T 0892/04 13-07-2006

I. The applicant lodged an appeal against the decision of the Examining Division to refuse the European patent application No. 98 908 563.4.

The Examining Division held that the amendments made to the main request as filed with letter of 1 September 2003 and according to the two auxiliary requests as filed with letter of 9 January 2004 met the requirements of Articles 123(2) and (3) EPC. However, the subject-matter of claims 1 and 8 according to the main request and according to the first auxiliary request was considered to lack novelty with respect to D1 (EP-A-0 753 596) and the subject-matter of claims 1 and 8 according to the second auxiliary request lacked an inventive step with respect to D1 either taken alone or taken in combination with D3 (US-A-4 572 748). Document D4 (WO-A-96 17964) although not considered in the decision was stated to be highly relevant to novelty and inventive step.

II. With a communication dated 22 March 2006 the Board informed the appellant that claims 1 to 14 of the main request and of the first auxiliary request, both requests as submitted with the grounds of appeal dated 5 July 2004, appeared to contravene Article 123(2) EPC for either defining a Mn concentration value of "less than 1.45 wt.%" (main request) or a lower bainite value of "at least 54 vol%" (auxiliary request) which appeared to have been taken as isolated features from examples representing an inadmissible extraction of an isolated feature. The Board further stated that in case that a request were to be considered to meet the requirements of Article 123(2) EPC the issues of novelty and of inventive step would be dealt with during the oral proceedings and that document D1 appeared to represent the closest prior art.

III. With fax of 9 June 2006 the appellant submitted an amended main request and new first to third auxiliary requests, each one containing a set of claims and corresponding substitute description pages, together with arguments concerning the allowability of the proposed amendments and the patentability of the claims.

IV. Oral proceedings before the Board were held on 13 July 2006. The appellant requested that the decision be set aside and a patent be granted on the basis of claims 1 to 15 in accordance with the main request, alternatively on the basis of claims 1 to 15 of the first auxiliary request or on the basis of claims 1 to 6 of the third auxiliary request, all requests as filed with letter of 9 June 2006.

V. Claims 1 and 9 according to the main request read as follows (emphasis in bold added by the Board):

"1. A steel having a tensile strength of at least 900 MPa (130 ksi), an impact energy as measured at -40ºC (-40ºF) of greater than 120J (90ft-lbs), and a microstructure comprising a mixed structure of martensite and lower bainite, wherein (i) said mixed structure occupies at least 90% vol. % in said microstructure, (ii) said lower bainite occupies at least 2 vol.% in said mixed structure, and (iii) prior austenite grains have an aspect ratio of at least 3, wherein said steel is produced from a reheated steel slab comprising the following additives in the weight percents indicated and the balance Fe: C: 0.02% to 0.1%; Si: 0% to 0.6%; Mn: 0.2% to 1.46%; Ni: 0.2% to 1.2%; Nb: 0.01% to 0.1%; Ti: 0.005% to 0.03%; Al: 0% to 0.1% N: 0.001% to 0.006%; Cu: 0% to 0.6%; Cr: 0% to 0.8%; Mo: 0% to 0.6%; V: 0% to 0.1%; B: 0% to 0.0025%; and Ca: 0% to 0.006%; and other impurities, including P: not greater than 0.015%; and S: not greater than 0.003%; and wherein said steel has a Vs value, as defined by equation {1} below, of 0.15 to 0.42, and further has a carbide size of less than 5 microns: {1}: Vs = C + (Mn/5) + 5P - (Ni/10) - (Mo/15) + (Cu/10) wherein each atomic symbol represents its content in wt.%."

"9. A method for preparing a steel plate having a tensile strength of at least 900 MPa (130 ksi), an impact energy as measured at -40ºC (-40ºF) of greater than 120J (90ft-lbs), and a microstructure comprising a mixed structure of martensite and lower bainite, wherein (i) said mixed structure occupies at least 90% in said microstructure, (ii) said lower bainite occupies at least 2 vol% in said mixed structure, and (iii) prior austenite grains have an aspect ratio of at least 3, the steel plate comprising the following additives in the weight percents indicated and the balance Fe; C: 0.02% to 0.1%; Si: 0% to 0.6%; Mn: 0.2% to 1.46%; Ni: 0.2% to 1.2%; Nb: 0.01% to 0.1%; Ti: 0.005% to 0.03%; Al: 0% to 0.1%; N: 0.001% to 0.006%; Cu: 0% to 0.6%; Cr: 0% to 0.8%; Mo: 0% to 0.6%; V: 0% to 0.1%; B: 0% to 0.0025%; and Ca: 0% to 0.006%; and other impurities, including P: not greater than 0.015%; and S: not greater than 0.003%; and wherein said steel plate has a Vs value, as defined by equation {1} below, of from 0.15 to 0.42, and a carbide size of less than 5 microns: {1}: Vs = C + (Mn/5) + 5P - (Ni/10) - (Mo/15) + (Cu/10) wherein each atomic symbol represents its content in wt.%, said method comprising the steps of: (a) heating a steel slab to a temperature of 950ºC (1742ºF) to 1250ºC (2282ºF); (b) hot rolling said steel slab, under the condition that the accumulated reduction ratio at a temperature of not higher than 950ºC (1742ºF) is at least 25%, to form steel plate; c) completing the hot rolling step at a temperature of not lower than the Ar3 transformation temperature or 700ºC (1292ºF), whichever is higher; and (d) cooling said steel plate from a temperature of not lower than 700ºC (1292ºF) at a cooling rate of 10ºC/sec to 45ºC/sec (18ºF/sec to 81ºF/sec) as measured at substantially the center of said steel plate until substantially the center of said steel plate is cooled to a temperature of not higher than 450ºC (842ºF) so as to facilitate completion of transformation of said steel plate to said mixed structure of martensite and lower bainite with said tensile strength and said impact energy values."

VI. Claims 1 and 9 according to the first auxiliary request differ from claims 1 and 9 of the main request in that the lower bainite value of feature (ii) has been amended to read "said lower bainite occupies at least 54 vol% in said mixed structure" and in that the Mn concentration range has been amended to read "Mn: 0.2% to 1.7%" (emphasis in bold added by the Board).

VII. Claim 1 according to the third auxiliary request corresponds to claim 9 of the first auxiliary request.

VIII. The appellant argued essentially as follows:

With respect to the main request: The upper Mn concentration value of 1.46% is derived from examples 1 and 2 in Table 1 and the new range of from 0.2% to 1.46% is not arbitrarily chosen since it includes the examples 3 and 10 with a Mn content of 1.45%. The Board's reasoning as stated in the communication cannot be followed. Firstly, while the Board appear to allude to the fact that in equation {1} C and P do not have any associated denominator, in the case of P it has an associated numerator, and the denominator for Ni, Mo and Cu is in each case somewhat larger than that for Mn, it has to be noted that the maximum amounts of each element specified in claim 1 vary significantly, so that the relative contribution of each element to the value Vs is not dependent solely on whether it has an associated denominator or an associated numerator; rather, it is the product of the numerator/denominator and the chosen amount of each element that determines the relative contribution (additive or subtractive) of each element to the value Vs. When the Mn content is at the upper limit of 1.46% the contribution of Mn to the value Vs lies close to the middle of the range defined by Vs. Consequently, there is considerable freedom to adjust the C, P, Ni, Mo and Cu amounts, such that the requirements of Vs lie within the range 0.15 <= Vs <= 0.42 is satisfied. Therefore it is clear that numerous combinations of amounts of Mn, P, Ni, Mo and Cu are possible within the permitted range for Vs. It follows that Vs does not determine a close association between the concentrations of said specified elements. Rather, for the reasons given, it is clear that equation {1} permits fairly wide variation in the relative concentrations of the different constituent elements. It is admitted that there has to be a constraint on the relative amounts of said constituent elements, in order that the resulting steel should have the required blend of properties, i.e. high strength and toughness, and low centreline segregation. There is no intrinsic link between the Mn concentration and the properties of the steel. The Mn concentration is independent similarly as that of Ni, Si or Mo. Therefore the amendment is in agreement with decision T 201/83 and with Article 123(2) EPC.

With respect to the first auxiliary request: The Mn range is re-amended to read 0.2 to 1.7% having a basis in the application as originally filed (see e.g. claims 6 and 7). The lower bainite value is provided by example 3 of Table 8. For product claim 1 it does not matter how the lower bainite content is achieved. The process parameters for heat treatment are irrelevant to the properties of the final steel so long as the specified lower bainite content requirement is met. A claim limited to the process parameters would have no practical value. Furthermore, although a composition change affects the microstructure there is no intrinsic link between the composition and the properties. As can be derived from Annex C of the letter dated 9 June 2006 the amount of lower bainite correlates with the toughness of the steel. An increased amount of at least 54 vol% according to of samples 3, 5, 8 and 9 resulted in the highest base steel Charpy test data values while the other test data of samples no longer covered by the claims have somewhat lower values. Therefore, since these results hold true irrespective of the manufacturing process used for the example steels which were non-tempered and tempered, the other process and chemical composition parameters for heat treatment necessary to arrive at the particular microstructure of the example of Table 8 are not necessary. Consequently, the amendments made to claims 1 and 9 of the first auxiliary request meet the requirements of Article 123(2) EPC.

With respect to the third auxiliary request: the arguments brought forward with respect to the process claim 9 of the first auxiliary request apply likewise.