M2高速钢中M2C共晶碳化物的相变行为

利用扫描电镜及能谱分析研究了不同加热温度和保温时间对M2高速钢中M2C共晶碳化物分解行为的影响.结果表明,M2C共晶碳化物的分解程度随加热温度的升高和保温时间的延长而增加,但温度起主要作用.讨论了M2C共晶碳化物的分解过程,得出其分解特点:M2C共晶碳化物的分解受原子的扩散行为控制;通过原子扩散,在原始M2C共晶碳化物的外层形成M6C碳化物,内层形成MC碳化物.     

含复合(Ti,Mo)C析出相的马氏体钢的氢捕获与解吸附

采用热脱氢分析装置 (TDS) 研究了含复合 (Ti,Mo)C析出相的马氏体钢的氢的捕获与解吸附行为。结果表明,36-60 nm的未溶球形(Ti,Mo)复合析出相在室温电化学充氢过程中不能捕获氢,而回火析出的1-5 nm的复合 (Ti,Mo)C析出相是有效的氢陷阱,尽管其氢陷阱激活能相对较低,为16.4-22.1 kJ/mol,与晶界、位错处的氢陷阱激活能相近,同时远低于纯的共格TiC析出相的氢陷阱激活能,但在大气中放置时,被回火析出的1-5 nm的复合 (Ti,Mo)C析出相捕获的氢无法解吸。     

M2高速钢工业铸带中共晶碳化物及其演化

在工业机组上制备了M2高速钢铸带,采用扫描电镜和透射电镜研究了热处理和热轧对铸带中的共晶碳化物特征的影响.结果表明:双辊薄带连铸工艺可以获得共晶碳化物尺寸细小、分布均匀的高速钢铸带,铸带中存在较多的M2C亚稳相碳化物;热处理后M2C碳化物分解生成M6C和MC碳化物,碳化物得到进一步细化;由M2工业铸带直接热轧而成的薄带中仍存在一些呈断续网状分布的碳化物,先进行合适的热处理再进行热轧对M2工业铸带更为合适.     

Using friction welding for producing heat exchanger equipment from martensitic 15Kh5M steel

The results of mechanical and other types of tests of metal of welded joints in pipe blanks of 15Kh5M martensitic steel, produced by friction welding with rotation, are presented. On the basis of the analysis of the test results it is concluded that 15Kh5M can be efficiently welded by friction welding and that the method can also be used for producing the tube–tube plate sections of heat exchangers made of 15Kh5M steel with appropriate modernization of welding equipment.     

Novel ultrafine Fe(C) precipitates strengthen transformation-induced-plasticity steel

A transmission electron microscopy study was conducted on nanoprecipitates formed in Ti microalloyed transformation-induced-plasticity-assisted steels, revealing the presence of Ti(N), Ti₂CS and a novel type of ultra-fine Fe(C) precipitate. The matrix/precipitate orientation relationships, sizes and shapes were investigated in detail. The ultrafine, disc-shaped Fe(C) precipitates have sizes of 2–5 nm and possess a hexagonal close packed crystal structure with lattice parameters a = 5.73 ± 0.05 Å, c = 12.06 ± 0.05 Å. They are in a well-defined Pitsch–Schrader orientation relationship with the basal plane of the precipitate parallel to the [1 1 0] habit plane of the surrounding body-centred-cubic ferritic matrix. Detailed analysis of precipitate distribution, orientation relationship, lattice mismatch and inter-particle spacing suggests that these ultrafine precipitates contribute considerably to the strengthening of these steels.     

固溶温度对Cr-Co-Mo马氏体钢碳化物演变及力学性能的影响

利用SEM和TEM研究了固溶温度对Cr-Co-Mo马氏体钢碳化物演变行为及力学性能的影响。结果表明,随着固溶温度的升高,基体中M₆C碳化物回溶,屈服强度下降而室温冲击吸收能量递增;原始奥氏体晶粒由于缺乏晶界上球形M₆C碳化物的钉扎作用迅速长大,细晶强化效果减弱,但晶界处裂纹源减少使得韧性提高。在1120 ℃固溶后晶粒尺寸最大,而马氏体基内析出与基体共格的纳米棒状M₂C碳化物平均粒径最小、单位面积百分数最高和颗粒间距最短,因此即使损失了细晶强化效果,但析出强化增补了强度,使得屈服强度在晶粒长大后不发生大幅下降;同时,由于共格析出提高了基体的变形协调性,韧性也未发生降低。     

The martensitic transformation in steel

Metal Science and Heat Treatment -     

Effect of γ2-phase precipitates on the martensitic transformation of a β-CuAlBe shape memory alloy

The influence of γ₂ precipitates on the MT of a Cu–22.66Al–2.98Be (at%) polycrystalline alloy was analysed by compression test, differential scanning calorimetry and microscopy. As the precipitate content (or size) increases, the stress-induced martensitic transformation occurs at higher stress levels. The thermally induced martensitic transformation is only significantly affected when the γ₂ phase content exceeds 14%, the thermal peaks are shifted to higher temperatures and less β phase transforms to martensite. TEM observations suggest good coherency between both phases, and dislocation bundles remain in the β side of the γ₂/β interface after the compression-induced transformation to martensite. The evolution of σ_s with fvγ₂ is analysed considering a chemical and a mechanical contribution.     

双相不锈钢表层沉淀相的晶体学特征

双相不锈钢00Cr25Ni7Mo3表层析出的奥氏体相具有可重复的多种形貌和晶体学特征,与块体材料内部的沉淀现象有显著差异.为探索非均匀约束条件下的相变晶体学规律,应用电子背散射衍射(EBSD)技术对表层沉淀相中主要的针状奥氏体的晶体学特征进行统计表征.统计结果表明,沉淀相倾向于沿表面生长.以在预抛光表面作为不变线方向的约束条件,计算了所有可能出现的不变线.对比实验观察发现,多数表层沉淀相的长轴方向趋向表面内的某一不变线.各不变线之间的晶体学非等价性是表层针状沉淀相取向多样性的成因.     

Evaluation of microstructure and creep damage in high-Cr ferritic steel welds

11Cr-0.4Mo-2W-CuVNb steel (ASME Gr.122) is used for boiler components in ultra-supercritical (USC) thermal power plants.The creep strength of high-Cr steel welds decreases due to the formation of Type IV creep damage in the heat-affected zone (HAZ) during long-term use at high temperatures.In the present study,the processes and mechanisms of Type IV creep damage were elucidated by investigating the long-term creep strength,microstructure and damage behavior of Gr.122 steel welds.Creep tests using thick weld...     

Nitriding of low-carbon martensitic steel 12Kh2G2NMFT

The structure and properties of low-carbon martensitic steel 12Kh2G2NMFT after nitriding and subsequent heat treatment from the intercritical temperature range, which yields high mechanical properties of the core and wear resistance of the surface layer, are studied. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 27–31, March, 2006.     

Sulfonitrocarburizing of low-carbon martensitic steel 12Kh2G2NMFT

The structure and properties of surface layers on low-carbon martensitic steel 12Kh2G2NMFT after low-temperature sulfonitrocarburizing in ecologically safe salt solutions based on sodium cyanate are studied. The phase composition and the distribution of elements and of the hardness over the thickness of diffusion layers are determined. The effect of the sizes of characteristic structural components on the morphology of the carbonitride phase of the diffusion layer and on the activation energy is investigated. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 48–52, May, 2007.     

Through-the-thickness residual stress analysis by neutron diffraction in inoxidizable martensitic steel samples with and without tungsten carbide coating

The residual stress (RS) induced in the substrate by thermal spray-coating plays a significant role in the behaviour of coated materials. The characterisation of High-Velocity Oxy-Fuel (HVOF) coatings through RS determination justifies various cases of failure or bad performance due to the delamination of coating which is not easily interpretable through more traditional microstructural analyses and mechanical tests.Two 13Cr4Ni inoxidizable martensitic steel samples, one having a thermal spray (WC–12% Co) HVOF coated surface, the other a shoot peened surface, were analyzed by neutron diffraction (ND) in order to determine the real RS depth-profile and investigate the effects of the thermal process on the considered materials.The stresses resulted in the range from − 80 to 50 MPa for the uncoated sample, while for the coated sample they increased gradually from a slight compressive status in correspondence of the uncoated surface, to greatest values of ~ 250 MPa in correspondence of the coating. A traditional X-ray investigation on the coated surface measured compressive RS values σ = − 550 ± 40 MPa, showing that ND investigation is very suitable for critical applications, where a much greater stress situation could be present at a diverse depth.The results achieved yielded trends that can be used in monitoring of the coating characteristics, in particular adhesion, thereby confirming the relevance of thermal stresses induced by HVOF coating processes.     

Characterization of M23C6 carbide precipitated at grain boundaries in a superalloy

Transmission electron microscopy studies were undertaken to characterize the formation, the imperfection, and the interfacial structure of grain boundary M₂₃C₆ carbide in a Ni-base superalloy. The carbides are nucleated separately on both sides of the grain boundary. Each carbide particle possesses a coherent boundary on its matrix side and a high-angle boundary on the other side. The particle is composed of several subgrains, and antiphase boundaries are observed between the subgrain. Lattice defects, such as dislocations, stacking faults, and microtwins, are revealed in the M₂₃C₆ carbides.     

5Cr15MoV马氏体不锈钢热加工过程碳化物析出

采用热模拟试验机对5Cr15MoV马氏体不锈钢热加工过程进行了模拟,并使用金相显微镜及物理化学相分析方法对热加工过程中的碳化物析出进行了分析。结果表明：与thermo-Calc热力学计算结果不同,热加工过程中在1100~1150 ℃之间,5Cr15MoV钢主要析出MC型碳化物,且随温度的降低,析出量逐渐加大,在1000~1100 ℃之间趋于平衡,而M23C6型碳化物则在1000 ℃左右析出,整个热加工过程中,并未发现M7C3型碳化物析出。