The continuous development of hot forming tool steels has resulted in steels with improved mechanical properties. A change in alloying composition, primarily a decreased silicon content, makes them tougher and more wear resistant at elevated temperatures. However, it is at the expense of their machinability. The aim of this study is to explain the mechanisms behind this negative side effect. Hot work tool steels of H13 type with different Si content were characterised mechanically, and evaluated analytically and by dedicated machining tests. Machining tests verified that materials with low Si content displayed reduced machinability due to their stronger tendency to adhere to the cutting edge. Three hypotheses were tested. The first hypothesis, that the improved toughness of the low Si steels is the reason behind their relatively poor machinability, was rejected after machining tests with one low Si steel heat treated to the same relatively low toughness as conventional hot work tool steels. The second hypothesis, that a change in oxidation properties, also associated with the change in Si composition, lies behind the reduced machinability was investigated by dedicated tests and evaluations. It was found that the oxide thickness increased with reduced Si content and that there was an enrichment of Cr at the oxide/steel interface. The differences in oxide thickness and the possible differences in oxidation properties may influence the machinability of the materials through their different abilities to adhere to the cutting edge. The third hypothesis, that a high enough temperature to initiate phase transformation from ferrite to austenite is generated during machining of the tool steels, was also investigated. This may lead to a reduced machinability because higher austenite content is directly related to higher compressive stresses and higher cutting forces. This causes accelerated tool wear. This hypothesis was verified by ThermoCalc calculation of austenite content in the steels, which showed a good agreement with Gleeble compression tests and cutting force measurements. This thesis confirms that a reduced Si content in conventional H13 steel improves the toughness, reduces the oxidation resistance and lowers the ferrite-to-austenite transformation temperature. The reduction in austenite temperature is probably the most important factor behind the reduced machinability.

Chromium martensitic hot-work tool steel (AISI H13) is commonly used as die material in hot forming techniques such as die casting, hot rolling, extrusion and hot forging. They are developed to endure the severe conditions by high mechanical properties attained by a complex microstructure. Even though the hot-work tool steel has been improved over the years by alloying and heat treatment, damages still occur. Thermal fatigue is believed to be one of the most common failure mechanisms in hot forming tools. In this thesis tools used in hot forging and die casting were examined to determine damage, material response, thermal fatigue crack initiation and propagation. Different chromium martensitic hot-work tool steels, heat treated at four different austenitizing temperatures were experimentally tested in thermal fatigue and isothermal fatigue. The materials were then evaluated using X-ray line broadening analysis and transmission electron microscopy to explore the relation between fatigue softening and the change in microstructure. The high temperature fatigue softening was also simulated using an elasto-plastic, non-linear kinematic and isotropic model. The model was implemented in a numerical simulation to support the integration of die design, tool steel properties and its use. It was found that the dominant damage mechanisms in the investigated tools were thermal fatigue and that tool material experiences a three stage softening at high temperature loading. The primary stage was concluded to be influenced by the dislocation density and the second stage by the temper resistance i.e. carbide morphology. The microstructural changes during the softening stages were also connected to the non-linear kinematic and isotropic model. The general aim of this thesis is to increase the knowledge of the chromium martensitic hot-work tool steel damage, performance and microstructure.

The National Fire Code of Canada (NFCC) is one model code which regulates hot work in Canada. The code specifies that hot work processes need only create heat to be considered hot work processes, and requires that precautions taken adhere to those in Canadian Standards Association (CSA) W117.2, which is intended for welding, cutting and allied processes. CSA W117.2 requires a 15 m spherical radius of separation in which combustibles are ideally relocated or, at minimum, be protected with fire blankets. Openings, cracks and other locations in which sparks or hot particles must also be protected within this distance. Additionally CSA W117.2 requires a fire watch during, and one hour following the completion of the work. The NFCC stipulates more stringent requirements on the fire watch than CSA W117.2, requiring a check back 4 hours after the work. The code in its current form requires the same precautions be taken when using a soldering iron or epoxy resin as when using an oxyacetylene torch to flame cut steel. The lack of hazard characterization of hot work processes, and the umbrella prescription of required fire safety precautions can result in insufficient measures to prevent fires in some scenarios, and inordinate precautionary measures in others. While not applicable law in all jurisdictions, the NFCC is relied on in various Canadian industries for regulative purposes. Nuclear power generation in Canada is one such industry facing onerous fire protection costs resulting from following these precautions for the smallest of jobs requiring heat producing tools. The literature review highlights the dearth of scientific knowledge regarding the propensity of hot work as an ignition source and how this shortcoming manifests itself in issues across the various standards governing hot work practices. The objective of this research is to assess fire hazards resulting from various processes considered hot work under the National Fire Code of Canada (NFCC). Due to the breadth of processes covered by the NFCC, a spectrum of hot work activities was investigated from processes as innocuous as the application of heated adhesive, to well known sources of ignition such as a variety of welding processes, oxyacetylene cutting and plasma cutting. To streamline the hazard assessment, processes were categorised into three groups based upon expected hazards such that testing could focus on the most prominent ignition danger presented by each. The groups were those processes exhibiting hot surface ignition hazards, processes with hot surface ignition hazards in addition to limited potential to generate hot particles, and those processes in which the generation of significant quantities of spark and hot particles is guaranteed. For the first two process categories, experimentation focused on determining a critical process temperature with which to rank processes and also compare with ignition temperatures of combustibles commonly involved in hot work fires. The critical process temperature was determined as the highest measured temperature of the workpiece or tool during the chosen process and was typically measured with the use of thermocouples and infrared thermography. Characterization of any hot particles in the second category was performed using infrared thermography, and in some cases, thermal paper. Literature sources indicated that sparks and hot particles are the largest factor in hot work fires, so specialised methodology was developed for the third category of processes to characterise the distribution of many thousands of hot work particles generated during welding, thermal cutting and other hot particle producing work. The distributions collected were used to determine the area enveloped by the ignition hazard of hot particles as well as areas encompassing the highest threat to combustibles in relative terms. Several of the processes as studied were found not to exhibit any measurable form of ignition hazard, including forms of manual sanding and filing and rotary filing of steel. Heated adhesive, cutting steel with a reciprocating saw and drilling of steel were shown to exhibit moderate degrees of hazard with temperature rise of 195\degree C or less, suggesting potential hazard to a limited group of combustibles. Welding and cutting processes were shown to have a relative ignition potential across a wide area. Typical welding procedures produced hot particles which travelled a maximum of approximately 3 - 4 m while thermal cutting processes ejected sparks, slag and hot particles up to 9.8 m from the work. Incorporated properly into updated standards and codes, the results and findings of this research could drastically improve the Canadian model codes regarding the regulation of hot work by decreasing cost and difficulty for Canadian Industry without increasing the risk of loss.

This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest. The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers. The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

Many phenomena determining the microstructure of a tool steel and consequently the properties of the material, are governed by multicomponent diffusion. The diffusion driven reactions that take place during, for example, tempering of a hot-work tool steel or when the microstructure develops during hot isostatic pressing of cold-work tool steel, are dependent on the types and amounts of alloying elements. In order for computational methods to be usable, these alloying effects need to be understood and incorporated in the models. In this work the influence of some typical tool steel alloying elements on the coarsening behavior of precipitates is investigated. Experimental coarsening studies are performed and the impact of the diffusion mobility descriptions and the thermodynamic descriptions are investigated by means of DICTRA coarsening calculations. The kinetic descriptions for diffusion in the body centered-cubic phase in the case of the chromium-iron-vanadium system and the chromium-iron-molybdenum system are improved by assessments of diffusion mobility parameters, and are shown to have a large impact on the calculated coarsening rate for vanadium-rich and molybdenum-rich precipitates. The effect of cobalt is examined by a coarsening experiment for vanandiumrich carbides and by a diffusion couple experiment for the investigation of the vanadium interdiffusion. The presence of cobalt is experimentally shown to have retarding effect on the coarsening rate of the carbides, but not on the vanadium diffusion. The coarsening rate of nitrogen-rich precipitates is compared to the coarsening rate of carbon-rich precipitates, and a lower coarsening rate for nitrides compared to carbides can be confirmed. Correlation between coarsening calculations and experiments is obtained suggesting that the thermodynamic description of the two systems is the underlaying reason for the different coarsening rates. Further, calculations utilizing the DICTRA software are combined with experimental investigations in order to study the possibility to apply computational methods for compound material development and explore application areas for high nitrogen alloyed tool steels produced by powder metallurgy. / <p>QC 20121011</p>

Purpose: The purpose of the degree project was to investigating fire protection work during construction at various companies and proposing improvement proposals to reduce the risk of fire at construction sites. Method: The method on which the thesis project was based on was a literature study, interviews and document analysis. The literature study has been carried out to gain in-depth knowledge regarding the fire protection during the construction phase. The interview study was conducted at different construction companies to get an idea of ​​how the different companies handle fire safety at construction sites. The document analysis has been carried out with the help of various companies requirements documents, which form the basis for the fire protection work at the construction sites. Results: The results present the companies fire protection work during construction. Prior to the start of construction, a fire protection description is projected that covers how to build to prevent fire safety, it also covers the how parts of the workplace should be designed. The fire protection that proved to exist mostly consists of two mutually independent escape routes with clearly visible escape signs, a dedicated collection point and strategically placed hand-held fire extinguishers that should be within a range of 25 meters. Hot work, electrical causes and arson have emerged as a recurring shortage and cause of most fires occurring at construction sites. There is room for improvement by, among other things, spending more time in planning, introducing a practice on fire and evacuation alarms and creating the company's fire protection description in connection with the production of the A-drawings. Conclusions: In conclusion, there are opportunities for improvement, but unfortunately nothing has been implemented in practice.

Hot-work tool steels make up an important group of steels that are able to perform with good strength and toughness properties at elevated temperatures and stresses. They are able to gain this behavior through their alloy composition and heat treatment, which relies on the precipitation of alloy carbides to counter the loss in strength as the tempered material becomes more ductile. As demand grows for materials that are suitable for even harsher applications and that show improved mechanical qualities, the steel industry must continuously investigate the development of new steel grades. Within this context, the present work focuses on examining the mechanical properties and microstructure of two hot-work tool steels, of which one is a representative steel grade (Steel A) and the second a higher-alloyed variant (Steel B), at different tempering conditions. To complement the experimental work, precipitation simulations are used to monitor the progression of secondary carbide precipitation and to examine the predicted microstructural changes through varying the alloy composition. The study finds that Steel B does not actually have improved properties with respect to Steel A and suggests that the precipitation behavior of both steels is virtually identical. Despite this, the simulation work reveals that this behavior can change dramatically to favor more positive hardness contributions by increasing the alloy content of V. In short, with the project being part of an ongoing investigation, there remain several areas of analysis that need to be completed before offering a complete picture that can ultimately play a part in the development of a new hot-work tool steel grade.

This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest. The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers. The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

Im Rahmen der vorliegenden Arbeit wurde die drahtbasierte additive Fertigung mittels Elektronstrahls (WEBAM) unter Nutzung einer lateralen Drahtzuführung und des Warmarbeitsstahls X37CrMoV5-1 untersucht. Die Schwerpunkte lagen auf der Analyse des Einflusses der Prozessparameter, der Drahtführungstechniken (schleppend, stechend und seitlich), des Substratwerkstoffes und des Materialübergangs auf die Prozessstabilität sowie die Auftraggeometrie. Das Ziel war die prozesssichere Herstellung von 3D-Geometrien mit bidirektionaler und kontinuierlicher Aufbaustrategie. Die Untersuchungen zeigten, dass die Auftraggeometrie und insbesondere der Materialübergang wesentlich vom Substratwerkstoff abhängig waren. Anhand eines aufgestellten Prozessfensters wurde ein Parametersatz ermittelt, welcher unabhängig von der Drahtführungstechnik nahezu identische Auftraggeometrien erzeugte. Mit Hilfe einer dynamischen Anpassung des Positionsversatzes für die jeweilige Drahtführungstechnik konnten rissfreie Aufbauten mit bidirektionaler, alternierender Aufbaustrategie generiert werden. Diese Aufbauten wurden anschließend hinsichtlich der Mikrostruktur sowie der mechanischen Eigenschaften in Abhängigkeit vom Wärmebehandlungszustand charakterisiert. Die Prozessstabilität und Reproduzierbarkeit konnte anhand von mehreren aufgebauten 3D-Geometrien mit hoher Konturtreu demonstriert werden.

Additive manufacturing (AM) is an emerging and interesting technology that enables some of theproduct development projects (PDPs) to produce products that have mechanical and tribologicalproperties comparable to products that are conventionally manufactured. Selective laser melting(SLM) is an additive manufacturing technology that is predominantly used for the production of metalbased components (i.e. it could be pure metal, alloys, and metal matrix composites). This workevaluates and ranks two different steel grades produced with SLM technology in tribological andcutting tool applications at AB Sandvik Coromant. The two steel grades used in this work were Cofree maraging steel alloy and Co-free W360 AMPO alloy. Both the grades are Cobalt free, hencedeveloped as a sustainable alternative for the future. The W360 AMPO alloy is a hot-work tool steelwith high temperature wear resistance and heat resistance. The work covers the characterization ofmicrostructure and chemical composition, mechanical properties, and tribological properties toevaluate the performance of the tool steel grades when used as tool bodies in drilling applications.The microstructure and chemical composition of the additive manufactured and heat-treated tool steelswere analyzed using SEM and EDS. The mechanical properties were evaluated using micro-Vickersindentation and scratch testing while the tribological properties were evaluated using pin-on-disctesting where counter material used was quenched and tempered steel. The application test included asimulated chip wear test using chip breakers (CB’s) and an actual drilling test, both performed at ABSandvik Coromant. To study the effect of surface topography on the adhesion tendency, the simulatedchip wear test was performed on both milled and grounded chip breaker (CB) samples. The drillingtest was done with three different test-set ups; function test, 30° inclined exit, and forced tool life test.The cellular microstructure was observed on Co-free maraging steel alloy sample, while themicrostructure was tempered martensite in W360 AMPO alloy. Elemental analysis revealed thechemical composition of the two steel grades. The measured hardness for both the samples Co-freemaraging steel alloy and W360 AMPO was found to be within the specification of demands (50-52HRC), although the hardness of W360 AMPO was a bit higher than Co-free maraging steel alloy. Theresults of the pin-on-disc tests showed that the wear resistance of the W360 AMPO alloy issignificantly higher than that of the Co-free maraging steel alloy, the tribo-system used was similarwhen compared to the actual application. Also, after analyzing the pin made up of quenched andtempered steel 34CrNiMo6 (SS2541) it can be seen that due to the W360 AMPO sample the volumeloss of the pin is almost 4 times when compared to Co-free maraging steel alloy. The result from thesimulated chip wear test showed that W360 AMPO has better wear characteristics. Adhesion ofworkpiece material (SS2541) was observed on both samples. In the simulated chip wear test, thesurface topography effect was studied by performing a test on milled and grounded CBs. GroundedCBs showed less adhesion tendency compared with milled CBs on both samples but the wearcharacteristics were similar irrespective of the surface roughness. The result from the drilling testshowed wear scar was predominant on a drill with Co-free maraging steel alloy and a drill with W360AMPO alloy was intact. Future possible investigations proposed after findings from experimentalresults may lead to future work.