Bulk and Surface Quenching of Structural Steel: Morphological Analysis of the Structure

Structures formed in medium-carbon low-alloy steels during bulk quenching from furnace heating and surface quenching initiated by a low-power high-current electron beam are investigated by the methods of diffraction electron microscopy. The influence of the carbon concentration, initial austenite grain size, and cooling rate on the morphology of martensitic crystals and self-tempered carbide particles, long-range stress fields inside a packet and plates, and their dislocation substructure is analyzed. The temperature intervals for the formation of high-temperature plate martensitic crystals and packet (lath) martensite are estimated. It is demonstrated that the structure formed at ultrahigh heating and cooling rates is determined mostly by the morphology of martensite in the initial steel samples.     

Mössbauer measurements backscattering technique (CXMS) of laser irradiated cold forming tool steel (X210CR12)

Conversion x-ray Mössbauer measurements (CXMS) in backscattering technique are performed on a commercial cold forming tool steel (X210Cr12), subjected to single-pass laser irradiation. The structure of the affected layer is examined for laser powers ranging from 2700 W to 3050 W at different depths. The results of the spectra analysis are discussed in connection with Vickers hardness and metallographic data. If a complete molten layer is quenched, a high carbon content austenite is retained down to room temperature. This phase is mixed with some low carbon martensite and (Cr 0.5 Fe 0.5)> C₃ carbide. The effects of carbon diffusion from the coating medium into the bulk are discussed. It is demonstrated that Mössbauer spectroscopy is a sensitive tool for phase analysis, including information about phase formation, and for delimiting the range of the quenched molten layer after laser treatment. It is thus a promising technique in this special kind of steel engineering.     

Study of the surface structure of tempered carbon steel

A CEMS and XMS study of carbon steel has shown that the microstructure of the bulk material as well as the surface depends on the temperature at which the steel was tempered. Ion milling of the surface results in no change to the surface microstructure which corresponds closely to the bulk properties. However, after polishing the surface with 3μm diamond, the surface composition is changed to a large extent. Polishing decreases the amount of retained austenite and also the fraction of interstitial carbon within the austenite on the surface of the non-tempered steel. A related increase in the amount of surface martensite is observed. The effects of polishing extends to depths of over 1000 Å. Both X- and θ-carbides are present in each of the tempered steels and only the amount of θ-carbide is seen to increase as the samples are tempered to decrease hardness. Tempering to higher temperatures decreases the martensite content and a corresponding increase is seen in the θ-carbide only. Polishing also removes a large feaction of the carbide from the surface and this may account for the anomalously high wear resistance previously determined for the steel.     

A new non-destructive method for estimating the remanent life of a turbine rotor steel by reversible magnetic permeability

We present a new magnetic and non-destructive procedure to evaluate the remanent life of 1Cr–1Mo–0.25V steel using the value of reversible magnetic permeability. The method is based on the existence of reversible magnetic permeability in the differential magnetization around the coercive force. The measurement principle is based on the foundation harmonics voltage induced in a coil using a lock-in amplifier tuned to a frequency of the exciting one. Results obtained for reversible magnetic permeability and Vickers hardness on the aged sample show that the peak interval of reversible magnetic permeability (PIRMP) and Vickers hardness decreases as aging time increases. A softening curve is obtained from the correlation between Vickers hardness and the PIRMP. This curve can be used as a non-destructive method to evaluate the remanent life of 1Cr–1Mo–0.25V steel.     

合金工具钢的X射线荧光光谱分析

本文介绍了用X射线荧光光谱仪测量合金工具钢中Mn,Cr,V,W,Ti,Nb,Co,Zr,Ni,Mo,S,P,Si和Cu十四个元素的方法,度样经砂轮抛光酒精棉擦拭后直接测量,结果与内控标样吻合,方法的精密度（n=8)除W,Tr,Nb和Zr外,大多数元素在0．13－9．59％,适应铬钒钢,锰钢,模具钢,中低合金钢等多种钢种的分析。     

Estimation of martensite feature size in a low-carbon alloy steel by microtexture analysis of boundaries

A methodology for classifying the hierarchy of martensite boundaries from the EBSD microtexture data of low-carbon steel is presented. Quaternion algebra has been used to calculate the ideal misorientation between product α variants for Kurdjumov–Sachs (KS) and its nearby orientation relationships, and arrive at the misorientation angle-axis set corresponding to packet (12 types), block (3 types) and sub-block boundaries. Analysis of proximity of experimental misorientation between data points from the theoretical misorientation set is found to be useful for identifying the different types of martensite boundaries. The optimal OR in the alloy system and the critical deviation threshold for identification of martensite boundaries could both be ascertained by invoking the ‘Enhancement Factor’ concept. The prior-γ grain boundaries, packet, block and sub-block boundaries could be identified reasonably well, and their average intercept lengths in a typical tempered martensite microstructure of 9Cr–1Mo–0.1C steel was estimated as 31 μm, 14 μm, 9 μm and 4 μm respectively.     

低活化马氏体钢热等静压焊接接头性能初步研究

研究了低活化马氏体钢(CLF-1)热等静压(HIP)焊接接头的性能,经980℃/1h/空冷+740℃/2h/空冷的性能热处理后,接头组织保持着CLF-1钢母材回火马氏体组织;常温拉伸性能与母材相当,断口为韧窝状且有第二相粒子产生,为塑性断裂且断于焊缝;常温冲击功最高为母材的26.2%。初步分析认为焊接表面制备状态、表面污染物、表面清洗状态、表面氧化膜都会影响基体原子充分扩散,导致界面扩散层不均匀,焊缝裂纹敏感性增强,冲击功低,且不稳定。     

Strength and wear resistance of nanocrystal structures on friction surfaces of steels with martensitic base

The formation of nanocrystal -martensite structures (NCS) in the surface layers of carbon and alloy steels under conditions of sliding friction and abrasion is investigated by electron microscopic, x-ray, and metallographic methods. The influence of the dynamic strain aging of martensite and strain dissolution of the carbide phase on the strength (microhardness and shear resistance) and tribological properties (wear resistance and friction coefficient) of nanocrystal surface layers of steels with martensitic base is demonstrated. The role of nanocrystal martensite in adhesive, abrasive, and fatigue wear resistance of steels is examined. The negative influence of the oxidizing air environment on the effective strength and wear resistance of friction NCS is demonstrated. The increased resistance of friction NCS of high-carbon steel to softening after tempering and friction heating is established.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 65–80, August, 2004.     

合金元素对钢中NbC异质形核影响的第一性原理研究

为了探索不同合金元素对Nb C异质形核的影响,本文利用第一性原理研究了合金元素X(X=Cr,Mn,Mo,W,Zr,V,Ti,Cu和Ni)对ferrite(100)/Nb C(100)界面性质的影响,并且分析了上述合金元素掺杂前后界面的黏附功、界面能和电子结构.研究结果表明,Cr,V和Ti掺杂的界面具有负的偏聚能,说明它们容易偏聚到ferrite/Nb C界面,但Mn,W,Mo,Zr,Cu和Ni却难以偏聚到此界面.当Mn,Zr,Cu和Ni取代界面处的Fe原子后,界面的黏附强度降低,即这些合金减弱铁素体在Nb C上的形核能力.然而Cr,W,Mo,V和Ti引入界面后,其黏附功比掺杂前的界面要大,且界面能均降低,即提高了界面的稳定性.因此,W,Mo,V和Ti,尤其是Cr,能够有效地促进铁素体形核和细化晶粒.电子结构分析表明,Zr和Cu引入界面后,界面处的Zr,Cu原子和C原子的相互作用变弱;然而Cr和W引入界面后,Cr,W和C原子之间形成了很强的非极性共价键,提高了ferrite/Nb C界面的结合强度.     

Mössbauer studies of a martensitic transformation and of cryogenic treatments of a D2 tool steel

A D2 tool steel X153CrVMo12 with composition C1.53 Cr12 V0.95 Mo0.80 Mn0.40(wt% Fe balanced) was studied by use of Mössbauer spectroscopy and X-ray diffraction. It was observed that the study of carbides by X-ray diffraction was difficult while Mössbauer spectroscopy gives some light on the process occurring during cryogenic treatment. With the increase of the martensitic phase the carbides decrease and are dissolved in solid solution of martensite as well as the chromium element.     

Atomic displacements in dilute alloys of Cr, Nb and Mo

Kanzaki lattice static method is used to calculate the atomic displacements due to substitutional impurities in 3d (Cr) and 4d (Nb, Mo) metals. Wills and Harrison interatomic potential is used to calculate dynamical matrix and the impurity-induced forces up to second nearest neighbors. The calculated atomic displacements for 3d, 4d and 5d impurities in Cr (V, Mn, Fe, Ni, Nb, Mo, Ta and W), Nb (V, Cr, Mn, Fe, Zr, Mo, Ta and W) and Mo (V, Cr, Mn, Fe, Zr, Nb, Ta and W) are tabulated up to 10 NN’s. The strain field due to 3d impurities is least in Cr metal while it is larger in Nb and Mo metals. For 4d and 5d impurities the strain is larger in Cr metal than in Nb and Mo hosts. Similar trend is found for relaxation energies also.     

Phase Transformations and Misorientations in Ferrite-Martensitic Steel upon Intense Plastic Deformation

Changes in the structural and phase state of low-carbon steel with a mixed structure of tempered martensite and ferrite, and deformed by equal channel angular pressing (ECAP), are analyzed by means of transmission electronic microscopy and X-ray diffraction. The impact ECAP has on the phase composition and morphology of the alloy is determined. The behavior of the carbide phase is studied. Grain misorientations are measured. Special attention is given to the problem of fine grain formation upon ECAP.     

Substructural and carbide transformations during plastic deformation in tempered chromium-nickel martensitic steel

The evolution of the defect and carbide subsystems has been studied during the plastic deformation of chromium nickel steel with the structure of tempered martensite. A correlation has been established between the substructural transformation and the change during plastic deformation. The nondislocation shear resistance has been estimated.Tomsk Civil Engineering Institute. Translated from Izvestlya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 25–32, December, 1992.     

Constitutive description of primary and steady-state creep deformation behaviour of tempered martensitic 9Cr–1Mo steel

The model based on the coupled sine hyperbolic creep rate relation with the evolution of internal stress as a function of strain provides better understanding of primary and secondary creep behaviour of tempered martensitic 9Cr–1Mo steel. The predicted evolution of internal stress as an increase in the internal stress value (or, decrease in effective stress) with strain/time appropriately described the observed decrease in creep rate during primary creep in the steel. The applicability of the model has been demonstrated by comparing experimental and predicted creep strain–time and creep rate–strain/time data of 9Cr–1Mo steel at 793 and 873 K for quenched and tempered and simulated post-weld heat treatment conditions. Irrespective of prior heat treatment and test temperature, the optimised parameters associated with the internal stress values exhibited linear variations with applied stress. The influence of prior heat treatment on primary and secondary creep characteristics of the steel is reflected on the rate constant values associated with the model. At all temperatures and heat treatment conditions, good agreement between the experimental and predicted steady-state creep rates demonstrate the further applicability of the model.     

X射线荧光光谱法测定不锈钢中的组分

用X射线荧光光谱法测定了不锈钢中Si、Mn、P、Cu、Ti、W、Mo、V、Ni、Cr、Nb等11种元素的含量。对磨样条件、准确度和精密度进行了实验,实验表明本方法与化学法所测结果相符。     

几种合金钢在高压下的状态方程

 本工作测定了合金钢45CrNiMoV、GCr15和W18Cr4V在室温下、4.5 GPa内的p-V关系，并给出了它们的Bridgman方程、格临爱森参数γ₀、体积模量B₀及B₀的压力导数B₀'。     

Kinetics of isochronal austenization in modified high Cr ferritic heat-resistant steel

Employment of high Cr ferritic steels as a main structural material is considered as a way to achieve economical competitiveness of main steam pipe and nuclear reactors in power plants. Differential dilatometry and microstructure observation were employed to investigate the isochronal austenitic transformation of the modified high Cr ferritic steel. The kinetics of the isochronal austenitic transformation were described by a phase-transformation model involving site saturation (pre-existing nuclei), diffusion-controlled growth, and incorporating an impingement correction. The experimental results and kinetic analysis indicate that an increase of the heating rate promotes the diffusion-controlled austenitic transformation. The dissolving degree of precipitates during the austenization process affects the activation energy for diffusion and the undissolved precipitates lead to an increase of the onset temperature of the subsequent martensite transformation upon cooling.     

Effect of cooling rate on microstructural formation and hardness of 30CrNi3Mo steel

The variation of microstructural formation and the hardness of the 30CrNi3Mo steel were systematically explored as a function of applied cooling rates in the range of 1–500°C/min. According to the measured Rockwell hardness results, four characteristic stages could be separated as different ranges of cooling rates, which corresponds well with the microstructural evolution observed. With the applied cooling rate increasing, the transformed structure evolves from granular bainite, lower bainite, self-tempered martensite, to finally martensite without self-tempering. Among them, the self-tempered martensite, obtained in the transformed specimens cooled with rates of 25–80°C/min, exhibits the highest hardness values due to the precipitation of fine carbides within it.     

Effect of magnetic field on the carbide precipitation during tempering of a molybdenum-containing steel

The influence of a high magnetic field on the carbide precipitation during the tempering of an Fe-2.8C-3.0Mo(wt%) steel was investigated. As-quenched steels were tempered at 200 °C for various times with and without the presence of 12-T magnetic field. The applied field effectively promoted the precipitation of the relatively high-temperature monoclinic χ-Fe₅C₂ carbide, compared to the usual ε-Fe₂C and η-Fe₂C carbides precipitated without magnetic field. It is believed that the effect of applying a magnetic field is due to the reduction in the Gibbs free energy of the relatively higher magnetization phase. The denser distributions of the metastable carbides are attributed to the increased nucleation rate due to additional transformation force. The dispersed precipitation strengthening compensated for the decrease of hardness due to the loss of supersaturation of carbon atoms in the matrix.     

30CrMnSiNi2A晶格参量的测量及回复规律研究

针对X射线衍射领域中晶面衍射峰重叠问题,提出一种新的重叠峰分离方法.采用RU-200V转靶衍射仪对30CrMnSiNi2A晶格参量及其回复规律进行研究,得出不同回火温度下晶格参量与碳含量的变化关系.研究结果发现:由于碳的过饱和度不同以及合金元素的影响,30CrMnSiNi2A与高碳马氏体晶格参量的变化规律虽基本符合,但其变化速率存在差异.在不同回火温度下晶格参量a基本与碳含量无关,随着回火温度升高,a值略有下降.晶格参量c则随碳含量的变化幅度较大,从淬火态到180℃回火态出现一个陡降过程,随着回火温度升高,其变化幅度又趋于平缓.