T 0373/96 25-05-2000

1. The appeal is admissible.

2. Admissibility of the requests

Respondent II's arguments, that the filing of new claims at this late stage was an abuse of procedure and was also prohibited for reasons given in the decision T 528/93, are not accepted. The new claims were filed one month before the oral proceedings before the Board, and met the time limit set out in the communication dated 25 November 1999 from the Board. Moreover, the present case is different to the case of the decision T 528/93, since in the latter case the patent had been maintained in amended form, whereas in the present case the patent had been revoked by the Opposition Division. In this case, the patentee is entitled to revert to a more broadly worded version of claims, in particular to the granted version, even if he had filed a restricted version at the commencement of the appeal proceedings, as explained in the decision T 89/85.

However, the main request and the first and third auxiliary requests are not admissible and the second auxiliary request is admissible for the reasons set out below:

Main request

Claim 1 contains changes of terminology ("extra low" to "ultra low" and "decarbonizing" to "decarburization"), a step that was already implicit in the granted claim but is recited explicitly in the new claim (tapping the molten steel into a ladle), and statements of purpose ("suitable for continuous casting without blocking of a continuous casting nozzle", "for decarburization of the ladle molten steel", "thereby to suppress oxygen supply from the ladle slag to cause shortage of oxygen during the decarburization", and "in that the oxygen blowing is required during the decarburization to ensure decarburization"), and is now cast in the two-part form. The statements of purpose do not alter the scope of the claim and are not inserted in order to meet a ground of opposition. The same applies to the changes of terminology and the use of the two-part form of claim.

The new dependent claims 2 to 5, 7, and 11 to 13 do not have any bearing on the grounds of opposition and are not admissible for this reason. All in all the changes are of a cosmetic nature and not allowable according to well established case law, see for example, the Board of Appeal decision T 0406/86, OJ 1989, 302.

First auxiliary request

The Appellant admitted, at the oral proceedings before the Board, that the addition of the words "the slag of" was only for clarification, and this request is, therefore, not admissible for the same reason as the main request.

Third auxiliary request

Claim 1 of the third auxiliary request is open to same objections as claim 1 of the main request, and is additionally objectionable under Article 123(2) EPC since the figure of 0.035% for the carbon content has been taken out of its context from the table on page 5, and there is no teaching in the description that this figure is significant or that the invention would not work outside the claimed range.

Second auxiliary request

The claims of the second auxiliary request correspond to the claims as granted but for an insignificant difference, the addition of a definite article. However, the Appellant stated at the oral proceedings before the Board that the intention was to revert to the granted version, so these claims will be treated as though they were the granted claims.

In view of the foregoing, only the second auxiliary request is admissible and only this request is to be examined as to its substantive merits.

3. Novelty

Lack of novelty has not been disputed during the appeal procedure and the Board is satisfied that none of the documents cited by the Respondents discloses a process for producing high cleanliness extra low carbon steel comprising the combination of all the steps defined in claim 1.

4. Inventive step

4.1. Closest prior art

The opposed patent is concerned with a process for producing an extra low carbon steel. The described process starts from molten steel tapped to a ladle and having relatively high carbon contents of 0.035 to 0.050% (see Table on page 5), and the steel is decarburized using the RH process, to attain ultra low carbon (ULC) levels (of the order of 10 ppm) necessary for use in the automobile industry in which deep drawability is an essential property.

The Document D8 also describes a process for obtaining a steel of ULC grade, starting from steels with relatively high carbon contents of around 0.04 % and applying the RH process to the molten steel tapped to a ladle. The Board considers this document as representing the closest prior art, in agreement with all the parties and the opposition division.

In the section "Ultra-low carbon treatment", on page 962 it is stated that "the OB-option is also applied in case of shortage of oxygen during the final decarburization of ULC steel". This means that oxygen may be blown into the steel if not enough is present to convert the carbon to attain ULC grade steel. The RH plants depicted in Figures 3 and 6 are equipped with oxygen tuyeres, accordingly.

Thus, this document describes the generally known apparatus and method of refining steel. That is, depending on the carbon content of the molten steel in the ladle, which in turn depends on the conditions prevailing in the converter, the steel is further reduced to ULC grade in the RH plant, whereby the remnant oxygen in the steel is combined with the carbon in the steel and the resulting carbon monoxide gas escapes from the steel, whose carbon and oxygen contents are thereby reduced. The steel is finally killed by the addition of aluminium to passivate any remaining oxygen.

The process according to claim 1 differs from this known process in that deoxidising agent is added to the ladle slag before the vacuum treatment in order to reduce the T.Fe to a level below or equal to 5%.

4.2. Technical problem

It is well known in the art that, when producing ULC grade steel, problems may arise with its cleanliness (see, for example, Document D1, page 385, "Technique for Making Clean Steel", Document D3, page 1, "Detailed Description of the invention", and Document D4, page 2, lines 3 to 8). This lack of cleanliness may lead to intolerable surface defects when the steel is used to produce outer panels for automobiles, for example.

Therefore, when performing the state of the art process according to Document D8, the person skilled in the art will always strive to carry out the process in a manner which results in the utmost cleanliness of the steel. This is also the problem underlying the patent in suit.

4.3. The Document D1 not only mentions this well known problem, but it also discusses the cause of surface defects and also provides the solution for avoiding the problem.

4.4. Inventive step

The person skilled in the art seeking to produce ULC grade steel of high cleanliness would be aware of the Document D1 since this discusses both the cause of surface defects as well as the solution to this problem.

According to Document D1, the high oxygen potential of slag is the cause of surface defects since FeO in the slag acts as an oxygen carrier and transfers oxygen from the atmosphere to the steel (see page 385, right column, penultimate paragraph). On page 385, right column under "Technique for Making Clean Steel" there are reviewed older methods of counteracting the problem and improving steel cleanliness, and it is stated that "slag stopping with refractory ball is not sufficient to prevent metal reoxidation by the highly oxidizing slag from the BOF." Therefore, the steel from a BOF furnace was tapped to a ladle where the slag was deoxidized by the addition of Al powder to lower the T.Fe % to "6% or less". Figure 14 depicts the relationship between the incidence of surface defects, which is connected with the steel's cleanliness, and the T.Fe content, and shows a clear correlation between the two, with several values of T.Fe below 6% and as low as about 1%. This slag treatment prevents metal re-oxidation.

In view of the explanation given in this document of the mechanisms involved in the production of surface defects and also of the fact that a solution to this problem, i.e. slag treatment is given, the person skilled in the art would find ample incentive to use the same solution in the process described in Document D8, and thereby produce a steel that is both clean and is of ULC grade. Indeed, the opposed patent describes the same mechanism (page 2, lines 25 and 26) that degrades the cleanliness of the steel, and employs the same solution, that of reacting the slag with a deoxidizing agent to reduce the T.Fe to less than or equal to 5%. Therefore, the person skilled in the art would arrive at the claimed process as an obvious combination of known measures.

This step would be inserted before the RH process as in Document D1. Given that the oxygen content of the slag had been adjusted to effect the decarburization, the person skilled in the art would be aware that the reduced oxygen content of the slag would no longer suffice to achieve a carbon level corresponding to the ULC grade. This oxygen deficiency, however, would not deter the person skilled in the art from using the RH process, since the RH plant of Document D8 anticipates this problem and is equipped with means for supplying additional oxygen to make up this deficiency, (see page 962 of D8, left column), and no further modification of the plant is required.

As regards the nozzle blocking problem, this is also related to the presence of insoluble oxides and the solution of the problem of cleanliness automatically brings with it a solution of the nozzle blocking problem.

The Appellant's arguments that no prior art document discussed the nozzle blocking problem and that the teachings of Documents D1 and D8 were incompatible and therefore the person skilled in the art would not have combined them, are not accepted for the following reasons.

No evidence of any prejudice against the use of slag treatment in combination with the RH process has been presented by the Appellant. The fact that Documents D1 to D4 do not use a combination of slag treatment and oxygen blowing is not sufficient evidence that a prejudice existed in this respect or that the teachings of Documents D1 and D8 are incompatible with each other.

In the absence of any strong evidence that it is not worth while attempting to perform the slag treatment of Document D1 in addition to blowing oxygen during the RH process as in Document D8, the person skilled in the art would indeed consider trying a combination of these processes in view of the very satisfactory results each of these processes individually promises, particularly when no further modification of the RH plant is necessary. The plant of Document D8 is already equipped with this facility so no extra effort is involved in the attempt.

The skilled person wanting to provide ULC grade steel that is very clean is incited to carry out the slag deoxidising step as described in D1, followed by the decarbonising step as described in D8, while using the option D8 of blowing oxygen in the RH process. Thus the process of claim 1 does not involve an inventive step. The fact that it also ensures that the nozzle of a continuous casting apparatus does not get blocked, is a bonus effect which occurs automatically as a by-product of the main effect and cannot impart inventivity to the claimed process.

Therefore, the second auxiliary request is not allowable since the process of claim 1 thereof lacks an inventive step.

5. Other matters

Since the Opposition Division had, in its decision, refused claims narrower in scope than the present claims for lack of inventive step, it had in effect already given its opinion on the present set of claims and remittal to first instance, as requested by the Respondent I, is not necessary, accordingly.