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Ugine, France

Iller C.,Schmolz Bickenbach Group
Stahl und Eisen | Year: 2015

Whether used to raise efficiency levels in an automotive powertrain, reliably deliver oil and gas or to improve the continuous loading of components used in aerospace applications - special long steel is indispensable for industrial users. What is paramount is the highest quality of product and service at minimal cost. Given the interaction between rising global competitive pressure, overcapacity as well as strict energy and environmental requirements, European steel producers increasingly face new, strategic challenges.

Usually niobium is added in ferritic stainless steels to avoid chromium carbides precipitation and then to improve corrosion resistance and to avoid embrittlemet. This study shows that a low Nb stabilization makes recrystallization nucleation much faster and prevents incomplete recrystallization. A qualitative interpretation, based on interaction with precipitates, is proposed and explains the main features of the softening kinetics as well as the microstructures obtained. Above a specific magnetizing frequency, the deformed state led to smaller losses than the recrystallized state. These results are believed to be attributed to a grain size effect. This leads to soft magnetic properties that makes 17%CrNb ferritic stainless steels a very interesting solution for the market of electromagnetic injection. Improving response-time of fuel injection valves is a great challenge for automotive industry in order to enhance car engine efficiency and to limit noxious gas emission.

Sourisseau T.,Schmolz Bickenbach Group | Chauveau E.,Schmolz Bickenbach Group | Mantel M.,Schmolz Bickenbach Group
7th European Stainless Steel Conference: Science and Market, Proceedings | Year: 2011

Due to low nickel content, the duplex family allows a reduction of the influence of the price fluctuation of raw materials on the price of stainless steel products. This economical advantage, associated with exceptional strength and chemical resistance, makes duplex very serious candidates as substitutes to standard austenitic grades for many applications where both corrosion resistance and mechanical properties are required. Among them, the grade EN 1.4062 that contains low Nickel (around 2,5%) and low Molybdenum (lower than 0,5%) shows a higher resistance to pitting and crevice in chloride media or to generalized corrosion in acidic environments than standard 1.4301 and 1.4310 grades. Moreover, by partial transformation of austenite to hard martensite during cold-working, 1.4062 drawn wires can reach mechanical tensile strength values which are similar to standard autenitic 1.4310 wires. For those main reasons, 1.4062 is suitable for replacing standard 1.4301 and 1.4310 grades used for spring applications, giving also springmakers the financial benefit of its less fluctuating price. More generally, this article reviews the main properties of drawn wires required for spring applications (especially for aerosol and automotive ones which have been targetted in this study): aptitude towards gliding during spring forming thanks to wire surface characteristics on one hand, spring stiffness and loss of charge after spring relaxation on the second hand, and lastly resistance to chloride environments (in the case of aerosol applications). A comparative study of 1.4062 and standard austenitic grades has been led at UGITECH Research Center for each of these properties in the case of compression springs, taking into account the influence of heat treatment and pickling conditions of the spring. The development of this new duplex grade, currently in progress with the partnership of a few selected European springmakers in the fields of both aerosol and automotive, shows interesting perspectives and first feedbacks from customers are very promising.

Meyer N.,Schmolz Bickenbach Group | Mantel M.,Schmolz Bickenbach Group | Gauthier A.,Schmolz Bickenbach Group | Bourgin C.,Schmolz Bickenbach Group
Revue de Metallurgie. Cahiers D'Informations Techniques | Year: 2011

Embrittlement of duplex stainless steels after aging below 500 °C is a well documented phenomenon, usually attributed to the unmixing of the ferritic Fe-Cr solid solution, either by spinodal decomposition or by nucleation and growth of Cr-rich α' phase, depending on aging temperature. Additional precipitation taking place during aging, like NiSiMo-rich G phase or Cu-e, are also known to participate to embrittlement, making the composition dependence of embrittlement kinetics even more intricate. In this study, long term aging treatments, up to 2 years at intermediate temperature (250-400 °C), have been performed for various duplex stainless steels grades containing different alloying contents in Cr, Mo, Si, Ni and N. Impact toughness has been measured after each aging condition, and an apparent activation energy could be deduced for the various grades. This quantity is a good indicator of embrittlement resistance. Fine microstructural characterizations have been performed in the ferrite: composition before aging was determined by EPMA, and precipitation state before and after aging was observed on TEM. The influence of alloying elements on the embrittlement phenomenon is analyzed on the basis of these results and of driving force calculations performed on Thermo-Calc R ®. © EDP Sciences, 2011.

Renaudot N.,Schmolz Bickenbach Group | Chauveau E.,Schmolz Bickenbach Group | Mantel M.,Schmolz Bickenbach Group
Revue de Metallurgie. Cahiers D'Informations Techniques | Year: 2011

Duplex stainless steels are known to have a good resistance to localised corrosion, especially thanks to their quiet high level of chromium (and for some of them molybdenum), but also because of their very low level of sulphur. These very low levels of sulphur are also useful to guaranty a good toughness and a good hot workability for these grades. Concerning long products like bars made in Duplex Stainless steels, one of their most important property, after corrosion resistance, is their machinability. Unfortunately, one of the most known way to improve the machinability of stainless steels is to increase their sulphur level, thus forming manganese sulphides in the stainless steels which induce better chip breaking and lubrication at the chip - cutting tool interface. So the question is: can the sulphur well-known way to improve machinability of stainless steels be used on Duplex Stainless Steels, without inducing hot rolling difficulties and too important a decrease of their other main properties, i.e. localised corrosion resistance and toughness? If not, are other ways possible? © EDP Sciences, 2011.

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