TWI768987B - Steel with low temperature toughness and method for producing the same - Google Patents

Abstract

The present invention relates to a steel with low temperature toughness and a method for producing the same. The steel comprises specific compositions, and the steel made by a hot rolling process, a cooling process and a coiling process with specific parameters has fine and uniformly distributed microstructures. Accordingly, the steel of the present application has excellent impact resistant property in a low temperature environment.

Description

Steel with low temperature toughness and method of making the same

The present invention relates to a kind of steel material, in particular to provide a kind of steel material with low temperature toughness and a manufacturing method thereof.

Because steel has better strength and can be shaped by applying external force, steel is often used to make any component. Among them, according to the difference of the use environment, the steel often needs to have corresponding properties to meet various application requirements. Generally speaking, steel has poor toughness in low temperature environment, so the application of steel in low temperature environment is limited.

In order to improve the low temperature toughness of the steel, the low temperature toughness of the steel is generally improved by adjusting the composition of the steel billet. In addition, a conventional method is by adding chromium, copper and nickel to the steel billet composition and performing the coiling process at a relatively low temperature (eg, 400°C to 650°C or 450°C to 650°C). Although the low-temperature toughness of the prepared steel can be improved, the cost of the added alloy is relatively high, and quenching equipment must be used for coiling, so it has a small process window and is difficult to meet application requirements.

In view of this, there is an urgent need to provide a steel material with low temperature toughness and a manufacturing method thereof, so as to solve the defect that the conventional steel material does not have toughness at low temperature.

Therefore, one aspect of the present invention is to provide a steel material with low temperature toughness, which has a specific composition, and can have lower raw material cost and better low temperature toughness at the same time.

Another aspect of the present invention is to provide a method for manufacturing a steel with low temperature toughness, which enables the steel to have a specific crystal phase structure of ferrite and bleb iron through specific hot rolling parameters and cooling process, And to ensure that the crystal structure in the steel is uniform and fine, which can improve the low temperature toughness of the steel.

According to an aspect of the present invention, a steel material with low temperature toughness is provided. The steel contains 0.03 to 0.15 weight percent carbon, 0.1 to 0.8 weight percent silicon, 1 to 2 weight percent manganese, not more than 0.05 weight percent phosphorus, not more than 0.05 weight percent sulfur, 0.01 wt% to 0.17 wt% aluminum, insignificant impurities and balanced iron.

According to some embodiments of the present invention, the aforementioned steel material may optionally include 0.01 to 0.08 wt % vanadium, 0.01 to 0.08 wt % titanium, 0.01 to 0.08 wt % niobium, 0.05 to 0.05 wt % to 0.5 weight percent molybdenum, and/or no more than 0.05 weight percent calcium.

According to some embodiments of the present invention, the aforementioned steel material includes a ferrite structure and a bleb iron structure, and the content of the ferrite structure is not less than 70%.

According to some embodiments of the present invention, the grain size of the aforementioned steel material is not less than No. 8.

According to some embodiments of the present invention, the impact value of the aforementioned steel at -40°C is not less than 150 J.

According to another aspect of the present invention, a method for manufacturing a steel material with low temperature toughness is provided. In this method, a steel billet is provided first, and a hot rolling process is performed on the steel billet to form finished rolled steel, wherein the finishing temperature of the hot rolling process is not lower than the Ar ₃ temperature. Then, a cooling process is performed on the finished rolled steel to form a cooled steel, wherein the cooling rate of the cooling process is not less than 10° C./s. Next, a coiling process is performed on the cooled steel material to obtain the aforementioned steel material with low temperature toughness.

According to some embodiments of the present invention, the manufacturing method can selectively heat the steel billet to not less than 1150° C. before the hot rolling process.

According to some embodiments of the present invention, the aforementioned cooling rate is 10°C/s to 100°C/s.

According to some embodiments of the present invention, the aforementioned cooled steel material is coiled at 660°C to 720°C.

According to some embodiments of the present invention, after the aforementioned coiling process is performed, the steel is subjected to a surface processing process.

Applying the steel material with low temperature toughness and its manufacturing method of the present invention, the hot rolling process is performed on a steel billet with a specific composition, and the formed finished rolled steel material has a specific finished rolling temperature, which can promote the crystallinity in the finished rolled steel material. The phase structure is transformed into an appropriate crystal phase structure and grain size. Then, with a faster cooling rate, the steel can have a fine ferrite and bleb iron structure, and the grain size is not easy to precipitate and become larger. In addition, starting the coiling at a specific temperature helps to precipitate the crystal structure in the steel at the same time, so the prepared steel has a uniform and fine crystal structure, and has better low temperature toughness.

The manufacture and use of embodiments of the present invention are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are provided for illustration only, and are not intended to limit the scope of the invention.

Please refer to FIG. 1 , which is a flowchart illustrating a method for manufacturing a steel material with low temperature toughness according to some embodiments of the present invention. In the method 100 , a steel billet is first provided, and a hot rolling process is performed on the steel billet to form a finished rolled steel material, as shown in operations 110 and 120 . The steel blank can be prepared by a method well known to those skilled in the art, so it is not repeated here. The composition of the billet can be appropriately adjusted according to the needs of the back-end application. In some embodiments, the steel billet may have a composition of carbon, silicon, manganese, phosphorus, sulfur, and aluminum, among others. In such embodiments, the steel billet may include 0.03-0.15 wt% carbon, 0.1-0.8 wt% silicon, 1-2 wt% manganese, 1-2 wt% manganese, based on 100 wt% steel billet. Phosphorus greater than 0.05 weight percent, sulfur not greater than 0.05 weight percent, aluminum from 0.01 weight percent to 0.17 weight percent, insignificant impurities and balanced amounts of iron. In some embodiments, the steel billet may optionally comprise 0.01 to 0.08 weight percent vanadium, 0.01 to 0.08 weight percent titanium, 0.01 to 0.08 weight percent niobium, 0.05 to 0.5 weight percent of molybdenum, and/or not more than 0.05 weight percent of calcium. In some embodiments, the steel billet may optionally contain a nitrogen content of no greater than 200 ppm. In some embodiments, the steel billet of the present invention preferably does not contain chromium due to lower raw material costs and welding requirements of back-end applications. In some embodiments, in order to balance the refining cost of the steel billet and the welding requirements of the back end, the steel billet may contain no more than 0.1 weight percent of chromium. In other embodiments, the steel billet of the present invention excludes the addition of copper and/or nickel. It should be noted that, in some specific examples, based on the requirements of back-end applications, if the application environment contains certain substances such as hydrogen sulfide (H ₂ S), the steel billet of the present invention can selectively contain copper and/or nickel. .

During the hot rolling process, the strands are rolled to the dimensions required for the end application. Among them, the finishing temperature of the hot rolling process is not lower than the Ar ₃ temperature. For example, the Ar ₃ temperature of the steel billet of the present invention may be, for example, about 686°C. Among them, the measurement and calculation of the Ar ₃ temperature are well known to those of ordinary knowledge, so they will not be repeated here. In some embodiments, if the finish rolling temperature is lower than the Ar ₃ temperature, although other process parameters can be further adjusted in the future to obtain steel that meets the requirements, but without deliberately changing other parameters, the finish is too low. The rolling temperature will cause the steel produced to not have the desired grain structure to meet the application requirements. In some embodiments, the finishing temperature of the hot rolling process is preferably 686°C to 950°C. When the finish rolling temperature of the hot rolling process is within this range, the finished rolled steel can have a more appropriate crystal structure and size, and the subsequent steel can have the desired crystal structure, and then meet the needs of the application.

In some embodiments, before the hot rolling process, the steel billet can be preheated by heating equipment to make the temperature of the steel billet uniform. In some specific examples, the steel billet may be heated to not lower than 1150° C. to facilitate the subsequent hot rolling process. Secondly, when the steel billet is first heated to a temperature of not lower than 1150, the steel produced subsequently can have better low-temperature impact properties. In other specific examples, the steel billet may be heated to 1200° C. to 1,350° C. for the hot rolling process.

After the hot rolling process is performed, the finished rolled steel is subjected to a cooling process, followed by a coiling process to obtain the steel with low temperature toughness of the present invention, as shown in operations 130 to 150 . In some embodiments, the manufacturing method of the steel of the present invention does not require a cold rolling process.

During the cooling process, the finished rolled steel system is cooled to 660°C to 720°C at a cooling rate of not less than 10°C/s. When the finished rolled steel is cooled, because the cooling rate is fast, the crystal structure in the steel is not easy to precipitate and become larger, so it can be ensured that the obtained steel can have a smaller grain size. In addition, in the cooling process, the faster cooling rate also helps to transform the structure of the steel into ferrite and bleb iron structure, so that the prepared steel has an appropriate crystal structure. In some embodiments, the cooling rate may be 10°C/s to 100°C/s. When the cooling rate is 10°C/s to 100°C/s, the crystal structure in the finished rolled steel obtained by the hot rolling process can have a more appropriate precipitation time, and the subsequent steel can have a better precipitation time. Appropriate crystal phase composition and size.

When the coiling process is performed, the rolled steel after cooling starts coiling at an initial temperature of 660°C to 720°C, but during coiling, the steel is naturally cooled. In other words, when the steel enters the coiler, the temperature of the steel is 660°C to 720°C, and when the steel starts to coil, the steel is not additionally heated or cooled. During the coiling process, the crystal structure in the steel will not precipitate and become larger, which can ensure that the obtained steel has a finer grain size, thereby making it have better low-temperature impact resistance. If the coiled steel is additionally heated during the coiling process, the grain structure in the steel is easily coarsened, thereby reducing the low-temperature impact resistance of the steel.

In some embodiments, after the coiling process is performed, the steel may be further subjected to a surface processing process to further improve the quality of the steel. For example, the surface treatment process can be, for example, pickling treatment, other surface treatment treatments, or any combination of the above treatment methods. The surface treatment process can be used, for example, to remove surface scale and/or other surface impurities from steel.

In some specific examples, the steel produced by the present invention contains ferrite and bleb. In other specific examples, the steel of the present invention is composed of more than 70% ferrite structure, bleb iron structure and other non-specific phases. Preferably, the content of the iron structure of the fertilizer granules is 70% to 90%. Secondly, the steel of the present invention has uniform and fine grain size. In some specific examples, according to the measurement specification of ASTM E112, the grain size in the steel of the present invention is not less than No. 8. Since the steel of the present invention has ferrite and bleb iron structure, and has a uniform and fine structure, it has good low-temperature impact resistance (for example: according to the measurement specification of ASTM E23, at -40 ° C, the steel has a The impact value is not less than 150 J. In other cases, the impact value of the steel is preferably not less than 230 J). Furthermore, the steel of the present invention has a tensile strength greater than 570 MPa, a yield strength greater than 485 MPa, and an elongation of not less than 25%.

In some application examples, the steel of the present invention can be used to make steel pipes, such as but not limited to, and it can meet the requirements of the American Petroleum Institute (API) pipe specification (API 5L X70), or other similar strengths usage requirements.

The following examples are used to illustrate the application of the present invention, but it is not intended to limit the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention.

Example 1

The steel material of Example 1 was produced using the steel billet composition in the first table shown below. Then, the billet is preheated to 1241°C for the hot rolling process. When the billet is rolled to 9.3 mm, the hot rolling process is finished, and the finishing temperature of the finished rolled steel is 850°C. Next, a cooling process is performed. After the rolled steel is cooled to 660° C., the coiling process is continued to obtain the steel with low temperature toughness of Example 1. The prepared steel is evaluated for crystal structure, yield strength, tensile strength, elongation and low temperature impact resistance by the methods and instruments commonly used in the technical field. The results obtained are shown in Table 1.

In addition, the steel material of Example 1 was made into a pipe material conforming to the specification of API 5L X70, and was further welded to make a pipe. The low temperature impact property of the weld bead of the prepared pipe is evaluated by the same method as above, and the low temperature impact value of the weld bead is not less than 124 J.

Example 2 and Example 3 and Comparative Example 1 and Comparative Example 2

The steel materials of Example 2 and Example 3 and Comparative Example 1 and Comparative Example 2 use the same process steps as the production method of the steel material of Example 1, the difference is that Example 2 and Example 3 and Comparative Example 1 are compared with Example 2 is to prepare steel by changing the composition of the steel billet and different parameter conditions. The evaluation results of the crystal structure, yield strength, tensile strength, elongation and low temperature impact resistance of the obtained steel are shown in Table 1, and will not be repeated here.

In the same way, the same process steps as the production method of the pipe in Example 1 were used to produce the pipes in Example 2 and Example 3 and Comparative Example 1 and Comparative Example, and the evaluation results of the low temperature impact of the pipe weld bead are shown in Table 1. shown.

According to the evaluation results in Table 1, when the steel billet has the specific composition disclosed in the present invention, when the finishing temperature of the hot rolling process is not lower than the Ar ₃ temperature, and the hot-rolled steel has a temperature of not less than 10°C/s. After the cooling rate is cooled to a specific temperature, the obtained steel can be composed of ferrite and bleb iron, and has mechanical properties that meet application requirements, and it also has better impact properties in low temperature environments. Accordingly, the steel prepared by the present invention can have good low temperature impact resistance, and can meet the application requirements.

In Comparative Example 1 and Comparative Example 2, although the low-temperature impact values were 217 J and 213 J, respectively, the steel billet composition contained more chromium, so Comparative Example 1 and Comparative Example 2 had higher raw material costs, and the subsequent The welding properties of the application are poor.

In addition, when the steel materials of each example and the comparative example are made into pipes, the steel of the present invention can have excellent low-temperature impact properties (low-temperature impact value not less than 124 J) for the low-temperature impact value of the weld bead, but the pipes of the comparative examples The low temperature impact value of the weld bead is not more than 67 J. Obviously, with the specific composition, production process and parameters, the pipe made from the steel of the present invention can have better low temperature impact properties and better applicability.

Accordingly, the manufacturing method of the present invention can produce steel with better low temperature toughness by lowering the cost of raw materials and matching with specific hot rolling parameters, cooling rate and coiling process, thus meeting application requirements. Among them, the present invention cools the hot-rolled steel with a specific finish rolling temperature and a relatively fast cooling rate, so as to ensure that the crystalline phase structure in the steel is transformed into a ferrite structure and a bleb iron structure, so as to meet the requirements of Requirements for the crystal structure of steel. Further, coiling is carried out at a specific initial temperature of coiling, so that the crystallographic structure in the steel can be uniformly precipitated and formed at the same time, so the prepared steel can have a uniform and fine crystallographic structure, and thus has a better quality. Low temperature toughness.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention pertains can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the appended patent application.

100: Method

110, 120, 130, 140, 150: Operation

In order to have a more complete understanding of the embodiments of the present invention and their advantages, please refer to the following description together with the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustrative purposes only. The contents of the relevant diagrams are described below. FIG. 1 is a flow chart illustrating a method of manufacturing a steel material with low temperature toughness according to some embodiments of the present invention.

Domestic storage information (please note in the order of storage institution, date and number) none Foreign deposit information (please note in the order of deposit country, institution, date and number) none

100: Method

110, 120, 130, 140, 150: Operation

Claims (7)

A steel material with low temperature toughness, comprising: 0.03 to 0.15 weight percent of carbon; 0.1 to 0.8 weight percent of silicon; 1 to 2 weight percent of manganese; not more than 0.05 weight percent of phosphorus; not more than 0.05 Sulfur in weight percent; 0.01 to 0.17 weight percent aluminum; and insignificant impurities and iron in a balanced amount, wherein the steel contains ferrite and bleb iron, and the content of ferrite is not less than 70% %, and the impact value of the steel at -40°C is not less than 150J. The steel with low temperature toughness according to claim 1, further comprising: 0.01 to 0.08 wt% vanadium; 0.01 to 0.08 wt% titanium; 0.01 to 0.08 wt% niobium; 0.05 to 0.05 wt% to 0.5 weight percent molybdenum; and/or no more than 0.05 weight percent calcium. The steel material with low temperature toughness as claimed in claim 1, wherein a grain size of the steel material is no less than No. 8. A method for manufacturing steel with low temperature toughness, comprising: providing a steel blank; performing a hot rolling process on the steel blank to form a finished rolled steel, wherein a finish rolling temperature of the hot rolling process is not lower than the Ar ₃ temperature; performing a cooling process on the finished rolled steel to form a cooling steel, wherein a cooling rate of the cooling process is not less than 10°C/s; and performing a coiling process on the cooled steel at 660°C to 720°C , so as to obtain the steel material with low temperature toughness as described in any one of claims 1 to 5. The method for manufacturing a steel material with low temperature toughness as claimed in claim 4, further comprising: heating the steel billet to not less than 1150° C. before performing the hot rolling process. The manufacturing method of the steel material with low temperature toughness according to claim 4, wherein the cooling rate is 10°C/s to 100°C/s. The method for manufacturing a steel material with low temperature toughness as claimed in claim 4, further comprising: performing a surface processing process on the steel material after performing the coiling process.

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