The heat input into the material during welding significantly affects the properties of high-strength steels in the near-weld zone. A zone of hardness decrease forms, which is called the soft zone. The width of the soft zone also depends on the cooling time t_8/5. An investigation of the influence of welding parameters on the resulting properties of welded joints can be performed by thermal physical simulation. In this study, the effect of the cooling rate on the mechanical properties of the heat-affected zone of the steel S960MC with a thickness of 3 mm was investigated. Thermal physical simulation was performed on a Gleeble 3500. Three levels of cooling time were used, which were determined from the reference temperature cycle obtained by metal active gas welding (MAG). A tensile test, hardness measurement, impact test with fracture surface evaluation, and microstructural evaluation were performed to investigate the modified specimen thickness. The shortest time t_8/5 = 7 s did not provide tensile and yield strength at the minimum required value. The absorbed energy after recalculation to the standard sample size of 10 × 10 mm was above the 27 J limit at −40 °C. The hardness profile also depended on the cooling rate and always had a softening zone.

The welding of fine-grained steels is a very specific technology because of the requirement for the heat input limit value. Applying temperature cycles results in an intense grain growth in a high-temperature heat-affected zone (HAZ). This has a significant effect on the changing of strength properties and impact values. The intensity of grain coarsening in the HAZ can be predicted based on the experimentally determined activation energy and material constant, both of which define grain growth kinetics. These quantities, together with real measured welding cycles, can be subsequently used during experiments to determine mechanical properties in a high-temperature HAZ. This paper shows a methodical procedure leading to the obtainment of the material quantities mentioned above that define the grain growth, both at fast and slow temperature cycles. These data were used to define the exposure temperature and the soaking time in a vacuum furnace to prepare test samples with grain sizes corresponding to the high-temperature HAZ of welded joints for the testing procedures. Simultaneously, by means of the thermo-mechanical simulator Gleeble 3500, testing samples were prepared which, due to a temperature gradient, created conditions comparable to those in the HAZ. The experiments were both carried out with the possibility of free sample dilatation and under a condition of zero dilation, which happens when the thermal expansion of a material is compensated by plastic deformation. It has been found that shape of the temperature cycle, maximal achieved cycle temperature, cooling rate, and, particularly, the time in which the sample is in the austenite region have significant effects on the resulting change of properties.

The nickel-iron-based alloy Inconel 718 is a progressive material with very good mechanical properties at elevated and lower temperatures. It is used both as wrought and cast alloys as well as material for additive manufacturing technologies. This is the reason why it has received so much attention, as supported by numerous publications. However, these are almost exclusively focused on a specific type of production and processing, and thus only report differences in the mechanical properties between samples prepared by different technologies. Therefore, the major aim of this research was to show how the structure and mechanical properties differ between samples produced by conventional production (wrought alloy) and additively manufactured SLM (Selective Laser Melting). It is shown that by applying appropriate heat treatment, similar strength properties at room and elevated temperatures can be achieved for SLM samples as for wrought samples. In addition, the mechanical properties are also tested up to a temperature of 900 °C, in contrast to the results published so far. Furthermore, it is proven that the microstructures of the wrought (here rolled) and SLM alloys differ significantly both in terms of grain shape and the size and distribution of precipitates.

The article presents the results of research on the influence of temperature and time changes of the annealing process on the values and distribution of stresses in the simulated heat-affected zone of S700MC steel welded joints. For this purpose, tests were carried out on a thermal cycle simulator, as well as heating the prepared samples in accordance with the recorded welding thermal cycles, and then annealing at temperatures from 200 to 550 °C. The stresses values in the tested samples before and after the annealing process were measured by using X-ray diffraction (XRD). The performed tests were verified with the results of numerical analyses using the finite element method (FEM) performed in the VisualWeld (SYSWELD) environment as, on the one hand, the verification of the obtained results, and, on the other hand, the source of data for the development of a methodology for conducting analyses of heat treatment processes of S700MC steel welded structures. Also presented are three examples of numerical analyses for Gas Metal Arc (GMAW), laser and hybrid welding and then the annealing process of the obtained joints at selected temperatures. The main purpose of the work was to broaden the knowledge on the influence of annealing parameters on the values and distribution of stresses in welded joints, but also to signal the possibility of using modern software in engineering practice.

High-strength steels are used more than general structural steel due to their combination of properties such as high strength, good toughness and weldability. They are mainly used in the manufacture of heavy vehicles for the mining industry, cranes, transportation, etc. However, welding these grades of steel brings new challenges. Also, a simulation for welding high-strength steel is required more often. To insert a material database into the simulation program, it is necessary to conduct investigations using CCT (Continuous Cooling Transformation) diagrams, welded joints research, and more. To investigate the behavior of S960MC steel during heating and cooling, we used dilatometry analysis supported by EBSD (Electron Backscatter Diffraction) analysis. A CCT diagram was constructed. The transformation temperatures of A_c1 and A_c3 increase with increasing heating rate. The A_c1 temperature increased by 54 °C and the A_c3 temperatures by 24 °C as the heating rate increased from 0.1 °C/s to 250 °C/s. The austenite decomposition temperatures have a decreasing trend in the cooling phase with increasing cooling rate. As the cooling rate changes from 0.03 °C/s to 100 °C/s, the initial transformation temperature drops from 813 °C to 465 °C. An increase in the cooling rate means a higher proportion of bainite and martensite. At the same time, the hardness increases from 119 HV10 to 362 HV10.

In this work, benefits of combining modern software for numerical simulations of welding processes with laboratory research was described. Proposed new method of processing heat treatment experiments leading to obtaining relevant input data for numerical simulations of heat treatment of large parts was presented. It is now possible, by using experiments on small tested samples, to simulate cooling conditions comparable with cooling of bigger parts. Results from this method of testing makes current boundary conditions during real cooling process more accurate, but also can be used for improvement of software databases and optimization of a computational models. The point is to precise the computation of temperature fields for large scale hardening parts based on new method of temperature dependence determination of the heat transfer coefficient into hardening media for the particular material, defined maximal thickness of processed part and cooling conditions. In the paper we will also present an example of the comparison standard and modified (according to newly suggested methodology) heat transfer coefficient data's and theirs influence on the simulation results. It shows how even the small changes influence mainly on distribution of temperature, metallurgical phases, hardness and stresses distribution. By this experiment it is also possible to obtain not only input data and data enabling optimization of computational model but at the same time also verification data. The greatest advantage of described method is independence of used cooling media type.