Ti-Nb复合微合金化高强度钢强化机理研究

以国内某钢厂的热轧高强度钢为研究对象,进行拉伸试验,利用OM和TEM分析了钢显微组织、第二相析出粒子形貌和尺寸等.结果表明,实验钢的屈服强度657 MPa、抗拉强度744 MPa、伸长率18.7％.微合金元素的加入使钢材晶粒明显细化,屈服强度的细晶强化增量为321.5 MPa,为提高材料强度的主要强化机制;研究析出的第二相粒子可知,基体中纳米级析出的(Nb,Ti)(C,N)粒子阻碍位错运动,是提高材料强度的主要机制之一,起到析出强化作用,屈服强度的析出强化量为78.58 MPa.     

Nb对中碳钢相变和组织细化的影响

针对无Nb和添加0.06%Nb的2种中碳钢,研究了Nb对0.47%C中碳钢相变及组织细化的影响规律.2种实验钢正火组织均为铁素体+珠光体,Nb微合金化能够有效细化中碳钢的奥氏体晶粒,从而导致正火后组织中铁素体体积分数明显增加.含Nb中碳钢的屈服强度相对无Nb钢提高了18%(70 MPa),抗拉强度基本保持不变,-20℃冲击韧性则由7 J提高到19 J,呈现显著提高.此外,由连续冷却转变(CCT)曲线发现,Nb微合金化中碳钢可在冷速≤10℃/s时获得较高体积分数的铁素体,因此,可保证工件在较大冷速范围内不出现大块珠光体或贝氏体/马氏体组织.结合TEM观察发现,Nb元素以微小析出物Nb(C,N)的状态均匀分布在钢中.Nb(C,N)析出物能有效细化奥氏体晶粒,并因此提高铁素体形核率,这是Nb在中碳钢中影响相变并提高韧性的主要机制.     

Nb/V/Ti微合金化对20MnSi钢组织和力学性能影响

采用扫描电镜(SEM)、电子背散射衍射(EBSD)技术和室温拉伸测试等研究了Nb、V、Ti微合金化元素对20MnSi钢显微组织和力学性能的影响。结果表明：Nb、V、Ti微合金化及其所形成的第二相粒子可以阻碍试验钢的晶界迁移、细化晶粒尺寸，经热轧-空冷后晶粒明显细化，晶粒尺寸可达12级，综合力学性能明显优于20MnSi穿水钢筋，并达到新国标中400 MPa级钢筋所要求的性能指标。根据理论模型计算，晶界强化、固溶强化和位错强化增量分别约占屈服强度的54%、22%和17%,而由于微合金化元素含量较低且所形成的第二相粒子体积分数较低，析出强化增量在试验钢屈服强度中的占比仅约7%,表明Nb、V、Ti微合金化设计而导致的晶粒细化对试验钢力学性能提升所产生的贡献十分显著。     

650MPa级V-N微合金化汽车大梁钢强化机制研究

采用OM,SEM和TEM对V微合金化钢与V-N微合金化钢的组织与析出相进行了分析,研究了强化机制.结果表明,V微合金化钢与V-N微合金化钢的显微组织主要为铁素体与少量珠光体的混合组织.随着卷取温度的升高,V-N微合金化钢的强度呈现出先增加后下降的规律,600℃时获得了最优的力学性能,其屈服强度与抗拉强度分别达到了605与687 MPa,延伸率为24.5%.与V微合金化钢相比,V-N微合金化钢的铁素体晶粒更细小,平均晶粒尺寸达到4.5 mm,析出相更细小弥散,尺寸在3~50 nm之间,平均尺寸达到8.0 nm,以及更高的位错密度.晶粒细化、析出强化与位错强化是V-N微合金化钢具有高屈服强度的主要原因,其中细晶强化是最主要的强化机制,占总屈服强度的43.05%,析出强化与位错强化对屈服强度的贡献高达34.44%.     

1000 MPa级热轧双相钢的微观组织及强化机制

研究了分段冷却工艺(超快冷+空冷+层流冷却)条件下一种钒微合金化双相钢的微观组织及强化机制。结果表明：试验钢的显微组织由(80.5%～83.7%)超细晶多边形铁素体和(16.3%～19.5%)块状马氏体组成,且80%以上的铁素体晶粒尺寸在1.0～2.5 μm之间,粒子直径为4～9 nm的V(C, N)弥散的分布于铁素体基体中并与高密度位错交互作用而钉扎位错。在细晶强化、析出强化、位错强化及第二相马氏体强化的综合作用下,试验钢的抗拉强度达到1000 MPa以上,且具有优异的综合性能：Rm≥1000 MPa,RP0.2≥530 MPa,δ≥23.5%,RP0.2/Rm≤0.54,n≥0.23。     

控轧控冷对Ti-Mo-Nb复合微合金化低碳钢组织和力学性能的影响

研究了控轧控冷的冷却速度对Ti-Mo-Nb微合金高强钢组织与性能的影响。结果表明,随着冷却速度的降低,试验钢中铁素体逐渐等轴化,铁素体的体积分数、晶粒尺寸逐渐增加。冷却速度的降低可显著细化析出相尺寸并增加其体积分数,析出方式由弥散析出向相间析出转变。铁素体通过析出强化实现提升材料强度的同时,成形性能得到改善。当冷却速度为28℃/s时,试验钢获得了优异的综合力学性能,抗拉强度为853 MPa,屈服强度为750 MPa,伸长率为18.6%,扩孔率为68.5%。组织细化与析出强化是试验钢的主要强化机制,当冷却速度为28℃/s时,细晶强化和析出强化强度增量分别为206 MPa和328 MPa。     

回火工艺对铌钛低碳贝氏体钢组织与性能的影响

通过光学显微镜、透射电镜和力学性能检验,研究了回火温度对TMCP型铌钛微合金化低碳贝氏体钢微观组织结构、第二相析出及力学性能的影响。结果表明,回火后力学性能非单调变化,归因于铌钛微合金化钢在回火过程中,贝氏体内位错亚结构回复软化与第二相析出强化及碳的脱溶机制综合作用。400～500℃回火,Nb、Ti第二相持续析出强化,随回火温度的升高,板条贝氏体回复作用逐渐加强并逐渐达到回复稳定状态。回火温度≥500℃时,M/A岛组织发生分解,贝氏体板条合并、组织粗化,析出相聚集长大,固溶元素脱溶,组织演变为贝氏体和铁素体,强度持续降低,但韧塑性得到改善。550℃回火后钢板具有最佳综合力学性能:抗拉强度为790 MPa,屈服强度为740 MPa,伸长率为16.5%,-20℃冲击吸收能量为250 J。     

微合金化技术开发800MPa级高韧直缝焊管钢

采用微合金化和热轧后超快冷等技术生产得到800 MPa级高韧直缝钢管钢,借助OM、SEM、TEM和室温拉伸等,研究了试验钢不同区域的组织与性能。研究表明,试验钢的热轧组织主要是粒状贝氏体+少量板条贝氏体;焊接热影响区粒状贝氏体体积分数减少到32.7%,板条贝氏体体积分数增加到30.5%,组织中出现针状铁素体和少量马氏体。试验钢热轧区主要以Ti为主进行复合微合金化,综合运用固溶强化、细晶强化、位错强化和析出强化,具有高的强韧性,屈服强度为804 MPa、抗拉强度为852 MPa、伸长率为21.5%。     

Softening Mechanism of Boron—Bearing Low--Carbon Hot Strips Produced by TSCR Route

通过薄板坯连铸连轧(TSCR)生产典型低碳铝镇静钢SPHC(一般用热轧钢带)流程的实验室模拟,分析了含(10- 50)×10-6 B,0．005％N热轧钢带的组织、析出物的特点以及性能变化．结果表明:由于粗大BN的优先析出抑制了细小AIN的析出,提高了晶粒的生长能力,以及B在奥氏体晶界的偏聚抑制了铁素体形核,使得含B热轧钢带晶粒明显粗化,通过测定,含B钢晶粒度达到7-8级,平均晶粒尺寸达到25μm．含B钢晶粒粗化以及钢中AlN析出量和自由N含量的降低,使得热轧钢带屈服强度与无B钢相比降低约94 MPa．     

V、N、Nb微合金化对薄板坯连轧带钢组织和性能的影响

在试验室模拟薄板坯连铸连轧过程,板坯均热后被轧制到7mm厚并通过控冷来模拟辊道冷却和带钢的缓慢卷取过程.本文选用低碳钢,研究了V、N、Nb微合金化对其组织和性能的影响.通过试验证明在V-N钢中加入Nb对钢的强化机制有较大影响,使V-N-Nb钢中的析出强化增大,这表明V-N-Nb微合金化可充分地发挥微合金元素在钢中的析出强化作用,析出强化对屈服强度的贡献比V-N微合金化提高17MPa.     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

THERMODYNAMICS STUDY ON THE DECOMPOSITION OF CHROMITE WITH KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

INFLUENCE OF HEAT TREATMENT ON DAMPING BEHAVIOUR OF THE MAGNESIUM WROUGHT ALLOY AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

An Easy Way to Quantify the Adhesion Energy of Nanostructured Cu/X(X=Cr,Ta,Mo,Nb,Zr) Multilayer Films Adherent to Polyimide Substrates

An approach based on film buckling under simple uniaxial tensile testing was utilized in this paper to quantitatively estimate the interfacial energy of the nanostructured multilayer films(NMFs) adherent to flexible substrates. The interfacial energies of polyimide-supported NMFs are determined to be *5.0 J/m2 for Cu/Cr, *4.1 J/m2 for Cu/Ta,*2.8 J/m2 for Cu/Mo, *1.1 J/m2 for Cu/Nb, and *1.2 J/m2 for Cu/Zr NMFs. Furthermore, a linear relationship between the adhesion energy and the interfacial shear strength is clearly demonstrated for the Cu-based NMFs, which is highly indicative of the applicability and reliability of the modified models.     

High-Speed Friction Stir Welding of SiC_p/Al–Mg–Si–Cu Composite

A 17 vol% SiCp/Al–Mg–Si–Cu composite plate with a thickness of 3 mm was successfully friction stir welded(FSWed) at a very high welding speed of 2000 mm/min for the first time. Microstructural observation indicated that the coarsening of the precipitates was greatly inhibited in the heat-affected zone of the FSW joint at high welding speed, due to the significantly reduced peak temperature and duration at high temperature. Therefore, prominent enhancement of the hardness was achieved at the lowest hardness zone of the FSW joint at this high welding speed, which was similar to that of the nugget zone. Furthermore, the ultimate tensile strength of the joint was as high as 369 MPa, which was much higher than that obtained at low welding speed of 100 mm/min(298 MPa). This study provides an effective method to weld aluminum matrix composite with superior quality and high welding efficiency.