Prediction of Ductile Fracture Behaviors for 42CrMo Steel at Elevated Temperatures

Abstract

The ductile fracture behaviors of 42CrMo steel are studied by hot tensile tests with the deformation temperature range of 1123-1373 K and strain rate range of 0.0001-0.1 s 21 . Effects of deformation temperature and strain rate on the flow stress and fracture strain of the studied steel are discussed in detail. Based on the experimental results, a ductile damage model is established to describe the combined effects of deformation temperature and strain rate on the ductile fracture behaviors of 42CrMo steel. It is found that the flow stress first increases to a peak value and then decreases, showing an obvious dynamic softening. This is mainly attributed to the dynamic recrystallization and material intrinsic damage during the hot tensile deformation. The established damage model is verified by hot forging experiments and finite element simulations. Comparisons between the predicted and experimental results indicate that the established ductile damage model is capable of predicting the fracture behaviors of 42CrMo steel during hot forging.

Damage in metal forming

“…The free surface cracks that may form on the surface undergoing free expansion are well predicted, showing that the minimization of the aspect ratio of the anvil edge geometry can minimize the surface crack generation. Also in [120], the effect of temperature and strain rate is incorporated into the critical damage variable of the normalized Cockcroft and Latham failure criterion to assess the fracture occurrence during a hot forging process, showing its capability to predict failure where the workpiece comes in contact with the die's corners (Fig. 23).…”

Numerical and experimental investigation of notch-induced high-speed precise shearing of 42CrMo bar

“…A modified Cockcroft-Latham model was applied as a fracture criterion, by introducing strain rate function H(ln⁡ε˙) 25 where sup⁡(σ1,σ2,σ3) is the maximum principal stress, σeq is the equivalent stress, trueε¯p is the equivalent plastic strain, trueε¯f is the equivalent fracture strain. And the function H(ln⁡ε˙) was derived by fitting fracture strains at different strain rates, 25 which were recorded by a 2 D strain measuring system based on a high-speed camera.…”

Experimental and FEM Analysis of Void Closure in the Hot Cogging Process of Tool Steel

“…The void closure process during forging in V-shaped anvils with an impression angle of 130° × 130° is shown in Figure 3. The process conditions in the FE simulation and some thermal physical properties of the workpiece were as follows: (1) The friction factor between the billet and the anvil was 0.7 (the friction factor was determined from additional ring compression tests); (2) The reduction ratio varied from 0.01 to 0.35 with an interval of 0.01 (the reduction ratio is defined as lnh1/h, where h and h1 are the height of the initial and the deformed billet, respectively); (3) The feed rate amounted to 0.75 in each pass; (4) The environment temperature was 293 K; (5) The initial forging temperature was 1373 K; (6) The initial anvils temperature was 573 K; (7) The convection coefficient to the environment was 0.02 N/(s•mm•°C); (8) The heat-transfer coefficient between the deformed billet and the anvils was 5 N/(s•mm•°C); (9) The anvil pressing speeds were 10 mm/s and 50 mm/s for the billet and the ingot, respectively.…”

“…The structure and properties of a billet shaped by means of the forging method are determined by the properties of the initial ingot and by the parameters of the technological process. The internal defects of ingots, such as porosity, internal voids, and damage ought to be removed in the course of the forging process or to be reduced to the greatest possible degree [1][2][3]. Computer simulations based on the finite-element method (FEM) have become a popular tool for the investigation of the void closure process in forging processes [4][5][6].…”