Papers by Keyword: Hot Working

Abstract: Ti-6Al-4V powder, produced by the hydride-dehydride (HDH) process, was hot isostatically pressed (HIP) into three bars. The 10 cm (4 in) diameter bars were hot worked (HW) to three different diameters: 5.1 cm (2 in) (75% reduction in area), 3.8 cm (1.5 in) (86% reduction in area), and 2.5 cm (1 in) (94% reduction in area). Three samples were machined out of each bar along the end, middle and transverse orientations. These samples were ground, polished, and etched. The microstructure of the samples was evaluated at 100X and 200X magnifications. The objective of this experiment was to examine the effect of deformation on the microstructure and properties of hot rolled titanium alloy bar product. Charpy impact samples were also machined out of each of the various diameter bars. Impact testing was used to quantify toughness by correlating the microstructure to the energy absorbed. The tensile properties of the hot bars were determined as well as the crystallographic texture. Scanning electron microscopy (SEM) was performed on the fractured surface of the Charpy impact samples.

Abstract: For the full characterization of the hot working behaviour of a given material a large number of laboratory experiments have to be performed. The experiments themselves are time consuming and the required specimen material can be quite expensive. With the increasing versatility of the testing machines, like dilatometry with easily variable temperatures, overthinking the classical approaches for materials characterization becomes expedient.In this paper a new technique for the reduction of the experimental effort is presented at the example of a 25MoCrS4 case hardening steel. To analyse the potential for the reduction of the experimental effort the classical approach of a full experimental test matrix is chosen. Here 55 flow curves with temperatures between 700 and 1200°C and strain rates from 0.01 to 100/s are experimentally determined. Then a semi-empirical model for strain hardening and dynamic recrystallization is fitted using an automated routine for parameter determination, taking all available flow curves into account. Subsequently, the number of flow curves used to fit the model parameters is gradually reduced. The model accuracy obtained with the reduced experimental data is compared to the initial fit. The natural decrease in accuracy with the use of less data compared to the gain due to the reduction of experimental effort is analysed. In addition optimal distribution of the sampling points in the experimental matrix for a reduced number of experiments is discussed. It is shown that less than a quarter of the full matrix is sufficient to reach accuracies comparable to using the full matrix. Using the vertices and symmetrical distribution of the data within the full experimental matrix allows a drastic reduction of experimental effort while maintaining the initial accuracy. The results suggest that it might be possible to reduce the costs and effort for material characterization by 50-80%.

Abstract: Thermo-Span alloy is an oxidation resistant, low thermal expansion superalloy with good mechanical properties at the service temperature. This paper investigated the hot working behavior of casting Thermo-Span alloy deformed at 900~1150°C, with strains of 20%, 40% and 60% at strain rates of 1 and 10 s^-1. Dynamic recrystallization (DRX) grains were formed at 1110°C with a strain of 20%, at 1050°C with a strain of 40%. Increasing the deformation rate and strain can promote the DRX. However, when the strain exceeded 60% or the deformation temperature was above 1150°C with 40% strain, the surface cracks occurred, indicating that the alloy should be deformed in one heat no larger than 60%. By forging and rolling at 1050°C, Thermo-Span alloy with good surface quality and homogeneous grains was produced, and the tensile properties were still acceptable.

Abstract: Bearing the gravity of rotary kiln barrel and the pressure between riding wheel and rolling ring, the surface defects appeared on casting large rotary kiln rolling ring, which caused large maintenance cost. While the life cycle of the rolling ring would be prolonged by using forging instead. The manufacture processing of large rotary kiln rolling ring was explored for changing casting to forging. The reasonable processing of smelting, forging and heat treatment were established.

Abstract: A new constitutive relationship based on the combination of the Garofalo and Hensel-Spittel equations has been developed and successfully used to model the plastic flow of a AA6082 aluminum alloy. Two regimes of temperature and strain rate were identified: the constitutive analysis suggested that in the low strain rate/high temperature regime, deformation was controlled by viscous glide of dislocations in atmospheres of Mg solute atoms, while in the high strain rate/ low temperature regime, deformation was controlled by climb.

Abstract: FeSi steels with and without addition of Al are widely used as electrical steels. To improve the knowledge of the effects by the addition of Si and Al on the hardening and softening under hot rolling conditions, the behaviour of the flow curves in a wide range of temperatures and deformation velocities have been studied.

Abstract: Gleeble 3500 thermo mechanical simulator was used to perform hot compression tests of GW103K (Mg-10Gd-3Y-0.6Zr) magnesium alloy at a temperature range of 573K-723K and strain rates of 0.001-1. The workability of the alloy can be evaluated by means of processing maps on the basis of dynamic materials model (DMM) and the superior processing condition is selected. Combining true compression stress-strain curves with the results of microstructure observation, it was found that the peak stress decreased observably as the decrease of strain rate and the increase of deformation temperature. Constitutive equation is built to reveal the accurate relationship among flow stress, temperature and strain rate.

Abstract: Hot working behavior of an aluminum alloy matrix composite reinforced with TiC particulates was investigated by a high temperature compression test. Power dissipation maps were constructed using a dynamic material model and the deformation mechanism was investigated by means of an EBSD analysis. The interrelationship between the microstructure evolution and the efficiency of power dissipation was derived and the roles of TiC particles and other constituent phases in determining processing maps were further discussed.

Abstract: A titanium alloy with the composition of Ti-Al-Sn-Zr-Mo-V-Si-Cr, named Ti-62A alloy, were rolled into thick plates by four different routes, followed by solution heat treated and aging treated. Effects of various rolling routes and heat treatment processes on tensile properties, fracture toughness and resistance to fatigue crack growth were investigated. The results reveal that a rolling heats above β-transus before final rolling pass is helpful to improve comprehensive properties. The properties of Ti-62A alloy can be adjusted in a large range depending on heat treatment.

Abstract: The dynamic recrystallisation (DRX) behaviour of magnesium AZ31 is investigated using a plane strain compression (PSC) testing machine at 450°C. The variables included strain rate, double hit including intermittent anneal and double hits with different strain rate at each hit. The alloy shows higher peak stress and strain with increasing strain rates. Predominant basal texture with different intensities are observed at different strain rates. The annealing treatment between double tests leads to strong basal texture. Reversal of strain rate during double hit results in similar flow curves. This shows that in AZ31 alloy, DRX mechanism is independent of the initial microstructure and only depends on the test condition viz. temperature, strain rate and total equivalent strain.