No abstract

Isothermal compression tests are carried out on 20CrMnTiH steel using a Gleeble-1500 thermal simulator in the temperature range of 1223–1423 K and in the strain rate range of 0·01–10 s−1. The flow behaviours of 20CrMnTiH steel are described, which are based on the analysis of true stress–true strain curves. The effects of hot deformation on the microstructure are investigated. The results show that there is a typical dynamic recrystallisation behaviour during deformation. A constitutive model coupling flow stress with strain, strain rate and temperature to 20CrMnTiH steel is proposed using a hyperbolic sinusoidal type equation. In the constitutive equation, the material constants α, n, ln  A and Q are found to be functions of strain. The validity of the constitutive equation is assessed by the correlation coefficient ( r), the average absolute relative error and the mean squared error.

The laser scanning parameters used in laser additive manufacturing (LAM) can impact the growth direction of the columnar grains produced during rapid solidification. This growth direction affects the mechanical properties of the manufactured parts after cladding. The effective use of a high laser power and a rapid scanning speed for LAM requires an accurate analysis of the relationships between the laser scanning process parameters and the grain growth direction and microstructural morphology of the scanned material. An experimental study was conducted to determine the macromorphology, microstructural morphology, and grain growth direction of 304 stainless steel material obtained during the laser scanning process at different scan speeds. The impact of the scan speed on different regions in the cladding layer (the clad zone (CZ), the heat affected zone (HAZ), and the dilution zone (DZ)) was determined, as well as on the direction of grain growth, the grain morphology and the grain size (which are the microstructures of the cladded materials), the degree of elemental mixing during laser scanning (which are changes in material composition of cladded material), and the microscopic hardness of the CZ (which is one of the mechanical properties of cladded material). With increasing scan speed, the CZ, HAZ, DZ, and dilution rate (DR) of the material gradually decreased, and grain growth gradually oriented towards the building direction of the cladding layer. At a 16 mm·s−1 scan speed, the angle between the grain growth direction and the scan direction was 84°. Changing the scan speed from 4 to 16 mm·s−1 caused the columnar grain size to gradually decrease from 13.3 to 9.2 μm and the corresponding microhardness to gradually increase.

No abstract

The hot deformation behavior of the 40MnBH alloy is investigated by isothermal compression tests at the temperature of 900–1200 °C with the strain rate of 0.05, 0.5, and 5s−1, and the degree of compression ranging from 15 to 60%. The effects of deformation parameters are studied through the true stress–strain curve under different deformation conditions. The processing maps are constructed based on the dynamic material model. Microstructures of 40MnBH steel at different deformation conditions are observed. The results show that the stress of the alloy has a dependence on strain rate and deformation temperature. A constitutive model is built, which described the flow stress behavior of the alloy. The processing maps reveal that with the increase in the degree of compression, the instability regions decrease. The results of processing maps have been verified through the microstructures of the 40MnBH steel.