Pulsed laser induced deformation in an Fe-3 Wt Pct Si alloy

The plastic deformation produced by laser induced stress waves was investigated on an Fe-3 wt pct Si alloy. The intensity and duration of the stress waves were varied by changing the intensity and pulse length of the high energy pulsed laser beam, and also by using different overlays on the surfaces of the specimens. The resulting differences in the distribution and intensity of the deformation caused by the stress waves within the samples were determined by sectioning the specimens and etching (etch pitting) the transverse sections. The magnitude of the laser shock induced deformation depended on the laser beam power density and the type of surface overlay. A combination transparent plus opaque overlay of fused quartz and lead generated the most plastic deformation. For both the quartz and the quartz plus lead overlays, intermediate laser power densities of about 5×10⁸ w/cm² caused the most deformation. The shock induced deformation became more uniform as the thickness of the material decreased, and uniform shock hardening, corresponding to about 1 pct tensile strain, was observed in the thinnest specimens (0.02 cm thick). 200 ns laser pulses caused some surface melting, which was not observed for 30 ns pulses, the pulse length used in most of the experiments. Deformation of the Fe-3 wt pct Si alloy occurred by both slip and twinning. B. A. WILCOX, formerly affiliated with Battelle, Columbus Laboratories     

The influence of subgrain boundaries on the rate controlling creep processes in Fe-3 Pct Si

Metallurgical and Materials Transactions A - The influence of subgrain boundaries on the kinetics of high temperature creep is studied by comparing the creep properties of textured Fe-3 pct Si with...     

The effect of hydrogen gas on the plasticity/cleavage balance in Fe-3.5 Pct Si

Notched specimens of grain-oriented iron-3.5 pct silicon were strained in air and in hydrogen gas at different displacement rates. The presence of hydrogen was found to induce cleavage fracture, mainly on the cube face planes, whereas fracture in air under the same conditions was ductile. A notable feature of the results is that some cleavage fracture, apparently occurring on the (1–10) plane, was seen in specimens strained at right angles to the rolling direction. The presence of hydrogen was found to induce cleavage most easily at the fast and intermediate displacement rates; at the slowest strain rate the specimens were much more ductile. It is believed that the dynamic component of the flow stress must be maintained above a critical level to allow the hydrogen to alter the balance between cleavage fracture and ductile plastic flow in favor of cleavage. Formerly with the University of Newcastle upon Tyne     

Microstructure and Magnetic Properties of 6.5 Wt Pct Si Steel Strip Produced by Simulated Strip Casting Process

Metallurgical and Materials Transactions A - An improved dip test apparatus was used to simulate the strip casting of 6.5 wt pct Si steel in this study. The results showed that the...     

Revisiting Temperature and Magnetic Effects on the Fe-30 Wt Pct Ni Martensite Transformation Curve

This work revisits the relationship between the volume fraction of martensite and the transformed microstructure. This relationship is analyzed by considering that although thermodynamic principles determine the possibility of transformation, the size and arrangement of the martensite units over the austenite grains is determined by the local surroundings. The proposed equation for the transformation curve incorporates the probabilistic aspect of the initial transformation in a limited number of scattered austenite grains and autocatalysis. The validation of the model, already verified with data typical of FeC steels, FeNiC and FeNiMn alloys, is extended in this study to a transformation that exhibits microstructure diversity. Finally, we show that the model fits the transformation curves typical of “18Cr-8Ni” stainless steel; this finding demonstrates that the model is applicable to transformation curves characteristic of other systems due to a conceptualization based on the intrinsic aspects of martensite transformation in steels.     

Formation mechanism of bainitic ferrite in an Fe-2 Pct Si-0.6 Pct C alloy

The bainite transformation at 723 K in an Fe-2 pct Si-0.6 pct C alloy (mass pct) was investigated with transmission electron microscopy (TEM) and quantitative metallography to clarify the growth mechanism of the ferritic component of bainite. In early stages of transformation, the bainitic ferrite was carbide free. The laths of bainitic ferrite within a packet were parallel to one another and separated by carbon-enriched retained austenite. The average carbon concentration of the bainitic ferrite was estimated to be 0.19 mass pct at the lowest, indicating that the ferrite was highly supersaturated with respect to carbon. The laths did not thicken during the subsequent isothermal holding, although they were in contact with austenite of which the average carbon concentration was lower than the paraequilibrium value. In the later stage of transformation, large carbide plates formed in the austenite between the laths, resulting in the decrease in the carbon concentration of the austenite. Subsequently, the ferrite with a variant different from the initially formed ferrite in the packet was decomposed for the completion of transformation. The present results indicate that the bainitic ferrite develops by a displacive mechanism rather than a diffusional mechanism. Formerly Graduate Student, Kyoto University, Kyoto 606-01, Japan This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation of Plate-Shaped Transformation Products,” held December 18-22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S Phase Transformations Committee.     

Effects of shock loading and cold rolling on the structure and high temperature creep properties of Fe-3.75 Pct Si

The effects of shock loading and cold rolling on the dislocation substructure and high temperature creep properties of Fe-3.75 pct Si at 923 K and 7000 psi (4.82×10⁷ Pa) have been investigated. We find the primary creep transients of this alloy to be “normal” ( \((d\dot \varepsilon /dt< 0)\) for the annealed contidtion and to change with increasing prestrain by rolling, becoming “inverted” ({ie1615-2}) for prestrains greater than about 11 pct. It is shown that both shock loading to about 70 kilobars (7×10⁹ Pa) and cold rolling 25 pct produce a fine subgrain size and an inverted creep transient with a minimum creep rate about one third of the steady state creep rate. During the inverted creep transient both the free dislocation density and the subgrain size increase and approach the steady state values. These structural changes are opposite to those observed for normal creep transients. Also it is found that the strengthening effect of shock loading is less stable than that produced by cold rolling. It is suggested that this difference is due to the greater instability of the shocked substructure as compared to the cold rolled substructure. Some effects of partial recrystallization are also discussed.     

The microstructure of discontinuously precipitated lamellae in an austenitic Fe-42.4 Wt Pct Ni- 4.15 Wt Pct AI-0.45 Wt Pct C alloy

Phase decomposition of austenitic Fe-42.4 wt pct Ni-4.15 wt pct Al-0.45 wt pct C on aging at 823 K was investigated by means of electron microscopy, selected area diffraction and microdiffraction, and microprobe chemical analysis. During annealing, κ phase of L′l₂ structure fully coherent with the matrix formedvia the nucleation and growth mechanism. The matrix phase and cubic κ carbide were later gradually encroached upon by discontinuously precipitated lamellar phases. The duplex fine lamellae are composed of alternately arranged carbon-depleted Ll₂ phase and cementite. Between the two constituents in the lamellae, the Pitsch orientation relationship is fulfilled, and at the same time, the matrix phase of the grain which the discontinuously precipitated lamellar colony has left behind maintains the crystallographic cube-to-cube correspondence with the product Ll₂ phase.     

Reaction sintering of an Fe-6 Wt Pct B-48 Wt Pct Mo alloy in the presence of liquid phases

The mechanism of liquid phase sintering of an Fe-6 wt pct B-48 wt pct Mo alloy was investigated by means of thermal dilatometry, differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). A fine composite microstructure of Mo₂FeB₂ and ferrite was produced from powders of Fe, Mo, and FeB by a reaction sintering process involving two liquid phases. The hard phase Mo₂FeB₂ is produced in the compact prior to liquid formation initially by the reaction 2Mo+2FeB=Mo₂FeB₂+Fe and later by the reaction 2Mo+2Fe₂B=Mo₂FeB₂+ 3Fe. Above 1365K, considerable densification results from the initial stage rearrangement of the solid phases (austenite and Mo₂FeB₂) coexisting with the first formed liquid phase (L₁). Another liquid (L₂) which forms above 1415K, where Mo₂FeB₂ is the only coexisting solid phase, is required for complete densification. L₂, having a high solubility for Mo₂FeB₂, provides for solution/reprecipitation processes which characterize the intermediate stage of liquid phase sintering. The effective separation of the initial and intermediate stages by L₁ and L₂ is considered essential for the control of the sintered microstructure of the ternary alloy. Teiichi Ando, formerly with the Technical Research Laboratory, Toyo Kohan Co., Ltd., is with the Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139.     

定向凝固Fe-6.5%Si合金显微组织的EBSD分析

采用定向凝固方法制备了Fe-6.5%Si实验合金板,并进行了金相观察、X射线衍射分析,EBSD分析和磁性测定。结果表明,合金板由沿定向凝固方向（100）生长的粗大柱状晶所组成,柱状晶的平均截面直径约为3mm,柱状晶之间绝大部分为大角晶界,其余为少量小角晶界和重位点阵晶界。合金板具有强的立主织构并显示出优良的磁性能,其矫顽力只有3．45A／m,小于其他方法制备的Fe-6.5%Si合金。     

The Tensile Properties of an Fe-4 Pct Mo-0.2 Pct C Martensite Tempered under Applied Stress

In Fe-4 pct Mo-0.2 pct C martensite which is a typical secondary hardening steel, premature failure occurred in tensile test at 600 °C to 700 °C where solute atoms could diffuse easily. To clarify this phenomenon, the quenched specimens were tempered under applied stress and tensile-tested at room temperature. The following results were obtained: (1) Typical intergranular fracture was observed in specimens tempered in a temperature range of 600 °C to 650 °C with tempering times of five minutes to 10 minutes and applied stress (70 MPa to 140 MPa). (2) Based on Auger analysis, this phenomenon was considered to be caused by segregation of P, S, and Mo on prior austenite grain boundaries due to applied stress. (3) The direction of applied stress was found to be very significant. Namely, when the tensile direction was parallel to the applied stress during tempering, the specimen was more brittle, and when tensile direction was normal to the applied stress, the specimen was not so brittle. (4) To reduce this embrittlement, solution treatment temperature was adjusted, and it was found that the embrittlement was considerably reduced both in specimens with fine prior austenite grains and with some ferrite phase on prior austenite grain boundaries. Formerly with Kyoto University Formerly with Kyoto University This paper is based on a presentation made at the “Peter G. Winchell Symposium on Tempering of Steel” held at the Louisville Meeting of The Metallurgical Society of AIME, October 12-13, 1981, under the sponsorship of the TMS-AIME Ferrous Metallurgy and Heat Treatment Committees.     

A study of the early stages of tempering in an Fe-1.2 Pct alloy

Mössbauer effect spectroscopy has been used to study changes in the microstructure of an Fe-1.22. wt pct C alloy due to tempering between 373 and 523 K. The orthorhombic transition carbide, η-Fe₂C, was identified by transmission electron microscopy and the similarity of ∈-carbide electron diffraction patterns to η-carbide diffraction patterns is noted. Systematic changes in the Mosbauer parameters of martensite and austenite are presented for the various stages of tempering. The same amount of C remains randomly dissolved in the retained austenite throughout tempering and some C is retained in the martensite throughout the range of transition carbide formation. Two sets of Mössbauer parameters corresponding to magnetic phases other than martensite and cementite have been found. These parameters may come from η-carbide, but alternative interpretations are presented.