EP0352597B1 - Process for producing hot-rolled strip or heavy plates - Google Patents

Abstract

The invention relates to a process for the production of hot rolled strip or heavy plates from stainless and refractory steels or from forgeable alloys on a nickel basis with a final thickness in the range of 5 to 60 mm by the production of a slab from monobloc casting or by continuous casting and heating the slab at a temperature above 1100 DEG C. followed by the hot rolling of the slab and accelerated cooling of the product rolled to the end thickness. The characterizing feature of the invention is that the heated slab is rolled without interruptions first to a maximum of 1/6 of its initial thickness, mainly by deformation passes in which the degree of deformation pass in the thickness direction is greater than the degrees of deformation shown by curve A in FIG. 1, in dependence on the surface temperature of the product. Then finish rolling is performed to the end thickness, mainly by deformation passes in which the degree of deformation per pass in the thickness direction is greater than the degrees of deformation shown by curve B1 or curve B2 in FIG. 1, in dependence on the surface temperature of the product and the pause between two adjacent passes as parameters. The surface temperature of the finish rolled product must be not less than 1030 DEG C., if the product contains up to 1.0% molybdenum and not less than 1050 DEG C., if the product contains more than 1.0% molybdenum. At the latest 100 seconds following finish rolling, the product is cooled at an accelerated rate with a speed in the core of more than 3 K/sec, more particularly more than 5 K/sec, to a temperature which is equal to or lower than 650 DEG C.

Description

The invention relates to a method for producing hot strip or heavy plates from rustproof and heat-resistant molybdenum-containing steels or from molybdenum-containing wrought alloys based on nickel with a final thickness in the range from 5 to 60 mm by producing a slab from ingot casting or by continuous casting, heating the slab at one Temperature above 1,100 ° C, subsequent hot rolling of the slab and accelerated cooling of the product rolled to its final thickness.

A method according to the preamble of claim 1 for the production of austenitic stainless steel plates with high corrosion resistance and high mechanical strength both at ambient temperature and at high temperatures is known from DE-OS 36 17 907. It can be seen from this prior art document that the steel plates, i.e. Heavy plates made of rust-proof austenitic steels of the composition specified in the publication after the roughing and finishing rolling and the subsequent cooling in air to room temperature usually have to be subjected to a subsequent heat treatment or solution annealing. This is carried out so that the hardening caused by the deformation is broken down and precipitations of intermetallic or carbidic phases are dissolved, which negatively affect the corrosion resistance of the product. In order to achieve this goal, the subsequent solution annealing must generally take place at temperatures of more than 1,000 ° C. and correspondingly long holding times which are sufficient to bring the precipitations back into solution. The deformation-related solidification is reduced simultaneously as a result of recovery and recrystallization. Accordingly, the stainless steel plates or heavy plates produced by this conventional method have in the solution-annealed state with regard to their mechanical properties, e.g. Strength and toughness, as well as corrosion resistance, a property profile for which a low mechanical strength is characteristic.

The solution annealing following the pre- and finish rolling and the subsequent cooling in air to room temperature means however, due to the reheating of the already rolled product to more than 1,000 ° C and the required holding times, high production costs and longer production times. Furthermore, this subsequent annealing process usually involves additional scaling of the product, which can cause its surface quality to deteriorate. As a rule, this means an additional effort for the required final scaling of the finished rolled product.

Among other things Proceeding from these disadvantages, the patent application described and claimed in DE-OS 36 17 907 is based on the object of creating a method for producing austenitic stainless steel plates which have better corrosion resistance and tensile strength both at ambient temperatures and at higher temperatures, without the need to use a downstream heating furnace as is required in the conventional process for subsequent solution annealing.

As a solution to this problem, it is proposed to first heat the slab from an austenitic stainless steel grade, which usually requires subsequent solution annealing and from which the steel plate is to be produced, to a temperature of more than 1,000 ° C. The heated slab is then hot-rolled in the recrystallization area of the austenite and preferably also in the non-recrystallization area with a finish-rolling temperature of more than 800 ° C. Finishing rolling in the non-recrystallization area is essential in order to achieve a higher mechanical strength. Immediately after the finish rolling to the final thickness, there is an accelerated cooling with an average cooling rate of more than 2 K / s to a temperature of at least 550 ° C. Provided that these rolling and cooling conditions are met, the subsequent subsequent solution treatment is usually no longer necessary.

As the exemplary embodiments show, in particular in comparison with finished rolled steel plates made from the same austenitic stainless steel grades, with the same final thickness, but in solution-annealed condition, the product produced by this process has a much better mechanical and comparable corrosion resistance. A higher strength is achieved in particular if the hot rolling also takes place in the non-recrystallization area. In particular, it can be seen from the exemplary embodiments that in this known method, with a final thickness of the product of 20 mm, the heating and heating temperature for the slab is preferably in the range from 1,100 to 1,200 ° C., and the finish-rolling temperature is in the range from 900 to Assumes 970 ° C, that is in any case less than 1,000 ° C and immediately after finish rolling with a temperature loss of only about 10 ° C the accelerated cooling begins, to a value of 500 ° C, preferably 300 ° C, in particular down to room temperature. Only when the final thickness of the product or heavy plate is 40 mm, in particular 100 mm, does a finish rolling temperature of more than 1,000 ° C result.

If hot strip or heavy plates are now to be produced from rustproof and heat-resistant steels or from wrought alloys based on nickel with the composition given in Table 1, but with a property profile that corresponds to the property profile of the same product in the solution-annealed state, this is a previously known method for the production of Heavy plates, especially hot strip, are not suitable for the following reasons:

If heavy plates with a final thickness of less than 60 mm are hot-rolled and finished-rolled using this method, the finish-rolling temperature drops so much that a property profile comparable to that of heavy plates in solution-annealed condition, for example with regard to strength, toughness and corrosion resistance, cannot be set. Rather, the method known from DE-OS 36 17 907 basically gives a higher mechanical strength. However, if this is not desired with regard to the processing and use properties of the heavy plates, the finished rolled plates must then be subjected to a subsequent solution treatment, provided that they have a final thickness of less than 60 mm, in particular less than 40 mm.

The same also applies to the production of hot strip, which has to be subjected to solution annealing after the final rolling, due to the high temperature losses due to the small strip thickness, particularly during the finish rolling phase. In addition, this heat treatment, which is usually carried out in a continuous furnace with a subsequent pickling line, limits the production of hot strip up to a maximum final thickness of about 10 mm, although it is in principle possible to also produce hot strip with a final thickness of the order of magnitude Finished approx. 20 mm warm.

Therefore, if the hot strip and the heavy plates should have a property profile as in the solution-annealed condition, then heat treatment or solution annealing is still essential to break down the deformation-related hardening and to dissolve excretions. For the reasons mentioned, hot strip and heavy plate with a final thickness of less than 60 mm are primarily affected, in particular those with a thickness in the range between 8 and 40 mm. Accordingly, if an increase in the strength properties is not desired, then with the method known from DE-OS 36 17 907 only heavy plates can be safely produced without subsequent solution treatment, which have a final thickness of more than 60 mm, but are rarely used in practice . On the other hand, so far only the production of hot strip with a final thickness of less than about 8 or 10 mm has been possible without problems, which, however, has to be solution-annealed in any case after the finish rolling.

However, in the production of hot strip and heavy plates from rustproof and heat-resistant steels or from wrought alloys based on nickel according to Table 1, it is increasingly necessary to use these products over the largest possible range, i.e. also with a thickness in the range of 5 to 60 mm, preferably 8 to 40 mm, by a uniform process.

In this regard, EP-OS 0 144 694 discloses a modified process for the production of flat, band-shaped or plate-shaped semi-finished products, for example with a final cross section of 15 mm × 40 mm, from a stainless austenitic or martensitic steel, but which provides solution annealing. With this In the process, the workpiece made of stainless steel with the composition specified in the publication is first heated to a high temperature in the order of 1200 ° C. and heated through at this temperature. It is then pre-rolled and finish-rolled warm at a temperature in the range of 1,000 to 1,100 ° C in such a way that a sufficiently high deformation during the rolling process ensures complete recrystallization of the rolling stock. After finish rolling to final thickness, solution annealing and subsequent quenching of the semi-finished product in water from this temperature range is carried out to almost room temperature. An essential feature of this process is that the solution annealing immediately following the rolling process is carried out in a heat after the last or the last rolling pass and the workpiece is then quenched directly from the solution annealing temperature in water without any additional treatment.

Since, as a rule, the finish rolling temperature is too low for immediate quenching, the workpiece produced according to this method must first be heated again by means of a heater after the finish rolling. As an alternative, this method provides for a roller heating system, which is intended to largely prevent premature and excessive cooling of the workpiece during rolling in order to prevent the finished workpiece from being reheated to the required solution solution and quenching temperature of more than 1,000 ° C. However, this additional heating for the reheating of the finished rolled product and in particular the proposed roller heating would mean a considerable additional outlay in the production of hot strip or heavy plates, which was previously customary.

The invention has for its object to provide a method of the type mentioned, according to which products in the form of hot strip or heavy plates with the composition given in Table 1 are hot-rolled and have a property profile after accelerated cooling, for example with regard to strength, toughness and corrosion resistance , which corresponds to that of solution annealed hot strip or heavy plate.

${\text{h}}_{\text{n}}\text{= Walzgutdicke nach dem n-ten Stich und}$

${\text{h}}_{\text{n-1}}\text{= Walzgutdicke nach dem (n-1)-ten Stich.}$

According to the invention, this object is achieved in accordance with the measures specified in the characterizing part of claim 1 as follows:
Initially, slabs are produced from ingot casting or by continuous casting from rustproof and heat-resistant steels or from wrought alloys based on nickel with the composition given in Table 1 and heated at a temperature of more than 1,100 ° C. before hot rolling. Immediately afterwards, the pre-rolling phase of the hot rolling of the heated slabs begins without interruptions to no less than 1/6 of their initial thickness, i.e. the slabs are reduced to as little as possible between the individual deformation passes in extreme cases to 1/6 of their initial thickness. Hot rolling is predominantly carried out with deformation stitches in which the degree of deformation per stitch in the thickness direction is greater than the degrees of deformation indicated by curve A in FIG. 1 as a function of the surface temperature of the product. The degree of deformation phi is defined as

${\text{phi = ln (h}}_{\text{n-1}}{\text{/H}}_{\text{n}}\text{)With}$

${\text{H}}_{\text{n}}\text{= Rolling stock thickness after the nth pass and}$

${\text{H}}_{\text{n-1}}\text{= Rolling stock thickness after the (n-1) th pass.}$

Since more than 50% of the selected deformation stitches have a degree of deformation which is greater than the degrees of deformation indicated by curve A in FIG. 1, this means that the hot rolling takes place predominantly in the recrystallization region, as in the process known from EP-OS 0 144 694 , which makes the very coarse-grained starting structure largely homogeneous in this first rolling phase, free of microscopic tears and fine-grained due to the high temperature.

The initial thickness of the slab or slabs is usually in the order of about 150 to 250 mm. If, however, the slabs produced by continuous casting have a thickness of less than about 50 mm or less, the reduction in the product in them can also be used according to the invention the first rolling phase. The finishing rolling to the final thickness is then carried out according to measure ba) and bb) of claim 1 above a minimum temperature which is dependent on the molybdenum content of the product and which must not be undercut.

In contrast to the common practice described in the two aforementioned publications, it is essential to the invention for the finish rolling according to the invention to the final thickness that not only in the recrystallization area, i.e. with deformation stitches with degrees of deformation according to curve A in Figure 1 and larger, but that the degrees of deformation of the majority of the selected deformation stitches must be greater than that depending on the surface temperature of the product and the pause time between two adjacent deformation stitches as a parameter by the Curve B1 or B2 in Figure 1 degrees of deformation. Curve B1 applies to a pause time between two adjacent stitches of less than 10 s (preferably hot strip) and curve B2 applies to a pause time between two adjacent stitches of more than 10 s (preferably heavy plate).

By using these degrees of deformation specified according to the invention it is primarily achieved that the structure is recrystallized homogeneously and finely grained during the finish rolling and the deformation-related solidification is broken down without the need for a subsequent heat treatment for recrystallization before the accelerated cooling of the product, as is the case with the EP -OS 0 144 694 previously known method is provided. In addition, this measure largely compensates for heat losses due to conduction and radiation.

If the hot strip or heavy plate is finished rolled to the final thickness above the minimum temperature specified in claim 1 according to measures bb), then accelerated cooling takes place at the core without more than 100 s thereafter, at a speed of more than 3 K / s, preferably more than 5 K / s, except for a temperature equal to or less than 650 ° C.

With the method according to the invention, hot strip and heavy plates made of the steels specified in Table 1 can be made to a final thickness in the range of 5 to 60 mm and with a property profile that corresponds to the mechanical properties and the corrosion resistance of solution-annealed hot strips and heavy plates. In contrast to this, the strips and sheets produced according to the invention, however, have a more uniform, in particular very fine-grained and largely excretion-free structure, as a result of which their processing and use properties are improved. In particular, thin strips and sheets with a preferred final thickness in the range from 8 to 40 mm can now be hot-rolled to the final thickness without additional heat input during the rolling out in such a way that subsequent solution annealing is no longer required .

The properties of the strips and sheets produced by the process according to the invention can be further improved and optimized by hot-rolling and the subsequent accelerated cooling in accordance with the measures specified in subclaims 2 to 6. The method according to claim 3 relates to the production of hot strip and the method according to claim 4 to the production of heavy plates. If at the same time all the deformation stitches of the roughing phase have a degree of deformation which is greater than the degrees of deformation indicated by curve A in FIG. 1, hot strip and heavy plates can be e.g. Manufacture with optimal values in terms of strength, toughness and corrosion resistance.

The method according to the invention can preferably be applied to the production of hot strip and heavy plates from rustproof and heat-resistant steels with an analysis according to claims 7 to 10 and 13 to 16 as well as from a wrought nickel base alloy with the composition specified in claims 11 and 12. If the method is preferably applied to rustproof and heat-resistant austenitic steels with the composition according to claims 15 and 16, hot strip and / or heavy plates with high toughness and increased corrosion resistance are obtained, which afterwards as a finished product are easy to process with regard to hot forming, cold forming and welding have.

${\text{Cr}}_{\text{aq}}\text{= Cr + Mo + 1.5*Si + 0.5*Nb + 4*Ti + 3*Al und}$

${\text{Ni}}_{\text{aq}}\text{= Ni + 0.5*Mn + 30*(C + N) + 0.5*Cu.}$

When the measures according to the invention are applied to stainless austenitic steels with the composition specified in claim 16, which form delta ferrite during solidification, it is advantageous if the requirements for corrosion resistance are correspondingly high if these steels are alloyed to a content of delta ferrite below 10 %, preferably less than 5%. This can be done according to the invention by lowering the contents of ferrite-forming elements, but preferably by - with the exception of carbon - increasing the contents of austenite-forming alloy elements individually or in groups. The following applies according to Table 3:

${\text{DF [\%] = (2.9004 * Cr}}_{\text{aq}}{\text{- 2,084 * Ni}}_{\text{aq}}\text{) - 25.62, with}$

${\text{Cr}}_{\text{aq}}\text{= Cr + Mo + 1.5 * Si + 0.5 * Nb + 4 * Ti + 3 * Al and}$

${\text{Ni}}_{\text{aq}}\text{= Ni + 0.5 * Mn + 30 * (C + N) + 0.5 * Cu.}$

The invention is explained in more detail below on the basis of individual exemplary embodiments:
Table 1 shows the composition of those stainless and heat-resistant steels and wrought alloys based on nickel, from which hot strip and heavy plates can be produced by the process according to the invention. Of these alloys, the five different alloys specified in Table 3 were selected, from which hot strip with a final thickness of 10 and 15 mm and heavy plates with a final thickness in the range from 10 to 40 mm were produced by the process according to the invention. These are two stainless austenitic steels with a molybdenum content of less than 1.0%, two further stainless austenitic steels with a molybdenum content of more than 1.0% and a nickel-based alloy with the composition given in Table 3.

From these five different alloys, preliminary slabs with a thickness in the range of 170 to 265 mm were first produced and then heated to a temperature of more than 1,100 ° C. and heated through at this temperature. The hot strip and the heavy plates were then heated from them According to the method according to the invention, the slabs were first rolled out to a final thickness in a pre-rolling phase and then in a subsequent finishing rolling phase, before the finished rolled product was accelerated to a temperature of less than 650 ° C. at a rate of more than 3 K / s. The degrees of deformation per pass were selected both in the roughing phase and in the finish-rolling phase in accordance with the dependence of the degree of deformation on the surface or surface of the material to be rolled, which is shown in Table 2 and shown in FIG. 1. In detail, the hot rolling and cooling conditions, according to which the five different alloys for hot strip (W) and heavy plates shown in Table 3 were rolled out to final thickness, are given in Table 4. The corresponding conditions of hot strip and heavy plate not produced according to the invention are also given. Table 5 compares the results obtained from hot strip and heavy plate produced according to the invention, from solution-annealed and annealed and not annealed according to the invention.

If hot strip and heavy plates with the composition specified in Table 3 are hot-rolled and finish-rolled by the process according to the invention according to claim 1 and then accelerated at the latest 100 s after finish-rolling, these strips and plates have a yield point and tensile strength according to Table 5 which: are comparable with the corresponding sizes of solution-annealed strips and sheets. As the corresponding column in Table 5 shows, the strips and sheets produced according to the invention have an improved, more uniform, fine-grained and largely excretion-free structure, which has a positive effect on the processing and use properties of these strips and sheets. The elongation and the notched impact strength are also comparable with the corresponding values of the products in the solution-annealed state and are in all cases within a narrow range.

As the comparative examples according to the invention, which are also given in Table 5, show in particular that they lead to products with higher strength values, in particular higher yield strength, lower elongation with surface cracks and with a coarser-grain mixed structure if the measures aa) (roughing phase), ab) (finish rolling phase), ac) (final rolling temperature) and b) (accelerated cooling) are not observed individually or in combination. The following results in detail in this regard:

As shown in Comparative Examples 1.7 and 3.6 in particular, hot rolling in the roughing phase with degrees of deformation of the deformation passages that are predominantly or in the majority smaller than the degrees of deformation indicated by curve A in FIG. 1 can lead to harmful surface cracks on the product. For this reason alone, the strips and sheets obtained cannot be used. The desired values for the yield strength, tensile strength and elongation cannot be set in these cases either. In this regard, the product has mechanical properties that differ from the property profile of the product in the solution-annealed state.

Hot rolling in the recrystallization area and at high temperatures, as is already known from EP-OS 0 144 694, on the other hand, is not sufficient to set the properties desired for the hot strip and the heavy plates. As the comparative examples 1.8, 3.8 and 4.8 in Table 4 and the associated values for the yield strength, tensile strength, elongation and impact strength in Table 5 show - in these cases measure a) according to the invention is fulfilled - in particular a significantly higher yield strength and a lower one Elongation set if the hot rolling condition according to the feature ba) in claim 1 is not met. It is therefore not only important that the products in the recrystallization area, i.e. are hot-rolled with degrees of deformation which are greater than the degrees of deformation indicated by curve A in FIG. 1, but the measures ba) and (bb) of claim 1 according to the invention must also be met, in particular in the finish rolling phase.

As can also be seen from Tables 4 and 5, a homogeneous and fine-grained structure which is improved compared to the solution-annealed state can be set provided the hot rolling conditions in the finish-rolling phase for hot strip according to subclaims 2 and 3 and for heavy plates according to subclaims 2 and 4 can be set. Fulfill on the other hand, the hot rolling conditions in the finish rolling phase, in addition to measure bb), only feature ba) according to claim 1, a generally fine-grained structure is also generally achieved, but to a small extent also has coarse grain. In these cases too, the hot strips and heavy plates produced according to the invention have comparable mechanical properties and corrosion resistance to the products in the solution-annealed state.

Overall, the exemplary embodiments according to the invention and the comparative examples in Tables 4 and 5 show that hot strip and heavy plates made of rustproof and heat-resistant steels or of wrought alloys based on nickel with the composition given in Table 1 with a final thickness in the range from 5 to 60 mm, preferably in the range from 8 to 40 mm, can be produced by the process according to the invention with a property profile which corresponds to the property profile of the corresponding strips and sheets in the solution-annealed state. The strips and sheets produced according to the invention advantageously have a homogeneous and fine-grained structure that is largely free of excretions, which further improves their processing and use properties. Furthermore, the method according to the invention now makes it possible, in particular, to produce hot strip with a final thickness greater than approximately 5 mm in a simple and inexpensive manner by controlled hot rolling with subsequent accelerated cooling without the need for subsequent solution annealing. Table 1 Stainless and heat-resistant steels Wrought alloys based on Ni ferritic and martensitic austenitic / ferritic austenitic Alloy element Alloy content in mass% Konlenstoff ≦ 0.35 ≦ 0.05 ≦ 0.15 ≦ 0.1 manganese ≦ 2.5 ≦ 10.0 ≦ 20.0 ≦ 4.0 silicon ≦ 1.5 ≦ 1.5 ≦ 4.0 ≦ 4.0 nickel ≦ 3.0 4 - 7 ≦ 35 (Rest Ni) chrome 6 - 30.0 10 - 30.0 10 - 30.0 10 - 30 molybdenum ≦ 3.0 ≦ 5.0 ≦ 7.0 ≦ 10 titanium ≦ 1.5 ≦ 1.5 ≦ 1.5 ≦ 1.5 Tantalum and / or niobium ≦ 1.5 ≦ 1.5 ≦ 1.5 ≦ 1.5 copper ≦ 5.0 ≦ 5.0 ≦ 5.0 aluminum ≦ 1.5 ≦ 0.5 ≦ 1.0 ≦ 0.5 nitrogen ≦ 0.5 ≦ 0.5 ≦ 0.5 ≦ 0.5 Other V ≦ 0.5 V ≦ 1.0 Fe ≦ 45 S ≦ 0.5 S ≦ 0.3 (Rest of Fe) (Rest of Fe) (Rest of Fe) Forming temperature T _U (surface of rolling stock) ° C Critical degree of deformation φ * Roughing phase Finishing rolling phase Curve A Curve B 1 ** Curve B₂ *** 1200 0.046 (0.061) (0.083) 1150 0.066 0.085 0.127 1100 0.094 0.116 0.178 1050 0.137 0.163 0.238 1030 0.163 0.191 0.269 1000 0.196 0.227 0.305 980 0.223 0.254 0.332 * = The individual values were rounded to 0.001. ** = for breaks of less than 10 seconds. *** = for break times longer than 10 sec.

Claims (17)

1. A process for the production of hot rolled strip or heavy plates from stainless and heat resisting molybdenum-containing steels or of molybdenum-containing forgeable alloys on a nickel basis having a final thickness in the range of 5 to 60 mm by producing a slab from ingot casting or by continuous casting, through-heating the slab at a temperature above 1100°C and then hot rolling the slab, whereafter the product rolled for the final thickness is rapidly cooled, wherein

   a) the through-heated slab, having a starting thickness greater than approximately 50 mm, is first rolled to not less than 1/6 of its starting thickness mainly with deforming passes in which the degree of deformation per pass in the thickness direction is greater than the degrees of deformation shown by curve A in Fig. 1 in dependence on the surface temperature of the product,

   ba) the slab, roughed down to not less than 1/6 of its starting thickness, or a through-heated slab produced by continuous casting and having a starting thickness smaller than approximately 50 mm, is then finish rolled to the final thickness mainly with deforming passes in which the degree of deformation per pass in the thickness direction is greater than the degrees of deformation shown as parameter in Fig. 1 in dependence on the surface temperature of the product and the duration of the pause between two successive passes by curve B1 for pauses shorter than 10 sec or by curve B2 for pauses longer than 10 sec, and

   bb) the surface temperature of the finish rolled product

   - does not drop below 1030°C, if the product contains up to 1.0% molybdenum and

   - does not drop below 1050°C, if the product contains more than 1.0% molybdenum

   or, if the finish rolled product consists of a stainless and heat resisting ferritic or martensitic steel, the surface temperature of the finish rolled product

   - does not drop below 980°C, if the product contains up to 1.0% molybdenum and

   - does not drop below 1000°C, if the product contains more than 1.0% molybdenum, and

   c) without solution annealing and at the latest 100 sec after finish rolling, the product is rapidly cooled at a speed in the core of more than 3 K/sec, more particularly more than 5 K/sec, to a temperature which is equal to or lower than 650°C.
2. A process according to claim 1, characterized in that all the deforming passes with which the through-heated slab is first rolled to not less than 1/6 of its starting thickness are performed with a degree of deformation which is greater than the degrees of deformation shown by curve A in Fig. 1 in dependence on the surface temperature of the product.
3. A process according to one of claims 1 or 2, characterized in that at least 2/3 of the deforming passes with which the product is rolled to the final thickness are performed with a degree of deformation which is greater than the degrees shown as parameter by curve B1 in Fig. 1 in dependence on the surface temperature of the product and the duration of the pause between two successive passes.
4. A process according to one of claims 1 or 2, characterized in that at least 3/4 of the deforming passes with which the product is rolled to the final thickness are performed with a degree of deformation which is greater than the degrees shown as parameter by curve B2 in Fig. 1 in dependence on the surface temperature of the product and the duration of the pause between two successive passes.
5. A process according to one of claims 1 to 4, characterized in that following the rapid cooling, the finish rolled product is slowly cooled to room temperature in air.
6. A process according to one of claims 1 to 5, characterized in that if it consists of a stainless and heat resisting ferritic, martensitic or austenitic-ferritic steel, the finish rolled product is rapidly cooled to a temperature which is equal to or lower than 400°C.
7. A process according to one of claims 1 to 6, characterized in that the slab is produced from a stainless and heat resisting ferritic or martensitic steel consisting of max. 0.35% C, max. 2.5% Mn, max. 1.5% Si, max. 3.0% Ni, 6.0 to 30.0% Cr, max. 3.0% Mo, residue iron and the unavoidable impurities.
8. A process according to claim 7, characterized in that max. 1.5% Ti, max. 1.5% Ta and/or Nb, max. 1.5% Al, max. 0.5% N, max. 0.5% V, max. 0.5% S are also added individually or in combination to the stainless and heat resisting ferritic or martensitic steel.
9. A process according to one of claims 1 to 6, characterized in that the slab is produced from a stainless and heat resisting austenitic-ferritic steel consisting of max. 0.05% C, max. 10.0% Mn, max. 1.5% Si, 4.0 to 7.0% Ni, 10.0 to 30.0% Cr, max. 5.0% Mo, residue iron and the unavoidable impurities.
10. A process according to claim 9, characterized in that max. 1.5% Ti, max. 1.5% Ta and/or Nb, max. 5.0% Cu, max. 0.5% Al, max. 0.5% N are also added individually or in combination to the stainless and heat resisting austenitic-ferritic steel.
11. A process according to one of claims 1 to 5, characterized in that the slab is produced from a forgeable alloy of a nickel base, consisting of max. 0.1% C, max. 4.0% Mn, max. 4.0% Si, 10.0 to 30.0% Cr, max. 10.0% Mo, residue nickel and the unavoidable impurities.
12. A process according to claim 11, characterized in that max. 1.5% Ti, max. 1.5% Ta and/or Nb, max. 5.0% Cu, max. 0.5% Al, max. 0.5% N, max. 45.0% Fe are also added individually or in combination to the forgeable alloy on a nickel base.
13. A process according to one of claims 1 to 5, characterized in that the slab is produced from a stainless and heat resisting austenitic steel, consisting of max. 0.15% C, max. 20.0% Mn, max. 4.0% Si, max. 35.0% Ni, 10.0 to 30.0% Cr, max. 7.0% Mo, residue iron and the unavoidable impurities.
14. A process according to claim 13, characterized in that max. 1.5% Ti, max. 1.5% Ta and/or Nb, max. 5.0% Cu, max. 1.0% Al, max. 0.5% N, max. 1.0% V, max 0.3% S are also added individually or in combination to the stainless and heat resisting austenitic steel.
15. A process according to one of claims 13 or 14, characterized in that the slab is produced from a stainless and heat resisting austenitic steel containing max. 3.0% Si, 7.0 to 35.0% Ni, max. 0.5% Al, max. 0.035% S.
16. A process according to claim 15, characterized in that the stainless and heat resisting austenitic steel is alloyed with 7.0 to 20.0% Ni, 15.0 to 25.0% Cr, max. 5.0% Mo.
17. A process according to claim 16, characterized in that the delta ferrite content of the stainless and heat resisting austenitic steel used is adjusted to a value below 10%, preferably by controlling the quantities of the alloying elements Ni, N, Mn and/or Cu added to the steel.

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