WO2020189762A1 - 高マンガン鋼鋳片の製造方法、高マンガン鋼鋼片および高マンガン鋼鋼板の製造方法 - Google Patents
高マンガン鋼鋳片の製造方法、高マンガン鋼鋼片および高マンガン鋼鋼板の製造方法 Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/108—Feeding additives, powders, or the like
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- the present invention is a steel that is a high manganese steel material for structural steel used in cryogenic environments such as nuclear fusion facilities, roadbeds for linear motor cars, mechanical structural members such as nuclear magnetic resonance fault chambers, and liquefied gas storage tanks.
- the present invention relates to a method for producing pieces and steel plates, and a method for producing high manganese steel slabs used for producing these pieces.
- High manganese steel which has an austenitic single-phase structure and non-magnetic properties, is in increasing demand as an inexpensive steel material to replace conventional austenitic stainless steels, 9% nickel steels, and 5000 series aluminum alloys. ..
- the steel slabs used as the raw material for these high manganese steels are generally manufactured by obtaining slabs by the ingot method and hot slabbing rolling, but recently, productivity improvement and cost From the viewpoint of reduction, production from slabs obtained by the continuous casting method has become indispensable.
- productivity improvement and cost From the viewpoint of reduction, production from slabs obtained by the continuous casting method has become indispensable.
- surface cracks of the slabs during continuous casting and surface cracks of steel pieces and steel sheets during hot rolling occur frequently and cracks occur. Increased maintenance for removing flaws and reduced yield are problems. Therefore, there has been a strong demand for the production of high manganese steel slabs capable of suppressing surface cracks during the production of steel slabs or steel sheets.
- Patent Document 1 states that one or more of Mg, Ca, and REM are 0.0002% or more in total.
- a high Mn steel having excellent low temperature toughness is disclosed, which contains components satisfying 30C + 0.5Mn + Ni + 0.8Cr + 1.2Si + 0.8Mo ⁇ 25 and O / S ⁇ 1.
- Patent Document 1 achieves excellent fine crystal grains by containing the above components, but controls the types of inclusions and precipitates that determine the crystal grain size as targeted. There was a problem that it was not enough.
- the present invention has been made in view of this situation, and is a method for producing high manganese steel pieces and steel sheets capable of controlling inclusions and precipitates that determine the crystal grain size and suppressing the occurrence of surface scratches, and production thereof. It is an object of the present invention to provide a method for producing a high manganese steel slab used in the above.
- C 0.10% or more and 1.3% or less
- Si 0.10% or more and 0.90% or less
- Mn 10% or more and 35% or less
- P 0.030% or less
- S 0.0070% or less
- Al 0.01% or more and 0.1% or less
- Cr 10% or less
- Ca 0.0001% or more and 0.010% or less
- Mg 0.0001% or more and 0.010 %
- Ti 0.001% or more and 0.03% or less
- N 0.0001% or more and 0.20% or less
- O 0.0100% or less
- the balance is composed of iron and unavoidable impurities.
- the ACR of the above formula (1) is calculated by the following formula (2).
- ACR ⁇ [% Ca]-(0.18 + 130 x [% Ca]) x [% O] ⁇ / (1.25 x [% S]) ...
- [% Ca] in the above formula (2) is the content of Ca in the molten steel (mass%)
- [% O] is the content of O in the molten steel (mass%)
- [% S] Is the content (mass%) of S in the molten steel.
- [2] The method for producing a high manganese steel slab according to [1], wherein the Ti, Mg and N contents of the molten steel in the tundish further satisfy the following formula (3).
- [% Ti] in the above formula (3) is the content of Ti in the molten steel (mass%)
- [% N] is the content of N in the molten steel (mass%)
- [% Mg] Is the Mg content (mass%) in the molten steel.
- Nb 0.001% or more and 0.01% or less
- V 0.001% or more and 0.03% or less
- Cu 0.01% or more and 1.00% or less
- Ni 0
- Mo 0.05% or more and 2.00% or less
- W 0.05% or more and 2.00% or less.
- high manganese steel slabs can be produced while suppressing the occurrence of surface scratches. Further, when the high manganese steel slab is hot-rolled into a steel slab or a steel plate, the high manganese steel slab or a steel plate can be produced while suppressing the occurrence of surface scratches during rolling.
- FIG. 1 is a diagram summarizing the formation behavior of inclusions and precipitates of high manganese steel in the solidification process from molten steel in the conventional example and the invention example.
- the high manganese steel according to the present embodiment has C: 0.10% or more and 1.3% or less, Si: 0.10% or more and 0.90% or less, Mn: 10% or more and 35% or less, P: 0.030.
- % Or less S: 0.0070% or less, Al: 0.01% or more and 0.1% or less, Cr: 10% or less, Ca: 0.0001% or more and 0.010% or less, Mg: 0.0001% or more It contains 0.010% or less, Ti: 0.001% or more and 0.03% or less, N: 0.0001% or more and 0.20% or less, O: 0.0001% or more and 0.0100% or less, and the balance is It has a component composition consisting of iron and unavoidable impurities.
- the composition of the above components is Nb: 0.001% or more and 0.01% or less, V: 0.001% or more and 0.03% or less, Cu: 0.01% or more and 1.00% or less, Ni: 0.01%.
- One or more selected from 0.50% or more, Mo: 0.05% or more and 2.00% or less, and W: 0.05% or more and 2.00% or less may be contained. “%” Representing the content of a component in the component composition means “mass%” unless otherwise specified. The content of all components is a total value, not a dissolved amount.
- C 0.10% or more and 1.3% or less C is added for the purpose of stabilizing the austenite phase and improving the strength. If the C content is less than 0.10%, the required strength cannot be obtained. On the other hand, if the C content exceeds 1.3%, the amount of carbides and cementite precipitated becomes excessive and the toughness decreases. Therefore, the content of C needs to be 0.10% or more and 1.3% or less, and preferably 0.30% or more and 0.8% or less.
- Si 0.10% or more and 0.90% or less Si is added for the purpose of deoxidation and solid solution strengthening. In order to obtain this effect, the Si content needs to be 0.10% or more.
- Si is a ferrite stabilizing element, and when added in a large amount, the austenite structure of high manganese steel becomes unstable. Therefore, the Si content needs to be 0.90% or less. Therefore, the Si content needs to be 0.10% or more and 0.90% or less, and preferably 0.20% or more and 0.60% or less.
- Mn 10% or more and 35% or less Mn is an element that stabilizes the austenite structure and brings about an increase in strength.
- Mn content 10% or more
- the characteristics such as non-magnetism and low temperature toughness expected of austenitic steel can be obtained.
- austenitic steel generally has poor hot workability, and among them, high manganese steel is known as a material having high crack sensitivity during continuous casting and hot rolling.
- the Mn content needs to be 10% or more and 35% or less, and preferably 20% or more and 28% or less.
- P 0.030% or less
- P is an impurity element contained in steel, which causes a decrease in toughness and hot embrittlement. Therefore, the smaller the P content, the better, but up to 0.030% is acceptable. Therefore, the content of P needs to be 0.030% or less, preferably 0.015% or less.
- S 0.0070% or less
- S is an impurity element contained in steel, and sulfides such as MnS serve as a starting point to reduce toughness. Therefore, the smaller the S content, the better, but up to 0.0070% is acceptable. Therefore, the content of S needs to be 0.0070% or less, and preferably 0.0030% or less.
- Al 0.01% or more and 0.1% or less Al is added for the purpose of deoxidation.
- the Al content must be 0.01% or more.
- the Al content needs to be 0.01% or more and 0.1% or less, and preferably 0.02% or more and 0.05% or less.
- the Cr content needs to be 10% or less, preferably 7% or less.
- Ca 0.0001% or more and 0.010% or less
- the Ca content needs to be 0.0001% or more.
- the Ca content needs to be 0.010% or less.
- the Ca content is preferably 0.0005% or more and 0.0050% or less.
- Mg 0.0001% or more and 0.010% or less Mg, like Ca, is very easy to bond with O and S elements and forms fine oxides and sulfides, so grain boundary embrittlement due to precipitation inclusions Can be expected to be suppressed. Therefore, the Mg content needs to be 0.0001% or more. On the other hand, if the Mg content is excessive, the reaction with the molten steel becomes violent at the time of addition, which not only raises a concern that the cleanliness of the molten steel is adversely deteriorated, but also has a concern that the precipitated inclusions are coarsened. Therefore, the Mg content needs to be 0.010% or less.
- the Mg content is preferably 0.0005% or more and 0.0020% or less.
- Ti 0.001% or more and 0.03% or less Ti binds to C and N elements under high temperature conditions, so it is effective in suppressing the formation of huge carbides and the precipitation of Nb and V carbonitrides with high crack sensitivity. Is. Therefore, the Ti content needs to be 0.001% or more. On the other hand, when a large amount of Ti is added, a huge carbonitride is generated, and deterioration of low temperature toughness becomes a problem. Therefore, the Ti content needs to be 0.03% or less. The Ti content is preferably 0.001% or more and 0.02% or less.
- N 0.0001% or more and 0.20% or less N stabilizes the austenite structure and increases the strength by solid solution and precipitation. Aiming at this effect, the content of N needs to be 0.0001% or more. On the other hand, if the N content exceeds 0.20%, the hot workability is lowered. Therefore, the content of N needs to be 0.0001% or more and 0.20% or less.
- the content of N is preferably 0.0050% or more and 0.10% or less.
- the O content is a value determined by the degree of deoxidation and removal of inclusions in the molten steel stage, and the O content is preferably smaller from the viewpoint of cleanliness.
- the content of O is the total content of O including O as an oxide (inclusion). If the content of O is too large, not only the above-mentioned elements such as Ca and Mg cannot generate a sufficient effect, but also solidification defects such as cavities are likely to occur frequently in the slab. Therefore, the content of O needs to be 0.0100% or less.
- the O content is preferably 0.0030% or less.
- the high manganese steel according to the present embodiment may contain one or more selected from the following elements, if necessary.
- Nb 0.001% or more and 0.01% or less
- V 0.001% or more and 0.03% or less
- Both Nb and V produce carbonitrides, and the produced carbonitrides trap diffusible hydrogen. Since it acts as a site, it has the effect of suppressing stress corrosion cracking. In order to obtain this effect, it is preferable to contain Nb: 0.001% or more and 0.01% or less, and V: 0.001% or more and 0.03% or less.
- Cu 0.01% or more and 1.00% or less
- Ni 0.01% or more and 0.50% or less
- Cu and Ni stabilize the austenite structure and contribute to the suppression of carbide precipitation.
- Mo 0.05% or more and 2.00% or less
- W 0.05% or more and 2.00% or less Mo and W contribute to the improvement of the base metal strength.
- the rest other than the above is iron and unavoidable impurities.
- the high manganese steel is an austenite single-phase steel, an austenite structure having a large crystal grain size is generated from the surface of the slab. Since the austenite grain size is coarse, the high-temperature ductility is low as compared with general steel, and impurity elements such as P and S are concentrated at the grain boundaries. The concentration of this impurity element makes the grain boundaries fragile, and surface cracks occur in the form of propagating the fragile grain boundaries.
- the high manganese steel has a high Mn concentration in the steel and has a high reactivity with S, so that the formation of MnS is more remarkable than that of the general steel. It also produces M 23 C 6 carbides (M: Mn, Cr, Fe, Mo). These precipitates are likely to precipitate at the grain boundaries of high manganese steel, and even when coarse sulfide or carbide precipitates are concentrated at the grain boundaries, the grain boundaries become fragile and surface cracks occur. Occurs.
- the austenite structure develops rapidly from just below the solidus temperature, so it is important to deposit inclusions that are pinning nuclei at least to the solidus temperature. .. Furthermore, it suppresses the precipitation of coarse sulfides and carbides that are harmful to cracks from concentrating on the grain boundaries, and finely deposits them in the crystal grains to disperse the strain concentrated on the grain boundaries. It is also important to let them do it.
- a method of suppressing the formation of MnS As a method of suppressing the formation of MnS, a method of adding Ca to steel is known. Suppression of MnS formation by the addition of Ca is performed with steel for sour line pipes and the like. Ca / S and ACR indexes (atomic concentration ratio indexes) are known as indexes of Ca addition. It is known that it is effective to add Ca so as to satisfy Ca / S> 2 or to satisfy the following equation (4) in order to suppress the formation of MnS.
- ACR ⁇ [% Ca]-(0.18 + 130 x [% Ca]) x [% O] ⁇ / (1.25 x [% S]) ...
- [% Ca] in the above formula (2) is the content of Ca in the molten steel (mass%) in the tundish
- [% O] is the content of O in the molten steel (mass%) in the tundish
- [% S] is the content (mass%) of S in the molten steel in the tundish.
- the Al 2 O 3 inclusions in the molten steel are morphologically controlled by CaO ⁇ Al 2 O 3 oxide, and the precipitation of MnS during solidification is suppressed by CaS.
- This idea also applies to high manganese steel.
- CaS-MnS is produced at the molten steel stage. CaS-MnS produced in the molten steel stage is easily agglomerated and coalesced and easily floated and removed. Even when it is incorporated into the slab after solidification, it is unlikely to become a pinning nucleus for grain refinement.
- Ca is added to the high manganese steel molten steel
- the Ca, O, and S contents of the high manganese steel molten steel in the tundish are expressed by the following equation (1). Adjust the ingredient composition to your satisfaction.
- the composition of the molten steel can be measured by component analysis of the molten steel sampled from inside the tundish.
- TLL liquidus temperature
- TSL solidus temperature
- the above-mentioned precipitates finely dispersed in the crystal grains also act as pinning nuclei for crystal grain refinement, the crystal grain size is refined and the weakening of the crystal grain boundaries due to the concentration of impurity elements is avoided. it can. As a result, the occurrence of surface cracks due to grain boundary cracks is further suppressed.
- the Ca, O and S contents of the high manganese steel molten steel in the tundish are set to ACR ⁇ 0.4, the amount of Ca added is too small, so that fine CaO / MnO / Al 2 O 3 intervening No substance is produced, and MnS is mainly produced at the grain boundaries after solidification.
- ACR> 1.4 CaS is likely to be generated at the molten steel stage, so that it does not function as a pinning nucleus for grain size miniaturization and the crystal grain size cannot be miniaturized.
- the Ca, O and S contents of the high manganese steel molten steel in the tundish preferably satisfy the following formula (5), whereby the pinning effect due to the fine MnS is enhanced and the crystal grain size can be further made finer. ..
- the temperature at which CaO, MnO, and Al 2 O 3 are precipitated is preferably between TLL and TSL, at which the solid phase ratio of the high manganese steel molten steel is 0.3 or more. This is because a solid phase ratio of 0.3 or more is close to the flow limit phase rule of molten steel, and the precipitated inclusions remain at the precipitated position without being washed away by the molten steel.
- Ti and N may be added to the molten steel to finely disperse the precipitates with MgO and TiN as nuclei.
- Ti and N are added to molten steel to reach the solubility product at a high temperature of 1300 to 1400 ° C. to precipitate TiN, and the precipitate is used as a pinning nucleus for grain refinement. Since fine TiN is stably generated in the presence of MgO, it is effective to include Mg in addition to Ti and N.
- the contents of Ti, Mg and N of the molten steel of high manganese steel in the tundish satisfy the following equation (3). In this case, it was found that MgO-TiN was finely dispersed and precipitated in the crystal grains immediately after solidification.
- [% Ti] is the Ti content (mass%) in the molten steel in the tundish
- [% N] is the N content (mass%) in the molten steel in the tundish
- [% Mg] is the content (mass%) of Mg in the molten steel in the tundish.
- Ti is set to 0.0001% by mass even when Ti is not added, and Mg is set to 0.0001% by mass even when Mg is not added.
- MgO-TiN takes the form of depositing MnS and CaS-MnS around the precipitates. Therefore, by finely dispersing the MgO-TiN precipitate in the crystal grains, it is possible to suppress the precipitation of coarse MnS precipitates at the crystal grain boundaries. Since the MgO-TiN precipitate functions as a pinning nucleus, the crystal grain size is further refined. As a result, the occurrence of surface cracks due to grain boundary cracks is further suppressed.
- FIG. 1 is a diagram summarizing the formation behavior of inclusions and precipitates of high manganese steel in the solidification process from molten steel in the conventional example and the invention example.
- Inclusions in the molten steel of a high manganese steel is Al 2 O 3 -MnO inclusions is oxide, are present in the molten steel of 1500 ⁇ 1600 ° C..
- Ca is added to adjust the composition of the components so that the Ca, O and S contents of the high manganese steel molten steel in the tundish satisfy the above equation (1).
- the Al 2 O 3 -MnO inclusions become CaO / MnO / Al 2 O 3 inclusions between the TLL and the TSL and are finely dispersed and precipitated in the crystal grains and at the grain boundaries.
- Ti, Mg and N are added to adjust the composition of the components so that the Ti, Mg and N contents of the high manganese steel molten steel in the tundish satisfy the above equation (3).
- MgO-TiN inclusions are finely dispersed and precipitated in the crystal grains and at the grain boundaries between TLL and TSL.
- the MnS, CaS, and M 23 C 6 that are precipitated thereafter are precipitated around the CaO / MnO / Al 2 O 3 precipitate and the MgO-TiN precipitate, so that the MnS precipitate is dispersed in the crystal grains and is coarse. It is suppressed that MnS precipitates are concentrated at the grain boundaries.
- the crystal grain size is also miniaturized.
- High manganese steel was melted using a 150-ton converter, an electrode-heated ladle smelter, and an RH vacuum degassing device, and after adjusting the molten steel composition and temperature, a tundish with a capacity of 30 tons was used, and the radius of curvature was 10.
- a slab having a cross-sectional size of 1250 mm width ⁇ 250 mm thickness was continuously cast using a 5 mR curved continuous casting machine. The casting speed was in the range of 0.7 to 0.9 m / min, and the amount of secondary cooling water was in the range of 0.3 to 0.6 L / kg.
- the slab is once lowered to a cold slab by slow cooling, the slab is charged into the heating furnace for a predetermined time so as to reach a predetermined target temperature, and then hot-rolled at a total reduction ratio of 48%.
- Table 1 shows the composition of the molten steel sampled from the tundish in Invention Examples 1 to 39, the calculated values of equations (1) and (3), and the investigation results of surface cracks.
- Tables 2 and 3 show the composition of the molten steel sampled from the tundish in Comparative Examples 1 to 70, the calculated values of the above equations (1) and (3), and the investigation results of surface cracks.
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Abstract
Description
[1]質量%で、C:0.10%以上1.3%以下、Si:0.10%以上0.90%以下、Mn:10%以上35%以下、P:0.030%以下、S:0.0070%以下、Al:0.01%以上0.1%以下、Cr:10%以下、Ca:0.0001%以上0.010%以下、Mg:0.0001%以上0.010%以下、Ti:0.001%以上0.03%以下、N:0.0001%以上0.20%以下、O:0.0100%以下を含有し、残部が鉄および不可避的不純物からなる成分組成を有する溶鋼を連続鋳造するにあたり、タンディッシュにおける前記溶鋼のCa、OおよびSの含有量が下記(1)式を満足する、高マンガン鋼鋳片の製造方法。
0.4≦ACR≦1.4・・・(1)
上記(1)式のACRは、下記(2)式で算出される。
ACR={[%Ca]-(0.18+130×[%Ca])×[%O]}/(1.25×[%S])・・・(2)
上記(2)式の[%Ca]は前記溶鋼中のCaの含有量(質量%)であり、[%O]は前記溶鋼中のOの含有量(質量%)であり、[%S]は前記溶鋼中のSの含有量(質量%)である。
[2]前記タンディッシュにおける前記溶鋼のTi、MgおよびNの含有量がさらに下記(3)式を満足する、[1]に記載の高マンガン鋼鋳片の製造方法。
[%Ti]×[%N]×[%Mg]≧2.0×10-8・・・(3)
上記(3)式の[%Ti]は前記溶鋼中のTiの含有量(質量%)であり、[%N]は前記溶鋼中のNの含有量(質量%)であり、[%Mg]は前記溶鋼中のMgの含有量(質量%)である。
[3]さらに質量%で、Nb:0.001%以上0.01%以下、V:0.001%以上0.03%以下、Cu:0.01%以上1.00%以下、Ni:0.01%以上0.50%以下、Mo:0.05%以上2.00%以下、W:0.05%以上2.00%以下のうちから選ばれる1種または2種以上を含有する成分組成を有する溶鋼を連続鋳造する、[1]または[2]に記載の高マンガン鋼鋳片の製造方法。
[4][1]から[3]の何れか1つに記載の高マンガン鋼鋳片の製造方法で製造された鋳片を熱間圧延して鋼片を製造する、高マンガン鋼鋼片の製造方法。
[5][1]から[3]の何れか1つに記載の高マンガン鋼鋳片の製造方法で製造された鋳片を熱間圧延して鋼板を製造する、高マンガン鋼鋼板の製造方法。
Cは、オーステナイト相の安定化と強度の向上を目的として添加される。Cの含有量が0.10%未満では必要な強度が得られない。一方、Cの含有量が1.3%を超えると炭化物やセメンタイトの析出量が過大となり靱性が低下する。このため、Cの含有量は0.10%以上1.3%以下である必要があり、0.30%以上0.8%以下であることが好ましい。
Siは、脱酸と固溶強化を目的として添加される。この効果を得るには、Siの含有量が0.10%以上である必要がある。一方、Siは、フェライト安定化元素であり、多量に添加すると高マンガン鋼のオーステナイト組織が不安定になる。このため、Siの含有量は0.90%以下である必要がある。したがって、Siの含有量は0.10%以上0.90%以下である必要があり、0.20%以上0.60%以下であることが好ましい。
Mnは、オーステナイト組織を安定化し、強度の増加をもたらす元素である。特に、Mnの含有量を10%以上とすることによって、オーステナイト鋼に期待される非磁性および低温靱性といった特性が得られる。一方で、一般にオーステナイト鋼は熱間加工性に乏しく、中でも高マンガン鋼は連続鋳造や熱間圧延時の割れの感受性が高い材料として知られている。特に、Mnの含有量が35%を超えると加工性が著しく低下する。従って、Mnの含有量は10%以上35%以下である必要があり、20%以上28%以下であることが好ましい。
Pは、鋼中に含まれる不純物元素であり、靱性の低下や熱間脆化を招く。このため、Pの含有量は少ないほどよいが、0.030%までは許容できる。したがって、Pの含有量は、0.030%以下である必要があり、0.015%以下であることが好ましい。
Sは、鋼中に含まれる不純物元素であり、MnS等の硫化物が起点となって靱性を低下させる。このため、Sの含有量は少ないほどよいが、0.0070%までは許容できる。したがって、Sの含有量は、0.0070%以下である必要があり、0.0030%以下であることが好ましい。
Alは、脱酸を目的として添加される。必要な脱酸効果を得るには、Alの含有量が0.01%以上である必要がある。一方、Alの含有量が0.1%を超えるほど添加されても脱酸効果は頭打ちとなると同時に過剰なAlNが生成して熱間加工性が低下する。したがって、Alの含有量は0.01%以上0.1%以下である必要があり、0.02%以上0.05%以下であることが好ましい。
Crは、固溶強化を目的として添加される。一方、Crを多量に添加すると高マンガン鋼のオーステナイト組織が不安定になり、脆化の原因となる粗大炭化物が析出する。したがって、Crの含有量は10%以下が必要であり、7%以下であることが好ましい。
Caは、適量添加すると微細な酸化物や硫化物を形成し、析出介在物による粒界脆化を抑制する。このため、Caの含有量は0.0001%以上である必要がある。一方、Caの含有量が過剰になると、析出介在物が粗大化し、逆に粒界脆化を促進する。このため、Caの含有量は0.010%以下である必要がある。Caの含有量は、0.0005%以上0.0050%以下であることが好ましい。
Mgは、Caと同様でO、S元素と非常に結合しやすく、微細な酸化物や硫化物を形成することから析出介在物による粒界脆化の抑制が期待できる。このため、Mgの含有量は0.0001%以上である必要がある。一方、Mgの含有量が過剰になると、添加時に溶鋼との反応が激しくなって溶鋼清浄を逆に悪化させる懸念を生じさせるだけでなく、析出介在物を粗大化させる懸念もある。このため、Mgの含有量は0.010%以下である必要がある。Mgの含有量は、0.0005%以上0.0020%以下であることが好ましい。
Tiは、高温条件でC、N元素と結合するので、巨大な炭化物の生成抑制や割れ感受性の高いNb、Vの炭窒化物の析出抑制に有効である。このため、Tiの含有量は0.001%以上である必要がある。一方、Tiを大量に添加すると巨大な炭窒化物を生成することになり、低温靱性の劣化が問題になる。このため、Tiの含有量は0.03%以下である必要がある。Tiの含有量は、0.001%以上0.02%以下であることが好ましい。
Nは、オーステナイト組織を安定化させ、固溶および析出によって強度を増加させる。この効果を狙って、Nの含有量は0.0001%以上である必要がある。一方、Nの含有量が0.20%を超えると熱間加工性が低下する。このため、Nの含有量は0.0001%以上0.20%以下である必要がある。Nの含有量は、0.0050%以上0.10%以下であることが好ましい。
Oの含有量は、溶鋼段階の脱酸ならびに介在物浮上除去の程度により決まる値であり、清浄性の観点からOの含有量はより少ないことが好ましい。ここで、Oの含有量は、酸化物(介在物)としてのOを含むトータルOの含有量である。Oの含有量が多すぎると上述したCa、Mgなどの元素が十分な効果を発生できなくなるばかりでなく、鋳片に巣などの凝固欠陥が多発しやすくなる。このため、Oの含有量は0.0100%以下であることが必要である。Oの含有量は、0.0030%以下であることが好ましい。
NbおよびVは、いずれも炭窒化物を生成し、生成した炭窒化物が拡散性水素のトラップサイトとして作用するので、応力腐食割れを抑制する効果を有する。この効果を得るには、Nb:0.001%以上0.01%以下、V:0.001%以上0.03%以下で含有することが好ましい。これら成分組成範囲であれば、表面傷の発生を抑制しながら高マンガン鋼鋳片を製造すること、および、当該高マンガン鋼鋳片を鋼片または鋼板に熱間圧延するに際し、圧延時の表面傷の発生を抑制しながら、高マンガン鋼鋼片または鋼板を製造することには影響しない。
CuおよびNiは、オーステナイト組織を安定化し、炭化物の析出抑制に寄与する。これらの効果を得るには、Cu:0.01%以上1.00%以下、Ni:0.01%以上0.50%以下で含有することが好ましい。これら成分組成範囲であれば、表面傷の発生を抑制しながら高マンガン鋼鋳片を製造すること、および、当該高マンガン鋼鋳片を鋼片または鋼板に熱間圧延するに際し、圧延時の表面傷の発生を抑制しながら、高マンガン鋼鋼片または鋼板を製造することには影響しない。
MoおよびWは、母材強度の向上に寄与する。これらの効果を得るには、Mo:0.05%以上2.00%以下、W:0.05%以上2.00%以下で含有することが好ましい。これら成分組成範囲であれば、表面傷の発生を抑制しながら高マンガン鋼鋳片を製造すること、および、当該高マンガン鋼鋳片を鋼片または鋼板に熱間圧延するに際し、圧延時の表面傷の発生を抑制しながら、高マンガン鋼鋼片または鋼板を製造することには影響しない。
上記ACRは、下記(2)式で算出される。
上記(2)式の[%Ca]はタンディッシュにおける溶鋼中のCaの含有量(質量%)であり、[%O]は、タンディッシュにおける溶鋼中のOの含有量(質量%)であり、[%S]はタンディッシュにおける溶鋼中のSの含有量(質量%)である。
上記ACRは、上記(2)式で算出される。
CaO・MnO・Al2O3を析出させる温度は、TLLからTSLまでの間であって、高マンガン鋼溶鋼の固相率が0.3以上となる温度とすることが好ましい。固相率0.3以上は、溶鋼の流動限界固相率に近く、析出した介在物が溶鋼に流されることなく析出した位置に留まるからである。固相率とは、鋼のTLL以上で固相率=0、鋼のTSL以下で固相率=1.0と定義されるものである。
上記(3)式において[%Ti]はタンディッシュにおける溶鋼中のTiの含有量(質量%)であり、[%N]はタンディッシュにおける溶鋼中のNの含有量(質量%)であり、[%Mg]はタンディッシュにおける溶鋼中のMgの含有量(質量%)である。分析下限を考慮し、Tiが無添加の場合であってもTiを0.0001質量%とし、Mgが無添加の場合であってもMgを0.0001質量%とする。
Claims (5)
- 質量%で、
C:0.10%以上1.3%以下、
Si:0.10%以上0.90%以下、
Mn:10%以上35%以下、
P:0.030%以下、
S:0.0070%以下、
Al:0.01%以上0.1%以下、
Cr:10%以下、
Ca:0.0001%以上0.010%以下、
Mg:0.0001%以上0.010%以下、
Ti:0.001%以上0.03%以下、
N:0.0001%以上0.20%以下、
O:0.0100%以下を含有し、残部が鉄および不可避的不純物からなる成分組成を有する溶鋼を連続鋳造するにあたり、タンディッシュにおける前記溶鋼のCa、OおよびSの含有量が下記(1)式を満足する、高マンガン鋼鋳片の製造方法。
0.4≦ACR≦1.4・・・(1)
上記(1)式のACRは、下記(2)式で算出される。
ACR={[%Ca]-(0.18+130×[%Ca])×[%O]}/(1.25×[%S])・・・(2)
上記(2)式の[%Ca]は前記溶鋼中のCaの含有量(質量%)であり、[%O]は前記溶鋼中のOの含有量(質量%)であり、[%S]は前記溶鋼中のSの含有量(質量%)である。 - 前記タンディッシュにおける前記溶鋼のTi、MgおよびNの含有量がさらに下記(3)式を満足する、請求項1に記載の高マンガン鋼鋳片の製造方法。
[%Ti]×[%N]×[%Mg]≧2.0×10-8・・・(3)
上記(3)式の[%Ti]は前記溶鋼中のTiの含有量(質量%)であり、[%N]は前記溶鋼中のNの含有量(質量%)であり、[%Mg]は前記溶鋼中のMgの含有量(質量%)である。 - さらに質量%で、
Nb:0.001%以上0.01%以下、
V:0.001%以上0.03%以下、
Cu:0.01%以上1.00%以下、
Ni:0.01%以上0.50%以下、
Mo:0.05%以上2.00%以下、
W:0.05%以上2.00%以下のうちから選ばれる1種または2種以上を含有する成分組成を有する溶鋼を連続鋳造する請求項1または請求項2に記載の高マンガン鋼鋳片の製造方法。 - 請求項1から請求項3の何れか一項に記載の高マンガン鋼鋳片の製造方法で製造された鋳片を熱間圧延して鋼片を製造する、高マンガン鋼鋼片の製造方法。
- 請求項1から請求項3の何れか一項に記載の高マンガン鋼鋳片の製造方法で製造された鋳片を熱間圧延して鋼板を製造する、高マンガン鋼鋼板の製造方法。
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