板条状马氏体的亚结构及形成机制

研究马氏体亚结构及形成机制具有重要理论意义和应用价值.应用35CrMo等材料,淬火为马氏体组织,采用JEM-2100电镜观察马氏体形貌和亚结构,发现35CrMo钢马氏体为板条状,亚结构除了高密度缠结位错外,还有高密度层错.结合2Cr13、Fe-15 Ni-0.6C合金试样的浮凸试验,应用隧道扫描显微镜观察表面马氏体浮雕形貌,测定浮凸的微细尺寸.综合上述试验结果,分析位错、层错形成机制.发现浮凸效应中没有出现位错滑移迹象,认为切变模型不能解释高密度位错和层错的形成.最后应用马氏体相变新机制分析了高密度缠结位错、精细层错的形成.     

N对TWIP钢马氏体相变及力学性能的影响

以传统TWIP钢为对比,测试了含N TWIP钢的力学性能,并利用XRD进行物相分析和TEM进行做观结构表征.结果表明,在由fcc或hcp结构向bcc结构马氏体进行相变时,晶体结构中的最大间隙由0.1047 nm降低至0.0725 nm.间隙原子N的存在显著增大bcc结构的晶格畸变能,提高α马氏体切变的阻力,因而强烈抑制α马氏体相变,导致组织中hcp结构ε相含量大幅度增加,提高了TWIP钢的强度,但也降低了钢的塑性.另外,奥氏体平均和区域层错几率的计算及微观组织分析结果表明,形变增加层错的数量,而马氏体相变消耗层错,从而减少层错数量.     

马氏体相变研究的最新进展(四)

正3.2.4有色金属合金中的马氏体孪晶图47是Cu-11.42Al-0.35Be-0.18B合金的马氏体组织中的孪晶形貌,可见呈现竹节状,竹节长短不等。图48是Cu-11Al合金的马氏体组织的电镜照片,可见马氏体片中存在贯穿的层错,层错微细而分布较为均匀。由于这类马氏体的亚结构以微细层错为主,甚至为全层错亚结构,故可称为层错型马氏体。层错亚结构也不能用切变机制解释。     

近几年马氏体相变研究的进展

综合整理了近年来马氏体相变试验研究的新成果.认为马氏体相变切变过程缺乏热力学可能性.指出马氏体在晶界、相界面、位错等缺陷处形核,并非共格切变过程.发现板条状马氏体、片状马氏体中均存在堆垛层错亚结构；高密度位错、孪晶、堆垛层错亚结构的形成并非切变所致；马氏体形貌的演化系应变能起主导作用,与切变无关；马氏体表面浮凸是相变比...     

马氏体相变理论研究的最新进展

马氏体相变的切变机制存在误区,研究马氏体相变的形核、长大、组织形貌及亚结构等具有重要理论价值和实际意义。本文综合整理了近年来马氏体相变试验研究的新成果,指出马氏体在晶界、相界面、位错等缺陷处形核,并非切变形核;发现板条状马氏体中存在层错亚结构。位错、孪晶亚结构的形成也非切变所致;马氏体组织形貌的演化与应变能有密切关系;马氏体表面浮凸是相变比体积增大所致,N型切变缺乏试验依据。     

固态相变研究的新发现

开展相变研究具有理论意义和工程应用价值。采用SEM、TEM、STM、XRD、LSCM等设备研究观察了钢铁材料中的固态相变,发现许多新的试验现象,如珠光体表面浮凸、钢中马氏体层错亚结构、低碳马氏体中的孪晶、位向关系偏差、新观察到的形核地点等。     

马氏体相变研究的最新进展(二)

正2马氏体组织形貌和物理本质马氏体虽为单相组织,但其组织形貌和亚结构却很复杂。20世纪后进行了大量的观测和研究,尤其是60年代初,应用电子显微分析技术清楚地观察了马氏体的组织形态和精细亚结构,证实马氏体内部存在高密度位错组态、精细孪晶、层错等亚结构。低碳钢(0.3%C)淬火后得板条状马氏体;高     

钢中马氏体的孪晶亚结构

采用JEM-2100高分辨透射电镜观察了含0.029％La纯铁、40Cr、60Si2CrV、W6Mo5Cr4V2和Mn13钢的马氏体组织形貌,并对马氏体组织中的孪晶亚结构的形成机制进行了探讨.研究表明:从超低碳钢到高碳钢,淬火马氏体中均有相变孪晶出现,随着奥氏体中碳含量的提高则马氏体中相变孪晶增加.孪晶亚结构的形成与马氏体相变应变能有关,随着转变温度降低,应变能增大,形成精细孪晶以调节应变能.     

异种钢焊接裂纹研究

采用 Cr29—Ni9型及 LZ60焊条焊接易淬火钢时,发现了三种形态的裂纹:底层焊道中部贯通裂纹、综合区奥氏体晶带裂纹和层间裂纹。它们与异种钢焊缝中马氏体层的存在,氢在奥氏体晶带和马氏体层交界处的富集,以及复杂的应力状态等有关。本文根据裂纹的特性,研究了它们的生成条件和影响因素,并提出了有效防止裂纹发生的低氢优化工艺。     

低碳马氏体钢的透射电镜分析

本文用透射电子显微镜研究了具有代表性的六种低碳马氏体钢的显微组织,结果表明:含碳量较低的马氏体钢(指0.1—0.25wt-%C),淬火后一般都存在薄膜状残余奥氏体,低碳马氏体钢淬火时不可避免有自回火现象,自回火沉淀出的碳化物是六方晶格的ε碳化物,六种钢都能找到具有局部孪晶亚结构的板条晶,低碳马氏体在350—400℃回火时,ε转化成Fe_3C;回火温度提高至500℃时,孪晶消失,但马氏体板条晶的轮廓在600℃时仍可维持原状.     

Structure,mechanical, and tribotechnical properties of an austenitic nitrogen steel after frictional treatment

The features of the structure and the mechanical and tribotechnical properties of an austenitic nitrogen steel (Cr16.5, Mn18.8, C0.07, N0.53, Si0.52 wt %, and Fe for balance) after frictional treatment have been studied. It has been shown that, along with twinning, the nitrogen austenite upon frictional treatment undergoes a γ → stacking fault → ε transformation. The strengthening of the steel by the frictional treatment manifests in a delay of the onset of the plastic flow. In the structure of the surface layer with a thickness of 5 μm, a high concentration of stacking faults has been detected. The mechanical properties depend on the orientation of the acting stresses relative to the direction of the frictional treatment. Upon the sliding friction of a ball made of hard alloy (94%WC + 6%Co) on the strengthened surface, an anomalously low coefficient of friction of 0.13 is observed. The coefficient of friction in the presence of abrasive particles in the form of wear debris increases to 0.50; however, the wear rate is almost two times lower compared to the same characteristic for a nonstrengthened surface of the nitrogen steel tested under the same conditions.     

淬火工艺对耐磨钢NM400组织性能的影响

采用微Nb、B,加少量Cr成分体系,研究不同离/在线淬火工艺对NM400钢显微组织和力学性能的影响,通过光学显微镜、SEM和TEM观察,分析离/在线淬火工艺对马氏体精细结构的演变规律。结果表明:在线淬火工艺马氏体块更细小,大角度晶界比例大,保留轧制奥氏体变形位错等缺陷,为碳化物在回火中析出提供位置,使析出物分布更弥散,同时拥有马氏体-下贝氏体复相组织,提高了钢的硬度、强度和韧性。     

Structure and Mechanical Properties of Nitrogen Austenitic Steel after Ultrasonic Forging

Electron microscopy and X-ray diffraction have been used to investigate a nitrogen 07Kh17AG18 steel with an austenitic structure after the surface deformation treatment—ultrasonic forging. During ultrasonic forging, an austenitic structure transforms into a new structure with an elevated concentration of deformation-induced stacking faults, a lot of deformation microtwins, ε-martensite crystals. The austenite lattice parameter is found to be decreased in the surface layer. After ultrasonic forging, nitrided steel exhibits enhanced strength properties with retained high plasticity.     

Structural stability of the Laves phase Cr2Ta in a two-phase Cr–Cr2Ta alloy

Detailed microstructural analysis of a two-phase alloy of composition Cr–9.8 at.% Ta and lying in the Cr–Cr₂Ta region of the Cr–Ta binary system confirmed that the existing phase diagram is inaccurate; in the cast and annealed condition (1273 K/24 h), blocky primary Cr₂Ta precipitates were observed although the phase diagram indicates the eutectic composition to be ∼13 at.% Ta. The eutectic structure is composed of Cr solid solution and the Laves phase Cr₂Ta; the morphology is primarily lamellar although the rod morphology was occasionally observed. The Laves phase eutectic microconstituent exhibits the C14 (2H) hexagonal structure with a low stacking fault (basal faults) density and an average composition corresponding to 28.5 at.% Ta. After a prolonged high-temperature anneal (1573 K/168 h), the morphology breaks down to form discrete particles of Cr₂Ta; the C14, C36 and C15 structures were all recognized in this annealed condition, often more than one form being present in a single precipitate. The C15 structure was not twinned but contained some stacking faults on the {111} planes. Composition measurements confirmed that these structural transformations were accompanied by composition changes, the precipitates becoming more Ta-rich as they transitioned from the C14 via the C36 to the C15 phase. These observations are coupled with the results from earlier studies to present a discussion on factors that influence the stability and C14/C36/C15 transformation kinetics.     

On the crystallographic structure of S-phase

Homogeneous, stress-free S-phase was synthesized by gaseous nitriding of AISI 316 stainless steel in ammonia/hydrogen gas mixtures. X-ray diffraction analysis was applied to assess unambiguously the Bravais lattice of S-phase and to identify the effect of stacking faults on the Bragg angle of X-ray line profiles.     

Atomistic simulation of stacking faults in (001), (010), and (100) planes of cementite

Molecular-dynamics method was used to study γ surfaces for the (001), (010), and (100) planes of cementite. Displacement vectors corresponding to stable stacking faults have been determined. The energy of these stacking faults has been calculated by the molecular-dynamics and ab initio methods. The energy of unstable stacking faults, which characterizes the tendency of a material to plastic relaxation, has been estimated. The reactions of the splitting of perfect dislocations have been suggested; the possibility of the propagation of stacking faults in the planes under consideration is discussed.     

Influence of carbon content on microstructure and mechanical properties of Mn13Cr2 and Mn18Cr2 cast steels

In this paper, a comparison study was carried out to investigate the influence of carbon content on the microstructure, hardness, and impact toughness of water-quenched Mn13Cr2 and Mn18Cr2 cast steels. The study results indicate that both steels＇ water-quenched microstructures are composed of austenite and a small amount of carbide. The study also found that, when the carbon contents are the same, there is less carbide in Mn18Cr2 steel than in Mn13Cr2 steel. Therefore, the hardness of Mn18Cr2 steel is lower than that of Mn13Cr2 steel but the impact toughness of Mn18Cr2 steel is higher than that of Mn13Cr2 steel. With increasing the carbon content, the hardness increases and the impact toughness decreases in these two kinds of steels, and the impact toughness of Mn18Cr2 steel substantially exceeds that of Mn13Cr2 steel. Therefore, the water-quenched Mn18Cr2 steel with high carbon content could be applied to relatively high impact abrasive working conditions, while the as-cast Mn18Cr2 steel could be only used under working conditions of relatively low impact abrasive load due to lower impact toughness.     

INFLUENCE OF INTERNAL HYDROGEN ON THE HYDROGEN EMBRITTLEMENT OF AUSTENITIC STAINLESS STEEL

1.IntroductionManyengineeringstructure8maybeaffectedbyhighpressurehydrogenafteral0ngtimesuchashydrogen-st0ragepressurevessel/hydrogen-transportpiping/highpressurehy-drogenpurificationandpressurizati0nequipment.Thesafetyofthesestructuresmaybedecreasedbecau8eofhydrogenembrittlementcausedbytheinteracti0nbetweenthestruc-turalmaterialandhydr0genresultinginlossofductilityinthematerial-Manyresearchersareinterestedinthestudyofhydrogenembrittlement0fmaterials,especiallytheausteniticstainlesssteel,andha…