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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • 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
  • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • C21D2211/005—Ferrite
• • 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

Definitions

• the present invention relates to a high tensile strength, refractory steel having excellent weldability and gas cuttability, and a method of producing the same.
• a refractory steel obtained by hot rolling a billet or slab has been described (see, for example, Japanese Unexamined Patent Application , First Publication No. H2-77523).
• This refractory steel generally belongs to so called 400 MPa class steel or 490 MPa class steel, and can include several examples of so called 590 MPa class steel having an yield strength of 440 MPa (45 kgf/mm 2 ) or more.
• the plate thickness can be regulated up to 100 mm.
• the plate thickness of the 590 MPa class steel can be at most, e.g., 40 mm, and thicker steel may not be supplied.
• a hot rolled steel can have a metallic texture mainly composed of, e.g., polygonal ferrite or pseudo polygonal ferrite having low strength. Therefore, even when a thick steel plate having a thickness of about 100 mm is produced by hot rolling, it may be difficult to ensure the strength of the steel stably by a technical control.
• a refractory steel corresponding to 590 MPa class steel may have a steel composition containing Mo of 0.7% or more, likely resulting in inferior cuttability by gas-cutting and high production cost.
• Mo weld crack sensitive composition
• Mo it may be preferable that the Mo content can be controlled to a low level.
• one of the objects of the present invention is to provide a high tensile strength, refractory steel and method of producing the same which has an excellent weldability and cuttability by gas cutting so as to allow mass production at low cost of a high tensile strength steel having a yield strength of 440 MPa or more and possibly having sufficient high temperature strength under a high temperature environment, such as, e.g., a fire.
• a high tensile strength, refractory steel having excellent weldability and gas cuttability can be provided.
• this steel can include, in mass %, approximately, : 0.04 to 0.14%, Si: 0.50% or less, Mn: 0.50 to 2.00%, P: 0.020% or less, S: 0.010% or less, Nb: 0.01 to 0.05%, Mo: 0.30% or more and less than 0.70%, Al: 0.060% or less, N: 0.0010 to 0.0060%, and the balance consisting of iron and unavoidable impurities.
• a weld crack sensitive composition PCM of the steel is 0.25% or less, and can be defined by the following equation:
• the area fraction of polygonal ferrite or pseudo polygonal ferrite in a 1 ⁇ 4 thick position in the plate thickness direction of a steel plate of the final rolling product can be 10% or less.
• This exemplary embodiment of the steel can further include, in mass %, approximately, Ni: 0.05 to 1.0%, Cu: 0.05 to 1.0%, and one or two or more selected from Cr: 0.05 to 1.0%, V: 0.01 to 0.06%, B: 0.0002 to 0.0030%, Ti: 0.005to 0.025%, Mg: 0.0002 to 0.0050%, and the Ni content may be at least half of the Cu content.
• Such exemplary steel can further comprise, in mass %, approximately, one or two selected from Ca: 0.0005 to 0.0040% and REM: 0.0005 to 0.0100%.
• the yield strength of the steel can be 440 MPa or more.
• a method for manufacturing a high tensile strength, refractory steel having excellent weldability and gas cuttability can be provided.
• a steel member in a form of billet or slab can be heated at a temperature of about 1100 to 1300° C., with the billet and/or slab having the steel composition that includes, in mass %, approximately, : 0.04 to 0.14%, Si: 0.50% or less, Mn: 0.50 to 2.00%, P: 0.020% or less, S: 0.010% or less, Nb: 0.01 to 0.05%, Mo: 0.30% or more and less than 0.70%, Al: 0.060% or less, N: 0.0010 to 0.0060%, and the balance consisting of iron and unavoidable impurities.
• the steel member is rolled at a temperature of 800 to 950° C.
• the steel member is directly quenched from a temperature not lower than a higher one selected from about 750° C. or a temperature about 150° C. lower than a temperature at a time of completing the rolling.
• the steel member is tempered at a temperature not higher than Ac 1 (e.g., a temperature at which generation of austenite starts at a time of heating).
• a method for manufacturing high tensile strength, refractory steel having excellent weldability and gas cuttability can be provided.
• a steel member can be hot-rolled in a form of billet or slab, which has the steel composition that includes, in mass %, approximately, : 0.04 to 0.14%, Si: 0.50% or less, Mn: 0.50 to 2.00%, P: 0.020% or less, S: 0.010% or less, Nb: 0.01 to 0.05%, Mo: 0.30% or more and less than 0.70%, Al: 0.060% or less, N: 0.0010 to 0.0060%, and the balance consisting of iron and unavoidable impurities.
• the steel member is self-cooled, and quenched after reheating the steel member at a temperature of about 900 to 950° C.
• the steel member is tempered at a temperature not higher than Ac 1 .
• a high tensile strength, refractory steel having excellent weldability and gas cuttability may have a weld crack sensitive composition PCM of about 0.25% or less and the balance consisting of iron and unavoidable impurities.
• an area fraction of polygonal ferrite or pseudo polygonal ferrite in a 1 ⁇ 4 thick position in the plate thickness direction of a steel plate of the final rolling product can be about 10% or less.
• refractory steel According to such a high tensile strength, refractory steel, it may be possible to perform mass production at low cost of high tensile strength steel having a yield strength of about 440 MPa or more, having excellent weldability and gas cuttability, and having sufficient high temperature strength under a high temperature environment such as a fire.
• a construction steel for architectural construction according to yet another exemplary embodiment of the present invention can be provided, composed of, e.g., the high tensile strength, refractory steel which can be applied as general construction steel for various applications including civil engineering, marine structures, ships and vessels, various storage tanks, industrial facilities such as plate-mills or the like. Since the exemplary embodiment of the high tensile strength, refractory steel according to the present invention has sufficient high temperature strength even under a severe environment, for example, at a time of fire, in which the steel is exposed to high temperature conditions, it may be possible to further enhance the safety of weld constructions.
• a steel member in a form of billet or slab having the steel composition can be heated at a temperature of about 1100 to 1300° C., and rolled at a temperature of about 800 to 950° C. After that, the steel member may be directly quenched from a temperature of not lower than a higher one selected from about 750° C. or a temperature about 150° C. lower than a temperature at a time of completing the rolling, and tempered at a temperature not higher than Ac 1 .
• the exemplary steel member after hot-rolling a steel member in a form of billet or slab having the steel composition as described herein above, the exemplary steel member can be self-cooled, and quenched after being reheated at a temperature of about 900 to 950° C., and tempered at a temperature of not higher than Ac 1 .
• an exemplary embodiment of a high tensile strength steel according to the present invention can includes, in mass %, approximately, C: 0.04 to 0.14%, Si: 0.50% or less, Mn: 0.50 to 2.00%, P: 0.020% or less, S: 0.010% or less, Nb: 0.01 to 0.05%, Mo: 0.30% or more and less than 0.70%, Al: 0.060% or less, N: 0.0010 to 0.0060%, and the balance consisting of iron and unavoidable impurities.
• a weld crack sensitive composition PCM can be defined by the following exemplary equation can be 0.25% or less:
• an area fraction of polygonal ferrite or pseudo polygonal ferrite in a 1 ⁇ 4 thick position in the plate thickness direction of a steel plate of the final rolling product can be about 10% or less.
• the composition of the high tensile strength, refractory steel may be limited.
• C likely has an influence on the property of the steel.
• the preferably minimum value of approximately 0.04% can be a minimum content so as to ensure the strength, and may be used to reduce or inhibit the over softening than necessary of a heat-affected portion such as a weld portion.
• too high a C content may enhance the hardenability of the steel to an unnecessary level, and can have a negative influence on the strength, toughness balance, and weldability as intrinsic properties of the steel. Therefore, the upper limit of the C content may be set to be about 0.14%.
• Si can have an influence on cleanability, weldability, and weld-portion toughness of the steel. Therefore, it may be used to control its upper limit value. Therefore, the Si content can be set to be about 0.50% or less. Si may also have an effect of deoxidizing of the steel. However, deoxidization of the steel can be performed by Ti or Al. Therefore, where weldability and weld-portion toughness are preferably used, it may not be necessary to add Si to the steel.
• Mn can be an important element for ensuring strength and toughness of the steel, and its minimum content may be, e.g., about 0.50%.
• the upper limit of the Mn can be set to be about 2.00%.
• the P can constitute an impurity in the steel of an exemplary embodiment of the present invention.
• the P content By reducing the P content, grain boundary deformation in the weld heat-affected portion may be reduced. Therefore, it may be preferable to control the P content to as low as possible. Therefore, so as not to deteriorate low temperature toughness of the base metal and weld heat-affected portion, the upper limit of the P content can be set to be about 0.020%.
• S may constitute an impurity in an exemplary embodiment of the steel of the present invention.
• the S content In order to ensure low temperature toughness of the steel, it may be preferable to control the S content to as low as possible. Therefore, so as not to deteriorate low temperature toughness of the base metal and weld heat-affected portion, the upper limit of the S content can be set to be about 0.010%.
• Nb is an element which can play a role in an exemplary embodiment of the present invention where Mo content can be depressed as far as possible.
• Nb can be an important element for elevating the recrystallization temperature of austenite, and exerting the effect of controlled rolling at a time of hot-rolling.
• Nb may also contribute to grain refining of heated austenite at a time of reheating preceding the rolling and has an effect of enhancing strength of the steel by precipitation hardening.
• Nb by composite addition with Mo, Nb can contribute to the high temperature strength of the steel.
• too high a Nb contents may result in a deterioration of toughness of the weld portion. Therefore, so as not to generate the deterioration of toughness of the weld portion, the upper limit of the Nb content can be set to be about 0.005%.
• Mo can be an important element for ensuring high temperature toughness of the steel.
• the steel In order for the exemplary embodiment of the steel to have sufficient high temperature strength under an environment, for example, at a time of fire, where the steel is exposed to high temperature conditions, it may be preferable for the steel to contain Mo of about 0.30% or more. On the other hand, too high of a Mo content can deteriorate weldability and gas cuttability of the steel. Therefore, the upper limit of the steel can be set to be less than 0.70%.
• Al is a deoxidizing element.
• deoxidization of the steel can be sufficiently performed, e.g., solely by Si or by Ti. Therefore, the lower limit of Al content may not be set according to an exemplary embodiment of the present invention.
• too high an Al content may impair cleanability of the steel, deteriorate toughness of the base metal, and deteriorate toughness of the weld-heat affected portion. Therefore, the upper limit of Al content may be set to be about 0.060%.
• N can be contained as an unavoidable impurity in the steel.
• Nb By bonding with the above-described Nb, N can form carbonitride and enhance the strength of the steel.
• N can enhance strength of the steel by forming TiN.
• the upper limit of N content can be set to be about 0.0060%.
• the high tensile strength steel according to the exemplary embodiment of the present invention can further include, in mass %, about Ni: 0.05 to 1.0%, Cu: 0.05 to 1.0%, and one or two or more selected from Cr: 0.05 to 1.0%, V: 0.01 to 0.06%, B: 0.0002 to 0.0030%, Ti: 0.005to 0.025%, Mg: 0.0002 to 0.0050%, wherein the Ni content may be at least half of the Cu content.
• One of the reason for adding these elements to the above-described exemplary basal composition can be to improve the properties such as strength and toughness of the steel without impairing excellent characteristics of the steel according to the exemplary embodiment of the present invention. Therefore, loadings of the exemplary elements may be restricted.
• Ni can improve strength and toughness of the steel without having a negative influence on weldability and toughness of the weld heat-affected portion of the steel.
• too high a loading of Ni may elevate the price of the steel and also has an undesirable effect on weldability. Therefore, the upper limit of Ni content can be set to be about 1.0%.
• the upper limit of the Cu content may be set to be about 1.0%.
• the steel in order to obtain a substantial effect, it may be preferable for the steel to contain a minimum amount of Cu. Therefore, the lower limit of the Cu content can be set to be about 0.05%.
• the Cr may improve strength and toughness of the base metal. However, too high a Cr content can deteriorate the toughness of the base metal and weld portion and weldability. Therefore, the upper limit of the Cr content may be set to be about 1.0%. On the other hand, in order to obtain a substantial effect, it may be preferable for the steel to contain a minimum amount of Cr. Therefore, the lower limit of the Cr content can be set to be about 0.05%.
• Ni, Cu and Cr can be effective for improving weather resistance as well as for improving strength and toughness of the base metal.
• V has similar effects as Nb. However, its effect may be less than that of Nb. V may have an influence on hardenability and contributes to improvement of high temperature strength.
• the steel In order to realize the same effect as Nb, it is necessary for the steel to contain at least 0.01% V. On the other hand, where the steel contains excessive V, toughness of the weld portion may be deteriorated. Therefore, so as not to deteriorate the toughness of the weld portion, the upper limit of the V content can be set to be about 0.06%.
• B can be segregated in the grain boundary of austenite, may depress occurrence of ferrite and thereby improves hardenability and strength of the steel.
• the upper limit of the B content can be set to be about 0.003%.
• Ti can be bonded with O and may form precipitates mainly composed of Ti 2 O 3 likely acting as nuclei of generation of ferrite by transgranular transformation and improving toughness of the weld portion.
• Ti can be effective by being bonded with N and forms TiN constituting fine precipitates in the slab, thereby depressing coarsening of austenite grain at the time of heating and reducing grain size of the rolled texture.
• fine TiN existing in a steel plate may reduce the grain size of the weld heat-affected portion at the time of welding.
• the upper limit of the Ti content may be set to be about 0.025%.
• Mg can depress the grain growth of austenite grains in the weld heat-affected portion and reduce the grain size. As a result, the weld portion may be given a high toughness. In order to realize such an effect, it may be preferable for the exemplary steel to contain Mg of about 0.0002% or more. On the other hand, where the Mg content can be increased, it may not be cost effective, because there may be less enhancement of the effect of Mg compared with the increase of Mg content. Therefore, the upper limit of the Mg content can be set to be about 0.0050%.
• the high tensile strength, refractory steel of an exemplary embodiment of the present invention can further include, in mass %, one or two selected from Ca: about 0.0005 to 0.0040% and REM (Rare Earth Metal): about 0.0005 to 0.0100%.
• rare earth metals such as Ce, La, and Nd or the like may be used.
• Ca and REM may be effective in controlling MnS morphologies and improving low-temperature toughness of the base metal.
• Ca and REM may be effective in reducing sensitivity for hydrogen-induced cracking, for example, hydrogen-induced cracking (HIC) under a humid hydrogen sulfide environment, SSC, and stress oriented HIC (SOHIC).
• HIC hydrogen-induced cracking
• SSC humid hydrogen sulfide environment
• SOHIC stress oriented HIC
• at least a content of about 0.0005% can be used.
• the upper limit of the Ca content can be set to be about 0.0040% and the upper limit of the REM content may be set to be about 0.0100%. Since Ca and REM can express a nearly similar effect, it is possible to load one of Ca and REM in the above-described range, or it is possible to load a mixture of Ca and REM in the above-described exemplary range.
• refractory steel in order to ensure the yield strength of about 440 MPa or more, and yield strength at about 600° C. of not less than about 2 ⁇ 3 of the yield strength at room temperature, that is, not less than about 294 MPa, while controlling Mo content to be lower than about 0.70%, it can be preferable to inhibit or reduce a control of the exemplary steel composition also to control its microstructure.
• an area fraction of polygonal ferrite or pseudo polygonal ferrite in a 1 ⁇ 4 thick position in the plate thickness direction of a steel plate of the final rolling product may be controlled to be about 10% or less.
• the Mo content may be restricted to be lower than about 0.70%, especially in a thick steel plate thicker than about 40 mm, it may be difficult to ensure not only the room temperature strength, but also the high temperature strength of the steel, when the area fraction of polygonal ferrite or pseudo polygonal ferrite exceeds about 10%.
• the microstructure is represented by the texture on the plane along the final rolling direction, where the plane is in a 1 ⁇ 4 thick position with respect to the section of the plate thickness.
• a weld crack sensitive composition PCM can be limited to be about 0.25% or less, where the PCM may be defined by the following exemplary equation:
• P CM C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B.
• the weld crack sensitive composition PCM can be a parameter indicating weldability, and weldability may be satisfactory as PCM shows a low value.
• the weld crack sensitive composition PCM may be 0.25% or less, it is possible to ensure excellent weldability while ensuring excellent high temperature strength.
• the high tensile strength, refractory steel according to the present invention can be manufacture by the first or by the second exemplary embodiment of a manufacturing method according to the present invention.
• the first exemplary embodiment of the manufacturing method can include: heating a steel member in a form of billet or slab having the steel composition according to the exemplary embodiment of the present invention at a temperature of about 1100 to 1300° C.; rolling the steel member at a temperature of about 800 to 950° C.; directly quenching the steel member from a temperature of not lower than a higher one selected from about 750° C. or a temperature about 150° C. lower than a temperature at a time of completing the rolling; and tempering the steel member at a temperature not higher than Ac 1 .
• the second embodiment of the manufacturing method can include: hot rolling a steel member in a form of billet or slab having the steel composition according to the exemplary embodiment of the present invention; self-cooling the steel member: quenching the steel member after reheating the steel member at a temperature of about 900 to 950° C.; and tempering the steel member at a temperature not higher than Ac 1 .
• a steel member in a form of billet or slab having the steel composition according to the exemplary embodiment of the present invention can be heated at a temperature of about 1100 to 1300° C.
• the exemplary reason for controlling the heating temperature preceding the rolling to be about 1100 to 1300° may be to inhibit the coarsening of austenite grains to an unnecessary size in the time of heating, and to refine the rolled texture.
• the temperature of approximately 1300° C. can be an upper limit of the temperature at which extreme coarsening of austenite is inhibited at the time of heating. Where the heating temperature exceeds the exemplary upper limit temperature, coarse grained austenite may be mixed in the texture, and rolled austenite grains also have a relatively large size.
• the metallographic structure after the phase transformation can be relatively coarse grained.
• the microstructure may tend to become a bainitic structure, possibly resulting in remarkable deterioration of toughness of the exemplary steel.
• the lower limit of the heating temperature can be set to be about 1100° C. based on the consideration of solution treatment of Nb so as to express the effect of controlled rolling at the time of hot-rolling and precipitation hardening.
• the exemplary steel member thus heated can be rolled at a temperature of about 800 to 950° C.
• the rolling temperature may be limited to be in the range of about 800 to 950° C. for the following exemplary reason.
• the rolling is performed at a temperature exceeding about 950° C., even though Mo and Nb are compositely loaded, grain size refining of the rolled austenite may not be sufficient, and therefore low-temperature toughness may not be ensured stably even by performing subsequent direct quenching and tempering.
• a temperature lower than about 800° C. depending on plate thickness, precipitation of ferrite can occur before the direct quenching and may cause difficulty in ensuring the microstructure, or Nb precipitates during rolling and does not contribute to the high temperature strength.
• the steel member After completing the rolling, the steel member is directly quenched from a temperature of not lower than a higher one selected from 750° C. or a temperature 150° C. lower than a temperature at a time of completing the rolling, that is a rolling finish temperature minus 150° C.
• the direct quenching temperature can be limited in the above-described range.
• the temperature in order to control the microstructure with a purpose of ensuring the microstructure, can be at least about 750° C. or more.
• the temperature is not lower than about 750° C., when a temperature drop from the rolling finish temperature exceeds about 150° C., there may be a high possibility of recovery and recrystallization after the rolling or precipitation of Nb. In such a case, there is a possibility of deterioration of toughness or reduction of strength including high temperature strength.
• the starting temperature of the direct quenching can be limited to be not lower than a higher one selected from about 750° C. or a temperature about 150° C. lower than a temperature at a time of completing the rolling.
• a tempering treatment can be performed at a temperature not higher than Ac 1 .
• a temperature of about 700° C. or less is not higher than Ac 1 .
• the practical treatment temperature can be set in accordance with target properties such as strength.
• the preferable temperature of the tempering treatment may be about 450 to 650° C.
• rolling temperature or the like can denote a surface temperature of the steel plate which may be monitored.
• the steel member after hot rolling a steel member in a form of billet or slab having a steel composition according to the exemplary embodiment of the present invention, the steel member may be self-cooled.
• the conditions of hot-rolling and self-cooling may not be limited because the metallographic structure and material quality of the steel member is determined depending on the subsequent treatments including reheating, quenching and tempering.
• the hot-rolled and self-cooled steel member can be reheated at a temperature of about 900 to 950° C. and subjected to quenching.
• reheating and quenching temperature may be higher than Ac 3 (a temperature at which transformation of ferrite to austenite is completed at the time of heating) in terms of metallurgical definition.
• a temperature of about 900° C. or more may be sufficient as the temperature not lower than Ac 3 .
• the maximum temperature of the reheating and quenching can be set to be about 950° C.
• the reheated and quenched steel member may be subjected to tempering treatment at a temperature of not higher than Ac 1 .
• the conditions of the tempering treatment or the like may be similar or exactly the same as the above-described first exemplary embodiment of the manufacturing method.
• the high tensile strength, refractory steel according to the exemplary embodiment of the present invention can be applied to general weld construction steel not only for architectural construction but also for various applications including civil engineering, marine structures, ships and vessels, various storage tanks, or the like.
• each steel plate of Examples 1 to 15 and Comparative Examples 16 to 22 was subjected to evaluation of the base metal structure, mechanical properties, toughness of weld heat-affected portion and roughness of gas-cut face.
• yield strength/tensile strength (%) yield strength/tensile strength (%)
• test piece was sampled from a direction perpendicular to the rolling direction in the central portion of the plate thickness. Configuration of the test piece was in accordance with a No.4 round bar for a test piece for testing tensile strength standardized by Japanese Industrial Standard JIS Z 2201 “metallic material tensile strength test piece”. After that, yield strength and tensile strength were evaluated based on measurements in accordance with Japanese Industrial Standard JIS Z 2241 “Method for tensile test of metallic material”.
• a test piece was sampled from a direction perpendicular to the rolling direction in the central portion of the plate thickness. Configuration of the test piece was in accordance with a 2 mmV notch impact test specimen standardized by Japanese Industrial Standard JIS Z 2202 “impact test specimen of metallic material”. After that, toughness was evaluated based on the measurement of fracture appearance transition temperature (vTrs (° C.)) of the impact test specimen in accordance with Japanese Industrial Standard JIS Z 2242 “Method for impacting test of metallic material”.
• a test piece was sampled from a 1 ⁇ 4 thick position of the plate thickness. Configuration of the test piece was in accordance with an impact test specimen standardized by Japanese Industrial Standard JIS Z 2202 “impact test specimen of metallic material”. Each test piece was subjected to a heat cycle corresponding to submerged arc welding (plate thickness 50 mm) of energy input of 60 kJ/mm. The toughness was evaluated based on the measurement of absorbed energy (vE 0 ) of the test piece at 0° C.
• the highest height (Ry) of the surface roughness of the surface of each steel plate was measured, where the definition of Ry was in accordance with Japanese Industrial Standard JIS B 0601 “Geometrical Property Standard (GPS) of a product-Surface Property: profile curve method-term, definition, and surface property parameter”.
• GPS Geographical Property Standard
• the maximum height (Ry) was 50 ⁇ m or less, roughness was evaluated as satisfactory (A), and where the maximum height (Ry) exceeded 50 ⁇ m, roughness was evaluated as unsatisfactory (B).
• Target values of respective properties were 440 MPa for yield strength, ⁇ 40° C. or less for fracture appearance transition temperature (vTrs), 294MPa or more for yield strength at 600° C., and 100 J or more for absorbed energy (vE 0 ) at 0° C.
• compositions of steels are shown in Table 1 and manufacturing processes of steel plates and various properties are shown in Table 2.
• Comparative Examples 16 to 22 having compositions out of the composition range of the present invention showed inferior values in fundamental properties such as strength and toughness, and in high temperature strength, toughness of weld-heat affected portion, gas cuttability or the like.
• a high temperature strength of a high tensile strength steel having a yield strength of 440 MPa or more can be stably ensured.
• a deterioration of weldability and gas cuttability can be limited to a minimum level.
• alloy elements such as C, Si, and Mn, as well as by limiting P CM , and further by limiting the microstructure of the steel and manufacturing conditions for same, composite properties such as excellent high temperature strength, weldability, gas cuttability are compatibly ensured.
• Such high tensile strength, refractory steel having excellent weldability and gas cuttability can be widely applied as general weld construction steel for architectural constructions, civil engineering, marine structures, ships and vessels, various storage tanks or the like, and therefore has very large industrial applicability.

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• 2005
  • 2005-03-04 JP JP2005060601A patent/JP4718866B2/ja active Active
• 2006
  • 2006-03-03 WO PCT/JP2006/304127 patent/WO2006093282A1/ja active Application Filing
  • 2006-03-03 KR KR1020077017575A patent/KR100920536B1/ko active IP Right Grant
  • 2006-03-03 US US11/816,015 patent/US20090025839A1/en not_active Abandoned
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  • 2006-03-03 CN CNB2006800036308A patent/CN100529139C/zh not_active Expired - Fee Related

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