Raahe, Finland
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Suikkanen P.P.,Ruukki Metals Oy | Cayron C.,CEA Grenoble | DeArdo A.J.,University of Pittsburgh | Karjalainen L.P.,University of Oulu
Journal of Materials Science and Technology | Year: 2013

The crystallography of bainite, transformed isothermally at 450 °C in 0.2C-2.0Mn-1.5Si-0.6Cr steel, was investigated by electron backscatter diffraction (EBSD) analysis. The orientation relationship (OR) was found to be closer to Nishiyama-Wassermann (N-W) than Kurdjumov-Sachs orientation relationship. Bainite microstructure consisted of parallel laths forming a morphological packet structure. Typically, there were three different lath orientations in a morphological packet. These orientations were dictated by a three specific N-W OR variants sharing the same {111} austenite plane. A packet of bainite laths with common {111} austenite plane was termed as crystallographic packet. Generally, the crystallographic packet size corresponded to the morphological packet size. Locally, crystallographic packets with only two dominant orientations were observed. This indicates strong local variant selection during isothermal bainite transformation. The relative orientation between the variants in crystallographic packets was found to be near 60°/<110>. This appears to explain the strong peak observed in the grain boundary misorientation distribution near 60°. Bainite also contained pronounced fraction of boundaries with their misorientation in the range of 2.5°-8° with quite widely dispersed rotation angles. Spatially these boundaries were found to locate inside the bainite laths, forming lath-like sub-grains. © 2013.

Siltanen J.,Ruukki Metals Oy | Tihinen S.,Ruukki Metals Oy | Komi J.,Ruukki Metals Oy
Journal of Laser Applications | Year: 2015

Welding trials have been carried out using direct-quenched 960 MPa ultrahigh-strength steel utilizing several welding processes: gas-metal-arc, laser, and laser gas-metal-arc hybrid welding. Laser power sources like the CO2-laser and the fiber-delivered solid state laser were used. In the trials, butt joints with various groove geometries were used and the thickness of the base material was a constant 6 mm. Welding filler materials varied from matching Union X96 (ISO 14341: G 89 5 M Mn4Ni2.5CrMo) to undermatching Esab OK 12.50 (G3Si1). The diameter of the filler wire varied from 1 to 1.2 mm. The highest hardness value, over 400 HV, was reached on laser welds. According to the results, the strength of the joints corresponded to the nominal strength of base materials (tensile strength of 960 MPa), regardless of the welding method and welding filler material used. As a whole, the results of transverse bend testing were poor as expected, especially when the face side of welds was under tension. The standardized bend and also the used impact toughness tests (Charpy-V) are not the best methods to evaluate the ductility or the toughness of a weld in direct-quenched steels. However, relatively good impact toughness values were achieved to the fusion line of the welds both with the continuous laser and laser hybrid welding process, reaching 57 J with the laser welding and 49 J with the laser hybrid welding when the matching filler material was used. © 2015 Laser Institute of America.

Ritakallio P.,Ruukki Metals Oy
Tubular Structures - Proceedings of the 15th International Symposium on Tubular Structures, ISTS 2015 | Year: 2015

The quality of steel strip is essential for tube quality. Conventional C-Mn steels are commonly used for hollow sections. These steels are susceptible to strain ageing, thus questioning their low temperature ductility in welded structures. To ensure good low temperature characteristics Ruukki shifted to thermomechanically-rolled steels. This study compares hollow sections from the early 1990s with current Ruukki hollow sections made of thermomechanically-rolled fine grain steels. Ageing is noticeable in conventional S355J2H hollow sections. In cold-formed areas, flat faces and in corners there is a risk that the toughness does not fulfill 27 J/−20◦C after welding. Ageing in Ruukki double grade S420MH/S355J2H hollow sections is still noticeable, but virtually insignificant. After ageing, the transition temperature T40J remains around −70◦C on the wide face, around −50◦C in corners and around −40◦C on the narrow face. There is only minor risk of toughness not conforming to the EN 10219 requirement of 40 J/−20◦C after welding. ©2015 Taylor & Francis Group, London.

Kemppainen A.,University of Oulu | Mattila O.,Ruukki Metals Oy | Heikkinen E.-P.,University of Oulu | Paananen T.,Ruukki Metals Oy | Fabritius T.,University of Oulu
ISIJ International | Year: 2012

Large amounts of injectants are used in the blast furnace (BF) process to reduce coke consumption, but this changes the gas composition in the BF shaft where iron ore reduction takes place. H2 and H2O gases change markedly in the gas atmosphere at high injection levels, which makes it important to investigate their effects on the reduction of iron oxides in a CO-CO2 atmosphere. The gaseous H2 and H2O content in the BF shaft atmosphere is approximately 8%. In the present work olivine pellets were reduced in H2-H2O-CO-CO2 and CO-CO2 atmospheres with equal reducing potentials of H 2 and CO by fixing the H2/H2O and CO/CO 2 ratios. No significant differences in the reduction rates of iron oxides were found between the H2-H2O-CO-CO2 and CO-CO2 atmospheres at high temperatures but at lower temperatures H2-H2O-CO-CO2 had higher reduction rate. Activation energies determined for hematite to magnetite reduction for both gas mixtures indicated better initial stage and later stage reduction in the H 2-H2O-CO-CO2 atmosphere. Field Emission Scanning Electron Microscope (FESEM) analysis was carried out on samples, and wüstite relics were found in the inner parts of pellets reduced to iron in the CO-CO2 gas but not in the samples reduced in the H 2-H2O-CO-CO2 gas. © 2012 ISIJ.

Metals R.,Ruukki Metals Oy
MPT Metallurgical Plant and Technology International | Year: 2013

The transition to pellets as feedstock for ironmaking and the related closure of the sinter plant together with more efficient dedusting technology at the blast furnaces have resulted in a significant decrease in emissions at Ruukki's steel plant in Raahe. Process changes and replacement of dust removal devices reduced particulate emissions have helped the facility to meet its emission reduction targets in 2012. The company has been making efforts to reduce emissions at the steel mill by investing in environmental technology and improving production processes. Its steel production has ranks higher than the European average in terms of carbon dioxide efficiency. The company continues to work on eco-efficiency at the Raahe steel mill where efforts are being made to install a dust removal system to collect fugitive dust emissions. The system is expected to reduce fugitive dust emissions and improve the air quality within the environment of the facility.

Valkonen I.,Ruukki Metals Oy
Welding in the World | Year: 2014

Ultra-high-strength steels are sensitive to heat input during welding, which can lead to softening in the heat-affected zone. This softening can also reduce the limit load capacity in non-load-carrying welds. One challenge is how to address this phenomenon in the design phase. To solve this problem, a method to determine material parameters for design and failure criteria is required. In this paper, a procedure using notched specimens to determine material parameters and failure criteria is presented. The results are compared with component-scale tests. The results show that the developed method results agree with results from the component tests. This procedure is a practical method to estimate the ultimate capacity of ultra-high-strength steels. © 2014, International Institute of Welding.

Kaijalainen A.J.,University of Oulu | Suikkanen P.,Ruukki Metals Oy | Karjalainen L.P.,University of Oulu | Jonas J.J.,McGill University
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2014

The effect of austenite pancaking in the non-recrystallization regime on microstructure and texture evolution and thereby on bendability was investigated in an ultrahigh-strength strip steel with a martensitic-bainitic microstructure. The results indicate that an increase in rolling reduction (R tot) below the non-recrystallization temperature, which improves the strength and toughness properties, increases the intensities of the ∼{554}〈225〉 α and ∼{112}〈110〉 α texture components along the strip centerline and of the ∼{112}〈111〉 α component at the surface region. Even with the highest R tot of 79 pct, the bendability along the rolling direction was good, but the preferred alignment of rod-shaped MA constituents along the rolling direction led to a dramatic decrease in the bendability transverse to the rolling direction, with severe cracking occurring even at small bending angles. The early cracking is attributed to localization of the strain in narrow shear bands. It is concluded that the Rtot value has to be limited to guarantee successful bendability. © 2013 The Minerals, Metals & Materials Society and ASM International.

Arasto A.,VTT Technical Research Center of Finland | Tsupari E.,VTT Technical Research Center of Finland | Karki J.,VTT Technical Research Center of Finland | Pisila E.,Ruukki Metals Oy | Sorsamaki L.,VTT Technical Research Center of Finland
International Journal of Greenhouse Gas Control | Year: 2013

In this study different possibilities for applying post-combustion capture at an integrated steel mill in order to reduce carbon dioxide emissions were studied. Implications of different amounts of CO2 captured, different solvents for post-combustion capture and different heat supply options for solvent regeneration to the energy balance and greenhouse gas emissions of the steel mill are compared to that of the base case for the steel mill. The case study is based on Ruukki Metals Ltd.'s Raahe steel mill that is situated on the coast of the Gulf of Bothnia. It is the largest integrated steel mill in the Nordic countries producing hot rolled steel plates and coils. It is also the largest CO2 point source in Finland emitting approximately 4Mt/year. Carbon capture processes were modelled using Aspen Plus process modelling software and results were used to estimate the potential for reducing CO2 emissions at an integrated steel mill from a plant operator's point of view. Different heat integration options and heat utilization scenarios were investigated. The heat available for solvent regeneration varied between these heat utilization scenarios and thus partial capture of CO2 was investigated with the CO2 amount captured depending on the heat available for solvent regeneration in the different case studies. The results of the study show a significant CO2 reduction potential using CCS. Approximately 50-75% of the emissions from the site could be captured using post-combustion capture. Capturing a larger amount of emissions would be technically less feasible due to the large number of small stacks around the large, integrated steel mill site. © 2012 Elsevier Ltd.

Tsupari E.,VTT Technical Research Center of Finland | Karki J.,VTT Technical Research Center of Finland | Arasto A.,VTT Technical Research Center of Finland | Pisila E.,Ruukki Metals Oy
International Journal of Greenhouse Gas Control | Year: 2013

In this paper the economics of the technical possibilities presented in Part I (Arasto et al., 2013) for applying post-combustion CO2 capture at an integrated steel mill were studied. Implications of different CO2 amounts captured, solvents and process integration levels to the greenhouse gas balances and economics of operation are compared to the reference case without CCS trough several case studies using variable market prices of electricity and CO2 emission allowances. The break-even price (BEP) of CO2 emissions (e.g. CO2 emission allowances), where CCS becomes more profitable than the reference case, is about 72€/t CO2 with an electricity price of 100€/MWh in the most favourable studied case using a MEA solvent. For the more advanced solvents considered, the BEP level is about 64€/t CO2. With higher prices of electricity, the costs for CCS increase rapidly. The costs for globally avoided emissions, based on a streamlined life-cycle analysis, are generally higher than the BEP's, depending on the fuels that are assumed to eventually compensate the decreased electricity production in the energy system. The amounts of captured CO2 corresponding to the above presented prices in the most favourable cases are typically in the range of 2-3Mt CO2/a, which accounts for 50-75% of the site emissions. © 2012 Elsevier Ltd.

Kaijalainen A.J.,University of Oulu | Suikkanen P.P.,Ruukki Metals Oy | Limnell T.J.,Ruukki Metals Oy | Karjalainen L.P.,University of Oulu | And 2 more authors.
Journal of Alloys and Compounds | Year: 2013

The effect of prior austenite grain structure on the microstructure and properties of two low alloyed hot-rolled and direct-quenched martensitic steels was investigated. Strength properties were determined using uniaxial tensile testing, while toughness properties were characterized by using Charpy-V and fracture toughness tests. Microstructures were characterized using OM, SEM, EBSD and a novel EBSD-based image quality (IQ) technique. It was found that an increase in the rolling reduction in the non-recrystallization temperature regime of austenite was an effective way to improve the strength, impact and fracture toughness without a significant decrease in uniform elongation. In addition, this approach also decreased the in-plane anisotropy of the tensile and toughness properties. Refinement of the equiaxed austenite grain structure during rolling in the recrystallization temperature regime (roughing) also improved the strength and toughness properties, but the effect was found to be weaker than the effect of rolling in the non-recrystallization regime. In toughness testing, a correlation was found between the Charpy-V 28J transition temperature and the fracture toughness characteristic temperature T0. However, the correlation differs significantly from that reported in the literature for lower strength ferritic steels. In all cases, the steel microstructures consisted of mainly auto-tempered martensite and lower bainite. A brief discussion of the microstructural features controlling the strength and toughness properties is given. © 2012 Elsevier B.V.

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