A. Śmiglewicz

Analysis of Substructure of High-Mn Steels in the Context of Dominant Stress Mechanism

In last ten years, leading research centers have been directed to the development of high-Mn steels for manufacturing of parts for automotive industry. The discussed steels with different values of Mn, Al, and Si addition have a medium value of EBU. They usually demonstrate a dominant stress mechanism like twinning induced plasticity TWIP. During the plastic deformation, they may demonstrate a two stress mechanisms like sliding and twinning. The paper presents the results of an analysis of the substructure of high manganese steel after deformation by cold rolling in the context of dominant stress mechanism. The substructure was analyzed by scanning transmission electron microscopy. In the steels, close weaves of dislocations, dislocations tangles, twins and microtwins were observed. It was revealed that the detailed analysis of substructure of the investigated steels after cold deformation could be helpful in determination of the dominant stress mechanism. The obtained results may be used for development of these steels and their plastic deformation models.

Heat treatment of high manganese type X57MnAl27-5 austenitic steel

In the paper, the influence of heat treatment parameters on microstructure and mechanical properties of high manganese type X57MnAl27-5 austenitic steel was investigated. The as-forged bar with diameter of 15 mm were underwent a saturation process at six different temperatures. The microstructural changes of austenite and the influence of heat treatment on the mechanical properties were considered. The quantitative analysis of austenite phase of the examined steel indicated that the parameters of saturation process resulted in changes of morphology and grain size of austenite. It was revealed that treatment temperature in the range of 950 °C-1100 °C slightly influenced grain size, stress limit and hardness of the investigated steel. Treatment at temperature higher than 1150 °C resulted in the growth of austenite grain size and the decrease of mechanical properties.

Study of Phase Transformation in Alloys of the Al-Fe System

In this paper, phase transformation in alloys of the Al-Fe and Al-Fe-Cr systems was investigated. The alloys were prepared by melting and gravity casting. The studies of phase transformation were carried out on samples after casting and annealing, using the differential thermal analysis (DTA) and dilatometric method. The knowledge on the phase transformations in these alloys including the information about order-disorder transition is very important from the point of view of obtained mechanical and physical properties of alloys of the Al-Fe system. These results are an important contribution in development of knowledge on iron aluminides. In the article, temperatures of phase transformations connected with a change in order type and transition into disordered solid solution were defined. Conformity of the recorded DTA results and dilatometric analysis was achieved.

Thermal Expansion of Alloys from the Al-Fe System

In this work, the results of a dilatometric study of alloys on the base of the Al-Fe system were presented. Thermal expansion investigations of the alloys of the Al-Fe system with concentration of Al equal to - 38, 48, 58 at.% were also presented. The alloys were obtained by classical casting technique. The thermal expansion studies of the alloys were carried out by dilatometric analysis method using a Setsys thermal analyzer made by Setaram. A linear thermal expansion coefficient α was calculated using standard methods. A temperature dependence of the α coefficient was noted. The results are an important supplement of knowledge on the alloys of the Al-Fe system.

Influence of Strain Rate Effects on the Structure and Mechanical Properties of the Fully Austenitic High Mn Steels under Dynamic Impact Deformation

The article presents the dynamic mechanical properties of two types of high manganese austenitic steels. The investigation were carried out for the wide range of strain rates from 1×10-4s-1 up to 4×103s-1 using servo-hydraulic testing machine and Hopkinson bar for the quasi-static and dynamic loading regime, respectively. The mechanical properties at different strain rates as well as the SEA indicator calculated were carried out on the base of the results of impact tests. In the next step, the microstructure of the steel after different deformation rate was observed and analyzed by light microscope in order to disclose a TWIP effect.

The Effect of High Strain Rate on Properties and Microstructure of the Fully Austenitic High Mn Steel

In the paper, results of impact bending tests of a high-manganese steel of X30MnAlSi26-4-3 grade are presented. The tests were carried out using a flywheel machine, suitable for dynamic tensile tests and impact bending tests in the range of linear velocity of the forcing element from 5 ÷ 40 m/s. The obtained test results were compared with the results of impact resistance of the studied steel determined using Charpy machine. Structural investigations were carried out using light microscope and scanning transmission electron microscopy. Creating a mechanical twins at different strain rates was analyzed. The surfaces of fractures formed in the break point during bending tests were analyzed, and they indicate a presence of mixed transcrystalline fractures with a predominance of plastic fractures. Substructure studies revealed the presence of mechanical twinning induced in a high strain rate for the X30MnAlSi26-4-3 steel.

Microstructure and Mechanical Properties of High Manganese TWIP Steel after Thermo-Forming Processes

In recent years, the leading scientific centres focus their research on improvement of mechanical properties of steels used for car manufacturing. These steels belong to a so-called 2nd generation of steels showing above-the-average plasticity while maintaining high strength. Thanks to these properties, they may be used successfully in automotive, armaments or railway industries for elements absorbing energy of a collision and ensuring high rigidity of a structure owing to their resistance to breaking. These steels are called TWIP (Twinning Induced Plasticity) steels based on their hardening mechanism. In this paper, results of studies on the influence of parameters of thermo-plastic deformation on selected properties and structure of an X45MnAl20-3V austenitic steel showing the TWIP effect are presented. Moreover, an analysis of influence of the deformation on the structure of the studied steel in tensile tests has been carried out. The studied steel was manufactured by classic casting to a concast mould, obtaining ingots with dimensions of 100×100 mm, then subjected to rolling in 4 roll passes to a final thickness of 12 mm and 3 mm. The finish-rolling temperature was 950°C and the sheets were cooled in 2 media, i.e. in air and in water. It was confirmed that the studied steel belongs to the TWIP group of steels, with mechanical twinning being the prevailing process of hardening during deformation.