Abstract Two tanks made of AISI type 304 stainless steel exhibited cracking in the heat-affected zone (HAZ) of the weld that joined the dished end and the shell. The dished ends had been produced by cold deformation. Hardness measurement and simulation tests showed that the deformation was equivalent to a 30% reduction in thickness. Residual stresses were measured at about 135 MPa (20 ksi). The HAZ was found to be sensitized. The tanks had been stored in a coastal atmosphere for about 4 years before installation. The failure was attributed to intergranular stress-corrosion cracking in a sensitized HAZ due to chloride from the environment. Use of low-carbon type AISI 304L was recommended. Minimization of fit-up stresses and covering with polyethylene sheets during storage were also suggested.

Titanium and its alloys demand a high magnitude of forming stresses in cold extrusion, which stresses can be reduced by utilising the deformation heat generated during cold forming. The deformation heat can be utilised effectively at high strain-rates, as under these conditions the heat loss by conduction is less, due to lesser contact time between the work-metal and the tool surface. In this investigation an attempt has been made to utilize deformation heat in the cold extrusion of commercially pure titanium. Extrusion tests, both solid and hollow forward, have been undertaken on cold commercially pure titanium, using both a hydraulic press (a low strain-rate machine) and an eccentric press (a high strain-rate machine) to evaluate the interaction of the deformation ratio and the strain rate with the adiabatic heating that effects lower forming stresses. The results show that at higher rates of working the forming stress is reduced. Post-extrusion tests have also been undertaken to examine the properties of the extrudes, in terms of standard tensile, hardness and corrosion tests, to establish their suitability for engineering applications.

Dynamic strain-ageing is a well known phenomenon in metal working, which phenomenon, however, is objectionable from the formability point of view. Dynamic strain-ageing is dependent upon the chemical composition of the work-metal, the deformation, the deformation rate and the temperature. The loss in ductility and the variation of the flow stress, the strength coefficient and the strain-hardening exponent, with variation in temperature, characterise the onset of dynamic strain-ageing. A sudden increase in the work-metal temperature due to adiabatic heating can also contribute to the occurrence of dynamic-strain ageing.

In this investigation, ring-compression tests have been carried out on commercially pure titanium, both with the recommended lubricant MoS2 and without lubricant, to evaluate the interface constant shear friction factor. The tests were conducted in the temperature range of from 303 to 573 K and the strain-rate range of from 0.07 to 32 s−1. The results of the investigation reveal that the friction factor for the combination commercially pure titanium (as the work material) and high-speed steel (as the tools) increases with strain rate and temperature and that MoS2 is a satisfactory lubricant up to a temperature of 473 K.

This paper reports the results of the ring and the solid-compression test carried out on commercially pure titanium in the temperature range of from 303 to 573 K and the strain-rate range of from 0.07 to 32 s−1. Analysis of flow-stress data and microstructural studies on the upset samples were undertaken to predict the optimal working conditions of strain rate and temperature so as to be able to obtain the full advantage of adiabatic heating in reducing the flow stress of the material. For the range of conditions explored, the results show that working at 303 K and 32 s−1 is optimal for the effective utilisation of adiabatic heating in reducing the flow stress.

In this investigation, a comparison is made between the flow stress as evaluated through the torsion test with that as evaluated through the compression test, for the prediction of the peak pressure in the extrusion of commercial purity titanium. Room temperature, ring- and solid-compression tests and torsion tests were carried out at nominal strain rates ranging from 0.05 to 32s−1 to evaluate the flow stress. Cold extrusion tests were also carried out on the same material, using MoS2 as the lubricant, to determine the actual peak extrusion pressure for various reductions, for two extrusion processes; namely solid forward and hollow forward extrusion. The peak extrusion pressures observed were compared with those predicted using the flow-stress data evaluated through the compression and the torsion tests, the results showing that the torsion-test data affords a closer prediction.

In this investigation a simple theoretical analysis of the solid compression test has been carried out so that the friction factor can be estimated quantitatively from the reduction-capacity test— the latter involves the compression of a cylindrical billet between flat parallel platens, using an energy-bound machine. Detailed experiments have been carried out on Armco iron to determine the friction factor using both the reduction-capacity test and the ring-compression test, in order to be able to obtain a comparative assessment of these two test methods. The results of the investigation indicate that if an aspect ratio of 2 or 2.5 is chosen in the reduction-capacity test, the friction factor corresponds with those obtained from standard ring-compression tests.

AISI type 316 austenitic stainless-steel plates were strengthened by warm rolling to different strain levels in the temperature range 823–1123 K. Samples from the plates were hardness tested at various temperatures up to 923 K. Hardness values have been correlated to yield- and ultimate tensile-strength using results of tensile tests carried out at 300 and 923 K. The results of the hot-hardness tests and correlations are discussed in terms of the retention of strength achieved by warm rolling in comparison to annealed material. It is seen that strengthening achieved through warm rolling is retained up to 0.5 Tm where Tm is the melting temperature of the material.

Solution treated Nimonic 105 superalloy was subjected to direct ageing at 1123 K and to double ageing treatments involving intermediate ageing at 1333 K and final ageing at 1123 K. The microstructures developed at different stages of these treatments were characterised by optical microscopy and scanning and transmission electron microscopy. The tensile properties of this alloy were evaluated at different temperatures and correlated with the microstructures produced at the end of the ageing treatments. The Kinetics of the growth of the γ' precipitates during ageing at 1123 K obeys the cubic law indicating that the growth is controlled by the diffusion of the γ' forming solutes through the matrix. A transition from spherical to cuboidal morphology of the γ' precipitates was noticed during their growth. Intermediate ageing at 1333 K led to the formation of discrete and globular precipitates of M23C6 along the grain boundaries. Strength properties evaluated at 300 K for the samples directly aged at 1123 K are found to be superior to those of the samples subjected to double ageing treatments. Tensile tests conducted at elevated temperatures showed that the yield strength of the alloy exhibited a weak temperature dependence while the ultimate tensile strength decreased steadily with an increase in the test temperature. The strengthening mechanisms operating at different stages of ageing are discussed and the experimental measurements of the strengthening contribution due to the γ' precipitates are compared with the theoretical estimates. It is shown that when the mean radius r̄ of γ' is below 40 nm, the γ' precipitates are invariably sheared by moving dislocations while precipitates with r̄ ⩾ 40 nm are bypassed by the Orowan mechanism.

This paper presents the results obtained from a series of experiments on double-curvature forming of 300 mm square and 15 mm thick plates of type 316L(N) stainless steel to evaluate the inherent springback and also to validate finite element method (FEM) based process model developed for forming of multiple-curvature sectors of large size vessels. The experimental results show that twisting of the plate occurs during pressing, which is unavoidable in an actual forming setup on the shop floor. Twisting increases with increase in slope of the die cavity. Springback in the plate changes in an ascending order towards the centerline of the plate from the edges. The final radius of curvature (ROC) on the pressed plate after springback does not remain constant along a particular axis although the die and the punch had constant ROC along that axis because of varying constraint to opening up of the plate from centerlines to the edges. Springback also increases with reduction in the stiffness of the die and punch. The simulated plate profiles obtained from the FEM process model for multiple-curvature plate forming compared well with the experiments, the maximum error being within 6%. The process model used a sequential dynamic explicit formulation for the plate pressing phase and a static implicit formulation for the unloading (springback) phase in the Lagrangian framework. Reduced integration shell elements were used for the plate and the die and the punch were considered rigid. Dynamic explicit FEM for pressing and static implicit FEM for the unloading phase are adequate and economic for modeling of plate forming process by using FEM. The necessary material and frictional property data needed for the FEM process model were generated in-house. This model can be applied to design of dies and punches for forming the petals of large pressure vessels. The FEM process model predicts the final shape of the product and the residual cold work level for a given die, punch and plate configuration and this information can be used to correct the die and punch shapes for springback to manufacture the petals to the desired accuracy.