Classifications

• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/005—Heat treatment of ferrous alloys containing Mn
• • 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 a wear-resistant member.
• a steel plate for wear-resistant members in the related art is manufactured by hardening a steel containing about 0.1% to 0.3% of C as disclosed in Patent Document 1 or the like to cause the metallographic structure to contain martensite.
• Such a steel plate has a Vickers hardness as significantly high as about 400 to 600 Hv and is excellent in wear resistance.
• the martensite structure is very hard, bending workability and toughness are poor.
• the steel plate for wear-resistant members in the related art contains C in a large amount in order to increase hardness, a C content of 0.2% or more causes a possibility of weld cracking.
• high Mn cast steel has been used as a material having both wear resistance and ductility.
• the high Mn cast steel has good ductility and toughness because the matrix is austenite.
• the high Mn cast steel has a characteristic that, when the surface portion undergoes plastic deformation due to a collision with a rock or the like, deformation twinning or, under certain conditions, a strain-induced martensitic transformation occurs, and only the hardness of the surface portion significantly increases. Therefore, the high Mn cast steel remains austenitic in the central part even when the wear resistance of the impact surface (surface portion) is improved and thus can be maintained in a state of being excellent in ductility and toughness.
• these high Mn cast steels contain C in an amount as large as 1% or more in order to improve wear resistance.
• C content of 1% or more even if austenite excellent in ductility and toughness is formed, there may be cases where the ductility and toughness decrease due to the precipitation of a large amount of carbides and the like.
• the water toughening treatment is a treatment performed to improve ductility and toughness by rapidly cooling the steel and thus suppressing the precipitation of carbides generated during normal air cooling.
• Refinement of grains is effective not only for improving ductility and toughness as described above, but also for improving a strain hardening property. Therefore, in order to refine the grains of a high Mn cast steel, lowering the casting temperature of the high Mn cast steel is proposed in addition to adding Ti, V, Nb, Zr, Ta, and the like. However, there is a limit to lowering the casting temperature of the high Mn cast steel, and there is also a problem that casting defects are easily generated when the casting temperature of the high Mn cast steel is lowered.
• the present invention has been made in view of such circumstances, and an object thereof is to provide an austenitic wear-resistant steel plate which is excellent in wear resistance and strength and excellent in toughness and ductility which conflict therewith.
• an austenitic wear-resistant steel plate In order to obtain the wear resistance, strength, toughness, and ductility of an austenitic wear-resistant steel plate, a structure primarily containing an austenite phase needs to be formed at a temperature at which the austenitic wear-resistant steel plate is used. Furthermore, it is necessary to improve the stability of austenite and cause a sufficient amount of austenite to be contained in steel so that a structure primarily containing a' martensite and ⁇ martensite is not formed.
• the refinement of austenite grains (hereinafter, sometimes simply referred to as "grains") is extremely effective, and this can be achieved by hot rolling.
• the refinement of grains has an effect of improving the toughness proportional to "the -1/2 power of grain size" as is known from the Hall-Petch relationship or the like.
• excessive refinement has a disadvantage of increasing the amount of carbides precipitated at grain boundaries by increasing the nucleation sites of carbides formed at austenite grain boundaries.
• the carbides at grain boundaries are very hard, and when the amount of the precipitated carbides increases, the toughness and ductility of the steel decrease.
• the present inventors found that the toughness and ductility of the steel plate can be improved by achieving the refinement of grains without excessively reducing the grains.
• the present invention provides the following austenitic wear-resistant steel plate by appropriately controlling the chemical composition of the steel plate and achieving the refinement of grains of the steel plate through hot rolling.
• an austenitic wear-resistant steel plate (hereinafter, simply referred to as "steel plate”) which is excellent in wear resistance and strength and excellent in toughness and ductility which conflict therewith.
• steel plate excellent in wear resistance and strength and excellent in toughness and ductility by appropriately controlling the chemical composition, appropriately controlling the metallographic structure through hot rolling, and achieving the refinement of grains of the steel plate.
• the steel plate 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 plate according to the present invention is not limited to a relatively small wear-resistant member to which an impact is applied, such as a crusher liner, and can also be used as a very large member for a construction machine and a wear-resistant structural member.
• steel pipes and shaped steels having similar characteristics to the steel plate according to the present invention can also be manufactured.
• coarsening of grains in a welding can be suppressed using oxysulfides, so that it is possible to provide a steel plate excellent also in the toughness of the weld.
• an austenitic wear-resistant steel plate having a structure primarily containing high hardness austenite as described above or utilizing martensitic transformation of the austenite structure is defined as austenitic wear-resistant steel.
• a steel plate having an austenite volume fraction of 90% or more is defined as an austenitic wear-resistant steel plate.
• the C content In order to secure a desired hardness of the steel plate and to improve the wear resistance of the steel plate, the C content needs to be more than 0.80%. In a case where particularly high wear resistance is required, the C content is preferably 0.90% or more, or 1.00% or more. On the other hand, when the C content exceeds 1.60%, a large amount of coarse carbides are formed in the steel, and the steel plate cannot achieve high toughness. Therefore, the C content is set to 1.60% or less. The C content is preferably set to 1.50% or less or 1.40% or less.
• Si is typically a deoxidizing element and a solid solution strengthening element, but has an effect of suppressing the formation of carbides of Cr and Fe.
• the present inventors conducted various examinations on the elements that suppress the formation of carbides, and found that the formation of carbides is suppressed by including a predetermined amount of Si. Specifically, the present inventors found that the formation of carbide is suppressed by setting the Si content to 0.01 to 2.00%. When the Si content is less than 0.01%, the effect of suppressing the formation of carbides is not obtained. On the other hand, when the Si content exceeds 2.00%, there may be cases where coarse inclusions are formed in the steel and thus the ductility and toughness of the steel plate deteriorate.
• the Si content is preferably set to 0.20% or more, or 0.50% or more.
• the Si content is preferably set to 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 set to 5.0% to 30.0%.
• the Mn content is preferably set to 7.0% or more, 10.0% or more, 12.0% or more, or 15.0% or more.
• the Mn content is preferably set to 25.0% or less, 20.0% or less, or 18.0% or less.
• the Mn content is set to, in relation to the C content, more than -20 ⁇ C + 30 (%) and -20 ⁇ C + 45 (%) or less (that is, -20 ⁇ C + 30 ⁇ Mn ⁇ -20 ⁇ C + 45). This is because when the Mn content is -20 ⁇ C + 30 (%) or less, the stability of austenite decreases, hard a' martensite and ⁇ martensite are generated in the steel plate after hot rolling and cooling, and thus the ductility, toughness, and workability of the steel plate decrease.
• the stability of austenite is sufficiently secured, and there is no need to include Mn, which is more expensive than C, in an amount of more than this value. Since the influence of C on austenite stabilization is very large, in the steel plate according to the present embodiment, the relationship between the Mn content and C content mentioned above is particularly important.
• the P content is set to 0.050% or less.
• the P content is preferably set to 0.030% or less or 0.020% or less.
• P is generally incorporated as impurities from scraps or the like during molten steel production, but the lower limit thereof is not particularly limited and is 0%. However, when the P content is excessively reduced, there may be cases where the manufacturing cost increases. Therefore, the lower limit of the P content may be set to 0.001% or more, or 0.002% or more.
• S is an impurity, and when S is contained excessively, S segregates at grain boundaries or forms coarse MnS, thereby reducing the ductility and toughness of the steel plate. Therefore, the S content is set to 0.0100% or less.
• the S content is preferably set to 0.0060% or less, 0.0040% or less, or 0.0020% or less.
• the lower limit of the S content is 0%.
• S has an effect of improving the toughness of the steel plate, particularly the toughness of a heat-affected zone (HAZ) by forming fine oxysulfides in the steel with O and Mg, Ca, and/or rare-earth metals (REM) and thus suppressing the growth of austenite grains.
• HZ heat-affected zone
• the S content may be set to 0.0001% or more, 0.0005% or more, or 0.0010% or more.
• oxysulfides include not only a compound containing both O and S but also oxides and sulfides.
• the steel plate according to the present embodiment further includes, in addition to the essential elements mentioned above, one or two or more of Cu, Ni, Co, Cr, Mo, W, Nb, V, Ti, Zr, Ta, B, N, O, Mg, Ca, and REM. These elements are not necessarily contained, and the lower limits of the amounts of all the elements are 0%. In addition, Al, which will be mentioned later, is not an optional element but an essential element.
• Cu, Ni, and Co improve the toughness of the steel plate and stabilize austenite.
• the amount of at least one of Cu, Ni, and Co exceeds 3.0%, the effect of improving the toughness of the steel plate is saturated, and the cost also increases. Therefore, in a case where these elements are contained, the amount of each of the elements is set to 3.0% or less.
• Each of the Cu content, the Ni content, and the Co content is preferably set to 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 set to 0.2% or less.
• the Cu content may be set to 0.02% or more, 0.05% or more, or 0.1% or more, and each of the Ni content and the Co content may be set to 0.02% or more, 0.05% or more, 0.1% or more, or 0.2% or more.
• the Cr content improves the strain hardening property of the steel.
• the Cr content exceeds 5.0%, precipitation of intergranular carbides is promoted, and the toughness of the steel plate is reduced. Therefore, the Cr content is set to 5.0% or less.
• the Cr content is preferably set to 2.5% or less, or 1.5% or less. In order to improve the strain hardening property, the Cr content may be set to 0.05% or more, or 0.1% or more.
• each of the Mo content and the W content is set to 2.0% or less.
• Each of the Mo content and the W content is preferably set to 1.0% or less, 0.5% or less, or 0.1% or less. In order to reliably obtain the effects, each of the Mo content and the W content may be set to 0.01% or more, 0.05% or more, or 0.1% or more.
• Nb, V, Ti, Zr, and Ta form precipitates such as carbonitrides in the steel. These precipitates improve the toughness of the steel by suppressing the coarsening of grains during solidification of the steel. Moreover, the elements reduce the activity of C and N in austenite, and thus suppresses the formation of carbides, such as cementite and graphite. Furthermore, the above elements strengthen the steel by solid solution strengthening or precipitation hardening.
• each of the Nb content, the V content, the Ti content, the Zr content, and the Ta content is set to 0.30% or less, and more preferably 0.20% or less, 0.10% or less, or 0.01 % or less. Furthermore, it is more preferable to set the sum of the Nb content, the V content, the Ti content, the Zr content, and the Ta content to 0.30% or less, or 0.20% or less.
• each of the Nb content and the V content may be set to 0.005% or more, 0.01% or more, or 0.02% or more.
• each of the Ti content, the Zr content, and the Ta content may be set to 0.001% or more or 0.01% or more.
• the B segregates at austenite grain boundaries and thus suppresses intergranular fracture, thereby improving the proof stress and ductility of the steel plate.
• the B content is set to 0.300% or less.
• the B content is preferably set to 0.250% or less.
• the B content may be set to 0.0002% or more, or 0.001% or more.
• Al is a deoxidizing element and is a solid solution strengthening element, but similarly to Si, suppresses the formation of carbides of Cr and Fe.
• the present inventors conducted various examinations on the elements that suppress the formation of carbides, and as a result, found that the formation of carbides is suppressed when the Al content is equal to or more than a predetermined amount. Specifically, the present inventors found that the formation of carbides is suppressed by setting the Al content to 0.001 to 0.300%. When the Al content is less than 0.001%, the effect of suppressing the formation of carbides is not obtained. On the other hand, when the Al content exceeds 0.300%, there may be cases where coarse inclusions are formed and thus the ductility and toughness of the steel plate deteriorate.
• the Al content is preferably set to 0.003% or more, or 0.005% or more.
• the Al content is preferably set to 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 plate.
• N has the same effect as C as an element for austenite stabilization.
• N does not have an adverse effect such as toughness deterioration due to grain boundary precipitation, and the effect of N increasing the strength at extremely low temperatures is greater than C.
• N also has an effect of dispersing fine nitrides in the steel by coexistence with nitride forming elements.
• the N content exceeds 1.000%, there may be cases where the toughness of the steel plate significantly deteriorates. Therefore, the N content is set to 1.000% or less.
• the N content is more preferably set to 0.300% or less, 0.100% or less, or 0.030% or less.
• N is incorporated as an impurity in a certain amount in some cases, but the N content may be set to 0.003% or more for the high-strengthening described above and the like.
• the N content is more preferably set to 0.005% or more, 0.007% or more, or 0.010% or more.
• O is incorporated into the steel as an impurity in a certain amount, but O has an effect of increasing the toughness by refining the grains in the HAZ.
• the O content exceeds 0.0100%, there may be cases where the ductility and toughness in the HAZ decrease due to the coarsening of oxides and the segregation to grain boundaries. Therefore, the O content is set to 0.0100% or less.
• the O content is more preferably set to 0.0070% or less or 0.0050% or less.
• the O content may be set to 0.0001% or more, or 0.0010% or more.
• each of the Mg content, the Ca content, and the REM content supress the formation of MnS which is abundantly generated in high Mn steel and deteriorate the ductility and toughness of the steel plate.
• each of the Mg content, the Ca content, and the REM content is set to 0.0100% or less.
• Each of the Mg content, the Ca content, and the REM content is more preferably 0.0070% or less or 0.0050% or less.
• each of the Mg content, the Ca content, and the REM content may be set to 0.0001% or more.
• Each of the Mg content, the Ca content, and the REM content may be set to 0.0010% or more, or 0.0020% or more.
• rare-earth metals mean a total of 17 elements including Sc, Y, and lanthanides.
• the amount of REM means the sum of the amounts of these 17 elements.
• the O content in addition to the O content being set to 0.0001% to 0.0100%, it is preferable to set the sum of the Mg content, the Ca content, and the REM content to 0.0001% to 0.0100%. That is, the amount of at least one element of Mg, Ca, and REM is preferably set to 0.0001% to 0.0100%.
• the O content may be set to 0.0002% or more, and set to 0.0050% or less.
• the sum of the Mg content, the Ca content, and the REM content may be set to 0.0003% or more, 0.0005% or more, or 0.0010% or more, and may be set to 0.0050% or less, or 0.0040% or less.
• the reason why the O content is set to 0.0001% or more and the sum of the Mg content, the Ca content, and the REM content is set to 0.0001% to 0.0100% is that coarsening of grains in the HAZ of the steel plate is prevented by forming oxides of Mg, Ca, and/or REM.
• the austenite grain size of the HAZ obtained by the austenite pinning effect of grain growth by the oxides is several tens ⁇ m to 300 ⁇ m and does not exceed 300 ⁇ m (However, a case where the austenite grain size of the steel plate (base metal) exceeds 300 ⁇ m is excluded).
• the above elements O, Mg, Ca, and REM
• S forms oxysulfides with O and Mg, Ca, and/or REM and is thus an element effective for grain refinement. Therefore, in a case where S is contained in the steel together with O and Mg, Ca, and/or REM, in order to obtain the effect of increasing the toughness through refinement of grains in the HAZ, the S content preferably set to 0.0001% or more. In a case where S is contained in the steel together with O and Mg, Ca, and/or REM, in order to obtain better ductility and toughness for the steel plate, the S content is preferably set to 0.0050% or less.
• the O content is set to 0.0001% to 0.0100%
• the sum of the Mg content, the Ca content, and the REM content is set to 0.0001% to 0.0100%
• S is contained in the steel
• the S content is set to 0.0001% to 0.0050% and the O content and the S content are set to O/S ⁇ 1.0.
• O/S ⁇ 1.5 or O/S ⁇ 2.0 is satisfied.
• the average grain size of austenite of the steel plate is less than 150 ⁇ m due to the above effect, the average grain size of austenite in the HAZ can be set to 150 ⁇ m or less under standard welding conditions.
• the upper limit of O/S does not need to be particularly determined, but may be set to 200.0 or less, 100.0 or less, or 10.0 or less.
• the remainder other than the above-mentioned elements consists of Fe and impurities.
• the impurities are elements that are incorporated due to various factors of the manufacturing process, including raw materials such as ore and scrap, when the steel plate is industrially manufactured, and are acceptable without adversely affecting the properties of the steel plate according to the present embodiment.
• the present inventors obtained the knowledge that the corrosion resistance of the steel plate can be improved when a CIP value expressed by -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 is 3.2 or more.
• the present inventors obtained the knowledge that the corrosion wear properties due to a material in which a slurry such as sand and gravel is mixed in salt water which is a corrosive environment can be improved by the improvement of the corrosion resistance.
• the upper limit of the CIP value is not particularly limited, but may be set to, for example, 64.0 or less, 50.0 or less, 40.0 or less, 30.0 or less, or 20.0 or less.
• C, Si, Mn, P, S, Cu, Ni, Co, Cr, Mo, W, Al, and N represent the amounts of the corresponding elements in mass%. In a case where the corresponding elements are not contained, 0 is substituted.
• the volume fraction of austenite in a metallographic structure is set to 90% to 100%.
• the toughness of the steel plate decreases.
• the volume fraction of austenite is preferably set to 95% or more, 97% or more, or 100% or more.
• the steel plate according to the present embodiment obtains a desired toughness by including a predetermined amount of austenite.
• the total volume fraction of ⁇ martensite and ⁇ ' martensite exceeds 10%, a sufficient amount of austenite is not obtained, and the toughness of the steel plate decreases. Therefore, the total volume fraction of ⁇ martensite and ⁇ ' martensite is preferably set to 10% or less, 5% or less, 3% or less, or 0% or less.
• the metallographic structure of the steel plate according to the present embodiment is preferably made of austenite and a residual structure consisting of ⁇ martensite and a' martensite.
• the residual structure in the metallographic structure may be 0%.
• the volume fractions of austenite, ⁇ martensite, and a' martensite are determined by the following method.
• a sample is cut out from the plate thickness center portion of the steel plate (1/2T depth (T is the plate thickness) from the surface of the steel plate).
• a surface of the sample parallel to the plate thickness direction and the rolling direction of the sample is used as an observed section, and after the observed section is finished to a mirror surface by buffing or the like, strain is removed by electrolytic polishing or chemical polishing.
• the volume fractions of austenite, ⁇ martensite, and a' martensite are obtained from the average value of the integrated intensities of the (311), (200), and (220) planes of austenite having a face-centered cubic structure (fcc structure), the average value of the integrated intensities of the (010), (011), and (012) planes of ⁇ martensite having a dense hexagonal close-packed structure (hcp structure), and the average value of the integrated intensities of the (220), (200), and (211) planes of ⁇ ' martensite having a body-centered cubic structure (bcc structure).
• a' martensite has a body-centered tetragonal structure (bct structure), and the diffraction peaks obtained by X-ray diffraction measurement have double peaks due to the anisotropy of the crystal structure. Therefore, the volume fraction of ⁇ ' martensite is obtained from the sum of the integrated intensities of the respective peaks.
• the mechanism of reducing the toughness of the high C and high Mn austenitic steel will be described.
• the C content and the Mn content are high, a large number of iron carbides are formed not only at austenite grain boundaries but also in the grains. Since these carbides are harder than the iron primary phase, stress concentration around the carbides is increased when an external force is applied. Accordingly, cracking occurs between the carbides or around the carbides, which causes fracture. When an external force is applied, the stress concentration that causes the steel to fracture decreases as the grain size of austenite decreases.
• excessive refinement increases the nucleation sites of carbides formed at austenite grain boundaries and has a disadvantage of increasing the amount of carbonitrides precipitated.
• the carbides at grain boundaries are very hard, and when the amount of the precipitated carbides increases, the toughness and ductility of the steel decrease. The present inventors found that by optimizing the grain size, the toughness and ductility of the steel plate can be improved.
• the toughness of the steel plate is improved basically by refining austenite while suppressing the formation of carbides.
• the steel plate according to the present embodiment includes austenite in a volume fraction of 90% to 100%. Furthermore, since the steel plate according to the present embodiment is manufactured by hot rolling, as will be described later in detail, austenite in the steel plate is refined by the hot rolling, and has excellent toughness.
• the average grain size of austenite in the steel plate is set to 40 ⁇ m or more.
• the average grain size of austenite in the steel plate is preferably set to 50 ⁇ m or more, 75 ⁇ m or more, or 100 ⁇ m or more.
• the average grain size of austenite in the steel plate is set to 300 ⁇ m or less.
• the average grain size of austenite in the steel plate is preferably set to 250 ⁇ m or less, or 200 ⁇ m or less.
• the upper and lower limits of the average grain size of the austenite are values which can be achieved by hot rolling as well as by the austenite pinning effect by the oxysulfides and the like according to the present invention.
• the average grain size of austenite in the HAZ can be reduced.
• the average grain size of austenite in a HAZ in the vicinity of a fusion line (FL) at a plate thickness center portion can be maintained in a range of 40 to 300 ⁇ m.
• the toughness of the welded joint obtained by welding the steel plate according to the present embodiment can be enhanced.
• a highly efficient welding method such as increasing a weld heat input can be used.
• a method of measuring the average grain size of austenite in the present embodiment will be described.
• a sample is cut out from the plate thickness center portion of the steel plate (1/2T depth (T is the plate thickness) from the surface of the steel plate).
• a cross section parallel to the rolling direction and the plate thickness direction of the steel plate is used as an observed section, and after the observed section is finished to a mirror surface by alumina polishing or the like, the observed section is corroded with a nital solution or picral solution.
• the metallographic structure of the observed section after the corrosion is enlarged and observed by an optical microscope, an electron microscope, or the like to obtain the average grain size of austenite.
• a visual field of 1 mm ⁇ 1 mm or more is enlarged at a magnification of about 100-fold, the mean lineal intercept length per austenite grain observed in the observed visual field is obtained by the linear intercept segment method in Annex C.2 of JIS Z 0551: 2013, and this is used as the average grain size, whereby the average grain size of austenite is obtained.
• the plastic strain at the time of hot rolling needs to be 0.056 or more.
• the plastic strain at the time of hot rolling needs to be 0.25 or more.
• the plastic strain at the time of hot rolling may be 2.1 or less.
• the plastic strain at the time of hot rolling calculated by Formula (1) for obtaining austenite having a predetermined grain size as described above is a standard, and in practice, needs to be finely adjusted in consideration of the grain growth of austenite after recrystallization and the effect of multi-pass rolling.
• the present inventors confirmed that the steel plate according to the present embodiment can be manufactured by the manufacturing method described below by the research to date including the above.
• Melting and slab manufacturing processes need not be particularly limited. That is, subsequent to melting by a converter, an electric furnace, or the like, various secondary refining processes are performed to achieve the above-described chemical composition. Thereafter, a slab may be manufactured by a method such as typical continuous casting.
• the slab manufactured by the above-described method is subjected to hot rolling after being heated.
• the slab heating temperature is preferably higher than 1250°C to 1300°C.
• the slab heating temperature is set to 1300°C or less.
• the cumulative rolling reduction in the temperature range of 900°C to 1000°C is set to 10% to 80%. It has been confirmed that this can cause the average grain size of austenite to be 40 to 300 ⁇ m.
• the steel plate according to the present embodiment can be obtained by setteing the cumulative rolling reduction to 10% to lower than 30% in the temperature range of 900°C to 1000°C and satisfying the conditions described later.
• the rolling finish temperature is set to 900°C or higher.
• accelerated cooling is performed except for a case where a heat treatment described later is performed.
• the purpose of the accelerated cooling is to increase the ductility and toughness of the steel plate by suppressing the formation of carbides after hot rolling.
• the average cooling rate during accelerated cooling is set to 1 °C/s or more. This is because, when 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) is not sufficiently obtained in some cases. On the other hand, when the cooling rate during accelerated cooling exceeds 200 °C/s, there may be cases where the amount of austenite in the steel decreases, and the toughness and ductility of the steel plate decrease. Therefore, the average cooling rate during accelerated cooling is set to 200 °C/s or less.
• Accelerated cooling after hot rolling starts from the high temperature side as much as possible. Since the temperature at which carbides actually start to precipitate is lower than 850°C, the cooling start temperature is set to 850°C or higher. The cooling finishing temperature is set to 550°C or lower.
• the 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 austenite grain growth, the hot rolling and the accelerated cooling described above performed in combination.
• the accelerated cooling described above is not performed, for example, in a case where cooling is performed by air cooling after hot rolling, it is necessary to perform a heat treatment on the steel plate after the hot rolling in order to decompose precipitated carbides.
• a heat treatment there is a solutionizing treatment.
• the solutionizing treatment for example, the steel plate is reheated to a temperature of 1100°C or higher, subjected to accelerated cooling from a temperature of 1000°C or higher at an average cooling rate of 1 to 200 °C/s, and cooled to a temperature of 500°C or lower.
• the plate thickness of the steel plate according to the present embodiment need not be particularly limited, but may be set to 3 to 100 mm. As necessary, the plate thickness may be set to 6 mm or more, or 12 mm or more, and may be set to 75 mm or less, or 50 mm or less.
• the mechanical properties of the steel plate according to the present embodiment need not be particularly defined, but according to JIS Z 2241: 2011, the yield stress (YS) may be set to 300 N/mm 2 or more, the tensile strength (TS) is 800 N/mm 2 or more, and the elongation (EL) may be set to 40% or more.
• the tensile strength may be set to 900 N/mm 2 or more or 950 N/mm 2 or more, and may be set to 2000 N/mm 2 or less or 1500 N/mm 2 or less.
• the toughness of the steel plate may be set such that the absorbed energy at -40°C according to JIS Z 2242: 2005 is 100 J or more, 200 J or more, or 300 J or more.
• an austenitic wear-resistant steel plate excellent in wear resistance and strength, and toughness and ductility can be obtained.
• the austenitic wear-resistant steel plate according to the present embodiment can be suitably used for small members such as a rail crossing, a caterpillar liner, an impeller blade, a crusher blade, a rock hammer, and large members that require wear resistance in the fields of construction machinery, industrial machinery, civil engineering, and architecture, such as columns, steel pipes, and outer plates.
• the volume fractions of austenite, ⁇ martensite, and ⁇ ' martensite were obtained from the average value of the integrated intensities of the (311), (200), and (220) planes of austenite having a face-centered cubic structure (fcc structure), the average value of the integrated intensities of the (010), (011), and (012) planes of ⁇ martensite having a dense hexagonal close-packed structure (hcp structure), and the average value of the integrated intensities of the (220), (200), and (211) planes of a' martensite having a body-centered cubic structure (bcc structure).
• XRD X-ray diffractometer
• volume fraction of austenite was 90% or more was determined to be within the range of the present invention and thus passed.
• volume fraction of austenite was less than 90% was determined to be outside of the range of the present invention and thus failed.
• a tension test piece collected so that the length direction of the test piece and the width direction of the steel plate were parallel to each other was used and evaluated according to JIS Z 2241: 2011.
• the tension test piece having a plate thickness of 20 mm or less was No. 13B of JIS Z 2241: 2011, and the tension test piece having a plate thickness of more than 20 mm was No. 4 of JIS Z 2241: 2011.
• the target value of the corrosion wear amount ratio to the plain steel was set to 0.80 or less.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)

Applications Claiming Priority (1)

Publications (2)

Family

ID=68058129

Family Applications (1)

Country Status (5)

Cited By (4)

Families Citing this family (8)

Family Cites Families (23)

• 2018
  • 2018-03-29 BR BR112020014123-2A patent/BR112020014123A2/pt not_active Application Discontinuation
  • 2018-03-29 EP EP18912208.8A patent/EP3778950A4/fr not_active Withdrawn
  • 2018-03-29 WO PCT/JP2018/013289 patent/WO2019186911A1/fr active Application Filing
  • 2018-03-29 CN CN201880089433.5A patent/CN111727267B/zh active Active
  • 2018-03-29 KR KR1020207023127A patent/KR102453321B1/ko active IP Right Grant

Also Published As

Similar Documents

Legal Events