Evolution of artificial defects during shape rolling

Very often defects are present in rolled products. For wire rods, defects are very deleterious since the wire rods are generally used directly in various applications. For this reason, the market nowadays requires wire rods to be completely defect-free. Any wire with defects must be rejected as scrap which is very costly for the production mill. Thus, it is very important to study the formation and evolution of defects during wire rod rolling in order to better understand and minimize the problem, at the same time improving quality of the wire rods and reducing production costs. The present work is focused on the evolution of artificial defects during rolling. Longitudinal surface defects are studied during shape rolling of an AISI M2 high speed steel and a longitudinal central inner defect is studied in an AISI 304L austenitic stainless steel during ultra-high-speed wire rod rolling. Experimental studies are carried out by rolling short rods prepared with arteficial defects. The evolution of the defects is characterised and compared to numerical analyses. The comparison shows that surface defects generally reduce quicker in the experiments than predicted by the simulations whereas a good agreement is generally obtained for the central defect.

The Legitimacy Process that Supports the Formation and Development of Cluster Initiatives : The Case of a Tourism Cluster Initiative in Dalarna

Today, large public investments are being made with the aim of creating and developing cooperation between businesses in inter-organizational networks. Such initiatives are commonly denoted cluster initiatives and their underlying purpose are to spur innovation and regional growth. Much research has been conducted in this field, but relatively few studies have examined the process of cluster initiatives. By following the case of a regional cluster project within the tourism industry in the region of Dalarna, Sweden, the objective of this thesis is to deepen the understanding of the formation and development process of cluster initiatives. The investigation has been conducted by examining two main themes; the internal relationships within the cluster initiative and the relationships between the cluster initiative and its external stakeholders, such as funding agencies, regional government and local businesses. The analysis is based on a legitimacy perspective and indicates that the coordinating body of the cluster initiative, the hub, principally deals with a legitimation process. What occurs within the cluster initiative, between the members themselves and between the members and the hub, is legitimation. This also applies to external relationships, between the hub and its external stakeholders. A prerequisite for the realization of its mission is that the hub obtain and sustain legitimacy; legitimacy for itself, for the other members, for the idea, for the different activities and for the industry as such.

Modeling precipitation and its effect on recrystallization during hot strip rolling of niobium steels

Using a physically based model, the microstructural evolution of Nb microalloyed steels during rolling in SSAB Tunnplåt’s hot strip mill was modeled. The model describes the evolution of dislocation density, the creation and diffusion of vacancies, dynamic and static recovery through climb and glide, subgrain formation and growth, dynamic and static recrystallization and grain growth. Also, the model describes the dissolution and precipitation of particles. The impeding effect on grain growth and recrystallization due to solute drag and particles is accounted for. During hot strip rolling of Nb steels, Nb in solid solution retards recrystallization due to solute drag and at lower temperatures strain-induced precipitation of Nb(C,N) may occur which effectively retard recrystallization. The flow stress behavior during hot rolling was calculated where the mean flow stress values were calculated using both the model and measured mill data. The model showed that solute drag has an essential effect on recrystallization during hot rolling of Nb steels.