Diss. (sammanfattning) Linköping : Univ., 2003. / Härtill 6 uppsatser.

Ternary transition metal cubic carbides have high hardness and are potential carbides in cemented carbide and cermet tools, as well as hard coatings used to improve metal cutting performance. In the present work, (Ti,Zr)C, (V,Nb)C, and (V,Ta)C ternary cubic carbides were synthesized using traditional powder-metallurgical methods. The effect of synthesis temperature and starting materials on synthesis is investigated, and the microstructure evolution during aging is studied. (Ti,Zr)C was found to decompose into lamellae upon aging at the temperature range from 1150 to 1800 °C. A similar microstructure was observed in (V,Ta)C and (V,Nb)C- 0.5 wt% Fe. All of these structures were found to form through discontinuous precipitation.The grain misorientation distribution of (Ti,Zr)C aged at 1400 °C is investigated. It was found that decomposition tends to occur at high-angle grain boundaries above 25°. The hardness of as-synthesized (Ti,Zr)C powder was found to be 41±6 GPa. Fully decomposed (Ti,Zr)C particles were found to be slightly harder than the undecomposed counterpart. On the other hand, in (V,Nb)C-0.5 wt% Fe, the decomposed structure formed upon aging at 1200 °C was found to have a hardness of 26±2 GPa, which is basically the same as the unaged alloy.Furthermore, the sintering behavior of (Ti,Zr)C with WC-Co is investigated. There are two γ-phases in the final microstructure, one TiC-rich and one ZrC-rich. (Ti,Zr)C was found to decompose at an early stage of sintering, and the final grain size of WC and the two γ-phases was found to be 10% smaller than that in a reference WC-TiC-ZrC-Co composite. / <p>QC 20170529</p>

I dagens industri utsätts verktyg vid plåtformning för allt större krafter. Material som ska formas blir starkare behövs också större krafter för at åstadkomma en geometrisk förändring. Detta har medfört att nötningseffekter vid tillverkning har ökat, och ett av dessa problem är galling. Galling, som är ett av huvudproblemen, är en nötningseffekt på verktygen där både adhesiv och abrasiv nötning förekommer. Detta innebär att material lossnar från värdmaterialet och fastnar på verktyget. Då material har överförts till verktyget har det inte längre ursprungsformen och kan leda till ojämnheter i materialet som ska formas. Hittills har företag använt sig av smörjmedel för att minska galling. Eftersom smörjmedel regleras allt hårdare av miljöskäl, måste industrin hitta nya lösningar. En lösning är att skapa verktygsstål som är motståndskraftiga mot galling genom sin mikrostruktur. Det finns fortfarande begränsad kunskap inom området och den här studien syftar till att jämföra två verktygsstål för att avgöra vilket som är mest beständigt mot galling. Verktygsstålen Caldie och Vancron Superclean kommer glida mot materialen DP600 och DP1000. De sistnämnda är de material som formas vid plåtformningen. Där materialen har olika sträckgränser, detta för att se om den har en inverkan vid plåtformning. För att avgöra vilket verktygsstål som är mest lämpligt vid plåtformning kommer en glidsträcka tas fram med hjälp av SOFS metoden. Glidsträckan kommer att ange hur snabbt galling uppstår och således kan ett bättre material bestämmas. Nötningsspåren hos materialen analyserades med hjälp av ett elektronmikroskop för att se hur galling hade påverkat verktygsstål och ytmaterial.Resultatet visade att Vancron Superclean var mer beständigt mot galling, då verktygsstålen gled över DP600, medan ingen slutsats kunde dras när de gled över DP1000. / In today's industry, tools are more exposed to larger forces in sheet metal forming. As materials become stronger, larger forces are also needed to achieve a geometric change of the materials. Because of this, abrasion effects in the processes have increased and one of the most common one is galling. Galling is a form of wear where both adhesive and abrasive wear occur. This means that material comes off of the host material and sticks to the tool. When material has been transferred to the tool, it no longer has the original shape and can lead to irregularities in the material to be formed. So far companies have used lubricants to minimize it. As lubricants are increasingly regulated for environmental reasons, the industry must find other solutions to the problem. One solution is to create materials that are resistant to galling through their microstructure. There is still limited knowledge in this area and the aim of this study is to compare two tool steels and investigate which of them is most resistant to galling. The tool steel Caldie and Vancron Superclean will be tested against the materials DP600 and DP1000 usually used in sheet metal forming. Where the materials have different yield strengths, this is to see if it has an impact on sheet metal forming. To decide which tool steel is most suitable for sheet metal forming, a sliding test will be produced using the SOFS method. The sliding distance will describe how quickly galling occurs and thus the better material is determined. The abrasive traces of the materials were analyzed using an electron microscope to see how galling affected the tool steel and surface material.The result showed that the Vancron Superclean was more resistant to galling, as the tool steel slid over the DP600, while no conclusion could be drawn when slipping over DP1000.

The thesis paper here focuses on the effects of the austempering temperature (TA) and the austempering time (tA) on the unalloyed fully ferrite Compacted Graphite Iron (CGI), to obtain improve in mechanical properties and the study of the microstructure. The unalloyed CGI samples were austenitised at 850oC for 60 and 90 min and were then heat treated at 275, 325 and 375oC with different holding times at 30,60,90, and 120 mins. Mechanical properties like the tensile strength, yield strength, young’s modulus, Brinell and Vickers harness were conducted to perform the analysis on the samples. LOM was used for the study of the microstructure and SEM was used for the study of fractography of the fractured tensile bar.

Superalloys such as alloy 718 and 925 possesses superior properties at elevated temperatures and corrosive environments. They are commonly found in application such as oil and gas extraction, turbine engines and in the chemistry industry. These alloys were developed during the 1950s but the demand of tubes and pipes of these alloys has rapidly increased. Sandvik has recently started produce these products and faces new challenges within the production.There are several studies within the area of superalloys but the hot working behavior and flow softening mechanism are not fully understood.The goal with this master thesis is to analyze two different steel grades, alloy 718 and 925 and correlate different process parameters that will influence the recrystallization initiation and nucleation.Two ingots manufactured through electric arc furnace, argon oxygen decarburization and refined by vacuum arc remelting were analyzed followed by a homogenization heat treatment. Samples were extracted from three positions, bottom, center, top and from half the radius in the ingot. The chemical composition was analyzed and the mechanical properties was tested trough hot compression testing (Gleeble). From Gleeble testing, the true strain, stress curves were analyzed in order to determine flow softening effects. The microstructure were studied trough light optical microscopy and electron backscatter diffraction.The results reveal that discontinuous dynamic recystallization is the dominant flow softening mechanism. There was no significant difference between the three positioning within the ingot.To maximize the recrystallized area fraction higher strain and temperatures must be provided or lower strain rates.

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This Independent Project reviews literature about the effect of pressure and temperature on thermal conductivity in packed beds and its relationship with electrical conductivity. Exploring the relationships between thermal conductivity, porosity and pressure can give useful knowledge for further improvements in manufacturing processes in the field of powder metallurgy. The resulting theoretical models describing the effective thermal conductivity show that gas and contact conductance dominate at lower temperatures and that radiation gains dominance as the temperature increases. Modifications of the models covered in this report can be made in order to simulate the process of interest more accurately. It was also shown that Wiedemann-Franz law could be of interest when wanting to quantify the thermal conductivity in a powder compact. Furthermore, a lab manual for a future Independent Project was developed.

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Mjukglödgning av kullagerstål är en förutsättning för att kunna vidareförädla stålet. Processen är idag väldigt tidskrävande vilket gjort den till en flaskhals i produktionen. Detta examensarbete har gått ut på att titta närmare på en snabbare mjukglödgningscykel, kallad puckelglödgning, som idag används i Hofors och ställa det i förhållande till nuvarande cykel som används i Rullhärdugn 1. Genom labbugnstest, dilatometertester samt en skarp körning har data tagits fram för hårdhet och struktur vilket sedan analyserats och jämförts med motsvarande data från dagens process.   Målet har varit att se om puckelglödgningen är en praktiskt gångbar process och om den uppfyller de krav på struktur och hårdhet som ställs på stålet efter mjukglödgning.   Resultatet har visat på att puckelglödgning ger en godkänd struktur och hårdhet i labbmiljö men att processen i sig ställer höga krav på ugnens kapacitet när det kommer till att använda den i den vanliga produktionen. Resultatet från den skarpa körningen visar att cykeln har svårt att få en likvärdig struktur när större volymer mjukglödgas. Puckelglödgningscykeln som används i Hofors har fördelar jämtemot den cykel som används i Hällefors, men slutsatsen är ändå att en optimering av nuvarande cykel i Hällefors är att föredra framför ett införande av en puckelglödgningscykel. / Soft annealing of ball bearing steels is a prerequisite to be able to further process the steel. The process today is very time-consuming which has made it into a bottleneck. The purpose of this thesis has been to study a faster soft annealing cycle called “hump annealing” which is used in Hofors and compare it to the current cycle used in “Rullhärdugn 1” (Roller hearth furnace 1). Through a test in a lab furnace, dilatometer tests and a live test data has been collected on hardness and structure which then has been analyzed and compared against data from the current day process.   The goal has been to see if hump annealing is a practically feasible process and if it fulfills the requirements in structure and hardness that is demanded of the steel following soft annealing.   The results concluded showed that hump annealing produces an acceptable structure and hardness in lab environment but that the process itself puts high demands on the furnaces capacity when it comes to using it in the regular production. The results from the live test shows that the hump annealing cycle has problems getting an equivalent structure when bigger volumes are soft annealed. The hump annealing cycle do have certain advantages compared to the cycle used in Hällefors but the conclusion is nevertheless that an optimization of the current cycle in Hällefors is preferred to adopting the hump annealing cycle.

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