Large Laths Research Articles

Do cracked jaws of the four-jaw chuck of a large lathe pose a danger?

Abstract All the jaws of a four-jaw chuck mounted on the faceplate of a large lathe were received by the material testing laboratory to undergo metallurgical failure analysis. Each of the four jaws exhibited cracks in the fillet radius between one of the gripping surfaces and the long horizontal part. The cracks were just visible to the unaided eye und had been discovered by an alert mechanic. One of the jaws was selected for further material analysis for which the crack was opened to undergo fractographic evaluation. The analysis also involved the evaluation of the material using optical emission spectrometry, the preparation of a metallographic sample, and hardness testing. The cracks occurred as a result of repeated overload at the crack initiation sites located in the fillet radius. This was not a single overload event which would not have caused the jaws to crack, but a series of overload events. The situation did not pose a safety hazard to the staff since the soft and tough core of the case-hardened jaws would have retarded, if not stopped, crack growth. A sudden disastrous failure of the jaws by breaking off, for example, and extremely heavy components crashing down as a result were not an imminent threat. This dangerous failure scenario would have been enabled if the jaws had been through-hardened. Instead, casehardening heat treatment had been applied which is the correct choice for this type of component.

Study on the effect of microstructure on toughness dispersion of X70 steel girth weld

The girth weld metal impact toughness would affect the safe operation of long transmission oil and gas pipeline. In order to further clarify toughness law of pipeline steel girth weld, the Charpy impact toughness of X70 steel girth weld at −10 °C was studied by standard impact method, and the impact energy range was determined to be 18–95 J. The impact energy range of girth welds varied significantly, and the toughness was discrete. The impact toughness of the different microstructures in the girth weld at −158 °C was studied by the small specimen impact test. The root weld metal mainly consisted of ferrite and a small amount of pearlite, and its impact toughness was low. The large effective grain size and dislocation density difference between large lath bainite (LB) and coarse granular bainite (GB) increased the strain heterogeneity during impact deformation. In fine GB, effective grain size reduction and uniform distribution of Martensite austenite (M–A) components reduced the local strain, resulting in more uniform deformation. Therefore, the sample with the fine GB had higher impact the toughness and ductile fracture mode. For the standard Charpy impact samples, the main reason for toughness dispersion was change of fine GB proportion. The fine GB proportions of P6-2, P3-3 and P3-2 were 46.7 %, 40.8 %, and 29.5 %, respectively. Simultaneously, the influence of position change on the impact energy was considered.

Microstructure and Mechanical Properties of Hybrid-Manufactured Maraging Steel Component Using 4% Nitrogen Shielding Gas Fabricated by Wrought-Wire Arc Additive Manufacturing

Recent advances in hybrid-manufactured steel components have provided more geometrical freedom for the manufacturing of parts with desired properties. The wrought-wire arc additive manufacturing (WAAM) components using different shielding gases were fabricated in this paper. The results showed that there were four parts in the microstructure, including the WAAM deposition zone, grain growth zone, heat affect zone (HAZ) and substrate zone. The grain growth zone containing large martensite laths had a significant effect on the final tensile strength. In the WAAM deposition zone, the austenite content increased from 2.5% to 7.6% because of the addition of 4% nitrogen. The fracture position shifted from the grain growth zone of the N2-0% sample to the WAAM deposition zone of the N2-4% sample owing to the strengthening machines of solid solution and finer grain. Nano-precipitate Cr2N plays an important role in grain refinement, which is believed to enhance the mechanical properties of the grain growth zone. Under a 4% nitrogen content in the shielding gas, the tensile strength of the hybrid-manufactured sample using 4% nitrogen shielding gas was 1186 MPa, which is approaching the level of the WAAM-fabricated sample.

TEM Study of Martensite Microstructure in the Junctions of Laths in Low-Carbon Chromium Steel after LCF III

TEM study of junctions between martensite packets (laths) and their microstructure in low-carbon martensitic steel were studied. It was revealed that formation of slip bands commences at junctions between laths. Heavy changes in microstructure occur at junctions of packets and in the near-boundary laths because of plastic deformation of martensite. A number of typical junctions between the laths after LCF are considered. Deformation process within the individual packet occurs inhomogeneously, some of the laths deform more heavily than the others. The coarser slip bands group within large laths and run along their whole lengths. It was shown that the above microstructure changes strongly affect the cyclic fracture of the steel. Some concrete sites of microcrack initiation are indicated.

Effects of laser additive manufacturing on microstructure and crystallographic texture of austenitic and martensitic stainless steels

Powder-fed laser additive manufacturing (LAM) based on directed energy deposition (DED) technology is used to produce S316-L austenitic, and S410-L martensitic stainless steel structures by 3D-printing through a layer-upon-layer fashion. The microstructural features and crystallographic textural components are studied via electron backscattering diffraction (EBSD) analysis, hardness indentation and tensile testing. The results are compared with commercial rolled sheets of austenitic and martensitic stainless steels. A well-developed <200> direction solidification texture (with a J-index of ∼11.5) is observed for the austenitic structure produced by the LAM process, compared to a J-index of ∼2.0 for the commercial austenitic rolled sheet. Such a texture in the LAM process is caused by equiaxed grain formation in the middle of each layer followed by columnar growth during layer-upon-layer deposition. A quite strong preferred orientation (J-index of 17.5) is noticed for martensitic steel developed by LAM. Large laths of martensite exhibit a dominant textural component of {011}<111> in the α-phase, which is mainly controlled by transformation during layer-by-layer deposition. On the other hand, the martensitic commercial sheet consists of equiaxed grains without any preferred orientation or completely random orientations. In the case of the austenitic steel, mechanical properties such as tensile strength, hardness and ductility were severely deteriorated during the LAM deposition. A ductility loss of about 50% is recorded compared to the commercially rolled sheets that is attributed to the cast/solidified structure. However, LAM manufacturing of martensitic stainless steel structures leads to a considerably enhanced mechanical strength (more than double) at the expense of reduced ductility, because of martensitic phase transformations under higher cooling rates.

Heterogeneous microstructure of low-carbon lath martensite with continuous yielding behavior in Fe-C-Mn alloys

High strength steels have been rapidly developed for several kinds of application fields such as light weight automobile bodies, multistory buildings, and oil well tubulars. With an increase of strength, the use of the low-carbon lath martensite phase puts this component as the main microstructure, or a part of the dual phase one. However, the martensite is a non-equilibrium phase, and the microstructure is also a heterogeneous composite-like one including of fine carbides and retained austenite. In order to understand the hierarchical structure, multi-scale microscopic techniques have been utilized. Internal twins in a lath and some large lath domains with fine carbides are revealed by scanning electron microscope (SEM) and transmission electron microscope (TEM) observations, although a conventional low-carbon martensite is known to include mainly dislocations in the lath structure. The heterogeneous microstructure is discussed based on a model of the local difference of transformation temperature of each lath block segment during cooling. On the plasticity of low-carbon lath martensite, the continuous yielding behavior is one characteristic property, and the elastic limit is obtained by the cyclic tensile test. The heterogeneous deformation behavior is detected as a periodic strain partitioning among lath blocks in a grain by digital imaging correlation analysis using in situ SEM tensile testing.

Microstructural Analysis of the Laser-Cladded AISI 420 Martensitic Stainless Steel

This study investigates the microstructural evolution and phase transformation of laser-cladded AISI 420 martensitic stainless steel. The microstructural morphologies of the laser-cladded sample were examined using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM) equipped with energy-dispersive spectroscopy. The three regions of bead zone, dilution zone, and an interface were investigated. The TEM study revealed various morphologies of martensitic phase in each region. The bead zone consisted of plate and lenticular martensite with internal twins, while lath and thin plate martensite and internal twins were presented in the dilution zone. Large lath martensite was observed in the interface zone the boundary between the dilution and heat-affected zones. The selected area electron diffraction identified those forms of martensite as the ά-martensite in three zones. Other microstructural features such as nano-carbide precipitates and high density of dislocations were also observed in each zone. The martensitic transformation with various morphologies provided crucial information about the development of residual stress throughout the three zones. It was concluded that due to the high cooling rate, the martensitic phase transformation first occurred in the bead zone with the formation of plate-like martensite. Combination of the plate and lath-like martensite formed subsequently in the dilution zone created high compressive stress in this zone and high tensile stress in the bead zone.

Further Observations of Linear Arrays of Transition-Iron-Carbide Precipitates in Tempered 4340 Steel

4340 steel was quenched to form lath martensite and then tempered at 200 °C for 1 h. Microstructural features of a large lath were examined in detail via transmission electron microscopy, including bright-field imaging, centered-dark-field imaging, and electron diffraction. Linear arrays of transition-iron-carbide precipitate were characterized. Rodlike arrays measured about 100 nm in length and were aligned predominantly along martensite directions. The rodlike arrays consisted of small, closely spaced, nearly equiaxed transition-iron-carbide precipitates of less than 10 nm in diameter. Kinks in the rodlike arrays resulted is deviations from directions by about 20°–30°. A less-common type of linear array measured 500 nm in length. These longer features were aggregates of kinked rodlike arrays that seemed to be “attached” by kinked segments, again at 20°–30° from martensite directions. Transition-iron-carbide precipitates showed little if any association with martensite matrix dislocations that were aligned predominantly along directions. A hypothesis was offered in which precipitates aligned along martensite directions are a remnant of spinodal decomposition that develops planar modulations of high- and low-carbon regions prior to the first stage of tempering.

Characterisation of primary and secondary carbonates in hypabyssal kimberlites: an integrated compositional and Sr-isotopic approach

Carbonates in fresh hypabyssal kimberlites worldwide have been studied to understand their origin [i.e. primary magmatic (high T) versus deuteric (‘low T’) versus hydrothermal/alteration (‘low T’)] and identify optimal strategies for petrogenetic studies of kimberlitic carbonates. The approach presented here integrates detailed textural characterisation, cathodoluminescence (CL) imaging, in situ major- and trace-element analysis, as well as in situ Sr-isotope analysis. The results reveal a wide textural diversity. Calcite occurs as fine-grained groundmass, larger laths, segregations, veins or as a late crystallising phase, replacing olivine or early carbonates. Different generations of carbonates commonly coexist in the same kimberlite, each one defined by a characteristic texture, CL response and composition (e.g., variable Sr and Ba concentrations). In situ Sr isotope analysis revealed a magmatic signature for most of the carbonates, based on comparable 87Sr/86Sr values between these carbonates and the coexisting perovskite, a robust magmatic phase. However, this study also shows that in situ Sr isotope analysis not always allow distinction between primary (i.e., magmatic) and texturally secondary carbonates within the same sample. Carbonates with a clear secondary origin (e.g., late-stage veins) occasionally show the same moderately depleted 87Sr/86Sr ratios of primary carbonates and coexisting perovskite (e.g., calcite laths-shaped crystals with 87Sr/86Sr values identical within uncertainty to those of vein calcite in the De Beers kimberlite). This complexity emphasises the necessity of integrating detailed petrography, geochemical and in situ Sr isotopic analyses for an accurate interpretation of carbonate petrogenesis in kimberlites. Therefore, the complex petrogenesis of carbonates demonstrated here not only highlights the compositional variability of kimberlites, but also raises concerns about the use of bulk-carbonate C-O isotope studies to characterise the parental melt compositions. Conversely, our integrated textural and in situ study successfully identifies the most appropriate (i.e. primary) carbonates for providing constraints on the isotopic parameters of parental kimberlite magmas.

Effect of intercritical rolling temperature on microstructure-mechanical property relationship in a medium Mn-TRIP steel containing δ ferrite

We elucidate the influence of intercritical rolling temperature on the microstructural evolution, mechanical properties and work-hardening behavior of a hot-rolled Fe-0.2C-6.5Mn-3Al-0.1V medium Mn transformation-induced-plasticity (TRIP) steel containing δ-ferrite. Tensile strength of 966 MPa, total elongation of 42.6% and yield strength of 705 MPa was obtained in the annealed steel subjected to a low intercritical rolling temperature. Rolling at a high intercritical rolling temperature promoted the partitioning of Mn from δ ferrite to prior austenite grains, and led to a martensitic matrix characterized by a fine lath structure. Subsequently, after intercritical annealing, the reversed austenite transformed from the martensitic matrix had high stability and small size. However, the reversed austenite with a high degree of Mn enrichment, fine lath structure and high stability provided a slow and less active TRIP effect. This was responsible for low work-hardening rate during deformation. In contrast, the high content of reversed austenite in the annealed steel subjected to low intercritical rolling temperature had relatively low stability and large lath width, exhibited serrated work-hardening behavior indicative of discontinuous TRIP effect. Additionally, the low intercritical rolling temperature led to a high density of dislocations in δ-ferrite, which effectively promoted VC precipitation after intercritical annealing, and enhanced yield strength. Furthermore, the formation of high angle boundary in δ-ferrite and the formation of pro-eutectoid ferrite at low intercritical rolling temperature also enhanced yield strength through grain boundary strengthening.

Numerical simulation on deformation and stress variation in resistance spot welding of dual-phase steel

In this study, an effective numerical simulation on resistance spot welding of dual-phase steel was conducted. The electrical, thermal and mechanical behaviours during squeezing, welding and holding stages were analyzed, respectively. Large lath martensite was formed in the fusion zone during the experiment. A good agreement on nugget development was obtained between numerical and experimental results. The size of contact region and pattern of contact pressure distribution at the squeezing stage were found to be force-independent. The variation of contact pressure distribution during the welding process was interpreted combining the temperature and deformation distribution of the workpiece. The contact pressure at both edges of contact interfaces was reconcentrated after nugget formation. The compressive state of axial and radial stress at the weld nugget was explained through the thermal expansion mismatch and the electrode force effect. The plastic annulus and notch between workpieces were also successfully simulated.

The Design and Simulation of Main Tool Carrier System in a Condition of Large Vertical Lathe

To solve excessivly large deformation and vibration problems in machining large tube section, ensure the machining accuracy and quality of the tube section, the main tool carrier system of a large vertical lathe is designed, by simulation means of finite element, static analysis, dynamic modal analysis and dynamic response analysis are respectively carried on the main tool carrier structures designed. A reasonable overhang length of the tool in the tool carrier system is given through static analysis, dynamic modal analysis show the higher natural frequency of the tool carrier system, the production of cutting resonance can be avoided, the maximum response and corresponding stress conditions of the system under the harmonic loads are given by dynamic response analysis, analysis results show that the sustainable dynamic characteristics of tool carrier system can meet the machining requirements.

Research on Processing Parameters of Large Lathe Bed's Vibratory Stress Relief

In order to enhance the actual effect of vibration aging on large lathe bed and optimize it, many technological parameters of vibration aging will be discussed in this paper, including exciting force, exciting frequency and exciting point, etc. Finite element method is used to analyze the casting stress distribution and natural mode of vibration of a large lathe bed. After the analysis, it is found that the distribution of the residual stress of the lathe bed is extremely uneven. By analyzing parameters of the natural vibration model and the exciting force as well as the exciting point, a reasonable parameter will be got when the lathe bed is vibrating. The “Selecting low-frequency to avoid torsion mode” which reduces the deformation to bed caused by the residual stress, was proposed. The parameters have been proved effective through experiment, and the proposed approach can be used in the research of vibratory stress relief.

Development of a high-strength high-conductivity Cu-Ni-P alloy. Part I: Characterization of precipitation products

The precipitation products of a Cu-1.5Ni-0.32P (wt.%) alloy isochronally aged at 400°C and 600°C were investigated by transmission electron microscopy (TEM). There are two different sizes of precipitates formed in the 600°C aged specimen. Large precipitates appear to be lath, the length of which varies from 100 nm to 500 nm, whereas small dotty contrasts around 10 nm in diameter are uniformly distributed in the matrix. Only small dotty contrasts are observed after 400°C aging. In the composition range 0–33.3 at.%P, both the previous studies and the calculated Ni-P binary phase diagram indicated that the possible nickel phosphide phases are Ni3P, Ni12P5, Ni5P2, and Ni2P. However, selected area electron diffraction (SAED) pattern analysis in conjunction with energy dispersive x-ray spectroscopy (EDS) identified the large lath precipitates as Ni12P5 phase. On the other hand, the small precipitates could not be analyzed by EDS due to thinness; thus, the structure is estimated to be a Ni5P4 phase from the relationships between d-spacing and angles between planes measured from a selected area diffraction pattern.

Post-crystallization reheating and partial melting of eucrite EET90020 by impact into the hot crust of asteroid 4Vesta ∼4.50 Ga ago

We performed petrologic, radiometric (Ar-Ar, Sm-Nd, and Mn-Cr ages), and ion microprobe studies of the basaltic eucrite, EET90020. This is one of the few rare basaltic eucrites whose 39Ar-40Ar age has not been reset during impact bombardment on the HED parent body ≤4 Ga ago and, thus, should provide a unique opportunity to study the nature of the early thermal events on its parent body (presumably asteroid 4Vesta). Hand specimen inspection shows that the rock consists of a fine-grained and a coarse-grained lithology. Microscopy indicates that the fine-grained lithology has a granulitic texture, with a coarser-grained area and a large opaque assemblage embedded in the granulitic matrix. The coarse-grained lithology has an igneous, subophitic texture. The rock has pyroxenes similar to those in type 5 eucrites (type 5 pyroxene) and experienced prolonged thermal metamorphism after rapid crystallization from a near-surface melt. However, minor mineral assemblages are unusual and suggest a complex thermal history. Tridymite occurs as large laths, irregular crystals (<1.5 mm), and in a large assemblage of tridymite-plagioclase-pyroxene about 4 mm in size. One large opaque assemblage (∼1.4 mm in size) is a decomposition product of Cr-ulvöspinel and consists of zoned Ti-chromite, ilmenite and minor Fe-metal. The opaques are often rimmed by Fe-rich olivine and pigeonite with some chemical variations, indicating disequilibrium with the surrounding type 5 pyroxenes. Ca-phosphate with low REE abundances, and the LREE signatures observed in plagioclase suggest that melt was present during metamorphism. This indicates that EET90020 was reheated above the subsolidus temperature of eucrites of ∼1060°C, causing partial melting. Tridymite, Cr-ulvöspinel, and some pyroxene and plagioclase crystallized from the melt. The presence of unequilibrated phases related to opaques suggests cooling rates greater than several °C/day. The reheating event was too short to destroy the exsolution textures of the type 5 pyroxenes. The temperature of the rock just before the reheating could have been ∼870°C, based on the two-pyroxene temperature of the type 5 pyroxenes. The absence of shock effects in plagioclases suggests that EET90020 did not experience shock events >1–5 GPa after the reheating event. EET90020 seems to have experienced the following thermal history; (1) crystallization during rapid cooling near the surface; (2) some brecciation by impact; (3) thermal metamorphism that produced type 5 pyroxene; and (4) short reheating that caused partial melting and rapid cooling. 39Ar-40Ar measurements show a relatively flat pattern and an age of 4.49±0.01 Ga, which is consistent with rapid cooling from high temperature (event 4). Resetting of the Sm-Nd ages at 4.51 ± 0.04 Ga appears to be closely related to the remelting of Ca-phosphates. Rb-Sr data suggest Rb-loss from tridymite during partial melting. The resetting of the Mn-Cr age may have been related to the formation of Cr-ulvöspinels (event 4). We suggest that all these ages were reset by partial melting (event 4). We further suggest that the partial melting event (event 4) that reset the ages ∼4.50 Ga ago was caused by an impact into EET90020 which was part of the hot crust of 4Vesta and resulted in an increase in the temperature from the ambient temperature of ∼ 870°C to above the subsolidus temperature of eucrites of ∼1060°C.

Particle Morphological Evolution During the Conversion of I/S to Illite in Lower Cretaceous Shales from Sergipe-Alagoas Basin, Brazil

AbstractThe illitic end of mixed-layer illite-smectite series (I/S) in shales from Lower Cretaceous Barra de Itiúba Formation, Sergipe-Alagoas basin, was examined with X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). A mathematical decomposition of XRD patterns shows different I/S and illite populations. All the samples contain ordered (R = 1) I/S, poorly crystallized illite (PCI) and well crystallized illite (WCI). A randomly interstratified (R = 0) I/S was also identified in a fractured zone at 1020 m. The percentage of expandable layers in ordered I/S decrease progressively from 20% to 10%. TEM observations show a continuous change in morphology between two basic particle shapes: elongated (lath) and isometric. The size and morphology of particles change with increasing depth. The proportion of laths decreases while isometric particles become predominant. However, both particle types continuously grow and enrich the larger size fraction. The growth process is driven by a mass transfer from the dissolving small particles of predominantly I/S (R = 1) composition to the larger (more illitic) lath and isometric ones. The proportion of lath-shaped particles decreases with depth indicating that the more stable population upon increased burial is the isometric well crystallized illite (WCI) particles. Very large laths are observed in the fault zone where conditions may favor faster growth processes.

Slags: Descriptions (CJS)

The following slags are described separately: see also full catalogue in microfiche Table 2. See analyses of each of the following items (with the exo tptioi of nr 69), including occasional metallic inclusions, in microfiche Table 9, where details of sample number and conte... are also given.55. Moderate-sized plano-convex,slag (type 4), with moderate porosity and few charcoal impressions (174 g). Microstructure: moderate-sized semi-dendritic iron-oxide FeO (40-60%) inhomogeneously distributed, in matrix of fayalite and fayalite plus iron oxide pseudo-eutectic. A little ternary glass+fayalite+iron oxide eutectic present. Some regions of pure fayalite; others with large laths of fayalite and iron oxides outlined by giass and iron oxide eutectic. A little metallic iron present.56. Fragment of dense plano-convex slag (50.5 g). Patchily distributed iron oxide (FeO), locally massive (100%), and distorted. Dendrite arm size and spacing varies through fine-moderate-large arms. Matrix of fayalite and unresolved eutectic. A little metallic iron.57. Piece of dense plano-convex slag (37 g). Moderate porosity. Metallic iron common in regions with less iron oxide. There are two regions: one with pools of massive semi-globular FeO with 90+% iron oxide (wustite), interspersed with regions with moderate or fine dendritic FeO in a matrix of unresolved material. Metallic iron contains several percent copper!

Electron Microscopic Investigations of Iron Oxyhydroxides and Accompanying Phases in Lateritic Iron-Crust Pisolites

AbstractPisolites from an iron crust in western Senegal were studied by conventional and high-resolution electron microscopy to determine their internal structure and the genetic processes that led to their formation. Each pisolite consisted of a concentric structure of hematite rimmed by goethite. Two types of goethite were distinguished: (1) large (≃ 0.6 μm long and 0.06 μm wide), euhedral laths arranged in fibrous aggregates of slightly misoriented grains devoid of internal defects as shown by their two-dimensional lattice images, and (2) a matrix of smaller (≃400 Å), anhedral grains surrounded by the larger laths. Based upon the crystal habit and the presence or absence of internal alveoles, the large goethite laths probably grew at the expense of the matrix goethite. Poorly crystalline kaolinite, presumably formed from well-crystalline precursor kaolinite, and clusters of partially dissolved quartz grains were also imaged. In addition, two uncommon phases were found—maghemite in topotactic relationship with hematite and a layered, Fe-rich, mica-like mineral with a 2M superstructure. Unlike kaolinite, this latter phase was likely in equilibrium with iron oxyhydroxides. Substituted Al probably was released during goethite recrystallization, and mass transfers probably took place through the heterogeneous porosity (i.e., large voids and cracks coupled with fine pores) revealed by transmission electron microscopy.

Characteristics of lath martensite: Part I. crystallographic and substructural features

This investigation, using an Fe-20 pct Ni-5 pct Mn (wt pct) alloy, was carried out to provide more detailed and accurate information on the crystallographic features of ferrous lath martensite than is presently available. The martensite observed was typical of that found in low carbon steels, but with the present alloy substantial amounts of retained austenite are found, which can be used as a crystallographic reference basis. Analysis of some twenty laths showe_d_the average austenite-martensite orientation relationship to be (lll)f ‖ (011)b: [•101]f 3.9 deg from [•1•1l]b, using an electron diffraction method involving an error of only a fraction of a degree. Adjacent laths within a packet of lath martensite were found to exhibit the same variant of the orientation relationship although such laths may be misoriented relative to each other by up to 2 deg. Thick layers of austenite found between adjacent laths indicate that the laths do not form by self-accommodation. The lath martensite habit plane is irrational, close to (575)f [equivalently (•154)b], but since the habit plane is of the type hkh, 12 apparent habit planes are observed although 24 variants of the orientation relationship may be found. The martensite-austenite interface on one side of a given lath is relatively planar, while that on the opposite side is irregular, suggesting that the laths thicken mainly in one direction. The martensite laths contain screw dislocations in all four ( 111 )b directions, but one set of the four with Burgers vector α/2 [•111]b is clearly dominant as a result of accommodation deformation imposed by the large lath martensite shape strain. Austenite dislocation arrays associated with the straight and irregular lath interfaces are very different, again suggesting that the thickening of a lath takes place mainly in one direction away from the initial straight interface.

Hydrogen-mineral reactions and their application to the removal of iron from spodumene

Pegmatitic deposits contain three distinctly different types of spodumene: 1.(1) Phenocrystic spodumene in unzoned pegmatites. This type is high-iron spodumene, with Fe2O3 = 0.6 − 0.9%.2.(2) Zonal spodumene. Large laths in central zones; it contains 0.01–0.03% Fe2O3.3.(3) Spodumene plus quartz aggregates pseudomorphous after petalite; Fe2O3 = 0.007 − 0.03%. Only Type 1 generally occurs in deposits sufficiently large and uniform to be economically exploitable. Two processes are presently available for iron removal. Both require initial inversion of the (a) spodumene to its β-dimorph: 1.(1) The chlorine process in which the isomorphous iron is converted to bon chloride and2.(2) The hydrogen process in which the Fe3+ ion is reduced to metallic iron.Hydrogen-mineral reactions, such as hydrogen-carbonate reactions, are potential sources of lime, methane and iron. They also are important for the benefication of such ceramic materials as spodumene and feldspar.