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Summary description of project context and objectives
Steels with high amounts of Critical Raw Materials (CRMs) such as Chromium, Nickel, Molybdenium and Vanadium are widely used in many industrial applications, particularly under extreme conditions where corrosion and wear resistance are needed. Stainless steel and superalloys play an important role in these areas, and have a great industrial impact on the European industry of several billion € p.a. The supply chain of these parts from steel mill process of the basic materials to CNC-machining of the final parts may be considered as a “mature technology” and not much may be expected to change within this class of high alloyed steels – as long as Cr/Ni/Mo do not run short.
However, Chromium is already placed on the list of Critical Raw Materials (CRMs) indicating the urgent need to develop alternative materials to substitute these alloys.
Since the late 80s it is known that ordered Fe-Al intermetallics (based on almost unlimited resources of Fe and Al - with minor amounts of CRMs or no CRMs) possess many attractive properties. These intermetallics have relatively low densities, high melting points, good thermal conductivity, high temperature strength, as well as high corrosion and wear resistance in general.
Unfortunately, these intermetallics are rather brittle at low to medium temperatures. As a result, they are difficult to machine to their final shape and their use is presently restricted to temperatures beyond the Ductile Brittle Transition Temperature (DBTT). Because of this ordered Fe-Al intermetallics are particularly suited for structural applications at elevated temperatures in “low volume, high added value markets” (such as F1-racing cars) where the disadvantage of cost effective matching to final geometry and poor room temperature ductility is of little significance.
The improvement of strength and ductility is one of the central research goals in materials science. However, it is well known that an increase in strength is usually associated with a decrease in ductility. For engineering applications not only the strength, but also sufficient ductility and toughness of a material is a mandatory requirement. The decrease in ductility with increasing strength is, therefore, the main problem in the development of any high strength material. For intermetallics this problem becomes even more dominant when state of the art materials must be used below their DBTT. Therefore the impact of these interesting (CRM-free) class of materials is presently close to zero in high volume consumer markets - as these markets usually work at room- to medium temperatures (in any case below the DBTT-level of conventional intermetallics).
Research directions to improve the economic impact for future applications of advanced CRM-free intermetallics in high volume markets should therefore aim to improve ductility at low to medium temperatures, while maintaining good tensile strength and optimum level of residual stress. The research strategy within EQUINOX will address this challenge by a clear focus on the structural factors at the submicron level, resulting from the consequences of a radically new production route. Stemming from this follows a new concept beyond sheer material composition.
Aspect of recycling: Despite the fact that up to 85% of stainless steel is presently recycled, only little of this material is recycled back to the high Chromium level of stainless steel, whereas most stainless steel scrap is used as Chromium-basis for the production of low alloyed steel grades. In other words, recycling of Chromium presently entails the dilution of the high Chromium content from usually 18 % (stainless steel scrap) down to 1,5 % in low alloyed steel. By simple considerations of mass balance it is evident that “Recycling of Chromium through downgraded dilution” works only as long as the low alloyed steel market exceeds the stainless steel market by one order of magnitude and as long as there is sufficient fresh feed of Chromium to cover the needs of the stainless steel market.
Recycling of EQUINOX material can be done completely free of any considerations on recycling of CRMs, as EQUINOX is based on abundant Fe and Al and is either completely free of CRMs or includes them at a very small % to tailor the grain boundaries –still justifying the “CRM-free” label. Moreover, it is worth mentioning that neither the EQUINOX material itself, nor its recycling products, nor the process chain raise any concerns with respect to health and safety issues. Therefore, an industrial impact can be achieved within the practical constraints imposed by REACH.
Based on these considerations, EQUINOX’s main objective can be summarized as follows:
A novel near net shape production technology that allows to substitute stainless steel parts in high volume end consumer markets by a new class of CRM-free, ductile Fe-Al based intermetallics.
This main objective is supported by the following specific objectives:
- To produce extremely fine grained Fe-Al material with high ductility via reactive infiltration of porous iron preforms with liquid aluminium.
- To understand how ultrafine particle based porous iron structures of complex 3D-shape may be tailored to be used as optimized preforms for reactive infiltration of liquid Al-alloys.
- To develop a reactive infiltration process by using two different techniques: suction and centrifugal casting.
- To simulate reactive infiltration process by physically based multi-scale models.
- To optimize mechanical properties of EQUINOX material with respect to microstructure based on process conditions and consecutive heat treatment.
- To scale up the process from lab to small pilot plant with respect to the industrial needs.
- To transfer the concept to at least one real demonstrator, which will be tested for high corrosion and wear resistance.
- To evaluate the industrial impact of EQUINOX-concept with respect to economic as well as technical aspects.
The following describes how the intermetallics technology proposed from EQUINOX will allow substituting Cr and Ni and thus will impact the whole value chain of the stainless steel industry globally.
The Call covers three basic aspects:
“Growing a Low Carbon, Resource Efficient Economy (aspect 1)
With a Sustainable Supply of Raw Materials (aspect 2)
for materials under severe conditions.” (aspect 3)
All three aspects are addressed by EQUINOX in a very straight forward way by substituting complex 3D-shaped stainless steel parts from 10 up to 1000 g that are usually made by CNC-technology, by a radical new process. The conventional way of making complex stainless steel products by CNC is given in Fig.7:
Figure 1: Production of stainless steel CNC-parts along the traditional process chain.
In Figure 1 we can identify four different steps that all use a lot of energy and produce a lot of CO2 as side product:
- Iron-oxide is reduced in a blast furnace by coal to crude (liquid) Fe with 14 tons of CO2 as side product per t of Fe.
- Liquid steel is made from crude iron by adding Cr/Ni/Mo etc. based additives and recycled scrap in a steel mill.
- Semi-finished products (rods, bars , pipes, sheet, etc.) are manufactured from liquid stainless steel in a continuous caster combined with a rolling mill
- Final products of complex 3D-shape are machined form semi-finished products by CNC-technology
Why does this route, which is established for more than 100 years tackle the Call?
Disadvantage of present route:
- In the blast furnace the crude iron reaches an intermediate temperature of 2300oC which exceeds the temperature that is needed for the reduction of iron oxide for thermodynamic reasons by appr. 1800 °C => a lot of energy is wasted.
- The reduction is based on coal, which does not allow to introduce renewable energy to the process and makes steel production one of the mayor sources for global CO2-emissions.
- Alloying of crude steel is a completely independent secondary operation which needs a lot of further process energy. In some cases blast furnace (step1) and steel mill (step 2) are at different locations – causing transportation costs.
- Step 3 is another independent operation with a lot of energy input, just in order to change from liquid state to a state that can be used for consecutive CNC-operation.
- CNC-company is usually located hundreds of km away from the steel mill – causing a lot of transport for semi-finished products.
- According to detailed studies only 57 % in average of the semi-finished products that are shipped to the CNC company end up as final parts in the endusers product (such as a car) – the remaining 43% are machined down to pieces in the CNC process – and are shipped back hundreds of km to the steel mill where this scrap is added as recycling material.
Obviously the conventional way of making 3D-shaped steel parts (up to 1 kg by CNC-technology as addressed in EQUINOX – alternative) is completely ineffective from the point of limited resources. It uses 4 different production sites and creates 43 % of scrap that has to be transported hundreds of kilometers for recycling. This is synonymous with a waste of energy in both, production as well as transport. The route that EQUINOX is following is completely different to conventional way of making steel parts as already given in figure 4.
The EQUINOX process well fits into “Growing a Low Carbon, Resource Efficient Economy (1) with a Sustainable Supply of Raw Materials (2) - for materials under severe conditions (3)” by many aspects:
- No CO2 is produced as side product as oxygen from raw material iron-oxide is fixed as H2O.
- No waste of material: 100 % of the material that enters into the process chain ends up as final product of complex 3 D-shape.
- No energy is used for “material tourism” All steps of the process run at one single location – Fe3O4 and Al entering through the front door and final 3D-shaped Intermetallic parts leaving through the back door.
- Solar heat may be used to cover most part of energy input as temperature level is just slightly above the melting point of Al in all steps involved.
- The process may be completely based on H2(which could be made from renewable energy).
- Materials with properties close to stainless steel are manufactured from abundant Fe and Al - without (or at least drastically reduced) CRM-materials Cr/Ni/Mo.
- EQUINOX materials exhibit properties that withstand corrosion, cavitation and wear offering good results on LCA (life cycle analysis).