TWI811081B - Manganese-boron steel and method for manufacturing the same - Google Patents

Abstract

A manganese-boron steel and a method for manufacturing the same, and the manganese-boron steel includes 0.1 wt% to 0.6 wt% carbon, 0.1 wt% to 0.5 wt% silicon, 0.1 wt% to 0.5 wt% chromium, 0.6 wt% to 3.0 wt% manganese, phosphorus with an amount that is not greater than 0.03 wt%, sulfur with an amount that is not greater than 0.005 wt%, 0.01 wt% to 0.07 wt% aluminum, 0.1 wt% to 0.5 wt% titanium, 0.001 wt% to 0.006 wt% boron, balanced amount of iron, and unavoidable impurities. The manganese-boron steel made by the manufacturing method has both high spheroidization rate and high strength.

Description

A kind of manganese boron steel material and its manufacturing method

The invention relates to manganese-boron steel and its manufacturing method, in particular to manganese-boron steel with high spheroidization rate and high strength and its manufacturing method.

Generally speaking, in order to improve the machinability of steel, steel is annealed to make the structure of steel spherical. By adjusting the steel structure before annealing or adjusting the annealing conditions, the spheroidization rate of the steel structure can be improved. If the steel before annealing is cooled at a slower cooling rate during the coiling process, a fine wave iron structure can be obtained. Compared with the steel with coarse wave iron structure, under the same annealing conditions, the spheroidization rate can be significantly improved after annealing the steel with fine wave iron structure. By adjusting the annealing conditions, the spheroidization rate can be increased by increasing the annealing temperature and increasing the annealing time. However, whether the annealing is performed by utilizing the fine wave iron structure or adjusting the annealing temperature and annealing time, although the spheroidization rate of the steel can be increased, the hardness and/or strength of the steel will be reduced.

In view of this, it is urgent to provide a method for manufacturing manganese-boron steel and manganese-boron steel to obtain manganese-boron steel with high nodularity and high strength.

An aspect of the present invention provides a method for manufacturing manganese-boron steel, wherein the manufacturing method can manufacture manganese-boron steel with good mechanical properties.

Another aspect of the present invention is to provide a manganese-boron steel, which is produced by the aforementioned manufacturing method, and the manganese-boron steel has good spheroidization rate and excellent strength.

According to one aspect of the present invention, there is provided a manufacturing method of manganese-boron steel, which includes: performing simulation calculation operations on steel billets to obtain a continuous cooling phase transition curve and a heating phase transition curve; according to the continuous cooling phase transition curve , to determine the ductile iron equilibrium transformation temperature (T _B ) and the wave-iron phase transformation initiation temperature (T _P ) of the steel billet, and determine the wave-to-iron inverse phase transformation initiation temperature of the steel billet according to the temperature rise phase transformation curve (Ac1); performing a hot-rolling process on a billet to obtain a hot-rolled steel product; performing a cooling process on a hot-rolled steel product to obtain a cooled steel product; performing a coiling process on the cooled steel product to obtain a steel coil, wherein the coil of the coiling process The coil temperature is greater than or equal to (T _B -100) °C and less than T _B °C; and an annealing process is performed on the steel coil to obtain manganese-boron steel, wherein the annealing temperature of the annealing process is lower than the initiation temperature of the wavelet iron reverse phase transformation (Ac1).

According to some embodiments of the present invention, the manufacturing method further includes heating the steel billet to 1050° C. to 1250° C. and maintaining the temperature for at least 3 hours before the hot rolling process.

According to some embodiments of the present invention, the finishing temperature of the hot rolling process is 820°C to 920°C.

According to some embodiments of the present invention, the cooling rate of the cooling process is at least 30° C./s.

According to some embodiments of the invention, the metallographic structure of the steel coil comprises at least 20% ductile iron.

According to some embodiments of the invention, the steel coil comprises 20% to 99% ductile iron with a balance of pulexite.

According to some embodiments of the present invention, the annealing temperature is 600°C to 710°C.

According to an aspect of the present invention, a manganese-boron steel material comprises: 0.1 wt% to 0.6 wt% carbon; 0.1 wt% to 0.5 wt% silicon; 0.1 wt% to 0.5 wt% chromium; 0.6 wt% to 3.0 wt% percent manganese; not more than 0.03 weight percent phosphorus; not more than 0.005 weight percent sulfur; 0.01 to 0.07 weight percent aluminum; 0.1 to 0.5 weight percent titanium; 0.001 to 0.006 weight percent boron; A balanced amount of iron; and unavoidable impurities, wherein the yield strength of the manganese-boron steel is at least 380 MPa, and the spheroidization rate of the manganese-boron steel is greater than 90%.

According to some embodiments of the present invention, the titanium-to-nitrogen ratio of the manganese-boron steel is at least 3.4.

According to some embodiments of the present invention, the tensile strength of the manganese-boron steel is at least 500 MPa, and the metallographic structure of the manganese-boron steel includes ferrite and spherical snow-white carbon iron.

Applying the method for manufacturing manganese-boron steel of the present invention and the manganese-boron steel, it is to quickly evaluate the toughening iron equilibrium transformation temperature, the wavelet iron phase transformation initiation by means of the continuous cooling phase transition curve and the heating phase transition curve The temperature and the starting temperature of the wavelet iron reverse phase transformation are used to perform the coiling process and the annealing process according to these temperatures. Therefore, this manufacturing method is beneficial for manufacturing manganese-boron steel with good spheroidization rate and excellent strength. Secondly, by controlling the initial composition of the manganese-boron steel, it is ensured that the manganese-boron steel after coiling and annealing can have suitable processability and mechanical strength.

In order to have a more complete understanding of the embodiments of the present invention and their advantages, please refer to the following descriptions together with the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustration purposes only. The contents of related drawings are explained as follows.

Please refer to FIG. 1 , which is a schematic flow chart illustrating a method 100 for manufacturing manganese-boron steel according to some embodiments of the present disclosure, wherein the billet composition for manufacturing manganese-boron steel includes 0.1% by weight to 0.6% by weight of carbon, 0.1 to 0.5 weight percent of silicon, 0.1 to 0.5 weight percent of chromium, 0.6 to 3.0 weight percent of manganese, no more than 0.03 weight percent of phosphorus, no more than 0.005 weight percent of sulfur, 0.01 weight percent to 0.07% by weight of aluminum, 0.1 to 0.5% by weight of titanium, 0.001 to 0.006% by weight of boron, a balance of iron and unavoidable impurities. In some embodiments, the titanium-to-nitrogen ratio of the steel billet is at least 3.4, so as to further enhance the strength of the steel billet through the affinity between titanium and nitrogen. When the ratio of titanium to nitrogen is not less than 3.4, the nitrogen element is not easy to combine with the boron element, so that the boron element can effectively impart the strengthening effect to the steel billet.

Please refer to FIG. 1 to FIG. 3 at the same time. As shown in operation 110, the simulation calculation operation is performed on the aforementioned steel billet to obtain the continuous cooling phase change curve shown in FIG. 2 and the heating phase change curve shown in FIG. 3 picture. Thereby, as shown in operation 120 , the Pelletic iron transformation initiation temperature T _P , the toughening iron equilibrium transformation temperature T _B , and the Piletic iron reverse transformation initiation temperature Ac1 can be determined. It should be noted that the continuous cooling phase transformation curve 200 shown in FIG. 2 and the steel billet corresponding to FIG. 3 all contain 0.35% by weight of carbon, 0.25% by weight of silicon, 0.15% by weight of chromium, and 1.25% by weight of manganese. , 0.013% by weight of phosphorus, 0.002% by weight of sulfur, 0.025% by weight of aluminum, 0.025% by weight of titanium, 0.0028% by weight of boron, the balance of iron, and unavoidable impurities.

Next, the aforementioned steel billet is heated so that the steel billet can be fully ironized. In some embodiments, the steel billet is heated at a temperature of 1050° C. to 1250° C., so that the steel billet can be fully liquefied without liquefaction. In some embodiments, the temperature for heating the steel billet is not particularly limited, but the preferred heating time is at least 3 hours to ensure that the steel billet is evenly heated.

As shown in operation 130, multiple hot-rolling processes are performed on the uniformly heated steel billet to obtain hot-rolled steel products. In some embodiments, the steel billet will gradually cool down due to air cooling. In some embodiments, water is properly sprinkled on the surface of the steel billet, so as to achieve the purpose of rust removal and cooling. In some embodiments, the temperature of the last hot rolling process (ie, finish rolling temperature) is 820°C to 920°C.

As shown in operation 140, after the hot-rolling process, the hot-rolled steel is subjected to a cooling process, so that the hot-rolled steel is cooled to the coil temperature described later, and the structure of the hot-rolled steel is changed to obtain the cooled steel. In some embodiments, the cooling process can use cooling water to properly reduce the temperature. In some embodiments, the cooling rate of the cooling process is 10° C./s to 100° C./s, preferably at least 30° C./s. When the cooling rate is within the aforementioned range, the steel can be effectively cooled so that the cooled steel can form a ductile iron metallographic structure.

As indicated by operation 150, the cooled steel is coiled to obtain a steel coil. Please refer to Figure 2. At a fixed cooling rate, the temperature intersecting with the onset of ductile iron transformation (slanted squares) is the onset temperature of the ductile iron transformation. The temperature at which the curves (reticulated line squares) intersect is the Pile-iron phase transition initiation temperature T _P . In addition, according to Fig. 2, it can be known that when the cooling rate is infinitely slow, the corresponding equilibrium transformation temperature (T _B ) of toughened iron is about 577°C, and the equilibrium transformation temperature of Pile iron is about 717°C. In order to make the obtained steel coil have a large amount of ductile iron structure and a small amount of fine wave iron structure, and can continuously produce manganese boron steel with high spheroidization rate and high strength, the coil temperature is greater than or equal to (T _B -100)°C and less than T _B °C. If the coiling temperature is lower than (T _B -100) °C, the resulting metallographic structure contains too much mosaic iron, which cannot effectively meet the needs of subsequent processing. If the coiling temperature is not lower than _TB , the formed metallographic structure contains too much pletic iron, and a large amount of dislocation cannot be effectively obtained, so a high-strength steel coil cannot be obtained. In some embodiments, depending on the cooling rate, the coil temperature can be greater than or equal to 477°C and less than 577°C. In some embodiments, the metallographic structure of the steel coil comprises at least 20% ductile ferrite. In some embodiments, the steel coil comprises 20% to 99% ductile iron structure with a balance of fine wave iron.

As shown in operation 160, a low-temperature annealing process is performed on the steel coil to obtain a manganese-boron steel material with a spheroidized structure. The annealing temperature of the annealing process is lower than the initiation temperature Ac1 of the reverse wavelet iron transformation. Please refer to Fig. 3, when the heating rate is 1°C/s, the initiation temperature Ac1 of the reverse phase transformation of Pellet iron is 727°C. It can be understood that in the above-mentioned Fig. 2, the temperature at which the cooling rate intersects with the wave iron transformation initiation curve is transformed into wave iron structure by the cooling phase transformation of Worth field iron structure, so the obtained wave iron transformation starts The initial temperature T _P will be lower than the wave iron equilibrium transformation temperature; while in Fig. 3, the wave iron structure is reversed to the wast iron structure during the heating process, so the wave iron reverse phase transformation initial temperature Ac1 is higher than the wave iron structure to iron equilibrium metamorphosis temperature.

Since the above-mentioned steel coil has a specific content of ductile iron structure, the temperature rise of low-temperature annealing is carried out at a specific heating rate, and the manganese-boron steel after low-temperature annealing at a specific temperature corresponding to the heating rate can still retain the ductile iron structure. The difference arrangement, so that the manganese-boron steel with spheroidized structure after annealing can have both good strength and machinability. If the annealing temperature is not lower than (that is, higher than or equal to) the initial temperature Ac1 of the inverse phase transformation of Polei iron, the metallographic structure in the steel coil is prone to inverse transformation, so that the metallographic structure is transformed into Voss field iron, and at Pletic iron is formed during cooling, which makes it impossible to meet the application requirements of high nodularization rate and high strength. Understandably, in order to ensure better spheroidizing effect of the steel, the annealing temperature should not be lower than 600°C. In some specific examples, the annealing temperature in this application may be 600°C to 710°C, preferably 650°C. Compared with the conventional technology, the annealing temperature generally used to increase the spheroidization rate is higher than 720°C. Accordingly, the annealing temperature in this case is lower than the annealing temperature in the general prior art. In some embodiments, the annealing time is controlled within 10 hours to 24 hours. When the annealing time of the annealing process is within the above-mentioned range, the carbides in the steel coil have enough time to fully diffuse, and the effect of spheroidization can be achieved, and the carbides in the steel coil can grow moderately to improve the strength of the manganese-boron steel. . In some embodiments, after the annealing process, the tensile strength of the manganese-boron steel is at least 500 MPa, and the metallographic structure of the manganese-boron steel includes ferrite and nodular snowy carbon iron.

Please refer to FIG. 4A and FIG. 4B , which respectively show micrographs of the metallographic structure of the manganese-boron steel material before and after the annealing process according to some embodiments. Figure 4A shows that the metallographic structure before annealing contains a large amount of ductile iron and a small amount of fine wave iron, and Figure 4B shows that there are spheroidized carbides in the metallographic structure after low temperature annealing.

The application examples below are used to illustrate the application of the present invention, but they are not intended to limit the present invention. Anyone skilled in this art can make various changes and modifications without departing from the spirit and scope of the present invention.

Example 1

In Example 1, the steel billet is simulated and calculated first to obtain the continuous cooling phase transition curve and the heating phase transition curve, wherein the composition of the steel billet includes 0.1% by weight to 0.6% by weight of carbon, 0.1% by weight to 0.5% by weight Silicon by weight, chromium from 0.1 to 0.5 percent by weight, manganese from 0.6 to 3.0 percent by weight, phosphorus not greater than 0.03 percent by weight, sulfur not greater than 0.005 percent by weight, aluminum from 0.01 to 0.07 percent by weight , 0.1% to 0.5% by weight of titanium, 0.001 to 0.006% by weight of boron, a balance of iron and unavoidable impurities, and the ratio of titanium to nitrogen of the steel billet is at least 3.4. According to the continuous cooling phase transition curve and the heating phase transition curve, the equilibrium transformation temperature of Pellet iron is 717°C, the equilibrium transformation temperature (T _B ) of toughening iron is 577°C and the onset temperature of the reverse phase transformation of Pleixon iron Ac1, and according to the subsequent cooling rate, the onset temperature T _P of the Pleitic phase transformation can be obtained. Next, the steel billet is heated at a temperature of 1050° C. to 1250° C. to fully ironize the steel billet. Next, the heated steel billet is subjected to a hot rolling process to obtain hot rolled steel products. In the hot rolling process, the temperature for finishing rolling is 820°C to 920°C. After the hot rolling process is completed, cooling is performed at a cooling rate of at least 30° C./s to obtain a cooled steel product. Wherein, according to the cooling rate of at least 30°C/s, and the above-mentioned continuous cooling phase transition curve and heating phase transition curve, the initial temperature Ac1 of the inverse phase transition of Pellet iron can be obtained. Next, in order to make the obtained steel coil have a large amount of ductile iron structure and a small amount of fine wavelite structure, manganese-boron steel with high spheroidization rate and high strength can be successively produced. As shown in Table 1, at 570 The cooled steel is coiled at ℃ to obtain a steel coil, wherein the steel coil has a large amount of ductile iron structure and a small amount of fine wave iron structure. Next, the steel coil is annealed at 650° C. to obtain a manganese-boron steel material with a spheroidized structure. As shown in Table 2, the spheroidization rate of the manganese-boron steel can be increased from 0% to 90% after annealing, and it also has good mechanical properties with a yield strength of 431 MPa and a tensile strength of 613 MPa. Among them, the detection methods of nodularization rate, yield strength and tensile strength are respectively measured by instruments and methods well-known to those with ordinary knowledge, so no further description is given.

Example 2 to Example 3

Embodiment 2 to Embodiment 3 use the same manufacturing method as the manganese-boron steel material of Embodiment 1, the difference is that the annealing temperature during the annealing process is changed in Embodiment 2 to Embodiment 3. The annealing temperatures of Examples 2 to 3, and mechanical properties such as spheroidization rate, yield strength, and tensile strength are shown in Table 2, and will not be repeated here.

Comparative Example 1 to Comparative Example 3

Comparative Example 1 to Comparative Example 3 use a manufacturing method similar to that of Example 1, the difference is that Comparative Example 1 to Comparative Example 3 respectively change the coiling temperature during the coiling process, and carry out with different annealing temperatures The annealing process, coiling temperature and annealing temperature, as well as the mechanical properties of the steel produced in Comparative Example 1 to Comparative Example 3 are shown in Table 1 and Table 2 respectively, so they will not be repeated here.

In Example 1 to Example 3, when the coiling temperature is greater than or equal to (T _B -100) ° C and less than T _B ° C (T _B is about 577 ° C), the metallographic structure after coiling has A large amount of toughened iron and a small amount of fine wave iron, and after the low-temperature annealing process is performed at an annealing temperature lower than the initial temperature Ac1 (about 727°C) of the reverse phase transformation of wave iron, the manganese-boron steel produced can have both High spheroidization rate and high strength mechanical properties.

In Comparative Example 1 to Comparative Example 3, since the coiling temperature is higher than the equilibrium transformation temperature of ductile iron, the metallographic structure of the formed steel mainly includes ferrite and fine wave iron. When the annealing process is continued, the spheroidization rate cannot be effectively improved, and the manganese-boron steel produced does not have good yield strength and tensile strength, so it cannot meet the application requirements.

Accordingly, through the above-mentioned manufacturing method of manganese-boron steel, it is possible to quickly evaluate the toughening-iron equilibrium transformation temperature, the wavelet iron transformation initiation temperature and The starting temperature of the reverse phase transformation of the wavelet iron is used to carry out the coiling process and the annealing process according to these temperatures, so that a manganese-boron steel with good spheroidization rate and excellent strength can be obtained.

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

100: method 110, 120, 130, 140, 150, 160: Operation 200: figure

In order to have a more complete understanding of the embodiments of the present invention and their advantages, please refer to the following descriptions together with the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustration purposes only. The contents of related drawings are explained as follows. FIG. 1 is a schematic flowchart illustrating a method for manufacturing manganese-boron steel according to some embodiments of the present invention. FIG. 2 is a diagram showing the phase transformation curve of manganese-boron steel according to some embodiments of the present invention during continuous cooling. FIG. 3 is a graph showing the temperature-rising phase transformation curve of manganese-boron steel according to some embodiments of the present invention. 4A and 4B are micrographs showing the metallographic structure of the manganese-boron steel before and after the annealing process according to some embodiments.

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

100: method

110, 120, 130, 140, 150, 160: Operation

Claims (10)

A method for manufacturing manganese-boron steel, comprising: performing a simulation calculation operation on a steel billet to obtain a continuous cooling phase transition curve and a heating phase transition curve; determining the steel billet according to the continuous cooling phase transition curve One toughening iron equilibrium transformation temperature (T _B ) and one wave iron phase transformation initiation temperature (T _P ), and according to the temperature rise phase transformation curve, determine the one wave iron reverse phase transformation initiation of the billet Temperature (Ac1); Carrying out a hot rolling process to the billet to obtain a hot-rolled steel; Carrying out a cooling process to the hot-rolled steel to obtain a cooled steel; Carrying out a coiling process to the cooled steel to obtain A steel coil, wherein a coil temperature of the coiling process is greater than or equal to (T _B -100) °C and less than T _B °C; and an annealing process is performed on the steel coil to obtain the manganese boron steel material, wherein the One of the annealing temperatures in the annealing process is lower than the initiation temperature (Ac1) of the reverse wavelet iron phase transition. The manufacturing method as claimed in claim 1, further comprising heating the steel billet to 1050° C. to 1250° C. and maintaining the temperature for at least 3 hours before the hot rolling process. The manufacturing method as claimed in claim 1, wherein a finishing temperature of the hot rolling process is 820°C to 920°C. The manufacturing method according to claim 1, wherein a cooling rate of the cooling process is at least 30° C./s. The manufacturing method as claimed in claim 1, wherein a metallographic structure of the steel coil includes at least 20% ductile iron. The manufacturing method as described in claim 5, wherein the steel coil contains 20% to 99% ductile iron and a balance amount of wave iron. The manufacturing method according to claim 1, wherein the annealing temperature is 600°C to 710°C. A manganese-boron steel material, comprising: 0.1 weight percent to 0.6 weight percent carbon; 0.1% by weight to 0.5% by weight of silicon; 0.1% by weight to 0.5% by weight of chromium; 0.6 weight percent to 3.0 weight percent manganese; Phosphorus not greater than 0.03% by weight; Sulfur not greater than 0.005% by weight; 0.01% by weight to 0.07% by weight of aluminum; 0.1% by weight to 0.5% by weight of titanium; 0.001 weight percent to 0.006 weight percent boron; a balanced amount of iron; and unavoidable impurities, and Wherein the yield strength of the manganese-boron steel is at least 380 MPa, and the nodularization rate of the manganese-boron steel is greater than 90%. The manganese-boron steel as claimed in claim 8, wherein the ratio of titanium to nitrogen of the manganese-boron steel is at least 3.4. The manganese-boron steel as claimed in claim 8, wherein a tensile strength of the manganese-boron steel is at least 500 MPa, and a metallographic structure of the manganese-boron steel includes ferrite and spherical snow-white carbon iron.