This work investigates and compares the fatigue performance of laser-welded joints of two press hardening steels: a standard 22MnB5 and a variant modified by a combination of niobium and molybdenum (NbMo) alloying. The results indicate that joint geometry aspects, superposed to an intrusion-generated damage mechanism, were prevalent in causing a poor fatigue life in the case of peak stress values greater than 11% of the base metal's ultimate strength being around 1450 MPa. As identical process procedures were employed, the tests allowed investigating the influence of the alloy design on fatigue performance. The results of geometrical analysis and fatigue tests indicated that the NbMo modified alloy performed better than the standard 22MnB5 steel. The results also suggest that, if extremely tight quality limits are used in the manufacturing procedures, laser-welded joints of press hardened steels could offer a very favorable fatigue performance being considerably better than that of conventional and high strength structural steels.

The application of press hardening steels is spreading from automobiles, where crashworthiness demands are critical, to other segments, such as the agricultural and road transport industries. However, the operational conditions to which such equipment is exposed requires the application of heavier sheet gages and adapted joining processes. In this context, fatigue is recognized as the critical failure mode. The present article describes the procedures and results of fatigue testing performed on GMAW-CSC and PAW butt-welded specimens of 1500 MPa press hardening steel. Both methods are suitable alternatives to laser welding when joining relatively heavy-gaged components. The obtained fatigue results are also related to heat-affected zone characteristics and weld bead surfaces. Additionally, some ground-flush GMAW-CSC specimens were tested. The test results indicate that both welding procedures provide suitable fatigue performance. As-welded GMAW-CSC joints on this ultra-high strength steel accomplished a fatigue performance similar to welds of conventional steel. However, a remarkable performance increase was observed after flush grinding the weld beads. The plasma welding process presented less good results due to the more extensive manufacturing and geometric variability. The results indicate that adopting a suitable arc welding process, in association with post-weld geometry improvement, provides a fatigue performance that is competitive with laser-welded press hardening steels.

Manufacturing operations produce surface characteristics that, although stochastic, can significantly affect functionality, especially in forming tools, impacting contact and lubrication conditions during operation. This study investigates the influence of stochastic microtextures resulting from milling on the tribological performance of cold work tool steels with two different carbon contents (0.8 and 2 wt%). Different surface textures were observed resulting from the different C contents, with 3D roughness parameters indicating rougher surfaces for the 2.0% wt. C steel. Tribological behavior was assessed using the strip drawing test to analyze friction, wear coefficients, and wear mechanisms. Surface analysis before and after testing was executed employing SEM, EDX, and CLSM, with CLSM also used to determine 3D roughness parameters of the worn tracks. Post-test macrographic analyses and 2D roughness measurements were conducted on the pulled sheets. Tribological test data revealed lower friction and wear coefficients for the 2.0 wt% C tool steel, with susceptibility to abrasion wear, while the 0.8 wt% C tool exhibited a higher tendency towards adhesion wear. Post-test analysis suggested smoother surfaces for the 2.0 wt% C steel compared to the 0.8 wt% C steel. Macrographic analysis showed no visible wear marks on sheets tested with the 2.0 wt% C steel, contrasting with wear grooves visible on sheets pulled against the 0.8 wt% C steel. Additionally, 2D roughness measurements indicated higher roughness after pulling against the 0.8 wt% C tool compared to the 2.0 wt. C tool. Overall, the study demonstrates that manufacturing-induced textures without the need of post-manufacturing texturing influence the tribological performance of the evaluated steels, opening an avenue to be explored to improve the tribological performance of forming tools.

This study evaluates the effect of through-tool high-pressure coolant (HPC) on internal boring of ST52-3 steel under production-representative industrial conditions, focusing on tool wear, cutting power, surface finish, and chip evacuation. Conventional flood cooling at 20 bar was compared with through-tool HPC at 25, 40, and 50 bar in an industrial machining line. Cutting speed and depth of cut were kept constant ( v _c = 220 m/min, a _p = 3 mm), while the feed was increased in the HPC trials (from 0.194 to 0.265 mm/rev) to assess whether HPC could sustain more severe and potentially more productive conditions. The results showed that HPC significantly delayed flank-wear progression: the VB growth rate decreased from 0.01220 mm·part⁻¹ under conventional cooling to 0.00486, 0.00405, and 0.00311 mm·part⁻¹ at 25, 40, and 50 bar, respectively, revealing diminishing returns beyond about 40 bar. Extended tests further showed that the 40 bar condition maintained consistently lower wear up to 65 machined parts. In addition, HPC at 40 and 50 bar reduced cutting power, while 40 bar provided the most consistent chip fragmentation and evacuation. Surface roughness met the component specification after run-in for all HPC conditions, and the 40 bar condition satisfied the requirement from the first checkpoint. Overall, the study shows that through-tool HPC can improve the robustness of industrial internal boring under more demanding cutting conditions, with ~ 40 bar providing the best overall balance between tool-life extension, energetic stability, surface-finish compliance, and chip control.