DE1934153A1 - Objects made of tough, high-quality steel and processes for their manufacture - Google Patents

Description

Dr. In g. E. BERKENFELD ■ Dipl.-Ing. H. BERKENFELD, patent attorneys, Cologne

^{~: ~~:} 1934133

Attachment file number

for the entry of the 2nd Jill! 1969 Sch // Name d. Note. ■ INLAND STEEL ÖOMPANY

Objects made of tough, high-quality steel and processes for their manufacture. -

The invention relates generally to objects made of steel, such as plates with a thickness of 4.68 to 31.25 mm # as well as Pipe strips or profile iron. The invention particularly relates to Steel objects of the type described, which are both a high yield strength as well as high impact strength or notch toughness exhibit. -

Conventional steel objects, such as plates, generally do not have a combination of high yield strength and high impact strength. A conventional steel plate with a thickness of 4.68 mm, which in the rolled state has a relatively high yield strength of approximately 4900 kg / cm, for example, has an impact resistance, expressed by a Charpy V-notch impact strength of 2.0745 mkg at a Transition temperature of no more than about -18 ° C to -4 ⁰ C. For a plate that is thicker than 4.68 mm, the impact resistance is lower. The lower the impact transition temperature, the higher the impact strength. "■" ■ "■

In accordance with the invention, a combination of the composition and treatment methods produces a steel article that has a controlled microstructure of ferrite and pearlite and has both high yield strength and high impact strength. A steel plate with a thickness of up to 31 * 25 mm can, for example, be given a yield strength of 4900 kg / cm together with a Charpy V-notch impact strength of 2.0745 mkg at a transition temperature of -VS ^ t to - ^^ 6 or less.

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The invention accordingly relates to a steel structure such as a plate, for example, which has a relatively high yield strength of, for example, 4900 kg / cm together with a relatively high yield strength. Has impact strength, for example a Charpy V-notch impact strength of 2.0745 mkg at a tlbergaogstempera-

door from -UPC to -38 C or less · * The microstructure? 'consists made of ferrite and pearlite. The grain size of the ferrite is 9.5 to dt? ASTM scale or finer * The composition in percent by weight is following ·

Carbon manganese silicon nitrogen Aluminum vanadium columbium tungsten

The article is hot-rolled, with, results in a deformation of at least $ 25 at a finishing temperature that is above the temperature of A _1, to obtain a microstructure, the fine-grained Aust'enit contains (9.5 on the ASTM scale or finer). The cooling takes place quickly but in a controlled manner in order to avoid conversion products in the microstructure that result at low temperatures. Annealing is optional. ;

Further features and advantages of the invention emerge from the description below.

According to one embodiment of the invention, a steel article hot rolled from a steel whose composition is the the following allowable ranges of the elements in percent by weight!

0.02 - 0.26 1.25 - 1.75 0.75 - 1.5 0.003 - 0, .015 0.01 - 0.08 0 0.07 0,. ■ - 0.03 0 0.1

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0.02 ■ - 0.26 1.25 "■ - 1.75 0.75 - - 1.5 0.005 - 0.015 0.01 - - 0.08 0 - 0.07 0 - 0.05 0 - 0.1 0.05 yes maximum 0.05 maximum Rgst

Carbon manganese

Silicon nitrogen aluminum vanadium columbium tungsten

Phosphorus sulfur iron

The composition described above includes both steel with low carbon content as well as steel with higher carbon content. The low carbon content is less than 0.18 weight percent and the higher carbon content is 0.18 weight percent or more. For a number of preferred compositions "either low or high carbon" the ranges are the others Items as follows, expressed in percent by weight

manganese

Silicon nitrogen aluminum vanadium columbium ι tungsten

Phosphorus, sulfur iron

The hot rolling step is completed by a finishing process in which hot rolling deformation of at least 25 # in total is carried out. The finishing process takes place at a temperature which is above the temperature A ₁ for the steel, the microstructure of the steel containing substantial amounts of austenite during the finishing process in order to achieve a grain size of 17/5 -5- - at the finishing temperature.

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- 1.7 - 0.05 1.2 - 1.5 - 0.05 0.008-0.01 - 0.05 0.02 - 0.1 0 maximum 0 maximum 0 0.05 0.03 rest

austenite size no greater than 9.5 on the ASTM scale. The temperature A ₁ is the temperature above which the microstructure contains both austenite and ferrite and below which no austenite is present under equilibrium conditions. '

After the finishing deformation, the hot-rolled object becomes cooled as quickly as is compatible with avoiding the formation of conversion products at low temperature, such as bainite and martensite, as well as at room temperature to obtain a micro-structure consisting essentially of fine-grained Consists of ferrite and pearlite. The term "fine-grained" means a grain size that is not larger than 9.5 on the ASTM scale. It should be noted that the higher the number on the ASTM scale, the smaller the grain size.

The following combinationί

the composition of steel described above, a deformation of at least $ 25 during the finishing process,

a temperature of the finishing process that is above the temperature Ä .. for the steel and what substantial amounts of austenite in the microstructure of the steel during the Finishing process results, as well as the cooling process described above

together result in a steel article that has a ferrite grain size of 9.5 on the ASTM scale or finer at room temperature having. This steel article has a yield strength greater than 3500 kg / cm and a Charpy V-notch impact strength of 2.0745 mkg with a transition temperature of not more than on.

The finishing process for a steel object that a higher carbon content (0.18 to 0.26 percent by weight) may differ from that for a steel object, which has a low carbon content (more than 0.02 percent by weight but less than 0.18 percent by weight) In either case, the deformation in the finishing operation is greater than 25% of the total hot rolling deformation. With steel with

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the low carbon content but the Pertigbearbeitungsteniperatur high enough, for example, higher than 871 ⁰ C, a microstructure to ensure ,, consisting of austenite during the final deformation just ·. In the case of steel with a higher carbon content, on the other hand, the finishing temperature does not have to be in a temperature range in which the microstructure consists only of austenite, but can also be a lower temperature in a two-phase range in which the microstructure contains both austenite and ferrite, e.g. 76O - 85 ⁰ This lower temperature is - substantially below the temperature A - for the steel with a higher carbon content, namely the temperature above which the microstructure consists only of austenite and below which the microstructure contains both austenite and ferrite under equilibrium conditions .

For steels with both carbon contents, the goal is to to obtain fine-grained recrystallized austenite, but; to report the complete recrystallization during the finishing process. Austenite fine grains are desirable worth it because the size of the ferrite grains in the finished item at room temperature is compared to that during finishing achieved grain size of the austenite is proportional. Finer ones Ferrite grains give increased strength.

The finishing in the lower temperature range, the is permitted for steel with a higher carbon content greater strength because more of the deformed defective structure in the final product is present than in the case of finishing at a higher temperature. There is less chance that the poor structure at the lower finishing temperature is annealed than at the higher finishing temperature. From the standpoint of strength, the lower the finishing temperature, the better. a substantial part of the austenite in the microstructure to be maintained, e.g. above about 704 ° C. ~

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The maximum amount of deformation that can be performed during the finishing operation is about $ 40, but this limit is imposed by the design of most conventional finish rolling mills and not by the present invention. Finishing mills usually consist of a single rolling mill that can produce a maximum deformation of about $ 40. Henn a finishing deformation of 60-80 # can be carried out, this would still be within the scope of the present invention. If a finishing train has two or three stands, the finishing operation could be carried out to give a deformation much greater than 40 #. With such an arrangement, however, the deformation would have to be carried out on the second and third roll stands of the finishing train before complete recrystallization of the austenite grains present on a preceding roll stand after the deformation takes place. In other words, all of the deformation on all two or three roll stands of the finishing mill should be done without such a delay between the roll stands that would allow the austenite to fully recrystallize. By preventing the austenite from recrystallizing, the deformation achieved on the successive roll stands would add up and in this way exceed the current limit of approximately 40 # deformation that can be achieved with a single roll stand. The greater the deformation, the higher the yield point.

According to the invention, one would be made from steel with a higher carbon content produced steel object after completion of the finishing process an austenite grain size of 12 or exhibit finer. On the other hand, a steel article made from steel having a low carbon content would after completion of the finishing process a grain size of the austenite of .9.5 or finer.

The elongation limit of the steel with a higher carbon content would be are in the range of 4900 - 5950 kg / cm, while the yield point of low Kohlersbff steel in the range of 5500

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-49OO kg / cm. The lower yield strength of the 17/3 * '-6-

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Low carbon steel is due to the larger grain size and due to the low carbon content. -,,

The impact strength of the steel with a higher carbon content is slightly higher than that of the steel with a lower carbon content * PUr the Charpy V-notch impact strength of 2.07 ^ 5 mkg for steel with a higher carbon content the transition temperature is -p ^ tT * or less compared to - 3O ⁰ C or less for steel with a low carbon content.

The steel object made of steel with a higher carbon content has a microstructure consisting essentially of ferrite and pearlite, the volume of the pearlite being in the range of ^ O - 50 # lies. In the case of the steel object made of steel with low Carbon content is less than the volume of the perlite $ 30 and consists of fine, randomly distributed perlite. the For example, the term "fine" used in connection with perlite refers to pearlescent grains approximately in size '0.0001 mm, spaced about 0.00025 rib from each other Coarse perlite lie in grains suit a size of about 0.0006 mm ^ at a distance of about 0.0019 mm lie apart.

The greater the Abkühlung.sg@sch&ind±gkeit bsi steel Feit higher carbon content is "more grfSßer is the Wahrseheinliehkeit unwanted conversion products to be obtained at a low temperature such as _s s Martensifc or bainite * represent the case of steel with a low carbon content bet relatively large cooling rates the check Urawandlungsprodukte resulting low temperature 'not a problem ₀ the greater the cooling rate 1st, the finer is the perlite. .

"Be sprinkling with Masser and by exposure performed with air .-" In StaTil! High or low carbon cooling process can t _s in still Luf In the methods of Wasserbedsselung and however the pressurisation must tighter control on the application come ^ if these methods can be used to cool higher carbon steel.

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If the final microstructure contains some low temperature transformation products accidentally obtained during cooling, these can be eliminated by annealing the steel article. Annealing consists of heating the object to a temperature at which the microstructure of the steel consists of austenite, e.g. 843 - 95 ° C, depending on the carbon content, and for a sufficient period of time to allow temperature equilibrium throughout the object and a To obtain a microstructure that consists only of austenite. The object is then cooled at as great a rate as possible compatible with avoiding the formation of conversion products at low temperature. The steel with low carbon content can be cooled more rapidly than the steel with higher carbon content without harmful effects. The steel with higher carbon content may be heated within the range of 843 954 ⁰ C to a lower temperature. A typical annealing temperature for the steel with a higher carbon content is in the range of 843 - 927 ° C and a typical annealing temperature for the steel with a low carbon content is in the range of 87I - 954 ° C.

After annealing the steel with higher or lower carbon content The end product is a steel article that has a microstructure consisting essentially of fine-grained Consists of ferrite and pearlite.

The resulting steel article exhibits regardless of whether it is made from higher or lower carbon steel exists, a relatively high yield strength and a relatively high impact resistance. It is the same without preheating and without regulating the temperature between welding passes easy to weld. With such properties, the article can be in the form of a plate or a strip of tubing exhibit. The composition of the steel with a higher mineral content is useful for plates with a thickness in the range of 4.68 - 31.25 mm and the composition of the steel with low carbon is for thinner panels in the area from 4/68 - 9.37 mm useful.

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The invention is not limited to the examples described Limited designs that experience various changes can without departing from the scope of the invention.

Claims

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Claims (2)

I! 934153 Or. Ing. E. BER (CENFELD ■ Dipl.-Jng. H. BERKENFELD, patent attorneys, Cologne, Anlas * '■ Files not xurEineabiv on July 2, 19Ö9 SOh // Named by INLAND STIEL COMEMIY patent claims 1. Steel object, characterized in that the same is made of steel having a composition consisting essentially, in percent by weight, of: Carbon 0.02-0.26 Manganese 1.25-1 * 75 Silicon 0.75-1.5 Nitrogen 0.003-0.015 Aluminum 0.01-0.08. Vanadium 0-0.07. . Columbium 0-0.03 Tungsten 0 "- 0.1 and a remainder consisting essentially of iron, that the steel object has a microstructure that essentially consists of ferrite and pearlite with a grain size of ferrite, which is not coarser than 9.5 on the ASTM scale, 2 that the steel object has a yield strength of more than 3500 kg / cm having. 2. Steel object according to claim 1, characterized ^ that the carbon content is 0.18-0.26% by weight, that the grain size of the ferrite is not; is coarser than 12 on the ASTM scale and that the yield point is more than 4900 kg / cm. * ^: ■ -10- 009S10 / 0424 3. Steel object according to claim 2, characterized in that that the volume of pearlite in the microstructure is in the range of 50 - 50 ^ lies. 4. A steel article according to claim 2, characterized in that it has a Charpy V-notch impact strength of 2.074-5 mkg at a transition temperature of not more than -τϊβ £ β ·. 5 · Steel object according to claim 1, characterized in that the nitrogen content is 0.008-0.012% by weight, that the vanadium content is not more than 0.03% by weight, that the columbium content is not more than 0.03% by weight that the aluminum content is 0.02-0.05 Ji by weight. 5. Steel object according to claim 1, characterized in that that the carbon content is less than 0.18% by weight and that it has a Charpy V-Notch Impact Count of J2 _r .0745 mkg at a transition temperature of not more than - »4-θ%. ' 7 * Steel object according to claim 1, characterized in that the carbon content is less than 0.18% by weight, that the volume of the pearlite in the microstructure is less than 30% and
that the pearlite is relatively fine and randomly distributed. Q. Vefffahren for producing a steel object, marked through the following steps: hot rolling an article of a steel having a composition which consists essentially in percent by weight of: Carbon 0.02-0.26 Manganese "1.25-1.75 "Silicon 0.75-1 * 5 Nitrogen 0.003 - 0> 015 - Aluminum 0 * 01 - Q, 08 Vanadium 0 ■ -. 0.07 ■ Columbium O- 0.03 .- '· ■' " Tungsten 0 -0.1. -11_ 009810/04 24 ■■ .- ■ .V- ■ ■,: ■ .... and a residue consisting essentially of iron, '- _: '"that the step of hot rolling comprises a finishing operation in which a hot rolling deformation of a total of at least $ 5 is carried out, that the finishing process is carried out at a temperature which is above the temperature A ₁ for the steel, the microstructure of the steel during the finishing process contains substantial amounts of austenite in order to obtain a grain size of the austenite at the finishing temperature which is not larger than 9.5 on the ASTM scale, that the hot-blown steel object after the finishing process is cooled as quickly as is compatible with avoiding the formation of transformation products at low temperature in the microstructure of the steel object, and in order to obtain a microstructure which ' consists essentially of ferrite and pearlite and ..- ■■■ = ■■ that the combination of the composition of the steel, the deformation of the finishing process, the temperature of the finishing process and the cooling process together result in a grain size of the ferrite which is not coarser than 9/5. on the ASTM scale. . ^: 9. The method according to claim 3, characterized in that the carbon content of the steel is 0.1c - 0, ::: 6% by weight, that the deformation of the finishing process is carried out at a temperature which is substantially below the temperature A- is for the steel, the microstructure of the steel during the finishing process consists essentially of austenite and ferrite, and that the grain size of the ferrite after the cooling process is not is coarser than 12 on the ASTM scale. . 10. The method according to claim 9 3, wherein the steel object is subjected to an annealing process after cooling, which comprises the following steps: 4es.Stahlgegenstandes heating to a temperature above the temperature A, located in the steel and up to 927 ⁰ C during a time period that results in a temperature compensation in the entire object and a microstructure of the steel, in the essential I 7/5 - * · ■ ■ - ■ '■ ". ■' - ■ ^: -12- 0 09810/0 ^ 24 BAOORlQfNAL ■ _n 1834153 chen aug Äustenit exists, as well. ■. cooling the heated steel object at a rate as high as is compatible with avoiding the 'formation of transformation products at low temperature in the microstructure of the steel object, and in order to obtain a macrostructure consisting essentially of ferrite and pearlite , ' ^: " 11. The method according to claim 8, characterized in> that the carbon content of the steel is less than 0.18 weight · »^, that the deformation of the finishing process at a Temperature is running above the temperature A, for the steel, the microstructure of the steel during the Finishing process consists essentially of austenite, and. that the cooling rate is sufficiently great to avoid the formation of coarse pearlite. . 12. The method of claim 11, wherein the steel article is subjected to an annealing process after cooling, which comprises the following steps:. Heating the steel object to a temperature above the temperature Ä, for the steel and up to 95 ^ C during a period of time that has a temperature calibration in the whole object and results in a microstructure of the steel, which is essentially consists of austenite, as well cooling the heated steel object with such a large one Faster than avoiding the formation of conversion products at low temperature in the microstructure door Steel object is compatible, and to have a microstructure obtained, which consists essentially of ferrite and fine, randomly distributed Per3.it. ■ 0098ΓΟ / Ο42 *