Orientador: Anselmo Eduardo Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-22T09:27:39Z (GMT). No. of bitstreams: 1 OliveiraJunior_CarlosAncelmo_M.pdf: 7354499 bytes, checksum: 05a6c099baa7c4f194f916c8e418d4db (MD5) Previous issue date: 2013 / Resumo: Os aços inoxidáveis super duplex são ligas extremamente resistentes à corrosão, desenvolvidas para aplicações com altos níveis de exigência, em que as peças terão contato com ambientes corrosivos como a água do mar, por exemplo. Devido à sua composição química e microestrutura, que proporcionam alta resistência mecânica, alta resistência ao calor e também alta ductilidade, que são fatores positivos para a aplicação, a usinabilidade dessas ligas é geralmente muito baixa o que resulta em longos ciclos de produção e alto custo de ferramental. Este trabalho trata do torneamento da liga UNS 32750 comercialmente conhecida como SAF2507 e sua consequente influência na resistência à corrosão apresentada ao longo da aplicação. Durante os ensaios, houve variação de velocidade de corte, classe e cobertura da ferramenta, além da condição de refrigeração com alternativas de alta e baixa pressão. Os resultados indicam que as pastilhas com cobertura PVD são mais resistentes ao desgaste e, combinadas ao uso de refrigeração de alta pressão, podem melhorar o seu desempenho em relação à vida útil e rugosidade bem como à posterior resistência à corrosão do material. Desgaste de entalhe e aderência encontrados na usinagem com pastilhas PVD, juntamente com lascamentos e quebras que ocorreram nas pastilhas CVD, foram os tipos e mecanismos de desgaste/avaria da ferramenta mais encontrados durante os ensaios / Abstract: Super duplex stainless steels are extremely corrosion-resistant alloys that were developed to work in very demanding applications, in which the workpieces are exposed to corrosive environments like sea water, for example. Due to their chemical composition and microstructure, that provide high mechanical and heat resistance besides high ductility, which are favorable factors for the application, the machinability of these alloys is generally poor and results in long production cycles and high tool costs. The goal of this research is to study turning operation of the UNS 32750 alloy, commercially called SAF2507, and its consequent influence in the corrosion resistance for application situations. During the tests, the input variables were cutting speed, grade and coating of the inserts, besides the cooling conditions with low and high pressure options. The results indicate that the PVD coated inserts are more wear-resistant than the CVD inserts and when they are combined with high pressure cooling, their performance related to tool life and workpiece roughness as well as the corrosion resistance of the material after machining is improved. Notch wear and attrition found in machining with PVD inserts, together with chipping and tool breakage that occurred in machining with CVD inserts, were the most frequent types of wear/damage and wear mechanism found during the tests / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Os aços inoxidáveis austeníticos são materiais atrativos para serem utilizados em vários setores industriais que operam sob meios corrosivos, como por exemplo: indústria química, alcooleira, petroquímica, de papel e celulose, na prospecção de petróleo e nas indústrias têxtil e farmacêutica. Contudo, apresentam propriedades tribológicas pobres. No sentido de melhorar essas propriedades, como aumentar a dureza superficial, a resistência ao desgaste e a resistência à fadiga, vários métodos de tratamentos superficiais vêm sendo utilizados. Dentre eles, o mais eficiente é a nitretação por plasma. Este processo é realizado em uma câmara de vácuo sob uma mistura gasosa de hidrogênio e nitrogênio. É aplicada uma diferença de potencial entre o cátodo (porta amostras) e o ânodo (paredes da câmara), acelerando os íons contra a superfície da peça, aquecendo-a e arrancando elétrons de sua superfície. Os íons reagem com espécies da superfície do plasma formando compostos instáveis do tipo FeN que se recombinam para formarem nitretos estáveis. O sucesso deste tratamento se deve à baixa temperatura de operação, ao menor tempo efetivo de tratamento e ao controle da uniformidade da espessura da camada. A camada de nitretos formada durante o tratamento possui uma influência positiva na vida em fadiga de um componente, graças a dois motivos principais. O primeiro é o atraso na nucleação da trinca devido ao aumento da resistência mecânica superficial. O segundo motivo está relacionado com a introdução de tensões residuais compressivas durante o processo de endurecimento da superfície, que retarda a iniciação da trinca e diminui o fator de intensidade de tensão. Os corpos de prova foram nitretados a 400ºC durante 6 horas, com uma pressão de 4,5 mbar e utilizando uma mistura gasosa de 80% vol.H2 e 20%vol.N2. Ocorreu um aumento da resistência mecânica próxima á superfície, devido à camada de nitretos, o que ficou evidente com o sensível aumento no valor do limite de fadiga do material nitretado em relação ao não nitretado. O limite de fadiga do aço AISI 316 não tratado foi de 400MPa e do nitretado foi de 510MPa, enquanto que, para o aço AISI 304, o limite de fadiga do material não tratado foi de 380MPa e o limite para material submetido ao tratamento de nitretação foi de 560MPa. / The austenitic stainless steels are attractive materials to many industrial sectors which work on corrosive environments, as chemical industry alcohol, petrochemical, cellulose industries, in the petroleum prospection and pharmaceutical and textiles industries. However, they present poor tribological properties. In order to improve these properties, like increasing superficial hardness, wear and fatigue resistance superficial heat treatment methods have being used. The most efficient is the plasma nitriding process which occurs in a vacuum container under hydrogen and nitrogen gas mixture. A potential difference is applied between the cathode (samples receptor) and the anode (container walls), accelerating the ions against the piece, heating it and removing electron from the surface of material. These atoms react with the surface plasma species, producing unstable compounds like FeN, which recombine producing stable nitrides. The success of this treatment is due to the low temperature operation, the short effective time of treatment and to the uniformity control of the layer’s thickness. The nitrides layer produced during the treatment have a positive influence in the fatigue life of a component, thanks to two main reasons. The first is the retardation in crack nucleation due to increasing of superficial mechanical strength. The second reason is due to introduction of compressive residual stress during the surface hardening process, which retards de crack initiation process. The specimens were nitriding at 400°C during 6 hours, at a 4,5mbar pressure and using a gas mixture of 80% vol. H2 and 20% vol. N2. The surface mechanical strength increased, due to the nitrides layer, which was evident with the sensitive increase in the fatigue limit of the nitriding specimens, comparing to the untreated ones. The fatigue limit of the AlSl 316 steel in untreated condition was 400 MPa and in nitriding condition was 510 MPa, whereas AlSl 304 steel, the fatigue limit of the untreated condition was 480 MPa and the fatigue limit for the nitrided condition was 560 MPa.

Este trabalho teve por objetivo estudar o efeito dos parâmetros de corte e dos tratamentos térmicos na usinagem de três aços inoxidáveis austeníticos (ABNT 303, 304 e 310). Estes aços apresentam mesma estrutura cristalina e microestrutura semelhante. O aço ABNT 303 tem composição próxima ao ABNT 304, exceto pelo elevado teor de enxofre. Já o aço ABNT 310 apresenta maiores teores de elementos de ligas. Esses materiais foram tratados termicamente (solubilização ou envelhecimento). Os aços estudados foram caracterizados microestruturalmente e foram realizadas medidas de dureza Vickers. Os aços foram então torneados em várias condições de usinagem, variando principalmente a relação avanço por profundidade de corte. Foram medidas as forças de corte e de avanço em algumas das condições e coletados os cavacos resultantes para análise morfológica, que foram realizadas utilizando-se principalmente microscopia óptica e eletrônica de varredura. Foram também medidas as rugosidades e determinados os perfis das superfícies usinadas para a avaliação do acabamento superficial. Os resultados obtidos neste trabalho permitiram determinar algumas diferenças no comportamento dos três aços inoxidáveis estudados. As maiores diferenças foram verificadas quando as superfícies foram observadas utilizando microscopia. O aço ABNT 303 apresentou as piores superfícies e os menores esforços de corte em relação aos aços ABNT 304 e 310. A utilização de diferentes ferramentas neste trabalho mostrou influência principalmente na formação do cavaco, não tendo muita influencia nos esforços de corte e tão pouco no acabamento superficial. Os tratamentos térmicos realizados propiciaram a formação de outras fases, as quais causaram alterações na microestrutura. No entanto, esses tratamentos térmicos não alteraram de forma significativa o processo de torneamento. Finalmente, a formação de martensitas induzidas por deformação foi identificada no cavaco, mas não pode ser quantificada. / The main objective of this work is to study and evaluate the effect of cutting parameters, the cutting tool and the heat treatments in the turning process of three different types of austenitic stainless steels (ABNT 303, 304 e 310). The steels studied are structurally and microstructurally comparable. The chemical composition of the ABNT 303 and the ABNT 304 is similar except for the presence of sulfur in the ABNT 303 steel which alloeds the manganese sulfide formation. On the other hand, the ABNT 310 steel is richer in alloying elements and has lower tendency to strain induced martensite formation than the other steels studied. The steels studied were also heat treated in different conditions (annealed and aged). The materials were microstructurally characterized and Vickers hardness was also measured. The turning tests were carried out by using different cutting parameters, mainly the feedcutting depth relations. These relations lead to a plane state of tension or a plane state of deformation. The cutting and feed forces were measured during turning tests. During the tests the chips were also collected for morphological analysis through optical and scanning electron microscopies. The roughness and the surfaces characteristics were also determined to evaluate the surface finishing. The major difference in the steels turned was related to surface finishing observed by using optical and scanning electron microscopies. On the whole, the ABNT 303 steel presented the worst surface and the lowest cutting forces. However, the differences among all results were not significant. The tests carried out also showed there was not considerable difference between the tools used except for the chip morphology. The heat treatments led to precipitation in the steels studied and changes in their microstructure. However, the microstructural changes hardly affected the results of the turning tests. Finally, the martensite formation was detected although this phase could be not quantified.

This diploma thesis deals with segregation cycles in austenitic CrNi steels. In first section deals with theory of macrosegregation and microsegregation cycles. The second part is focused on this cycles in experimental casting. Macrosegregation was measured by spectrometric analyser and by MAGMA simulation program. Microsegregation was measured by electron microscope. The aim of this diploma thesis is verify the influence of setting conditions on heterogenity chemical composition in austenitic CrNi steel. For experimental casting with a wall thickness of about 500 mm will be verified effect of the setting time, residence time between solid and liquid phases and others parameters for macrosegregation and microsegregation in selected elements.

The master thesis deals with processes of segregation in austenitic-ferritic stainless steels. The introductory part consists of characteristics features of austenitic-ferritic steels and theoretical analysis of segregation processes. The second part shows practical measurements of segregation in experimental casting. Macrosegregation was measured on a spectrometric analyzer and simultaneously solved in the simulation program MAGMA. The aim of this thesis is to verify the effect of solidification time and dwell time between liquidus and solidus temperature on the chemical heterogeneity of duplex stainless steel casting of about 500 [mm]. Chemical heterogeneity was solved for selected alloying and accompanying elements such as C, Mo, Ni, Mn, Cr. The microsegregation was not addressed. Comparison of the mechanical properties of cast and heat treated duplex steel was done by tensile testing of samples cut from the center of the casting.

This thesis deals with temporary corrosion protection of stainless steel for the conditions of oversea sailing. At first the theoretical part describes types of the stainless steels focusing on their corrosion resistance and negatively or positively impacts affect of their resistance. There is also a proposal of methods of the temporary corrosion protection and testing its effectiveness. The recherché are summarized knowledge in testing resistance of stainless steels to pitting corrosion. The task of the study was to test the effectiveness of three different preservatives and comparing the quality of their temporary corrosion protection compared with unprotected chemically passivated stainless steels.

The last seven hot rolling passes of the ferritic stainless steels (FSS) AISI 430 and AISI 433 (the latter an Al-added variant of 430) were simulated on Gleeble-1500D® and Gleeble-3800TM® thermo-mechanical simulators to investigate the effect of temperature, strain rate and inter-pass time on the development of texture in these steel grades and its subsequent influence on ridging. The compression tests were carried out over a wide range of strain rates (0.1 s-1 to 5 s-1, 25 s-1 and 50 s-1) and temperatures (1100 to 820 oC) with different inter-pass times (2 s, 10 s, 20 s and 30 s). The transition temperature from dynamic recrystallization (which may introduce a texture change) to dynamic recovery (in which no texture changes are expected) was determined by examining the relationship between the mean flow stress and the deformation temperature in multi-pass tests. Both macrotexture (XRD) and microtexture (EBSD) analyses were employed to characterise and study the texture present in these steels. It was found that the texture in the central layer of the compressed sample is a strong recrystallization-type. The through-thickness textural and microstructural banding was found to be responsible for ridging in these grades of stainless steels. Dynamic recrystallization which promotes the formation of the desired ã-fibre texture leading to high ductility, formability and eventually reduction or elimination of ridging, was found to occur in both AISI 430 and AISI 433 at high temperatures, low strain rates and longer inter-pass times with multi-pass testing. Generally AISI 433 has a stronger gamma texture developed than the AISI 430 when hot rolled under similar conditions, which leads to improved ductility and less ridging in AISI 433 than AISI 430. / Dissertation (MSc)--University of Pretoria, 2012. / Materials Science and Metallurgical Engineering / unrestricted

The “475°C embrittlement” occurring in ferritic and duplex stainless steel is considered to be detrimental and it limits the application of ferritic and duplex stainless steel at elevated temperatures, i.e., above about 300°C . In this study, the effect from alloying elements Ni, Cu and Mn on 475°C embrittlement was examined based on microhardness measurement and Charpy V-notch tests as well as atom probe tomography (APT). It was found that, after aging for 10h, 3% Ni accelerates the ferrite decomposition dramatically, 5% Mn has minor effect and no effect of 1.5% Cu was seen. The hardness increase tested at 450°C and 500°C was consistent with the observations from APT. The embrittlement based on room temperature Charpy tests was observed mainly during the first 10h. The embrittlement in Fe-20Cr-3Ni alloy was attributed to ferrite decomposition, while the other three alloys may be influenced by other phenomenon as well. A clustering effect of Cu has been observed in Fe-20Cr-1.5Cu and it was supposed to contribute to the mechanical changes.

The “475°C embrittlement” occurring in ferritic and duplex stainless steel is considered to be detrimental and it limits the application of ferritic and duplex stainless steel at elevated temperatures, i.e., above about 300°C . In this study, the effect from alloying elements Ni, Cu and Mn on 475°C embrittlement was examined based on microhardness measurement and Charpy V-notch tests as well as atom probe tomography (APT). It was found that, after aging for 10h, 3% Ni accelerates the ferrite decomposition dramatically, 5% Mn has minor effect and no effect of 1.5% Cu was seen. The hardness increase tested at 450°C and 500°C was consistent with the observations from APT. The embrittlement based on room temperature Charpy tests was observed mainly during the first 10h. The embrittlement in Fe-20Cr-3Ni alloy was attributed to ferrite decomposition, while the other three alloys may be influenced by other phenomenon as well. A clustering effect of Cu has been observed in Fe-20Cr-1.5Cu and it was supposed to contribute to the mechanical changes.

Super duplex stainless steels are applied in highly corrosive environments. To withstand such conditions, they designed with increased content of alloying elements and a duplex microstructure consisting of austenitic and ferritic phases. The result of this combination is the desired improvement in corrosion resistance, but also, the enhancement of mechanical properties. Machining super duplex stainless steels involves strain hardening of the workpiece, intense adhesive wear and elevated temperatures within the cutting zone leading to rapid tool wear and poor machined surface integrity. This research pertains to the application of commercially available PVD coatings to minimize the detrimental effects when turning super duplex stainless steel S32750. The selected coatings for this study were Alcronos (AlCrN), Alnova (AlCrN + AlCrSiN), Formera (CrN + CrAlTiN), Croma Plus (Cr + CrN + OX), Fortiphy (CrN) and Certiphy (TiAlN). The wear behavior and mechanisms in two distinct machining experiments were evaluated, and all tools failed by chipping preceded by intense adhesive wear and BUE formation. The use of AlCrN coatings improved tool life significantly. Data on the cutting force, chip formation, and workpiece surface integrity indicate less workpiece strain hardening effects, improved friction conditions at the tool/chip interface, as well as thinner chips being formed when machining with Alcronos coated carbide inserts. The micro-mechanical properties of the selected coatings were assessed and Alcronos combined high hardness and elastic modulus with a high plasticity index value that allows this coating to better manage the friction in the cutting zone and better dissipate the energy generated during cutting. / Thesis / Master of Applied Science (MASc) / Super duplex stainless steels are designed to be applied in highly corrosive environments. Like any other stainless steels, processing the super duplex grade can be challenging, especially when it comes to machining. The major causes of poor machined surface quality and rapid tool wear are high temperature, the workpiece enhanced mechanical properties, surface hardening and the tendency to stick to the cutting tool causing adhesive wear. This research explores the application of coated cutting tools to improve the machinability of the super duplex stainless steel UNS S32750. Different commercially available coatings were tested and two, Alcronos and Alnova, improved tool life significantly. These two coatings were capable of improving the friction conditions within the cutting zone which, in turn, helps with the formation of the chips and leads to a better machined surface integrity and an approximately 5 to 6 times longer tool life.