Hardfacing alloys are utilised in pump and valve components in pressurised water reactors (PWR's). They are designed to withstand wear and galling effects, which occur as a result of surface-to-surface contact, where surface roughness increases by localised plastic deformation, resulting in fracture and material transfer. Typically, alloys that exhibit suitable hardness and galling resistance are known as the Stellites; a Co-base alloy family. Whilst these Co alloys perform well in a hardfacing capacity, they suffer from neutron activation and subsequently decay, forming 60Co isotopes, which emit hazardous γ-rays, contributing to plant worker exposure. The present study was developed to characterise and assess the metallurgical properties of two candidate Co-free replacement alloys; stainless Fe-based alloys Tristelle 5183 and a derivative alloy, developed and patented by Rolls-Royce, known as RR2450. The alloys are produced as gas-atomised powders before undergoing hot isostatic pressing (HIP) into usable parts in-service. As part of this work, we have identified a novel, high-strength Fe-Cr-Ni silicide phase, which precipitates extensively within the RR2450 alloy after HIP consolidation, resulting in the formation of a triplex (austenite/delta- ferrite/silicide) matrix. The use of automated diffraction tomography (ADT) has allowed the crystallography of this phase to be determined as a trigonal R3 space group setting. A carbon atom, identified at a trigonal bipyramidal site along [111] within the silicide phase unit cell, indicates a carbon solubility of up to 1.2 wt% within this phase. HIP cycles were studied in situ using synchrotron X-ray diffraction (XRD), which revealed that the silicide phase decomposes within the metastable gas-atomised RR2450 powder by a eutectoid γ → delta + M7C3 transformation. The starting fraction of metastable delta-ferrite within the RR2450 gas-atomised powder is shown to directly influence the rate of transformation from γ to delta-ferrite during the HIP cycle. The wear resistance of the triplex RR2450 alloy at 300 °C is shown to be superior when compared to the austenitic Tristelle 5183. This is attributed to the high strength silicide phase, which is shown to offer a hardness up to 2 to 2.5 times greater than the austenite and delta-ferrite phases. By producing an elastic angular distortion of the unit cell, the silicide phase is able to withstand loading up to 1 GPa without yielding. The Tristelle 5183 alloy, which produces a lower fraction of silicide phase compared to RR2450, is reliant on the formation of stacking faults and a strain induced martensitic transformation to provide a high wear resistance. These transformations are shown to reduce substantially during wear testing at 190 °C, leading to a loss of high temperature wear resistance in the Tristelle 5183 alloy. Future work into developing silicide based Fe hardfacings is suggested, the microstructures of which can be tailored by controlling Si and Ni additions.

<p>The general trend in the car body manufacturing industry is towards low-series production and reduction of press lubricants and car weight. The limited use of press lubricants, in combination with the introduction of high and ultra-high strength sheet materials, continuously increases the demands of the forming tools. To provide the means of forming new generations of sheet material, development of new tool materials with improved galling resistance is required, which may include tailored microstructures, introducing of specific(MC, M(C,N))carbides and nitrides, coatings and improved surface finish. In the present work, the wear mechanisms in real forming operations have been studied and emulated on a laboratory scale by developing a test equipment. The wear mechanisms identified in the real forming process, were distinguished into a sequence of events consisting of initial local adhesive wear of the sheets resulting in transfer of sheet material to the tool surfaces. Successive forming operations led to growth of the transfer layer and initiation of scratching of the sheets. Finally, scratching changed into severe adhesive wear, associated with gross macroscopic damage. The wear process was repeated in the laboratory test-equipment in sliding between several tool materials, ranging from cast iron to conventional ingot cast tool steels to advanced powder metallurgy tool steel, against dual-phase carbon steel sheets. By use of the test-equipment, selected tool materials were ranked regarding wear resistance in sliding against ferritic-martensitic steel sheets at different contact pressures.</p><p>Wear in sheet metal forming is mainly determined by adhesion; initially between the tool and sheet surface interaction and subsequently, after initiation of material transfer, between a sheet to sheet contact. Atomic force microscopy force curves showed that adhesion is sensitive to both chemical composition and temperature. By alloying of iron with 18wt.% Cr and 8wt.% Ni, alloying in itself, or changes in crystal structure, led to an increase of 3 times in adhesion at room temperature. Hence, alloying may be assumed a promising way for control of adhesive properties. Additionally, frictional heating should be controlled to avoid high adhesion as, generally, adhesion was found to increase with increasing temperature for all investigated materials.</p>

The general trend in the car body manufacturing industry is towards low-series production and reduction of press lubricants and car weight. The limited use of press lubricants, in combination with the introduction of high and ultra-high strength sheet materials, continuously increases the demands of the forming tools. To provide the means of forming new generations of sheet material, development of new tool materials with improved galling resistance is required, which may include tailored microstructures, introducing of specific(MC, M(C,N))carbides and nitrides, coatings and improved surface finish. In the present work, the wear mechanisms in real forming operations have been studied and emulated on a laboratory scale by developing a test equipment. The wear mechanisms identified in the real forming process, were distinguished into a sequence of events consisting of initial local adhesive wear of the sheets resulting in transfer of sheet material to the tool surfaces. Successive forming operations led to growth of the transfer layer and initiation of scratching of the sheets. Finally, scratching changed into severe adhesive wear, associated with gross macroscopic damage. The wear process was repeated in the laboratory test-equipment in sliding between several tool materials, ranging from cast iron to conventional ingot cast tool steels to advanced powder metallurgy tool steel, against dual-phase carbon steel sheets. By use of the test-equipment, selected tool materials were ranked regarding wear resistance in sliding against ferritic-martensitic steel sheets at different contact pressures. Wear in sheet metal forming is mainly determined by adhesion; initially between the tool and sheet surface interaction and subsequently, after initiation of material transfer, between a sheet to sheet contact. Atomic force microscopy force curves showed that adhesion is sensitive to both chemical composition and temperature. By alloying of iron with 18wt.% Cr and 8wt.% Ni, alloying in itself, or changes in crystal structure, led to an increase of 3 times in adhesion at room temperature. Hence, alloying may be assumed a promising way for control of adhesive properties. Additionally, frictional heating should be controlled to avoid high adhesion as, generally, adhesion was found to increase with increasing temperature for all investigated materials.

Sheet metal forming processes are mechanical processes, designed to make products from metal sheet without material removal. These processes are applied extensively by the manufacturing industry to produce commodities such as heat exchangers or panels for automotive applications. They are suitable for production in large volumes. A typical problem in forming operations is accumulation of local sheet material adherents onto the tool surface, which may deteriorate the subsequent products. This tool failure mechanism is named galling. The aim of this work is to explain the mechanisms behind galling and establish factors how it can be reduced. The focus of this work is on the influence of tool material for minimum risk of galling. Experimental tool steels alloyed with nitrogen were designed and manufactured for systematic tribological evaluation. Reference tool materials were conventional cold forming tool steels and coated tool steels. The sheet material was austenitic stainless steel AISI 304, which is sensitive for galling. A variety of lubricants ranging from low to high viscous lubricants were used in the evaluation. The properties of the tool materials were characterized analytically and their tribological evaluation included industrial field tests and several laboratory-scale tests. The testing verified that nitrogen alloying has a very positive effect for improving galling resistance of tool steels. Tool lives comparable to the coated tool steels were achieved even with low viscous lubricants without poisonous additives. The hypothesis used for the explanation of the positive effect of nitrogen alloying is based on the critical local contact temperature at which the lubrication deteriorates. Therefore, the contact mechanism at the tool-sheet interface and the local energy formation were studied systematically. Theoretical considerations complemented with FEA analysis showed that a small size of hard particles with a high volume fraction gives low local contact loads, which leads to low frictional heating. Also, an even spacing between the hard particles and their frictional properties are of importance. Nitrogen alloyed tool steels have these properties in the form of small carbonitrides. The finding of this work can be applied to a wide range of applications that involve sliding metal contacts under severe tribological loading.

The general trend in the car body manufacturing industry is towards low-series production and reduction of press lubricants and car weight. The limited use of lubricants, in combination with the introduction of high and ultrahigh-strength sheet materials, continuously increases the demands on the forming tools. The major cause for tool failure during the forming process is transfer and accumulation of sheet material on the tool surfaces, generally referred to as galling. The adhered material creates unstable frictional conditions and scratching of the tool/sheet interface. To provide the means of forming new generations of sheet materials, development of new tool materialswith improved galling resistance is required, which may include tailored microstructures introducing specific carbides and nitrides, coatings and improved surface finish. In the present work, the galling wear mechanisms in real forming operations have been studied and emulated at a laboratory scale by developing a test equipment. The wear mechanisms, identified in the real forming process, were distinguished into a sequence of events. At the initial stage, local adhesive wear of the sheets led to transfer of sheet material to the tool surfaces. Successive forming operations resulted in growth of the transfer layer with initiation of scratching of the sheets. Finally, scratching changed into severe adhesive wear, associated withgross macroscopic damage. The wear process was successfully repeated in the laboratory test equipment in sliding between several tool materials, ranging from cast iron and conventional ingot cast tool steels, to advanced powder metallurgy tool steel, sliding against medium and high-strength steel sheets. By use of the test equipment, selected tool materials were ranked regarding galling resistance. The controlling mechanism for galling in sheet metal forming is adhesion. The initial sheet material transfer was found to occur, preferably, to the metallic matrix of the tool steels. Hence, the carbides in the particular steels appeared less prone to adhesion as compared to the metallic matrix. Therefore, an improved galling resistance was observed for a tool steel comprising a high amount of small homogeneously distributed carbides offering a low-strength interface to the transferred sheet material.Further, atomic force microscopy showed that nanoscale adhesion was influenced by temperature, with increasing adhesion as temperature increases. A similar dependence was observed at the macroscale where increasing surface temperature led to initiation of severe adhesive wear. The results were in good agreement to the nano scale observations and temperature-induced high adhesion was suggested as a possible mechanism.

High strength boron steels are commonly used as structural reinforcements or energy absorbing systems in automobile applications due to their favourable strength to weight ratios. The high strength of these steels leads to several problems during forming such as poor formability, increased spring back, and tendency to work-harden. In view of these difficulties, high strength boron steels are usually formed by press hardening at elevated temperatures with a view to facilitate forming and simultaneous hardening by quenching of complex shaped parts.The high strength steel sheets are used with an Al–Si coating with a view e.g. to prevent scaling of components during hot-metal forming. The Al-Si coated high strength steel can lead to problems with galling (i.e. material transfer from the coated sheet to the tool surface) which have a negative influence on the quality of the produced parts as well as the process economy. The available results in the open literature pertaining to high temperature galling are very scarce. With this in view, the friction and wear behaviours of different tool steel coatings and different roughness lay directions sliding against Al–Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature reciprocating friction and wear tester at temperature of 900 °C.The results have shown that parallel sliding with respect to the surface roughness lay reduces the severity of galling compared to perpendicular sliding. None of the coatings included in this study have shown beneficial effects in view of galling. The DLC coating experienced less galling compared to the AlCrN and TiAlN. Post polishing of the coated tool steel has resulted in more severe material transfer with higher and more unstable friction. / <p>Validerat; 20111022 (anonymous)</p>

No description available.

<p>Abstract</p><p>Today sheet metal forming is used to make a variety of mass production because it has a high production rate. One of the biggest concerns in sheet metal forming is wear of the tool in form of galling. Galling in sheet metal forming is characterised by an increased tool surface roughness, unstable friction in the forming process and undesirable scratches on the final products.</p><p>Several ways of ranking materials resistance to galling exist today but only ASM G98 is standardised. Nevertheless, some different methods developed for ranking tool materials’ tendency to galling have also been developed.</p><p>The aim of this thesis is to develop and improve the Uddeholm Tooling Tribo Test rig located at Uddeholm Tooling AB. The rig, which is a variation of cylinder-on-cylinder test equipment, was improved with a new tool holder, a utilization of the real sheet material counter face and a new data acquisition system and software. The galling was detected using scratches on the sheet, metallographic analysis of the material adhered on the tool specimen, monitoring of coefficient of friction and the standard deviation of the coefficient of friction.</p><p>The obtained results show difficulties with ranking of tool materials in terms of galling resistance under non-lubricated conditions. The tool steels tested were SVERKER21 and UNIMAX. AISI304-10, DC04 and DOCOL1000DP sheets were used. Additionally a low friction coating of BalinitC on SVERKER21 was also included. All specimens of the tool steels showed signs of galling on every run, only the low friction coating showed a transition in behaviour of friction coefficient corresponding to galling initiation. The standard deviation of the coefficient of friction increased at low loads. A decrease of the test loads led to stability loss of the system detected by an increase in the standard deviation of the coefficient of friction. This might happen because the Kistler platform is originally designed for larger loads. Although, the test rig does not work properly in its present state, the concept looks promising.</p>

Baccharis dracunculifolia (Asteraceae), conhecida popularmente como \"alecrim do campo\" ou \"vassourinha\", é uma planta nativa brasileira amplamente distribuída nos estados de São Paulo e Minas Gerais. Esta espécie tem se destacado pela rica interação com insetos, galhadores e especialmente Apis mellifera, e na produção de metabólitos secundários com inúmeras atividades biológicas. A interação com as abelhas A. mellifera possibilita a produção da própolis verde, produzida a partir de fragmentos vegetativos, material resinoso e balsâmico da B. dracunculifolia. Esta espécie também possui uma rica interação com insetos galhadores, os quais formam estruturas atípicas no tecido vegetal, conhecidas como galhas. Dessa forma, o objetivo desse trabalho foi investigar as correlações existentes entre os metabólitos secundários da B. dracunculifolia com os insetos galhadores e a visitação de abelhas A. mellifera na produção de própolis verde. Os indivíduos de B. dracunculifolia foram cultivados na região de cerrado no estado de Minas Gerais, Bambuí-MG. Dentre as 400 espécies plantadas, 48 indivíduos de B. dracunculifolia, sendo 24 fêmeas e 24 machos, foram investigados quanto ao grau de infestação por galhas, número de abelhas visitantes e o tempo de coleta de resina pelas abelhas. As folhas da B. dracunculifolia e as própolis verdes foram analisadas tanto por cromatografia gasosa (CG-DIC), avaliação dos componentes voláteis, quanto por cromatografia liquida (CLAE-DAD), avaliação dos componentes fixos. Os dados de observações de campo e as quantificações dos componentes majoritários foram analisados frente aos testes estatísticos de Wilcoxon-Mann-Whitney e Spearman para diferenças e correlações estatísticas, respectivamente. Estatisticamente foi possível observar diferenças significativas entre os indivíduos machos e fêmeas, sendo que os machos apresentaram maior infestação por insetos galhadores e as fêmeas foram mais visitadas pelas abelhas, nas quais também permanecem mais tempo coletando resina para a produção da própolis verde. Correlações entre o trans-cariofileno e a substância D (substância fenólica ainda não identificada), com o número de abelhas e o tempo de coleta de resina também foram observadas. Essas duas substâncias apresentaram valores de concentrações maiores nas fêmeas e parecem ter uma pequena contribuição para as diferenças de visitação encontradas entre os indivíduos machos e fêmeas de B. dracunculifolia. A galha de maior infestação foi quantificada e coletada, sendo identificada como sendo do inseto Baccharophelma dracunculifolia. Importante destacar também que houve sucesso na criação do pasto apícola, uma vez que as abelhas estão coletando resina das plantas cultivadas no campo de pesquisa em Bambuí- MG possibilitando maior produtividade e qualidade da própolis verde produzida nesta região / Baccharis dracunculifolia (Asteraceae), popularly known as \"alecrim do campo\" or \"vassourinha\", is a Brazilian native plant widely distributed in the states of São Paulo and Minas Gerais. This species stands out for the rich interaction with insects, galling insects and especially Apis mellifera, and in the production of secondary metabolites, which display important pharmacological activities. The interaction with bees A. mellifera allows the production of green propolis, produced from vegetative fragments, resinous and balsamic material of B. dracunculifolia. This species also has a rich interaction with galling insects, which form atypical structures in the plant tissue, known as galls. Therefore, the aim of this work was to investigate the correlations between the secondary metabolites of B. dracunculifolia with galling insects and the visitation of A. mellifera in the production of green propolis. The individuals of B. dracunculifolia were cultivated in the cerrado region of the State of Minas Gerais, Bambuí-MG, and among the 400 planted species, 48 individuals of B. dracunculifolia, 24 females and 24 males, were investigated for the degree of galls infestation, number of visiting bees and the time of resin collection by the bees. Samples from plants and green propolis were analyzed by gas chromatography (GC-FID), for volatile components evaluation, and by liquid chromatography (HPLC-PDA), for evaluation of fixed components. Statistically, the data from field observations and quantifications of major components were analyzed by Wilcoxon-Mann-Whitney and Spearman for statistical differences and correlations, respectively. Statistically significant differences were observed between males and females, with males showing higher infestation by galling insects and females more visited by bees, in which they also spent more time collecting resin for the production of green propolis. Correlations between trans-caryophyllene and compound D (phenolic compound not yet identified), with the number of bees and the time of resin collection were also observed. These two compounds had higher concentration values in females and seem to have a small contribution to the differences in visitation found between males and females of B. dracunculifolia. The gall with highest infestation was quantified and collected, being identified as the insect Baccharophelma dracunculifolia. It is also important to note that there was success in the bee pasture formation, since the bees are collecting resin from the plants cultivated in the research field in Bambuí - MG, allowing greater productivity and quality of the green propolis produced in this region

<p>Metal forming is widely used in the industry to produce cans, tubes, car chassis, rods, wires etc. Forming certain materials such as stainless steel, aluminium and titanium, is often difficult, and problems associated with transfer of work material to the tool material are frequent. Transferred material may scratch and deform the following manufactured pieces, a phenomenon named galling. Lubricants can, to some degree, solve these problems. However, many forming oils are hazardous to the environment, and therefore it is highly desirable to replace them or get rid of them.</p><p>This thesis investigates the nature of the galling phenomenon and tries to explain under which conditions such problems arise. Dry sliding tests have been performed in a dedicated load-scanner equipment. Difficult work materials have been tested against tool materials under various conditions and the samples have then been studied by advanced analytical techniques, such as ESCA and TEM, to study the detailed tribological mechanisms occurring in the contact between work and tool material.</p><p>The general assumption is that material transfer only occurs when there is metal to metal contact. In this work it has been found that, for stainless steel, the oxide plays a very important role for the sticky behaviour of stainless steel, and that metal to metal contact is not a necessary condition for galling.</p><p>Several PVD-coated tool materials have been tested and it was found that vanadium nitride coatings can be tuned regarding their chemical composition, to be more galling resistant than conventional coatings.</p><p>The surface roughness of the tool material is very strongly coupled to the tools ability to resist galling. The smoother the tool surface, the less risk of material transfer and galling.</p><p>Some work materials, like aluminium and titanium, transfer to even the smoothest tool materials. A proposed explanation for this is that their oxides are much harder than the bulk material and the tool material matrix. When deforming the work material, the oxide will fracture into small hard scales, which can indent the tool material. Indented hard scales will then contribute to material transfer of more work material to the tool.</p>