The study presents the effect of annealing process parameters on the microstructure, hardness, and strain-hardening coefficients, that is, the strength coefficient c and the strain-hardening exponent n, of 42CrMo4 steel. Seven selected annealing time–temperature schemes are examined for superior steel formability in cold metal forming conditions. The c and n coefficients are first determined in experimental upsetting of annealed samples and then used in FEM (finite element method) simulations of the upsetting process. The results demonstrate that the strain-hardening coefficients (c and n) depend on the employed annealing scheme. Compared with the as-received sample, the annealing process reduces the true stress and effectively decrease the hardness of 42CrMo4 steel; improves microstructural spheroidization; and, consequently, facilitates deformability of this material. The annealing schemes, relying on heating the material to 750 °C and its subsequent slow cooling, lead to the highest decrease in hardness ranging from 162 to 168 HV. The results obtained with the SEM-EDS (scanning electron microscopy-energy dispersive spectrometer), LOM (light optical microscopy), and XRD (X-ray diffraction) methods lead to the conclusion that the employed heat treatment schemes cause the initial ferritic-pearlitic microstructure to develop granular and semi-lamellar precipitation of cementite enriched with Mo and Cr in the ferrite matrix. In addition, the annealing process affects the growth of α-Fe grains. The highest cold hardening rate, and thus formability, is obtained for the annealing scheme producing the lowest hardness. The results of FEM simulations are positively validated by experimental results. The obtained results are crucial for further numerical simulations and experimental research connected with developing new cold metal forming methods for producing parts made of 42CrMo4 steel.

The paper describes a new method for producing stepped rail axles. The method is based on the skew rolling process. With this method, the product is formed by three tapered rolls located every 120• on the perimeter of the billet. Positioned askew to the centerline of the billet, the rolls rotate in the same direction and with the same velocity. At the same time, they get closer together or go apart depending on the desired cross sectional reduction of an axle step. In addition, the workpiece is shifted lengthwise relative to the rolls by the translational motion of the workpiece-holding chuck. In order to verify the designed method for producing rail axles, a series of numerical simulations were performed using the Simufact.Forming v.12 simulation software. The numerical modeling enabled the determination of maps of the effective strain and temperature in the finished product as well as variations in the loads and torques during rolling. The numerical results unambiguously confirm that the skew rolling method can be applied to form parts of considerable dimensions (the modeled axles had a length of 2146 mm and their maximum diameter was 202 mm).Keywords: Skew rolling, rail axle, FEM W artykule opisano metodę wytwarzania stopniowanej osi wagonowej bazującą na procesie walcowania skośnego. W metodzie tej wyrób kształtowany jest za pomocą trzech rolek stożkowych, rozmieszczonych na obwodzie wsadu co 120• . Rolki te ustawione są skośnie względem osi wsadu, a w trakcie kształtowania obracają się z jednakową prędkością w tę sa-mą stronę oraz jednocześnie zsuwają lub rozsuwają się -w zależności od redukcji przekroju poprzecznego kształtowanego stopnia osi. Dodatkowo, wyrób kształtowany przesuwany jest wzdłużnie względem rolek, w wyniku ruchu postępowego uchwytu utwierdzającego jeden z jego końców. Sprawdzenia poprawności założonej koncepcji kształtowania osi wagonowej dokonano w drodze symulacji numerycznej wykonanej w programie Simufact.Forming v.12. W efekcie wykonanych obliczeń uzyskano mapy intensywności odkształcenia i temperatury w ukształtowanym wyrobie oraz wyznaczono przebiegi sił i momentów w trakcie walcowania. Jednoznacznie potwierdzono możliwość kształtowania wyrobów o dużych gabarytach (długość osi wynosi 2146 mm, a jej średnica maksymalna 202 mm) metodą walcowania skośnego.

No abstract

This paper presents the results of a numerical analysis of a cold forging process for a hollow flanged part. The analysis was performed using Deform 2D/3D. 42CrMo4 steel tubes were used as the billet material, and their material model in the annealed state was described by a constitutive equation. The forming process was performed in six stages with the use of methods such as extrusion with a movable sleeve, open-die extrusion, and upsetting. The objective of the study was to determine whether the proposed forging technique could be used to produce hollow parts with flanges. The determination was made based on the analysis of product geometry quality and process parameters, including the Cockcroft-Latham ductile fracture criterion and forming forces.

No abstract