STEELS FOR ENAMELLING DEVELOPMENT AIMING AT GLOBAL COST REDUCTION AND ENVIRONMENTAL PROCESSES, AN ARCELOR CONTRIBUTION TO HE COMPETITIVITY OF THE ENAMELLING INDUSTRY
P. Gousselot¹, L. Duprez², P. Schouller Guinet³, P. Harlet^3
1 Arcelor Sales Support Services, Avenue des Tilleuls 17, 57190 Florange, France
² Arcelor Industry Research Centre, John Kennedylaan 3, 9060 Zelzate, Belgium
³ Arcelor Industry Research Centre, Boulevard de Colonster B57, 4000 Liège, Belgium

Abstract
Arcelor is the European leader in the market of enamelling steels, with the most important markets being the sanitary market, the boiler market and household appliances. A new developing market for the use of enamelled steel parts is the architecture. This paper presents an overview of the different product developments performed by the Arcelor Group thanks to win-win partnerships with enamellers and enamel frit producers. The general guidelines for these product developments are environmental issues and cost reductions for the final enamelled part. This gives raise to the following developments:

Introduction
In 2002, Arcelor was founded by the merging of the ACERALIA, ARBED and USINOR Groups.
The new group produces about 42 million tonnes of steel per year and employs more than 98000 people in more than 60 countries. Arcelor has an extensive amount of production units in Europe and expands outside Europe by means of joint ventures, e.g. in Canada, Brazil, Russia and China.
Together with the merging, the Arcelor R&D structure was reorganised. The new organisation is highlighted briefly in this presentation.
In Europe, Arcelor is the market leader for enamelling steels and intends to keep this position in the future. In this paper, the current Arcelor market situation is summarised. Based on the ongoing evolutions in the market of enamelling steels, the Arcelor strategy is explained. Finally, an overview is given of the different product developments performed to obtain Arcelor’s strategic objectives.

The Arcelor R&D Organisation
In the flat carbon steel sector of Arcelor, the merger of 2002 was followed by a reorganisation of the R&D department. The total number of research centres was reduced to 5, with each centre having its own research field, Fig. 1:

Fig. 1 Geographic presentation of the R&D centres of the Arcelor Group.

Arcelor’s market position
Market. Arcelor is the European leader in the market of enamelling steels with important market shares in the following sectors: household appliances, the sanitary market and the boiler market.
This is shown schematically in Fig. 2. The use of enamelled steel parts for architectural panels is a smaller but growing market in which Arcelor would like to take its share.

Fig. 2 Distribution of the Arcelor tonnages for enamelling steels over the various market segments.

For the above mentioned markets Arcelor wishes to be the main steel provider for the enamellers with the aim to promote the enamelled steel solution by emphasizing environmental issues and creating value for the customer. Therefore, Arcelor disposes of large number of production sites and an extended and efficient distribution network all over Europe. In addition, a large network of steels service centres (SSC) was built for high quality technical support to customers.
Catalogue. One of the commercial strengths of Arcelor is that it offers the most complete range of enamelling steels with a well-recognised quality, Table 1.
For household appliances the SOLFER grade is the reference material, which can be used for direct enamelling as well as for any other enamelling procedure. For the latter, alternative, more economic grades are available, such as the DC04EK, the DC04ES and the DC06EK. In this way, various grades are offered for each type of enamelling process and for all types of deep drawing operations.
For the sanitary market, Arcelor developed the steel grades DC05EK and DC06EK with enhanced mechanical properties, which makes these grades suitable for severe deep drawing operations, e.g. the making of bathtubs. The use of these materials allows the customer to minimise the rejects after deep drawing and to increase the deep drawing cadence.
For the boiler market, two hot rolled steel grades have been developed for the one sided enamelling of boiler parts, i.e. the S240EK and S300EK. The latter has an excellent resistance to fish scaling and retains its mechanical properties after enamelling (Re > 300 MPa after firing at 850 °C during 10 min). This allows to:

Market evolution for enamelled steel
General: The evolution in the use of enamelled steels seems to differ between the various market segments. For reasons of cost price, the use of enamelled steel parts has decreased significantly in the household and sanitary market during the last years. For the sanitary market however, the decrease appears to stabilise. Contrary to these classic markets, the enamelled solution appears in new applications such as architecture and construction.
Household appliances: Currently, enamelled parts are often replaced by competitive materials such as ceramics, aluminium or stainless. The enamelled solution is only used when it’s absolutely necessary, i.e. in those applications where temperature resistance (oven cavities) and easy-toclean behaviour (cooking hobs) are demanded. Nevertheless, the steel tonnages consumed are relatively stable due to the fact that the absolute number of enamelled parts increased simultaneously.
Sanitary: A huge shift has occurred in this market segment towards the use bathtubs with acrylic coatings, which has now taken 60% of the market. Consequently, this has caused a decrease in the consumed tonnages of enamelled steel. Nevertheless, it appears that for reasons of durability and long-term quality, the use of acrylic coated bathtubs ceases to increase.
Boiler: In this sector, the use of enamelled steel has increased strongly during the last years, at the cost of Zn-coatings, paints and concrete. In the future, up to 90-95 % of the boilers could be made from enamelled steel parts, which in the end constitutes the best balance of cost, quality and easiness of supply. However, for cost reasons, some customers are trying to use cheap nonenamelling qualities, thereby staking the quality of their boiler product.
Architecture: Currently, this market only consumes a small amount of enamelled steel. However, this market is increasing due to the use of enamelled architectural panels for stations, tunnels, signalisation, interior, etc. Indeed, enamelled steels have several properties that make it perfect for the use in architecture: durability, aesthetics, and environmental friendly,

Fig. 3 Examples (OMERAS, Germany) of the use of enamelled steel in non-classic applications such as construction, architecture, signalisation, etc.

Arcelor’s strategy
Issues related to the protection of the environment become increasingly important. The public awareness that grew during the last decades has passed over to political movements, which shift now from the North to the South of Europe. For this reason, the extension of the Arcelor catalogue for steels for enamelling mainly aims at solving certain environmental issues by simplifying the enamelling process. On the other hand, economical aspects must always be considered in the sense that new, commercial products should create an added value for Arcelor and its clients.
Therefore, the Arcelor policy is to develop products that result in more ecological processes and at the same time result in a more economical enamelling process, for example:

Arcelor product development
EASYFILM EKE for enamelling without degreasing
This surface treatment has a dry aspect and is applied on steels suited for enamelling. In this way:

Fig. 4 Lubricating properties of the EASYFILM EKE product in comparison with two frequently used reference oils.

In addition, the EASYFILM EKE:

illustrates that the EASYFILM EKE is perfectly compatible with the enamelling process. Whereas needlepoints, craters or black points (2C/1F) occur with classical organic coatings, a nice surface aspect is obtained using the EASYFILM EKE product.

Enamelling on metallic coated steel surfaces
The aim of these products is to achieve direct white enamelling (1C/1F) without the use of the preliminary pickling or nickeling treatment. The advantage for the customer is twofold. First, eliminating the use of pickling baths and nickeling baths simplifies the process and is much more ecologically sound. Second, significant cost savings are obtained by the removal of these surface preparation steps.
Fig. 5 shows the binary Fe-Zn diagram, which allows understanding the phenomena during enamelling of Zn-coated steels. During the firing the diffusion of Fe into the Zn will induce the formation of a series of intermetallic Fe-Zn compounds. The exact “alliation path” will determine the properties of the enamelled part. Several technical options exist to tackle this challenge, i.e. electro galvanised steel, hot dip galvanised steel and galvannealed steel, each solution having its own advantages and drawbacks. Although some question remain to be answered, some things are clear:

Several factors play a determining role in the adhesion of the enamel. First, the alloying of the Zn-coating must be well regulated to obtain a good adherence. Second, Ti-Si-Fe-Zn containing phases will be formed at the interface between the Zn and the enamel. Although it is certain that these compounds will influence the enamel adhesion, a complete understanding of their formation mechanisms is not obtained yet.

Fig. 5 The enamelling results on Zn-coated steels are determined by the diffusion of Fe into the Zn and the type of phases that are formed during this operation.

Fig. 6 Adhesion results for a Zn-coated steel after enamelling without pickling of nickeling. Good adhesion is obtained after firing at 820 °C. Metallographic investigation shows the formation Ti-Fe-Si-Zn compounds at the interface Zn-enamel.

Hot rolled steels suited for two-sided enamelling
Two hot rolled steel grades were developed with an excellent fish scaling resistance, similar to that of cold rolled steels. Because of this high resistance to fish scaling, these steels are perfectly suited to be enamelled on both sides and with multiple enamel layers. The following grades were developed:

The chemical compositions of these two grades are shown in Table 3. As in hot rolled grades it is very difficult to create physical traps, such as micro cracks in deformed cementite, the fish scaling resistance is obtained by introducing a large amount of TiC, which are known to be very efficient hydrogen traps. Fig. 7 shows the predicted equilibrium precipitation state in the deep drawing grade. Due to the low S content, the precipitation is shifted to the formation of carbides instead of carbosulfides.
This metallurgy offers the advantage of a high α/γ transformation temperature as the Ti ties up all C. Hence; fish scaling problems related to the high hydrogen solubility in austenite are avoided.
Enamelling tests with the fish scale sensitive enamel Ferro 2290 revealed no fish scales.

Fig. 7 Equilibrium precipitation evolution with temperature for the drawing quality, indicating that TiC are the main type of precipitates present in the steel.

The mechanical properties of the two grades are shown in Table 4. The drawing grade is developed for the sanitary market, where it may be used for the production of bathtubs and shower bases. The high strength grade aimed at the production of silos and tanks.

Steels for architectural applications
As mentioned before, this market only consumes a small amount of enamelled steel. However, enamelled steels have several properties that make it perfect for the use in architecture. Therefore, a project was started in Arcelor on steels that are suited for this potential market.

The aim of these products is to reduce the thickness of large architectural panels whilst retaining the flatness after enamelling. This will reduce the risk of deterioration of the panel and allows signifcant cost savings for the customer. In a further approach, it is the aim to remove the use of core materials and stiffeners. From Table 54n that the enamelled steel solution can be competitive with aluminium and stainless steel. Compared to painted steel however, it is more expensive. However, here the enamelled steel part has certain advantages such as easy-to-clean properties and longer lifetime. In a further approach, this family of steels has to be tested on their fire resistant properties.

Conclusions
Arcelor is the European leader in the market of enamelling steels, with the most important markets being the sanitary market, the boiler market and household appliances. A new developing market for the use of enamelled steel parts is the architecture. This paper presents an overview of the different product developments performed by the Arcelor Group thanks to win-win partnerships with enamellers and enamel frit producers. The general guidelines for these product developments are environmental issues and cost reductions for the final enamelled part. This gives raise to the following developments: