JP2011038181A - Method for producing rem-containing steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a REM-containing steel castable without causing a nozzle blockade. <P>SOLUTION: In the method for producing the REM-containing steel composed, by mass%, of 0.01-0.15% C, ≤1.2% (no containing 0%) Si, ≤3.8% (not including 0%) Mn, ≤0.03% (no containing 0%) P, ≤0.03% (no containing 0%) S, ≤0.01% (no containing 0%) N, ≤0.2% (no containing 0%) Ti and 0.0003-0.05% REM and the balance with inevitable impurities; a dissolved oxygen quantity Q<SB>Of</SB>in the molten steel before adding the REM, is adjusted in the range of 0.0001-0.015 and thereafter, when the REM additional quantity Q<SB>REM</SB>, is aqdded so as to satisfy the following formula (1): 2logQ<SB>REM</SB>+3logQ<SB>Of</SB>≤-11, and melted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a REM-containing steel containing a rare earth element (REM).

  REM is an element useful for improving the toughness of the weld heat affected zone (HAZ portion) in welded structures such as bridges, high-rise buildings, and ships, and for reducing spatter during welding. Therefore, the REM-containing steel is suitably used for welded structural steel and welding materials. For example, in Patent Documents 1 to 3, a technology in which HAZ toughness is increased by adding REM to mechanical structural steel used for a welded structure and generating a REM-containing oxide to refine the structure of the HAZ part. Has been proposed. Patent Documents 4 and 5 propose a method of reducing spatter generation by adding REM to a welding material such as a welding wire.

  By the way, in Patent Documents 6 and 7, if a Ti-based oxide in an amount effective for the structure control of the base material and the HAZ part is present in the REM-containing steel, Nords clogging is likely to occur when casting molten steel, It has been pointed out that the quality deteriorates.

JP 2002-363687 A JP 2003-221463 A JP 2003-286540 A JP 2003-225792 A Japanese Patent Laid-Open No. 2005-46878 Japanese Patent Laid-Open No. 2001-20031 Japanese Patent Laid-Open No. 2001-20033

  In the above Patent Documents 1 to 5, when producing REM-containing steel useful for machine structural steels and welding materials, no attention has been paid to the problem that nozzle clogging occurs at the time of casting and productivity is lowered. . On the other hand, Patent Documents 6 and 7 describe the relationship between the Ti-based oxide and the nozzle clogging, but did not pay attention to the relationship between the REM-containing oxide and the Nord clogging.

  The present invention has been made paying attention to the above circumstances, and an object of the present invention is to provide a method for producing REM-containing steel that can be cast without causing nozzle clogging.

The manufacturing method of the REM-containing steel according to the present invention that can solve the above-mentioned problems is: C: 0.01 to 0.15% (meaning mass%; the same applies to the following components), Si: 1.2% Or less (excluding 0%), Mn: 3.8% or less (not including 0%), P: 0.03% or less (not including 0%), S: 0.03% or less (0% N: 0.01% or less (not including 0%), Ti: 0.2% or less (not including 0%), and REM: 0.0003 to 0.05%, the balance being This is a method for producing a REM-containing steel made of iron and inevitable impurities, in which the amount of dissolved oxygen Q _Of in the molten steel before REM addition is adjusted to a range of 0.0001 to 0.015%, and then REM is added. Is the amount of _{REM in} which the dissolved oxygen amount Q _Of and the REM addition amount Q _REM satisfy the following formula (1): It has a gist in that it is added and melted.
2logQ _REM + 3logQ _Of ≦ -11 (1)

The REM-containing steel is still another element,
[1] A group consisting of Zr: 0.1% or less (not including 0%), Al: 0.1% or less (not including 0%), Ca: 0.01% or less (not including 0%) At least one selected from
[2] Cu: 2% or less (not including 0%) and / or Ni: 12% or less (not including 0%),
[3] Cr: 3% or less (not including 0%) and / or Mo: 1% or less (not including 0%),
[4] Nb: 0.25% or less (not including 0%) and / or V: 0.1% or less (not including 0%),
[5] B: 0.005% or less (excluding 0%),
It is also effective to contain such elements.

According to the present invention, when melting REM-added molten steel, the dissolved oxygen amount Q _Of in the molten steel before REM addition is adjusted to a predetermined range, and an appropriate REM added amount Q _REM according to the dissolved oxygen amount Q _Of is adjusted. REM-containing oxides that cause nozzle clogging can be reduced because of the addition of smelting, and operational troubles due to nozzle clogging during casting (decrease in the amount of molten steel produced, deterioration in productivity, etc.) are avoided. it can.

FIG. 1 is a graph showing a change in the amount of steel output (kg) with respect to the elapsed time (seconds) after the start of steel output. FIG. 2 is a graph showing the relationship between the dissolved oxygen amount Q _Of and the REM addition amount Q _REM of the molten steel before REM addition. FIG. 3 is a graph showing the relationship between the value (Z value) on the left side of equation (1) and the amount of steel output (kg).

The inventors of the present invention have repeatedly studied from the viewpoint that the main cause of nozzle clogging during casting of REM-containing steel is the REM-containing oxide. As described above, the REM-containing oxide is useful for improving HAZ toughness such as steel for machine structural use, but has a high melting point, and since it exists as a solid rather than a liquid in the molten steel, it easily adheres to the inner wall of the nozzle. The inner diameter of the nozzle is gradually narrowed and finally the nozzle is closed, resulting in problems such as a decrease in the amount of molten steel and a decrease in productivity. Therefore, if the dissolved oxygen amount Q _Of contained in the molten steel before REM addition is appropriately controlled and the REM addition amount Q _REM is appropriately controlled according to the dissolved oxygen amount Q _Of and melted, the nozzle clogging at the time of casting will be blocked. As a result, the present invention has been completed.

  In the present invention, the nozzle clogging means clogging (clogging) of a ladle nozzle or immersion nozzle used at the time of casting or an injection pipe used at the time of ingot making. Below, although the clogging of a ladle nozzle is mentioned as an example and demonstrated, it is not the meaning limited to this.

  Hereinafter, the production method of the present invention will be specifically described.

The method for producing REM-containing steel according to the present invention is characterized by a melting process, specifically,
[A] Adding REM after adjusting the amount of dissolved oxygen Q _Of contained in the molten steel before adding REM to the range of 0.0001 to 0.015%;
[B] The addition of REM is characterized in that the dissolved oxygen amount Q _Of and the REM addition amount Q _REM are controlled so as to satisfy the following expression (1).
2logQ _REM + 3logQ _Of ≦ -11 (1)

[A] Dissolved oxygen amount Q _Of : 0.0001 to 0.015% The dissolved oxygen amount Q _Of of the molten steel before REM addition is in the range of 0.0001 to 0.015%. The range of the dissolved oxygen amount Q _Of is set mainly for effectively exhibiting the HAZ toughness improving effect by the addition of REM. If the dissolved oxygen amount Q _Of is less than 0.0001%, the dissolved oxygen amount Q _Of is insufficient, and a fine REM-containing oxide useful for improving HAZ toughness cannot be obtained sufficiently. In addition, when the dissolved oxygen amount Q _Of is insufficient, REM that does not bond with oxygen combines with S to form REM sulfide, or Ca or Zr added as an optional element forms Ca sulfide or Zr carbide. Cause deterioration of the toughness of the steel material itself. Therefore, the dissolved oxygen amount Q _Of is set to 0.0001% or more, preferably 0.001% or more, more preferably 0.0015% or more. On the other hand, when the amount of dissolved oxygen Q _Of exceeds 0.015%, the amount of dissolved oxygen is too large, so when REM is added, the reaction between REM and oxygen becomes intense, which is not preferable for melting work. A coarse REM-containing oxide is generated in the nozzle, causing nozzle clogging. Therefore, the amount of dissolved oxygen Q _Of is suppressed to 0.015% or less, preferably 0.01% or less, more preferably 0.008% or less.

In the present invention, dissolved oxygen means free oxygen that does not form an oxide and exists in the molten steel. The dissolved oxygen amount Q _Of of the molten steel before REM addition may be measured by a general electromotive force measurement method using a solid electrolyte.

[B] Formula (1) In the present invention, the range of the dissolved oxygen amount Q _Of of the molten steel before REM addition is appropriately controlled as in the above [A]. It is necessary to control the dissolved oxygen amount Q _Of while paying attention to satisfy the equation. This formula (1) is a formula set based on the viewpoint that “the generation of coarse REM-containing oxides should be reduced in order to prevent nozzle clogging during REM-added molten steel casting”. Specifically, based on the above viewpoint, “REM” (REM addition amount Q _REM in the above formula (1)) constituting the REM oxide generation reaction formula (see the following formula (2)) in molten steel and “ “O (oxygen)” (dissolved oxygen amount Q _Of in the above equation (1)) is used as an index, and the dissolved oxygen amount Q _Of and the REM addition amount Q _REM with respect to the dissolved oxygen amount Q _Of are obtained through a ladle nozzle. It was set based on a basic experiment in which the effect on the amount of molten steel (the amount of steel output) when steel was discharged from a mold was examined. As shown in FIG. 3 to be described later, when the value on the left side of the above equation (1) is the Z value, the amount of steel output changes greatly with the Z value at -11 as a boundary so that the Z value becomes -11 or less. If the dissolved oxygen amount Q _Of and the REM addition amount Q _REM are adjusted, it has been found that the molten steel can be discharged from the ladle nozzle without causing nozzle clogging, and the above equation (1) is determined. The respective coefficients (the coefficient 2 of “logQ _REM ” and the coefficient 3 of “logQ _Of ”) on the left side of the above equation (1) are represented by the following equation (2): REM oxide generation reaction formula in molten steel (Coefficient 2 of “REM” and coefficient 3 of “O”).
2REM + 3O = REM ₂ O ₃ (2)

That is, in the above equation (1), the Z value should be a reference value for preventing nozzle blockage. In the present invention, the amount of dissolved oxygen Q _Of and the amount of added REM Q _REM satisfy the above equation (1) means that the minimum amount of dissolved oxygen necessary for the production of fine REM-containing oxides that contribute to the improvement of HAZ toughness It means that the REM addition amount Q _REM is added as little as possible for each dissolved oxygen amount Q _Of so that a coarse REM-containing oxide that adversely affects nozzle clogging is not generated with Q _Of secured. . According to the present invention, fine REM-containing oxide is sufficiently generated, but generation of coarse REM-containing oxide is suppressed, so that it is considered that nozzle clogging during casting can be prevented.

When the Z value exceeds -11, the balance between the dissolved oxygen amount Q _Of and the REM added amount Q _REM becomes poor, and the REM added amount Q _REM increases with respect to the dissolved oxygen amount Q _Of , resulting in a coarse REM-containing oxide. And nozzle clogging is likely to occur. Therefore, the Z value is set to -11 or less. The smaller the Z value, the better, preferably -12 or less, more preferably -13 or less, and still more preferably -14 or less. The lower limit of the Z value is not particularly limited, but in consideration of the amount of REM in steel and the like, it is preferably about -15.

The REM addition amount Q _REM is appropriately determined according to the dissolved oxygen amount Q _Of based on the above formula (1), but the range of the REM addition amount Q _REM is generally in the REM-containing steel as the final product. It is set larger than the amount of REM included. This is because the REM added to the molten steel before casting is difficult to get in the steel material because it volatilizes in the casting process or is dispersed in the slag, so compared to the REM addition amount Q _REM contained in the REM added molten steel. This is because the amount of REM contained in the REM-containing steel is reduced. The method of the present invention is suitably used to produce a REM-containing steel containing 0.0003 to 0.05% REM, as described in detail below. REM addition amount Q _REM at the time of melting may be appropriately controlled so as to ensure the above.

  The outline of the melting process characterizing the present invention is as described above, but a more specific method will be described according to the melting procedure.

First, in the present invention, the dissolved oxygen amount Q _Of of the molten steel before REM primary refined in a converter, electric furnace, or the like is adjusted to the range of 0.0001 to 0.015% as necessary. Since the dissolved oxygen amount Q _Of in the primary refined molten steel usually exceeds 0.01%, the dissolved oxygen amount Q _Of in the molten steel is in the range of more than 0.01% to 0.015%. Although it can be used as it is without special adjustment, if it exceeds 0.015%, it is necessary to separately adjust the dissolved oxygen amount Q _Of .

Examples of the method for adjusting the dissolved oxygen amount Q _Of in this case include a method of vacuum deoxidation using an RH type degassing refining device, a method of adding a deacidifying element such as Si, Mn, Ti, Al, and the like. The dissolved oxygen amount Q _Of may be adjusted by appropriately combining these methods. Further, instead of the RH type degassing device, by using a ladle heating refining apparatus and a simple type molten steel processing facility may adjust the above dissolved oxygen content Q _Of. In this case, since the amount of dissolved oxygen Q _Of cannot be adjusted by vacuum deoxidation, a method of adding a deacidifying element such as Si may be adopted to adjust the amount of dissolved oxygen Q _Of . When employing a method of adding a deoxidizing element such as Si, for example, the deoxidizing element may be added when steel is removed from the converter to the ladle.

Next, in the present invention, the dissolved oxygen content Q _Of the REM added before the molten steel as described above, adjust the above-mentioned range, cast by the addition of REM. In the present invention, it is important that the relationship between the dissolved oxygen amount Q _{Of of the} molten steel before REM addition and the REM addition amount Q _REM satisfies the relationship of the above formula (1), and the constituent elements other than REM (Ti, Zr) , Ca, etc.) are not particularly limited in the order of addition. Since REM is an extremely active element and is very easy to bind to oxygen compared to other component elements, the REM addition amount Q _REM that is largely involved in the generation of coarse REM-containing oxides that cause nozzle clogging. Special attention should be paid as in the above formula (1), but the reactivity between component elements other than REM and oxygen is inferior to that of REM, and therefore the influence of the component elements is less than that of REM. It is. That is, as long as the above equation (1) is controlled, nozzle blockage during casting can be prevented regardless of the order of addition of component elements other than REM.

However, in producing the REM-containing steel of the present invention, it is preferable to add Ti before adding REM to the molten steel. Since Ti oxide has lower interfacial energy with molten steel than REM-containing oxide, adding Ti to REM after adding REM to molten steel with adjusted dissolved oxygen content Q _Of produces coarse Ti oxide. On the other hand, Ti oxide can be refined by adding Ti before REM addition, and as a result, a fine oxide that contributes to HAZ toughness can be generated. Thereafter, REM (Zr or Ca if necessary) is added to obtain a REM-containing oxide that becomes a nucleus of intragranular ferrite transformation and contributes to improvement of HAZ toughness.

Even when REM is added after adding Ti as described above, the REM addition amount Q _REM satisfies the above equation (1) according to the dissolved oxygen amount Q _Of of the molten steel before REM addition. Is added, the formation of coarse oxides containing REM is suppressed, so that nozzle clogging can be effectively prevented. That is, even in the above case, it is not necessary to consider the amount of Ti added to prevent nozzle clogging. If Ti is added prior to REM, dissolved oxygen in the molten steel combines with Ti to form an oxide, so the amount of dissolved oxygen combined with REM decreases, but Ti is less likely to bond with oxygen than REM. And since Ti oxide has low interface energy with molten steel, it is hard to form a coarse oxide compared with REM, and it is hard to become the cause of nozzle blockage.

  The form of REM, Ca, Zr, and Ti added to the molten steel is not particularly limited. For example, as REM, pure La, pure Ce, pure Y, or pure Ca, pure Zr, pure Ti, and further Fe-Si- Add La alloy, Fe-Si-Ce alloy, Fe-Si-Ca alloy, Fe-Si-La-Ce alloy, Fe-Ca alloy, Ni-Ca alloy, Fe-Zr alloy, Fe-Ti alloy, etc. Good. REM may be added in the form of misch metal. Misch metal is a mixture of cerium group rare earth elements, and specifically contains about 40 to 50% of Ce and about 20 to 40% of La. However, since misch metal often contains Ca as an impurity, when the misch metal contains Ca, it is preferable to adjust the Ca amount to be contained in the steel material in consideration of this Ca amount.

The REM-added molten steel thus produced may be continuously cast according to a conventional method to form a slab, and then hot-rolled (cold rolled as necessary) according to a conventional method to produce a REM-containing steel. . The REM-containing steel of the present invention obtained by the above melting method is not particularly limited as long as it contains REM. However, when it is desired to effectively exhibit the HAZ toughness improving effect and the spatter generation reducing effect by adding REM, The composition of the steel is preferably controlled as follows. Below, the composition of the REM containing steel used suitably when the case where it applies to a welding structure, a welding material, etc. is assumed is described. What is necessary is just to use what was adjusted so that the composition of the said steel might be obtained for such molten steel for REM containing steel.
C: 0.01 to 0.15%
Si: 1.2% or less (excluding 0%)
Mn: 3.8% or less (excluding 0%)
P: 0.03% or less (excluding 0%)
S: 0.03% or less (excluding 0%)
N: 0.01% or less (excluding 0%)
Ti: 0.2% or less (excluding 0%)
REM: 0.0003 to 0.05%
Hereinafter, each component will be described in detail.

  C is an element indispensable for ensuring the strength of the steel material (base material) and the hardenability of the welded portion, and needs to be contained in an amount of 0.01% or more. The amount of C is preferably 0.02% or more, more preferably 0.03% or more. However, if the amount of C exceeds 0.15%, a large amount of island martensite (MA) is generated in the HAZ at the time of welding, leading to a deterioration in the toughness of the HAZ, and also adversely affecting the weldability. Therefore, the C content is 0.15% or less, preferably 0.1% or less, more preferably 0.08% or less.

  Si is an element that has a deoxidizing action and contributes to improving the strength of the steel (base material) by solid solution strengthening. Si is an element that acts to ensure the ductility of the weld. In order to exhibit such an action effectively, Si is preferably contained in an amount of 0.01% or more. Si is more preferably 0.02% or more, further preferably 0.05% or more, and particularly preferably 0.1% or more.

  However, when the amount of Si exceeds 1.2%, when the REM-containing steel is used as a welding material, hot cracking occurs in the first layer weld. Therefore, the Si content is 1.2% or less, preferably 1% or less, more preferably 0.8% or less. Moreover, when using the said REM containing steel as steel materials used for a bridge, a high-rise building, a ship, etc., in order to improve the weldability and HAZ toughness of steel materials, Si amount may be 0.3% or less. Recommended, preferably 0.2% or less, more preferably 0.1% or less, particularly preferably 0.05% or less. Although the HAZ toughness is improved as the amount of Si is suppressed, the strength of the steel material may be reduced.

  Mn is an element that contributes to improving the strength of the steel material (base material). In order to exhibit such an effect effectively, it is good to contain 0.4% or more, preferably 0.8% or more, more preferably 1% or more. However, if the amount of Mn exceeds 3.8%, the weldability of the steel (base material) is deteriorated and the toughness of the welded portion is reduced. Therefore, the amount of Mn needs to be suppressed to 3.8% or less, preferably 3% or less. In particular, when the above REM-containing steel material is used as a steel material used for bridges, high-rise buildings, ships, etc., the Mn content is 2.5% or less, preferably 2% or less, more preferably 1.8% or less. It is good to suppress.

  P is an element that is easily segregated, and in particular, is an element that segregates at a grain boundary in a steel material and deteriorates toughness. Therefore, the P amount needs to be suppressed to 0.03% or less. The amount of P is preferably 0.02% or less, more preferably 0.015% or less. In general, P is unavoidably contained in an amount of about 0.001%.

  S is a harmful element that combines with Mn to produce sulfide (MnS) and degrades the toughness of the base material and the ductility in the thickness direction. In addition, when S is combined with REM such as La or Ce to generate REM sulfide (for example, LaS or CeS), generation of REM-containing oxide is suppressed, so that occurrence of nozzle clogging is suppressed. However, since the production of fine REM-containing oxides that contribute to the improvement of HAZ toughness is also inhibited, a useful REM-containing steel cannot be obtained. Therefore, the S amount needs to be suppressed to 0.03% or less. The amount of S is preferably 0.02% or less, more preferably 0.015% or less, still more preferably 0.01% or less, and particularly preferably 0.006% or less. Note that S is usually unavoidably contained in an amount of about 0.0005%.

  N is an element that precipitates nitrides (for example, ZrN and TiN), and the nitrides prevent the austenite grains formed in the HAZ during welding from being pinned and prevent intragranular ferrite transformation. And contribute to the improvement of HAZ toughness. In order to effectively exhibit such an effect, N is preferably contained in an amount of 0.003% or more. The amount of N is more preferably 0.004% or more, and still more preferably 0.005% or more. The more N, the more nitrides are formed to promote the refinement of austenite grains and effectively act to improve the toughness of HAZ. However, if the N content exceeds 0.01%, the solid solution N content increases and the toughness of the base metal itself deteriorates. Therefore, the N amount needs to be suppressed to 0.01% or less. The N amount is preferably 0.009% or less, more preferably 0.008% or less.

  Ti is an element that contributes to refinement of the steel material structure by generating nitrides and oxides in the steel material, and effectively acts to improve the HAZ toughness and to suppress hot cracking in the weld. In order to exert such an effect, Ti is preferably 0.005% or more, more preferably 0.007% or more, and still more preferably 0.01% or more. However, if added excessively, a large amount of coarse nitrides and oxides are generated to cause nozzle clogging, and the toughness of the steel material is deteriorated. Therefore, Ti is 0.2% or less. Ti is preferably 0.18% or less, more preferably 0.15% or less, still more preferably 0.1% or less, and particularly preferably 0.08% or less.

  The action of REM is as described above. For example, in welded structural steel, REM-containing oxides and REM-containing sulfides are generated in the steel to promote the formation of intragranular ferrite transformation nuclei. It is an element that contributes to improving HAZ toughness. Moreover, when REM is contained in a welding material such as a welding wire, it is possible to prevent spatter from being generated during welding. In order to exert such an action, REM needs to be contained by 0.0003% or more, preferably 0.001% or more, and more preferably 0.002% or more. However, when REM is added excessively, solid solution REM is generated and segregates, thereby degrading the toughness of the steel itself (base material). Therefore, the amount of REM should be suppressed to 0.05% or less. The amount of REM is preferably 0.03% or less, more preferably 0.01% or less, and still more preferably 0.007% or less.

  In the present invention, REM means a lanthanoid element (15 elements from La to Lu), Sc (scandium) and Y (yttrium). Among these elements, it is preferable to contain at least one element selected from the group consisting of La, Ce and Y, more preferably La and / or Ce.

  The remaining components of the REM-containing steel are iron and inevitable impurities (for example, Mg, As, Se, etc.).

The REM-containing steel is still another element,
[1] A group consisting of Zr: 0.1% or less (not including 0%), Al: 0.1% or less (not including 0%), Ca: 0.01% or less (not including 0%) At least one selected from
[2] Cu: 2% or less (not including 0%) and / or Ni: 12% or less (not including 0%),
[3] Cr: 3% or less (not including 0%) and / or Mo: 1% or less (not including 0%),
[4] Nb: 0.25% or less (not including 0%) and / or V: 0.1% or less (not including 0%),
[5] B: 0.005% or less (excluding 0%),
It is also effective to contain such elements. The reasons for setting these ranges are as follows.

<< [1] Zr, Al, Ca >>
Zr, Al, and Ca are all elements involved in improving the HAZ toughness of the steel material, and may contain two or more selected alone or arbitrarily.

  In particular, Zr is an element having the same action as Ti. That is, it is an element that contributes to the refinement of the steel material structure by generating nitrides and oxides in the steel material, and effectively acts to improve the HAZ toughness and to suppress the hot cracking of the welded portion. In order to exert such an effect, Zr is preferably 0.001% or more, more preferably 0.003% or more, and further preferably 0.005% or more. However, if added excessively, a large amount of coarse nitrides and oxides are generated to cause nozzle clogging, and the toughness of the steel material is deteriorated. Therefore, Zr is preferably 0.1% or less. Zr is more preferably 0.08% or less, still more preferably 0.06% or less.

  When Zr and Ti are used in combination, the total is preferably 0.005% or more, more preferably 0.007% or more, still more preferably 0.01% or more, preferably 0.3%. Below, more preferably 0.2% or less, still more preferably 0.1% or less, particularly preferably 0.07% or less, and most preferably 0.06% or less.

  Al is an element having a strong deoxidizing power, and if it is added in an appropriate amount, it is an element that contributes to improving the cleanliness and stabilizing the yield of other elements. However, if excessively added, the REM-containing oxide that effectively works to improve the HAZ toughness of the steel material cannot be reduced to improve the HAZ toughness, and in the case of a welding material, spatter cannot be prevented during welding. For this reason, the welding workability is deteriorated. Therefore, the Al content is preferably suppressed to 0.1% or less. The amount of Al is more preferably 0.05% or less, still more preferably 0.03% or less, and particularly preferably 0.01% or less. Al is usually unavoidably contained in an amount of about 0.0005%.

  Ca is an element that contributes to improving toughness by controlling the form and composition of oxides and sulfides in steel. In order to effectively exhibit such an effect, the content is preferably 0.0003% or more, more preferably 0.0005% or more. However, when Ca is added excessively, coarse sulfides are generated and the toughness of the steel (base material) is deteriorated. Therefore, the Ca content is preferably 0.01% or less, more preferably 0.007% or less, and still more preferably 0.005% or less.

<< [2] Cu and / or Ni >>
Cu and Ni are both elements that contribute to increasing the strength of the steel material, and can be added alone or in combination. However, if the amount of Cu exceeds 2%, the strength of the base material is remarkably increased and the toughness of the base material is deteriorated, so that the HAZ toughness is also lowered. Therefore, the amount of Cu is preferably 2% or less, more preferably 1.8% or less, and still more preferably 1.5% or less. In order to effectively exhibit the action of Cu addition, it is preferably 0.05% or more, more preferably 0.1% or more, and still more preferably 0.2% or more.

  When the Ni content exceeds 12%, the strength of the base material is remarkably increased and the toughness of the base material is deteriorated as in the case of Cu, so that the HAZ toughness is also lowered. Therefore, the Ni content is preferably 12% or less, more preferably 11.5% or less, still more preferably 11% or less, particularly preferably 5% or less, and most preferably 3.5% or less. In order to effectively exhibit the effect of Ni addition, it is preferably 0.05% or more, more preferably 0.1% or more, and still more preferably 0.2% or more.

<< [3] Cr and / or Mo >>
Cr and Mo are both elements that contribute to increasing the strength of the steel material, and can be added alone or in combination. However, if Cr exceeds 3%, the strength of the base material is remarkably increased and the toughness of the base material is deteriorated, so that the HAZ toughness is lowered. Therefore, the Cr content is preferably 3% or less, more preferably 2% or less, and still more preferably 1% or less. In order to effectively exhibit the effect of Cr addition, it is preferably 0.05% or more, more preferably 0.1% or more, and still more preferably 0.15% or more.

  Similarly to Cr, when Mo exceeds 1%, the strength of the base material is significantly increased and the toughness of the base material is deteriorated, so that the HAZ toughness is lowered. Therefore, the Mo amount is preferably 1% or less, more preferably 0.9% or less, and still more preferably 0.8% or less. In order to effectively exhibit the effect of adding Mo, it is preferably 0.05% or more, more preferably 0.1% or more, and still more preferably 0.15% or more.

<< [4] Nb and / or V >>
Nb and V are elements that have the action of precipitating as carbonitride and preventing the austenite grains of HAZ from coarsening during welding due to the pinning effect of the carbonitride and improving the HAZ toughness. . Nb and V can be added alone or in combination. However, if the Nb content exceeds 0.25%, the precipitated carbonitrides become coarse and deteriorate the HAZ toughness. Accordingly, the Nb content is preferably 0.25% or less, more preferably 0.2% or less, and still more preferably 0.15% or less. In order to effectively exhibit the effect of Nb addition, the content is preferably 0.002% or more, more preferably 0.01% or more, and still more preferably 0.02% or more.

  If V exceeds 0.1% as in Nb, the precipitated carbonitrides become coarse and deteriorate the HAZ toughness. Therefore, the V amount is preferably 0.1% or less, more preferably 0.09% or less, and still more preferably 0.08% or less. In order to effectively exhibit the effect of V addition, the content is preferably 0.002% or more, more preferably 0.005% or more, and still more preferably 0.01% or more.

<< [5] B (boron) >>
B is an element that suppresses the formation of grain boundary ferrite and improves toughness. However, if the amount of B exceeds 0.005%, it precipitates as BN at the austenite grain boundary, leading to a decrease in toughness. Therefore, the B content is preferably 0.005% or less, more preferably 0.004% or less. In order to effectively exhibit the effect of addition of B, the content is preferably 0.001% or more, more preferably 0.0015% or more.

  A REM-containing steel that satisfies the above component composition is a steel material having good HAZ toughness even if it is affected by heat during welding. This steel material exhibits good HAZ toughness even as a thick steel plate having a plate thickness of about 3.0 mm or more. Moreover, when the above-mentioned REM-containing steel material is used as a welding material (welding wire, for example, a solid wire), generation of spatter can be prevented.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention. The following experiment was conducted in a laboratory.

Using a high-frequency induction melting furnace (capacity: 500 kg), test steels having the component composition (mass%) shown in Table 2 below (the balance is iron and inevitable impurities) were melted, cast into a 150 kg ingot, and cooled. Specifically, first, the raw steel is melted in a high-frequency induction melting furnace, and the dissolved oxygen amount Q _Of of the molten steel before REM addition is at least selected from C, Si, Mn, Al and Ti in a state where the raw steel is maintained at 1600 ° C. It adjusted by deoxidizing using 1 type of elements. This dissolved oxygen amount Q _Of was measured by a general electromotive force measurement method using a solid electrolyte. The measurement results are shown in Table 1 below.

Next, before the REM addition and / or after the REM addition, the amount of REM (Q _REM ) shown in Table 1 below is adjusted to the above molten steel while adjusting the components other than the REM within the range shown in Table 2 below. Added. Table 1 below also shows Z values (values on the left side of the above equation (1)) calculated by substituting the values of the dissolved oxygen amount Q _Of and the REM addition amount Q _{REM into} the following equation (1) ′. .
Z = 2logQ _REM + 3logQ _Of ... (1) '

  REM is in the form of misch metal containing about 25% La and about 50% Ce, Ti is in the form of Fe-Ti alloy, Zr is in the form of Fe-Zr alloy, and Ca is in the form of Ni-Ca alloy. Each was added in form.

  The molten steel after the addition of REM was quickly put out from a high frequency induction melting furnace into a ladle, and the ladle was suspended above a mold equipped with a weight measuring device (load cell). Then, the φ12 mm ladle nozzle provided at the bottom of the ladle was opened, and molten steel was put out in a mold below the ladle. The temperature of the molten steel was adjusted with a high-frequency induction melting furnace so that the molten steel temperature when the steel was drawn from the ladle into the mold was about 1600 ° C. While the molten steel was discharged from the ladle to the mold via the ladle nozzle, the weight of the molten steel flowing out into the mold (the amount of steel output) was continuously measured by a load cell attached to the mold.

  In this example, the presence or absence of nozzle clogging was evaluated based on the amount of steel output. Specifically, the amount of steel output at the time when 120 seconds have passed since the start of steel output is taken as a reference value, and when this amount of steel output is 145 kg or more, there is no nozzle clogging and the result is passed. Table 1 below shows the steel output (kg) when 120 seconds have elapsed since the start of steel output.

  FIG. 1 is a graph showing the change over time in the amount of steel output (kg) with respect to the elapsed time (seconds) from the start of steel output. In addition, in FIG. 1, No. is shown as a representative example among the examples shown in Table 1 below. Nos. 1 and 5 (invention examples above), No. 1 The result of 10 and 14 (above, a comparative example) is shown. In FIG. As a result of No. 1, the fine dotted line is No. As a result of FIG. As a result of No. 10, the rough dotted line is No. 14 results are shown respectively.

  The following table 1 and FIG. 1 can be considered as follows. No. 1 to 9 and 17 are examples in which the REM-added steel was manufactured so as to satisfy the conditions specified in the present invention. In these examples, 145 kg or more of REM-added molten steel has been produced when 120 seconds have elapsed from the start of steeling, and nozzle clogging does not occur even when steeling is continued, and the REM in the ladle All of the added molten steel was produced in the mold.

In contrast, no. 10 to 16 are examples in which the REM-added steel was manufactured without satisfying any of the conditions defined in the present invention. Of these, No. 10 to 15 are examples in which the Z value exceeds -11, and the balance between the dissolved oxygen amount Q _Of and the REM addition amount Q _REM of the molten steel before REM addition is poor, and a large amount of REM-containing oxide is generated in the molten steel. Then, this REM-containing oxide adhered to the inner wall of the nozzle, resulting in nozzle clogging. As a result, the steel output weight at the time of 120 seconds after the start of steel output was as low as less than 145 kg. When the steel output was further continued, the nozzle was completely closed and the REM-added molten steel remained in the ladle. On the other hand, no. 16 is an example in which the amount of dissolved oxygen Q _{Of the} molten steel before REM addition exceeded 0.015%, although the Z value satisfies the requirements specified in the present invention. In addition to the REM-containing oxide, REM Many oxides of other elements were also produced, and these oxides adhered to the inner wall of the nozzle and caused nozzle clogging. As a result, the steel output weight at the time of 120 seconds after the start of steel output was as low as less than 145 kg. When the steel output was further continued, the nozzle was completely closed and the REM-added molten steel remained in the ladle.

  The above results can be read more clearly with reference to FIG. As is apparent from FIG. In 1 and 5 (solid line and fine dotted line), 145 kg or more of molten steel has been produced when 120 seconds have elapsed since the start of steel production, and the amount of steel output has increased with time. On the other hand, no. In Nos. 10 and 14 (dashed line and coarse dotted line), the amount of molten steel produced is less than 145 kg when 120 seconds have elapsed since the start of steel production, and the amount of steel produced remains almost unchanged even after more time has passed. There wasn't. Specifically, no. No. 10 from the point when 100 seconds passed, In FIG. 14, it can be seen that the amount of steel output is almost flat after 150 seconds, and the steel output from the ladle is almost stopped.

Furthermore, it will be clarified with reference to FIGS. 2 and 3 that the above formula (1) defined in the present invention is a useful index of nozzle clogging during casting. In these figures, in Table 1 below, the dissolved oxygen amount Q _Of deviates from the requirement defined in the present invention. No. 16 was removed. The results of 1 to 15 and 17 are plotted.

First, FIG. 2 shows the relationship between the dissolved oxygen amount Q _Of and the REM addition amount Q _REM of the molten steel before REM addition. Specifically, in FIG. The results of Nos. 1 to 9 and 17 (no nozzle clogging) are indicated by ◯, and No. 1 does not satisfy any of the requirements of the present invention. The results of 10 to 15 (with nozzle clogging) are indicated by x.

The straight line shown in FIG. 2 shows the above formula (1) ′, and whether or not the nozzle is blocked is clearly divided by the above formula (1) ′, and the dissolved oxygen amount Q _Of and the REM addition amount Q It can be seen that _REM has a very high correlation. That is, after adjusting the dissolved oxygen amount Q _Of of the molten steel before REM addition to a range of 0.0001 to 0.015%, when adding REM, the Z value is -11 or less according to the dissolved oxygen amount Q _Of. It can be seen that if REM is added so as to be (region below the straight line), nozzle clogging can be prevented when steel is extracted from the ladle to the mold.

  FIG. 3 is a graph showing the relationship between the Z value and the amount of steel output. As is clear from FIG. 3, the amount of steel output changes greatly with the Z value at -11 as a boundary, and it can be seen that the Z value is a useful index for preventing nozzle clogging.

Claims (6)

C: 0.01 to 0.15% (meaning mass%, the same applies to the following components),
Si: 1.2% or less (excluding 0%),
Mn: 3.8% or less (excluding 0%),
P: 0.03% or less (excluding 0%),
S: 0.03% or less (excluding 0%),
N: 0.01% or less (excluding 0%),
Ti: 0.2% or less (excluding 0%) and REM: 0.0003-0.05%,
A method for producing REM-containing steel, the balance of which is iron and inevitable impurities,
When the dissolved oxygen amount Q _Of in the molten steel before REM addition is adjusted to a range of 0.0001 to 0.015% and then REM is added, the dissolved oxygen amount Q _Of and the REM addition amount Q _REM are as follows. (1) A method for producing a REM-containing steel, wherein an amount of REM satisfying the formula is added and melted.
2logQ _REM + 3logQ _Of ≦ -11 (1) The REM-containing steel is still another element,
Zr: 0.1% or less (excluding 0%),
Al: 0.1% or less (excluding 0%),
The manufacturing method according to claim 1, comprising at least one selected from the group consisting of Ca: 0.01% or less (not including 0%). The REM-containing steel is still another element,
The manufacturing method according to claim 1 or 2, comprising Cu: 2% or less (not including 0%) and / or Ni: 12% or less (not including 0%). The REM-containing steel is still another element,
The manufacturing method in any one of Claims 1-3 containing Cr: 3% or less (excluding 0%) and / or Mo: 1% or less (not including 0%). The REM-containing steel is still another element,
The manufacturing method according to any one of claims 1 to 4, comprising Nb: not more than 0.25% (not including 0%) and / or V: not more than 0.1% (not including 0%). The REM-containing steel is still another element,
B: The manufacturing method in any one of Claims 1-5 containing 0.005% or less (0% is not included).

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