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.     

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.     

The martensitic transformation in steel

Metal Science and Heat Treatment -     

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.     

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.     

Neodymium-rich precipitate phases in a high-chromium ferritic/martensitic steel

Neodymium being considered as nitride forming element has been used in a design of advanced ferritic/martensitic (FM) steels for fossil fired power plants at service temperatures of 630 °C to 650 °C to effectively improve the creep strength of the steels. To fully understand the characteristics of neodymium precipitates in high-Cr FM steels, precipitate phases in an 11Cr FM steel with 0.03 wt% addition of Nd have been investigated by transmission electron microscopy. Three neodymium phases with a face-centered cubic crystal structure and different composition were observed in the steel. They consisted of neodymium carbonitride with an average lattice parameter of 1.0836 nm, Nd-rich carbonitride mainly containing Mn, and Nd-rich MN nitride mainly containing Mn and Co. Other three Nd-rich and Nd-containing phases, which appear to be Nd-Co-Cr/Nd-rich intermetallic compounds and Cr-Fe-rich nitride containing Nd, were also detected in the steel. Nd-relevant precipitates were found to be minor phases compared with M₂₃C₆ and Nb/V/Ta-rich MX phases in the steel. The content of Nd in other precipitate phases was very low. Most of added Nd is considered to be present as solid solution in the matrix of the steel.     

Study on the precipitation of M2C in high Co-Ni alloy steel

High CoNi ultrastrength alloy steel is a typical tempered martensite steel in which the secondary hardening is accomplished by the precipitation of fine-scale alloy carbides with a black-white contrast in a bright-field image until peak hardening. The crystal structure of precipitates is well determined as hexagonal M₂C by microbeam diffraction. From their lattice image in a high-resolution transmission electron microscope, M₂C carbides are shown to be completely coherent with the ferrite matrix completely and to have their own structure.     

Highly efficient TIG welding of Cr13Ni5Mo martensitic stainless steel

A double-shielded TIG welding process using pure He gas as the inner shielding layer and He and CO₂ mixed gas as the outer shielding layer was proposed for the welding of Cr13Ni5Mo martensitic stainless steels. This proposed welding process can successfully address the problem of electrode oxidation with mixed-gas TIG welding and the issue of low weld depth and welding efficiency of traditional TIG welding. A change in the direction of the surface tension convection mode was the primary mechanism that affected the fusion zone profile. When the oxygen content in the weld pool was in the range of 80–120 ppm, the surface tension convection direction changed from outward to inward, resulting in both a larger weld depth and a larger weld depth/width ratio. This process not only allows for a high welding efficiency comparing with traditional TIG welding but also produces better weld impact properties than those of MAG welding (metal active gas welding).