热处理对2 000 MPa超高强度不锈钢组织和性能的影响

 运用Thermal-calc热力学软件、光学显微镜（OM）、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等手段研究了热处理工艺对一种新型的超高强度不锈钢微观组织及力学性能的影响。结果表明,经过固溶处理后钢的基体为高密度位错的板条马氏体组织;强度随着时效温度的升高而逐渐升高,在520～540 ℃时可达到2 000 MPa,且冲击吸收功在540 ℃时达到最大值37 J。此时在板条马氏体上析出大量、细小、弥散以μ相为主的第二相,同时在板条与板条界面上有块状的逆转变奥氏体生成,这是该钢具有超高强度与高韧性的主要原因。     

常化后冷却工艺对1600MPa级超高强钢组织性能的影响

为改善高强度钢的塑性和韧性,对中碳低合金马氏体高强度钢分别采用常化后空冷＋回火和常化后控冷＋回火工艺,研究常化后冷却工艺对钢中残余奥氏体及力学性能的影响.采用扫描电镜获得钢的组织形态,利用X射线衍射和电子背散射衍射技术分析钢中残余奥氏体的体积分数、形貌和分布.发现两种工艺下均得到板条马氏体＋残余奥氏体组织,残余奥氏体均匀分布在板条之间,随工艺参数不同,其体积分数在3%~10%变化.常化后加速冷却能显著细化马氏体板条,提高钢的屈服强度和抗拉强度100 MPa以上,冲击功下降4 J.残余奥氏体的体积分数随常化控冷终冷温度的升高呈现先升高后降低的变化,常化后的控制冷却也可以作为进一步改善马氏体类型钢组织和性能的方法     

Nonbasal plane defects in 18r martensite and the effect of abnormal defects on thermoelastic martensitic transformation

This investigation, using a Cu-26.4 pct Zn-4.8 pct Al (wt pct) alloy, was carried out to provide more detailed and accurate information on the crystal defects in martensite. By comparing direct-quenched and step-quenched specimens, it has been found that some abnormal defects of martensite, such as nonbasal plane (NBP) planar defects and dislocations, often exist in the martensite obtained by direct quenching. Trace analysis showed that the NBP planar de-fects are often located in the -125 plane of the martensite lattice. High-resolution electron microscopy (HREM) has revealed that the NBP planar defects resulted from basal plane stack-ing faults which break off inside the plate of martensite.In situ observations during heating in the transmission electron microscope (TEM) have proved that martensites which have a great amount of abnormal crystal defects are stable even when heated to high temperature, and the existence of abnormal defects may be one of the reasons for the stabilization of martensite.     

TEM study of precipitates in laser clad NiAl bronze

Transmission electron microscopy (TEM) examination of sheet martensite in laser clad NiAl bronze reveals precipitates with diameter of about 20 nm. It is found that the hardness of the sheet martensite shows a pronounced decrease with increasing test temperature. Heat treatment at 673 K for 4 h doubled the size of the precipitates. Convergent beam electron diffraction (CBED) and microdiffraction (MD) in TEM are used to examine the crystal structure of the precipitates in heat treated material. CBED patterns suggest two point groups:4/mmm and m3m. Three MD patterns of the precipitates show complete agreement with B₂ structure. The crystal structure of precipitates in as-clad material is studied by high resolution electron microscopy (HREM) and optical diffraction. The HREM images are a close match with simulated images based on a B₂ crystal structure model.     

Quasi-cleavage and martensite habit plane

Quasi-cleavage (QC) is often observed on the fracture surfaces of hydrogen embrittled iron and steels. For quenched-and-tempered martensitic high strength steels, most QC facets show geometrical markings that are made up of fine oblong elements arrayed at well defined angles. To better understand this mode of failure, scanning and transmission electron microscopy (SEM and TEM) and etch-pit analysis have been applied to the study of quasi-cleavage and of martensitic structure in an AISI 4340 steel (tempered at 478 K). A special technique was developed for determining martensite habit planes without the need for concomitant presence of retained austenite or annealing twins in the microstructure. Quasi-cleavage in this AISI 4340 steel has been shown to be cleavage along {110}_α′ planes through martensites, and {225}_γ have been unambiguously determined as the martensite habit planes. The methods of analyses are described. The relationship between surface features of QC facets and the martensitic microstructure and the possible interaction between hydrogen and slip are discussed. Potential application of the analysis method to studies of martensitic transformation is considered.     

Effect of center microstructure on fracture mechanism of ultra-thick high strength steel

In order to study the relationship between microstructure and fracture mechanism of ultra-thick steel plate, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) were used to characterize and analyze the microstructure and crack morphology of 1/4 and 1/2 thickness (center) of the test plate. The results show that the low temperature impact toughness at the center is significantly lower than that at the 1/4 thickness, which is due to the microstructure of the center is tempered lath bainite and tempered granular bainite, and the proportion of granular bainite is higher. The presence of M-A island in granular bainite promotes the initiation of micro pores or micro cracks. The 1/4 thickness is a mixed microstructure of tempered lath martensite and tempered lath bainite. The dislocation movement between laths releases local stress concentration, and relieves the stress at the crack tip region, resulting in crack passivation, hindering crack propagation and improving low temperature impact toughness.     

Morphological and structural studies of thermoelastic martensites in a Ag-38 At. Pct Zn alloy

Thermoelastic martensites formed upon subzero cooling a Ag-38 at. pct Zn alloy have been studied by means of optical and electron microscopy, electron diffraction, and electrical resistivityvs temperature measurements. Two different morphologies, slender banded and spear shaped, are observed in cooled bulk specimens, both being thermoelastic. The slender banded martensite is retained at room temperature in thin foils after subzero cooling and possesses the 9R type long period stacking order structure with internal stacking faults on the basal plane. This 9R martensite is “normal” with an orthorhombic lattice:a=4.81,b=2.82 andc=20.5Å (a:b:c=1.71:1:7.27). The spear shaped martensite is also retained at room temperature in subzero cooled thin foils and in shape memory cycled ribbons as well. This morphology exhibits a monoclinic 3R type stacking order structure with internal twins and stacking faults. Lattice parameters of the 3R martensite area=4.83,b=2.87,c=6.94Å and β=87.4 deg (a:b:c=1.68:1:2.41). This structure is equivalent to that of AuCuI (L1₀, fct) with lattice parametersa=4.07,c=3.89, andc/a=0.96. The twin and stacking fault planes in the 3R martensite are the (201) and (001) planes respectively. The basal planes of the 9R and 3R martensites are common, being generated from the {110} plane of the CsCl type parent phase, and the two martensites differ only in the shuffling mode on the {110} plane upon transformation. The thermelastic nature of the 3R martensite is slightly different from that of the 9R one.     

变形对亚稳态奥氏体不锈钢低温敏化的影响

采用扫描电镜(SEM)、X射线衍射分析(XRD)及透射电镜(TEM)研究了不同形变量下的亚稳态不锈钢(AISI 304)经过低温敏化处理(380 ℃、240 h的真空热处理)后组织的变化。通过双循环电化学动电位活化技术(DL-EPR)对敏化态的试样进行敏化度(DOS)测试,并用电化学阻抗谱表征了不同试样的耐腐蚀性能。结果表明,随着变形量的增加,低温敏化试样的敏化度递增,材料的耐腐蚀性能下降,当变形量达到40%时,敏化度达到71%。经过DL-EPR测试后,试样奥氏体晶粒和大部分晶界完好,马氏体区域是主要腐蚀区域,腐蚀模式为穿晶腐蚀。马氏体板条和基体中的滑移带是碳化物容易形核的位置。     

超厚高强钢心部组织对断裂机制的影响

摘要：为了研究超厚钢板心部显微组织与微观断裂机制的关系,利用扫描电子显微镜（SEM）、透射电子显微镜（TEM）和电子背散射衍射（EBSD）等技术手段对试验钢板1/4厚度、1/2厚度（心部）显微组织及裂纹形貌进行表征和分析。结果表明,心部处低温冲击韧性较1/4厚度处有明显的降低,这是由于心部组织为回火板条贝氏体和回火粒状贝氏体,其中粒状贝氏体的比例较高,粒状贝氏体中M-A岛的存在促进了微孔或微裂纹的启裂;1/4厚度处为回火板条马氏体与回火板条贝氏体二者的混合组织,板条间的位错运动释放局部应力集中,而舒缓裂纹尖端区域所受应力,产生裂纹钝化、阻碍裂纹扩展,提高低温冲击韧性。     

Microstructural, compositional, and microhardness variations across a gas-metal arc weldment made with an ultralow-carbon consumable

An experimental gas-metal arc (GMA) weldment of HSLA-100 steel fabricated with an ultralowcarbon (ULC) consumable of interest for United States Navy applications, designated “ARC100,” was studied to determine the relationships among the microstructure, the solute redistributions at various positions across the weldment, and the local properties (microhardness). These relationships were investigated by a variety of techniques, including microhardness mapping, optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) (including compositional X-ray mapping), and parallel electron energy-loss spectroscopy (PEELS). The microconstituents observed in this weld include lath ferrite, degenerate ferrite, lath martensite, retained austenite, and oxide inclusions; no carbides or other solid-state precipitates are present within the weld metal. Microhardness mapping indicates an undermatched weld metal (lower hardness as compared to the base plate) in which the hardest regions are in the first and last top beads, the root passes, and between highly ferritic soft bands associated with the outer portion of each weld bead’s heat-affected zone (HAZ) (within the fusion zone). The majority of the gradient in the substitutional alloying elements (Ni, Cu, Mn, and Cr) occurs within a region of less than about 0.5 mm of the fusion boundary, but the composition still changes even well into the fusion zone. Appreciable segregation of Ni and Cu to solidification cell boundaries occurs, and there is appreciable enrichment of C, Ni, Cu, and Mn in thin films of interlath retained austenite. This ULC weld metal is softer than the base plate due to the preponderance of lath ferrite rather than lath martensite, even at the high cooling rates experienced in this low-heat-input weld. Alternatively, the strength of the weld metal is due to the presence of at least some untempered lath martensite and the fact that the majority of the ferrite is lath ferrite and not polygonal ferrite. The interlath retained austenite might enhance toughness, but might also serve as a source of hydrogen in solution, which could potentially contribute to hydrogen-assisted cracking.     

微钒Cr-B系NM400耐磨钢的热处理工艺

 采用在Cr-B系中添加微量钒的低成本设计思路来确定NM400耐磨钢的合金成分,详细研究了不同淬火温度和回火温度对NM400耐磨钢显微组织和力学性能的影响,获得了适合工业生产的热处理工艺制度。通过光学显微镜、SEM和TEM观察,分析了经不同温度回火后马氏体组织精细结构的演变规律。结果表明：试验钢具有良好的淬透性,经900~930℃淬火、250℃保温90min回火后得到均匀细小的回火板条马氏体组织;TEM分析表明,回火板条马氏体的宽度在0.1~0.2μm,板条内分布细小均匀的碳化物析出粒子（主要是10~20nm碳氮化钒）,提高钢的综合力学性能。     

Microstructure and Mechanical Properties of TRIP Steel with Annealed Martensite

The microstructure and mechanical properties of cold rolled TRIP steel containing C 0.2, Si 0.5, Mn 1.5, A1 1.3, and Nb-kV 0.13 （mass%） with annealed martensite （TAM steel） were investigated using optical microscopy, field emission gun scanning electronic microscope （FEG SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, and mechanical testing. The mierostructure of the TAM steel mainly consisted of polygonal ferrite, bainite, annealed martensite and retained austenite. The martensite after annealing did not spheroidize, which consisted of annealed lath martensite structure and interlath second phase. Compared with the traditional TRIP steel with polygonal ferrite matrix （TPF steel）, the TAM steel has more excellent elongation rate over 32%. The TAM steel also has better strain hardening behavior than the TPF steel. The excellent elongation and strain harden- ing behavior of TAM steel result from high retained austenite stability of the TAM steel, which is attributed to its fine distribution and medium strength ratio of second phase to matrix.     

十六胺有机膜对羟基磷灰石晶体生长与形貌调控

采用X射线XRD、红外光谱FTIR、扫描电镜SEM、透射电镜TEM等分析手段,研究了十六胺有机膜对羟基磷灰石(HA)晶体结构、形核、晶体形貌和结晶学定向生长的调控作用及其机理。结果表明:无有机膜时,生成物为磷酸八钙(OCP)和羟基磷灰石(HA)的混合物,其生长速率很慢且晶体排列无一定规则;而在十六胺有机膜调控下,生成物为按规则排列、沿〈0001〉定向生长、结晶良好的纳米片状羟基磷灰石晶体,且其形核和生长速度均很快。其原因是:十六胺有机膜上带有的大量极性强、电荷密度高的—NH_3基团,通过静电作用在有机膜/溶液界面处形成局域过饱和浓度,促进羟基磷灰石晶体形核;另一方面,十六胺有机膜的二维晶格尺寸与HA(0001)面的晶格参数具有良好的匹配关系,构造了一个有利于HA以(0001)面形核生长的结构框架,从而促进了HA相沿〈O001〉方向定向生长。     

HB450低合金超高强耐磨钢回火过程中的组织性能演变

  利用透射电镜（TEM）、扫描电镜（SEM）等试验方法,研究了新型低成本HB450低合金超高强耐磨钢在不同回火条件下组织和性能演变规律,并分析了其强韧变化机制。结果表明：回火对试验钢的硬度和强度均有较大影响。在200~250℃回火,试验钢表现出良好的强韧性配合,满足国标工程机械用高强度耐磨板GB/T24186—2009中NM450级别要求;在250℃回火时,试验钢出现硬化迹象。透射电镜分析表明,在该温度下回火,析出物中除了有大量弥散分布的ε 碳化物外,还出现了少量30~50nm的（Nb,Ti）（C,N）粒子,该2类粒子对试验钢的强化起着较大的作用。     

高压热处理诱导工业纯铁马氏体相变

 为了研究高压下马氏体组织形态特征及高压淬火马氏体相变机制,利用CS-1V型六面顶高压设备、在3、4和5 GPa高压下对工业纯铁进行热处理,利用SEM、EBSD等分析手段研究了高压淬火对工业纯铁马氏体组织形态及力学性能的影响。结果表明,GPa级高压下奥氏体化后,工业纯铁以6 ℃/s冷却速率就能淬火获得马氏体。3 GPa下,工业纯铁淬火马氏体呈现典型的低碳马氏体组织形貌;4 GPa下,其板条马氏体形成过程与典型的片状马氏体类似,先形成的板条束贯穿整个奥氏体晶粒并将其分割,后形成的板条束尺寸大小受限;5 GPa下,以协作方式通过母相转变为马氏体的“协作方阵”数量多、尺寸小、整齐性高,并多呈“梯形”生长。5 GPa下淬火工业纯铁的力学性能接近常压下淬火的0.2%C钢水平,硬度达415HV,屈服强度达700 MPa。     

锰对中锰耐磨钢组织形态及相变的影响

通过DIL805A热分析仪、扫描电子显微镜、电子背散射衍射、透射电子显微镜、力学分析等方法研究Mn对中锰耐磨钢组织形态、相变及力学性能的影响.随着Mn的质量分数以2%的增量从3%提高到9%,室温奥氏体含量逐渐增多,抗拉强度及硬度逐渐降低,抗拉强度和室温奥氏体体积分数都在5%到7%时变化明显,马氏体与奥氏体的位向关系发生改变,马氏体形态类型逐渐由亚结构以位错为主的板条状α马氏体变化为亚结构以位错、相变内孪晶和层错为主的束状细片α马氏体和细片状ε马氏体.     

30SiMnCrB5热成形钢的微观组织和力学性能

为了提高热成形钢的综合性能,设计了一种C-Si-Mn-Cr-B系热成形钢,采用热膨胀仪测定并研究了30SiMnCrB5热成形钢的连续冷却转变曲线和相变规律.分析了经轧制、退火及热成形模拟后钢板的微观组织形貌和力学性能,结合等密度线极图的方法,判定了热成形模拟后钢板中马氏体变体与母相的取向关系.30SiMnCrB5热成形钢具有较好的淬透性,临界冷速为5℃·s^-1,有效抑制了珠光体和贝氏体的形成,完全马氏体组织的硬度可达600 HV以上.热成形模拟后的微观组织由板条马氏体和残余奥氏体构成,残余奥氏体主要以薄膜状分布在马氏体板条间,质量分数为6%~8%,抗拉强度为1800 Mpa左右,总伸长率可达10%以上,强度和塑性的匹配较好.热成形模拟后30SiMnCrB5热成形钢板中马氏体变体与母相的取向关系更接近N-W关系,12种变体没有都出现在原始奥氏体内.     

GaN 纳米结构的制备

提出一种通过对溅射Ga2O3薄膜后氮化技术制备GaN纳米结构的方法，已成功地制备出CaN纳米线、纳米棒和纳米带。该方法既不需要催化剂，也不需要模板限制，不仅避免了杂质污染，而且简化了纳米结构的制造工艺，对于纳米结构的应用非常有利。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和选区电子衍射(sAD)研究了CaN纳米结构的形貌和晶格结构。结果表明CaN纳米结构是具有六角纤锌矿结构的GaN晶体，不存在Ga2O3或Ga的其他相。研究结果证明在高温氮化过程中由于晶格缺陷的降低和晶化的改进能够得到高质量的GaN晶体。简要地讨论了GaN纳米结构的生长机制。     

An investigation of the effects of austenite strength and austenite stacking fault energy on the morphology of martensite in Fe-Ni-Cr-0.3C alloys

The relative effects of austenite stacking fault energy and austenite yield strength on martensite morphology have been investigated in a series of three Fe-Ni-Cr-C alloys. Carbon content (0.3 wt pct) andM ₆ temperature (− 15°) were held constant within the series. Austenite yield strength atM _s was measured by extrapolating elevated temperature tensile data. Austenite stacking fault energy was measured by the dislocation node technique. Martensite morphologies were characterized by transmission electron microscopy and electron diffraction techniques. A transition from plate to lath martensite occurred with decreasing austenite stacking fault energy. The austenite yield strength atM _s for the low SFE, lath-forming alloy was found to be higher than previously reported for lath-forming alloys. The relative effects of these variables on martensite morphologies in these alloys is discussed.     

V、Ta微合金化12Cr低活性F/M钢的优化设计

采用Thermo-Calc热力学模拟计算与实验相结合的方法,优化设计了一种V、Ta微合金化的低活性F/M钢12Cr3WVTa,经1 050℃水淬及780℃回火后对其显微组织及析出相进行光学显微镜、扫描电镜和透射电镜观察以及能谱分析.实验钢淬火回火后显微组织由回火马氏体和少量δ铁素体相组成,析出相主要为M₂₃C₆和MX相(M=V,Ta;X=C,N),其中M₂₃C₆主要分布于回火马氏体板条界和相界,而MX弥散析出于回火马氏体板条内以及δ铁素体内.实验钢室温和高温(600℃)拉伸力学性能良好,600℃下材料抗拉强度为507 MPa,屈服强度为402 MPa,满足超临界水冷堆用包壳管的拉伸性能要求.