Papers by Keyword: AISI 4140

Abstract: Hot forging is a complex process involving the mutual influence of numerous thermo-mechanical-metallurgical material phenomena. In particular, the strains of transformation-induced plasticity (TRIP) have a significant influence on the distortions and residual stresses of the components. The TRIP strains refer to the anisotropic strains depending on the orientation and significance of the stress conditions during cooling superimposed to the phase transformation. With the use of numerical models, the impact of this effect can be investigated in order to ensure the production of high quality components. However, an experimental determination of the characteristic values of TRIP is challenging, which is why only few corresponding data are available in the literature. Therefore, this paper presents an experimental and numerical methodology as well as the results of studies on the interaction between stresses and phase transformations in the materials AISI 4140 and AISI 52100. The investigations of the TRIP strains are carried out using hollow specimens, which are thermo-mechanically treated in the physical forming simulator Gleeble 3800-GTC. The specimens are austenitised, quenched to test temperature and held there while diffusion controlled phase transformation takes place. The extent of TRIP as a result of different superimposed tensile or compressive loads is determined by means of dilatometry. In addition, the extent of TRIP for diffusionless martensitic phase transformations was investigated by continuous cooling tests under tensile and compressive loads. It was found that the transformation plasticity varies depending on the material, the phase type, the temperature and the tensile or compressive stresses. Subsequently, simulations of the physical experiments using the FE software Simufact.Forming verified the determined phase specific values of TRIP.

Abstract: Generating compressive residual stress states with high gradients and low penetration depths offers high capability regarding increase of fatigue limit of parts. In this work the determination of such specific residual stress distributions by using X-ray diffraction and a little material removal is introduced. Measurements are compared using two interference peaks of different penetration depths, at which confocal microscopy enables high accuracy in determination of the step sizes in electrochemical machining. Furthermore the realisation of these states by two different peening processes using micro blasting media is described. The suitability of the processes micro peening and ultrasonic wet peening as surface treatment methods to improve fatigue limit are shown. Micro peening is based on the shot peening principle with small shots and ultrasonic wet peening on the acceleration of small blasting particles by cavitation. The investigations were conducted at AISI 4140 in a quenched and tempered state. Besides the residual stresses and the integral width of interference peaks as well as the depth distributions, the surface topography was examined. The beneficial effects of these conditions on the fatigue limit in bending tests are described.

Abstract: Piezo peening is a new alternative mechanical surface treatment process. Thereby a piezo actuator with an indenter is causing mechanical deformation of the surface area by multiple impacts in a defined way. First results for quenched and tempered AISI 4140 show a great potential: large surface compressive residual stresses of up to -1200 MPa could be generated. In order to obtain a process understanding different process parameters are systematically changed. After the mechanical surface treatments the residual stress and full width at half maximum (FWHM) depth distribution were measured using X-ray diffraction technique. By varying the process parameters path distance, feed rate and amplitude several combinations of residual stress and FWHM depth distributions were generated. The dependency of surface residual stresses, penetration depth, FWHM on the process parameters is analyzed.

Abstract: The numerical modelling of heat treatment has become an essential tool in understanding distortion potentials for case hardening. When looking at other surface hardening processes such as induction or laser hardening, high heating and cooling rates automatically lead to higher strain rates during the heat treatment cycle. So far, there have been almost no investigations on the strain rate as well as temperature dependency of the mechanical properties of supercooled austenite. In this paper, the typical induction and laser hardening steel AISI 4140 has been used in order to determine the influence of strain rate and temperature on the mechanical behaviour. The experiments are based on tensile tests, using a specifically designed thermo-mechanical simulator. The experimental results show that a positive strain rate sensitivity for strain rates up to 1 s^-1 results. Especially in the temperature interval where austenite formation occurs during heating, the strain rate sensitive flow stress might lead to an alteration of the plastic strains in comparison to conventional heat treatments at low heating rates. The material model presented in this paper allows a good reproduction of the experimental data over a wide range of strain rates and temperatures.

Abstract: PCBN cutting tool is widely used in turning process and known as second best cutting tool after Diamond. This study investigates the suitability of PCBN cutting tool to cut variety types of steel. Experimental results for three major parameters which are cutting speed 150, 175 and 200 m/min, depth of cut 0.1, 0.2 and 0.3 mm, and feed 0.1, 0.2, and 0.3 mm/rev were converted into surface roughness analysis to look on the performance of PCBN to cut three different types of steels. The selected work materials of carbon steel AISI 1040, alloy steel AISI 4140 and tool steed AISI D2 were machined in dry tuning process with constant cutting length 50 mm and initial workpiece diameter 40 mm. At the end of this study, it is shown that higher cutting speed produced better surface roughness for AISI 1040 and AISI D2 but worsen the surface of AISI 4140. Low feed value is the most practical parameter to be used to produce fine surface finish using PCBN cutting tool. Fluctuate roughness value produced by increasing depth of cut use in turning parameters and no specific relationship can be concluded between depth of cut and surface roughness value.

Abstract: The objective of this research was to investigate cold work of alloy steel which was affected on scale in annealing process. Material used in the experiment was alloy steel, AISI 4140, that widely used in automotive industry and it have been annealing after cold forming operation. The experiment was conducted on four level of percentage of cold work, 0% - 30%. The annealing temperature was set up at three levels between 845– 900°C and three type of controlled atmosphere in annealing consist of normal atmosphere and reduction atmosphere with two inert gas, nitrogen and argon. The result was indicated that percentage of cold work affected to formation of scale, high percentage of cold work, more percent weight of scale. Furthermore, the controlled atmosphere in annealing with nitrogen can be producing less scale surface than reduction with argon and normal condition, respectively. Moreover, the scale was a few affected by temperature of heat treatment in annealing. High temperature could be produced more scale surface than low temperature in all percentage of cold work

Abstract: Shot Peening is a well established mechanical surface treatment to induce compressive residual stresses and work hardening into the surface layer of components exposed to cyclic loading. Due to the induced changes in the surface layer, the fatigue limit increases significantly. The concept of local fatigue strength is based on the comparison of the locally effective fatigue limit with locally active loads in order to estimate the maximum outer loading that will not exceed fatigue limit. In this paper an approach of using simulated surface characteristics after shot peening for the determination of the local fatigue strength will be presented. The complex stress distribution due to cyclic bending of notched geometries will also be determined by FEM. Finally the simulated estimation of the fatigue limit of differently notched specimens of AISI 4140 will be verified with experimentally determined fatigue limits.

Abstract: In a three-dimensional Finite-Element-Simulation of shot peening, a combined isotropickinematic viscoplastic material description was introduced in order to describe the cyclic softening effects during peening. After verifying the model in the simulation of push-pull tests at different strain amplitudes it could be used for the shot peening simulation. The simulated residual stress profile is compared with experimental results determined by X-ray diffraction and with simulated results of a simpler isotropic viscoplastic material model.

Abstract: Friction welding of dissimilar materials, Ni-base superalloy IN713LC and oil-quench plus tempered AISI 4140 steel, was investigated. Friction welding was carried out with various process variables such as friction pressure and time. The quality of welded joints was tested by applying bending stresses in an appropriate jig. Microstructures of the heat-affected zone (HAZ) were investigated along with micro-hardness tests over the friction weld joints. DEFORM-2D FE code was used to simulate the effect of welding variables in friction welding process on the distributions of the state variables such as strain, strain rate and temperature. The formation of the metal burr during the friction welding process was successfully simulated, and the temperature distribution in the heat-affected zone indicated a good agreement with the variation of the microstructures in the HAZ.