Hot turning of a difficult-to-machine steel (sae xev-f) aided by infrared radiation

A possible way for increasing the cutting tool life can be achieved by heating the workpiece in order to diminish the shear stress of material and thus decrease the machining forces. In this study, quartz electrical resistances were set around the workpiece for heating it during the turning. In the tests, heat-resistant austenitic alloy steel was used, hardenable by precipitation, mainly used in combustion engine exhaustion valves, among other special applications for industry. The results showed that in the hot machining the cutting tool life can be increased by 340% for the highest cutting speed tested and had a reduction of 205% on workpiece surface roughness, accompanied by a force decrease in relation to conventional turning. In addition, the chips formed in hot turning exhibited a stronger tendency to continuous chip formation indicating less energy spent in material removal process. Microhardness tests performed in the workpieces subsurface layers at 5 m depth revealed slightly higher values in the hot machining than in conventional, showing a tendency toward the formation of compressive residual stress into plastically deformed layer. The hot turning also showed better performance than machining using cutting fluid. Since it is possible to avoid the use of cutting fluid, this machining method can be considered better for the environment and for the human health.

Heat Treatment and Yb-Fiber Laser Welding of a Maraging Steel

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo da fragilização ao revenido em aço liga de 2,25CR-1MO através do ensaio de indentificação instrumentada

2,25Cr-1Mo alloy steels are widely used in petrochemical plant equipments working in high temperature conditions because of their good mechanical proprieties in these conditions. Although, when exposed for a long time at high temperature, in the rage of 343 °C to 593 °C, may present the temper embrittlement phenomenon. The component named stripper of assembly converter of fluid catalytic cracking unit (UFCC) of studied plant is manufactured using this material, which is subject to temper embrittlement. The phenomenon of temper embrittlement refers to progressive lose of toughness, making the material brittle. With embrittlement, equipaments manufactured with this material are under risks to suffer brittle fracture in the cool down and start-up situations of them, which can cause catastrophic failures. By this reason, this research studies presence of temper ebrittlement phenomenon on this material. To verify the toughness of the material is conventionally used charpy V-notch test. However, this test requires the removing of samples of the material to make specimens. This fact becomes critical when talk about structural components of an equipment. So, this research also studies a non-destructive test that can be executes in-situ, known as instrumented indentation, as an alternative detection of the phenomenon at the component stripper, by comparative of the mechanical proprieties obtained by conventional tests in similar samples

Determinação experimental da tenacidade à fratura em baixas temperaturas de tubos de aço API 5L X70

Because of the great metallurgical advances, the welded tubes by HF / ERW (High Frequency / Electrical Resistance Welding) have played a more active role in the oil and gas, gradually replacing tubes produced by other processes (UOE, SAW, and others) to deep water applications, in high and extremely low temperatures, highpressure conditions and in highly corrosive environments. However, studies have revealed that defects in the welded joints are in one of main causes of failures in pipelines. Associated with damage external and the stringent requirements of this sector, the welded joints become particularly critical for his toughness and the determination of this particular property is fundamental. This study aims to evaluate the toughness of the HF / ERW pipes in HSLA steel API X70 class, used in pipelines transport systems of gas and oil from data obtained with CTOD tests (Crack Tip Opening Displacement). The main objectives of this project are: mechanical and microstructural characterization of steels API X70 manufactured in Brazil; and evaluation of the toughness of weld process by HF / ERW steel API X70 national. After having the tests done, mechanical, chemical and metallurgical, we have the conclusion that those pipe are in agreement to API 5L 42ª edition for X70MO and the toughness behaves like the expected

Avaliação de fração volumétrica de austenita retida e martensita em aço trip 800 utilizando três métodos diferentes

In the second half of the last century the automobile industries suffered from the petroleum crisis caused mainly by the wars in the Middle East. These crises led the automakers rethink their vehicles. One of the most important events after that was the adoption of new steels by the industry. One example is the TRIP steels (Transformationinduced plasticity). It is known that the macroscopic behavior of a material is strongly dependent on its microstructure and therefore the quantitative metallography is important to understand and relate the material properties to its microstructure. In this work, different specimens of TRIP steels were etched using LePera reagent. The obtained images were analyzed using digital processing. Using the ImageJ software the methods threshold and watershed were studied as well as a comparison with the ASTM E562 standard. The methods were compared and finally the morphological characteristics and volumetric fraction of the retained austenite and martensite phases were analyzed. The results showed that the threshold led to a higher number of identified grains with lower mean area and total area fraction than the watershed method and ASTM standard

Estudo das propriedades mecânicas do aço SAE 1312 modificado ao nióbio

The study of mechanical properties of high-alloy special steels is of great interest of the steel industry due to the great demand by companies that manufacture automotive components of high criticality, and also because of its high commercial value. However, the development of this type of alloy metals demand highly technical knowledge. Among these extremely important kinds of steel, the subject which is the interest of this study is the special steel modified by niobium. The manganese and niobium are the main alloying elements in the composition of these steels, both of them increase the stability of the austenite region, however, manganese increases the hardenability and tensile yield strength, and niobium increases the mechanical strength and promotes refining the grain. The mechanical characterization of steel SAE 1312 modified the niobium was made in order to gain a better understanding of the influence on the mechanical properties caused by aging at different temperatures and for different reductions in the drawing of gauge material. This characterization was made by means of tensile test and hardness. This material showed an increase in yield strength and hardness when gauge with large reductions during the wiredrawing, but when subjected to aging temperatures higher than 300 ° C had a slight loss of these properties

Estudo em fadiga no aço API 5L X80 soldado pelo processo HF/ERW

The technological advancement in order to improve the methods of obtaining energy sources such as oil and natural gas is mainly motivated by the recent discovery of oil reserves. So, increasingly , there is a need for a thorough knowledge of the materials used in the manufacture of pipelines for transportation and exploration of oil and natural gas. The steels which follow the API standard (American Petroleum Institute), also known as high strenght low alloy (hsla), are used in the manufacture of these pipes, as they have, with their welded joints, mechanical properties to withstand the working conditions to which these ducts will be submitted . The objective of this study is to evaluate the fatigue behavior in microalloyed steel grade API 5L X80 welded by process HF / ERW . For this, axial fatigue tests to obtain S-N curve (stress vs. number of cycles ) were conducted. To complement the study, it was performed metallographic , fractographic , Vickers hardness tests and tensile tests to characterize the mechanical properties of the steel and check whether the values satisfy the specifications of the API 5L standard . From the fatigue tests , it was concluded that the surface finish influences directly on the fatigue life of the material

Aços avançados de alta resistência: avaliação da microestrutura e propriedades dos aços DP 600 E DP 780

This work aims to study the Dual-Phase 600 and 780 steels, which are part of technology development project materials for the automotive industry. It is worth underscoring the antagonistic properties as the Dual-Phase steel assemble, high mechanical strength and elongation due its microstructure, ferrite and martensite. These properties are obtained by a intercritical heat treatment which facilitates the formation of a hardness metastable microstructure shaped plates of low carbon steels. The applicability of Dual Phase steel in the structure of vehicles is huge and its production is already on a commercial scale, so the study and development of this material implies lower cost in automobile manufacturing processes. The dual phase steels DP600 and DP780 underwent tensile, hardness and metallographic analysis to evaluate and comparing its properties. The results indicate that the DP780 steel has higher strength and hardness than the DP600 steel and its microstructure consists of martensite higher fraction which accounts for the higher resistance and hardness. However, the DP600 has higher conformability to DP780 steel

Estudo da velocidade de despassivação de aços em estruturas de concreto armado, em meio de cloreto

The aim of the present study was to investigate the corrosion resistance in chloride medium of two cylindrical steel samples from civil construction (CA-50 and CA-60). For this purpose, electrochemical measurements were performed in NaCl solution, 4.0 g/L, naturally aerated. According to electrochemical responses, it was observed an active dissolution process at open circuit potential for both steels. In this comparative study, the differences between CA-50 and CA60 were not significant, since the values of polarization resistance estimated by EIS were the same order of magnitude for both types of steel (oscillating between 200 and 500 Ohm). For all evaluated thicknesses of concrete reinforcement, these values ranged between 2 and 9 kOhm, and the lower value was associated with lower thickness, particularly at 7, 21 and 35 days. When these results were compared with those determined for the CA-60, it was found that the layer of concrete reinforcement provide a protection against corrosion in chloride medium at least ten times larger

Estudo do comportamento em fadiga de um tubo de aço microligado, grau API 5L X70

This work focuses on a study on the fatigue behavior of a microalloyed steel API 5L X70, used in pipes lines to transport oil and gas. These types of steels have excellent mechanical resistance values and ductility and therefore increased their study driven by increased demand for oil and especially natural gas, which consequently raises the need to build new pipelines to transport these products. The oil extraction units, composed of the risers (pipelines connecting the oil well to the ship), are dimensioned to remain installed for periods of 20 to 30 years in the marine environment, a hostile environment for high pressure, corrosion, low temperatures and the stresses caused by the movement of water and tides. For analysis, the S-N (stress versus number of cycles) curves were obtained from data collected from bodies-of-proof cylindrical longitudinal, transverse and that one removed from the weld area of the pipe, tested in accordance with ASTM E466. Tensile tests were performed for characterizing the mechanical properties of the samples and welded joints, concluded that the values meet the specifications of the standard API 5L. To characterize microstructural material, also metallographic analysis was made of regions of the base metal and the HAZ. The results of fatigue tests demonstrated a higher life for the specimens removed from the longitudinal direction the pipe, followed by those in the transverse direction and, finally, the welded joint. The origins of the fatigue cracks were determined by scanning electron microscopy (SEM)

Técnicas de caracterização microestrutural, por microscopia óptica e microscopia eletrônica de varredura, de aços bifásicos e multifásicos aplicados à indústria automobilística

This project developed microstructural characterization technics of commercial dualphase and multi-phasic (TRIP) steels that were provided by the automotive industry and are currently used as the raw material for the production of automobiles. Inserted in this context, there is the development of the advanced high strength steels in consonance with the ULSABAVC project, which aims the production of safe, economically viable and efficient in terms of fuel consumption vehicles for the 21st century. The micro-structural characterization of biphasic and multiphase steels was done by the identification and quantification of the coexistent phases. In this item, a special attention was given to the technics that were performed using optic microscopy and scanning electron microscopy. An important contribution to this work was the utilization of different alternative chemical reagents (Beraha, Heat-Tinting technics) in addition to the classical ones (Nital and LePera)already used conventionally by the UNESP's Group of Mechanical, Microstructural and Fractografic Characterization of Materials. The revealed microstructures were correlated with the materials' mechanical properties determined through traction tests, such as ultimate tensile strengths, yield strength and stretching important since the material has structural application in the automotive industry. As a result, it was observed the superiority concerning the studied mechanical properties for the biphasic and multiphasic steels when compared to the conventional carbon steels. Besides, it was perceived a large potential for the industrial scale utilization of the Heat Tinting technics in this field, seen its differentiation of the existent phases and easy reproducibility

Recuperação de turbinas hidráulicas danificadas por erosão cavitacional por soldagem com aço inoxidável/cobalto

Pós-graduação em Engenharia Mecânica - FEIS

Análise comparativa dos métodos MQL, MQL/Água e convencional na retificação cilíndrica do aço ABNT 52100, com rebolo de óxido de alumínio

Pós-graduação em Engenharia Mecânica - FEB

Influência da adição do nióbio no comportamento mecânico e microestrutural do aço SAE 6150

Pós-graduação em Engenharia Mecânica - FEG

Estudo experimental do uso de rebolos convencionais na usinagem do aço VP-50 utilizado na retificação cilíndrica, por meio de diferentes métodos de lubri-refrigeração

Pós-graduação em Engenharia Mecânica - FEB