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
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • 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
  • C21D6/002—Heat treatment of ferrous alloys containing Cr
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • 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
  • C22C38/02—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
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
• • 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
  • 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
  • C21D2211/004—Dispersions; Precipitations
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/16—Selection of particular materials

Definitions

• the present invention relates to a Cr-containing steel having excellent thermal fatigue characteristics that is optimal for use in exhaust system members that particularly require high-temperature strength and oxidation resistance.
• Exhaust system components such as automobile exhaust manifolds, CFC top pipes, and center pipes pass high-temperature exhaust gas discharged from the engine, so the materials that make up the exhaust members include oxidation resistance, high-temperature strength, heat Various characteristics such as fatigue characteristics are required.
• pig iron has generally been used for automobile exhaust members, but stainless steel exhaust manifolds have been used from the viewpoints of stricter exhaust gas regulations, improved engine performance, and lighter vehicle bodies. It has come to be used.
• the exhaust gas temperature has increased to about 800 to 900 ° C., and there is a demand for a material having oxidation resistance, high temperature strength and thermal fatigue characteristics in an environment where the exhaust gas is used at a high temperature for a long time.
• austenitic stainless steel is excellent in heat resistance and workability, but because of its large thermal expansion coefficient, when applied to a member that repeatedly receives heating and cooling, such as an exhaust manifold. Thermal fatigue destruction is likely to occur.
• ferritic stainless steel has a lower thermal expansion coefficient than austenitic stainless steel, and therefore has excellent thermal fatigue characteristics.
• steel with adjusted alloy additions such as Cr, Mo, Nb is used.
• Exhaust gas high temperature Although the amount of these alloys added has increased with the progress of the process, the thermal fatigue life, which is the most important characteristic, has not necessarily increased.
• excessive increase in the amount of alloy added leads to an increase in cost, and may have disadvantages that are not economical.
• Japanese Laid-Open Patent Publication No. 7-145453 discloses ferrite stainless steel excellent in oxidation resistance, high temperature strength, and thermal fatigue characteristics for automobile exhaust manifolds.
• the Cr content is 11-14%, which is a relatively low Cr content.
• this technology improves oxidation resistance, high temperature strength, and thermal fatigue characteristics at 900 ° C or higher.
• thermal fatigue properties are achieved under the condition of 50% restraint at 200-900 ° C.
• the invention steel has a long thermal fatigue life, but the restraint rate is low, or the temperature is about 800 ° C. Therefore, sufficient characteristics could not be obtained under the condition that the applied cycle was long.
• Japanese Patent Application Laid-Open No. 9-279316 discloses an invention in which Si / Mn is controlled to improve the high temperature characteristics by increasing the resistance to 900 MPa at 15 MPa or more. In this case as well, it was not enough in a long-term use environment to specify the tensile strength of the product plate at 900 ° C. In addition, since Mn was added in an amount of 0.7 to 3%, the ductility was low, and there was a problem that the formability when processing into a member and the thermal fatigue life decreased due to the decrease in high hot ductility.
• Japanese Patent Laid-Open No. 2002-105605 discloses that the 0.2% resistance to 18 MPa or more after holding at 900 ° C. for 1 hour by adjusting the components. Here, it is possible to maintain a strong environment in the environment by holding it for 1 hour at a high temperature. The technical idea is to improve the temperature, but when subjected to a thermal cycle, the thermal fatigue life may not be improved only by improving the high-temperature strength.
• steel containing B is disclosed as a ferrite stainless steel having excellent high temperature characteristics. It has been added to improve workability, and its influence on high-temperature properties has not been clear from conventional knowledge.
• the role of B in improving workability is to improve the grain boundary strength due to grain boundary segregation and improve secondary workability.
• the addition of B refines the precipitate, It is intended to improve high temperature strength.
• V was added to the above three patents, but in some cases it was added from the viewpoint of improving the corrosion resistance of the weld and improving the workability by fixing C and N. Disclosure of the invention
• the present invention provides excellent oxidation resistance, high temperature strength, and thermal fatigue characteristics especially in an environment where the exhaust temperature is near 800 ° C, which is used for a long time at high temperatures, or repeatedly subjected to heating and cooling. And providing relatively inexpensive Cr-containing steel.
• the present inventors investigated the relationship between the components and the high temperature deformation characteristics regarding the oxidation resistance, high temperature strength, and thermal fatigue characteristics of the Cr-containing steel.
• the deformation characteristics in the low temperature range in addition to the deformation characteristics in the high temperature range affect the thermal fatigue life.
• the following findings were obtained.
• This feature is mainly due to the addition of Cr and Si from the viewpoint of oxidation resistance, the addition of Nb-Ti composite from the viewpoint of improving high-temperature characteristics, and the adjustment of each component in the new ingredients added with V and B. Therefore, it ensures the strength and ductility during long-term use and greatly improves the thermal fatigue characteristics.
• the gist of the present invention is as follows.
• Figure 1 shows the relationship between (Nb + 1.9Ti) / (C + N) and the elongation at break at room temperature.
• Figure 2 shows the effect of Ti addition on the thermal fatigue life.
• Figure 3 shows the resistance to 800 ° C after aging at 800 ° C.
• Figure 4 shows the aperture value at 200 ° C after aging at 800 ° C.
• Figure 5 shows the aperture at 200 ° C after aging at 800 ° C.
• FIG. 6 is a graph showing the relationship between MnZTi and Cr 20 3 thickness when subjected to a continuous oxidation test at 900 ° C. for 200 hours.
• C degrades the formability and corrosion resistance and lowers the high-temperature strength. Therefore, the lower the content, the better. Therefore, C was made 0.015% or less. However, excessive reduction leads to an increase in fine cost, so 0.001 to 0.005% is more desirable.
• N like C, deteriorates formability and corrosion resistance and lowers the high-temperature strength.
• excessive reduction leads to an increase in fine cost, so 0.00 to 0.010% is also desirable.
• Si is an important element for improving oxidation resistance and high temperature characteristics in the present invention. Oxidation resistance and high-temperature strength improve with increasing Si content, and the effect is manifested at 0.8% or more.
• Si promotes precipitation of intermetallic compounds mainly composed of Fe and Nb called Laves phase at high temperatures. If the Laves phase precipitates excessively, the amount of dissolved Nb necessary to ensure high temperature strength is reduced. If Si is added excessively, the room temperature workability deteriorates and the ductility during long-time use is reduced, leading to a reduction in thermal fatigue life. From these viewpoints, the upper limit was set to 1.0%. Further, it is preferably 0.8 to 0.9%.
• Mn is an element that is added as a deoxidizer and improves the high-temperature strength, and the effect is manifested from 0.2% or more.
• the addition of Mir suppresses the oxidation of Ti during continuous oxidation and improves the oxidation resistance of the steel with a composite addition with Ti.
• addition over 1.5% reduces ductility
• the upper limit is preferably 0.03%.
• the lower limit is preferably 0.01%.
• 0.012 to 0.025% is desirable.
• S is an element that degrades corrosion resistance and oxidation resistance, but since the effect of improving workability by combining with Ti and C is manifested from 0.0001%, the lower limit was set to 0.0001%.
• the upper limit is set to 0.01% because the high-temperature strength decreases because it combines with Ti and C by appropriate addition to reduce the amount of solid solution Ti and cause coarsening of precipitates. Furthermore, if considering the sickle cost and high temperature oxidation characteristics, 0.0010 to 0.0090% is desirable.
• Cr is an essential element for ensuring oxidation resistance in the present invention. If it is less than 13%, the effect is not manifested, and if it exceeds 15%, the workability is deteriorated or the toughness is deteriorated. Furthermore, considering high temperature ductility and manufacturing cost, 13.2 to 14.5% is desirable.
• Ni is effective in improving toughness and resistance to high temperature salt damage and corrosion.
• it is an austenite-forming element, has an adverse effect on oxidation resistance, and is expensive.
• Cu is effective for improving high-temperature strength, but it lowers the ductility and adversely affects oxidation resistance.
• Mo is effective for improving corrosion resistance, suppressing high-temperature oxidation, and improving high-temperature strength by strengthening solid solution. However, it is not more than 0.2% because it causes high hot ductility and is expensive. More desirably, it is 0.1% or less.
• Nb improves the high-temperature strength by strengthening solid solution and refining precipitates. It is an element necessary for the purpose. It also has the role of fixing C and N as carbonitrides and contributing to the development of recrystallization textures that affect the corrosion resistance and r-value of product plates. These effects appear from 0.3% or more. On the other hand, if it is precipitated as a LaFez phase depending on the temperature in the environment of use, the effect will be saturated even if it is added excessively because it loses its solid solution strengthening ability. Moreover, excessive addition reduces ductility at low temperatures and shortens the thermal fatigue life. In the present invention, the amount of solute Nb is ensured by the combined addition with Ti. In this case, the action is saturated at 0.55%, so it was set to 0.3 to 0.55%. Furthermore, if considering moldability, intergranular corrosion and manufacturing cost, 0.32 to 0.45% is desirable.
• Ti is an element that combines with C, N, and S to improve corrosion resistance, intergranular corrosion resistance, and deep drawability.
• the addition of an appropriate amount brings about the improvement of high-temperature strength and high-temperature ductility after exposure at high temperature for a long time, and improves thermal fatigue properties.
• These effects are manifested from 0.05% or more, but addition of more than 0.2% increases the amount of solid solution Ti and degrades formability, as well as surface toughness, toughness, and oxidation resistance. Therefore, the content is set to 0.05 to 0.2%. Furthermore, considering the manufacturability, 0.05 to 0.15% is desirable.
• A1 is an element that improves high-temperature strength through oxidation resistance and solid solution strengthening, and is an essential element in the present invention. The effect starts from 0.015%, but addition of more than 1.0% hardens, deteriorates surface flaws and weldability, so 0.015 to 1.0% . In addition, 0.03 to 0.7% is desirable considering the cost of fertility.
• B is an element that improves secondary workability during product press working.
• Ti-added steel is an essential element in the present invention because secondary work cracks are likely to occur.
• the component system to which Nb and Ti are added and Si is added as in the present invention contributes to the improvement of the high temperature strength.
• B is considered to form (Fe, Cr) 23 (C, 6) 6 and Cr 2 ⁇ at high temperatures and segregate at grain boundaries, but in the component system to which Si is added, These precipitates did not precipitate, and it was found that they had the effect of precipitating Laves as described above.
• the Laves phase reduces the amount of dissolved Nb and usually coarsens, so there is almost no high-temperature strengthening ability after long-term aging, but it has precipitation strengthening ability because it precipitates finely by adding B. It will contribute to the improvement of strength.
• B precipitates the Laves phase finely is presumed that the interfacial energy decreases due to grain boundary segregation, making it difficult for grain boundaries to precipitate.
• the elongation at break at room temperature can be secured at 32% or more.
• JIS No. 13 B specimens were taken in the rolling direction, subjected to a tensile test, and the elongation at break was measured. If the elongation at break is 32% or more, cracking and constriction will not occur even if the pipe material is bent after press working from the plate material to the exhaust member or after bending into a pipe shape.
• the product plate was pipe-formed (outside diameter 38. lmm) by electro-welding and subjected to a thermal fatigue test.
• the thermal fatigue test was conducted with a computer-controlled electrohydraulic control fatigue tester.
• the temperature cycle to be applied was such that the temperature was raised from 200 to 800 ° C in 120 seconds, held at 800 ° C for 30 seconds, then cooled to 300 ° C in 120 seconds, and further cooled to 200 ° C in 90 seconds. Heating was performed with a high-frequency induction heating coil, and cooling was performed by supplying air into the test tube.
• the restraint rate was set so that compressive strain was applied so as to be a constant ratio with respect to the amount of free expansion. That is, for example, in the case of 50% restraint, compression strain was mechanically applied so that the expansion amount was half of the free expansion.
• the chemical composition of the test material is shown in Table 1.
• Steel A is a compatible steel of the present invention and Steel B is a comparative steel.
• Steel B is a heat-resistant stainless steel plate used for general purposes.
• the steel of the present invention has a longer life than the comparative example at any constraint. This is because the high ductility is maintained in the low temperature region of the thermal cycle, in addition to the fact that there is almost no decrease in strength even when high temperature strength is aged, that is, a long time thermal cycle is applied. During a thermal cycle, a compressive load is applied to the material at a high temperature, and creep deformation or stress relaxation occurs at 800 ° C. Therefore, an increase in 0.2% proof stress at 800 ° C It is considered effective for extending the fatigue life.
• Figures 3 and 4 show the tensile strength and drawing at high temperatures after aging at 800 ° C.
• the steel of the present invention has high strength at a high temperature strength of 20 MPa or more and a drawing value of 35% or more at 200 ° C, even when subjected to long-term aging treatment at 800 ° C for 10 hours or more. This means that even when subjected to a long thermal cycle process during thermal fatigue, the strength at the highest temperature is high and the ductility at the lowest temperature is high. As a result, as shown in Fig. 2, it is considered that the thermal fatigue life is improved at any constraint rate. In the conventional invention, the technical idea was only to improve the strength at the maximum temperature when subjected to the thermal cycle, but in the present invention, the thermal fatigue life is remarkably improved by improving the ductility at the minimum temperature. I found out.
• the improvement of the drawing value at 200 ° C is considered to be due to the above-mentioned securing of the elongation at break at room temperature and the suppression of aging deterioration.
• the present invention has revealed that the addition balance of Ti and Nb is important.
• the improvement in high-temperature strength at 800 is affected by the amount of solute Nb and the amount of solute Ti.
• Figure 5 shows the relationship between the amount of solute Nb + solute Ti after aging at 800 ° C and the high temperature strength at 800 ° C.
• the solid solution Nb + solid solution Ti content is 0.08% or more
• the high-temperature strength at 800 ° C is 20MPa or more.
• the solid solution Nb amount + the solid solution Ti amount was set to 0.08% or more.
• the present invention by adding a proper amount of Ti and Nb in combination, thermal fatigue properties are improved by improving high-temperature strength and high-temperature ductility after long-term aging. There is a deterioration effect.
• the steel containing Si, Cr, Mn, Ti shown in the present invention is continuously oxidized in the atmosphere, the scale is composed of spinel oxide mainly containing Ti0 2 , Cr, Mn in the outer layer, and Cr 2 in the inner layer. 0 3 is formed. As the Ti content increases, the inner Cr 2 O 3 film becomes thicker and the oxidation resistance deteriorates.
• Figure 6 shows the inner layer of Cr 2 0 3 film thickness after 200 h continuous oxidation with Ti / Mn and 900 ° C. If the thickness of the Cr 20 3 inner scale exceeds 5 / m, scale peeling will occur and oxidation resistance will be inferior. However, if Mn / Ti ⁇ 3, the thickness of the Cr 20 3 inner scale will be thin. Excellent in oxidation resistance.
• Ti diffuses outward through the inner layer of Cr 2 0 3, but the result of outward diffusion of Ti is inhibited by Mn, and considered Erareru growth of the inner layer of Cr 2 0 3 film is suppressed.
• Mn Cr 2 0 3 coating
• Cr 2 0 3 it is important to suppress the growth of the inner layer of Cr 2 0 3 coating, Cr 2 0 3 to be generated when 200 h, was continuously oxidation in air at 900 ° C
• MnZTi ⁇ 3 In order to make the inner scale thickness 5 xm or less, MnZTi ⁇ 3.
• Example Steels with the composition shown in Table 2 were melted and formed into slabs, and the slabs were hot-rolled to form hot rolled coils with a thickness of 5M.
• the hot rolled coil was annealed and pickled, cold-rolled to a thickness of 2 mm, and annealed and pickled to obtain a product plate.
• the annealing temperature of the cold rolled sheet was set to 980 to 1050 ° C in order to make the grain size number about 6 to 8.
• high-temperature tensile test pieces were collected and subjected to tensile tests at 200 ° C and 800 ° C.
• a high temperature tensile test was conducted in the same manner as described above.
• the product plate was pipe-formed (outer diameter 38.1 mm) by electro-welding and subjected to a thermal fatigue test.
• the temperature cycle to be applied is a pattern in which the temperature is raised from 200 to 800 ° C in 120 seconds, held at 800 ° C for 30 seconds, then cooled to 300 ° C at 120sec and further cooled to 200 ° C in 90 seconds. The rate was 50%.
• oxidation resistance a 20 mm wide and 25 mm long test piece was cut from the product plate, polished to # 600 with emery paper, and then continuously oxidized in the atmosphere at 900 ° C for 200 h. A test was conducted. The thickness of the Cr 20 3 inner layer scale was determined by observing a cross section with a SEM (scanning electron microscope).
• the thickness of the inner layer of the steel of the present invention is good at 5 m or less.
• Si deviates from the scope of the present invention, and steels Nos. 14, 17, 23, 24, and 26 with small MnZTi have an inner layer scale thickness exceeding 5 m, and are inferior in oxidation resistance.
• the manufacturing method of the steel sheet is not particularly specified, but hot rolling conditions, hot rolled sheet thickness, hot and cold rolled sheet annealing temperatures, atmosphere, etc. may be selected as appropriate. Further, temper rolling or tension leveler may be applied after cold rolling / annealing. Furthermore, the product thickness may be selected according to the required member thickness.

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• 2007
  • 2007-05-29 JP JP2007141481A patent/JP5208450B2/ja active Active
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