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Ricercatore t.d. art. 24 c. 3 lett. B
Dipartimento di Ingegneria "Enzo Ferrari"

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2024 - A methodology to reduce the computational effort in 3D-CFD simulations of plate-fin heat exchangers [Articolo su rivista]
Torri, Federico; Berni, Fabio; Giacalone, Mauro; Mantovani, Sara; Defanti, Silvio; Colombini, Giulia; Bassoli, Elena; Merulla, Andrea; Fontanesi, Stefano

The analysis of a plate-fin heat exchanger performance requires the evaluation of key parameters such as heat transfer and pressure drop. In this regard, computational Fluid Dynamics (CFD) can be proficiently adopted, at the design stage, to predict the performance of plate-fin heat exchangers. However, these last are often characterized by a complex geometry, such as in the case of plate exchangers with turbulators, leading to a huge computational effort, which often exceeds the available resources. In this study, a numerical methodology for the simulation of plate heat exchangers is proposed, to bypass the limits imposed by the computational cost. The methodology relies on the simulation of a minimal portion of the exchanger (two plates, one per fluid) characterized by periodic boundary conditions (that mimic the presence of several layers). The total heat exchanged is obtained simply multiplying the calculated heat transfer by the number of plate couples composing the device. Moreover, the two plates allow to calibrate porous media which are adopted to rebuild (in a simplified version) the two fluid circuits of the whole exchanger and obtain the overall pressure drop across the device for both the hot and cold fluids. The proposed approach is validated against experimental data of an oil cooler for automotive application, that is a plate-fin heat exchanger characterized by the presence of turbulators. The numerical outcomes are compared to the experiments in terms of pressure drop and heat transfer for a wide range of volumetric flow rates. Particular attention is devoted to the mesh sensitivity and the adopted computational grid minimizes the number of cells (and, thus, the computational cost), without compromising the accuracy. Moreover, the Reynolds-Stress-Transport turbulence model is accurately selected among the most diffused ones, in order to properly match the test bench data. The proposed methodology allows to reduce of nearly one order of magnitude the total number of cells required for the simulation of the heat exchanger performance. The heat transfer is predicted with high accuracy, i.e. error is always lower than 4%. As for the pressure loss, the deviation compared to the experiments increases up to nearly 15% (for one of the simulated conditions) but it is considered still acceptable.

2024 - Additive Manufacturing of Locally Weakened Parts to Obtain a Designed Fracture [Articolo su rivista]
Galati, Manuela; Defanti, Silvio

2024 - Dimensional and Mechanical Assessment of Gyroid Lattices Produced in Aluminum by Laser Powder Bed Fusion [Relazione in Atti di Convegno]
Defanti, Silvio; Giacalone, Mauro; Mantovani, Sara; Tognoli, Emanuele

The study investigates the use of aluminum gyroid lattices for structural purposes, with a particular focus on feasibility, dimensional accuracy, and compressive load performance. Gyroid lattice samples were built using laser powder bed fusion technology with AlSi10Mg, utilizing cell sizes of 6, 8, and 12 mm and a wall thickness of 0.5 mm. The compression performance of the samples was tested. The study revealed differences in dimensional accuracy in different directions, which was attributed to the fabrication process. All samples were heavier than expected, with additional materials being proportional to cell size. However, the samples exhibited high compressive strength and stiffness, indicating their potential use in load-bearing applications.

2024 - Life cycle assessment of lattice structures: Balancing mass saving and productivity [Articolo su rivista]
Colombini, Giulia; Rosa, Roberto; Ferrari, Anna Maria; Defanti, Silvio; Bassoli, Elena

Additive Manufacturing has revolutionized manufacturing processes, offering design flexibility and advances in various applications. The integration of lattice structures into lightweight designs has attracted attention due to their ability to optimize properties such as stiffness, strength and energy absorption. This paper explores the trade-off between mass reduction and productivity while evaluating the environmental sustainability of lattice structures manufactured with Laser-based powder bed fusion for metals Using Life Cycle Assessment, two design variants for an automotive component are compared: a topologically optimized version with a solid bulk section, and a second design with lattice structures for additional weight reduction. Experimental measurements and a detailed analysis of the laser strategy were performed to build the Life Cycle Assessment inventory. The integration of lattice structures allowed a weight reduction of 6 %, but resulted in a significant decrease in productivity and a higher environmental impact. Surprisingly, lattice geometries, often perceived as green solutions, can have negative sustainability implications due to longer manufacturing times and impact of auxiliary equipment. Successful implementation of environmentally sustainable designs requires a balance between mass reduction and productivity while addressing potential environmental consequences.

2023 - Evaluation of TPMS Structures for the Design of High Performance Heat Exchangers [Relazione in Atti di Convegno]
Torri, F.; Berni, F.; Fontanesi, S.; Mantovani, S.; Giacalone, M.; Defanti, S.; Bassoli, E.; Colombini, G.

The development of the additive manufacturing tech nology has enabled the design of components with complex structures that were previously unfeasible with conventional techniques. Among them, the Triply Periodic Minimal Surface (TPMS) structures are gaining scientific interest in several applications. Thanks to their high surface-to-volume ratio, lightweight construction, and excep tional mechanical properties, TPMS structures are being investigated for the production of high-performance heat exchangers to be adopted in different industrial fields, such as automotive and aerospace. Another significant advantage of the TPMS structures is their high degree of design flexibility. Each structure is created by replicating a characteristic unit cell in the three spatial dimensions. The three key parameters, namely cell type, cell dimension and wall thickness can be adjusted to provide considerable versatility in the design process. As for the heat exchangers, the variation of these parameters results in different values of heat transfer and pressure drop. If, on the one and, this flexibility leads to a wide range of design possibilities, on the other hand it generates uncertainty when the most suitable cell (with the best set of parameters) has to be selected. Therefore, the aim of the paper is to address the initial challenge in the design process of an innovative heat exchanger that incorporates a TPMS structure, which is the selection of the unit cell. Based on a literature review, four TPMS structures are selected as the most promising ones for the purpose, namely Gyroid, I-WP, Primitive and Diamond. Small prototypes of the selected structures are numerically tested at laminar and turbulent flow conditions to compare their performances in terms of heat transfer and pressure drop against a more traditional solution. In order to ensure an unbiased comparison between the structures, they are compared on equal volume of the specimen, wall thickness and unit cell dimension. Finally, a compact plate heat exchanger based on turbulators is added to the comparison, to investigate the capabilities of the TPMS structures compared to a more conventional solution.

2023 - Improved biomechanical behavior of 316L graded scaffolds for bone tissue regeneration produced by laser powder bed fusion [Articolo su rivista]
Gatto, Maria Laura; Cerqueni, Giorgia; Groppo, Riccardo; Santecchia, Eleonora; Tognoli, Emanuele; Defanti, Silvio; Mattioli-Belmonte, Monica; Mengucci, Paolo

Graded lattice scaffolds based on rhombic dodecahedral (RD) elementary unit cell geometry were manufactured in 316L stainless steel (SS) by laser powder bed fusion (LPBF). Two different strategies based on varying strut thickness layer-by-layer in the building direction were adopted to obtain the graded scaffolds: a) decreasing strut size from core to edge to produce the dense-in (DI) structure and b) increasing strut size in the same direction to produce the dense-out (DO) structure. Both graded structures (DI and DO) were constructed with specular symmetry with respect to the central horizontal axis. Structural, mechanical, and biological characterizations were carried out to evaluate feasibility of designing appropriate biomechanical performances of graded scaffolds in the perspective of bone tissue regeneration. Results showed that mechanical behavior is governed by graded geometry, while printing parameters influence structural properties of the material such as density, textures, and crystallographic phases. The predominant failure mechanism in graded structures initiates in correspondence of thinner struts, due to high stress concentrations on strut junctions. Biological tests evidenced better proliferation of cells in the DO graded scaffold, which in turn exhibits mechanical properties close to cortical bone. The combined control of grading strategy, printing parameters and elementary unit cell geometry can enable implementing scaffolds with improved biomechanical performances for bone tissue regeneration.

2023 - On the Technological Feasibility of additively manufactured self-supporting AlSi10Mg lattice structures [Articolo su rivista]
Bassoli, Elena; Mantovani, Sara; Giacalone, Mauro; Merulla, Andrea; Defanti, Silvio

The capability to design and manufacture metal lattice structures is today one of the most promising targets of Powder Bed Fusion technologies. Not only additively manufactured lattices offer great lightweighting possibilities, but they open the way to tailored and graded mechanical response. To best capitalize on this opportunity, research effort is first needed to assess the feasibility of reticular structures and to quantify the expected deviations from the nominal geometry, as a function of the cell topology and dimensions. Notwithstanding the inherent suitability of additive processes to complex shapes, this paper proposes a more exact definition of the technological boundaries for body-centred cubic lattices, showing to what extent specific dimensional ratios, as well as a self-supporting cell structure, can be favourable to minimize thedeviation from the nominal reticulum in terms of dimensions, density and presence of defects.

2023 - The Corrosion Behaviour of Additively Manufactured AlSi10Mg Parts Compared to Traditional Al Alloys [Articolo su rivista]
Gatto, Andrea; Cappelletti, Camilla; Defanti, Silvio; Fabbri, Fabrizio

Additive manufacturing of metal parts in the motorsport industry is becoming a decisive technology for producing lightweight and rigid parts, with increasing applications as the costs decrease. Among the available metal alloys, AlSi10Mg is one of the most widely used. In this paper, the corrosion resistance of additively manufactured AlSi10Mg is compared with that of other traditionally manufactured aluminium alloys widespread in the automotive industry. Several potentially corrosive agents, typical of vehicle applications, were used: salty water, motor oil, suspension oil, cooling fluid and gasoline. Corrosion tests were conducted at both room temperature and 90 C. The effects of heat and surface treatments were evaluated separately. The samples were visually inspected and weighed to evaluate the corrosion rate with the aid of SEM and EDS analysis. Additively manufactured AlSi10Mg generally showed better corrosion resistance in the stress-relieved condition as compared to the T6-treated state, with slightly better results for the polished samples. Motor oil, suspension oil, cooling fluid and gasoline did not significantly corrode the specimens, except for the T6-treated AlSi10Mg samples at 90 C. However, the corrosion rate was always higher than traditionally manufactured aluminium alloys tested for comparison.

2022 - A preliminary account of electro-chemical machining of Ti-48Al-2Nb-2Cr produced by electron beam melting [Relazione in Atti di Convegno]
Galati, M.; Defanti, S.; Vincenzi, N.; Marchiandi, G.; Gatto, A.; Iuliano, L.

2022 - An investigation on the processing conditions of Ti-6Al-2Sn-4Zr-2Mo by electron beam powder bed fusion: Microstructure, defect distribution, mechanical properties and dimensional accuracy [Articolo su rivista]
Galati, M.; Defanti, S.; Saboori, A.; Rizza, G.; Tognoli, E.; Vincenzi, N.; Gatto, A.; Iuliano, L.

2022 - Boosting Productivity of Laser Powder Bed Fusion for AlSi10Mg [Articolo su rivista]
Defanti, S; Cappelletti, C; Gatto, A; Tognoli, E; Fabbri, F

The Laser Powder Bed Fusion (L-PBF) process is recognized for high-end industrial applications due to its ability to produce parts with high geometric complexity. If lightweighting is one of the main strengths of L-PBF, a weakness is still the trade-off between high mechanical properties and competitive productivity. This objective can be targeted through a fine tuning of the process parameters within the manufacturing window. The paper pursues the combined optimization of part quality and process productivity for AlSi10Mg by going beyond the commonly used approach based solely on volumetric energy density. The effects of hatch distance and scan speed on the two targets were analyzed in detail. The best results were achieved by the adoption of a high scan speed and a low hatch distance, with notably different outcomes for nearly the same energy density.

2022 - Effective Mechanical Properties of AlSi7Mg Additively Manufactured Cubic Lattice Structures [Articolo su rivista]
Mantovani, Sara; Giacalone, Mauro; Merulla, Andrea; Bassoli, Elena; Defanti, Silvio

Lattice structures, whose manufacturing has been enabled by additive technologies, are gaining growing popularity in all the fields where lightweighting is imperative. Since the complexity of the lattice geometries stretches the technological boundaries even of additive processes, the manufactured structures can be significantly different from the nominal ones, in terms of expected dimensions but also of defects. Therefore, the successful use of lattices needs the combined optimization of their design, structural modeling, build orientation, and setup. The article reports the results of quasi-static compression tests performed on BCCxyz lattices manufactured in a AlSi7Mg alloy using additive manufacturing. The results are compared with numerical simulations using two different approaches. The findings show the influence of the relative density on stiffness, strength, and on the energy absorption properties of the lattice. The correlation with the technological feasibility points out credible improvements in the choice of a unit cell with fewer manufacturing issues, lower density, and possibly equal mechanical properties.

2022 - Performance Analysis of Electro-chemical Machining of Ti-48Al-2Nb-2Cr Produced by Electron Beam Melting [Articolo su rivista]
Galati, M.; Defanti, S.; Denti, L.

Ti-48Al-2Nb-2Cr is a challenging and difficult-to-cut titanium aluminide (TiAl) alloy with several manufacturing issues because of the high sensitivity to crack formation and oxygen picking up. Electron beam powder bed fusion (EB-PBF) made feasible TiAl near net shape components, but the surfaces are particularly rough and present complex surface topographies. In this present investigation, experimental analysis and optimization are proposed for electro-chemical machining (ECM) on as-built Ti-48Al-2Nb-2Cr surfaces manufactured using EB-PBF. Experimental runs are performed under pulsed machining conditions and varying specific process metrics to understand the machining effects on the process efficiency and removal phenomena. In particular, the morphology and isotropy of the surface are studied before and after the machining by scanning electron and confocal microscopies. The results establish the optimal machining conditions and a range for the active machining time that produce, compared to the as-built surface, an extremely smooth and isotropy surface without any detrimental effect on the surface integrity and microstructure.

2021 - Design for additive manufacturing and for machining in the automotive field [Articolo su rivista]
Bassoli, E.; Defanti, S.; Tognoli, E.; Vincenzi, N.; Esposti, L. D.

High cost, unpredictable defects and out-of-tolerance rejections in final parts are preventing the complete deployment of Laser-based Powder Bed Fusion (LPBF) on an industrial scale. Repeatability, speed and right-first-time manufacturing require synergistic design approaches. In addition, post-build finishing operations of LPBF parts are the object of increasing attention to avoid the risk of bottlenecks in the machining step. An aluminum component for automotive application was redesigned through topology optimization and Design for Additive Manufacturing. Simulation of the build process allowed to choose the orientation and the support location for potential lowest deformation and residual stresses. Design for Finishing was adopted in order to facilitate the machining operations after additive construction. The optical dimensional check proved a good correspondence with the tolerances predicted by process simulation and confirmed part acceptability. A cost and time comparison versus CNC alone attested to the convenience of LPBF unless single parts had to be produced.

2021 - Repeatability of the fatigue performance of additively manufactured A357.0 under different thermal treatment conditions [Articolo su rivista]
Defanti, S.; Bassoli, E.

A357.0 parts were produced by laser-based powder bed fusion. An in-situ annealing strategy was applied by pre-heating the build platform, in order to relieve residual stresses and reduce anisotropic effects upon processing. The mean value and standard deviation for the fatigue strength at the given life time of 1 × 107 cycles were determined according to the staircase method, before and after T6 heat treatment. Samples parallel to the build platform and parallel to the growth direction were analysed separately and compared. The fatigue behaviour was substantially insensitive to post-processing heat treatment, since fracture initiation was governed by sub-surface lack-of-fusion defects that remained unchanged in the T6 conditions. The heat treatment caused an increase in porosity, yet without significant detriment to the fatigue resistance. The build orientation was not found to affect the average value of the fatigue strength, but it caused variations of the repeatability.

2021 - Surface roughness prediction model for Electron Beam Melting (EBM) processing Ti6Al4V [Articolo su rivista]
Galati, M.; Rizza, G.; Defanti, S.; Denti, L.

Electron Beam Melting (EBM) is an Additive Manufacturing technique to produce functional components. Because of the high temperature during the EBM process, the surface texture of the as-built parts is extremely complex and unique. This distinctiveness of the surface depends on many factors and needs to be well understood to predict final surface properties accurately. Chief among these factors is the surface design. A proper surface design makes it possible to tailor a surface with specific properties such as biomimetics. However, predictive models are difficult to determine especially for downskin surfaces. To properly tailor a surface, a full factorial Design Of Experiment (DOE) was designed, and 2D and 3D roughness profiles were collected on an ad-hoc artefact using a profilometer and a confocal profilometer. This reference part comprises several surfaces to investigate the effect on surface roughness of different sloping angles, including upskin and downskin surfaces and cavities. The data are analysed using descriptive and inferential statistical tools, also by distinguishing the role of roughness and waviness in the overall surface texture. A deep investigation of the causes of surface roughness made it possible to obtain analytical predictive models. These models are robust and consistent with respect to the experimental observations. Finally, the accurate design of the artefact allows highlighting the relationship between the roughness and the surface slope.

2020 - Disclosing the build-up mechanisms of multi jet fusion: Experimental insight into the characteristics of starting materials and finished parts [Articolo su rivista]
Galati, M.; Calignano, F.; Defanti, S.; Denti, L.

Multi Jet Fusion (MJF) is an emerging additive manufacturing (AM) technique that enables the production of prototypes and functional parts starting from a thermoplastic-based powder, mainly polyamide 12 (PA12). Layer upon layer, the polymeric particles are selectively impregnated with two different inks and then fused and consolidated by an infrared (IR) lamp. Much faster than other AM techniques for polymers, MJF has shown exciting potentialities. However, little is known about the consolidation mechanisms acting in MJF and about the effect on the properties of the finished parts of the quality of the materials, powder and inks, and of the printing conditions. The present contribution investigates these issues. The study also compares virgin PA12 powder with pure PA12, recycled PA12 for MJF and PA12 for in selective laser sintering (SLS). The powders showed slight differences. The two inks have the same composition, except for the presence of graphitic carbon. Tensile tests showed that the printed parts are isotropic. However, the deformation at break is affected by building direction of the sample. Occasionally, poor inter-layer adhesion is observed and the tensile strength and the deformation at break collapse. Printed tensile specimens are found to be representative of the material behaviour of a printed component, apart from the deformation at break which is systematically overestimated.

2020 - Preliminary assessment of electro-chemical machining for aluminum parts produced by laser-based powder bed fusion [Articolo su rivista]
Defanti, S.; Denti, L.; Vincenzi, N.; Gatto, A.

Electro-chemical machining (ECM) is a nonconventional machining process based on the anodic dissolution of the workpiece. The peculiar features of this process make it suitable for application in the aerospace, automotive, or medical fields where laser-based powder bed fusion (L-PBF) is consolidating as a manufacturing solution for high-performance components. The roughness of as-built L-PBF parts often requires surface finishing before usage in order to enable a correct operation as well as to prevent early fatigue failure. The viability of ECM on L-PBF components is still scarcely investigated in the literature. In this article, the process was applied to AlSi10Mg parts produced by L-PBF. An experimental plan was designed to select the process parameters and to study their effect on the surface roughness and morphology. Process variables including feed rate, time, voltage, and water pressure were investigated. As a result, it was observed that the ECM performance was different for parts produced by traditional processes or by L-PBF, even for comparable composition. Owing to the presence of satellite particles on L-PBF surfaces, ECM was only effective in the pulsed mode.

2020 - Technological Feasibility of Lattice Materials by Laser-Based Powder Bed Fusion of A357.0 [Articolo su rivista]
Sola, A.; Defanti, S.; Mantovani, S.; Merulla, A.; Denti, L.

Lattice materials represent one of the utmost applications of additive manufacturing. The promising synergy between additive processes and topology optimization finds full development in achieving components that comprise bulky and hollow areas, as well as intermediate zones. Yet, the potential to design innovative shapes can be hindered by technological limits. The article tackles the manufacturability by laser-based powder bed fusion (L-PBF) of aluminum-based lattice materials by varying the beam diameter and thus the relative density. The printing accuracy is evaluated against the distinctive building phenomena in L-PBF of metals. The main finding consists in identification of a feasibility window that can be used for development of lightweight industrial components. A relative density of 20% compared with fully solid material (aluminum alloy A357.0) is found as the lowest boundary for a 3-mm cell dimension for a body-centered cubic structure with struts along the cube edges (BCCXYZ) and built with the vertical edges parallel to the growth direction to account for the worst-case scenario. Lighter structures of this kind, even if theoretically compliant with technical specifications of the machine, result in unstable frameworks.

2019 - Cross-contamination quantification in powders for additive manufacturing: A study on Ti-6Al-4V and maraging steel [Articolo su rivista]
Santecchia, E.; Mengucci, P.; Gatto, A.; Bassoli, E.; Defanti, S.; Barucca, G.

Metal additive manufacturing is now taking the lead over traditional manufacturing techniques in applications such as aerospace and biomedicine, which are characterized by low production volumes and high levels of customization. While fulfilling these requirements is the strength of metal additive manufacturing, respecting the tight tolerances typical of the mentioned applications is a harder task to accomplish. Powder bed fusion (PBF) is a class of additive manufacturing in which layers of metal powder are fused on top of each other by a high-energy beam (laser or electron beam) according to a computer-aided design (CAD) model. The quality of raw powders for PBF affects the mechanical properties of additively manufactured parts strongly, and therefore it is crucial to avoid the presence of any source of contamination, particularly cross-contamination. In this study, the identification and quantification of cross-contamination in powders of Ti-6Al-4V and maraging steel was performed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques. Experimental results showed an overall good reliability of the developed method, opening the way for applications in machine learning environments.

2019 - Effect of powder recycling in laser-based powder bed fusion of Ti-6Al-4V [Articolo su rivista]
Denti, L.; Sola, A.; Defanti, S.; Sciancalepore, C.; Bondioli, F.

Additive manufacturing (AM) has shown promise to process parts for end-use applications, however stringent requirements must be fulfilled in terms of reliability and predictability. The expensiveness of raw materials for AM, especially for metal-based Powder Bed Fusion (PBF), brings about the need for a careful recycling of powder, but the effect of powder reuse on both processing conditions and final part performance is still the focus of intensive research in the open literature. Although ASTM F2924-14 specifies the virgin-to-used powder ratio to be introduced to manufacture titanium-6aluminum-4vanadium (Ti-6Al-4V) components by PBF, a deeper understanding of the effect of powder recycling on the mechanical properties of finished parts is expected to foster a more efficient and safe reuse. The present contribution is therefore addressed to investigate the consequence of Ti- 6Al-4V powder recycling on the flowability, particle size distribution and morphology of the feedstock material as well as on the density and tensile performance of built parts. In order to quantify the recyclability of powders, a new "average usage time" (AUT) parameter is defined to account for both the real usage time of the powder and the virgin-to-used powder mixing ratio. The new parameter, whose applicability can be readily extended to any kind of feedstock powder, offers a significant contribution to achieve a more consistent and economical recycling of raw materials for PBF processing.

2017 - DREAM: Driving up reliability and efficiency of additive manufacturing [Relazione in Atti di Convegno]
Sciancalepore, Corrado; Bondioli, Federica; Gatto, Andrea; Defanti, Silvio; Denti, Lucia; Bassoli, Elena

The DREAM project, financed by the EU Commission (H2020, Work program: FOF-13-2016: Photonics Laser-based production) is an end-user driven action which aligns the research and development of Additive Manufacturing (AM) technologies to the specific needs of its three industrial end users, Ferrari SpA, Adler Ortho France SARL, and RB Srl. The Action brings together experts in the field of AM technologies, powder and material characterization, component engineering, laser-matter interaction, to deliver an optimized approach that will be developed and demonstrated to the requirements of the end users. The first results of the project are here reported.

2015 - Effect of deep cryogenic treatment on the properties of AISI M2 steel [Relazione in Atti di Convegno]
Sola, Ramona; Poli, Giorgio; Defanti, Silvio; Veronesi, Paolo; Parigi, Giovanni

Deep cryogenic treatment is a special kind of bulk hardening heat treatment performed on a big variety of tool and carburized steels, to improve mechanical properties and wear resistance. The mai reason for this is the complete transformation from austenite into martensite plus the formation of submicrometric carbides dispersed in the tempered martensitic structure. The greatest improvement in properties is obtained by carrying out the deep cryogenic treatment between quenching and tempering. However, a significant improvement can be obtained even by treating the tools at the end of the usual heat treatment cycle, i.e. the finished tools. This last solution is more flexible than the other one and can extend the use of the treatment to many practical applications. In order to check the potential of deep cryogenic treatment on the performance of the finished products, an investigation was carried out on the AISI M2 high speed steel quenched, tempered and deep cryogenically treated. The findings shows that the cryogenic treatment promotes the precipitation of submicrometric carbides, that increment wear resistance and nano-hardness and decrease residual stresses.