TW202039880A - Steel with resistance to tempered martensite embrittlement and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a steel with resistance to tempered martensite embrittlement and a method of manufacturing the same. A slab including a specific total amount of niobium, titanium and vanadium is rolled in a finish rolling step at a specific start rolling temperature, so as to obtain the steel with resistance to tempered martensite embrittlement. The steel with resistance to tempered martensite embrittlement has a texture of {112}<110> crystallographic orientation, thereby enhancing its impact absorbed energy and possessing excellent low-temperature impact toughness.

Description

Steel material resistant to temper brittleness of Matian loose iron and its manufacturing method

The present invention relates to a steel material, in particular to a steel material resistant to temper brittleness of loose iron from Matian and its manufacturing method.

Matian loose iron is a kind of microstructure with super high strength, but it is also accompanied by obvious brittleness. Therefore, the tempering step of 150°C to 700°C is often used to change its mechanical properties. According to different tempering temperature, Matian loose iron has different changes in microstructure and mechanical properties. When the matian bulk iron passes through the temper brittleness zone of 250℃ to 400℃, the flaky carbides precipitated at the grain boundary of the matian bulk iron will seriously damage the toughness of the steel, resulting in a substantial increase in the temper brittleness of the matian bulk iron, but a sharp decrease The low temperature impact absorption energy of steel reduces its low temperature impact toughness.

In view of this, there is an urgent need to provide a steel material that resists the temper brittleness of Matian loose iron and its manufacturing method to solve the above problems.

Therefore, one aspect of the present invention is to provide a method for manufacturing a steel material resistant to temper brittleness of Asada scattered iron, which utilizes a steel blank containing a specific sum of niobium, titanium and vanadium, and is refined at a specific starting rolling temperature. Rolling step to produce a steel material with an aggregate structure of {112}<110> crystal orientation that is resistant to temper brittleness of Asada scattered iron.

Another aspect of the present invention is to provide a steel material resistant to temper brittleness of Asada loose iron, which is produced by the above-mentioned manufacturing method, and the steel material resistant to temper brittleness of Asada loose iron has good impact absorption. Maintain excellent low temperature impact toughness.

According to the above aspect of the present invention, a method for manufacturing a steel material resistant to temper brittleness of Asada scattered iron is proposed. First, a hot rolling step is performed on the steel billet to form a hot-rolled steel sheet, wherein the sum of niobium, titanium, and vanadium in the steel billet is 0.01 wt% to 0.10 wt%. Next, the hot-rolled steel sheet is subjected to a finishing rolling step to obtain a finishing-rolled steel sheet, wherein the starting rolling temperature of the finishing rolling step is 850°C to less than 900°C, and the finishing temperature is at least Ar ₃ +50°C, and Ar ₃ Calculated according to formula (I): Ar ₃ =910-310C-80Mn-20Cu-15Cr-55Ni-80Mo+0.35(h-8)......(I)

In the formula (I), C, Mn, Cu, Cr, Ni, and Mo are in weight %, and h is the thickness (mm) of the finished rolled steel sheet. Then, a quenching step is performed on the finished rolled steel sheet to obtain a steel material resistant to temper brittleness of Asada scattered iron, wherein the quenching step is to cool the finished rolled steel sheet at a cooling temperature of Ar ₃ +20°C to Ar ₃ +50°C Treated and resistant to temper brittleness of Asada scattered iron, the steel has an aggregate structure of {112}<110> crystal orientation.

According to an embodiment of the present invention, the hot rolling temperature in the hot rolling step is 1050°C to 1200°C.

According to an embodiment of the present invention, the above-mentioned cooling treatment is performed at a cooling rate of 10° C./s to 50° C./s.

According to an embodiment of the present invention, the complete cooling temperature of the aforementioned cooling treatment is at most 250°C.

According to an embodiment of the present invention, a rolling rate of the above-mentioned finishing rolling step is 50% to 70%.

According to an embodiment of the present invention, the average pole density of the collective structure in the above-mentioned {112}<110> crystal orientation is 4.0 to 6.0.

Another aspect of the present invention provides a steel material resistant to the temper brittleness of Matian loose iron, which is produced by the above-mentioned manufacturing method of the steel material resistant to temper brittleness of Matian loose iron. Among them, the steel with resistance to temper brittleness of scattered iron contains 0.10% to 0.25% by weight of carbon, not more than 0.40% by weight of silicon, 0.7% to 1.5% by weight of manganese, not more than 0.01% by weight of phosphorus, and not more than 0.005 Wt% sulfur, not more than 1.00 wt% chromium, not more than 0.50 wt% molybdenum, 0.01 wt% to 0.10 wt% of the sum of niobium, titanium and vanadium, not more than 1.00 wt% nickel, 0.01 wt% to 0.05 wt% The weight% of aluminum, not more than 0.05 weight% of calcium, not more than 0.01 weight% of nitrogen, and the balance are iron and unavoidable impurities. Among them, the steel material resistant to temper brittleness of Matian scattered iron has an aggregate structure of {112}<110> crystal orientation, and an average pole density of the aggregate structure of this {112}<110> crystal orientation is 4.0 to 6.0, and anti-matian powder iron For tempered brittle steel, the L-direction low-temperature impact absorption energy at -40°C is at least 70J and the T-direction low temperature impact absorption energy is at least 37J.

The steel material with resistance to tempering brittleness of Asada scattered iron and its manufacturing method of the present invention uses a steel billet containing a specific sum of niobium, titanium and vanadium, and performs a finishing rolling step at a specific starting rolling temperature to produce a steel with {112 }<110> The steel material with the aggregate structure of crystal orientation and anti-tempering brittleness of Asada scattered iron can improve the impact absorption energy of the steel, so that the steel has excellent low-temperature impact toughness.

100‧‧‧Method

110‧‧‧The steps of hot rolling the steel billet

120‧‧‧Finish rolling step to obtain the step of finishing rolled steel plate

130‧‧‧The process of quenching the finished rolled steel plate to obtain the steel material with resistance to temper brittleness of scattered iron

401/403/405/407/409/411/413/415/417/419/421/423‧‧‧ points

In order to make the above and other objectives, features, advantages and embodiments of the present invention more comprehensible, the detailed description of the accompanying drawings is as follows

[Fig. 1] is a flow chart showing a method of manufacturing a steel material resistant to temper brittleness of Matian scattered iron according to an embodiment of the present invention.

[Fig. 2] is a SEM photograph showing the microstructure of the tempered steel with anti-tempering brittleness of Asada loose iron according to Example 3 of the present invention.

[Figure 3] is a photograph showing the collective structure of the crystalline azimuth weave of the temper brittleness-resistant steel of Asada scattered iron according to Example 1 of the present invention.

[Figure 4] is a drawing showing the fold line of the impact absorption energy of the tempered and temper brittleness-resistant steel materials of Examples 1 to 4 and 6 to 7 and Comparative Examples 1 to 4 and 6 to 7 of the present invention Figure.

Based on the above, the present invention provides a method for manufacturing a steel material resistant to temper brittleness of Asada scattered iron, which utilizes a specific sum of niobium, titanium and vanadium The steel billet, at a specific starting rolling temperature, is produced with a {112}<110> crystalline orientation of the aggregate structure of the matian loose iron tempering brittleness steel, which can improve the impact absorption of the steel and keep the steel excellent Low temperature impact toughness.

Please refer to FIG. 1, which is a flow chart of a method 100 for manufacturing a steel material with resistance to temper brittleness of Asada scattered iron according to an embodiment of the present invention. First, as shown in step 110 of the method 100, a hot rolling step is performed on the steel blank. In this embodiment, the components of the steel billet include niobium, titanium, and vanadium, and the sum of niobium, titanium, and vanadium is 0.01% to 0.10% by weight. If the sum of niobium, titanium and vanadium is less than 0.01% by weight, the subsequently obtained steel material with resistance to temper brittleness of Asada scattered iron will not be able to form an aggregate structure of {112}<110> crystalline orientation, which will reduce the low-temperature impact absorption energy of the steel . If the sum of niobium, titanium and vanadium is higher than 0.10% by weight, the cost is too high. In other embodiments, the steel blank may optionally contain iron, carbon, nickel, copper, chromium, silicon, zirconium, cobalt, aluminum, manganese, tungsten, molybdenum, calcium, phosphorus, sulfur, nitrogen, and other similar elements. , Inevitable impurities and an alloy composed of any combination of the above components. In one embodiment, the conventional hot rolling temperature can be used for the hot rolling step, but the hot rolling temperature of 1050°C to 1200°C is preferred in the present invention.

Next, as shown in step 120 of the method 100, a finishing rolling step is performed to obtain a finishing rolled steel sheet. The start rolling temperature of the finishing rolling step is 850°C to less than 900°C, and the finishing temperature of the finishing rolling step is at least Ar ₃ +50°C. If the starting rolling temperature is lower than 850°C, the heat dissipation rate of the finished rolled steel sheet will be faster, and the temperature at the finish rolling will not meet the aforementioned finish rolling temperature, thereby reducing the tempering brittleness of the subsequently produced loose iron Low temperature impact absorption of steel. If the start-up rolling temperature is equal to or higher than 900℃, the subsequently obtained anti-Asada scattered iron temper brittleness steel will not be able to form an aggregate structure of {112}<110> crystal orientation, resulting in an inability to increase the Astian scattered iron temper brittleness The toughness of steel.

If the finishing temperature is lower than Ar ₃ +50°C, the microstructure of the finished rolled steel sheet will be changed, and it will not be possible to subsequently obtain a steel with resistance to temper brittleness of Matian scattered iron with a cross section of at least 95%. The aforementioned Ar ₃ is calculated according to the following formula (I): Ar ₃ =910-310C-80Mn-20Cu-15Cr-55Ni-80Mo+0.35(h-8) (I)

In the formula (I), C, Mn, Cu, Cr, Ni, and Mo are in weight %, and h refers to the thickness (mm) of the finished rolled steel sheet.

In one embodiment, the rolling rate of the finishing rolling step is 50% to 70%. If the rolling rate falls outside the aforementioned range value, the subsequently produced steel with resistance to temper brittleness of Asada loose iron cannot meet the requirements of mechanical properties required for application, and the desired form of the present invention cannot be obtained {112} <110> The collective organization of crystal orientation.

Next, as shown in step 130 of the method 100, a quenching step is performed on the finished rolled steel sheet to obtain a steel material resistant to temper brittleness of the loose iron in Matian. The quenching step is to heat the finish-rolled steel sheet to a certain temperature and cool it in water, salt water or oil, etc., to obtain a steel that is resistant to temper brittleness of the scattered iron of Matian. The aforementioned cooling treatment temperature starts from Ar ₃ +20°C to Ar ₃ +50°C. If the cooling temperature is lower than Ar ₃ +20°C, the ferrite phase transformation is likely to occur during the cooling process. If the cooling temperature is higher than Ar ₃ +50°C, the grains of the finished rolled steel sheet will grow and become coarser, which will deteriorate the mechanical properties of the temper brittleness-resistant steel material obtained after the quenching step.

In one embodiment, the cooling treatment is performed at a cooling rate of 10°C/s to 50°C/s. In one embodiment, the complete cooling temperature of the cooling treatment is at most 250°C. Based on the obtained cross-sectional area of the steel with resistance to temper brittleness of Matian scattered iron is 100%, the cross section of the steel with resistance to temper brittleness of Matian scattered iron has at least 95% of Matian scattered iron structure, and its yield strength (Yield Strength, YS ) Is at least 1150 MPa, but 1164 MPa is preferred. The tensile strength (Tensile Strength, TS) is at least 1250 MPa, but 1309 MPa is preferred. The elongation is at least 10%, preferably 10.1%. The Brinell Hardness (BH) measured by a tungsten carbide indenter is 370HBW to 430HBW, but 393HBW is preferred. The low-temperature impact absorption energy of the steel with resistance to temper brittleness of Matian loose iron in the L-direction (Longitudinal direction) at -40°C is at least 70J, but 73J is preferred. Its T-direction (Transverse direction) low-temperature impact absorption energy is at least 37J.

In other embodiments, the tempering brittleness-resistant steel of Matian scattered iron of the present invention can be further subjected to a tempering step at 250°C to 400°C, so that the tempered brittleness-resistant steel of Matian scattered iron has the mechanical properties required for subsequent use . If the tempering temperature is lower than 250°C, the carbides are likely to be precipitated at the grain boundaries of the α phase of the steel that is resistant to temper brittleness of Asada scattered iron, and the original Asada scattered iron has a body-centered tetragonal (BCT) structure. The part will be transformed into body-centered cubic (BCC) fat iron. When the tempering temperature is higher than 250°C, the flake carbides produced by the conventional steel will greatly increase the brittleness of the steel. Although the temper brittleness-resistant steel material of the present invention may also precipitate flaky carbides, the aggregate structure of the {112}<110> crystal orientation can greatly improve the anti-seizure resistance of the present invention. The low-temperature impact toughness of tempered brittle steels. In some other embodiments, the tempering step can be performed at a conventional tempering time, but 1 hour is preferred in the present invention.

The temper brittleness-resistant steel material obtained by the above-mentioned method for manufacturing the steel material against the temper brittleness of the Matian scattered iron is a low-alloy high-strength Matian scattered iron steel material, which has a collection of {112}<110> crystal orientations The average pole density of the aggregated structure in the {112}<110> crystal orientation is 4.0 to 6.0. The aggregate structure of these specific crystal orientations can produce delamination cracks in the temper brittleness-resistant steel of Matian scattered iron, so that the tempered brittleness-resistant steel material of Matian scattered iron can pass through the temper brittleness zone of 250℃ to 400℃. The delamination crack deflects the main cracks generated by the flaky carbides, thereby enhancing the impact absorption energy of the steel, so that the steel has excellent low-temperature impact toughness. However, after the steel of the conventional technology passes through the temper brittle zone of 250°C to 400°C, the flaky carbides precipitated at the boundary of Asada scattered iron will seriously damage the toughness of the steel, and the aggregate structure without specific crystal orientation can be deviated. Folding cracks cause the temper brittleness of Asada loose iron to increase significantly, resulting in poor low-temperature impact toughness.

A steel material with resistance to temper brittleness of Asada scattered iron produced by the above manufacturing method, which contains 0.10% to 0.25% by weight of carbon, not more than 0.40% by weight of silicon, 0.7% to 1.5% by weight of manganese, and not more than 0.01 Wt% of phosphorus, not more than 0.005 wt% of sulfur, not more than 1.00 wt% of chromium, not more than 0.50 wt% of molybdenum, 0.01 wt% to 0.10 wt% of the sum of niobium, titanium and vanadium, not more than 1.00 wt% The amount of nickel, 0.01% to 0.05% by weight of aluminum, not more than 0.05% by weight of calcium, not more than 0.01% by weight of nitrogen, and the remainder are iron and unavoidable impurities. In this example, anti-anaesthesia The tempered brittle steel of Tiansan Iron has an aggregate structure of {112}<110> crystal orientation. The aggregate structure of this {112}<110> crystal orientation has an average pole density of 4.0 to 6.0 and a temperature of -40℃ The temperature has an L-direction low-temperature impact absorption energy of at least 70J and a T-direction low-temperature impact absorption energy of at least 37J.

Several embodiments are used below to illustrate the application of the present invention, but they are not used to limit the present invention. Those with ordinary knowledge in the technical field of the present invention can make various changes and modifications without departing from the spirit and scope of the present invention. Retouch.

Example 1

First, as shown in Table 1, a steel blank containing 0.01% to 0.10% by weight of niobium, titanium, and vanadium is heated to 1050°C to 1200°C to perform a hot rolling step. Next, the rolling of the finishing rolling step is started at a starting temperature of 850°C to below 900°C, and rolling is completed at a finishing temperature of at least Ar ₃ +50°C. Then, perform a quenching step with Ar ₃ +20°C to Ar ₃ +50°C starting cooling temperature, 10°C/s to 50°C/s cooling rate, and up to 250°C complete cooling temperature, to obtain anti-matian powder Iron is tempered and brittle steel. Among them, Ar ₃ is calculated according to the above formula (I), and will not be repeated here.

Next, the temper brittleness-resistant steel material of Matian scattered iron was tempered at a tempering temperature of 250°C for 1 hour to obtain the tempered steel material of Example 1 with the tempered brittleness-resistant Matian scattered iron. After the tempered steel with resistance to temper brittleness of Matian loose iron is cooled, test its low temperature impact absorption energy in T and L directions.

Examples 2 to 7

Examples 2 to 7 used the same manufacturing method as that of Example 1, and performed the same hot rolling step, finish rolling step, and quenching step to obtain tempered steel that is resistant to the temper brittleness of Asada scattered iron. The difference is that the tempering temperatures of Examples 2 to 7 are 300°C, 350°C, 400°C, 450°C, 150°C, and 200°C, respectively.

Comparative example 1

Comparative Example 1 uses the same manufacturing method as Example 1, and performs the same hot rolling step, quenching step, and tempering step to obtain steel. The difference is that the sum of niobium, titanium and vanadium contained in the steel billet of Comparative Example 1 is less than 0.03% by weight, and the start temperature of the finishing rolling step is 900°C to 950°C.

Comparative examples 2 to 7

Comparative Examples 2 to 7 used the same manufacturing method as Comparative Example 1, and performed the same hot rolling step, finish rolling step, and quenching step to obtain steel materials. The difference is that the tempering temperatures of Comparative Examples 2 to 7 are 300°C, 350°C, 400°C, 450°C, 150°C, and 200°C, respectively.

Evaluation method

1. Mechanical properties

The T-direction tensile test was carried out on the untempered steel materials of the untempered Asada scattered iron temper brittleness of Examples 1 to 7 to test their mechanical properties. Among them, the T direction represents the direction perpendicular to the rolling direction of the steel sheet. The results show that the yield strength of the steel materials with resistance to temper brittleness of Asada scattered iron in Examples 1 to 7 is 1164 MPa, the tensile strength is 1309MPa, the elongation is 10.1%, and the Brinell hardness is 393HBW.

2. Microstructure

(1) Grain boundary microstructure

A scanning electron microscope (SEM) was used to observe the microstructure of the temper brittleness-resistant steel of Asada scattered iron in Example 3.

Please refer to FIG. 2, which is a SEM photograph showing the microstructure of the temper brittleness-resistant steel of Matian loose iron tempered according to Example 3 of the present invention. Among them, the scale bar is 5μm.

In Fig. 2, the temper brittleness resistant steel of Asada scattered iron tempered at 350°C of Example 3 has flaky carbides (arrows) precipitated along the grain boundaries, which tends to reduce the low-temperature impact absorption energy . However, although Example 3 has flaky carbides, the low-temperature impact test results show that its L-direction low-temperature impact absorption energy is still higher than 60J (please refer to the point 409 in FIG. 4). Therefore, the aggregate structure of {112}<110> crystal orientation can improve the shock absorption energy of steel.

Secondly, in the tempered and tempered brittleness resistant steel materials of Asada scattered iron of Examples 1 to 7 and the tempered steel materials of Comparative Examples 1 to 7, the grain boundaries of Examples 1 to 7 exhibited a pancake structure , So it has high low-temperature impact absorption, but the grain boundary isometric structure of Comparative Examples 1 to 7, so the tempered steel of Comparative Examples 1 to 7 has higher brittleness.

(2) Collective organization of crystal orientation

The electron backscattered diffraction (EBSD) technique is used to analyze the microstructure and aggregate structure of the untempered anti-Asada scattered iron temper brittle steel.

Please refer to FIG. 3, which is a photograph of the collective structure of the microstructure of the anti-Asada scattered iron temper brittleness steel according to Example 1 of the present invention.

Figure 3 shows the steel material of the present invention that is resistant to temper brittleness of Asada scattered iron and has an aggregate structure of {112}<110> crystal orientations with a pole density of 4.0 to 6.0.

3. Low temperature impact test

(1) Untempered steel

After cooling the unrecovered steel to -40°C, perform the Charpy impact test to measure the low-temperature impact absorption energy of the steel plate. It is processed into the standard test piece size (10mm×10mm×55mm) with V-shaped groove. Next, fix both ends of the test piece on the impact tester. Then, swing the pendulum of the impact tester to impact the test piece. When the test piece is broken, calculate the low-temperature impact absorption energy based on the height difference of the pendulum before and after the impact.

The results show that the L-direction low-temperature impact absorption energy of the non-tempered Matian loose iron temper brittleness-resistant steel materials of Examples 1 to 7 is 73J, and the T-direction low-temperature impact absorption energy is at least 37J. In contrast, the untempered steel materials of Comparative Examples 1 to 7 have an L-direction low-temperature impact absorption energy of 60J.

(2) Tempered steel

After the tempered steel is cooled to -40°C, the Charpy impact test is carried out, and the Charpy impact test uses the same method as the aforementioned low temperature impact test of the untempered steel.

Please refer to FIG. 4, which shows the impact absorption of the tempered and tempered brittleness-resistant steel materials of Examples 1 to 4 and 6 to 7 and Comparative Examples 1 to 4 and 6 to 7 of the present invention Line chart of energy. Among them, the X axis represents the tempering temperature during the tempering step, and the Y axis represents the impact absorption energy.

The results in Fig. 4 show that the L-direction low-temperature impact absorption energy of points 401 and 403 (ie, Examples 6 and 7) and points 405 to 411 (ie, Examples 1 to 4) can be maintained at least 40J. The L-direction low-temperature impact absorption energy of points 413 and 415 (ie, Comparative Examples 6 and 7) and points 417 to 423 (ie, Comparative Examples 1 to 4) is at least 10J.

It can be seen from the above-mentioned embodiments that the steel material resistant to temper brittleness of Asada scattered iron of the present invention has the advantage of using a steel blank containing a specific sum of niobium, titanium and vanadium at a specific starting rolling temperature to produce {112 }<110> The steel with the aggregate structure of the crystal orientation and the anti-tempering brittleness of Asada scattered iron can improve the impact absorption energy of the steel, so that the steel has excellent low-temperature impact toughness.

Although the present invention has been disclosed in several embodiments as above, 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 modifications without departing from the spirit and scope of the present invention. Modifications and modifications, therefore, the scope of protection of the present invention shall be subject to the scope of the attached patent application.

100‧‧‧Method

110‧‧‧The steps of hot rolling the steel billet

120‧‧‧Finish rolling step to obtain the step of finishing rolled steel plate

130‧‧‧The process of quenching the finished rolled steel plate to obtain the steel material with resistance to temper brittleness of scattered iron

Claims (7)

A method for manufacturing a steel material resistant to temper brittleness of scattered iron in Matian, comprising: performing a hot rolling step on a steel blank to form a hot rolled steel sheet, wherein the sum of one of niobium, titanium and vanadium in the steel blank is 0.01% by weight To 0.10% by weight; the hot-rolled steel sheet is subjected to a finishing rolling step to obtain a finishing-rolled steel sheet, wherein one of the finishing steps has a starting rolling temperature of 850°C to less than 900°C, and a finishing temperature of at least Ar ₃ +50°C, and the Ar ₃ is calculated according to formula (I): Ar ₃ =910-310C-80Mn-20Cu-15Cr-55Ni-80Mo+0.35(h-8) (I) in the formula ( In I), the C, the Mn, the Cu, the Cr, the Ni, and the Mo are calculated in weight %, and the h refers to a thickness (mm) of the finished rolled steel sheet; and the finished rolled steel sheet A quenching step is performed to obtain the steel material resistant to temper brittleness of Asada scattered iron, wherein the quenching step is to perform a cooling treatment on the finished rolled steel sheet at a cooling temperature of Ar ₃ +20°C to Ar ₃ +50°C, and The steel with resistance to temper brittleness of scattered iron in Matian has a collective structure of {112}<110> crystal orientation. As described in the first item of the scope of patent application, the method for manufacturing a steel material with resistance to temper brittleness of loose iron from Matian, wherein one of the hot rolling steps has a hot rolling temperature of 1050°C to 1200°C. As described in the first item of the scope of the patent application, the method for manufacturing a steel material with resistance to temper brittleness of scattered iron from Matian, wherein one of the cooling treatments has a cooling rate of 10°C/s to 50°C/s. As described in the first item of the scope of patent application, the method for manufacturing a steel material resistant to temper brittleness of Asada scattered iron, wherein one of the cooling treatments has a cooling temperature of up to 250℃ more. As described in the first item of the scope of the patent application, the method for manufacturing a steel material with resistance to temper brittleness of Asada scattered iron, wherein a rolling rate of the finishing rolling step is 50% to 70%. As described in the first item of the scope of patent application, the average pole density of one of the aggregate structures of the {112}<110> crystal orientation is 4.0 to 6.0 for the method for manufacturing a steel material resistant to temper brittleness of Asada scattered iron. A steel material resistant to temper brittleness of Matian scattered iron, which is prepared by the method for manufacturing a steel material resistant to tempering brittleness of Matian scattered iron described in any one of items 1 to 6 of the scope of patent application, wherein the Iron-tempered brittle steel contains: 0.10 wt% to 0.25 wt% carbon; not more than 0.40 wt% silicon; 0.7 wt% to 1.5 wt% manganese; not more than 0.01 wt% phosphorus; not more than 0.005 wt% Sulfur; not more than 1.00% by weight of chromium; not more than 0.50% by weight of molybdenum; 0.01% to 0.10% by weight of the sum of one of niobium, titanium and vanadium; not more than 1.00% by weight of nickel; 0.01% to 0.05% by weight Aluminum; not more than 0.05% by weight of calcium; not more than 0.01% by weight of nitrogen; and the remainder is iron and unavoidable impurities, and the steel with resistance to temper brittleness of Asada scattered iron has {112}<110> structure An aggregate structure in the crystal orientation, an average pole density of the aggregate structure in the {112}<110> crystal orientation is 4.0 to 6.0, and the temper brittleness-resistant steel of Matian scattered iron is at a low temperature of -40°C in the L direction The impact absorption energy is at least 70J and the one T-direction low temperature impact absorption energy is at least 37J.

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