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• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/005—Heat treatment of ferrous alloys containing Mn
• • 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
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • 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
• • 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
• • 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
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
• • 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
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • 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
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • 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
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • 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
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • 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
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • 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
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys

Definitions

• the present invention relates to an austenitic wear-resistant steel plate used for wear-resistant members.
• Conventional steel plates for wear-resistant members are manufactured by quenching steel containing about 0.1 to 0.3% C as disclosed in Patent Document 1 and the like to make the metal structure martensite.
• the Such a steel sheet has a remarkably high Vickers hardness of about 400 to 600 Hv, and is excellent in wear resistance.
• the martensite structure is very hard, bending workability and toughness are inferior.
• conventional steel plates for wear-resistant members contain a large amount of C in order to increase the hardness, but if containing 0.2% or more of C, weld cracks may occur.
• high Mn cast steel is used as a material having both wear resistance and ductility.
• High Mn cast steel has good ductility and toughness because the matrix is austenite.
• high-Mn cast steel has the characteristic that when the surface part is subjected to plastic deformation due to rock collisions, deformation twins, or work-induced martensitic transformation occurs depending on conditions, and only the hardness of the surface part is significantly increased. Have. For this reason, the high Mn cast steel can be maintained in a state in which ductility and toughness are excellent because the central portion remains austenite even if the wear resistance of the impact surface (surface portion) is improved.
• steel with a C content of 1% or more is proposed to be manufactured by performing a solution heat treatment in the austenite region after casting and then performing a water-cooling heat treatment (water toughness treatment). ing.
• the water toughness treatment is a treatment performed to rapidly cool the steel to suppress precipitation of carbides generated during normal air cooling and improve ductility and toughness.
• carbide forming elements such as Ti, V, Nb, Zr, Ta, etc.
• Japanese Unexamined Patent Publication No. 2014-194042 Japanese Patent Publication No.57-17937 Japanese Patent Publication No. 63-8181 Japanese Patent Publication No. 1-14303 Japanese Patent Publication No. 2-15623 Japanese Unexamined Patent Publication No. 60-56056 Japanese Unexamined Patent Publication No. 62-139855 Japanese Laid-Open Patent Publication No. 1-142058
• an object of the present invention is to provide an austenitic wear-resistant steel sheet that is excellent in wear resistance and strength, and toughness and ductility contrary to these.
• the C content is increased to around 1%, twin deformation is caused by plastic deformation due to rock collisions, etc., and remarkable work hardening occurs on the steel sheet surface. It is necessary to remarkably increase the hardness of the surface portion of the steel sheet by generating hard martensite by processing-induced martensite transformation. Since the hardness of martensite containing a large amount of carbon is high, causing the work-induced martensitic transformation in the steel plate surface portion significantly improves the wear resistance of the austenitic wear-resistant steel plate.
• the structure of the austenitic wear-resistant steel sheet is a structure mainly composed of austenite at the time of manufacture
• the stability of austenite is controlled so that it undergoes processing-induced martensitic transformation when rocks collide. It is necessary to.
• the content of C and Mn is controlled.
• crystal grains In order to improve the toughness of a steel sheet, it is extremely effective to refine austenite crystal grains (hereinafter sometimes referred to simply as “crystal grains”), and this can be achieved by hot rolling. Refinement of crystal grains has an effect of improving toughness in proportion to “ ⁇ 1/2 to the crystal grain size” as known from the relationship of Hall Petch.
• excessive refinement has a drawback in that the amount of carbide precipitation at the grain boundaries is increased by increasing the number of carbide nucleation sites generated at the austenite grain boundaries. Grain boundary carbides are very hard, and as the amount of precipitation increases, the toughness and ductility of the steel decrease.
• the present inventors have found that the toughness and ductility of a steel sheet can be improved by controlling the crystal grains so as not to become excessively small while miniaturizing the crystal grains.
• the austenitic wear-resistant steel sheet according to one aspect of the present invention has a chemical composition of mass%, C: more than 0.80% to 1.60%, Si: 0.01 to 2.00% Mn: 5.0 to 30.0%, P: 0.050% or less, S: 0.0100% or less, Cu: 0 to 3.0%, Ni: 0 to 3.0%, Co: 0 to 3.0%, Cr: 0 to 5.0%, Mo: 0 to 2.0%, W: 0-2.0%, Nb: 0 to 0.30%, V: 0 to 0.30%, Ti: 0 to 0.30%, Zr: 0 to 0.30%, Ta: 0 to 0.30%, B: 0 to 0.300%, Al: 0.001 to 0.300%, N: 0 to 1.000% O: 0 to 0.0100%, M
• the chemical composition may satisfy the following formula. ⁇ C + 0.8 ⁇ Si ⁇ 0.2 ⁇ Mn ⁇ 90 ⁇ (P + S) + 1.5 ⁇ (Cu + Ni + Co) + 3.3 ⁇ Cr + 9 ⁇ Mo + 4.5 ⁇ W + 0.8 ⁇ Al + 6 ⁇ N + 1.5 ⁇ 3.2
• Each element symbol in the above formula indicates the content of each element in mass%.
• the metal structure is a volume fraction, ⁇ martensite: 0-10%, ⁇ 'martensite: 0-10%, The total of the ⁇ martensite and the ⁇ ′ martensite may be 0 to 10%.
• the chemical composition is in mass%, O: 0.0001 to 0.0100%, Total of Mg content, Ca content and REM content: 0.0001 to 0.0100% may be sufficient.
• the chemical composition is in mass%, S: 0.0001 to 0.0050%, The content in mass% of O and S may satisfy O / S ⁇ 1.0.
• the chemical composition is in mass%, Cu: 0 to 0.2% may be used.
• an austenitic wear-resistant steel plate (hereinafter simply referred to as “steel plate”) that is excellent in wear resistance and strength, and toughness and ductility contrary to these.
• the chemical composition is appropriately controlled, the metal structure is appropriately controlled by hot rolling, and the crystal grains of the steel sheet are refined, thereby improving the resistance.
• a steel sheet excellent in wear and strength, toughness and ductility can be provided.
• the steel sheet according to the present invention can be manufactured to a width of about 5 m and a length of about 50 m with various plate thicknesses ranging from about 3 mm to about 200 mm.
• the steel sheet according to the present invention can be used not only as a relatively small wear-resistant member to which impact such as a crusher liner is applied, but also as a very large construction machine member and wear-resistant structural member.
• the steel plate which concerns on this invention the steel pipe and shape steel which have the characteristic similar to the steel plate which concerns on this invention can also be manufactured.
• the preferred embodiment of the present invention since coarsening of crystal grains in the welded portion can be suppressed using oxysulfide, it is possible to provide a steel plate that is excellent in the toughness of the welded portion.
• a steel sheet using a structure mainly composed of high-hardness austenite as described above or a martensitic transformation of the austenite structure is defined as an austenitic wear-resistant steel.
• a steel sheet having an austenite volume fraction of 90% or more is defined as an austenitic wear-resistant steel sheet.
• C Over 0.80% to 1.60%
• C stabilizes austenite, improves the wear resistance of the steel sheet, and further increases the hardness.
• the C content needs to be more than 0.80%.
• the C content is preferably 0.90% or more, or 1.00% or more.
• the C content exceeds 1.60%, carbides are coarsely produced in a large amount in the steel, so that high toughness cannot be obtained in the steel sheet. Therefore, the C content is 1.60% or less.
• the C content is preferably 1.50% or less, or 1.40% or less.
• Si is usually a deoxidizing element and a solid solution strengthening element, but has the effect of suppressing the formation of Cr and Fe carbides.
• the present inventors have studied various elements that suppress the formation of carbides and found that the generation of carbides is suppressed by containing a predetermined amount of Si. Specifically, the present inventors have found that the formation of carbides is suppressed by setting the Si content to 0.01 to 2.00%. If the Si content is less than 0.01%, the effect of suppressing the formation of carbides cannot be obtained. On the other hand, if the Si content exceeds 2.00%, coarse inclusions are generated in the steel, which may cause deterioration of the ductility and toughness of the steel sheet.
• the Si content is preferably 0.20% or more, or 0.50% or more.
• the Si content is preferably 1.50% or less, 1.20% or less, or 1.00% or less.
• Mn is an element that stabilizes austenite together with C.
• the Mn content is 5.0 to 30.0%.
• the Mn content is preferably 7.0% or more, 10.0% or more, 12.0% or more, or 15.0% or more.
• the Mn content is preferably 25.0% or less, 20.0% or less, or 18.0% or less.
• the Mn content is more than ⁇ 20 ⁇ C + 30 (%) and not more than ⁇ 20 ⁇ C + 45 (%) in relation to the C content (ie, ⁇ 20 ⁇ C + 30 ⁇ Mn ⁇ ⁇ 20 ⁇ C + 45).
• the Mn content is ⁇ 20 ⁇ C + 30 (%) or less, the stability of austenite is lowered, and hard ⁇ ′ martensite and ⁇ martensite are generated in the steel sheet after hot rolling and cooling. This is because the ductility, toughness and workability of the steel sheet are lowered.
• the stability of austenite is sufficiently secured, and it is not necessary to include Mn, which is higher than C and exceeds this value. Because. Since the influence of C on the stabilization of austenite is very large, in the steel sheet according to the present embodiment, the relationship between the Mn content and the C content is particularly important.
• the P content is 0.050% or less.
• the P content is preferably 0.030% or less, or 0.020% or less.
• P is generally mixed as an impurity from scrap or the like during the production of molten steel, but there is no need to particularly limit the lower limit thereof, and the lower limit is 0%. However, if the P content is excessively reduced, the manufacturing cost may increase. Therefore, the lower limit of the P content may be 0.001% or more, or 0.002% or more.
• S is an impurity. If it is excessively contained, it segregates at the grain boundary or produces coarse MnS, which lowers the ductility and toughness of the steel sheet. Therefore, the S content is set to 0.0100% or less.
• the S content is preferably 0.0060% or less, 0.0040% or less, or 0.0020% or less.
• the lower limit of the S content is 0%.
• S suppresses the growth of austenite crystal grains by generating fine oxysulfides in O and Mg, Ca and / or REM (rare-earth metal) and steel. In addition, there is an effect of improving the toughness of the steel sheet, particularly the toughness of the heat-affected zone (HAZ).
• the “oxysulfide” includes not only a compound containing both O and S but also an oxide and a sulfide.
• the steel sheet according to the present embodiment further includes the following Cu, Ni, Co, Cr, Mo, W, Nb, V, Ti, Zr, Ta, B, N, O, Mg, and Ca.
• one or more of REM may be selectively contained.
• the content of these elements is not essential, and the lower limit of the content of all these elements is 0%.
• Al mentioned later is not an arbitrary element but an essential element.
• Cu, Ni and Co improve the toughness of the steel sheet and stabilize austenite.
• the content of any one of Cu, Ni, and Co exceeds 3.0%, the effect of improving the toughness of the steel sheet is saturated and the cost increases. Therefore, when these elements are contained, the content of each element is set to 3.0% or less.
• the Cu content, Ni content, and Co content are each preferably 2.0% or less, 1.0% or less, 0.5% or less, or 0.3% or less. In particular, the Cu content is more preferably 0.2% or less.
• the Cu content may be 0.02% or more, 0.05% or more, or 0.1% or more
• the Ni content and Co content may be 0.02% or more, 0%, respectively. .05% or more, 0.1% or more, or 0.2% or more.
• Cr 0 to 5.0%
• Cr improves the work hardening characteristics of steel. If the Cr content exceeds 5.0%, precipitation of grain boundary carbides is promoted and the toughness of the steel sheet is lowered. Therefore, the Cr content is 5.0% or less.
• the Cr content is preferably 2.5% or less, or 1.5% or less. In order to improve work hardening characteristics, the Cr content may be 0.05% or more, or 0.1% or more.
• Mo and W reinforce the steel, lower the C activity in the austenite phase, suppress precipitation of Cr and Fe carbides precipitated at the austenite grain boundaries, and improve the toughness and ductility of the steel sheet.
• Mo content and W content shall be 2.0% or less, respectively.
• the Mo content and the W content are 1.0% or less, 0.5% or less, or 0.1% or less, respectively.
• the Mo content and the W content may be 0.01% or more, 0.05% or more, or 0.1% or more, respectively.
• Nb 0 to 0.30%, V: 0 to 0.30%, Ti: 0 to 0.30%, Zr: 0 to 0.30%, Ta: 0 to 0.30%
• Nb, V, Ti, Zr and Ta generate precipitates such as carbonitrides in the steel. These precipitates improve the toughness of the steel by suppressing the coarsening of crystal grains during the solidification of the steel.
• the said element reduces the activity of C and N in austenite, and suppresses the production
• the Nb content, the V content, the Ti content, the Zr content, and the Ta content are each 0.30% or less, 0.20% or less, 0.10% or less, or 0.01% or less. It is more preferable. Furthermore, it is still more preferable that the total of Nb content, V content, Ti content, Zr content and Ta content is 0.30% or less, or 0.20% or less.
• the Nb content and the V content may be 0.005% or more, 0.01% or more, or 0.02% or more, respectively.
• the Ti content, the Zr content, and the Ta content may be 0.001% or more, or 0.01% or more, respectively.
• B segregates at the austenite grain boundaries to suppress grain boundary fracture and improve the proof stress and ductility of the steel sheet.
• the B content is set to 0.300% or less.
• the B content is preferably 0.250% or less.
• the B content may be 0.0002% or more, or 0.001% or more.
• Al is a deoxidizing element and a solid solution strengthening element, but suppresses the formation of Cr and Fe carbides as with Si.
• the present inventors have found that the generation of carbides is suppressed when the Al content exceeds a predetermined amount. Specifically, the present inventors have found that the formation of carbide is suppressed by setting the Al content to 0.001 to 0.300%. If the Al content is less than 0.001%, the effect of suppressing the formation of carbides cannot be obtained. On the other hand, if the Al content exceeds 0.300%, coarse inclusions are generated, which may cause deterioration of the ductility and toughness of the steel sheet.
• the Al content is preferably 0.003% or more, or 0.005% or more. Further, the Al content is preferably 0.250% or less, or 0.200% or less.
• N is an element effective for stabilizing austenite and improving the proof stress of the steel sheet.
• N has the same effect as C as an element for stabilizing austenite.
• N has no adverse effect such as deterioration of toughness due to grain boundary precipitation, and the effect of increasing the strength at extremely low temperatures is greater than that of C. Further, N has the effect of dispersing fine nitrides in the steel by coexisting with the nitride-forming elements. If the N content exceeds 1.000%, the toughness of the steel sheet may deteriorate significantly. Therefore, the N content is 1.000% or less.
• the N content is more preferably 0.300% or less, 0.100% or less, or 0.030% or less. Although a certain amount of N may be mixed as an impurity, the N content may be 0.003% or more for the purpose of increasing the strength.
• the N content is more preferably 0.005% or more, 0.007% or more, or 0.010% or more.
• O may be mixed in steel in a certain amount as an impurity, but has an effect of increasing toughness by refining crystal grains in HAZ.
• the O content exceeds 0.0100%, ductility and toughness in the HAZ may decrease on the contrary due to oxide coarsening and segregation to grain boundaries. Therefore, the O content is 0.0100% or less.
• the O content is more preferably 0.0070% or less, or 0.0050% or less.
• the O content may be 0.0001% or more, or 0.0010% or more.
• Mg, Ca, and REM are produced in large amounts in high-Mn steel, and suppress the production of MnS that significantly reduces the ductility and toughness of the steel sheet.
• the Mg content, the Ca content, and the REM content are each set to 0.0100% or less.
• the Mg content, Ca content and REM content are more preferably 0.0070% or less, or 0.0050% or less, respectively.
• the Mg content, Ca content, and REM content may each be 0.0001% or more.
• the Mg content, Ca content, and REM content may be 0.0010% or more, or 0.0020% or more, respectively.
• REM rare earth metal element
• the content of REM means the total content of these 17 elements.
• the total of the Mg content, Ca content and REM content may be 0.0001 to 0.0100%. preferable. That is, the content of at least one element in Mg, Ca, and REM is preferably 0.0001 to 0.0100%.
• the O content may be 0.0002% or more and 0.0050% or less.
• the total of Mg content, Ca content and REM content may be 0.0003% or more, 0.0005% or more, or 0.0010% or more, or 0.0050% or less, or 0.0040% or less. Good.
• the reason why the O content is 0.0001% or more and the total of Mg content, Ca content and REM content is 0.0001 to 0.0100% is that oxidation of Mg, Ca and / or REM in steel This is because a product is generated and the coarsening of crystal grains is prevented by the HAZ of the steel plate.
• the HAZ austenite crystal grain size obtained by the pinning effect of grain growth by the oxide is from several tens of ⁇ m to 300 ⁇ m under standard welding conditions, and does not exceed 300 ⁇ m (however, the steel plate (mother Except when the grain size of the austenite of the material exceeds 300 ⁇ m).
• S forms an oxysulfide with O and Mg, Ca and / or REM, and is therefore an effective element for refining crystal grains. Therefore, when S is contained in the steel together with O and Mg, Ca and / or REM, the S content is 0.0001% in order to obtain the effect of increasing toughness by refining crystal grains in HAZ. The above is preferable. Further, when S is contained in the steel together with O and Mg, Ca and / or REM, the S content is preferably 0.0050% or less in order to obtain a more excellent ductility and toughness of the steel sheet.
• the S and O contents satisfy the relationship of O / S ⁇ 1.0.
• the effect of increasing toughness can be remarkably exhibited. Since sulfides are thermally unstable with respect to oxides, if the ratio of S in the precipitated particles increases, pinning particles that are stable at high temperatures may not be ensured. Therefore, when the O content is 0.0001 to 0.0100%, the total of the Mg content, Ca content and REM content is 0.0001 to 0.0100%, and S is contained in the steel,
• the content is preferably 0.0001 to 0.0050%, and the O content and the S content are preferably O / S ⁇ 1.0.
• the precipitation state of the oxysulfide in the steel becomes more preferable, and the effect of refining crystal grains can be remarkably exhibited.
• the average particle size of the austenite of the steel sheet is less than 150 ⁇ m due to the above effects, the average particle size of austenite in the HAZ can be made 150 ⁇ m or less under standard welding conditions.
• the upper limit of O / S is not particularly required, but may be 200.0 or less, 100.0 or less, or 10.0 or less.
• the balance other than the above components is composed of Fe and impurities.
• the impurities in the present embodiment are components that are mixed due to various factors in the manufacturing process, including raw materials such as ore and scrap, when the steel plate is industrially manufactured.
• the steel plate according to the present embodiment It means that it is allowed as long as it does not adversely affect the characteristics of
• the present inventors have found that the corrosion wear resistance due to a substance in which slurry such as gravel is mixed with salt water which is a corrosive environment can be improved by improving the corrosion resistance.
• the upper limit of a CIP value is not specifically limited, For example, it is good also as 64.0 or less, 50.0 or less, 40.0 or less, 30.0 or less, or 20.0 or less.
• the corrosion resistance and corrosion wear resistance of the steel sheet can be improved. However, when the CIP value is less than 3.2, the corrosion resistance and corrosion wear resistance of the steel sheet are not significantly improved.
• C, Si, Mn, P, S, Cu, Ni, Co, Cr, Mo, W, Al, and N are in mass%. The content of each element is shown. If the element is not included, 0 is substituted.
• the steel sheet according to the present embodiment has an austenite volume fraction of 90 to 100% in the metal structure in order to obtain desired toughness. If the volume fraction of austenite in the steel sheet is less than 90%, the toughness of the steel sheet decreases.
• the volume fraction of austenite is preferably 95% or more, 97% or more, or 100%.
• the steel sheet according to this embodiment obtains a desired toughness by containing a predetermined amount of austenite.
• the total volume fraction of ⁇ martensite and ⁇ ′ martensite is preferably 10% or less, 5% or less, 3% or less, or 0%.
• the metal structure of the steel sheet according to the present embodiment is preferably composed of austenite and the remaining structure of ⁇ martensite and ⁇ ′ martensite.
• the remaining structure in the metal structure may be 0%.
• iron-based carbonitrides such as cementite, and carbonitrides of metal elements other than iron , Ti, Mg, Ca, REM and other oxysulfides, and other inclusions and other measurement results may be obtained suggesting the presence of trace amounts (for example, less than 1%).
• the volume fraction of austenite, ⁇ martensite and ⁇ ′ martensite is determined by the following method.
• a sample is cut out from the central portion of the steel plate thickness (1 / 2T depth from the steel plate surface (T is the plate thickness)).
• T is the plate thickness
• a surface parallel to the plate thickness direction and the rolling direction of the sample is used as an observation surface, and the observation surface is mirror-finished by buffing or the like, and then distortion is removed by electrolytic polishing or chemical polishing.
• the average integrated intensity of the (311) (200) (220) plane of austenite having a face-centered cubic structure (fcc structure) and a dense hexagonal lattice structure (hcp) The average value of the integrated intensity of the (010) (011) (012) plane of the ⁇ martensite of the structure) and the (220) (200) (211) plane of the ⁇ ′ martensite of the body-centered cubic structure (bcc structure)
• the volume fraction of austenite, ⁇ martensite and ⁇ ′ martensite is obtained from the average value of the integrated intensity.
• ⁇ ′ martensite has a body-centered tetragonal structure (bct structure), and the diffraction peak obtained by X-ray diffraction measurement has a crystalline structure. Due to the anisotropy of the double peak. Therefore, the volume fraction of ⁇ ′ martensite is obtained from the sum of the integrated intensities of the respective peaks.
• the toughness of the steel sheet is basically improved by refining austenite while suppressing the formation of carbides.
• the steel sheet according to the present embodiment includes austenite having a volume fraction of 90 to 100%.
• the austenite in a steel plate is refined
• the average particle diameter of austenite in the steel sheet is set to 40 ⁇ m or more.
• the average particle size of austenite in the steel sheet is preferably 50 ⁇ m or more, 75 ⁇ m or more, or 100 ⁇ m or more.
• the average particle size of austenite in the steel sheet is set to 300 ⁇ m or less.
• the average particle size of austenite in the steel sheet is preferably 250 ⁇ m or less or 200 ⁇ m or less. Note that the upper and lower limits of the average particle size of the austenite are values that can be achieved by the pinning effect of hot rolling or oxysulfide according to the present embodiment.
• the average particle size of austenite in the HAZ can be reduced even when exposed to high temperatures by welding.
• FL melting
• SMAW Shielded Metal Arc Welding
• the average particle size of HAZ austenite in the vicinity can be maintained in the range of 40 to 300 ⁇ m.
• the mass ratio of O and S in the steel sheet is further set to O / S ⁇
• the average particle size of austenite in the HAZ near the FL after the welding can be maintained at 150 ⁇ m or less, or in the range of 40 to 150 ⁇ m.
• the toughness of the welded joint obtained by welding the steel plate according to this embodiment can be increased.
• highly efficient welding methods such as enlarging welding heat input, can be used.
• a method for measuring the average particle size of austenite in the present embodiment will be described.
• a sample is cut out from the plate thickness central portion of the steel plate (1 / 2T depth from the steel plate surface (T is the plate thickness)).
• a cross section parallel to the rolling direction and the plate thickness direction of the steel sheet is used as an observation surface, and is mirror-finished by alumina polishing or the like, and then corroded with a nital solution or a picral solution.
• the average grain size of austenite is obtained by magnifying and observing the metal structure of the observation surface after corrosion with an optical microscope or an electron microscope.
• a field of view of 1 mm ⁇ 1 mm or more is enlarged to a magnification of about 100 times, and annex C. of JIS Z0551: 2013 is used.
• the average section length per austenite crystal grain observed in the observation field is obtained by the cutting method using the straight test line of No. 2, and the average grain size of the austenite is obtained by setting this as the average grain size.
• the average particle diameter of the austenite after recrystallization is expressed by, for example, the following formula (1).
• D rex is the average grain size of austenite after recrystallization
• D 0 is the average grain size of austenite before recrystallization
• ⁇ is the plastic strain due to hot rolling
• p and q is a positive constant
• r is a negative constant.
• austenite having a predetermined crystal grain size can be obtained by performing plastic rolling at the maximum as much as possible and performing rolling a plurality of times.
• the initial grain size that is, the average grain size of austenite before recrystallization is 600 ⁇ m
• the average grain size of austenite after recrystallization is 300 ⁇ m or less.
• the plastic strain during hot rolling needs to be 0.056 or more.
• the plastic strain during hot rolling needs to be 0.25 or more.
• the plastic strain during hot rolling may be 2.1 or less.
• the plastic strain at the time of hot rolling calculated by the above formula (1) for obtaining austenite having a predetermined crystal grain size is a guideline, and in practice, grain growth of austenite after recrystallization. It is necessary to make fine adjustments in consideration of the effects of multi-pass rolling.
• the present inventors have confirmed that the steel sheet according to the present embodiment can be manufactured by the following manufacturing method based on the research up to now including the above.
• Melting / slab manufacturing process need not be particularly limited. That is, following the melting by a converter or an electric furnace, various secondary refining is performed to adjust the above-described chemical composition. Then, what is necessary is just to manufacture a slab by methods, such as normal continuous casting.
• the slab heating temperature is preferably more than 1250 ° C to 1300 ° C.
• the steel sheet surface may be oxidized to reduce the yield, and austenite may be coarsened and may not be easily refined even by hot rolling after slab heating. Therefore, slab heating temperature shall be 1300 degrees C or less.
• the cumulative rolling reduction in the temperature range of 900 to 1000 ° C. is 10 to 80%. As a result, it has been confirmed that the average particle size of austenite can be made 40 to 300 ⁇ m.
• the cumulative rolling reduction in the temperature range of 900 to 1000 ° C. is less than 10 to 30%, and the steel sheet according to this embodiment is manufactured by satisfying the conditions described later. It has been confirmed that it can be done.
• the rolling finishing temperature is also important to control the finishing temperature during hot rolling (hereinafter sometimes referred to as the rolling finishing temperature). If the rolling finish temperature is less than 900 ° C., austenite may not be completely recrystallized, or even if austenite is recrystallized, it may be excessively refined and the average particle size may be less than 40 ⁇ m. If austenite is not completely recrystallized, many dislocations and deformation twins are introduced into the metal structure, and a large amount of carbide may be formed in the subsequent cooling. When a large amount of carbide is generated in steel, the ductility and toughness of the steel sheet are lowered. The above-mentioned problems can be prevented by setting the rolling finishing temperature to 900 ° C. or higher. Therefore, in this embodiment, the rolling finishing temperature is set to 900 ° C. or higher.
• accelerated cooling is performed except when the heat treatment described later is performed.
• the purpose of accelerated cooling is to suppress the formation of carbides after hot rolling and increase the ductility and toughness of the steel sheet.
• the average cooling rate during accelerated cooling is 1 ° C / s or higher. This is because if the average cooling rate during accelerated cooling is less than 1 ° C./s, the effect of accelerated cooling (the effect of suppressing the formation of carbides) may not be sufficiently obtained. On the other hand, if the cooling rate during accelerated cooling exceeds 200 ° C./s, the amount of austenite in the steel may decrease, and the toughness and ductility of the steel sheet may decrease. Therefore, the average cooling rate during accelerated cooling is set to 200 ° C./s or less.
• Accelerated cooling after hot rolling starts as high as possible. Since the temperature at which the carbide actually starts to precipitate is less than 850 ° C., the cooling start temperature is set to 850 ° C. or higher. The cooling end temperature is 550 ° C. or lower. Accelerated cooling has not only the effect of suppressing the formation of carbides as described above, but also the effect of suppressing austenite grain growth. Therefore, also from the viewpoint of suppressing the grain growth of austenite, the above-described hot rolling and accelerated cooling are performed in combination.
• the solution treatment includes, for example, reheating the steel sheet to a temperature of 1100 ° C. or higher, performing accelerated cooling at an average cooling rate of 1 to 200 ° C./s from a temperature of 1000 ° C. or higher, and a temperature of 500 ° C. or lower. Allow to cool.
• the plate thickness of the steel plate according to this embodiment is not particularly limited, but may be 3 to 100 mm. If necessary, the plate thickness may be 6 mm or more, or 12 mm or more, and may be 75 mm or less, or 50 mm or less. Is not particularly necessary to define the mechanical properties of the steel sheet according to the present embodiment, JIS Z 2241: According to 2011, the yield stress (YS) of 300N / mm 2 or more, a tensile strength of the (TS) 800N / mm 2 or more The elongation (EL) may be 40% or more.
• the tensile strength of 900 N / mm 2 or more, or 950 N / mm may be 2 or more, 2000N / mm 2 or less, or 1500 N / mm 2 may be less.
• the absorbed energy at ⁇ 40 ° C. according to JIS Z 2242: 2005 may be 100 J or more, 200 J or more, or 300 J or more.
• the austenitic wear-resistant steel sheet according to the present embodiment is a rail crossing, a caterpillar liner, an impeller blade, a crusher blade, a rock hammer, and other small members and construction machines, industrial machinery, civil engineering, and columns that require wear resistance in the construction field, It can be suitably used for large members such as steel pipes and outer plates.
• Volume fraction of austenite, ⁇ martensite and ⁇ 'martensite Cut out three samples from the plate thickness center of the steel plate (1 / 2T depth (T is the plate thickness) from the steel plate surface), and use the plane parallel to the plate thickness direction and rolling direction of the sample as the observation surface. After finishing to a mirror surface by buffing or the like, distortion was removed by electrolytic polishing or chemical polishing. Using the X-ray diffractometer (XRD: RINT2500, manufactured by Rigaku Corporation), the average value of the integrated intensity of the (311) (200) (220) plane of austenite having a face-centered cubic structure (fcc structure) with respect to the observation surface.
• XRD X-ray diffractometer
• ⁇ ′ martensite has a body-centered tetragonal structure (bct structure), and the diffraction peak obtained by X-ray diffraction measurement becomes a double peak due to the anisotropy of the crystal structure. From the total, the volume fraction of ⁇ ′ martensite was obtained.
• volume fraction of austenite was 90% or more, it was determined to be acceptable as being within the scope of the present invention. A case where the volume fraction of austenite was less than 90% was determined to be unacceptable as being outside the scope of the present invention.
• Average particle size of austenite Cut out three samples from the plate thickness center of the steel plate (1 / 2T depth (T is the plate thickness) from the steel plate surface), and use the cross section parallel to the rolling direction and the plate thickness direction of the steel plate as the observation surface. After being mirrored, it was corroded with a nital solution. In the observation surface, a field of view of 1 mm ⁇ 1 mm or more is enlarged to a magnification of about 100 times, and Annex C. JIS Z0551: 2013 is attached. The average section length per crystal grain of austenite observed in the observation field was determined by the cutting method using the straight test line of 2, and this was used as the average grain size.
• HAZ austenite was determined by the same method as above for HAZ near the FL (melting line) at the center of the plate thickness. The particle size was measured.
• Yield stress is 300N / mm 2 or more
• a tensile strength is 800 N / mm 2 or more
• elongation is the case of 40% or more was judged to be acceptable as excellent strength and ductility. A case where even one of the above conditions was not satisfied was determined to be unacceptable.
• Abrasion resistance Scratching abrasion test (peripheral speed 3.7 m / sec, 50 hours) using a mixture of silica (JIS G5901: No. 5 of 2016) and water (mixing ratio of silica sand 2: water 1) as a wear material
• the weight loss of wear was evaluated based on plain steel (SS400 of JIS G3101: 2015).
• the wear amount ratio of ordinary steel in Table 2-1 and Table 2-2 was obtained by dividing the wear loss of each steel by the wear loss of ordinary steel. However, when the plate thickness was more than 15 mm, a test piece reduced to a plate thickness of 15 mm was used.
• Corrosion wear For evaluation of corrosive wear, a scratching wear test (peripheral speed 3.7 m / sec) using a mixture of silica sand (average particle size 12 ⁇ m) and seawater (mixing ratio 30% silica sand, 70% seawater) as a wear material. , 100 hours) was evaluated based on plain steel (SS400 of JIS G3101: 2015).
• the ratio of corrosion wear of ordinary steel in Table 2-1 and Table 2-2 was determined by dividing the corrosion wear loss of each steel by the corrosion wear loss of ordinary steel. However, when the plate thickness was more than 15 mm, a test piece reduced to a plate thickness of 15 mm was used.
• the target value of the corrosion wear ratio of normal steel to 0.80 or less was set to 0.80 or less.
• Toughness The toughness of the steel plate (base material) is JIS, in which a test piece is taken in parallel with the rolling direction from a position of 1 / 4T (T is the plate thickness) of the steel plate, and a notch is provided in the direction in which cracks propagate in the width direction.
• T the plate thickness
• J the absorbed energy at ⁇ 40 ° C.

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