Web strength of rolled steel joists

This work is concerned with the behaviour of thin webbed rolled steel joists or universal beams when they are subjected to concentrated loads applied to the flanges. The prime concern is the effect of high direct stresses causing web failure in a small region of the beam. The review shows that although many tests have been carried out on rolled steel beams and built up girders, no series of tests has restricted the number of variables involved to enable firm conclusions to be drawn. The results of 100 tests on several different rolled steel universal beam sections having various types of loading conditions are presented. The majority of the beams are tested by loading with two opposite loads, thus eliminating the effects of bending and shear, except for a small number of beams which are tested simply supported on varying spans. The test results are first compared with the present design standard (BS 449) and it is shown that the British Standard is very conservative for most of the loading conditions included in the tests but is unsafe for others. Three possible failure modes are then considered, overall elastic buckling of the web, flexural yielding of the web due to large out of plane deflexions and local crushing of the material at the junction of the web and the root fillets. Each mode is considered theoretically and developed to establish the main variables, thus enabling a comparison to be made with the test results. It is shown that all three failure modes have a particular relevance for individual loading conditions, but that determining the failure load given the beam size and the loading conditions is very difficult in certain instances. Finally it is shown that there are some empirical relationships between the failure loads and the type of loading for various beam serial sizes.

Some effects of friction and lubrication during hot forging steel.

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Modelling of transient heat transfer in annealing furnaces

This is a study of heat transfer in a lift-off furnace which is employed in the batch annealing of a stack of coils of steel strip. The objective of the project is to investigate the various factors which govern the furnace design and the heat transfer resistances, so as to reduce the time of the annealing cycle, and hence minimize the operating costs. The work involved mathematical modelling of patterns of gas flow and modes of heat transfer. These models are: Heat conduction and its conjectures in the steel coils;Convective heat transfer in the plates separating the coils in the stack and in other parts of the furnace; and Radiative and convective heat transfer in the furnace by using the long furnace model. An important part of the project is the development of numerical methods and computations to solve the transient models. A limited number of temperature measurements was available from experiments on a test coil in an industrial furnace. The mathematical model agreed well with these data. The model has been used to show the following characteristics of annealing furnaces, and to suggest further developments which would lead to significant savings: - The location of the limiting temperature in a coil is nearer to the hollow core than to the outer periphery. - Thermal expansion of the steel tends to open the coils, reduces their thermal conductivity in the radial direction, and hence prolongs the annealing cycle. Increasing the tension in the coils and/or heating from the core would overcome this heat transfer resistance. - The shape and dimensions of the convective channels in the plates have significant effect on heat convection in the stack. An optimal design of a channel is shown to be of a width-to-height ratio equal to 9. - Increasing the cooling rate, by using a fluidized bed instead of the normal shell and tube exchanger, would shorten the cooling time by about 15%, but increase the temperature differential in the stack. - For a specific charge weight, a stack of different-sized coils will have a shorter annealing cycle than one of equally-sized coils, provided that production constraints allow the stacking order to be optimal. - Recycle of hot flue gases to the firing zone of the furnace would produce a. decrease in the thermal efficiency up to 30% but decreases the heating time by about 26%.

The influence of non-metallic inclusions upon the properties of linepipe steels

The principal aim of this work was to determine the role of non-metallic inclusions in the process of hydrogen stepwise cracking (SWC). Additionally, the influence of inclusions upon the notch ductility of hydrogen charged (HC) and uncharged (UN) tensile specimens was examined. To obtain a basis for experiment a series of low carbon-manganese steels were prepared by induction melting. In order to produce variations in the composition, morphology, volume fraction, size and distribution of the inclusions the steel chemistry was adjusted prior to casting by additions of deoxidiser and Ca-Si injection. Sections of each ingot were hot rolled. Metallography, image analysis, mechanical tests and hydrogen SWC tests were then carried out. The volume fraction, morphology, and shape of inclusions influenced the tensile ductility of the steels. Marked anisotropy was found in the steels containing type II MnS inclusions at all rolling temperatures, whereas the fully Ca treated steel was isotropic. It was found that several inclusion parameters (projected length PL, mean free distance MFD, nearest-neighbour distance NND) correlated with fracture strain. An increase in inclusion volume fraction and/or the dimension of inclusions on a plane parallel to the plane of fracture led to a decrease in fracture strain. The inclusion parameters did not correlate with the fracture strains for the HC tensile specimens. However, large or clusters of inclusions acted as the principal sites for crack initiation. `Fisheyes' or areas of `flat' fracture were often found on these fracture surfaces. The criteria for SWC initiation was found to be either large inclusions or clusters of inclusions. As the PL of inclusions increased the probability of large SWCs occurring increased. SWC initiation at inclusions was believed to occur at a critical concentration of hydrogen. Factors which assisted the concentration of hydrogen at inclusions were discussed. None of the proposed mechanisms of hydrogen embrittlement could be identified as the single cause of SWC.

Toughness measurement of hot work die steel

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The influence of die temperature and hardness on the wear of no. 5 die steel under hot forging conditions

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Nonmetallic inclusion modification and its effect on the final properties of a linepipe steel

Five linepipe type steels were produced in order to study the effect of calcium and magnesium injection on their final properties. Two of these steels were at the extremes of the sulphide range i.e. 0.003 and 0.017% sulphur with no injection attempted; thereby, providing standards to compare with the injected steels. The oxygen level varied from 21 to 63 p.p.m. The cast ingots were controlled-rolled and isothermally rolled in order to study the deformation characteristics of the residual non-metallic inclusions. The structure and cleanliness of these steels was evaluated metallographically using the light microscope, SEM, and image analysis and the results related to their Charpy toughness and HIC resistance. Increasing sulphur levels decreased final properties of the steel. In the untreated state, with as little as 0.003% sulphur, test orientation was highly influential. Modification of sulphur bearing steels was achieved with low modifying element to sulphur ratios provided that the oxygen content was very low. Injection of calcium into steel caused interaction with oxide and sulphide inclusions which was biased toward oxide reduction relative to sulphur removal. Magnesium again reduced oxides and appeared to be linked with aluminia containing inclusions in the final product. It produced improved toughness values relative to a similar sulphur containing calcium treated steel. The results of this work could be extended to establish the mechanism of inclusion modification with magnesium additions to sulphur bearing steels.

Mechanics of longitudinal rolling of tube through three-grooved rolls

This investigation examined the process of the longitudinal rolling of tubes through a set of three driven grooved rolls. Tubes were rolled with or without internal support i.e. under mandrel rolling or sinking conditions. Knowledge was required of the way in which the roll separating force and rolling torque vary for different conditions of rolling. The objective of this work being to obtain a better understanding and optimization of the mechanics of the process. The design and instrumentation of a complete experimental three-roll mill for the rolling of lead tube as an analogue material for hot steel, with the measurement of the individual roll force and torque is described. A novel type of roll load cell was incorporated and its design and testing discussed. Employing three roll sizes of 170 mm, 255 mm and 340 mm shroud diameter, precise tube specimens of various tube diameter to thickness ratios were rolled under sinking and mandrel rolling conditions. To obtain an indication of the tube-roll contact areas some of the specimens were partially rolled. For comparative purposes the remaining tubes were completely rolled as a single pass. The roll forces, torques and tube parameters e.g. reduction of area, D/t ratio, were collated and compared for each of the three roll diameters considered. The influence of friction, particularly in the mandrel rolling process, was commented upon. Theoretical studies utilising the equilibrium and energy methods were applied to both the sinking and mandrel rolling processes. In general, the energy approach gave better comparison with experiment, especially for mandrel rolling. The influence of the tube deformation zones on the two processes was observed and on the subsequent modification of the tube-roll arc contact length. A rudimentary attempt was made in the theoretical sinking analysis to allow for the deformation zone prior to roll contact; some success was noted. A general survey of the available tube rolling literature, for both the sinking and mandrel processes has been carried out.

Effect of poor curing conditions and remedies on the durability of steel in concrete

An investigation was undertaken to study the effect of poor curing simulating hot climatic conditions and remedies on the durability of steel in concrete. Three different curing environments were used i.e. (1) Saturated Ca(OH)2 solution at 20°C, (2) Saturated Ca(OH)2 solution at 50°C and (3) Air at 50°C at 30% relative humidity. The third curing condition corresponding to the temperature and relative humidity typical of Middle Eastern Countries. The nature of the hardened cement paste matrix, cured under the above conditions was studied by means of Mercury Intrusion Porosimetry for measuring pore size distribution. The results were represented as total pore volume and initial pore entry diameter. The Scanning Electron Microscope was used to look at morphological changes during hydration, which were compared to the Mercury Intrusion Porosimetry results. X-ray defraction and Differential Thermal Analysis techniques were also employed for looking at any phase transformations. Polymer impregnation was used to reduce the porosity of the hardened cement pastes, especially in the case of the poorly cured samples. Carbonation rates of unimpregnated and impregnated cements were determined. Chloride diffusion studies were also undertaken to establish the effect of polymer impregnation and blending of the cements. Finally the corrosion behaviour of embedded steel bars was determined by the technique of Linear Polarisation. The steel was embedded in both untreated and polymer impregnated hardened cement pastes placed in either a solution containing NaCl or an environmental cabinet which provided carbonation at 40°C and 50% relative humidity.

Influence of pretreatment on corrosion behaviour of duplex zinc/polymer coatings on steel substrates

An investigation has been undertaken to determine the major factors influencing the corrosion resistance of duplex-zinc coatings on steel substrates.Premature failure of these systems has been attributed to the presence of defects such as craters and pinholes in the polymer film and debonding of the polymer film from the zinc substrate.Defects found on commercially produced samples have been carefully characterised using metallographic and scanning electron microscopy techniques. The influence of zinc substrate surface roughness, polymer film thickness and degassing of conversion coatings films on the incidence of defects has been determined.Pretreatments of the chromate, chromate-phosphate, non chromate, and alkali-oxide types were applied and the conversion coatings produced characterised with respect to their nature and composition. The effect of degassing on the properties of the films was also investigated. Electrochemical investigations were carried out to determine the effect of the presence of the eta or zeta phase as the outermost layer of the galvanized coating.Flow characteristics of polyester on zinc electroplated hot-dip continuous and batch galvanized and zinc sprayed samples were investigated using hot-stage microscopy. The effects of different pretreatments and degassing after conversion coating formation on flow characteristics were determined.Duplex coatings were subjected to the acetic acid salt spray test. The effect on adhesion was determined using an indentation debonding test and the results compared with those obtained using cross-cut/peel and pull-off tests. The locus of failure was determined using scanning electron microscopy and X-ray photoelectron spectroscopy techniques.