This paper describes a study of explosively welded titanium-carbon steel S355J2+N plates. Following the welding, plates underwent heat treatment at temperature of 600 °C for 90 min with cooling in furnace to 300 °C and in air to room temperature. The structure of the bonding was examined by using light, scanning electron (SEM) and transmission electron microscopy. The mechanical properties before and after heat treatment were examined applying three-point bending tests with cyclic loads and hardness measurements. Fracture surfaces were investigated using computer tomography and SEM. It has been found that the bonding areas are characterized by a specific chemical composition, microstructure and microhardness. Between the steel and the Ti cladding, a strongly defected transition zone was formed and melted areas with altered chemical composition were observed. It was also demonstrated that the heat treatment commonly applied to welded steel-Ti plates had a significant and negative impact on the microstructure and mechanical properties of the welded plates due to formation of brittle intermetallic phases.

The paper presents the results of measurement thermal diffusivity temperature characteristic of the Titanium Grade 1 (Ti Grade 1, with density 4.34 g/cm³ at RT) in wide temperature range from (-)60 ℃ to (+)1100 ℃. Two kinds of the Netzsch laser flash apparatuses for the measurement of thermal diffusivity and conductivity were used, i.e. the low temperature LFA 467 and the high temperature LFA 427. As a reference material a sample from a stainless steel A310. Reference material was used to verify the test results of thermal diffusivity and to determine the thermal conductivity by the comparative method. The results of the thermal diffusivity tests of the Titanium Grade 1 performed by means of LFA 467 and LFA 427 apparatuses showed to be consistent to each other. In calculation of the thermal diffusivity and thermal conductivity temperature characteristics the influence of thermal expansion of the tested material was taken into account. Tests of temperature characteristics of thermal diffusivity of Ti Grade 1 showed the occurrence of structural change during the first heating at a temperature of about 890 °C. This effect has been confirmed by thermal expansion studies, which were carried out in the range from room temperature (RT) up to 1100 °C using the Netzsch high temperature dilatometer DIL 402.

Nowadays high strength steels are gained increasing popularity for use in steel constructions and machinery components. Their fatigue properties, however, are not yet well characterized, especially in comparison with widespread conventional structural steel S355J2. In this study were conducted the assessment of use HSS steel in extremely loaded components with existing plastic strains. In order to obtain the necessary characteristics and fatigue properties, materials were tested under LCF strain-based mode with strain ratio Rɛ = 0,1 and strain rate of 10-2 1/s. Because of its higher strength, S960QL steel exhibits a slightly higher fatigue resistant under the total strain amplitude lower than 0,5% compared to mild steel and similar under higher strains. Obtained results show that investigated HSS steel can successfully supersede presently used conventional mild steel in heavily loaded components simultaneously decreasing dead weight of the structure

The full benefits of application the high strength low alloyed steels HSLA can be achieved if the structures will be able to carry the alternate loads and fatigue cracks will not be formed, even in the vicinity of welded joints. For this reason the purpose of this study is to find and to explain the influence of different factors on fatigue crack initiation and the nature of crack propagation in HSLA steel and its welded joints. The S960QL steel and two types of welded joints were subjected to low cycle fatigue (LCF) tests at a strain mode and the received surfaces of fractures were analyzed using SEM microscope. Additionally, the microhardness measurements and the residual stress analyze in a cross-section of the joint were conducted. The maximum hardness was determined on the fusion line and more favorable hardness distribution was in the square joints than in single-V. Compiled maps of residual stresses have shown that the local orientation and values of the principal stress vector near the fusion line can influence negative the fatigue life. Finally, the square joints tested in the low cycle fatigue regime have shown a slightly higher fatigue life in comparison with single-V.

In the study, there were investigated the effects of friction stir processing (FSP) which was applied in order to improve the surfaces of notched specimens made of S235JR and S355J2 carbon steels, on their fatigue crack growth rates in the air. There were presented the results of comparative fatigue tests conducted at asymmetric tension (R= -0.2) for these steels treated by means of FSP and for the ones in the delivery state. The method of successive etched material layers used revealed the presence of internal tensile stresses in the surface layers of treated specimens. Crack growth rates were described on the basis of non-linear fracture mechanics, taking the effects of internal stresses into account.

The aim of this research was to examine the mechanical and fatigue properties of friction stir welded Sc-modified 5 mm thick AA2519-T62 extrusion. The joint was obtained using the following parameters: 800 rpm tool rotation speed, 100 mm/min tool traverse speed, 17 kN axial, and MX Triflute as a tool. The investigation has involved microstructure observations, microhardness distribution analysis, tensile test with digital image correlation technique, observations of the fracture surface, measurements of residual stresses, low cycle fatigue testing, and fractography. It was stated that the obtained weld is defect-free and has joint efficiency of 83%. The failure in the tensile test occurred at the boundary of the thermo-mechanically affected zone and stir zone on the advancing side of the weld. The residual stress measurements have revealed that the highest values of longitudinal stress are localized at the distance of 10 mm from the joint line with their values of 124 MPa (the retreating side) and 159 MPa (the advancing side). The results of low cycle fatigue testing have allowed establishing of the values of the cyclic strength coefficient (k′ = 504.37 MPa) and cyclic strain hardening exponent (n′ = 0.0068) as well as the factors of the Manson–Coffin–Basquin equation: the fatigue strength coefficient σ′_f = 462.4 MPa, the fatigue strength exponent b = −0.066, the fatigue ductility coefficient ε′_f = 0.4212, and the fatigue ductility exponent c = −0.911.