DE2425624A1 - PROCESS FOR MANUFACTURING HOT-ROLLED STEELS WITH HIGH STRENGTH AND EXTRAORDINARY TOUGHNESS, IN PARTICULAR FOR USE AT MINUS TEMPERATURES - Google Patents

Description

Process for the production of hot rolled steels with high strength and extraordinary toughness, especially for use at sub-zero temperatures

The invention relates to a process for producing a hot-rolled high-strength and low-alloy steel with a yield strength of at least 4-5.7 kg / mm and an extraordinary toughness at temperatures below -17i8 ° C, which is characterized by transition temperatures at ^ 0% shear fracture (1ATT ₅₀ values according to ASTH hormone AJ7O-72a) down to -62 C.

The invention further relates to a steel produced using the inventive method and to a steel produced therefrom Conduit pipe.

The keen need for improved strength and notch toughness in hot rolled high strength and low-alloy steels has made considerable research

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activities in the fields of alloy development as well as the process control set in motion. In particular, extensive natural gas has been discovered there has been considerable interest in Alaska in developing steels that are superior in quality Strength and toughness properties in terms of have the construction of arctic pipelines or pipelines.

The widespread ways of grain refinement and Curing through a suitable choice of composition and process management has become so refined in recent years It has been suggested that hot-rolled steels having conventional polygonal ferrite microstructures have been developed, which in view of to push the combination of strength and toughness close to the limit of what is possible. Although a controlled one Rolling of steel plates at low temperature is currently widely used in the manufacture of high strength, low alloy steels, It can generally be stated that the yield strength of such steels is essentially unaffected by the final rolling temperatures remains, while the notched impact strength, in particular the impact transition temperature, continuously and is noticeably improved to the extent that the final rolling temperature is improved is lowered within the single-phase austenite range. It has been found that finish rolling at too low a temperature, i.e. a temperature below the upper critical transition temperature of the conversion austenite in ferrite brings about an improvement in the yield strength, but with the impact strength is adversely affected, which is a consequence of the presence of "cold-stressed" or non-recrystallized ferrite grains is. It has also been shown that hot rolling occurs in the austenite + ferrite intercritical phase range can lead to undesired recrystallization and undesired grain growth of the ferrite, which is disadvantageous

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both on the yield strength and on the notched impact strength affects.

The invention is based on the development of a new, improved, hot-rolled, high-strength, low-alloy steel with yield strengths of 45.7 to 70.31 kg / mm in connection with at temperatures below -17 »8 ° G at Charpy- V specimens determined transition temperatures at 50% shear ^{failure ("I 1} ATQVq" according to ASTM standard A37O-72a). This steel was developed by combining the conventional hardening and grain refining processes with hardening or hardening based on the dislocations. The invention is based on the object of creating a method of the type mentioned above, with the help of which hot-rolled, high-strength and low-alloy steels can be produced, many are characterized by an extraordinary combination of strength and toughness and are particularly suitable for the construction of arctic pipelines.

This object is achieved according to the invention in that

(a) a steel billet containing 0.03 to 0 carbon, up to 0.04% phosphorus, up to 0.04% sulfur, 0.5 to 2.0% manganese, 0.1 to 0.40% molybdenum, 0.01 to 0.10% niobium, 0 to 0.20% vanadium, the remainder iron and manufacturing-related Impurities is produced,

(b) this billet on one for austenitizing the peing structure and in order to dissolve all carbide and nitride precipitates in the austen.it structure is heated sufficiently above the Ar, transition temperature,

(c) the heated billet at a temperature above the Ar, transition temperature lying temperature so far vxarmge-

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is rolled that no more than 90% of the desired Heat reduction can be achieved,

(d) the partially hot-rolled billet _{is cooled to a temperature below the Ar, transition temperature, but above the Ar x} , transition temperature with partial conversion of the austenitic structure into ferrite,

(e) the partially hot-rolled billet is further hot-rolled at a temperature lying between the Ar 1 and the Ar ^ transition temperature in such a way that a thickness reduction of 10 to HO% is achieved, and that

(f) the hot rolled steel then to ambient temperatures is cooled, in which the steel by the presence of both equiaxed and cold forming perite grains with uniform distribution of carbide and nitride precipitates.

The inventive method is therefore characterized in that the composition of the steel within must be certain content limits and that the rolling of the steel takes place in a controlled manner. This invention Rolling treatment represents a combination of the conventional hardening and grain refinement processes with a solidification or hardening process, which is based on the dislocations. It is of particular importance that the hot rolling process is below the upper critical (Ar, -) temperature is continued, being further provided within the method according to the invention can subject the material to a heat treatment (tempering or tempering) in order to improve the yield point, without having to take on any significant impairment of ductility or toughness.

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A particular advantage of the method according to the invention can be seen in the fact that with its help steels can be produced, which with the help of a "special hot-working technique can be machined in such a way that they have high strengths in the hot-rolled state as well as have good toughness values. Furthermore, these steels can be tempered or tempered in certain cases or cold worked in order to bring about a further increase in the strength properties without this serious reductions in ductility or impact strength can be caused.

A particular advantage of the invention can be seen in the fact that a high-strength and low-alloy steel with contents of Manganese, molybdenum and niobium is created, which is processable in such a way that it has an extraordinary combination of strength and toughness, which is the consequence of the fact that in the steel according to the invention the effects of Hardening, grain refinement and solidification due to have been united by dislocations.

The invention thus leads to a new and improved hot rolled high strength and low alloy steel

a yield strength of 4 to 5.7 to 70.31 kg / mm and an extraordinary toughness at temperatures below - 17> 8 ⁰ C, characterized by FATT Trnsfer-angsteniperaturen% at 50 shearing of down to - 62 ⁰ O according to ASTM standard A 37O-72a (FATT = fracture appearance transition temperatures). As already mentioned, the invention relates to a new and improved low-carbon and low-alloy steel, which has been produced with the help of a special hot-forming or hot-working method in order to combine high strength and toughness, this being achieved through a combination of hardening, grain refinement and dislocation Solidification results.

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The alloy according to the invention has the following composition in% by weight:

Wider More preferred area area carbon 0.03 to 0.15% 0.05 to 0.10% phosphorus 0.04% max. 0.04% max. sulfur 0.04% max. 0.04% max. manganese 0.5 to 2.0% 1.0 to 1.6% molybdenum 0.1 to 0.40% 0.15 to 0.40% niobium 0.01 to 0.10% 0.02. up to 0.05% Vanadium 0 to 0.20% 0.02 to 0.05% rest Iron and manufacture is-dependent

inappropriateness

In addition, the steel can be deoxidized with aluminum or silicon or with both of the mentioned elements and if so if desired, the alloys according to the invention can also contain additional elements such as nickel, copper and / or chromium which can be added as a strengthening agent or to increase corrosion resistance.

As already mentioned, the alloys according to the invention relate to their unique combination of strength and Toughness from a new hot rolling technology that optimizes the following three factors: 1. The solidification effect a fine polygonal ferrite grain size, 2. the precipitation of fine carbides and / or nitrides within the Ferrites and 3. the high decomposition density, which is caused by the excretions are preserved and stabilized. In order to achieve this, a steel of the composition given above must be used in the form of a stick or in other forms

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be hot rolled. As with most of the known working methods, the steel to be hot-rolled is heated to a temperature which is sufficient to dissolve all carbides and nitrides in an austenitic matrix. With the above composition, this requires the steel to be heated to a temperature of more than 1093 ° C. After a homogeneous austenitic fine structure has been achieved, ie by heating to more than 1093 ⁰ C ₄ , the hot rolling of the steel is either at the maximum heating temperature of more than 1093 ⁰ C or at any other sufficiently high above the Ar ^ austenite ferrite -Conversion temperature, which is high enough to keep the carbides and nitrides in solution. The core of the process according to the invention, however, consists in not completing the hot rolling at these temperatures, but rather not undertaking more than about 90% of the desired hot reduction above the Arx transformation temperature. The partially hot-rolled steel is then cooled to a temperature which is below the Ar ^ transformation temperature, but above the Ar ^ transformation temperature, so that some, but not all, of the austenite is converted into ferrite. The partially converted metal is then subjected to final hot rolling in order to achieve a thickness reduction of at least 10% without, however, triggering recrystallization and / or grain growth of the ferrite grains, which means that usually no more than 40% thickness reduction is made. Ideally, this intercritical final deformation should lead to a reduction in thickness within the range of 20 to 30%. Thickness reductions of less than 10% do not result in a uniform stress on the metal over the entire cross-section and consequently the deformed ferrite grains and the hardening effect triggered by them are not uniform over the

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distributed across the entire cross-section. The upper limit of 4-0% Thickness reduction is chosen somewhat arbitrarily, whereby the limit observed in practice depends on the strength of the Rolling device and depends on the toughness of the steel, to withstand deformation without recrystallization. However, experience has shown that there is a maximum limit of around 40% reduction in thickness, both from a practical point of view as well as seems appropriate from a metallurgical point of view.

It should be noted that the solidification caused by the deformed ferrite is a function of the amount in which such ferrite is present in the steel. It is therefore preferable to cool the steel to a temperature of at least about 14 ⁰ C below the Ar ^ new enzymes or critical temperature for the intercritical hot rolling, in order to ensure a sufficient ferrite fraction in the steel. The deeper the steel has been cooled below the Arx transformation or transition temperature, the greater the amount of ferrite formed and the greater the resulting yield strength.

After completion of the intercritical hot rolling between the Ar ^ and Ar ^ transformation or transition temperatures, the steel is cooled to room or ambient temperatures. The fine structure of the steel is characterized by the presence of both equiaxed and "cold-worked" ferrite grains in a ratio which depends on the extent of the austenite-ferrite transformation before the final deformation at temperatures below the Ar, temperature, with a smaller one Share of pearlite and / or bainite is present. The aforementioned austenite-ferrite conversion is understood to mean the conversion of austenite into ferrite. The equiaxed grains naturally come from the transformation of the austenite after the rolling is complete

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and cooling the steel. The cold-worked ferrite grains have an elongated appearance and a high dislocation density, with the carbide and nitride precipitates being uniformly distributed within the two types of ferrite grains. In this hot-rolled state, the steel has a yield strength of at least 4-5 * 7 kg / mm and determined on the Charpy V-notch impact specimen lateral strain transition temperatures (lateral expansion transition Temperatures = LETT) of - 68 to - 101 ⁰ C in Lateral expansion (enlargement of the specimen width on the pressure side of the broken Charpy V specimen opposite the notch) by 381, by according to ASTM standard A37O ~ 72a and by transition temperatures at 50% shear fracture (I ¹ ATT) of - 4-3 to - 68 ⁰ G.

Although 'the unique combination of strength and toughness is in fact primarily due to that described above Hot-rolling technology is due, it should be underlined that the composition of the steel is equally important is to achieve the desired end product. Were other low alloy steel compositions in the rolled out intercritical austenite-flux-ferrite phase range, thus undesirable recrystallization and grain growth of the deformed ferrite grains were indeed obtained, which has a negative effect on both the yield strength and the toughness.

With regard to the alloy composition, it should be noted that the carbide and nitride formers molybdenum and mob are natural represent important components of the known curing process. In addition, the precipitated carbide and nitride particles must are formed during hot rolling and / or during transformation, so that the dislocations and sub-grain boundaries in the deformed ferrite grain structure can be set and stabilized to thereby

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to avoid recrystallization and grain growth in order to maintain the strengthening effect of the dislocations. However, the mere presence of the carbide and nitride formers alone is not sufficient to prevent recrystallization and grain growth. This means that in addition to molybdenum and niobium for the purpose of stabilization, the contents of carbon and manganese and, to a certain extent, the contents of the carbide and nitride formers must be critically controlled in order to control the austenite-to-ferrite transformation temperature Ar, so that this is not too low, so as not to complicate the processing at lower temperatures in the final hot rolling and is not so high as that the deformed ferrite grains recrystallize and grow, although the carbide and nitride precipitations take place. For this purpose the content limitations of steel alloys must be adjusted so that an Ar ^ transition temperature is preferably within the range 732-816 ⁰ C ₁ achieved 782-801 ⁰ C. In quantitative terms, an increase in either the carbon or manganese content leads to a decrease in the Ar ^ transition temperature. Accordingly, a good balance of the two elements is preferred. This means that in the case of an exceptionally low carbon content, manganese contents are preferred which are in the direction of the upper limit of the content. If the case is reversed, SD is proceeded accordingly. Since the carbon content of the alloy is preferably kept low at about 0.08% or slightly lower in order to ensure good weldability and ductility and also to ensure the dissolution of the carbides in the austenite during the initial heating before hot rolling, carbon is used in these held a manganese content preferred which is between 1.0 and 2.0%, but particularly preferably about 1.5%.

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Of course, the carbon content must not be too low, i.e. not below about 0.03% because of carbon is necessary for the formation of the carbide precipitations. It is also known that the dissolved in austenite The amount of niobium has a strong influence on the Ar ^ transformation temperature owns. Since niobium, carbides or carbonitrides are located above the ar? - Transition temperature, the amount of niobium is indeterminate or uncertain, which in the transformation into Solution remains. It is also known that lowering the final temperature and / or increasing the Deformation or the degree of deformation to a slight Raising the Arz conversion temperature lead. As a result should the Ar ^ -TJmwanderung Temperatur preferably below the actual rolling conditions can be determined, although the above content limits and hot rolling conditions sufficient to practice the advantages of the invention for any given alloy composition and to ensure optimal results under all given hot rolling conditions. It should also be noted that that high contents of the three components manganese, molybdenum and niobium and especially high contents Manganese should be avoided to ensure conversion to polygonal ferrite instead of acicular ferrite, since the Ar ^ temperature of the acicular ferrite

ο
is about 677 C, which temperature is below the target range mentioned above. In order to achieve both excellent strength and toughness in the steel of the invention, the use of vanadium should be avoided. In cases where the toughness is not the primary concern, up to 0.2% vanadium can be added to the steel

2 be to the yield point up to 7 * 03 kg / mm with one Add 0.08% vanadium or up to 10.55 kg / mm for one

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Increase the addition of 0.20% vanadium. However, there is It should be noted that although vanadium improves the yield strength, it has an adverse effect on the toughness transition temperature which is related to the well-known excretion effects.

Another unexpected feature of the steel according to the invention can be seen in the fact that the tempering of the steel following hot rolling leads in some cases to an increase in the yield strength of 7.03 kg / min, the toughness properties not at all or only slightly impaired will. Normally, those skilled in the art will assume that the relatively high Ar ^ transition temperature characteristic of these steels results in full hardening of the steel in the hot rolled condition and that no second or secondary hardening can be expected. On the other hand, secondary hardening of such magnitude in other steels is usually accompanied by an increase (deterioration) of 28 to 39 ^° G in the toughness transition temperature. However, no such thing is observed with the steel according to the invention. The response of the steels to tempering or tempering can be very rapid, but the overaging is so slow that a wide variety of tempering or tempering times and temperatures ranging from one minute to two hours and temperatures within a range of about 593 to 677 ⁰ C can be applied in order to achieve uniform mechanical properties without the risk of overaging. Although this process has not yet been fully clarified, it is assumed that this secondary hardening does not result from the hardening, but from the reduction of the remaining micro-stresses associated with it.

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As mentioned above, this unusual tempering or annealing response occurs only in a few cases. In particular it can only be realized or come to light in those alloys in which the contents of manganese and / or Molybdenum are more in the direction of the specified upper content limits., Although these content limits (in the range the claimed upper content limits) not clearly defined these tempering or tempering improvements will not be effective if the alloys are less as Ί contain 20% manganese and less than 0.2% molybdenum, whereas they are effective when in the alloy Manganese content of more than 1.30% and / or a molybdenum content of more than 0.25% is included. In the area in between, further solidification or hardening by means of a tempering or tempering treatment may occur, depending on the total content of manganese and molybdenum.

Although these steels with relatively low contents of manganese and molybdenum have essentially no tendency to solidify or harden during tempering or tempering, these steels are somewhat stronger than the steels with a higher manganese and / or molybdenum content in the hot-rolled State. This peculiarity makes these steels with low manganese and molybdenum contents more suitable for applications, at which the additional costs or burdens of tempering or tempering cannot be tolerated.

In view of the above discussions, a preferred composition of the steel according to the invention contains to be used in the hot-rolled condition, 0.05 to 0.1% carbon, 1.0 to 1.3% manganese, 0.15 to 0.25% Molybdenum and 0.02 to 0.05% niobium. If this composition is hot rolled at a temperature higher than 816 C, cooled to about 760 C and then again at this

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intercritical temperature hot-rolled to achieve a thickness reduction of 20 to 30% , so stretching

Limits of about 52.7 kg / mm in connection with excellent notch toughness, ie with so-called FATT values of about -62 ⁰ G can be achieved. On the other hand, an optimal composition of the steel according to the invention, which can be strengthened by tempering or tempering, will differ from the above composition in that 1.3 to 1.6% manganese and 0.20 to 0.40% molybdenum are required. If this latter composition is hot-rolled at temperatures of more than 816 C, cooled to about 760 C and then hot-rolled again at this intercritical temperature to a 20 to 30% strength

To cause a reduction in thickness, so can yield strengths

2
from about 49.2 kg / mm in the hot rolled condition and from about

56.2 kg / mm in the tempered or tempered condition can be achieved in any case, which with excellent notch toughness]
are.

Toughness, that is connected to FATT Verten of about -62 ⁰ C

The combination of low carbon contents and medium manganese contents given in the steels according to the invention ensures good weldability. Although one might assume that the welding would turn out to be very unfavorable affect the base plate in the area of the heat-affected zone (HAZ) and that during intercritical rolling Caused mechanical properties could affect, tests have shown that this is not the case is. Tests have shown that the strength and toughness properties of the heat-treated Zone (HAZ) were definitely comparable with those properties that were determined outside the named zone became. Tensile tests were carried out in the transverse direction over the weld on line pipes with large diameters made with the help of the submerged arc welding process

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were made from the steel of the invention. To determine the toughness, impact tests in the transverse direction were carried out with the Charpy V sample where the notch was in the HAZ area.

Another unexpected and advantageous property of the steel according to the invention can be obtained in that the steel is processed into conduit pipes using the conventional "U and 0 process". If steel plates or sheets are used which, in terms of their composition and their rolling treatment, correspond to those that are customary for types of steel intended for pipelines, the yield strength of the pipeline, determined after forming and welding, is usually much lower than that of the original plate or the Starting sheet, which is a consequence of the well-known Bauschinger effect. As a result, such conduit is cold expanded (increasing the diameter) by up to about 2% in order to stress harden the steel, thereby increasing the yield strength to a value approximately equal to that of the original plate. However, even in such an expanded state, conventional conduit pipes often exhibit yield strengths below that of the parent plate.

Although cold expansion is generally aimed at To achieve suitable dimensional tolerances (diameter and roundness), the amount of cold expansion must not be too large because such a plastic stress is at the expense of the overall ductility of the steel. Also do the unreliable fluctuations in the yield strength in known steels for line pipes, as mentioned above, very much difficult, if not possibly impossible, to estimate the actual yield strength of the line pipe,

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if only the strength of the original plate is known. As a result, plates, which lead to pipes with unacceptable Yield limits could not always be sorted out before the production and testing of the line. This can of course result in a rather costly procedure.

Surprisingly, it has been found that steel plates according to the invention, using the U and 0 method have been processed into lines, in the non-expanded State have an improved yield strength and that they still have increased strength properties in the expanded state exhibit. Thus, the strength of the finished pipeline or the finished conduit is substantially the same or even considerably greater than the strength of the original plate. With those steels where the largest Increases in the yield strength are observed, those rolled steels, which the higher contents of manganese and / or molybdenum, i.e. those that have a hardening or solidifying effect by tempering or tempering showed. The increase in the yield strength achieved through the formation of the tube is closely related to the increase in the yield strength together, which has been achieved by tempering or tempering. It follows that, consequently, two solidification processes appear to be closely related and it is believed that the two processes are a consequence of the degradation of residual stresses in the plates in the hot-rolled state are.

As a result, show panels with compositions that normally after annealing, there would be no increase in the yield strength and plates which had been tempered or annealed are, after processing into pipes with the help of the U and O process and after expansion, yield strengths that

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have remained constant or have only increased slightly. On the other hand, those are steel plates with compositions responsive to annealing treatment using the U and O method to conduit pipes processed and expanded, they show an improved or increased yield strength, eliminating any need in the absence of this, the steel comes before or after the pipe production tempering or tempering.

The invention is explained in more detail below with the aid of examples.

In a series of tests, a number of steels in the form of 45.35 kg batches were inductively melted and cast into billets. These billets were heated to around 1232 to 1260 ° G and then rolled out in fourteen heat-reducing passes to 12.7 ™ & thick plates, the first rolling pass at around 1204 · ⁰ C and the last rolling pass either at 838 or 760 ⁰ C was carried out, while the remaining rolling passes were distributed more or less uniformly over the temperature ranges from 1204 to 838 ⁰ C, or from 1204 to 760 ^0C. A hole was drilled in each billet and a thermocouple (thermocouple) was inserted into this hole on each billet in order to maintain the stick temperature. The beginning of the transformation from austenite to ferrite could be determined by the visible change in the cooling rate (breakpoints of the cooling curve), which was caused by the heat of transformation.

Table 1 shows the chemical compositions and Table 2 shows the mechanical properties of these steels. Some of the steels got their final rolling at 838 C, i.e. above their upper critical transformation temperature, while the other steels got their final rolling at 760 ° C received what is below for all these steels

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the upper critical temperature. The fine structure of these steels showed the characteristic vein-like and deformed ferrite grains, the volume fraction of this deformed ferrite fluctuating with the alloy composition in a way that was associated with the influences on the change in the upper critical transformation temperature, those of carbon, manganese, molybdenum, niobium and vanadium be exercised. All of these finish-rolled at 760 ⁰ C steel plates or sheets received a 11.5 "j5 to 31% strength with thickness reduction lies below its upper critical temperature transition temperature that varied from about 774- to 816 ⁰ C.

Table 3 below illustrates the increase in the yield strength which can be achieved by using steel plates from steel according to the invention to conduit using the conventional U and O method as well processed with the help of an expansion. Steels 1 and 2 are conventional steels for piping while steels 3 to 12 represent steels according to the invention. The steels became conduit pipes with diameters of 76.2; ^ »^ Or 106.7 cm 0 processed.

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Table 1

Chemical composition (weight-5 Steel * C Mn Mo Fb

0.067 1.22 0.18 0.035 - E. 0.064 1.25 0.14 0.028 - 0.069 1.25 0.31 0.037 - G 0.075 1.14 0.27 0.034 0.071 H 0.072 1.13 0.18 0.035 0.085 I. 0.076 1.10 0.14 0.030 0.071 J 0.070 1.10 0.32 0.035 0.081 K 0.079 1.14 0.27 0.034 * 0.005 L. 0.075 1.38 0.25 0.034 0.091 M. 0.079 1.43 0.25 0.038 0.089 N 0.087 0.91 0.37 0.035 0.084 0 0.080 1.23 0.32 0.033 0.078 P. o:, O69 1.40 0.34 0.028 0.091 Q 0.080 1.43 0.26 <^ O, O1

* All steels were killed and contained with Si-Al

about 0.01% P; 0.011 to 0.022% S and about 0.004 to 0.007% N.

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Table 2

Mechanical properties of the hot rolled

as well as the still tempered plates with a thickness of 12.7 mm

Steel end temp. Condition 0.2% - tensile strength - transitional

⁰ C ** stretching temp. At 50%

Ν Shear fracture
(Charpy-V sample)

H 3

+ T

838
838 MR
MR 760
760 MR
MR 838
838 MR
MR 760
760 MR
MR 838
838 MR
MR OO
CNCN MR
MR 838
838 MR
MR 760
760 MR
MR 760
760 MR
MR 760
760 MR
MR 760
760 MR
MR 760
760 MR
MR 760
760 MR
MR 760
760 MR
MR

+ T

43.95
44.15 50 ', 83 -57
-68 49.22
50.41 55.19
54.70 - bl 41.55
46.75 53.79
52.73 - 65
- 65 47.60
53.65 58.50
58.71 - 60 46.82
45.84 52.80
52.64 - 46
- 43 53.15
51.75 59.83
57.58 - 43 45.91
47.53 53.72
54.21 - 54
- 60 54.84
57.09 65.17
62.51 - 46 47.46
52.94 59.65
57.09 - 62 49.00
59.06 63.77
64.47 - 46 53.29
61.38 64.47
67.21 - 29 49.85
62.36 62.22
66.09 *
- 46 45.35
62.79 60.18
64.47 - 62
- 43 42.54
50.48 58.28
56.74 - 49

+ τ

+ T

+ T

+ T

+ α? + τ

** HR denotes the hot-rolled condition, while HR + T denotes the hot-rolled and heat-treated (1 hour at 649 C) condition.

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Plate 3

In the transverse tensile test on plates and pipes made of line pipe steels properties determined *

stole 8th Chemical composition + Mn ο / Λ Nb 0 V plates 0.29 0.033 - 13.09 Plate fixing ) Train- 65.30 0.31 0.06 - 12.7 55.96 59.27 .Strengths . Zugf. - Strengths . Zugf. I. N) 1 1.34 • - / ο J 0.035 0 , 06 strength 0.16 0.032 - 13.09 keiten ^ firm 65.30 0.31 0.06 - 20.32 56.46 60.82 of the unknown 61.87 - of the widened 62.86 ro
68.55 f 1.34 0.035 0 , 06 (mm) 0.17 0.044 - 13.09 (k'g / mm; 62.22 59.90 0.31 0.06 - 20.32 53.01 57.09 ten pipe 62.93 60.18 (-1.5%) pipe it 63.21 69.39 N) 2 ++ 9 1.36 Mon 0 , 08 0.17 0.054 - 13.09 Stretch 62.15 63.07 0.31 0.06 25.4 52.03 58.57 (kg / mm ² ) 61.66 66.44 (kg / mm ² ) 64.12 67.14 cn 10 C. 1.36 - , 08 0.18 0.05 - 7.92 border 61.45 60.25 Stretch 61-, 52 Stretch 63.84 65.11 624 11 0.14 —— 11.73 0.18 0.05 - 12.7 50.06 61.73 59.83 47.81 50.97 64.61 3 0.14 1.42 __ 11.73 0.19 0.04 - 7.92 52.38 Walzz. Condition 61.59 48.02 _ 48.58 65.04 4th 12th 0.14 1.41 - 10.77 0.19 0.04 - 12.7 48.02 50.27 57.02 42.04 - 51.75 64.69 5 0.14 1.15 10.77 0.19 0.04 - 15.87 49.29 44.58 53.72 45.91 - 50.41 59.55 6th 1.15 Mn-Mo-Fb plates in 0.19 0.05 - 17.46 52.87 56.39 - 55.75 σ
CD 7th 0.08 1.29 0.20 0.05 - 22.22 56.60 54.91 _ - 58.85 61.10 OO 0.08 1-, 29 0.28 0.06 - 25.4 52.17 60.11 - - 56.25 58.57 cn 0.08 1.24 52.73 Mn-Mo-Fb plates after 1.5 hours - - 58.07 66.02 0.07 1.24 50.34 - - 58.92 *** 0.08 1.24 45.63 - 54.21 66.23 ο
00 0.08 1.24 45.84 - 59.41 52.73 63.91 O 0.07 1.11 47.74 - 57.09 54.84 62.43 CD 0.07 1.30 45.98 - 66.37 47.95 64.61 0.07 47.81 - Heat treatment at 45.21 0.10 1.24 45.07 T- 49.22 0.10 1.24 43.38 - 48.23 0.13 1.24 57.51 53.08 56.67 1.24 53.22 593 ⁰ C 0.06 57.09 0.06 57.02 0.06 52.24 0.06 58.01

Legend for panel 3 '

* Determined on strip test specimens for the tensile test
+ All steels were killed with Si-Al

++ Steel 2 also contained $ 0.18 copper, 0.18% chromium and 0.08% nickel.

409851/0806

Claims (16)

Claims 1. Process for the production of a hot-rolled high-strength and low-alloy steel with a yield strength of at least 45.7 kg / mm and an extraordinary toughness at temperatures below - 17 »8 ⁰ C, which is characterized by transition temperatures at 50% shear failure (PATT-cQ- Values according to ASTM standard A 370-72a) down to -62 C, characterized in that (a) a steel billet containing 0.03 to 0.15% carbon, up to 0.04% phosphorus, up to 0.04% sulfur, 0.5 to 2.0% manganese,
0.1 to 0.4% molybdenum, 0.01 to 0.1% niobium,
O _; up to 0.20% vanadium, the remainder iron and production-related impurities,
will be produced, (b) this billet is heated to a temperature sufficiently above the Ar j transition temperature to austenitize the fine structure and to dissolve all carbide and nitride precipitates in the austenite structure, (c) the heated billet at a temperature above the Ar, transition temperature lying temperature is hot rolled so far that not more than 90% of the desired hot reduction be achieved, 409851/0806 (d) the partially hot rolled billet onto a below the Arz transition temperature, but above the ATyi transition temperature lying below partial Transformation of the austenitic structure into ferrite is cooled, (e) the partially hot-rolled billet at a temperature between the Ar3 and Ar ^ transition temperatures is further hot-rolled in such a way that a thickness reduction of 10 to 40% is achieved, and that (f) the hot rolled steel then to ambient temperatures is cooled, in which the steel is deformed by the presence of both equiaxed and cold Ferrite grains with a uniform distribution of carbide and nitride precipitates. 2. The method according to claim 1, characterized in that the steel billet produced is vanadium-free and 0.05 to 0.1% carbon up to 0.04% phosphorus, up to 0.04% sulfur, 1.3 to 1.6% manganese, 0.20 to 0.40% molybdenum, 0.02 to 0.05% niobium, the remainder iron and production-related impurities, contains. 3. The method according to claim 1, characterized in that g e k e η η - · draws that the manufactured steel billet is vanadium free and 409851/0806 242562Λ 0.05 to 0.10% carbon, up to 0.04% phosphorus, up to 0.04% sulfur, 1.0 to 1.3% manganese, 0.15 to 0.25% molybdenum, 0.02 to 0.05% niobium, The remainder is iron and production-related impurities contains. 4. The method according to any one of claims 1 to 3 »thereby characterized in that the steel billet produced still has small additions to at least one of the elements Contains nickel, copper and chromium, which act as hardening or strengthening elements and to provide corrosion resistance have been added. 5. The method according to any one of claims 1 to 4, characterized in that the steel billet before hot rolling to a temperature of more than 1093 0 is heated to ensure the dissolution of all carbide and nitride precipitates and that then the process step (c) is carried out, the hot rolling at a temperature between 816 and said temperature of more than 1093 ° 0. 6.Verfahren according to any one of claims 1 to 5 »thereby characterized in that the hot rolling between the Ar + and the Ar ^ transition temperature according to process step (e) takes place in such a way that a reduction in thickness of 20 to 30% is achieved. 7 · The method according to any one of claims 1 to 6, characterized gekenn ζ ei chnet that the partially hot-rolled steel in process step (d) to at least one 409851/0806 is cooled by 14 ⁰ C below the Ar, transition temperature lying temperature. 8. The method according to any one of claims 1 to 6, characterized in that the partially hot-rolled Steel in process step (d) to a temperature just above the Ar ,, transition temperature is cooled. 9 · The method according to claim 2, characterized in that the finish-rolled in the heat Steel tempered or tempered at a temperature between 593 and 677 G for a period of 1 to 120 minutes becomes to the yield strength of the hot rolled steel by about 7 kg / mm with a slight impairment of the impact properties of the steel. 10. The method according to any one of claims 1 to 9i characterized in that the hot-rolled steel after performing process steps (a) to (e) Is cooled to ambient temperatures, with multiple marches the steel through a yield point of at least 45.70 kg / mm, and that the hot rolled steel by using the known U and O method is processed into conduit, whereupon the conduit ο has a yield point of at least 45.70 kg / mm. 11. The method according to claim 10, characterized in that the steel billet 1.3 to 1.6% Manganese and 0.20 to 0.40% molybdenum and that the Leitangsrohr is through a yield point of at least 49.22 kg / mm. 409851/0806 12. JF er ritisch er, hot-rolled, high-strength and low-alloy steel, produced by the method according to claim 1, with a yield strength of at least 45.7 kg / mm and an extraordinary toughness at temperatures below -17.8 ⁰ G, which characterized by FATT transition temperatures at 50% shear failure down to -62 C according to ASTM standard A 37O-72a, consisting of 0.03 to 0.15% carbon, up to 0.04% phosphorus, up to 0.04% sulfur, 0.05 to 2.0% manganese, 0.1 to 0.4% molybdenum, 0.01 to 0.10% niobium, 0 to 0.20% vanadium, Remainder iron and manufacturing-related impurities, the steel subjected to both equiaxed and cold stresses Has a fine structure containing polygonal ferrite grains in which carbide and nitride precipitations are uniform are distributed "and where these precipitates are used to harden or strengthen the steel by hardening effects, grain refinement effects and fixing and stabilizing the cold-stressed ferrite grains by creating a high dislocation density in the structure and the resulting hardening or solidification effects are preserved. 13. Ferritic, hot-rolled, high-strength and low-alloy vanadium-free steel according to claim 12, consisting the end 0.05 to 0.10% carbon, up to 0.04% phosphorus, 409851/0806 2Λ25624 up to 0.04% sulfur, 1.3 to 1.6% manganese, 0.20 to 0.40% molybdenum, 0.02 to 0.05% niobium, The remainder is iron and production-related impurities. 14. Ferritic, hot-rolled, high-strength and low-alloy vanadium-free steel according to claim 12, consisting the end 0.05 to 0.10% carbon, up to 0.04% phosphorus, up to 0.04% sulfur, 1.0 to 1.3% manganese, 0.15 to 0.25% molybdenum, 0.02 to 0.05% niobium, The remainder is iron and production-related impurities. 15 · High-strength and low-alloy steel conduit pipe, produced according to the method according to claim 10, with ο a yield point of at least 45.7 kg / mm and one Extraordinary toughness at temperatures below - 17.8 C, as a result of FATT transition temperatures at 50% shear failure down to -62 C according to ASTM-ITorm A. 370-72a, consisting of 0.03 to 0.15% carbon, up to 0.04% phosphorus, up to 0.04% sulfur, 0.5 to 2.0% manganese, 0.1 to 0.40% molybdenum, 409851/0806 0.01 to 0.10% niobium, 0 to 0.20% vanadium, the remainder iron and production-related impurities, the steel subjected to both equiaxed and cold stresses Fine structure containing polygonal ferrite grains has, in which carbide and nitride precipitates are evenly distributed, and where the cold stressed Ferrite grains have a high dislocation density, and are determined by the carbide and nitride precipitations is stabilized. 16. Line pipe according to claim 15? marked by a manganese content of 1.3 to 1.6% and a molybdenum content of 0.20 to 0.40%, whereby the Line pipe through a yield strength of at least 4-9.22 kg / mm excels. 409851/0806