US20100047107A1 - Steel material superior in high temperature strength and toughness and method of production of same - Google Patents

Steel material superior in high temperature strength and toughness and method of production of same Download PDF

Info

Publication number
US20100047107A1
US20100047107A1 US12/450,762 US45076208A US2010047107A1 US 20100047107 A1 US20100047107 A1 US 20100047107A1 US 45076208 A US45076208 A US 45076208A US 2010047107 A1 US2010047107 A1 US 2010047107A1
Authority
US
United States
Prior art keywords
toughness
high temperature
less
steel
steel material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US12/450,762
Other languages
English (en)
Inventor
Suguru Yoshida
Hiroshi Kita
Teruhisa Okumura
Hirokazu Sugiyama
Teruyuki Wakatsuki
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Steel Corp
Original Assignee
Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Individual filed Critical Individual
Assigned to NIPPON STEEL CORPORATION reassignment NIPPON STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KITA, HIROSHI, OKUMURA, TERUHISA, SUGIYAMA, HIROKAZU, WAKATSUKI, TERUYUKI, YOSHIDA, SUGURU
Publication of US20100047107A1 publication Critical patent/US20100047107A1/en
Abandoned legal-status Critical Current

Links

Images

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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • 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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

Definitions

  • the present invention relates to a steel material superior in high temperature strength and toughness and a method of production of the same.
  • fire resistant steel material reducing the Mo and utilizing the solid solution and precipitation of Cu has also been proposed (for example, see Japanese Patent Publication (A) No. 2002-115022).
  • This does not use the solid solution Nb to raise the high temperature strength, but uses the addition of Nb to lower the recrystallization temperature and increase the fineness of the crystal grains and, further, to utilize the precipitation strengthening of Nb.
  • the present invention provides a steel material superior in reheat embrittlement resistance characteristics and other high temperature characteristics at the weld heat affected zone and toughness of the base material and HAZ able to be used as a fire resistant steel material or extremely thick H-section steel as hot rolled, that is, without cold rolling or quenching, tempering, or other heat treatment for thermal refining after hot rolling, and a method of production of the same.
  • the present invention limits the contents of C and N, adds a suitable quantity of Nb to define the relationship of C and Nb, and utilizes the drag effect of the solid solution Nb (phenomenon where the solid solution Nb concentrates at dislocations and other lattice defects, becomes resistance to movement of defects and dislocations, and improves the strength) to raise the high temperature strength, furthermore, utilizes the fine Ti-based oxides for pinning of the crystal grain boundaries and formation of intra-granular ferrite nucleation to suppress coarsening of the HAZ, reduce fluctuation of mechanical characteristics due to thickness, and improve reheat embrittlement resistance and other high temperature characteristics, and further secures toughness of the base material and the HAZ by adjusting the concentration of solute oxygen in the molten steel at the time of addition of Ti to disperse fine oxides of Ti in the steel to provide a steel material and a method of production of the same.
  • This gist of the present invention is as follows.
  • a steel material superior in high temperature characteristics and toughness characterized by containing by mass %, C, 0.001% to 0.030%, Si: 0.05% to 0.50%, Mn: 0.40% to 2.00%, Nb: 0.03% to 0.50%, Ti: 0.005% to less than 0.040%, and N: 0.0008% to less than 0.0050%, restricting P: 0.030% or less and S: 0.020% or less, and having a balance of Fe and unavoidable impurities, where the contents of C and Nb satisfy
  • Ti-based oxides of a grain size of 0.05 to 10 ⁇ m are present in a density of 30 to 300/mm 2 .
  • a steel material superior in high temperature characteristics and toughness as set forth in (1) characterized by containing, by mass %, one or both of V: 0.10% or less and Mo: less than 0.10%.
  • a steel material superior in high temperature characteristics and toughness as set forth in (1) or (2) characterized by containing, by mass %, one or more of Zr: 0.03% or less and Hf: 0.01% or less.
  • a method of production of a steel material superior in high temperature characteristics and toughness characterized by adjusting steel comprised of ingredients as set forth in any of the above (1) to (6) to a solute oxygen of 0.003 to 0.015 mass %, then adding Ti, melting, and casting to obtain a steel slab, and heating this to 1100 to 1350° C. and hot rolling.
  • steel material having a sufficient ordinary temperature strength and high temperature strength and superior in base material and HAZ toughness and reheat embrittlement resistance characteristics in particular, fire resistant H-section steel and extremely thick H-section steel, can be produced without cold working and heat treatment for thermal refining or extremely thick H-section steel having a thickness of a large size, for example, of up to a flange thickness of 140 mm or more can be produced as hot rolled while securing strength and toughness.
  • H-section steel produced by hot rolling is broken down by shape into flange, web, and fillet part locations.
  • the rolling temperature history and cooling speed differ according to these shapes, so even with the same ingredients, the mechanical characteristics will sometimes greatly change depending on the part location, but steel having the composition of ingredients of the present invention has relatively small rolling finishing temperature dependency and cooling speed dependency on the strength and toughness, the variation in quality in cross-sectional part locations in H-section steel can be lightened, and, further, the changes in quality due to thickness can be made smaller, so, in particular, strength and toughness at thicknesses of large sizes such as with extremely thick H-section steel can be secured and variations in quality in the cross-sections of H-section steel can be reduced.
  • FIG. 1 is a view showing the effects of C and Nb on the high temperature strength of a steel material.
  • FIG. 2 is a view showing the effects of the number density distribution of Ti oxides on the toughness of the HAZ of a steel material.
  • FIG. 3 is a view showing the effects of the number density distribution of Ti oxides on the reheat embrittlement characteristics of a steel material.
  • FIG. 4 is a view showing the effects of the relationship between the amount of solute oxygen before addition of Ti and the amount of Ti on the density of Ti-based oxides.
  • FIG. 5 is a schematic view of a process for production of shaped steel as an example of the layout of facilities for working the method of the present invention.
  • FIG. 6 is a view showing the cross-sectional shape of H-section steel and the position of sampling a mechanical strength test piece.
  • Lowering the C and lowering the N are effective for suppressing the formation of polygonal ferrite and securing solid solution Nb.
  • the Nb carbide of NbC and nitride of NbN forms the nuclei for formation of polygonal ferrite. Further, due to their precipitation, the solid solution Nb is reduced. In particular, if small amounts of carbides and nitrides of Nb precipitate, this contributes to the improvement of strength by precipitation strengthening, but if heated to a high temperature again after welding, NbC will precipitate at the crystal grain boundaries of the austenite at the HAZ (below, also called “ ⁇ grain boundaries”) and reheat embrittlement may be exhibited.
  • the crystal grains are pinned and their growth suppressed, so the crystal grain size becomes finer.
  • the inventors further studied in detail (1) the relationship of C and Nb and the high temperature strength of a steel material and (2) the effects of the grain size and number density distribution of Ti-based oxides on the HAZ toughness and reheat embrittlement resistance characteristics when using primary deoxidation to adjust the solute oxygen, then adding Ti and further deoxidizing.
  • the inventors produced steel containing, by mass %, C: 0.001% to 0.030%, Si: 0.05% to 0.50%, Mn: 0.4% to 2.0%, Nb: 0.03% to 0.50%, Ti: 0.005% to less than 0.040%, and N: 0.0008% to less than 0.0050%, restricting P: 0.03% or less and S: 0.02% or less, and having a balance of Fe and unavoidable impurities by changing the amount of solute oxygen when adding Ti, cast this to obtain a steel slab, heated it to 1100 to 1350° C., and hot rolled this to a cumulative reduction rate at 1000° C. and below of 30% or more to produce steel plate of a thickness of 10 to 40 mm.
  • FIG. 1 shows the relationship between the contents of C and Nb and the high temperature strength, specifically, the 0.2% proof stress (600° C. YS) at 600° C., with respect to C—Nb/7.74.
  • ⁇ and ⁇ indicate the 600° C. YS of steel materials of an ordinary temperature tensile strength of the 400 MPa class, while ⁇ show the 600° C. YS of steel material of the 490 MPa class.
  • FIG. 2 shows the effects of the number density distribution of Ti-based oxides of a grain size of 0.05 to 10 ⁇ m in the steel on the HAZ toughness. From FIG. 2 , it is learned that to obtain a good HAZ toughness, it is necessary to include Ti-based oxides of a grain size of 0.05 to 10 ⁇ m by dispersion in a ratio of 30 to 300/mm 2 .
  • the inventors used rod-shaped tensile test pieces, heated them by a temperature elevation rate of 10° C./s to 1400° C. and held them there for 1 second, then cooled them to 100° C. while making the time required for cooling from 800° C. to 500° C. 10 second for HAZ reproduction heat treatment, then reheated them by a temperature elevation rate of 10° C./s to 600° C. and measured them for the draw rate, that is, reheat draw rate.
  • FIG. 4 shows the effects of the relationship between the amount of solute oxygen before the addition of Ti and the amount of Ti on the density of the Ti-based oxides.
  • the numerical values of FIG. 4 show the density of Ti-based oxides of a grain size of 0.05 to 10 ⁇ m. From FIG.
  • suitability quenchability is maintained by the solid solution Nb and the balance of elements contributing to steel material strength and toughness is extremely good, there is almost no dependency of strength or toughness by the cooling speed in the cooling process after heating, and the variation in characteristics is extremely small, so when applied to large thickness sizes, the strength and toughness can be maintained at a high level at all part positions. It was learned that the chemical ingredients were suitable for extremely thick H-section steel.
  • the present invention provides fire resistant steel which utilizes finely dispersed Ti-based oxides to suppress in particular crystal grain coarsening at the HAZ by the pinning effect and improve the HAZ toughness and reheat embrittlement characteristics.
  • the lower limit of the grain size of the Ti-based oxides effective for pinning is 0.05 ⁇ m or more. If the grain size of the Ti-based oxides exceeds 10 ⁇ m, the oxides will form starting points of fracture and obstruct toughness.
  • Ti-based oxides is the general term for TiO 2 , Ti 2 O 3 , complex oxides of these with SiO 2 and other Si-based oxides and Al 2 O 3 and other Al-based oxides, and oxides containing Ti in which MnS and other sulfides and TiN and other nitrides have complexly precipitated.
  • Ti-based oxides can be measured by a scan type electron microscope (SEM).
  • SEM scan type electron microscope
  • Ti-based oxides are preferably identified by an SEM having an energy dispersion type X-ray analyzer. Ti-based oxides precipitate in the liquid phase and are not flattened in the hot rolling either, so are observed as spherical inclusions. If using an energy dispersion type X-ray analyzer, it can be confirmed if spherical inclusions are oxides containing Ti.
  • the density can be calculated. Note that inclusions with a grain size of less than 0.05 ⁇ m or more than 10 ⁇ m do not contribute to improvement of toughness, so are ignored when calculating the density.
  • the amount of solute oxygen before the addition of Ti when producing the steel is important. If the amount of solute oxygen before the addition of Ti is less than 0.003%, the Ti-based oxides become smaller in grain size and fall in density. On the other hand, if the amount of solute oxygen before the addition of Ti exceeds 0.015%, the Ti-based oxides will coarsen to a grain size exceeding 10 ⁇ m and the toughness will be damaged. Therefore, the amount of solute oxygen before the addition of Ti was made 0.003 to 0.015% in range. If performing deoxidation using Si and Mn as deoxidizing agents before adding Ti when producing the steel, the amount of solute oxygen can be made 0.003 to 0.015%.
  • C is an element strengthening the steel. To obtain the strength required as structural steel, addition of 0.001% or more is necessary. On the other hand, if adding over 0.030% of C, coarse carbides form at the HAZ and the toughness and reheat embrittlement resistance are reduced and, further, island-shaped martensite forms between the laths of the bainite phases and the toughness of the base material falls. Therefore, the lower limit of the amount of C was made 0.001% and the upper limit was made 0.030%. Note that, from the viewpoint of securing reheat embrittlement resistance and toughness, the lower limit is preferably made 0.005% and the upper limit 0.020%.
  • Si is an important deoxidizing agent in the present invention. Further, it is an element contributing to the improvement of strength as well. To make the solute oxygen of the molten steel before addition of Ti 0.003 to 0.015 mass % and, further, to secure strength of the base material, addition of 0.05% or more of Si is necessary. On the other hand, if the amount of Si exceeds 0.50%, low melting point oxides will form and the descalability will deteriorate. For this reason, the amount of S is made 0.05% to 0.50%. Further, if the amount of Si exceeds 0.40%, unevenness will occur at the time of hot dipping and the beauty will be harmed. Therefore, the upper limit of the amount of Si is preferably made 0.40% or less.
  • Mn is an important deoxidizing agent in the present invention. Further, it is an element raising the quenchability and increasing the amount of formation of the bainite structures to contribute to the improvement of strength and toughness. To make the solute oxygen of the molten steel before addition of Ti 0.003 to 0.015 mass % and, further, to secure strength and toughness of the base material, addition of 0.40% or more is required.
  • Mn is an element which easily segregates at the center of the steel slab when producing a steel slab in continuous casting. If adding over 2.00% of Mn, the quenchability of the segregated part will excessively rise and the toughness will deteriorate.
  • the amount of Mn is made 0.40% to 2.00%.
  • addition of 1.10% or more is preferable.
  • Nb is added for securing the solid solution Nb extremely important in the present invention.
  • the quenchability can be raised to improve the ordinary temperature strength. Further, due to the drag effect of dislocations, the deformation resistance can be increased and strength secured even in the high temperature region.
  • addition of 0.03% or more of Nb is required.
  • the upper limit was made 0.50%.
  • addition of 0.10% or more of Nb is preferable.
  • Nb is a powerful carbide-forming element. It precipitates by forming NbC with excessive C, so the solid solution Nb is decreased. For this reason, to secure solid solution Nb and improve the high temperature strength, it is necessary to satisfy
  • C and Nb are the contents of C and Nb in units of mass %.
  • the lower limit of C—Nb/7.74 can be found from the lower limit value of C and the upper limit value of Nb, so is not particularly defined.
  • the mass concentration product of Nb and C is an indicator of the amount of solid solution Nb. To further improve the high temperature strength, it is preferably made 0.0015 or more.
  • the “mass concentration product of Nb and C” is the product of the contents of Nb and C expressed by mass %. The upper limit of the mass concentration product of Nb and C is found from the upper limit values of the contents of Nb and C, so is not particularly defined.
  • Ti is an important element for forming Ti-based oxides in this way. Further, it is an element forming carbides and nitrides and easily forms TiN stable at a high temperature. By the formation of TiN, it is possible to suppress the precipitation of NbN, so addition of Ti is also extremely effective for securing solid solution Nb. To obtain this effect, addition of 0.005% or more of Ti is necessary. On the other hand, if adding 0.040% or more of Ti, the Ti-based oxides and TiN will coarsen and the toughness will be harmed.
  • the amount of Ti is made 0.005% to less than 0.040%.
  • the upper limit is preferably 0.020%.
  • N is an impurity element forming nitrides. Reduction of the amount of N is effective for securing the solid solution Nb.
  • the upper limit is made less than 0.0050%.
  • the content of N is preferably extremely low, but making it less than 0.0008% increases the production costs. Further, from the viewpoint of securing toughness, the upper limit of the amount of N is preferably made 0.0045%.
  • P and S are impurities. If included in excess, weld cracks due to solidification segregation and a drop in toughness will occur. Therefore, P and S should be reduced as much as possible. The upper limits of the contents of these are made 0.030% and 0.020%.
  • this system of ingredients may have further added to it as necessary V, Mo, Zr, Hf, Cr, Cu, Ni, Mg, Al, REM, and/or Ca so as to improve the characteristics.
  • these optionally added ingredients will be explained.
  • V is known as a precipitation strengthening element, but in the present invention where the C content is low, it contributes to solution strengthening. V becomes saturated in effect even if added in over 0.10% and detracts from the economy, so the upper limit is preferably made 0.10%.
  • Mo is an element contributing to strengthening of the structure by solution strengthening and improvement of the quenchability. It is preferably added in accordance with the targeted strength. However, if adding 0.10% or more of Mo, the economy is detracted from and, further, the toughness and high temperature embrittlement resistance of the HAZ sometimes fall, the upper limit is preferably made less than 0.10.
  • Zr is an element forming ZrN—a nitride stabler at high temperature than even TiN.
  • ZrN a nitride stabler at high temperature than even TiN.
  • Hf like Ti, is an element forming nitrides and contributes to reduction of the solid solution N. However, if adding over 0.01% of Hf, the HAZ toughness sometimes falls. Therefore, the upper limit of Hf is preferably made 0.01%.
  • Cr, Cu, and Ni are elements which improve the quenchability and thereby contribute to a rise in strength.
  • Mg is a powerful deoxidizing element and has the function of forming Mg-based oxides stable at a high temperature, not entering into solid solution in the steel even when heated to a high temperature during welding, and pinning the ⁇ grains. Due to this, it refines the structure of the HAZ and suppresses the drop in toughness. However, if adding over 0.005% of Mg, the Mg-based oxides become coarser and no longer contribute to pinning of the ⁇ grains. They sometimes form coarse oxides and detract from the toughness, so the upper limit is preferably made 0.005%.
  • Al is a powerful deoxidizing agent and may be added to control the concentration of solute oxygen after primary deoxidation to 0.003 to 0.015%. However, if including over 0.030% of Al, island-shaped martensite is formed and the toughness is sometimes damaged, so the upper limit is made 0.030%. From the viewpoint of improvement of the toughness, the upper limit is preferably 0.02%.
  • REMs rare earth elements undergo oxidation reactions and sulfurization reactions in the steel to form oxides and sulfides. These oxides and sulfides are stable at a high temperature. They will not enter solid solution even when heated to a high temperature at the time of welding and have the function of pinning the grain boundaries. Due to this function, it is possible to refine the HAZ structure and suppress the drop in toughness.
  • addition of a total content of all rare earth elements of 0.001% or more is preferable.
  • the upper limit is preferably made 0.01%.
  • Ca by addition in a small amount, has the effect of suppressing flattening of the sulfides in the rolling direction during hot rolling. Due to this, the toughness is improved, in particular, this contributes to an improvement of the Charpy value in the thickness direction. To obtain this effect, addition of 0.001% or more of Ca is preferable. On the other hand, if adding over 0.005% of Ca, the volume fraction of the oxides and sulfides will become higher and the toughness will be lowered in some cases, so the upper limit is preferably made 0.005%.
  • the metal structure of the steel of the present invention is not particularly limited, but the contents of the elements raising the quenchability should be adjusted to obtain a structure in accordance with the required strength. To raise the strength, raising the area ratio of one or both of the massive ferrite or bainite is preferable.
  • Massive ferrite is a structure resulting from the diffusion and transformation of austenite to ferrite of the same composition in the cooling process. Since the compositions before and after the transformation are the same, not the diffusion of C, but the self diffusion of the Fe atoms, that is, the rearrangement of the lattice, becomes the speed setting stage. Therefore, the massive ferrite is formed with a short distance of movement of atoms and a relatively fast transformation speed, so the crystal grain size becomes larger than polygonal ferrite and the dislocation density is high.
  • the massive ferrite formed by this mechanism differs from the polygonal ferrite in crystal grain size under observation of the structure under an optical microscope, but is no different in form. Therefore, to clearly differentiate these, observation by a through type electron microscope is necessary. Further, bainite forms plate structures and can be distinguished from massive ferrite and polygonal ferrite by an optical microscope.
  • the formation of massive ferrite and bainite is promoted by raising the quenchability of steel. For this reason, making the quenchability indicator Ceq 0.05 or more is preferable. Further, if Ceq is too high, the strength rises and the toughness is sometimes impaired, so the upper limit is more preferably made 0.60 or less. Note that,
  • the obtained steel slab is hot rolled into steel plate or shaped steel and then cooled.
  • the steel material covered by the present invention includes rolled steel plate, H-section steel, I-section steel, angle steel, channel steel, unequal angle steel, and other shaped steel.
  • H-section steel for building materials where fire resistance and reheat embrittlement resistance characteristics are required, in particular H-section steel is suitable. Further, when used as column materials, steel material of a thickness of a large size such as extremely thick H-section steel is suitable.
  • a steel material of the present invention containing Ti-based oxides with a grain size of 0.05 to 10 ⁇ m in a ratio of 30 to 300/mm 2 adjustment of the solute oxygen before the addition of Ti and after primary deoxidation is extremely important. It is necessary to adjust the amount of solute oxygen to a mass % of 0.003 to 0.015%. To form the Ti-based oxides, a 0.003% or more amount of solute oxygen is necessary. If over 0.015%, the grain size of the Ti oxides becomes larger, so a sufficient number of oxides of a grain size of 0.05 to 10 ⁇ m can no longer be obtained. From this viewpoint, the upper limit of the solute oxygen is preferably made 0.010%.
  • the lower limit of the heating temperature of the steel slab has to be made 1100° C.
  • the heating temperature is preferably made 1200° C. or more.
  • the upper limit of the heating temperature of the steel slab was made 1350° C. in view of the performance of the heating furnace and economy.
  • the upper limit of the heating temperature of the steel slab is preferably made 1300° C.
  • the cumulative reduction rate at 1000° C. and below is preferably made 10% or more. Due to this, recrystallization during the hot working is promoted, the ⁇ grains are made finer, and the toughness and strength can be improved.
  • the thickness of the product is less than 40 mm, there are few restrictions in thickness of the material before rolling.
  • the strength can be improved, so when the thickness is less than 40 mm, the cumulative reduction rate range is preferably 30% or more.
  • the end temperature of the hot rolling is preferably made 800° C. or more.
  • controlled cooling is preferably used to make the average cooling speed in the 800 to 500° C. temperature range 0.1 to 10° C./s.
  • the average cooling speed in the 800 to 500° C. temperature range is preferably made 0.1° C./s or more.
  • the upper limit is preferably made 10° C./s.
  • FIG. 5 shows the process of production of shaped steel.
  • the steel slab heated by a heating furnace 4 was rough rolled by a rough rolling mill 5 , then rolled to H-section steel by a universal rolling mill train comprised of an intermediate universal rolling mill 6 and finish universal rolling mill 8 .
  • Water cooling was performed between the rolling passes by water cooling apparatuses 7 provided before and after the intermediate universal rolling mill 6 .
  • the outside surface of the flange was repeatedly spray cooled and reverse rolled.
  • the cooling after the hot rolling was performed by a cooling apparatus 9 set behind the finishing universal rolling mill 8 .
  • tensile test pieces were taken at the center part of thickness t 2 of the flange 2 (1 ⁇ 2t 2 ) at the positions of 1 ⁇ 4 of the total flange width (B) (called “flange”) and 1 ⁇ 2 (called “fillet”) based on the JIS Z 2201.
  • the reheat draw rate of the reproduced weld heat affected zone (Tables 2 to 4) is an important characteristic. This was evaluated by subjecting the test steel to a weld heat cycle, heating it again, applying tensile stress at a high temperature, and using the draw rate when breaking.
  • a rod shaped tensile test piece taken from the flange was held at 1400° C. for 1 second, then cooled down to 100° C. with a cooling time from 800° C. to 500° C. of 20 seconds as a weld heat cycle, then was further heated as is by a 1° C./s temperature elevation rate to 600° C., held at 600° C. for 600 seconds, then given tensile strength to breakage by a 0.5 MPa/s tensile increase rate and measured for draw rate.
  • the toughness of the reproduced weld heat affected zone (HAZ) (Table 2), in the same way as the reheat draw rate, was evaluated by subjecting the test steel to a weld heat cycle, then applying a Charpy impact test based on JIS Z 2242 at 0° C. and finding the absorbed energy. That is, V-notch test pieces were taken from small pieces heat treated by holding them at 1400° C. for 1 second, then cooling down to 100° C. with a cooling time from 800° C. to 500° C. of 20 seconds as a weld heat cycle and were used for a Charpy impact test.
  • the targets of the JIS standard SM400 are an ordinary temperature yield strength YP of 235 MPa or more, preferably 355 MPa or less, a tensile strength TS of 400 to 510 MPa, and a 600° C. 0.2% proof stress PS of 157 MPa or more.
  • the targets of SM490 are a YP of 325 MPa or more, preferably 445 MPa or less, a TS of 490 to 610 MPa, and a PS of 217 MPa or more. Further, in both the SM400 class and SM490 class, the target value is the 0° C. impact absorption energy is 100 J or more and the preferable upper limit of the yield ratio YP/TS is 0.80.
  • an impact absorption energy at the fillet part of the base material at the Charpy test temperature of 0° C. is preferably 54 J or more.
  • the target of the reheat draw rate is 30% or more and the target of the toughness is 27 J or more.
  • a reheat draw rate of 50% or more is preferable.
  • each of the steels of the Production Nos. 1 to 15 and 35 to 39 of the present invention has ordinary temperature mechanical characteristics and high temperature mechanical characteristics within the target value ranges.
  • the yield point is the lower limit value of the JIS standard or more, while the yield ratio YP/TS is 0.8 or less or within the preferable range.
  • the Charpy impact value at 0° C. obtained is a value of the target value or more.
  • the reheat draw rate of the reproduced weld heat affected zone of 30% or more is sufficiently satisfied.
  • each of the comparative steels that is, the steels of Production Nos. 16 to 22 and 40 to 42, has ingredients C—Nb/7.74 and a density of Ti-based oxides outside the range of the present invention, so the mechanical characteristics satisfying the target are not obtained.
  • a steel material having sufficient ordinary temperature strength and high temperature strength and superior in toughness of the base material and HAZ and reheat embrittlement resistance characteristics in particular, fire resistant H-section steel
  • fire resistant H-section steel can be produced without cold working and heat treatment for thermal refining or extremely thick H-section steel of a thickness of a large size, for example, a flange thickness of up to 140 mm or so, can be produced as hot rolled while securing strength and toughness. Due to this, it is possible to reduce installation costs, shorten the work period, and thereby greatly cut costs. The improvement in the reliability of large buildings, guarantee of safety, economy, and other industrial effects are extremely remarkable.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Heat Treatment Of Steel (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
US12/450,762 2007-04-11 2008-04-11 Steel material superior in high temperature strength and toughness and method of production of same Abandoned US20100047107A1 (en)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
JP2007-103876 2007-04-11
JP2007103876 2007-04-11
JP2007309289 2007-11-29
JP2007-309289 2007-11-29
PCT/JP2008/057563 WO2008126944A1 (ja) 2007-04-11 2008-04-11 高温強度、靭性に優れた鋼材並びにその製造方法

Publications (1)

Publication Number Publication Date
US20100047107A1 true US20100047107A1 (en) 2010-02-25

Family

ID=39864030

Family Applications (1)

Application Number Title Priority Date Filing Date
US12/450,762 Abandoned US20100047107A1 (en) 2007-04-11 2008-04-11 Steel material superior in high temperature strength and toughness and method of production of same

Country Status (6)

Country Link
US (1) US20100047107A1 (zh)
EP (1) EP2143814A1 (zh)
JP (1) JP5079794B2 (zh)
KR (1) KR20090122371A (zh)
CN (1) CN101657555B (zh)
WO (1) WO2008126944A1 (zh)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120085209A1 (en) * 2010-03-30 2012-04-12 Toshiharu Aiso Cutting method of steel for machine structural use
TWI449798B (zh) * 2010-11-22 2014-08-21 Nippon Steel & Sumitomo Metal Corp An aging hardening type steel sheet excellent in aging resistance after coating and a method for producing the same
US20140301888A1 (en) * 2011-12-15 2014-10-09 Nippon Steel & Sumitomo Metal Corporation High-strength h-beam steel exhibiting excellent low-temperature toughness and method of manufacturing same
CN111074148A (zh) * 2018-10-19 2020-04-28 宝山钢铁股份有限公司 一种800MPa级热冲压桥壳钢及其制造方法
US20220177994A1 (en) * 2019-05-09 2022-06-09 Nippon Steel Corporation Steel sheet and method for producing same

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4855553B2 (ja) * 2009-11-27 2012-01-18 新日本製鐵株式会社 高強度極厚ｈ形鋼及びその製造方法
JP5471524B2 (ja) * 2010-01-29 2014-04-16 新日鐵住金株式会社 靱性に優れた高強度極厚ｈ形鋼およびその製造方法
JP5381828B2 (ja) * 2010-03-15 2014-01-08 新日鐵住金株式会社 母材の高温強度及び溶接熱影響部の高温延性に優れた耐火鋼材とその製造方法
CN105568139B (zh) * 2016-03-02 2018-03-27 东营富茂建设工程有限公司 一种h型钢及其生产方法
CN107904368A (zh) * 2017-11-03 2018-04-13 山东钢铁股份有限公司 一种轧后微合金化h型钢低温性能挽救方法
CN108754335B (zh) * 2018-08-22 2019-09-10 武汉钢铁有限公司 一种屈服强度≥550MPa的焊接结构用耐火耐候钢及生产方法
CN113840937B (zh) * 2019-05-23 2023-07-25 日本制铁株式会社 热冲压成型体及其制造方法
CN112410665B (zh) * 2020-11-10 2021-10-29 马鞍山钢铁股份有限公司 一种抑制晶粒长大的厚重热轧h型钢及其生产方法

Family Cites Families (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04362156A (ja) * 1991-06-05 1992-12-15 Sumitomo Metal Ind Ltd 耐火性・溶接継手部靱性の優れた鋼材
JP3232120B2 (ja) * 1992-02-10 2001-11-26 川崎製鉄株式会社 耐火性と靱性に優れた建築用低降伏比熱延鋼帯およびその製造方法
JP3202310B2 (ja) * 1992-04-02 2001-08-27 新日本製鐵株式会社 大入熱溶接熱影響部靱性の優れた建築用耐火鋼板の製造法
JP3550721B2 (ja) 1994-05-02 2004-08-04 Ｊｆｅスチール株式会社 耐火性および靱性に優れた建築用熱延鋼帯の製造方法
JPH1068018A (ja) * 1996-08-27 1998-03-10 Sumitomo Metal Ind Ltd 溶接熱影響部靭性の優れた構造用耐火鋼板の製造法
JP3462968B2 (ja) 1996-10-16 2003-11-05 新日本製鐵株式会社 低降伏比型耐火用熱延鋼板及び鋼管並びにそれらの製造方法
JP3559455B2 (ja) 1998-08-10 2004-09-02 新日本製鐵株式会社 低降伏比型耐火用鋼材及び鋼管並びにそれらの製造方法
JP3635208B2 (ja) 1999-03-29 2005-04-06 新日本製鐵株式会社 靱性に優れた低降伏比型耐火用鋼板及び鋼管並びにそれらの製造方法
JP4362219B2 (ja) 2000-10-11 2009-11-11 新日本製鐵株式会社 高温強度に優れた鋼およびその製造方法
JP4837171B2 (ja) * 2001-01-16 2011-12-14 新日本製鐵株式会社 低降伏比高靭性耐火ｈ形鋼の製造方法
JP2002294391A (ja) * 2001-03-29 2002-10-09 Kawasaki Steel Corp 建築構造用鋼及びその製造方法
CN1132958C (zh) * 2001-10-17 2003-12-31 武汉钢铁(集团)公司 高性能耐火耐候建筑用钢及其生产方法
CN1240866C (zh) * 2003-02-25 2006-02-08 鞍山钢铁集团公司 耐火钢及其制造方法
JP4031730B2 (ja) * 2003-05-14 2008-01-09 新日本製鐵株式会社 溶接性、ガス切断性に優れた構造用４９０ＭＰａ級高張力耐火鋼ならびにその製造方法
JP2004360361A (ja) * 2003-06-06 2004-12-24 Nippon Steel Corp 無耐火被覆鉄骨構造物

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120085209A1 (en) * 2010-03-30 2012-04-12 Toshiharu Aiso Cutting method of steel for machine structural use
US8545137B2 (en) * 2010-03-30 2013-10-01 Nippon Steel & Sumitomo Metal Corporation Cutting method of steel for machine structural use
TWI449798B (zh) * 2010-11-22 2014-08-21 Nippon Steel & Sumitomo Metal Corp An aging hardening type steel sheet excellent in aging resistance after coating and a method for producing the same
US20140301888A1 (en) * 2011-12-15 2014-10-09 Nippon Steel & Sumitomo Metal Corporation High-strength h-beam steel exhibiting excellent low-temperature toughness and method of manufacturing same
US9644372B2 (en) * 2011-12-15 2017-05-09 Nippon Steel & Sumitomo Metal Corporation High-strength H-beam steel exhibiting excellent low-temperature toughness and method of manufacturing same
CN111074148A (zh) * 2018-10-19 2020-04-28 宝山钢铁股份有限公司 一种800MPa级热冲压桥壳钢及其制造方法
US20220177994A1 (en) * 2019-05-09 2022-06-09 Nippon Steel Corporation Steel sheet and method for producing same

Also Published As

Publication number Publication date
KR20090122371A (ko) 2009-11-27
CN101657555B (zh) 2011-08-03
WO2008126944A1 (ja) 2008-10-23
JPWO2008126944A1 (ja) 2010-07-22
EP2143814A1 (en) 2010-01-13
CN101657555A (zh) 2010-02-24
JP5079794B2 (ja) 2012-11-21

Similar Documents

Publication Publication Date Title
US9023158B2 (en) Steel material superior in high temperature characteristics and toughness and method of production of same
US20100047107A1 (en) Steel material superior in high temperature strength and toughness and method of production of same
US8641836B2 (en) Steel plate for line pipe excellent in strength and ductility and method of production of same
WO2013089156A1 (ja) 低温靭性に優れた高強度ｈ形鋼及びその製造方法
WO2015093321A1 (ja) Ｈ形鋼及びその製造方法
EP2729590A1 (en) Hot-rolled high-strength steel strip with improved haz-softening resistance and method of producing said steel
JP7411072B2 (ja) 低温衝撃靭性に優れた高強度極厚物鋼材及びその製造方法
US8097096B2 (en) Fire resistant steel excellent in high temperature strength, toughness, and reheating embrittlement resistance and process for production of the same
WO2014175122A1 (ja) Ｈ形鋼及びその製造方法
JP2023506822A (ja) 低温衝撃靭性に優れた高硬度耐摩耗鋼及びその製造方法
JPH10306316A (ja) 低温靭性に優れた低降伏比高張力鋼材の製造方法
JP3817887B2 (ja) 高靭性高張力鋼およびその製造方法
JP3873540B2 (ja) 高生産性・高強度圧延ｈ形鋼の製造方法
JP6795083B2 (ja) 鋼板およびその製造方法
JP4220830B2 (ja) 靭性および延性に優れたパーライト系レールおよびその製造方法
JP2002363685A (ja) 低降伏比高強度冷延鋼板
JP6295632B2 (ja) 靭性に優れた高強度ｈ形鋼
JP2017186594A (ja) 低温用ｈ形鋼及びその製造方法
CN115369318B (zh) 一种低成本高强度耐火建筑结构用钢及其生产方法
JP7439241B2 (ja) 強度及び低温衝撃靭性に優れた鋼材及びその製造方法
US20220025476A1 (en) High strength hot rolled steel sheet having excellent elongated and method for manufacturing the same
JP2023554299A (ja) 延性に優れた高強度鋼板及びその製造方法

Legal Events

Date Code Title Description
AS Assignment

Owner name: NIPPON STEEL CORPORATION,JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:YOSHIDA, SUGURU;KITA, HIROSHI;OKUMURA, TERUHISA;AND OTHERS;REEL/FRAME:023381/0702

Effective date: 20090813

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION