CN109680135B - X80 hot-rolled coil with thickness larger than or equal to 22mm for pipeline and production method - Google Patents
X80 hot-rolled coil with thickness larger than or equal to 22mm for pipeline and production method Download PDFInfo
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Abstract
An X80 hot-rolled coil for a pipeline with the thickness of more than or equal to 22mm comprises the following chemical components in percentage by weight: c: 0.025 to 0.045%; 0.15 to 0.30 percent of Si; 1.70-1.85% of Mn; p is less than or equal to 0.001 percent; s is less than or equal to 0.0012 percent; and (3) Alt: 0.015-0.045%; nb: 0.060-0.080%; ti: 0.008-0.020%; cr: 0.15-0.30%; mo: 0.10-0.25%; 0.10 to 0.25 percent of Ni; control of harmful elements: n is less than or equal to 0.006 percent, As is less than or equal to 0.012 percent, Sb is less than or equal to 0.01 percent, Sn is less than or equal to 0.015 percent, Pb is less than or equal to 0.01 percent, Bi is less than or equal to 0.01 percent, and Ca is less than or equal to 0.006 percent; the production method comprises the following steps: heating a casting blank after conventional smelting and casting into a blank; rough rolling; fine rolling; cooling; coiling; and air-cooling to room temperature. The invention ensures the mechanical property under the precondition that the traditional production line is not required to be modified: rt0.5≥570MPa，Rm≥625MPa，YR≤0.91，A50Not less than 28 percent, HV10 not more than 260 percent, the thickness of the steel plate can be more than 22mm and up to 23mm, and the KV is at minus 20 DEG C2≥300J，‑15℃DWTTSA≥95%。
Description
Technical Field
The invention relates to X80 steel for pipelines and a production method thereof, and belongs to an X80 hot-rolled coil with the thickness of more than or equal to 22mm for pipelines and a production method thereof.
Background
With the development of the urbanization process in China and increasingly outstanding environmental problems brought by coal combustion, the demand of China for natural gas energy is explosively increased. From the characteristics of steel used in natural gas pipeline projects such as the first and second pipelines of west gas and east gas transmission to the Xinyue Zhejiang and the middle and Ruseast pipelines which are constructed in the recent years, the development of pipeline steel towards the direction of high-grade steel, large-caliber, large-wall thickness and high-pressure transmission can be seen, on one hand, the gas transmission efficiency of a single pipeline project can be obviously improved, and on the other hand, the operation cost can be reduced. However, as the wall thickness increases, the low temperature toughness, particularly the low temperature drop weight performance, decreases dramatically. In the art it is believed that: when the product thickness of the pipeline steel reaches more than 18.4mm, the difficulty of the drop weight tearing toughness is increased by 10 times when the thickness is increased by 1 mm. Therefore, the most critical process is to solve the problem of low-temperature drop hammer toughness by developing thick X80.
Generally, a backbone network for high-pressure natural gas transportation mainly adopts a longitudinal submerged arc welded pipe made of an X80 hot-rolled wide and thick plate with the thickness of more than 22mm, but the wide and thick plate has low production efficiency and higher manufacturing cost. Although the ability of producing X80 with more than 22mm by using a hot continuous rolling production line is provided along with the recent domestic new production of 2250mm hot continuous rolling production line or the improvement of cooling and strong coiling of an old production line, the X80 development of the intermediate billet with more than 22mm has a series of problems of insufficient thickness of the continuous casting billet, small rolling force, limited limit thickness of the intermediate billet and the like, and has a plurality of difficulties.
Through retrieval, the document with Chinese patent publication No. CN 107177784A discloses a rolling method of 22mm thick specification X80 heavy caliber pipeline steel: firstly, the thickness of an intermediate billet is required to be 68mm, the final secondary reduction rate is more than or equal to 25 percent, and the finish rolling compression ratio is more than or equal to 3 times. But the limit thickness of the intermediate blank of the conventional production line is 58 mm; the final pass reduction rate is more than or equal to 25 percent, the requirement on production line equipment is too high, roll breakage accidents are easy to occur, the method is only suitable for producing hot-rolled coils with the thickness of 22mm, and the requirements cannot be met when the thickness is increased, if the thickness is more than 22 mm.
Chinese patent publication No. CN 104726665 a discloses a hot rolling process of an X80 pipeline steel coil plate. The method solves the problem of poor DWTT performance stability when X80 pipeline steel coils with the thickness of more than or equal to 20mm are produced in the prior art, but requires that the thickness of an intermediate billet is 58-60 mm, the finish rolling compression ratio is more than or equal to 62 percent, and the finish rolling inlet temperature is less than or equal to 920 ℃. It is not only that the thickness of the intermediate slab cannot be reached on the conventional production line, but also that the rolling load is too large due to the too low finish rolling entry temperature, the biting process is unstable, the finish rolling equipment is seriously damaged, and the piling accident is very likely to occur, and it is seen from its illustrative example that the method also satisfies only the production of X80 of 22mm or less, and thus the requirement is satisfied when the thickness of the finished product is further increased.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a novel production line which is characterized in that the mechanical property is ensured on the premise that the conventional production line is not required to be modified: rt0.5≥570MPa，Rm≥625MPa，YR≤0.91，A50Not less than 28 percent, HV10 not more than 260 percent, the thickness of the steel plate can be more than 22mm and up to 23mm, and the KV is at minus 20 DEG C2X80 hot-rolled coil for pipelines with DWTTSA of more than or equal to 95% at-15 ℃ and production method thereof.
The measures for realizing the aim are as follows:
an X80 hot-rolled coil for a pipeline with the thickness of more than or equal to 22mm comprises the following chemical components in percentage by weight: c: 0.025 to 0.045%; 0.15 to 0.30 percent of Si; 1.70-1.85% of Mn; p is less than or equal to 0.001 percent; s is less than or equal to 0.0012 percent; and (3) Alt: 0.015-0.045%; nb: 0.060-0.080%; ti: 0.008-0.020%; cr: 0.15-0.30%; mo: 0.10-0.25%; 0.10 to 0.25 percent of Ni; control of harmful elements: n is less than or equal to 0.006 percent, As is less than or equal to 0.012 percent, Sb is less than or equal to 0.01 percent, Sn is less than or equal to 0.015 percent, Pb is less than or equal to 0.01 percent, Bi is less than or equal to 0.01 percent, Ca is less than or equal to 0.006 percent, and the balance of Fe and inevitable impurities; the metallographic structure is as follows: the grain size of the acicular ferrite and the granular bainite which does not exceed 10 percent of the volume ratio content is 13-14 grades.
Preferably: the Cr content is 0.15-0.27% by weight.
Further preferably: the Cr content is 0.15-0.23 wt%.
Preferably: the weight percentage content of Mo is 0.11-0.22%.
Preferably: the Ni content is 0.10-0.23 wt%.
Further preferably: the Ni content is 0.13-0.19 wt%.
The method for producing the X80 hot-rolled coil with the thickness of more than or equal to 22mm for the pipeline comprises the following steps:
1) heating the casting blank after conventional smelting and casting into the continuous casting blank, wherein the heating temperature is controlled to be 1150-1200 ℃, and the furnace time is 200-240 min;
2.) carrying out rough rolling, carrying out reversible rolling by adopting a seven-pass rolling mill, and controlling the finish temperature of the rough rolling to be 970-1010 ℃, wherein: the reduction rate of the last reverse first and reverse third passes of rough rolling is 20-21%, and the reduction rate of the reverse second pass is 18-20%; rolling is carried out only after each pass of the last three passes is separated by 10-30 s; after rough rolling is finished, controlling the thickness of the intermediate blank to be 55-58 mm;
3) finish rolling is carried out by adopting seven-rack units F1-F7, and only pass rolling is carried out on the frames F5 during finish rolling; controlling the inlet temperature of finish rolling to be 925-960 ℃, the total reduction ratio of finish rolling to be not less than 60%, and the reduction ratio of finish rolling to be not less than 8% in the F6 th and F7 th racks; the outlet temperature of the finish rolling is controlled to be 780-820 ℃;
4) carrying out rapid cooling, wherein the cooling speed is controlled to be 30-40 ℃/s;
5) coiling, wherein the coiling temperature is controlled to be 300-350 ℃;
6) and air-cooling to room temperature.
Preferably: the heating temperature of the casting blank is 1150-1175 ℃.
Preferably: and rolling is carried out after each pass of the last three passes is separated by 14-26 s.
Preferably: and the inlet temperature of the finish rolling is 935-955 ℃.
The reason for the action and control of the components and the main process in the invention is as follows:
c: 0.025-0.045%, carbon is the most economically important strengthening element in steel, and can greatly improve the strength of the steel, but for the ultra-thick pipeline steel, in order to reduce the central carbon segregation generated in the casting blank solidification process as much as possible and improve the cleanliness of the steel blank, the ultra-low carbon component design is adopted, and the carbon content is limited to 0.025-0.045%. If the content of the carbon is less than 0.025%, the strength of the steel coil is greatly reduced, a large amount of Mo, Ni, Cr, Nb and other alloys need to be added for compensation, and if the carbon content is more than 0.045%, the carbon enrichment at the core part of the casting blank is easily caused, so that the low-temperature drop hammer tear toughness is difficult to meet the requirements of technical conditions.
Si:0.15 to 0.30%, the element has solid solution strengthening and deoxidizing effects, and the content of the element is less than 0.15% and cannot play a strengthening effect, but if the content is more than 0.30%, the plasticity and toughness of the pipeline steel are deteriorated, and particularly the impact on a welding heat affected zone is remarkably reduced.
Mn: 1.70-1.85%, and a higher economic alloying element manganese is added, so that the strength loss caused by low carbon can be compensated, and meanwhile, the manganese can refine grains to a certain extent, so that the impact toughness of steel is improved, but excessive manganese easily forms central segregation, so that the components and the structure of the steel are uneven, and the low-temperature drop hammer toughness is deteriorated.
P: less than or equal to 0.001%, S: less than or equal to 0.0012%: p, S is the most harmful element in steel, P is easy to be deviated in the center of casting blank, which causes the plasticity and impact toughness to be reduced obviously, especially at low temperature, it makes the steel become brittle obviously. S is easy to combine with Mn to form MnS to reduce the low-temperature toughness of the steel, so the P, S content is strictly controlled in the scheme.
And (3) Alt: 0.015-0.045%, wherein aluminum is a main deoxidizing element in the steel, so that the oxygen content in the steel can be remarkably reduced, and meanwhile, AlN is formed by the combination of the aluminum and nitrogen, so that grains can be effectively refined. However, when the content of aluminum in the steel exceeds a certain amount, the oxide inclusion of aluminum is easily increased obviously, the cleanliness of the steel is reduced, and the low-temperature toughness of the steel is unfavorable.
0.060-0.080% of Nb, wherein the Nb can obviously improve the austenite recrystallization temperature of the steel, enlarge the range of a non-recrystallization region, facilitate the realization of high-temperature controlled rolling and reduce the load of a rolling mill, can inhibit the growth of austenite grains, has obvious functions of fine grain strengthening and precipitation strengthening, and can compensate the strength reduction caused by the reduction of carbon and obviously refine the grains to improve the low-temperature toughness for thick steel plates. If the content is less than 0.06%, the effect is insufficient, and if it is more than 0.08%, the cost is high.
0.008-0.020% of Ti, similar effects of titanium and niobium in steel, stronger fine grain strengthening and precipitation strengthening effects, and trace titanium can be combined with carbon and oxygen at high temperature to form precipitates which are refractory at high temperature, so that austenite grains in a welding heat affected zone can be inhibited from growing greatly, and the toughness of the welding heat affected zone is obviously improved. Excessive Ti can be combined with N to form large-particle TiN particles, and the low-temperature toughness of the steel is obviously reduced. Therefore, the Ti content in the scheme is designed to be 0.008-0.020% of micro-titanium treatment.
Cr: 0.15-0.30%, preferably 0.15-0.27% by weight of Cr, and more preferably 0.15-0.23% by weight of Cr. The chromium has strong solid solution strengthening effect and low price, can effectively replace precious alloy elements such as Mo, Ni and the like, and reduces the production cost. In addition, certain chromium is added to improve the weather resistance, corrosion resistance and hardenability of the steel. If the content is less than 0.15%, the strengthening effect cannot be achieved; if it exceeds 0.30%, the low-temperature toughness of the steel deteriorates.
0.10 to 0.25% of Mo, preferably 0.11 to 0.22% of Mo. The element strongly promotes medium-temperature structure transformation element, and effectively generates phase transformation strengthening. Meanwhile, Mo has the effects of improving hardenability and homogenizing wall thickness structure for thick plates. The Mo content designed in the invention is 0.10-0.25%. If the content is less than 0.10%, the effect cannot be obtained, and if the content is more than 0.25%, the alloy cost is high, while excessive Mo promotes the formation of MA, and deteriorates the impact toughness of the steel sheet.
Ni: 0.10-0.25%, preferably Ni content of 0.10-0.23%, and more preferably Ni content of 0.13-0.19%. The nickel can effectively improve the hardenability of the steel, has a certain solid solution strengthening effect, and can also obviously improve the low-temperature toughness of the steel. However, nickel is similar to molybdenum and belongs to precious metals, which easily causes the manufacturing cost of steel to be greatly increased, and in addition, too high nickel content easily causes the scale of the steel plate to be difficult to remove, which causes the surface quality problem of the steel plate.
N is less than or equal to 0.006 percent, the influence of N on the performance of the steel is similar to that of C, P, and with the increase of the content of N, the strength of the steel is obviously improved, the plasticity, particularly the toughness, is also obviously reduced, the weldability is poor, and the cold brittleness is aggravated. Therefore, in this embodiment, N must be controlled to 60ppm or less.
As: less than or equal to 0.012 percent, Sb: less than or equal to 0.01 percent, Sn: less than or equal to 0.015 percent, Pb: less than or equal to 0.01 percent, Bi: less than or equal to 0.01 percent, Ca: less than or equal to 0.006 percent, five-harmful elements reduce the purity of the steel, increase the cold brittleness and hot brittleness tendency of the steel, and influence the low-temperature toughness, plasticity and the like of the product, so the lower the content, the better the product.
The invention adopts the lower heating temperature of 1150-1200 ℃, preferably the heating temperature of a casting blank is 1150-1175 ℃, the low-temperature drop hammer toughness is one of the most main difficulties of the pipeline steel with the ultra-thick specification, and the key control principle is that the fully refined structure after phase transformation is realized by controlling the fine austenite grains before phase transformation. However, for an extra-thick plate, because the finished product has a thick specification, the rolling force cannot well penetrate into the core of a rolled piece, and meanwhile, the core temperature is high, so that the core austenite is not refined sufficiently, and therefore, the austenite grain size must be controlled from the source. According to research, the size of austenite grains is closely related to the heating temperature, when the temperature is higher than 1200 ℃, the austenite grains can grow rapidly, and in order to fully dissolve alloy elements in steel, the heating temperature must be higher than 1150 ℃, so that the heating process is adopted to ensure fine homogenization of prior austenite, simultaneously ensure full dissolution of the alloy elements and ensure other mechanical properties of the product.
The invention adopts the low-temperature high-pressure technology to refine the prior austenite grains, controls the rough rolling finishing temperature to 970-1010 ℃ above the complete recrystallization temperature, and increases the last three-pass depression rate as much as possible under the permission of equipment conditions to promote the recrystallization; the rolling is carried out 10-30 s apart between each pass of the last three passes, preferably 14-26 s, because it is found in the experiment that: when the single-pass reduction is insufficient, if the cumulative reduction is increased, the austenite grains are promoted to be refined, but there is a time interval until the recrystallization is sufficient, but when the time interval is less than 10 seconds, the single-pass recrystallization is insufficient, and a mixed crystal structure is likely to occur; when the time interval is more than 30s, recrystallization occurs and crystal grains grow.
The invention controls the finish rolling inlet temperature to be 925-960 ℃, preferably 935-955 ℃, because the finish rolling needs to be rolled in a non-recrystallization area, the higher temperature can cause mixed crystals of the final structure, and the lower temperature can cause overlarge biting force and easily cause steel piling accidents.
The finish rolling compression ratio is improved as much as possible on the basis of the prior equipment; the finish rolling compression ratio of the F6-F7 frame is controlled to be not less than 8%, the finish rolling outlet temperature is controlled to be 780-820 ℃, and the method is mainly used for flattening austenite before phase change as much as possible and promoting phase change energy accumulation to provide nucleation points for refining tissues in the subsequent cooling process.
The cooling rate is controlled to be 30-40 ℃/s, mainly in order to obtain an acicular ferrite + granular bainite structure with uniform thickness direction and proper grain size.
The coiling temperature is controlled to be 300-350 ℃, and the rolling piece needs to be cooled to the temperature interval at an ultra-fast speed in order to ensure good matching of strength and toughness mainly aiming at the component system of the thick specification X80 and obtain the structure of acicular ferrite and granular bainite. If the temperature is higher than 350 ℃, coarse quasi-polygonal ferrite and a small amount of pearlite structures with weakened grain boundaries are easy to appear in the structures of the wall thickness cores, the low-temperature toughness of the cores is seriously deteriorated, and if the temperature is lower than 300 ℃, the martensite-austenite-island component with larger size is easy to appear in the structures, and the low-temperature toughness is deteriorated.
Compared with the prior art, the invention is not applicable to the prior traditional production lineUnder the precondition of needing to be modified, the mechanical property is ensured: rt0.5≥570MPa，Rm≥625MPa，YR≤0.91，A50Not less than 28 percent, HV10 not more than 260 percent, the thickness of the steel plate can be more than 22mm and up to 23mm, and the KV is at minus 20 DEG C2≥300J，-15℃DWTTSA≥95％。
Drawings
FIG. 1 is a metallographic structure (surface) of the present invention;
FIG. 2 is a metallographic structure of the invention (at 1/4 thickness);
FIG. 3 is a metallographic structure of the invention (at 1/2 thickness).
Detailed Description
The present invention is described in detail below:
table 1 is a list of values for each example and comparative example of the present invention;
table 2 is a table of the main process parameters of each example of the present invention and comparative example;
table 3 is a table of the performance test of each example and comparative example of the present invention.
The embodiments of the invention are produced according to the following steps:
1) heating the casting blank after conventional smelting and casting into the continuous casting blank, wherein the heating temperature is controlled to be 1150-1200 ℃, and the furnace time is 200-240 min;
2.) carrying out rough rolling, carrying out reversible rolling by adopting a seven-pass rolling mill, and controlling the finish temperature of the rough rolling to be 970-1010 ℃, wherein: the reduction rate of the last reverse first and reverse third passes of rough rolling is 20-21%, and the reduction rate of the reverse second pass is 18-20%; rolling is carried out only after each pass of the last three passes is separated by 10-30 s; after rough rolling is finished, controlling the thickness of the intermediate blank to be 55-58 mm;
3) finish rolling is carried out by adopting seven-rack units F1-F7, and only pass rolling is carried out on the frames F5 during finish rolling; controlling the inlet temperature of finish rolling to be 925-960 ℃, the total reduction ratio of finish rolling to be not less than 60%, and the reduction ratio of finish rolling to be not less than 8% in the F6 th and F7 th racks; the outlet temperature of the finish rolling is controlled to be 780-820 ℃;
4) carrying out rapid cooling, wherein the cooling speed is controlled to be 30-40 ℃/s;
5) coiling, wherein the coiling temperature is controlled to be 300-350 ℃;
6) and air-cooling to room temperature.
TABLE 1 list of chemical compositions (wt%) of inventive and comparative examples
TABLE 2 List of the main process parameters of the examples of the invention and the comparative examples
TABLE 2
TABLE 3 statistical table of main performance test of each example and comparative example of the present invention
As can be seen from Table 3, through the implementation of the chemical components and the technical process in the invention, the production of the thick (not less than 22mm) X80-grade hot rolled pipeline steel plate coil is realized, the performances are excellent, the market requirements are met, and the production enterprises do not need to modify the existing equipment.
The above examples are merely preferred examples and are not intended to limit the embodiments of the present invention.
Claims (2)
1. A production method of an X80 hot-rolled coil with the thickness of more than or equal to 22mm for pipelines comprises the following steps:
1) heating the casting blank after conventional smelting and casting into a continuous casting blank, wherein the heating temperature is controlled to be 1160-1178 ℃, and the in-furnace time is 200-240 min;
2.) carrying out rough rolling, carrying out reversible rolling by adopting a seven-pass rolling mill, and controlling the finish temperature of the rough rolling to be 970-1010 ℃, wherein: the reduction rate of the last reverse first and reverse third passes of rough rolling is 20-21%, and the reduction rate of the reverse second pass is 18-20%; rolling is carried out only after each pass of the last three passes is separated by 10-30 s; after rough rolling is finished, controlling the thickness of the intermediate blank to be 55-58 mm;
3) performing finish rolling by adopting seven-rack units F1-F7, wherein the rolling is not performed on the F5 rack but only passes through the F5 rack; controlling the inlet temperature of finish rolling to be 925-960 ℃, the total reduction ratio of finish rolling to be not less than 60%, and the reduction ratio of finish rolling to be not less than 8% in the F6 th and F7 th racks; the outlet temperature of the finish rolling is controlled to be 780-820 ℃;
4) carrying out rapid cooling, wherein the cooling speed is controlled to be 32-40 ℃/s;
5) coiling, wherein the coiling temperature is controlled to be 300-345 ℃;
6) air cooling to room temperature;
the X80 hot-rolled coil for the pipeline with the thickness of more than or equal to 22mm comprises the following chemical components in percentage by weight: c: 0.025 to 0.045%; 0.15 to 0.30 percent of Si; 1.70-1.85% of Mn; p is less than or equal to 0.001 percent; s is less than or equal to 0.0012 percent; and (3) Alt: 0.015-0.022%; nb: 0.060-0.080%; ti: 0.008-0.020%; cr: 0.15 to 0.18 percent; mo: 0.16-0.18%; 0.16 to 0.19 percent of Ni; control of harmful elements: n is less than or equal to 0.006 percent, As is less than or equal to 0.012 percent, Sb is less than or equal to 0.01 percent, Sn is less than or equal to 0.015 percent, Pb is less than or equal to 0.01 percent, Bi is less than or equal to 0.01 percent, Ca is less than or equal to 0.006 percent, and the balance of Fe and inevitable impurities; the metallographic structure is as follows: the grain size of the acicular ferrite and the granular bainite which does not exceed 10 percent of the volume ratio content is 13-14 grades.
2. The method for producing the X80 hot-rolled coil for the pipeline with the thickness of more than or equal to 22mm according to claim 1, wherein the method comprises the following steps: and rolling is carried out after each pass of the last three passes is separated by 14-26 s.
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| CN111057954A (en) * | 2020-01-02 | 2020-04-24 | 鞍钢股份有限公司 | High-strength pipeline rolled plate for large thick wall acidity and manufacturing method thereof |
| CN112126865A (en) * | 2020-09-25 | 2020-12-25 | 湖南华菱湘潭钢铁有限公司 | Rolling method of X80 pipeline steel plate |
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| JP3444244B2 (en) * | 1999-08-26 | 2003-09-08 | 住友金属工業株式会社 | High tensile strength steel excellent in toughness and method of manufacturing the same |
| KR100723203B1 (en) * | 2005-12-26 | 2007-05-29 | 주식회사 포스코 | Linepipe steel sheet with superior low temperature toughness and high hic resistance and method for manufacturing the steel sheet |
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| CN102534408A (en) * | 2012-02-01 | 2012-07-04 | 河北钢铁股份有限公司邯郸分公司 | X80 pipeline steel coil with low cost and high toughness and production method thereof |
| CN103225047B (en) * | 2013-05-10 | 2015-09-23 | 武汉钢铁(集团)公司 | The X80 pipeline steel of thickness >=26.5mm and production method thereof |
| CN103981462A (en) * | 2014-05-30 | 2014-08-13 | 秦皇岛首秦金属材料有限公司 | Excellent-toughness large-wall-thickness X80 steel for low-temperature stations, and manufacturing method thereof |
| CN104805375B (en) * | 2015-04-02 | 2017-03-01 | 江阴兴澄特种钢铁有限公司 | A kind of ultra thick gauge high tenacity X80 pipeline steel and its manufacture method |
| CN107541664B (en) * | 2016-06-28 | 2019-11-22 | 宝山钢铁股份有限公司 | A kind of X80 grades of think gauge pipeline steel composite board and its manufacturing method |
| CN106834932A (en) * | 2016-12-05 | 2017-06-13 | 马鞍山钢铁股份有限公司 | A kind of low-carbon (LC) X80 pipe line steels coiled sheet and its manufacture method |
| CN108411197B (en) * | 2018-03-27 | 2020-01-24 | 宝钢湛江钢铁有限公司 | Thick X80 hot-rolled coil for phi 1422mm ultra-large-caliber spiral submerged arc welding pipe and manufacturing method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP3444244B2 (en) * | 1999-08-26 | 2003-09-08 | 住友金属工業株式会社 | High tensile strength steel excellent in toughness and method of manufacturing the same |
| KR100723203B1 (en) * | 2005-12-26 | 2007-05-29 | 주식회사 포스코 | Linepipe steel sheet with superior low temperature toughness and high hic resistance and method for manufacturing the steel sheet |
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