DE2323738A1 - PROCESS FOR MANUFACTURING HIGH STRENGTH, NOTCHED STEEL - Google Patents

Description

Patent attorney Dipl.-Phys. Gerhard Liedl 8 Munich 22 Steinsdorfstr. 21-22 Tel. 29 84 62

cone QmJALlL ²³²

The Algoma Steel Corporation, Limited Sault Ste. Marie, Ontario

Process for the production of high-strength, notch-resistant steel

The present invention relates to steel. In particular concerns the present invention steel of improved yield strength and

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Notch toughness at low temperatures, in particular below -17.8 ⁰ C, and a process for producing this steel.

There is a continuing and increasing need for steel of improved strength and notch toughness, and with the development of arctic regions such as arctic gas and oil fields, the demand for steel with high notch toughness at lower temperatures and yield strength has increased. This is true
for example, the production of pipelines.

In the manufacture of such steels it has hitherto been customary to subject soft steels modified with a suitable grain refiner, such as niobium and / or vanadium, to a content of approximately 0.05% by weight of the steel, to a controlled rolling process. The conventionally controlled rolling processes include the heating of the ingot or the slab on one
Temperature of more than 1232 ° C and the rolling of the ingot or the slab according to a rolling program that includes delays in the pass sequence, so that the substantial reduction in the
Thickness takes place below a temperature in the range from 927 to 95U ° C, with a temperature of approximately 788 ⁰ C the
Finishing is carried out. Typically, the delays are in the temperature range from 927 ° to 1O3 8 ° C
introduced. They are necessary to ensure a sufficient reduction at low temperature to ensure a fine grain

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to create structure. The degree of reduction required below 8H3 ° C brings difficulties in Making flat panels with it. In addition, the properties that are achieved with this steel are less consistently as desirable, which can be attributed to the need for precise temperature and rolling control is. For this reason it is often necessary to normalize the panels produced in this way, in particular when the thickness of the rolled plates is 12.7 mm or more. This normalization procedure brings with regard to Costs and time additional expenses. Furthermore, the low-temperature notch toughness and the strength are low alloyed soft iron plates which have been manufactured by being rolled in a conventional controlled manner, with or without normalization were relatively low and a substantial improvement is desirable.

The present invention results in an improved steel with significantly higher notch toughness at lower temperatures, i.e. below -17.8 ° C, which makes it highly suitable for constructions makes it suitable that are subject to low temperatures, i.e. in the Arctic, for example in pipelines and power transmission masts, the steels being made by a simple and more efficient rolling process than the conventional one controlled rolling processes can be produced.

309847/0924

It has been found that an improved steel plate can be made by rolling an ingot or slab of low carbon, high niobium steel according to a known rolling technique, provided that the steel is continuously in the temperature range of 92 7 to 10 38 ° C and is preferably rolled at 927 to 1066 ^{° C.}

The present invention also relates to a method of manufacture a high-strength steel with improved notch toughness at temperatures below -17.8 ° C, the process is characterized in that an ingot or a slab of this steel with a chemical composition that further is described below, and at a temperature of at least 1149 ° C, preferably at least 1232 ° C, a diminishing Is subjected to rolling, the rolling being carried out continuously through the temperature range of 103 8 to 927 ° C.

The present invention also provides a fully killed steel with a high yield strength and high notch toughness below -17.8 ° C available, which contains up to 0.20% by weight carbon, at least 0.75% manganese and at least 0.015% by weight niobium, said steel having a substantially uniform fine-grained, substantially ferritic grain structure with an average Has grain size finer than 9.0, as determined by ASTM Test No. E 112 is determined.

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The present invention further provides, according to a preferred embodiment, a fully killed steel is available, which has a high yield strength and high notch toughness below -17.8 ⁰ C and substantially according wt.% From 0.02 to 0.12% carbon , 0.09 to 0.18% niobium, 1.0 to 2.0% manganese, 0 to 0.5% molybdenum, not more than 0.025% phosphorus, not more than 0.035% sulfur, 0 to 0.6% copper , 0 to 1.0% nickel, 0 to 1% chromium, 0 to 0.2% zirconium, 0 to 0.06% rare earth metal and the plague of iron and incidental impurities, this steel being a substantially uniform fine-grained, im has a substantial ferritic grain structure with an average grain size finer than 9, as it is according to ASTM Test No. E 112 is determined ■

Carbon is present in the steel in an amount up to about 0.20%, and preferably from about 0.02% to 0.12% by weight. available. At amounts in excess of 0.12% by weight, the steel tends to maintain its high notch toughness through the formation of substantial Losing quantities of austenite grains in the structure of the steel. It was also found that the notch toughness of steel is also largely reduced, as is its weldability, which is highly desirable in the case of steel plates is. It has also been found that the lower carbon content increases the Ag transformation temperature and so does the Crystallization of the austenite subsequent to the final

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Rolling of steel diminished. The lower the carbon content of the steel, the better the notch toughness. The manganese content of the steel is usually with Provided the help of a ferromangan additive that Contains carbon as an impurity, so that there is practically a lower limit for the carbon present in the steel lies. Preferably carbon is in an amount of 0.04 to 0.10 percent, and more preferably in an amount of 0.06 to 0.07 wt% present. It has been found that the fine-grain structure in steel, which is primarily due to the Niobium content is established, can still be achieved with steels that have a carbon content of up to about 0.20%, despite the formation of austenite grains in the structure. This steel still has reasonably high impact strength and percentage shear, especially if the carbon content is below 0.16%. However, at such a high carbon content To maintain weldability in steel, the niobium content must be reduced. A high carbon content in steel, which lowers the impact strength and the percentage shearing in the steel and a lower niobium content, which also lowers the impact strength and the percentage shear in the steel is therefore not preferred.

Niobium is preferably present in steel in an amount from 0.09 to

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^, Ϊ́β% and still b ivor'zuf> tfel · present in the range from 0/12 to 0.15% by weight of the steel. It is believed that the net result of the lower Koh.!. Ens ^; cf T;> uha "its and the higher than usual niobium content be. ^ - ihi to supply a volume fraction of niobium carbide and niobium carbon nitride precipitates in the steel, which is f. to hinder the austenite grain growth at higher temperatures assumed that the combination of low carbon content and high niobium content L- _n steel ei α greater potential for the precipitation of niobium carbon nitride and niobium carbide in the 'temperature range from 927 ° C to 103S ⁰ C, since the solubility limit of l'iob in the increases austenitic steel with eggs decrease of the carbon content, ie a larger Volumbruchteil the · precipitation of niobium carbide and niobium carbon nitride is present at a & eg "beni-.ii temperature, the carbon content of the steel woün reduced and the niobium content is increased. It has been _v found that through the continuous reduction of the steel in the temperature range from 927 to 1O3 8 ° C according to a rolling program, which is designed, for example, that a 50% e reduction of the thickness of the grinding is carried out below about 982 ° C., a very fine, essentially uniform grain size is achieved and maintained. The rolling reduction takes place in the temperature range from 927 to 1O3 8 ° C. With a niobium content of less than 0 _} 09% by weight, the degree of grain refinement that can be achieved in the austenite is

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. reduced. However, it is possible to achieve the fine grain structural steel by the rolling technique of the present invention with significantly less than 0.09 % niobium with consequent high impact strength and high ¹ percent shear as required. In particular, it has been found that-the Miobgebalt.% May be as low as 0.015 percent and still the fine grain structure with high percentage * shearing and high impact strength is achieved Suitably, the niobium content of at least 0 _s mud 04% in more suitably wide · " at least 0.06 new,%. It has been found that the impact strength and percent shear increase with the percentage of niobium, and it is believed that above about 0.06% dAs niobium, niobium acts, inter alia, to increase tensile strength.

The manganese is present in aera steel to give it strength, including both yield strength and tensile strength. In particular, manganese is believed to be Gives strength in the ferrite grains in the steel. The strength of the steel is also determined to an extent by its thickness of the steel plate and the amount of manganese present in the steel. The thicker the steel, the lower it is generally the yield strength and tensile strength for a given chemical composition. By increasing the manganese content of the steel, the strength of the steel becomes as well

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reinforced. £ s has been found i-Λ general that, with steel plates which dHnn-ii "old 10.7 mm, a high strength steel is obtained DER e_.ne yield strength of more than about 4200 kg / cm 'has, WOI ^ ei de * ·! '^ n -.- an ^ ehdlt should preferably be more than about 1% and, in the case of thick steel, at least 1 to 2% by weight. The content of the steel can, however, be as low as about 0.5%, and the advantages of the present invention can still be achieved. A manganese content below 0.76% produces a steel which tends to have a low percentage shear. The maximum manganese content is determined to a large extent by the carbon equivalent required in the steel for weldability. In the case of thin steel plates, the manganese content of the steel should preferably be in the range from 1.30 to 1.70% by weight and more preferably from 1.30 to 1.5% by weight. For steels that are thicker than 10.7 mm, the manganese content is in the range from 1.6 to 2% by weight. Where it is desired to increase tensile strength, molybdenum will also be present in the steel, suitably in an amount of no more than about 0.5% by weight. It has been found that molybdenum increases the tensile strength, but lowers the yield strength of the steel rolled in this way. The presence of molybdenum is particularly useful on thicker plates to increase tensile strength.

Sulfur is present as an impurity in steels and

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lowers the bending impact strength of the steel and combines in particular with the manganese present in the steel Formation of manganese sulphide strings that extend lengthways extend through the steel and cause the directivity of the impact properties. The bending impact strength is determined by ' Increased addition of rare earth metals, which are able to react with sulfur in the molten steel. The rare earth metals also react with the oxygen in the steel and the steel is' appropriately controlled by the addition of tranquilizers, such as aluminum, or by adding larger amounts of the rare earth than they are needed for the reaction with the sulfur necessary, soothes. The rare earth can therefore be used both as a sedative and as a binding agent be used for sulfur. Desirably the rare earth metals are present in amounts up to 0.06 percent by weight of the steel. Zircon can be used with contents up to 0.2% and preferably up to 0.10% by weight instead of the rare earth metals Sulphide modifiers and / or sedatives can be used. Aluminum is the most expedient sedative and is present in an amount sufficient to calm the steel. If too little aluminum is added, the Steel doesn't calm down. If there is too much aluminum, surface problems can occur in the killed steel. That Aluminum is useful as a depressant in steel in an amount of from 0.02 to 0.10 weight percent, and preferably from 0.03 to 0.06 wt. * Available. The sulfur content of the steel

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is kept below 0.035% by weight and in a desirable Way below 0.020 wt.%,

Phosphorus is also an impurity in steel and tends to make the steel brittle. The phosphorus content in the steel is maintained below 0.025 wt% and desirably below about 0.015 wt%.

The steel can also contain conventional strengthening additives such as copper, nickel and chromium or mixtures thereof contain up to 1% of each. Copper is preferably in an amount of from 0.2 to 0.6 weight percent, and preferably up to 0.4% by weight present. Another such means which It should be mentioned is vanadium, which can be present in an amount up to about 0.12% by weight.

The rolling of the steel from bars or slabs into plates can be carried out on a roughing mill and on a post-mill The transport between the rolling mills is carried out at a temperature outside the range of 1038 to 927 ° C will. On the other hand, the rolling can also be carried out with the aid of a single rolling mill. It is A critical feature of the present invention that the steel is continuous in the temperature range of about 1038 to about 927 ° C and preferably from about 1066 ° C to about 927 ° C. It has been found that it goes even further

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it is preferable to roll continuously until the steel temperature has reached "over 99 ° C". It is further stated in the original disclosure ₄ that there should be no unnecessary delay in the continuous rolling and that the transport between the pre-rolling mill and the downstream mill should take place within the above-mentioned temperature interval. However, it should be noted that, provided that the transport between the plants is fast, ie less than 20 seconds, the transport ^{can take place at temperatures below about 1010 0} C without the fine-grain structure, the impact strength and the percentage shearing of the produced steel can be significantly reduced.

When the steel is rolled, the initial temperature of the barrers at least 11H9 ° C, preferably at least 1232 ° C to ensure that niobium is in solution in the austenitic steel is held. This allows the niobium to be used as niobium carbide and / or niobium carbon nitride particles at a temperature in the range from 927 to 1038 ° C when the continuous rolling of the steel the niobium carbide and / or niobium carbon nitride fails and so refines the austenitic cone structure. Accordingly, it is a critical feature of the present invention that the slab be continuous in the temperature range from 1038 to 927 ° C and preferably at 1066 to 927 ° C without

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undue delay is rolled between the stitches, desirably, there is at least a 50% thickness reduction of the steel plate at a temperature below 982 ⁰ C. It is believed that during the rolling of a conventional steel according to the known controlled rolling method, a fine austenite grain size above 927 ° C cannot be established and maintained. The rolling of conventional steel in the temperature range from 927 ° C down to 788 ° C serves to develop a fine grain structure in the rolled steel plate. In contrast, the rolling reduction process of the present invention, in combination with the low carbon content of the steel, largely reduces the formation of austenite during cooling of the steel and the high niobium content of the steelB allows fine grain particles of niobium carbide and / or niobium carbon nitride (the nitrogen is as natural impurity present in the steel). Continuous rolling of the steel in the range from 927 to 1038 ° C. and preferably from 927 to 1066 ° C. ensures that niobium carbide and / or niobium carbon nitride particles precipitate and a largely uniformly fine, essentially ferritic grain steel with improved notch toughness is generated at low temperatures below -17.8 ° and also below -15.6 °.

DLe finishing temperature of the steel in the process of present invention is usually much higher, i.

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in the range of 816 to 871 ° C, indicating the production of tabular Steel sheet makes it easier than the known controlled rolling process possible. However, it is in the claimed The scope of the present invention to continue rolling at lower temperatures than the controlled rolling process, to further improve the toughness and strength properties of the steel sheet. It has been found that the after The steel produced according to the invention has a very fine grain structure that is largely uniform in a average grain size finer than 9 and preferably at least 9.5 and more, at least 10 (determined according to ASTM Test No. E 112). It has been found that this is uniform Fine grain size in thinly rolled plate steel with a thickness of 3.175 mm and in thicker rolled plate steel in Range from 12.7 mm to about 28.575 mm is present. It is believed that it is this ferritic, uniform, fine-grain structure in steel, which is particularly important for its high notch toughness, especially at low temperatures in the range of -17.8 contributes down to -45.6 ° C. It is from the examples below it can be seen that at temperatures below -17.8 ° C. the steel has longitudinal Charpy slack values of at least 8.26 mkg, preferably at least 11.02 mkg, more preferably at least 26.2 mkg and very particularly preferably at least 27.6 mkg with a percentage shear of at least 90% and transverse Charpy impact values of at least 8.26 mkg at -17.8 ° C, to-

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has at least 6.9 mkg at -2 8.9 ° C and at least 5.53 mkg at -45.6 ⁰ C.

The present invention is further developed by the following examples in conjunction with the accompanying drawings , with Figures 1, 2, 3 and 4 being photomicrographs showing the grain structure of steels produced according to processes according to the invention and by other rolling processes.

example 1

Three panels were made from one batch of electric arc furnace having the following composition.

Element quantity

carbon 309847 / 092- 0.07% 4th manganese 1.25% sulfur 0.021% phosphorus 0.010% silicon 0.02% niobium 0.14% Aluminum. 0.060% Iron and impurities worked rest

Three slabs measuring 21.26 2.76 χ 33.86 cm were in a 2 HI roughing mill and then in a 4 HI post mill to a final (as rolled) plate size of 259.08 x 1.588 χ 1135.9 cm according to a program that is shown in Table 1 below.

Of these plates, plate 544 had that continuous was rolled in the temperature range from 816 to 1116 ° C, the best combination of properties, 11.46 mkg impact energy with 95% shear in the fracture surface down to -45.6 ° C.

The plate 545 has been substantially continuously rolled 1204 ⁰ C down to 96O ° C. Although good impact properties were measured at -17.8 ° C, the percentage of shear area compared to plate 544 is lower at all temperatures.

The plate 541 was not rolled in the temperature range from 1014 to 1061 ⁰ C. It exhibited impact properties inferior to those of panels 544 and 545.

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plates 2 HI Mill Tabel 1 4 HI mkg ⁰ C -28, 9 ° C -45 Output temp. 541 No. Input temp 7.05 % Section mkg % Section mkg 943 544 1218 . Output temp. : Mill 11.48 40 5.53 15th 2.9 816 545 1213 1061 Input temp. 13th 95 11.61 95 11.48 960 1204 1151 1014 90 12.3 90 10.37 3098 1116 , 6 ⁰ C -J
«S. plates 1010 1007
Chart »y hit values % Section O
"O 541 No. Longitudinal direction 5 IO
* ^ 544 -17.8 95 545 80

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309847/0924

Example 2

Five plates approximately 12.7 mm thick were made from a basic oxygen steel mill batch in the subsequent one Composition made:

Element quantity

carbon 0.10% manganese 1.23% silicon o, ou% sulfur 0.020% phosphorus 0.007% niobium 0.11% aluminum 0.050% Iron and dirt
cleanings rest

Five slabs of the above composition were placed on one 2 HI Vorwalawerk and then rolled on a 4 HI Nachwerk. The rolling temperature program used and the properties obtained are summarized in Table 2.

From Table 2 it can be seen that the panels, all were continuously rolled in the temperature range from 103 8 to 927 ° C, Charpy impact values of more than 11.02 mkg and a had percentage deposition of at least 90fr.

3098 4 7/0924

Table 2

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Plates no. . Input T. Edition T. Είης.Τ. Edition T. thickness 39714 1232 1116 1080 831 1.16 3971S 1232 1119 1044 821 1.18 O 39716 1232 1106 1047 826 1.27 co
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309847/0924

Example 3

Five steel plates were made from a basic oxygen steel mill batch from a steel of the following composition from slabs measuring 188 × 17.78 × 259.08 cm manufactured:

Element quantity

carbon 0.07% manganese 1.35% silicon 0.08% sulfur 0.010% phosphorus 0.009% niobium 0.13% aluminum 0.06% cerium 0.021% Iron and dirt rest cleanings

These steel slabs were rolled first on a 2 HI rough mill and then on a 4 HI post mill to a final (as rolled) plate size of 353.5 x 1.07 x 1956 cm using the rolling program of Table 3.

The tensile strength and Charpy impact values of the steel plate obtained are shown in Table 3. The essential

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improved Charpy impact values of the steel plates are those of Example 3, it being assumed that this is due to the presence of the rare earth metals (e.g. cerium), which reduces the sulfur content of the steel and reduces the effect of the sulfur remaining in the steel. The steel had a largely uniform ferritic grain structure with a very fine grain size of 12, which was determined in accordance with ASTM E 112. This is shown in the photomicrograph (alcoholic nitric acid etching χ 100) from FIG.

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Plates no. E ing Table 3 2 HI rolling mill Input 4 HI ' - Section Rolling mill , 10 -HS, 6 ° Temp. Temp Output Temp -28.9 ° C 90 , 08 mkg 832 4858 1193 Temp. 1034 • mkg% 95 exit , 09
, 10 26.13 837 4859 1193 1052 1031 28.07 95 "Thickness , 10 29.17 830
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1 31.24 Charpy punch values 30.83 1 'C' O
co Plates no. -17, Longitudinal direction % Off « mkg 8 ° C 90 4858 28.07 % Section 95 4859 28.9 95 90 4860 26.96 100 90 4861 28.48 95 95 4862 30.42 95 100

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Example 4 .

Table 4 shows the temperature program of the three plates which have the same composition as in Example 2.

The plate 3106 8 was rolled in the manner of conventional control rolled steel, as a result of which a high yield strength and tensile strength was found.

Plate 3 9716 was rolled in such a way that the reduction was carried out continuously in the temperature range from 927 to 1O3 8 ° C, with the finishing temperature being considerably higher was 8 than with plate 3106.

Plate 3 9087 represents a plate that was rolled on a 4 HI plant without control restrictions.

Table 4 shows the definitive improvement in impact properties, which were achieved with plate 39716.

Figures 2, 3 and 4 show the microstructures were achieved in each plate. It can be seen that plate 3 9716 (Figure 2) has the best structure, being completely free of the undesirable bands of coarse grain observed in the other plates.

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Example 5

H5.72 cm by 19 cm by 59.5 kg / m wide flange parts were made a basic oxygen steel mill batch with the following Composition made:

Element quantity

carbon 0.07% manganese 1.39% silicon <0.10% sulfur 0.018% phosphorus 0.008% niobium 0.13% aluminum 0.050% cerium nothing Iron and dirt rest cleanings

A bloom measuring 55.9 χ 38.1 cm became too

Raw pieces with the dimensions 57.2 χ 27.91 χ 10.16 cm were rolled, which were ^{reheated to 1149 0} C, pre-rolled in a rolling mill and then transported to a parallel flange system, where they were continuously in the temperature range from 871 to 1066 ⁰ C were rolled.

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Table 5 2
Yield point, kg / cm mkg flange leg 2
Tensile strength, kg / cm % Shear 5105.2 5310.5 Elongation (% at 20.32 cm meas
length) 5649.3 5965.7 ' Longitudinal impact results 20th 23 (Charpy test pieces -17.8 ° C, 2/3 size) 31.93 26.96 100 100

The present invention has heretofore been described in terms of the manufacture of panels. However, she also finds Used in the production of sheet metal products in general and rolled shapes, e.g. products for building purposes, i.e. I-beams, wide flange beams and commercial forms.

The temperatures specified in the disclosure and the claims concern the average temperature of the steel being rolled and not the surface temperature of the steel, which is typically 27.8 to Ul.7 ° C lower than the average temperature. In the examples given, the average temperature of the steel using a

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Computers based on the mean soaking temperature calculated during reheating, which can be determined fairly accurately. The computer makes corrections to the calculated Average temperature of the steel at each particular point in the rolling process based on hard mill operating parameters such as Rolling speed, measured wall forces (e.g. hardness of the steel that forms the plate), water sprays and the like. Such computer control of the rolling process and the calculation of the average temperature of the steel from the rolling past and the properties of the steel plate are techniques known to the Canadian General Electric Company, among others and do not form part of the present invention.

If the inventive method is carried out using pyrometers that only measure the surface temperature of the steel, it is possible to determine the average temperature of the steel based on the history of the The rolling process of the steel, usually calculated within an error of + 11 ° C, if the pyrometer is set up correctly and are calibrated. In rolling mills that work with pyrometers, i.e. without computer control, in accordance with be proceeded with the present invention by making appropriate corrections to the critical temperature range, such as it is measured by the pyrometer, e.g. in the case of continuous rolling in the temperature range of

309847/0924

1010-899 ° C, the correction is based on the assumption that a temperature difference between the surface of the steel and the average temperature of the steel consists of 28 ⁰ C '

Example 6

Four plates with a thickness as shown in the following Table 6 A were made from four batches of a basic one Oxygen steel mill produced, with the composition is shown in the following Table 6.

Table 6

Composition in% by weight Batch no. C Mn S P Nb Al contaminated.

D 7085 0.14 1.38 0.008 0.009 0.060 0.065 remainder

F 1403 0.15 1.42 0.010 0.007 0.060 0.060 remainder

F 1057 0.14 1.34 0.008 0.009 0.060 0.059 remainder

F 1237 0.15 1.58 0.009 0.013 0.062 0.042 remainder

The steel of each batch was treated with rare earths, so that it contained sufficient rare earth metal values to achieve 70% to 100% sulfide modification.

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One slab from each of the above batches was rolled on a 2 HI roughing mill and then on a 4 HI post mill. In the the slab entering the 2 HI roughing mill was 22.6 cm thick, entered the mill at a temperature of 1224 ° C and was rolled to a thickness of 8.6H cm and left the mill at a temperature of 1057 ° C. The 8.64 cm thick plate was then immediately brought to a 4 HI Nachw £ rk in which it came in at a temperature of 1025 ° C. It was rolled to the final thickness shown in Table 6A and left the rolling mill at a temperature of 896 ° C.

The results obtained are shown in Table 6A.

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Charge, plates No. No. F 1237 19139 F 1403 19998 D 7085 14497 309 F 1057 14498

Table 6 A 2 Str. Gr, Zugf. kg / cm kg / cm 4820.4 5934 8th 480 * 4.3 6050 2 4414.8 5581, Charpv hit results 4344.5 5453,

Elongation 20.32 cm

21 25 26 25

Charge, no, lengthwise, crosswise

mkg% shear mkg% shearr (_j

F 1237 15.9 24.33 21.15 100 100 100 8.57 7.05 7 _S 47 50 40 40 F 1403 16 17 65 65 65 7.47 10.23 9.4 95 95 95

D 7085 15.62 14.66 17.28 100 100 100 10.78 12.86 14.24 100 100 100 F 1057 27 20 18.94 100 100 100 13.83 13.83 13.83 100 100 100

Batch No. Test temperature plate thickness

F 1237. -28.9 1.588

F 1403 -28.9 1.588 J ^

D 7085 -17.8 1.905 yrs.

F 1057 -17.8 1.905 ^

Example 7-

In a manner similar to Example 6, panels that were 1.27 cm to 1.905 cm thick were made from batches of slabs a basic oxygen steelworks of the following Rolled composition:

element Amount (wt.%) carbon 0.10 manganese 1.20 sulfur 0.009 phosphorus 0.007 silicon 0.080 aluminum 0.060 Vanadium 0.01 * 0 niobium 0.040 Iron and impurities rest worked

Each batch was made in a similar manner to Example 6 Rare earth treated, each batch was continuously reduced in the temperature range of 1043 ° C to one Rolled finish temperature of approximately 843 ° C, whereby below 982 ° C the reduction was more than 50%.

309847/0924

The panels obtained in this way had the following properties}

Physical properties (batch average)

Yield strength 46 74.9 kg / cm ² tensile strength 5511.5 kg / cm ² elongation - 32% at 5.08 cm

Impact Properties (Full Size Charpy Specimen)

-17.8 ° C -28.9 ° C -40.0 ⁰ C -62.2 ° C -73.3 ° C -95.6 ° C

Lengthwise alignment mkg 30.28 28.62

% Shear 100 100

Transverse direction mkg /N.T. 16.31% shear / N.T. 73

Micro structure?

Grain size (1.905 cm slab) - Surface - ASTH # 10.5

Core - ASTM # 10

/ N.T. - Not checked

4.47 23.5 20.73 / 12.58 95 80 65 ./■ 23 16 13th 13.82 N.T. 72 42 49 N.T.

309847/0924

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Example 8

In a manner similar to Example 7, panels that were 1.27 cm thick were prepared using exactly the same program as in Example 7 rolled from slabs of a batch of the following composition /

element Amount (wt,%) carbon 0.100 manganese 0.91+ sulfur 0.028 phosphorus 0.009 silicon 0.240 chrome 0.540 nickel 0.290 copper 0.340 niobium 0.025 aluminum 0.040 Iron and dirt rest cleanings

The batch was not treated with rare earths. The obtained plate had the following properties. Physical Properties Yield Strength - 4527.3 kg / cm ² Tensile Strength - 5634.5 kg / cm ² Elongation - 20% at 20.32 cm

3Q9847 / 0924

Impact properties (full size Charpy specimens)

-17.8 ⁰ C -28.9 ° C -45.6 ⁰ C -51.1 ° C longitudinal

tung mgk 11.34 8.57 4th 4.15 % Shear 95 70 30th 5 Microstructure

Grain size (1.27 cm slab) - Surface - ASTM ^ 12.5

Core - ASTM φ 12.0

When rolling a slab of similar composition, however with the exception that niobium was absent, a plate was obtained following the same program as were the following Had properties

Impact properties - 4.29 mkg and 25% shear -28.9 ° C grain size (1.27 cm plate) - surface - ASTM 8.0

Core - ASTM 8.0

From this it can be seen that the presence of niobium contributes to the manufacture of the steel of the present invention fine grain size is necessary.

Figure 5 shows a drawing of a 1.27 cm plate. Here, the niobium content of the steel is against the percentage shear in a standard Charpy sample that was broken at -28.9 ° C. The results were the previous ones Examples taken.

309847/0924 6069

It can be seen that the invention Walzver- drive to some extent in steel with a niobium content of 0 to 0.14% effective. For best results , the 1.27 cm steel should contain at least 0.04% niobium. This optimal niobium content fluctuates with the plate thickness, it is higher with thinner plates and vice versa.

309.847 / 0924 6069

Claims (1)

Claims Contains% niobium 1. Completely killed steel with high yield point and a high notch toughness below -17.8 ⁰ C, of up to 0.2 wt.% Carbon, at least 0.75% Hangan and at least 0.015 wt., Said steel in a has a substantially uniform fine-grained, essentially ferritic grain structure with an average grain size finer than 9.0, determined according to ASTM test no. E 112, 2. Steel according to claim 1, characterized in that it contains at least 0.04 wt.% Niobium. 3. Steel according to claim 1, characterized in that it contains at least 0.06% by weight of niobium. 4. Steel according to claims 1, 2 or 3, characterized in that it contains at least 0.02% by weight of carbon. 5. Steel according to claims 1, 2 or 3, characterized in that it contains up to 0.16% by weight of carbon. 6. Steel according to claim 1, characterized in that it is in essentially according to% by weight of 0.02 to 0.2% by weight of carbon, 0.015 to 0.18% by weight of niobium, 0.75 to 2% by weight of manganese, 0 to 0.5% molybdenum, no more than 0.025% phosphorus, no more __ _RO 309847/0924 buoy as 0.035% sulfur, 0 to 1% copper, 0 to 1% nickel, 0 to 1% chromium, 0 to 0.12% vanadium and the remainder of iron and incidental impurities, the steel being a substantially uniformly fine-grained, substantially has a ferritic grain structure with an average grain size finer than 9.0, determined according to ASTM Test No. E 112, 7. Steel according to claim 6, characterized in that it is at least Contains 0.04% by weight niobium. 8. Steel according to claim 6, characterized in that it is at least Contains 0.06% by weight niobium. 9. Steel according to claims 7 or 8, characterized in that it contains up to 0.16% by weight of carbon. 10. Steel according to claims 7 or 8, characterized in that it contains at least 1% by weight of manganese. 11. Steel according to claims 1 or 6, characterized in that it has a longitudinal Charpy impact strength of at least 8.29 mkg. 12. Completely calmed steel according to claim 1. with high yield strength and high notch toughness below -17.8 ° C, which is up to 309847/0924 0.2 wt.% Carbon, at least 1 wt.% Manganese and at least Contains 0.09% by weight of niobium, this steel being an essentially uniformly fine-grained, essentially ferritic steel Grain structure with an average grain size finer than 9.0 determined according to ASTM Test No. E 112. 13, completely killed steel according to claim 1 with high yield strength and high notch toughness below -17.8 ° C, which essentially consists of 0.02 to 0.12% by weight of carbon, 0.09 to 0.18% by weight niobium, 1 to 2% manganese, 0 to 0.5% molybdenum, not more than 0.025% phosphorus, not more than 0.035% sulfur, 0 to 1% copper, 0 to 1% nickel, 0 to 1% chromium and the remainder of iron and incidental impurities, where this steel has an essentially uniform fine-grained, essentially ferritic grain structure with an average Grain size finer than 9.0, determined according to ASTM Test No. E 112, 14, steel according to claim 12, characterized in that it consisting essentially of 0.06 to 0.1% carbon, 0.12 to 0.15% niobium, 1.3 to 1.6% manganese, not more than 0.015% phosphorus, not more than 0.02% sulfur and the remainder iron and incidental impurities. 15, steel according to any one of the preceding claims, which has an average grain size of at least 10.0. determined after 309847/0924 6069 ASTM Test No. E 112 has. 16, steel naoh one of the preceding claims, the one longitudinal Charpy impact strength of at least 8.29 mkg Has. 17, steel according to one of the preceding claims, the one longitudinal Charpy impact value at -17.8 ° C of has at least 11.06 mkg, 18, steel according to any one of the preceding claims, which has a longitudinal Charpy impact value at -17.8 ⁰ C of at least 26.27 mkg. 19, steel according to any one of the preceding claims, which has a longitudinal Charpy impact value at -17.8 ° C of has at least 27.65 mkg. 20, steel according to one of the preceding claims, which has a longitudinal Charpy impact strength value at -45.6 ⁰ C of at least 11.06 mkg, 21 »steel NaOH any preceding Ansprüohe having a longitudinal -45.6 at ⁰ C Charpy Sohlagzähigkeitswert of at least 26.27 mkg has. 8089 309847/0924 22. Steel according to one of the preceding claims, which has a percentage shear of at least 90%. 23. Steel according to one of the preceding claims in the
Form of a 0.635 to 2.8575 cm plate. 2U. Steel according to one of the preceding claims, aluminum Contains in an amount of 0.02 to 0.1% by weight. 25. Steel according to one of the preceding claims, which is a rare earth metal capable of binding sulfur in a Contains an amount sufficient to bind the sulfur present in this steel, the steel being an improved one Has flexural impact strength. 26. The steel of claim 25, wherein the rare earth metal
Includes cerium. 27. The steel of claim 25 containing up to 0.06% rare earth metals. 28. Steel according to one of the preceding claims, which contains up to 0.2% zirconium. 29. Steel according to one of the preceding claims in the form 309847/0924 a flat rolled product or a sheet product. 30, steel according to one of the preceding claims, which has been rolled into standard shapes or hand-made products _a 31, a process for the production of a high-strength steel with improved notch toughness at a temperature below »17 _S 8 ° C, characterized in that a steel ingot with a composition as specified in the preceding claims and at a temperature of at least 1149 ⁰ C subjecting this steel to the reduction by rolling and continuously subjecting this steel to the reduction by rolling in an average temperature range of 1038 to 927 ° C of the steel, 32, The method of claim 31 _ö characterized in that "the orphan performed in the medium temperature range from 1066 to 927 ° C continuously wi 33, the method according to claim 31, daäiir-eh. characterized in that the reduction is accomplished by rolling both in a roughing mill and subsequently in a machinist, the steel being transported from the roughing mill to the finishing plant above or below the average temperature range of 1038 to 927 ° C of the steel. 309847/0924 3 * 4, method according to claim 31, characterized in that the average starting temperature of the ingot is at least 1232 ° C. 35. The method according to claim 31, characterized in that the rolling is continuous in the average temperature range from 1038 to 899 ° C. 36, method according to claim 31, characterized in that the rolling is carried out continuously in the average temperature range of 1066 to 899 ° C. 309847/0924 6069 ■ V 6- L e r s e ί t e