EP0336161A1 - Method for improving the fatigue strength of welded high strength steels - Google Patents

Abstract

Components and workpieces made of welded high strength steels (tensile strength greater than 500 N/mm<2>) which are subjected to fatigue loading, have the disadvantage that the fatigue strength in the region of the weld is considerably less than the fatigue strength of the base metal. This applies also to high strength steels in which the weld interfaces have been aftertreated using the known tungsten inert-gas method. According to the invention, the aftertreatment of the welds can be carried out by supplying energy locally, preferably by means of inert-gas arc welding using a tungsten electrode, in such a way that the workpiece is preheated at least to the saturation preheat temperature dependent upon the steel grade, and then the weld zone is aftertreated with a certain heat input per unit length (kJ/cm). In this process, a corresponding fatigue strength is achieved in weld and base metal. In Fig. 4, the total area contained within the reference numerals 1 to 7 shows the usable regions of the current strength, the heat input per unit length and the electrode feed rate. For welded workpieces and components which are used in the off- shore sector and therefore not fatigue-loaded in air, but in sea water, there is additionally the risk of corrosion fatigue cracking, which can be avoided by the preheating to the hardness limit temperature </= saturation preheat temperature. <IMAGE>

Description

The invention relates to a method for improving the fatigue strength of welded high-strength steels, in which the weld seam transitions are treated with local energy supply and with a path energy (kJ / cm) selected from a predetermined range. It is known that the weld seam transition to the base material is the critical area and dominant starting point for the vibration fractures of weld seams and that the measures for improving the fatigue strength are also to be applied here. It is also known that the untreated butt weld connections made from low-strength steels, just like from high-strength and high-strength steels, only achieve a maximum fatigue strength of approximately 200 N / mm² (at S = 0).

TIG post-treatment of the weld seam transitions can, however, increase the vibration resistance of the welded joints. With the previous TIG post-treatment method, the fatigue strength of the base material is achieved with low-strength steels, with the high-strength and high-strength steels the fatigue strength of the welded joint is considerably lower than the fatigue strength of the base material. At the moment (ZIS-Mitteilungen, Hall 28 (1986) 9, page 959 - 966 and IIW DOC.VIII-829-77, 1- 28) the highest individual values of the fatigue strength of TIG-treated welded joints in air are max. 345 N / mm² at S = 0 (S is defined as σ _U / σ ₀ , this is the ratio of the undervoltage to the upper stress of an oscillation amplitude).

Only rough guidelines are known from the literature for the TIG post-treatment of the weld seam transitions of connections that are subjected to vibration stress in air. The current standard of the guidelines is in "The method of TIG dressing", Welding in the world, 3/4 1976 (V, 14), 1 - 7, as is also evident from the comparison with the latest literature, VBK 0024, "Regulation for calculation and construction 0024 ", edition 12/1982, VEB heavy machinery combine TAKRAF, Leipzig.

While a minimum preheating temperature is prescribed for the production of welded joints depending on the carbon equivalent, e.g. Welding Inst. Contract report C 215/22/71, 1 - 16, IIW Doc XIII-698-73, preheating is not used in the TIG post-treatment of the welded joints, both in the guidelines cited above and in practice. This is based, among other things, on on the fact that targeted investigations in the TIG aftertreatment of butt welds made of HT 80 (a steel with a strength of 850 N / mm²) with preheating to 200 ° C and without preheating showed no differences in the fatigue strength.

Based on this prior art, the object of the invention is seen to improve the fatigue strength of welded joints made of high-strength steel by means of an improved TIG aftertreatment of the weld seams, preferably to increase the fatigue strength of the non-welded steel (base material).

This object is achieved in that the weld seams to be treated are preheated to a temperature above room temperature. Investigations by the applicant have shown that - in contrast to the view set out above - a significant increase in the fatigue strength of the welded high-strength steels up to the fatigue strength of the non-welded base material can be achieved.

In particular, the invention can be advantageously configured as follows.

It is possible to introduce the local energy supply necessary for melting the critical weld seam transitions by inert gas arc welding with tungsten electrodes (TIG welding).

Laser beams can also be used for this.

It is useful to work with a TIG path energy in the range of 17 - 21 kJ / cm, which e.g. with 200 A current, 16 V voltage and 10 cm / min feed speed.

The TIG treatment of the butt welds made of StE 500 can be carried out at room temperature.

For the TIG treatment of the butt welds made of StE 690, a saturation preheating temperature of at least 30 ° C is to be used with a sheet thickness of 14 - 16 mm. With preheating above 30 ° C, almost the same fatigue strength is achieved in the weld zone as that of the base material. When preheating to around 70 ° C, the fatigue strength of the TIG-treated weld zone and the base material are fully in agreement. For reasons of economy, preheating will not significantly exceed the temperature that leads to almost the same or corresponding fatigue strength on the one hand of the weld seam and on the other hand of the base material. This temperature is therefore called "saturation preheating temperature" in the application text for the short description.
For the TIG treatment of the butt welds made of StE 890, the saturation preheat temperature is at least 80 ° C with the same sheet thickness and distance energy, with preheating to 180 ° C the fatigue strength of the weld seam is just as high as that of the base material.
For steel grades with a tensile strength that lies between that for StE 500, StE 690 and StE 890, the saturation is determine the preheating temperature by linear interpolation between the above temperatures and, if in doubt, choose a little higher as a precaution.

For steel grades with even higher tensile strengths, the required saturation preheating temperature is determined by extrapolation.

With a track energy above 19 kJ / cm you can choose a lower saturation preheat temperature, in such a way that the preheat temperature is lowered by around 4 ° C per kJ / cm by which the track energy exceeds 19 kJ / cm. In the case of path energies below 19 kJ / cm, a higher saturation preheating temperature is expedient, in such a way that the preheating temperature is increased by around 6 ° C. per kJ / cm by which the path energy falls below 19 kJ / cm.

With steel grade StE 690, a saturation preheating temperature of at least 30 ° C must be maintained with a section energy of approx. 28 kJ / cm and at least 120 ° C with a section energy of approx. 9 kJ / cm.

With steel grade StE 890, the saturation preheat temperature is at least 145 ° C with a track energy of about 28 kJ / cm and at least 235 ° C with a track energy of about 9 kJ / cm.

With the steel quality StE 690, the saturation preheat temperatures at different line energies can be obtained by interpolation between the three value pairs (28 kJ / cm; 35 ° C), (19 kJ / cm; 70 ° C), (9 kJ / cm; 125 ° C) will.

With the steel quality StE 890, this saturation preheating temperature can be achieved for different line energies by interpolation between the three value pairs (28 kJ / cm; 145 ° C), (9 kJ / cm; 180 ° C), (9 kJ / cm; 235 ° C) determine.

It is expedient to maintain at least the value of the saturation preheating temperature for the preheating temperature in order to achieve the same fatigue strength in the welding area as in the rest of the workpiece area.

For high-strength steel grades with a fatigue strength between 250 and 600 N / mm², the saturation preheating temperatures can be determined from the characteristic curves analogous to StE 890 and StE 690.

Favorable process parameters, in which welding errors such as hollows and pores are avoided, are at a distance between the welding electrode used for the TIG aftertreatment from the weld surface between about 2 to 8 mm, in particular 5 mm, a current of about 150 A to 250 A, one Electrode feed rate of about 2 to 33 cm / min and a path energy of about 6 to 60 kJ / cm.

With a path energy between approx. 20 to 60 kJ / cm, the work is advantageous and reliable and trouble-free in a range which is expediently limited by the following four pairs of current strength and feed rate: (150 A; 2 cm / min), (150 A; 7 cm / min); (250 A; 4 cm / min), (250 A; 10 cm / min).

With a path energy between approx. 6 and 10 kJ / cm, a range is advantageous which is characterized by three value pairs (150 A; 20 cm / min), (250 A; 23 cm / min), (250 A; 33 cm / min) is limited.

In the specified ranges of the current strength, the intermediate range for the feed speeds, ie between approx. 20 and 10 cm / min, can also advantageously be used, for example the value pairs (150 A; 7 cm / min), (150 A; 20 cm / min ), (250 A; 10 cm / min), (250 A; 23 cm / min).

In the case of welded materials that are to be used in the offshore area, there is an additional risk of stress corrosion cracking in the hardened weld seam areas of the welded structures subjected to vibration in sea water. To this end, the invention recommends that the welded workpieces to be post-treated are preheated to at least one hardness limiting temperature and WIG-treated with such a stretching energy that the hardness areas in the post-treated weld area are at least approximately limited to the maximum hardness values permitted by the acceptance companies. The weld seam must be heated to at least the saturation preheating temperature in order to maintain the fatigue strength and, if the preheating temperature is higher for the hardness limitation, at least to the latter temperature.

It is advantageous to select the hardness limitation preheating temperature so high that the hardness values of approx. 300 HV 10 are not exceeded.

With a TIG path energy of 20 kJ / cm, the preheating temperature for the hardness limitation to approx. 300 HV 10 should be at least approx. 300 ° C for the steel quality StE 890, at least approx. 200 ° C for the steel quality StE 690 and for the steel quality StE 500 must be at least approx. 100 ° C.

With a track energy over 20 kJ / cm a lower and a higher hardness limitation preheating temperature should be chosen with a track energy under 20 kJ / cm.

For steel grade StE 890, a hardness limitation preheating temperature of at least approx. 200 ° C should be selected for a section energy of approx. 30 kJ / cm and a hardness limitation preheating temperature of at least approx. 400 ° C for a section energy of approx. 10 kJ / cm.

For the steel quality StE 690, the hardness limitation preheating temperature is about 30 kJ / cm with a track energy approx. 100 ° C and at a track energy of approx. 10 kJ / cm at least approx. 300 ° C. The workpieces should be preheated to a hardness limit preheating temperature that is at least as high as the saturation preheating temperature. If the latter is lower, it must be exceeded during preheating up to the hardness preheating temperature.

The workpieces should be preheated to at least one hardness limitation preheating temperature, which is appropriate for the steel quality StE 890 depending on the distance energy (kJ / cm) by interpolation between the three pairs of values (30 kJ / cm; 200 ° C), (20 kJ / cm; 300 ° C), (10 kJ / cm; 400 ° C).

For the StE 690, the hardness limitation preheating temperature should be interpolated between the three pairs of values (30 kJ / cm; 100 ° C), (20 kJ / cm; 200 ° C), (10 kJ / cm; 300 ° C).

Workpieces made of high-strength steel with a fatigue strength between 250 and 600 N / mm² should be heated to at least one hardness limitation preheating temperature, which results from the analog characteristics in the remaining areas for the dependence of the hardness limitation preheating temperature on the section energy for StE 890 and StE 690.

The saturation preheating temperature or the hardness limitation preheating temperature can also be introduced into the workpiece by the preceding connection welding, but must then also be maintained during the subsequent TIG aftertreatment.

The heating is usually done with burners.

To relax, the welded workpieces can be left on before or after the TIG treatment. In the case of tempering treatment after the TIG treatment, however, the tempering temperatures must be chosen so low that there is no significant drop in fatigue strength.

TIG post-treatment of high-strength steels (e.g. StE 690, StE 890 etc.) without or without a sufficient preheating temperature leads to pre-damage to the workpiece, which cannot be reversed by tempering treatment.

The TIG post-treatment of weld seams on steel workpieces disclosed above requires, as explained, a preheating temperature which is dependent on the material, the TIG path energy and the geometry. Since the heat dissipation from the weld into other parts of the workpiece depends on the geometry (thickness, type of seam) of the weld area, it is readily apparent to the person skilled in the art that the parameters of the TIG treatment must be adapted accordingly. Accordingly, it is proposed according to the invention that the values for the stretch energy (kJ / cm) and / or the saturation preheating temperature and / or the hardness limiting temperature in the case of a different workpiece geometry (valid for the TIG treatment of butt welds in sheets with a thickness range of 14 to 16 mm) eg different sheet thicknesses, type of seam) can be adjusted according to the changed heat dissipation in the workpiece.

Steel grades with a high carbon equivalent have a particularly crack-sensitive structure. Therefore, the section energy and / or the saturation preheating temperature and / or the hardness limiting temperature must be increased in comparison with the values previously communicated in such steels.

• Fig. 1 eine Darstellung, bei der die Dauerschwingfestigkeit in N/mm² gegen die Vorwärmtemperatur in °C aufgetra­gen ist, für drei Stahlqualitäten,
• Fig. 2 eine Darstellung der Dauerschwingfestigkeit in N/mm² gegen die WIG-Streckenenergie kJ/cm, für die Stahl­qualität StE 890,
• Fig. 3 eine Darstellung der WIG-Streckenenergie in kJ/cm gegen die Sättigungsvorwärmtemperatur für die Stahl­qualitäten StE 500, StE 690 und StE 890,
• Fig. 4 eine Darstellung der Stromstärke in Ampere gegen die Vorschubgeschwindigkeit in cm/min, aus der die vor­teilhaften Bereiche ersichtlich sind,
• Fig. 5 eine Darstellung der Vickershärte in HV 10 gegen die Streckenenergie für die Stahlqualität StE 890 bei mehreren Sättigungsvorwärmtemperaturen,
• Fig. 6 eine Darstellung der Vickershärte HV 10 gegen die Streckenenergie ohne Vorwärmen für die Stahlqualitä­ten StE 500, StE 690 und StE 890.

Exemplary embodiments of the invention are explained below with reference to the drawings. In detail, each with a butt seam and 15 mm sheet thickness, show:

• 1 is a diagram in which the fatigue strength is plotted in N / mm 2 against the preheating temperature in ° C. for three steel qualities,
• 2 shows the fatigue strength in N / mm² against the TIG line energy kJ / cm, for the steel quality StE 890,
• 3 shows the TIG distance energy in kJ / cm against the saturation preheating temperature for the steel qualities StE 500, StE 690 and StE 890,
• 4 shows the current strength in amperes versus the feed speed in cm / min, from which the advantageous ranges can be seen,
• 5 shows a representation of the Vickers hardness in HV 10 against the section energy for the steel quality StE 890 at several saturation preheating temperatures,
• 6 shows the Vickers hardness HV 10 against the track energy without preheating for the steel qualities StE 500, StE 690 and StE 890.

In this process to improve the fatigue strength, in which the fatigue strength - that is the fatigue strength below the fatigue strength in the time and short-term strength range - is inevitably increased, the weld seam transitions of the workpieces made of high-strength steels are made by inert gas arc welding using a tungsten electrode or by one Aftertreated laser beam or other local energies with an electrical path energy selected from a predetermined range. The welded workpiece zones to be treated are preheated.

1 shows the fatigue strength achieved for the butt seam (15 mm) made of the three steel grades StE 890, StE 690 and StE 500 at different preheating temperatures and section energies, which increases with increasing section energy and preheating temperature and finally that on the right side of the illustration apparent respective Limit (horizontal straight line), namely the fatigue strength of the respective base material, is reached. For example, with StE 890 at 180 ° C preheat temperature and a path energy of 19 kJ / cm in the weld seam the same fatigue strength is achieved as in the base material (saturation preheat temperatures).

In Fig. 2 it is shown on the basis of individual dimensions that the fatigue strength of the butt seam (15 mm) (steel grade StE 890) increases with increasing track energy and preheating temperature, but without preheating (room temperature RT = 20 ° C) from approx. 30 kJ / cm ( 200 A) decreases again without even reaching the fatigue strength of the base material. At 200 ° C preheating temperature, however, the fatigue strength of the base material is already reached at 15 kJ / cm section energy and this level is maintained even at higher section energies, so that a wide working range of the section energy is available from the saturation preheating temperature.

Fig. 3 shows the relationship between the path energy and the preheating temperature, which must be maintained at least in order to achieve the same fatigue strength in the butt seam (15 mm) as in the base material, i.e. it shows the saturation preheating temperature curves for the steel grades StE 890, StE 690 and StE 500.

4 the current strength is plotted against the feed rate. The surface area surrounded by the circles with the reference numerals (1) to (7), current strength approx. 150 to 250 A and path energy approx. 6 to 60 kJ / cm, generally gives a good result in the TIG aftertreatment. It is particularly surprising that good results are achieved in the partial area which is surrounded by the circles (1), (2), (6), (7), ie 150 to 250 A current strength with a path energy of approximately 20 up to 60 kJ / cm, and further in the partial area that is surrounded by the circles (3), (4), (5) and which is determined by a current between 150 and 250 A and a path energy between about 6 and 10 kJ / cm. It is advisable to set the distance between the welding electrode and the weld surface to approx. 5 mm (with a tolerance of up to + 2 mm).

From FIG. 5, in which the maximum hardness is plotted against the track energy, the values of the track energy and preheating temperature can be selected so that the Vickers hardness HV 10 does not exceed a limit value which is given as expedient. In the figure, the indication TIG means the measured values obtained in the TIG seam area and the indication "WEZ" means the measured values of the "heat affected zone", which immediately follows the workpiece.

Fig. 6 shows the corresponding curves at To = RT (room temperature 20 ° C) for the three steel grades designated there. The meaning of the information "TIG" and "WEZ" corresponds to that of FIG. 5.

With TIG post-treatments of the weld seams carried out according to the above diagrams, path energies between 6 and 60 kJ / cm TIG seam widths between 5 and 12 mm were achieved, the approximate transition radii between 10 and 30 mm and shape numbers between 1.12 and 1.02 Consequence, in such a way that higher TIG seam widths as well as transition radii and by the latter lower shape numbers and thus higher and even taking into account the saturation preheating temperature even maximum values of the fatigue strength are achieved by the higher path energies.

The operational control with regard to the adherence to the treatment parameters for lowering the number of shapes, which leads to an increase in the fatigue strength, can be carried out primarily by the simple and inexpensive control of the TIG seam width, since between the TIG seam width and the transition radius is a direct proportionality and there is an inverse proportionality between the TIG seam width and the number of shapes. Therefore, the fatigue strength can be calculated from the TIG seam width at constant preheating temperature with path energies up to approx. 50 kJ / cm.

The disclosed size values valid for the TIG post-treatment of butt welds (15 mm sheet metal) can be converted to other sheet thicknesses and weld types using the correction factors according to the t _8/5 concept (steel-iron material sheet 088). With the help of the carbon equivalent, this is still possible for steels with comparable strength but a very different carbon equivalent.

Claims (26)

1. A method for improving the fatigue strength of welded workpieces made of high-strength steels, in which the weld seam transitions with local energy supply are post-treated with a selected path energy (kJ / cm), characterized in that the welded workpiece zones to be post-treated are at a temperature preheated above room temperature (20 ° C). 2. The method according to claim 1, characterized in that the local energy supply is carried out by an inert gas arc welding by means of tungsten electrode (TIG treatment). 3. The method according to claim 1, characterized in that the local energy supply is effected by laser beam exposure. 4. The method according to any one of the above claims, characterized in that for butt welds with sheet thicknesses of 14 to 16 mm and a line energy of 17 to 21 kJ / cm, the saturation preheating temperature for steel grades from StE 500 to StE 890 is in the range above room temperature, namely for the steel quality StE 690 at least 30 ° C and for the steel quality StE 890 at least 80 ° C, and that for steel qualities with the tensile strength in between, the minimum preheating saturation temperature is interpolated approximately linearly and for steel qualities with higher tensile strength extrapolated. 5. The method according to any one of the above claims, characterized in that a lower Sättigungsvorwärmtemperatur is selected at a higher energy per unit length, and such that, preferably in a method according to claim 4, the preheating to each about 4 ° C is decreased depending kJ / cm by which the track energy exceeds 19 kJ / cm. 6. A method according to any one of claims 1 to 4, characterized in that at a lower energy per unit length greater Sättigungsvorwärmtemperatur is chosen in such a way that, is preferably increased in a method according to claim 4, the preheating of each approximately 6 ° C per kJ / cm by which the track energy falls below 19 kJ / cm. 7. The method of claim 4, 5 or 6, characterized in that for the steel quality StE 690 at a heat input of about 28 kJ / cm, a Sättigungsvorwärmtemperatur of at least 30 ° C and at a heat input of about 9 kJ / cm a Sättigungsvorwärmtemperatur of at least 120 ° C is selected. 8. The method according to claim 4, 5 or 6, characterized in that for the steel quality StE 890 at a heat input of about 28 kJ / cm, a Sättigungsvorwärmtemperatur of at least 145 ° C and at a heat input of about 9 kJ / cm a Sättigungsvorwärmtemperatur of at least 235 ° C is selected. 9. The method according to one or more of claims 1 to 8, characterized in that for the steel quality StE 690 as a function of the section energy (kJ / cm) at least the saturation preheating temperatures are observed, which are determined by interpolation between the three pairs of values (28 kJ / cm; 30 ° C), (19 kJ / cm; 70 ° C), 9 kJ / cm; 120 ° C). 10. The method according to one or more of claims 1 to 8, characterized in that for the steel quality StE 890 as a function of the section energy (kJ / cm) at least the saturation preheating temperatures are observed, which are determined by interpolation between the three pairs of values (28 kJ / cm; 145 ° C), (19 kJ / cm; 180 ° C), 9 kJ / cm; 235 ° C). 11. The method according to one or more of the above claims, characterized in that for high-strength steel qualities with fatigue strengths between 250 and 600 N / mm², the saturation preheating temperatures have at least the values that result from the analog characteristics such as those for StE 890 and StE 690 according to Claims 9 and 10 result. 12. A method for improving the fatigue strength of welded, high-strength steels, in which the weld seam transitions are post-treated by an inert gas arc welding using a tungsten electrode (TIG) and with an electrical path energy (kJ / cm) selected from a predetermined range, in particular after or more of claims 1, 2, 4 to 11, characterized in that at a distance of the welding electrode from the weld surface between about 2 to 8 mm, preferably 3 to 7 mm, in particular 5 mm, the current intensity is at least 150 A and at most 250 A is that the electrode feed speed is at least 2.0 cm / min and at most 33 cm / min, and that the path energy is in the range of 6 to 60 kJ / cm. 13. The method according to claim 12, characterized in that at a track energy between about 20 to 60 kJ / cm in a range that is by the four pairs of values (current; feed rate) of (150 A; 2 cm / min), (150 A; 7 cm / min), (250 A; 4 cm / min), (250 A; 10 cm / min) is limited. 14. The method according to claim 12, characterized in that at a track energy between about 6 to 10 kJ / cm in a range that is by the three pairs of values (current; feed rate) of (150 A; 20 cm / min), (250 A; 23 cm / min), (250 A; 33 cm / min) is limited. 15. The method according to one or more of the above claims, characterized in that the welded workpieces to be post-treated are preheated to at least such a hardness limitation preheating temperature and TIG-treated with such a path energy that the hardness values are limited to approximately 300 HV 10. 16. The method according to claim 15, characterized in that at a TIG distance energy of 20 kJ / cm, the hardness limitation preheating temperature for the steel quality StE 890 at least about 300 ° C, for the steel quality StE 690 at least 200 ° C and for the steel quality StE 500 is at least 100 ° C. 17. The method according to claim 16, characterized in that a lower hardness limitation preheating temperature is selected at a track energy above 20 kJ / cm. 18. The method according to claim 16, characterized in that a higher hardness limitation preheating temperature is selected at a track energy below 20 kJ / cm. 19. The method according to any one of claims 15 to 18, characterized in that for the steel quality StE 890 with a track energy of about 30 kJ / cm a hardness limitation preheating temperature of at least about 200 ° C and with a track energy of about 10 kJ / cm a hardness limitation preheating temperature of at least approx. 400 ° C is selected. 20. The method according to any one of claims 15 to 18, characterized in that for the steel quality StE 690 with a track energy of about 30 kJ / cm a hardness limitation preheating temperature of at least about 100 ° C and with a track energy of about 10 kJ / cm a hardness limitation preheating temperature of at least approx. 300 ° C is selected. 21. The method according to one or more of the above claims, characterized in that the workpieces are preheated to at least one hardness limitation preheating temperature which is suitable for the steel quality StE 890 as a function of the track energy (kJ / cm) by interpolation between the three pairs of values (30 kJ / cm; 200 ° C), (20 kJ / cm; 300 ° C), (10 kJ / cm; 400 ° C). 22. The method according to one or more of the above claims, characterized in that the workpieces are heated at least to the value of the hardness limitation preheating temperature which is appropriate for the steel quality StE 690 as a function of the section energy (kJ / cm) by interpolation between the three pairs of values ( 30 kJ / cm; 100 ° C), (20 kJ / cm; 200 ° C), (10 kJ / cm; 300 ° C). 23. The method according to one or more of claims 19 to 22, characterized in that workpieces made of high-strength steel qualities with a fatigue strength between 250 and 600 N / mm² are heated to at least one hardness limiting preheating temperature, which results from the analog characteristics in the remaining areas for the dependency the hardness limitation preheating temperature from the stretch energy for StE 890 and StE 690. 24. The method according to one or more of the above claims, characterized in that the saturation preheating temperature or the hardness limitation preheating temperature is introduced and held in the workpiece by the connection welding preceding the post-treatment. 25. The method according to one or more of the above claims, characterized in that the values for the path energy (kJ / cm) and / or the saturation preheating temperature which are valid for the TIG treatments of butt weld seams in sheets with a thickness range of 14 to 16 mm If the workpiece geometry differs (eg sheet thickness, type of seam), it must be adapted to the changed heat dissipation in the workpiece. 26. The method according to one or more of the above claims, characterized in that for steels with a higher carbon equivalent and the resulting crack-sensitive structure types, the path energy and / or the saturation preheating temperature are increased accordingly.

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