Deformation of pearlite

Pearlite with its lamellae oriented mainly parallel to the longitudinal direction was prepared by Bolling's method of transformation in a steep temperature gradient. The Fe-0.7 pct Mn-0.9 pct C pearlite was drawn into wire and also into strip in dies designed to minimize macroscopically nonuniform deformation. Cross sections of the drawn wires and strip were examined by conventional and high-voltage transmission electron microscopy and were analyzed by quantitative metallography for a) average interlamellar spacing, b) distribution of interlamellar spacings, and c) orientation relationship between the cementite lamellae and the slip systems in the ferrite. The strength of pearlite is proportional to the reciprocal square root of the average interlamellar spacing, and the proportionality constant analogous to the Hall-Petch constant (k) is related to the strength of the cementite lamellae. If the stress for the propagation of slip through the cementite is assumed constant, a Hall-Petch type of equation can be derived for the strengthening of the pearlite against slip in the ferrite by piled-up groups of dislocations. Evidence for the plastic deformability of cementite is presented; sufficiently thin cementite plates were fully plastic. The exponential strain hardening of drawn pearlitic wires and of rolled pearlite is explained in terms of locally inhomogenous deformation revealed by the lack of fragmentation of the lamellae. This paper is based on a presentation made at a symposium on “Mechanical-Thermal Processing and Dislocation Substructure Strengthening,” held at the Annual Meeting in Las Vegas, Nevada, on February 23, 1976, under the sponsorship of the TMS/IMD Heat Treating Committee.     

Kinetics of pearlite spheroidizations

A study of the kinetics of pearlite spheroidization under static annealing conditions was carried out in two materials — AISI 1080 steel and pure Fe-C alloy. A stereological “shape factor”,F, defined asF =S _v ^p/3• K_m, was introduced for the kinetic study. The significance of this shape factor in relation to the geometrical characters of lamellar structures is discussed. For constant temperature a linear relation betweenF and the logarithm of time was obtained. Analysis of the time and temperature dependencies for a constant shape factor gave an activation energy of 70 kcal/mole for AISI 1080 steel and 58 kcal/mole for Fe-C alloy which indicates that volume diffusion of Fe in ferrite is the rate-controlling mechanism. The modified fault migration theory, which was developed from the mechanism study of this research, was applied to predict the kinetics of the pearlite spheroidization. For both the AISI 1080 and the Fe-C alloy experimental results have a good match with the theoretical prediction.     

Hot deformation-enhanced globularization of pearlite

A plain high-carbon steel (0.74% C) was used to study the globularization (spheroidization and coalescence) of pearlite. In order to induce and/or enhance this process, specimens were deformed in the temperature range of austenite-to-pearlite transformation. It was found that only hot deformation applied after the completion of pearlite transformation leads to spheroidization of pearlite. The rate of this process is accelerated by a factor of 10⁴ compared with annealing without deformation. The kinetics of pearlite spheroidization are dependent on the pearlite lamellae thickness as well as pearlite orientation with respect to the direction of deformation. The final microstructure is, compared with that after a conventional soft annealing, considerably finer, the strength properties thus being largely retained.     

形变对共析钢连续冷却过程中珠光体相变的影响

摘要：为掌握形变对共析钢连续冷却过程中珠光体相变的影响,研究了共析钢在720～920℃温度范围内进行形变后,在连续冷却过程中奥氏体向珠光体相变的规律,建立了相变时的过冷度和珠光体片层间距的相互关系,并预测了试验钢的力学性能。结果表明：形变储存能促进共析钢在50℃/s高冷速下发生珠光体相变,形成片层间距为129～187 nm的超细片层珠光体,抗拉强度达到近1000MPa,且随着形变温度提高,形变储存能减小,珠光体相变温度降低,珠光体片层间距减小,屈服强度和抗拉强度提高。     

Fracture of steels containing pearlite

The relative effects of pearlite and spherodite on ductile, cleavage, and fatigue failure are summarized. Neither the cleavage strength nor the fatigue endurance limit appear to depend directly on cementite contentper se. Spherodized steels cleave less readily than ferrite/pearlite steels. Ductile fracture resistance is lowered considerably by both types of cementite, pearlite being more deleterious. Ferrite/pearlite steels appear to exhibit slower fatigue crack growth rates at low stress intensity levels than high strength steels. At high stress intensity levels the behavior is reversed. Slip-incuded cracking of carbide lamellae appears easier than that of spherodized carbides. In ductile fracture situations the crack spreads progressively through a pearlite colony via preferential cracking of carbides and rupture of the intervening ferrite accompanied by large local shear strains. Fatigue fracture proceeds with formation of frequent branches, preferentially along the pearlite colony interface. This paper is based on a presentation made at a symposium on “The Cellular and the Pearlite Reactions,” held at the Detroit Meeting of The Metallurgical Society of AIME, October 20, 1971, under the sponsorship of the IMD Heat Treatment Committee.     

宽带材拉伸弯曲变形的理论模型

应用板弯曲理论,引入平面变形假设和横截面始终保持为平面假设,采用米塞斯屈服准则,建立了各向同性理想弹塑性金属带材的拉伸弯曲变形的一般解析分析方法和模型.它突破了基于初等梁弯曲理论建立的解析分析方法的局限性,得到了在过去同类研究中无法计算的带材厚度方向的应力和应变,实现了对带材拉伸弯曲变形过程更贴切的表征.通过以某冷轧带钢厂拉伸弯曲矫直机为算例的比较计算表明,本文所提出的带材拉伸弯曲变形的\     

Precipitation of VC in ferrite and pearlite during direct transformation of a medium carbon microalloyed steel

Transmission electron microscopy of an air-cooled medium carbon (0.5 wt pct) steel containing 0.1 wt pct vanadium has shown that VC precipitates by the interphase mecha-nism during transformation to both proeutectoid and pearlitic ferrite. Depending upon the rate of transformation, a considerable proportion of the available vanadium may remain in supersaturated solid solution and can be precipitated as VC upon subsequent aging at 700°C. It was found that the proportion of proeutectoid ferrite, the interlamellae pearlite spac-ings and the VC precipitate dispersion parameters all decreased with increasing cooling rate in as-transformed material. G. FRIMODIG were formerly undergraduate students     

Thermomechanical treatments of a 1050 pearlite steel

A study of the microstructures and mechanical properties of thermomechanically treated 1050 steel has been carried out. The materials were first transformed to fine and coarse lamellar pearlite structures. These samples were reduced 75 pct in thickness by cold rolling, then heat treated at 780 °C (up-quenching) or 650 °C (annealing) for different periods of time, followed by air-cooling. The mechanical properties were found to be vastly improved by suitable thermomechanical treatments. A significant improvement in yield strength was accompanied by moderate increase in ultimate tensile strength, and the elongations were maintained above 15 pct in 3 cm gage length. The optimal mechanical properties were developed between 30 and 120 seconds during 780 °C up-quenching for coarse pearlite samples and 100 to 400 seconds for both annealed coarse and fine pearlite specimens. In these instances the relatively long duration of heat treatment time shall facilitate the industrial processing of the steel. The improvement in mechanical properties was correlated with distinct microstructures in pearlite regions, which were fine subgrains (or grains) less than 1 μm in size and dispersed globular carbide particles along the subgrain (or grain) boundaries. Formerly with the Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan.     

The effect of alloying elements on pearlite growth

The model developed by Sharma 1 and Sharmaet al. 2 for the mechanism of pearlite growth in ternary Fe-C-Cr alloys has been extended to other systems. Detailed thermodynamic and semi-empirical kinetic calculations have been carried out to determine pearlite growth rates for a number of Fe-C-X alloys (X = Mn, Cr, Ni, Si) and compared with the experimental data from the literature. It has been shown that the pearlite growth is, in general, controlled by the alloying element boundary diffusion at low supersaturations and carbon volume diffusion at high supersaturations, as predicted by the model. The transition temperature between the two mechanisms is a function of the amount and type of alloying element. Formerly a at the Department of Metallurgical Engineering, Indian Institute of Technology, Kanpur, India     

Behavior of pure gallium in water and various saline solutions

This study investigated the chemical stability of pure gallium in water and saline solutions in order to obtain fundamental knowledge about the corrosion mechanism of gallium-based alloys. A pure gallium plate (99.999%) was suspended in 50 mL of deionized water, 0.01%, 0.1% or 1% NaCl solution at 24 +/- 2 degrees C for 1, 7, or 28 days. The amounts of gallium released into the solutions were determined by atomic absorption spectrophotometry. The surfaces of the specimens were examined after immersion by x-ray diffractometry (XRD) and x-ray photoelectron spectroscopy (XPS). In the solutions containing 0.1% or more NaCl, the release of gallium ions into the solution was lowered when compared to deionized water after 28-day immersion. Gallium oxide monohydroxide was found by XRD on the specimens immersed in deionized water after 28-day immersion. XPS indicated the formation of gallium oxide/hydroxide on the specimens immersed in water or 0.01% NaCl solution. The chemical stability of pure solid gallium was strongly affected by the presence of Cl- ions in the aqueous solution.     

The effect of morphology on the strength of pearlite

The effects of various morphological features on the strength of high-purity pearlite were studied. A continuous-cooling mode of transformation from different austenitizing temperatures was used to produce variations in average nodule diameter and minimum interlamellar spacing. It was found that, for a constant transformation temperature, nodule size was directly related to prior austenite grain size. On the other hand, minimum interlamellar spacing is controlled by transformation temperature, independent of prior austenite grain size and nodule size. Both the yield strength and fracture stress of pearlite was found to be inversely proportional to interlamellar spacing and independent of prior austenite grain size and nodule size.     

The effect of morphology on the strength of pearlite

The effects of various morphological features on the strength of high-purity pearlite were studied. A continuous-cooling mode of transformation from different austenitizing temperatures was used to produce variations in average nodule diameter and minimum interlamellar spacing. It was found that, for a constant transformation temperature, nodule size was directly related to prior austenite grain size. On the other hand, minimum interlamellar spacing is controlled by transformation temperature, independent of prior austenite grain size and nodule size. Both the yield strength and fracture stress of pearlite was found to be inversely proportional to interlamellar spacing and independent of prior austenite grain size and nodule size.     

Behavior of blood pressure during pregnancy

In 948 women of the blood-pressure behaviour was registered weekly, from the 12. up to the 42. week of normal pregnancy. The normal range is stated with the single and double dissemination of the blood-pressure values; depending from the number of weeks being pregnant, and dessignation and meening to the pathological behaviour are represented. Desides, the frequency of various course-types of the blood-pressure during pregnancy is given, their possible meaning being discussed. For this purpose, 1337 single courses of the blood-pressure behaviour within pregnancy were explored.     

Behavior of secondary alumina during heating

The losses of weight and F-containing compounds by secondary alumina at various temperatures which can be reached in a bunker of automated feeding by alumina (AFA)—i.e., to 80, 100, 200, 300, and 400°C-are evaluated. The fluorine content in alumina after being held at a specified temperature was determined by the photocolorimetric method. Upon the heating of secondary alumina, noticeable losses of weight and fluorine were observed in it starting from t > 80°C, which is associated with the removal of the latter with physically adsorbed moisture. However, the larger part of fluorine remains in secondary alumina even at t = 400°C, because it consists of solid fluorides and chemisorbed particles. The desorption of fluorine from alumina even at relatively low temperatures (starting from 80°C) means that constructive and technological measures are necessary to decrease them in AFA bunkers.