T 0024/81 (Metal refining) of 13.10.1982

Summary of Facts and Submissions

I. European patent application No. 79 101 414.5 (publication number 0 000 506) filed on 9 May 1979 and published on 28 November 1979, claiming priority from the German prior application of 11 May 1978, was refused by the decision of the Examining Division of the European Patent Office dated 17 February 1981, on the basis of the eight claims as filed, taking into consideration the deletion in Claim 2 requested in a letter dated 26 November 1980. Claim 1 is worded as follows: Method for treating melts of pig-iron and steel or steel alloys in a converter, crucible or other vessel, characterised in that the entire oxidising (for carbon elimination) and treatment process is carried out using carbonic acid (Kohlensäure - The German term is traditionally used also to denote carbon dioxide) in one vessel on a continuous basis until the finished steel is produced.

II. The grounds given for the refusal were that the subject-matter according to Claim 1 does not involve an inventive step. A method for treating pig-iron melts in a converter is known from DD-A-103 266, the entire oxidising and scavenging process being carried out in one converter on a continuous basis. Oxygen is used as the oxidising gas and carbon dioxide as one of the possible scavenging gases. The method according to the application differs from this known method only insofar as both the oxidising and the scavenging are carried out with gas containing carbon dioxide. The advantages of flushing steel melts with carbon dioxide are already known from GB-A-869 953 and 1 258 451. The use of such scavenging treatment in the case of the method known from the above-mentioned DD-A is therefore obvious to the man skilled in the art, particularly since the last-mentioned citation refers to the possible use of carbon dioxide as a scavenging gas. It is also known from DE-C-934 772 that carbon dioxide and carbon dioxide-oxygen mixtures could be used advantageously as oxidising agents in steel production. Contrary to the applicant's assumption that the carbon dioxide is supplied essentially in solid form as lime, this patent specification is mainly concerned with the use of carbon dioxide in a gaseous, liquid or solid state and mentions the use of lime only in the case of those methods in which large quantities of lime would be needed to build up the slag. The use of carbon dioxide as an oxidising agent in the method known from the above-mentioned DD-A does not therefore involve inventive step. The applicant's argument that it could not have been obvious to the man skilled in the art to combine the cited publications, because otherwise the suggestion for the method as applied for would have come from the steel industry, is incomprehensible to the Examining Division. The fact that the applicant normally deals with fields of technology other than that of the present application is not evidence for the presence of inventive step.

III. The applicant lodged an appeal against this decision on 31 March 1981 and set out the grounds of appeal on 6 June 1981. He requested in effect that the impugned decision be set aside and that the patent sought be granted on the basis of the claims submitted on 19 April 1982. These claims are worded as follows:

"1. Method for treating melts of pig-iron and steel or steel alloys by means of oxidising and scavenging in one and the same converter, crucible or other vessel, characterised in that the pig-iron melt is oxidised with about 100 to 250 kg CO2/t of steel and is after-treated until the finished steel is produced with about 0.25 to 50.0 Kg CO2/t of steel, the entire oxidising and after-treating process being carried out using carbonic acid in one and the same vessel on a continuous basis until the finished steel is produced.

2. Method as in Claim 1, characterised in that liquid carbonic acid is blown into the pig-iron melt at a pressure of 4.0 to 20.0 bar, preferably at a pressure of 2 to 15 bar.

3. Method as in Claim 1, characterised in that gaseous and liquid carbonic acid is blown into the pig-iron melt though separate jets at a pressure of 0.2 to 20.0 bar, preferably at a pressure of 2 to 15 bar.

4. Method as in Claims 1 to 3, characterised in that during the oxidising or the after-treating of the melt, or in both processes, an additional oxidising gas is blown in with the carbonic acid in varying concentrations and for varying durations.

5. Method as in Claim 4, characterised in that oxygen is used as a further oxidising gas.

6. Method as in Claims 1 to 4, characterised in that during the oxidising or during the after-treatment of the melt, or in both processes, an additional inert or reducing gas is blown in with the carbonic acid in varying amounts and for varying durations.

7. Method as in Claim 6, characterised in that argon, nitrogen and/or carbon monoxide is used as the inert or reducing additional gas." In the alternative the appellant requested oral proceedings, which took place on 13 October 1982.

IV. The grounds for appeal are essentially as follows: The objective facts as to novelty and technical effect have not been contested. As opposed to this, inventive step can only be assessed subjectively. Thus by mosaicking the prior art retrospectively, i.e. with knowledge of the invention, it could always be argued that a combination of the various features results in the subject-matter of the application without any inventive effort. In the present case, however, even appropriate linking of the prior art would not have led to the method claimed. The essential inventive idea in the present application resides in carrying out the treatment of pig-iron and steel melts, comprising oxidising and subsequent scavenging, by using carbonic acid as oxidising and scavenging agent on a continuous basis in a single vessel until the finished steel is produced. DD-A describes a method for treating pig-iron melts in the converter whereby the oxidising and scavenging process is carried out continuously in one vessel, but in that case oxygen is used for the oxidising gas and carbon dioxide is used for the scavenging gas, as one of several possibilities. This is the conventional method of refining with oxygen, whereby undesirable gas inclusions can be reduced by pulsating flushing with nitrogen, argon or carbon dioxide. The method according to the invention differs from this in that both the oxidising and the scavenging is carried out with carbon dioxide. The other citations did not deal with the entire metallurgical process, but only with particular aspects thereof, and could not therefore impart any technical teaching for the overall process claimed. It is stated in DE-C 934 772 that when oxidising steel melts, carbon dioxide can also be used by adding uncalcined limestone (CaCo3). A method such as this, using carbon dioxide in a combined form as CaCo3, differs fundamentally from the oxidising according to the invention, in that the liberation of carbon dioxide from CaCo3 results in an increased heat loss which has to be made good by supplying heat. It is not contested that in this patent specification the use of gaseous carbon dioxide is also disclosed; however, the skilled man would not have taken this embodiment into consideration, because it was not stressed as the preferred method. FR-A-1 058 181 merely describes the joint use of oxygen and carbon dioxide in the refinement of iron and provides no stimulus for the method according to the invention. The fact that the invention made a significant and economically simple contribution to solving the steel industry's environmental problems and yet was not discovered by experts in this field provides additional evidence for the presence of inventive step.

Reasons for the Decision

1. The appeal complies with Articles 106 to 108 and Rule 64 EPC and is therefore admissible.

2. The present verson of the claims cannot be objected to from a formal point of view. Claim 1 results from the combination of the original Claims 1 and 2. Claims 2 to 7 correspond to Claims 3 to 8 as first disclosed.

3. The method claimed in the present version of the main claim as restricted in the appeal proceedings concerns essentially the continuous treatment of pig-iron and steel melts by oxidising and subsequent scavenging in a single vessel using carbonic acid as an oxidising and scavenging agent in varying specific amounts. Such a method cannot be deduced from the publications before the Board; it is therefore deemed to be new.

4. When assessing inventive step for this method, it is not a question of the subjective achievement of the inventor, so that the case history of the invention presented at the oral proceedings is irrelevant. It is rather the objective achievement which has to be assessed. As in the case of novelty, inventive step is an objective concept. Objectivity in the assessment of inventive step is achieved by starting out from the objectively prevailing state of the art, in the light of which the problem is determined which the invention addresses and solves from an objective point of view (see Decision "Carbonless copying-paper" OJ 7/1981, 206, headnote I), and consideration is given to the question of the obviousness of the disclosed solution to this problem as seen by the man skilled in the art and having those capabilities which can be objectively expected of him. This also avoids the retrospective approach which inadmissibly makes use of knowledge of the invention, as feared by the appellant.

5. If this yardstick is applied to the present case, the inventive step must be considered from the point of view of a practitioner in the steel sector who was already familiar with the publications cited in the lower instace and with the oxygen-blowing process which, according to the appellant, was introduced into technology thirty years ago. The marked overheating of the melt during the oxidising is regarded as a disavantage in this method, since the converter lining is thereby damaged, leading to the steel melt becoming contaminated with particles from the lining (see introduction to the description of the present application, page 1, lines 12 to 16). A proposed solution to avoid these disadvantages is already described in DD-A-103 266. In order, among other things, to increase the cooling effect of the gases and thus increase the durability of the converter lining (see page 8, lines 20 to 26), the pig-iron melt is here oxidised with a pulsating oxygen jet surrounded by a blanketing medium, especially steam (Claims 1 to 10), and the steel melt is subsequently scavenged by introducing an inert or low-reactivity pulsating gas jet with surrounding blanketing medium to reduce undesirable gas inclusions (Claim 14). Nitrogen, argon, carbon dioxide or flue gas are used as the scavenging gas (Claim 15).

6. In the search for a further solution to the known problem the appellant set himself the dual task of both (a) avoiding an overheating of the melt which necessarily leads to a reduction in the service life of the converter lining and to contamination of the melt with converter particles and (b) preventing the formation of red iron-oxide smoke during the oxidising process, in order thereby to dispense with the need for costly filtering equipment. The problem thus defined was determined from an objective point of view on the basis of the result aimed at and actually attained by the invention (see present application page 2, last line, page 3, lines 2 to 5, page 4, line 1 and page 8, lines 24 to 26) (see "Aryloxybenzaldehydes" OJ 6/1982, 217).

7. To solve this problem the application proposes essentially the use of carbonic acid as oxidising and scavenging agent.

8. The skilled practitioner seeking a new solution to this problem in the prior art was aware of the fact that pig-iron melts cool off when oxidises with carbon dioxide (see DE-C-934 772, Claim 1 and page 2, lines 24/25 and 81/82). The cooling off is a result of the endothermic reaction of the carbon contained in the pig-iron with the carbon dioxide oxidising agent to form carbon monoxide (see also page 1, lines 17 to 24 in conjunction with page 2, lines 34 to 36 of this citation). The use of carbon dioxide as an oxidising agent therefore presented itself from the point of view of the skilled practitioner as a solution to sub-problem (a).

9. FR-A-1 058 181 was able to provide the required suggestion for solving sub-problem (b). This publication imparts the teaching that the formation of the feared red iron-oxide smoke in the treatment of pig-iron melts with oxygen can be significantly reduced by adding to the oxygen blowing gas a compound which undergoes an endothermic reaction through dissociation or reduction (Résumé 1°), e.g. carbon dioxide (Résumé 2°b). On the basis of this teaching it was to be expected that - with a view to solving sub-problem (a) - switching over to carbon dioxide as oxidising agent would lead to complete suppression of the red smoke. Moreover, the close connection between the two sub-problems is already clear from the above-mentioned FR-A- (see page 3, left column, lines 1 to 5).

10. If these teachings from the prior art are combined, a man skilled in the art could expect the dual problem posed to be solvable by using carbon dioxide as the oxidising agent. In addition it was clear that - unlike the single-stage process as in the above-mentioned DE-C- and FR-A for which patent applications were filed in 1938 and 1951 respectively - the stringent requirements as to the purity of steel at the date of priority (11 May 1978), particularly with regard to undesirable gas inclusions, could only be met by additional subsequent scavenging of the steel melt with a scavenging gas, as exemplified in the above-mentioned DD-A-103 266. Since the solution of the overall problem posed demanded the use of carbon dioxide for the oxidising, it was obvious, for reasons of simplifying the process, to use the same inexpensive gas as a scavenging gas as well.

11. Once the development of a method for refining pig-iron by oxidising and subsequent scavenging of the melt by means of carbon dioxide as oxidising and scavenging agent in a single converter bacame obvious, determination of the amounts of carbon dioxide required for this was purely a matter of routine experimentation.

12. It is not necessary to deal with the publications cited by the appellant or the items of literature introduced by the Board, since the appellant stated at the oral proceedings that he did not wish to derive anything from these to support the inventive step of his application.

13. The appellant, on the other hand, takes the view that by combining these publications a man skilled in the art would not have arrived at the claimed method without inventive effort, because he would have only taken into consideration those embodiments which were particularly emphasised therein. The above-mentioned DE-C is thus to be interpreted as providing at most a suggestion for using the particularly emphasised uncalcined limestone as oxidising agent (Claim 2). Of the scavenging agents mentioned together in the above-mentioned DD-A as being of equal value (Claim 15), the skilled practitioner would have been more likely to turn to nitrogen or argon than to carbon dioxide. Let it be noted in particular that the applicant's argument regarding the above-mentioned DE-C is based on a misinterpretation. According to the main claim therein carbonic acid is to be used as oxidising agent. Even in the terminology of the year of filing (1938) this term must be interpreted as meaning carbon dioxide, since carbonic acid (H2CO3) is non-existent. The appellant himself in his own application interpreted carbonic acid (see original Claim 1) as meaning carbon dioxide in the gaseous, liquid or solid state (see page 1, paragraph 2 and the equations on pages 2 and 3 in conjunction with page 3, lines 20 to 23), not the calcium salt of carbonic acid. Claim 2 of the citation mentions "carbon dioxide chemically combined with lime" as an alternative for the carbon dioxide used primarily according to Claim 1. This is also clear from the description (see page 2, lines 67 to 71). Thus carbon dioxide must be regarded as the preferred oxidising agent according to this citation. The use of lime is only recommended for the basic steel-making process (page 2, lines 72 to 78).

14. Apart from this the Board does not share the appellant's view that only those embodiments described as being preferred in a citation are to be considered when assessing the inventive step. In fact, when examining for inventive step, the state of the art must be assessed from the point of view of the man skilled in the art at the time of priority relevant for the application. Consequently all previously published embodiments must be taken into consideration which offered a suggestion to the skilled practitioner for solving the problem addressed, even where the embodiments were not particularly emphasised. It is therefore not a matter of what was regarded as advantageous at that time in the publications constituting the prior art. At the time of priority applicable in this case the skilled practitioner, in replacing oxygen with "carbonic acid" as oxidising gas, would have given preference to carbon dioxide rather than "carbon dioxide chemically combined with lime" - not only because in the steel making technology gases are particularly readily applied, but also because even the subsequent scavenging with carbon dioxide gas as exemplified by the above-mentioned DD-A (Claim 15) indicated the suitability of using carbon dioxide in the same aggregate state in the preliminary stage (of oxidising). If the appellant considers that the use of nitrogen or argon had been more obvious than that of carbon dioxide, he overlooks the fact that the detrimental effect of nitrogen on the quality of steel was known from DE-C (page 1, lines 4 to 9). Additionally the skilled practitioner would have certainly given preference to the inexpensive carbon dioxide rather than the costly noble gas argon. Since the solution to the problem demanded the use of carbon dioxide as oxidising agent, the use of the same compound for the scavenging treatment also presented itself for reasons of economy.

15. The appellant sees the fact that the steel industry has passed by the method as applied for, despite the significant economic contribution it makes to solving the environmental problems in this field, as an indication of the presence of inventive step. The Board takes the view that, as against the assessment of inventive step from the objective point of view - as set out in point 4 - a mere investigation for indications of the presence of inventive step is no substitute for the technically skilled assessment of the invention vis-à-vis the state of the art, pursuant to Article 56 EPC. Where any such indications are present, the overall picture of the state of the art and consideration of all significant factors may indeed show that inventive step is involved, without however leading to the compelling conclusion that inventive step must generally follow from this situation. The considerable technical effect here claimed provides no basis for the presence of inventive step, if only because it is not suprising, but was on the contrary certainly to be expected in view of the problem facing the skilled practitioner.

16. The fact that the steel industry has passed by the method as applied for becomes understandable if the question is considered as to whether and when the appellant's method met an urgent need. The appellant has himself stated that the oxygen-blowing process was rational and economically attractive when introduced into technology thirty years ago, but that the advent and especially the tightening of environmental laws over the last few years have raised investment costs for dust-removal and filtering equipment by about 25%, leading to an increase in the price of steel by 5 to 10 DM/t. In the view of the Board this indicates that over a long period of time there was no motive for breaking away from the oxygen-blowing process which had been successfully introduced and moreover involved expensive plant of long service life, and that the need for the appellant's method which from the present-day point of view is environmentally innocuous arose relatively shortly before the date of priority of the present application. A process developed in the light of a need which arose relatively shortly before the application cannot be regarded as involving inventive step if this need could be readily met by an obvious combination of teachings from the prior art.

17. These statements apply not only to Claim 1, but equally to dependent Claims 2 to 7 based on the main Claim, which merely represent preferred embodiments of the method according to Claim 1 and thus fall with it.

18. ...the Board regards the appeal as lacking foundation.

ORDER

For these reasons, it is decided that:

The appeal against the Decision of the Examining Division of the European Patent Office dated 17 February 1981 is rejected.