了试验研究,利用光学显微镜研究冷却速度、变形对试验钢显微组织的影响,探讨了硼对转变行为的影响规律。结果表明：适量硼延缓多边形铁素体生成,有利于获得贝氏体组织;无硼及wB=00020%时,分别在1~25及05~25℃/s的冷速都能得到贝氏体组织;wB=00030%时,冷速在2℃/s 以上能得到贝氏体组织;与未变形相比,变形导致试验钢贝氏体冷速区间变窄。在同一冷速下,随硼含量增加贝氏体开始转变温度先降低再升高,显微硬度随硼含量增加先增加而后降低。     

A Semi‐Empirical Model for the evolution of Retained Austenite via Bainitic Transformation in Multiphase TRIP Steels

Multiphase TRIP steels exhibit unique combinations of strength and cold formability, characteristics especially desirable in automotive applications. This behaviour is largely determined by the amount and stability of the retained austenite dispersion in the microstructure, produced by a two‐stage heat‐treatment, consisting of intercritical annealing followed by an isothermal bainitic treatment. The amount and stability of retained austenite is mainly determined by the proper selection of the temperature and temporal duration of the bainitic treatment. In the present work an approach is presented which allows for the calculation of the amount of retained austenite in the microstructure, as a function of bainitic treatment conditions. The approach is based on the physical characteristics of the bainitic transformation and on the stabilizing effects of the formation of bainitic ferrite in austenite. Each bainitic ferrite platelet is considered to chemically stabilize a part of the surrounding austenite due to carbon rejection. The spatial and temporal extent of this stabilization is determined by solving the corresponding carbon‐diffusion problem, and thus the amount of retained austenite contributed by any individual platelet is determined. Subsequently, the evolution of the population of the platelets in the entire microstructure is determined and, thus, the volume fraction of retained austenite as a function of transformation time is calculated. Application and comparison of calculations with experimental results, obtained from four different multiphase TRIP steel compositions, exhibited very good qualitative and quantitative agreement.     

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。     

Effect of Deformation on Continuous Cooling Phase Transformation Behaviors of 780 MPa Nb‐Ti Ultra‐High Strength Steel

For the purpose of achieving the reasonable rolling technology of 780 MPa hot‐rolled Nb‐Ti combined ultra‐high strength steel, the effect of deformation and microalloy elements Nb and Ti on phase transformation behaviors was investigated by thermal simulation experiment. The results indicated: the deformation promoted ferritic transformation; due to the carbon content of the experimental steel was lower (<0.12% wt), the deformation indirectly impacted perlitic transformation through promoting ferritic transformation; the effect of the deformation on bainitic transformation was subject to condition whether proeutectoid ferrite precipitated before bainitic transformation. At low cooling rate of 0.5 °C/s, Nb and Ti promote transformation process γ → α, but that not good for refining the ferrite grain; at high cooling rate of 25 °C/s, Nb and Ti to a certain extent promote bainitic transformation. The recrystallization stop temperature of experimental steel was greater than 1000 °C, and phase transformation point A_r3 was 764 °C. In order to obtain the fully bainite microstructure in the practical rolling process, the cooling rate should be controlled above 15 °C/s, the start finish rolling temperature between 950–980 °C, the finishing temperature between 830–850 °C, the coiling temperature between 450–550 °C.     

塑料模具718钢变形奥氏体连续冷却转变后的显微组织

采用Ｇｌｅｅｂｌｅ １５００热模拟试验机研究了变形温度、冷却速度对塑料模具７１８钢显微组织和硬度和影响。试验结果表明，７１８塑料模具钢在奥氏体区变形后，从６００℃开始以不高于０．０２℃／ｓ的速度缓慢冷却，可获得贝氏体组织，硬度（ＨＲＣ）为４０￣４４；在奥氏体未再结晶区变形产生的位错缠结抑制了贝氏体铁素体的长大，并使７１８钢的硬度提高。