Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
  • B21B3/02—Rolling special iron alloys, e.g. stainless steel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/24—Selection of soldering or welding materials proper
  • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
  • B23K35/3053—Fe as the principal constituent
  • B23K35/308—Fe as the principal constituent with Cr as next major constituent
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/24—Selection of soldering or welding materials proper
  • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
  • B23K35/3053—Fe as the principal constituent
  • B23K35/308—Fe as the principal constituent with Cr as next major constituent
  • B23K35/3086—Fe as the principal constituent with Cr as next major constituent containing Ni or 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
  • C22C38/001—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
  • C22C38/40—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
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/0204—Non-porous and characterised by the material
  • H01M8/0206—Metals or alloys
  • H01M8/0208—Alloys
  • H01M8/021—Alloys based on iron
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
  • B21B1/024—Forging or pressing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
  • B21B1/026—Rolling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
  • B21B2001/022—Blooms or billets
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/02—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling heavy work, e.g. ingots, slabs, blooms, or billets, in which the cross-sectional form is unimportant ; Rolling combined with forging or pressing
  • B21B2001/028—Slabs
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K15/00—Electron-beam welding or cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/02—Iron or ferrous alloys
  • B23K2103/04—Steel or steel alloys
  • B23K2103/05—Stainless steel
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the present invention relates to a neutron shielding material for nuclear power-related equipment such as a container for transporting nuclear fuel, a used nuclear fuel storage rack, etc., and an application in which austenitic stainless steel exhibits excellent functions by containing 0.3% or more of B.
• the present invention relates to a B-containing stainless steel piece used as a fuel cell separator material and a method for producing a B-containing stainless steel material.
• Austenitic stainless steel has excellent corrosion resistance due to the formation of a passivation film on its surface, and the inclusion of B improves the electrical resistance characteristics, so current-carrying electrical components that require corrosion resistance It can be used as An example of the application of a current-carrying electrical component that requires excellent corrosion resistance and low contact electric resistance is a fuel cell separator that generates DC power using hydrogen and oxygen.
• Hot working of B-containing stainless steel is performed while ensuring hot workability by preventing the temperature of the work material from dropping by repeatedly heating the slab with a heating furnace and performing processes such as forging and rolling. Has been done.
• B content increases Therefore, it is necessary to perform the processing while preventing the temperature of the workpiece from lowering, and as a result, the number of repetitions of heating and processing must be increased. Therefore, an increase in the B content and thinning of steel will lead to an increase in manufacturing costs.
• Japanese Unexamined Patent Publication No. Hei 4-255306 discloses that a side portion of an austenitic stainless steel material containing 0.3 to 2.0 mass% of B is provided with a steel material having a smaller deformation resistance than a stainless steel material. (Hereinafter, also referred to as “side plate”) is finish-rolled at a temperature of (53 B + 700) ° C (where B : B content (% by mass)) or more.
• B B content (% by mass)
• Japanese Patent Application Laid-Open No. 2001-2393964 discloses that when hot rolling an austenitic stainless steel slab containing 0.3 to 2.5 mass% of B, N i: 4% or less, B: 0.1 to 0.4% stainless steel containing a build-up welding coating layer of 3 mm or more in thickness and hot working. A method is disclosed.
• Japanese Patent Application Laid-Open No. 9-269398 discloses a slab of austenitic stainless steel containing 0.6 to 2.0% by mass of B and a build-up weld metal formed on a side surface of the slab.
• a material for hot rolling is disclosed that has a ⁇ ferrite amount of 3 to 12% by volume, a ⁇ content of 0.3% by mass or less, and a thickness of 3 mm or more in the build-up weld metal layer. Have been.
• the number of welding passes is increased to secure a sufficient welding thickness to prevent cracking, and the number of welding steps is increased.
• a weld crack when a weld crack occurs, it may be a starting point and lead to the occurrence of an ear crack, and it is difficult to completely prevent the occurrence of an ear crack.
• the present invention has been made in order to solve the above-mentioned problems of the prior art, and its object is to cut a stainless steel piece having a high B content into a predetermined thickness with a small number of welding man-hours.
• An object of the present invention is to provide a hot rolling method, a cold rolling method, and a steel material having a high B content, which can be rolled without generating cracks in a part.
• An object of the present invention is to provide a method for producing a B-containing stainless steel material capable of preventing occurrence of cracks. Means for Solving the Problems
• the present inventors have repeatedly studied a method for producing a B-containing stainless steel material, obtained the following findings (a) to (d), and completed the present invention.
• a stainless steel piece containing 0.3% by mass or less of B is provided on at least two opposing surfaces except for a machined surface of a stainless steel piece containing 0.3 to 2.5% by mass of B.
• Protected material made of stainless steel can be welded with stainless steel having a specific Cr equivalent and Ni equivalent and hot-rolled to prevent edge cracks in steel .
• the stainless steel slab is a low B content material having a B content in the range of 0.3 to 0.7%
• the protect material is a material that does not contain B, the susceptibility of the weld metal to cracks increases, and weld cracks may occur. In this case, welding cracks can be prevented by using an insert material containing B in the range of 0.4 to 2.5 ° / 0 .
• the protect material of (a) above is desirably joined by high-efficiency electron beam welding with a high energy density, and the thickness of the protect material is desirably 10 mm or more.
• Desirable conditions for electron beam welding are welding current: 3 O OmA or more, welding speed: 20 OmmZ min or less, and electron beam amplitude: ⁇ 1.0 to 3.0 mm.
• the present invention has been completed based on the above findings, and its gist lies in the following B-containing stainless steel pieces, B-containing stainless steel materials, and methods for producing the same.
• FIG. 1 is a diagram schematically showing a B-containing stainless steel piece.
• stainless steel slab refers to a continuous forged slab, a forged slab, a forged rolled slab, and a forged ingot (steel ingot), and the base material shown in FIG. These slabs are generally rectangular parallelepipeds, and are subjected to hot working such as hot rolling or forging to stretch in the longitudinal direction.
• At least two opposing surfaces excluding the processed surface refers to at least two opposing surfaces out of surfaces other than the processed surfaces subjected to rolling or forging.
• two longitudinal side surfaces that do not come into contact with the rolling rolls, or the end surfaces of the head and tail including these two side surfaces may be included.
• forging it may include two opposing sides that do not come into contact with the ram, or three to four sides including these.
• the chamfered surface may be included.
• Protective material thickness refers to the thickness of the protective material from the side of the billet in a plane parallel to the work surface before joining the protective material to the base material, as shown in Fig. 1. Say. For the steel slab after joining, it refers to the total thickness of the protect material alone and the thickness of the weld metal in the protect material.
• welding metal refers to a part of the joint where the base material and the protect material before joining are melted and solidified by joining.
• the heat-affected zone (HAZ) that only causes solid phase transformation Is not included.
• “Insert material” is a material inserted or sandwiched between a stainless steel piece (base material) and a protect material, and specifically, a material such as a plate, foil, or powder is exemplified.
• FIG. 1 is a diagram schematically showing a B-containing stainless steel piece.
• FIG. 2 is a diagram showing the relationship between the weld metal composition and weld cracking and rolling performance.
• FIG. 3 is a diagram showing a relationship between a welding current and a penetration amount of a bead.
• FIG. 4 is a diagram showing the relationship between welding speed and bead penetration.
• Figure 5 shows the distribution of longitudinal tension in the width direction of a steel sheet during rolling.
• FIG. 6 is a diagram showing an analysis result by the finite element method.
• the present inventors joined a protected material having a constant thickness to the side surface of the billet, We studied a method of turning steel into a steel material.
• Electron beam welding was used as the joining method for the protect material.
• Table 1 summarizes the chemical compositions of the base steel slab and the protect material used in the test.
• the B content in the B-containing stainless steel slab to be hot worked is less than 0.3%, the thermal neutron absorption capacity is not sufficient, and the electrical resistance characteristics of the fuel cell separator material are not sufficiently improved. Therefore, the B content should be 0.3% or more. Thermal neutron absorption capacity and electrical resistance characteristics improve with increasing B content When the S and B content exceeds 2.5%, the ductility and toughness at room temperature deteriorate markedly. Should be 2.5% or less.
• the base metal may be austenitic stainless steel or ferritic stainless steel, but is limited to austenitic stainless steel when it functions as a fuel cell separator material. . Desirable ranges for other steel composition:
• C is an element having an effect of securing strength. However, if it is contained in excess of 0.08%, it causes deterioration of corrosion resistance and hot workability. Therefore, the content is desirably 0.08% or less. More preferably, it is 0.01% or more.
• Si is an element that is added as a deoxidizing agent and also has an effect of improving oxidation resistance.
• the content exceeds 1%, the susceptibility to weld cracking increases. Therefore, it is desirable that the content be 1% or less.
• P is an impurity element in steel and its content is 0.04 ° /. If the content exceeds 0.005%, the weld cracking susceptibility will be high. S: 0.01% or less:
• S is an impurity element in steel, and if its content exceeds 0.01%, the susceptibility to weld cracking increases, so it is desirable that the content be 0.01% or less.
• Cr is an element having an effect of improving corrosion resistance, and when its content is 5% or more, desirable effects can be obtained. Therefore, it is desirable that the content be 5 ° / 0 or more. On the other hand, if the content exceeds 30%, hot working may be difficult, so that the content is more preferably 30% or less.
• N combines with B to reduce toughness.
• the content be 0.05% or less.
• the component composition of the weld metal that forms the joint between the protect material and the base material will be described.
• welding When joining a protected material to a base material with high efficiency, such as by electron beam welding, it is essential to avoid cracks that occur during joining and to prevent cracking during hot rolling of the protected material itself. .
• the cracks that occur during welding (welding) include solidification cracking and insufficient ductility cracking.
• the chemical composition of the weld metal that forms the joint between the protect material and the base metal is expressed by the following equations (1) to (4). Needs to be satisfied. 1 5 ⁇ C req ⁇ 3 0 (1)
• Weld solidification cracking is due to the superposition effect of the formation of a low melting point phase due to B and thermal stress peculiar to electron beam welding and the like.
• the ferrite phase remains until late coagulation.
• solidification cracking can be avoided even under high thermal stress such as electron beam welding. Therefore, (
• adjusting the component composition of the weld metal to an appropriate range represented by equations (1) to (4) avoids cracks that occur during welding when performing high-efficiency welding of protect materials. In addition, this is an essential requirement for preventing cracking during hot rolling of the weld metal.
• the desirable composition range of the weld metal in the present invention is as follows.
• C is an element that has the effect of ensuring effective strength for suppressing deformation during heating of billets.
• the content exceeds 0.08%, it causes deterioration of hot workability. Therefore, it is desirable that the content be 0.08% or less. 0.01% or more is more desirable.
• Si is an element that is added as a deoxidizing agent and also has an effect of improving oxidation resistance.
• the content exceeds 1%, the susceptibility to weld cracking increases. Therefore, it is desirable that the content be 1% or less.
• P is an impurity element in steel, and if its content exceeds 0.04%, the susceptibility to weld cracking increases, so it is desirable that the content is not more than 0.04%.
• S is an impurity element in steel, and if its content exceeds 0.01%, the susceptibility to weld cracking will increase. desirable.
• Cr is an element having an effect of improving corrosion resistance, and when its content is 5% or more, desirable effects can be obtained. Therefore, it is desirable that the content be 5% or more. On the other hand, if the content exceeds 30%, hot working may be difficult, so that the content is more preferably 30% or less.
• the content of the steel for protect material exceeds 0.3 ° / 0 , the protect material itself will crack at the end where the tension during rolling is large, and the effect of the protect material Will not do. Therefore, the content is set to 0.3% or less.
• the content of other elements such as Cr and Ni is substantially determined by the fact that the weld metal formed by melting and mixing with the base material needs to satisfy the above equations (1) to (4). Is limited by the composition of the weld metal.
• the component composition of the weld metal generated when joining by electron beam welding is close to the arithmetic mean of the component compositions of the base metal and the protect material. Therefore, once the component composition of the base material to be used is determined, the range of the component composition other than B, such as Ni and Cr, in the protected material can be obtained by using the above equations (1) to (4). .
• the preferable range of the component composition of the protect steel is as follows.
• c has the effect of ensuring effective strength to suppress deformation during heating of billets. Element. However, if the content exceeds 0.08%, it causes deterioration of hot workability. Therefore, it is desirable that the content be 0.08% or less. 0.01% or more is more desirable.
• Si is an element that is added as a deoxidizing agent and also has an effect of improving oxidation resistance.
• the content exceeds 1%, the susceptibility to weld cracking increases. Therefore, it is desirable that the content be 1% or less.
• P is an impurity element in steel, and if its content exceeds 0.04%, the susceptibility to weld cracking increases, so it is desirable that the content is not more than 0.04%.
• S is an impurity element in steel, and if its content exceeds 0.01%, the susceptibility to weld cracking increases, so it is desirable that the content be 0.01% or less.
• Cr is an element having an effect of improving corrosion resistance, and when its content is 5% or more, desirable effects can be obtained. Therefore, it is desirable that the content be 5% or more. On the other hand, if the content exceeds 30%, hot working may be difficult, so that the content is more preferably 30% or less.
• the stainless steel slab is a low B content material with a B content of 0.3 to 0.7%, for example, and the protection material is welded with a combination of materials that do not contain B, Metal cracking susceptibility increases, and welding cracks may occur.
• the B content of the protect material is increased, the B content of the weld metal is increased, but the hot workability deteriorates with this, and the original function of the protect material is provided. Can not be demonstrated. For this reason, it is desirable to use an insert material containing B so that it is inserted or sandwiched between the stainless steel piece and the protect material at the time of joining. It is desirable that the B content and other component compositions at this time are as follows.
• B content of the insert material is less than 0.4%, the thermal neutron absorption capacity is not sufficient considering the dilution during welding, and the electrical resistance characteristics of the fuel cell separator material are not sufficiently improved.
• B content should be 0.4% or more.
• the B content exceeds 2.5%, the deterioration of ductility and toughness at room temperature becomes remarkable, so the content should be 2.5% or less.
• C is an element having an effect of securing strength. However, if it is contained in excess of 0.08%, it may cause deterioration of corrosion resistance and hot workability. Therefore, the content is desirably 0.08 ° / 0 or less. More preferably, it is at least 0.01%.
• Si is an element that is added as a deoxidizing agent and also has an effect of improving oxidation resistance. However, if it exceeds 1%, the susceptibility to weld cracking is high. It becomes. Therefore, the content is desirably 1 ° / o or less.
• P is an impurity element in steel, and if its content exceeds 0.04%, the susceptibility to weld cracking will increase. Therefore, it is desirable to set P to 0.04% or less.
• S is an impurity element in steel, and if its content exceeds 0.01%, the susceptibility to weld cracking will increase. Therefore, it is desirable that the content be 0.01% or less.
• Cr is an element having an effect of improving corrosion resistance, and when its content is 5% or more, desirable effects can be obtained. Therefore, it is desirable that the content be 5% or more. On the other hand, if the content exceeds 30%, hot working may be difficult, so that the content is more preferably 30% or less.
• Protected material made of stainless steel is welded to the side of a slab (thick slab) with a side thickness of 80 mm or more and a thickness of 1 Omm or more in a plane parallel to the processing surface. It was found that the conditions for joining without losing the joint surface and for the entire thickness of the slab side surface in the thickness direction were as follows.
• Electron beam amplitude ⁇ 1.0 to soil 3.0 mm
• FIG. 3 is a diagram in which the relationship between the welding current and the amount of penetration of the bead was determined at a welding speed of 20 Omm / min.
• FIG. 4 is a graph showing the relationship between the welding speed and the amount of bead penetration, where the welding current is 3 O OmA.
• the amplitude should be in the range of ⁇ 1.0 to soil 3.0 mm. 30H276 is desirable.
• the thickness of the protect material is preferably 1 Omni or more.
• the effect of preventing ear cracks increases with an increase in the thickness, but an excessive increase in the thickness is not preferable because the yield of the protect material is deteriorated.
• a laboratory test was conducted to evaluate ear cracks using a base material and a protect material satisfying the range of the steel components of the present invention.
• a 200 mm wide, 50 mm thick, 100 mm long slab made of B-containing austenitic stainless steel with steel number M1 in Table 1 was used as the material to be rolled.
• Protective material consisting of austenitic stainless steel (TP304L) with steel number P1 in the table was welded to the part by the above-mentioned electron beam welding to obtain a test material.
• the conditions of electron beam welding were as follows: welding current: 35 OmA, welding speed: 130 mm / min, and beam amplitude: soil 2 mm.
• Protective material is polished after electron beam welding, and the thickness of the protective material from the side surface of the base material slab before welding in the plane parallel to the work surface (thickness of the protective material alone excluding the weld metal part) This slab was adjusted in the range of 0 to 1 Omm in a heating furnace at 1180 ° C for 1 hour or more, and the finishing temperature was 6
• the value of the above-mentioned total draft ratio was set to the same or higher value than the value of the total draft ratio assumed in actual operation. This is because if the total reduction ratio is small, ear cracks are unlikely to occur, and this is not a laboratory test for accurate evaluation of ear cracks assuming actual operation.
• * 1 Indicates the thickness of the protected material that has not been melted by welding.
• the thickness of the protect material alone indicates the thickness of the protect material that was not melted by welding
• the thickness of the protect material weld metal indicates the thickness of the protect material that was melted by welding.
• the thickness of the protect material indicates the total thickness of the protect material itself and the thickness of the weld metal of the protect material, and is converted into the thickness of the protect material before welding.
• the evaluation of the side edge cracks is based on the evaluation of Visual observation is made, and if the length of the crack is less than 0.1 mm, it is judged that there is no crack, and it is indicated by ⁇ . If the length of the crack is more than 0.1 mm, it is judged that there is a crack, and X is indicated. Indicated by.
• test results are the results when rolling is performed by a test rolling mill having a scale ratio of 1/2 to 1Z5 as compared with an actual rolling mill used in actual operation. Therefore, it is necessary to estimate the protect thickness necessary for preventing ear cracks in actual operation based on the test results.
• Edge cracks are caused by the tensile tension at the edge that occurs during rolling deformation. Therefore, we investigated the distribution of tension in the steel sheet generated during rolling deformation.
• Fig. 5 is a diagram showing the results of analysis by the finite element method (FEM) of the distribution of longitudinal tension in the width direction of a steel sheet during rolling. This analysis was performed using the three-dimensional rigid-plastic FEM under the following analysis conditions.
• FEM finite element method
• a tensile force acts on a region about 10 mm from the width direction end, and the edge tension is maximum near the width direction end.
• the protect thickness L required for preventing ear cracks in actual operation is R for the work roll radius of the actual rolling mill, h for the finished plate thickness, RO for the work roll radius of the test rolling mill, and h for the finished plate thickness.
• O assuming that the thickness of the single protect material is L0, it can be obtained by the following equation (6).
• H is the initial plate thickness in actual operation rolling
• H O is the initial plate thickness in test rolling
• the hot working refers to slab forging, plate rolling, hot strip rolling, and the like.
• the heating temperature of the slab is desirably set to a high temperature within a range that does not cause melt embrittlement.
• the temperature is preferably in the range of 110 to 1200 ° C.
• B-containing stainless steel is used as a fuel cell separator material
• cold-rolled steel strip rolling is performed as cold working to finish-process the cold-rolled steel sheet. Is press-formed into a predetermined cross-sectional shape.
• the B-containing stainless steel material obtained as described above, backed by high reliability and productivity, is suitable as a steel material for applications that exhibit functions such as neutron shielding containers and separator materials for fuel cells.
• Example 1 a laboratory test was conducted to evaluate ear cracks using a base material and a protect material satisfying the range of steel components specified in the present invention.
• the test material used as the material to be rolled is a slab made of B-containing austenitic stainless steel with steel numbers M1 to M5 in Table 1 and having a width of 20 mm, a thickness of 50 mm, and a length of 100 mm.
• the slab was manufactured by welding the end of the slab in the width direction with a protect material made of stainless steel having steel numbers P1 to P9 in the same table by the above-described electron beam welding.
• Table 3 shows the weld metal in the billet that combines various base materials and protect materials.
• the electron beam welding conditions were as follows: welding current: 35 O mA, welding speed: 130 mm / min, and beam amplitude: ⁇ 2 mm.
• the base metal of B-containing austenitic stainless steel and the stainless steel protect material are each melted for about 5 mm, and a total thickness of about 1 Omm is obtained.
• a metal part was formed.
• the chemical composition shown in Table 3 is the chemical composition of the weld metal part.
• the protect material is polished after electron beam welding, and the protect material from the side face of the base material slab in a plane parallel to the machined surface.
• the thickness of the unit (the thickness of the protect material excluding the weld metal) was adjusted to l mm.
• the slab was heated in a heating furnace at 118 ° C. for 1 hour or more, and rolled at a finishing temperature of 600 ° C. to 700 ° C. Multi-pass using a two-high rolling mill with a work hole diameter of 35 Omm so that the finished plate thickness is 1 mm and the total draft ratio (initial plate thickness / finished plate thickness (1)) is 50.0.
• the value of the above-mentioned total draft ratio was set to the same or higher value than the value of the total draft ratio assumed in actual operation. The reason for this is that, as described above, if the total reduction ratio is small, ear cracks are less likely to occur, so that it is not a laboratory test that simulates actual operation and enables accurate evaluation of ear cracks.
• Table 3 shows the presence or absence of weld cracks by ultrasonic inspection, and the results of evaluation tests for ear cracks after rolling.
• For evaluation of side edge cracks visual observation of the state of cracking was performed on the entire width end of the rolled material, and if the length of the crack was less than 0.1 mm, it was judged that there was no crack, and a mark ⁇ When the length of the crack was 0.1 mm or more, it was judged that there was a crack and indicated by an X mark.
• test numbers S5 and S7 cracks did not occur before rolling, but ear cracks occurred after rolling.
• the value of equation (1) exceeded 30; in test number S7, the value of equation (2) exceeded 17; In each case, the requirements specified in the present invention were not satisfied, and as a result, ear cracks occurred after rolling.
• a protected material having the steel composition shown in Table 1 was welded to the longitudinal side surface of the base steel slab having the copper composition shown in Table 1 by electron beam welding to produce a rolled material. After heating, a rolling test was performed using an actual rolling mill, and the results were evaluated.
• Table 4 shows the test conditions such as steel number, billet dimensions, protector material thickness, welding conditions, heating temperature, finish thickness, total reduction ratio and finish temperature, and the test results for edge cracking conditions. It is shown together. Table 4
• the evaluation of the test results is based on the judgment that there is no ear crack when the crack length is less than 0.1 mm, and when the crack length is 0.1 mm or more and less than 18 mm by the mark m. A small ear crack was determined to have occurred and was marked with an X mark. If the length of the crack was 8 Omm or more and 120 mm or less, a large crack was determined to have occurred.
• Table 5 shows the rolling pass schedule.
• Test numbers B1 to B5 are tests of the present invention example in which the protect material was joined, and among them, test numbers B1 to B3 were tests in which the finishing temperature was changed, and test numbers B4 And B5 are tests where the thickness of the protected material was reduced.
• Test No. B6 is a test of a comparative example in which the protect material was not joined.
• Test Nos. B1 to B5 of the present invention examples, in Test No. B5 in which the thickness of the protect material was 8 mm, no ear cracks occurred except for small ear cracks.
• the small ear cracks generated in Test No. B5 were small enough to have no adverse effect on the product quality at the stage of removing the protector material into a product. This result fully demonstrates the effect of the present invention for bonding the protect material.
• Test Nos. B1 to B4 of the present invention examples are cases where the thickness of the protector material is 1 Omm or more, which is a desirable range in the present invention, and there are no ear cracks. The product is obtained. In addition, good results were obtained in test number B1, which had a low finishing temperature.
• Test No. B6 which is a comparative example, large ear cracks were generated, resulting in inferior results having a bad influence on the quality of the product steel material.
• Example 3 a laboratory test was conducted to evaluate ear cracks depending on whether or not an insert material was used, using a base material and a protect material satisfying the range of steel components specified in the present invention.
• test material used as the material to be rolled satisfies the range of steel components specified in the present invention, but steel No. M5 (B: 0.42%) in Table 1 above, which corresponds to low B content steel, was used. did. Then, a 200 mm wide, 50 mm thick, 100 mm long slab made of the M5 low B content austenitic stainless steel was used. A test material was manufactured by combining the protect materials made of stainless steels of Nos. P1 to P9 and welding by the above-mentioned electron beam welding.
• Example 1 After the electron beam welding, the protect material was polished, and the thickness of the protect material from the side surface of the base material slab in a plane parallel to the processing surface was adjusted in a range of 0 to 1 Omm.
• the conditions of electron beam welding were as follows: welding current: 350 mA, welding speed: 130 mmZ, and beam amplitude: earth 2 mm.
• the conditions of the electron beam welding were changed to welding current: 40 OmA N welding speed: 17 OmmZ and beam amplitude: ⁇ 2 mm. The test was performed.
• Table 6 shows the combinations of base material and protect material used in the test, as well as the type, thickness, and composition of the insert materials. As shown in Table 6, a plate material, a powder and a foil material were used for the insert material. Among them, the powder layer was formed by mixing a B-containing powder with a binder material such as water glass and wall-coating the groove surface. Table 6
• Table 7 shows the chemical composition of the weld metal in the slab obtained by combining the base material of steel No. M5 with various protect materials and insert materials, and the results of evaluation of the weld cracks and rolling cracks. Evaluation conditions for welding cracks and rolling cracks were the same as in Example 1.
• test numbers C1 to C7 the component compositions of the base metal, the protect material, and the weld metal all satisfy the ranges specified in the present invention, but the test numbers in which no insert material was used were used.
• C1 and C2 the cross section was observed with a microscope at a magnification of 100 ⁇ , and as a result, it was confirmed that fine cracks had occurred. After the rolling of the steel slab, fine cracks were observed.
• test numbers C3 to C7 which use low-B content in the base metal and insert materials
• the cross-section was observed with a microscope of 100x magnification despite high-speed welding. No cracks were observed at all, and no cracks were observed even after rolling the billet.
• Test Nos. 3 and 4 where the B content of the insert material was within the desired range, even better ductility, higher thermal neutron absorption capacity and lower contact electrical resistance were obtained. Table 7
• the protection material is joined to the side of a stainless steel slab having a high B content by high-efficiency electron beam welding and rolled, thereby preventing the occurrence of ear cracks, thereby achieving high productivity and excellent productivity.
• We can provide B-containing stainless steel with excellent quality. Furthermore, if an insert material is used at the time of welding, the cracking susceptibility of the weld metal can be further reduced.
• the B-containing stainless steel material of the present invention can be widely used for applications requiring functions such as a material for a neutron shielding container for nuclear-related equipment and a separator material for a fuel cell. It can greatly contribute to the development of the industrial field where manufacturing is used.

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