CA1291400C - Method of manufacturing extra-thick, high strength steel sheets - Google Patents
Method of manufacturing extra-thick, high strength steel sheetsInfo
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- CA1291400C CA1291400C CA000517272A CA517272A CA1291400C CA 1291400 C CA1291400 C CA 1291400C CA 000517272 A CA000517272 A CA 000517272A CA 517272 A CA517272 A CA 517272A CA 1291400 C CA1291400 C CA 1291400C
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Abstract
Abstract of the Disclosure A method of manufacturing extra-thick, high strength steel sheets comprises hot rolling a steel slab having the given chemical composition at a draft of not less than 30% within a predetermined temperature range, directly quenching by cooling at an average cooling rate of 1.0°C/sec or cooling and reheating to 800-950°C and quenching, and then subjecting to Cu precipitation hardening by heating to 500-650°C.
The thus obtained steel sheets have excellent weldability and low-temperature toughness and a tensile strength of not less than 80 kgf/mm2.
The thus obtained steel sheets have excellent weldability and low-temperature toughness and a tensile strength of not less than 80 kgf/mm2.
Description
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_0-193,019 METHOD OF MANUFACTURING
EXTRA-THICK, HIGH STRENGTH STEEL SHEETS
This invention relates to a method of manufac-turing extra-thick ('50 mm), high strength steel sheets having excellent weldability and low-temperature toughness, which are used as a material for large size 05 industrial machines, welded steel pipes, ocean structures, bridges, pressure vessels and so on.
The conventional high strength steel sheets have a high carbon equivalent for ensuring the high strength, so that thèy are generally high in the susceptibility to weld cracking. Further, there are high strength steel sheets having improved crack susceptibility by reducing C amount, but their strength is limited to 60 kgf/mm2 class (tensile s-trength:
60-70 kgf/mm2).
Moreover, in the steels standardized in ASTM-A 710, A 736 and described in U.S. Patent Specifica-tion No. 3692514, the strength is attempted to be made high by utilizing Cu precipitation hardening, but these steels are a component system of low carbon equivalent considering the weldability. In only this component system, it is difficult to ob-tain high strength steel sheets having a tensile strength of not less than 80 kgf/mm2 at an extra thickness of not less -than 50 mm.
In the aforementioned conventional high , ~-~9~
strength steel sheets, steel corresponding to A 710A
defined in ASTM standard is steel sheets A and B as shown in the following Tables 1 and 2, which are good in the weldability but poor in the strength. In the 05 same tables, steel sheet E is a known example attempting high strength by adding B, but the strength is still insufficient at an extra thickness of not less than 100 mm.
Furthermore, there are some examples attempting o high strength by making the alloying higher than the case of the steel sheet A as in steel sheets C, D and F
showing known examples. In the steel sheet D, tensile strength (TS) of 80 kgf/mm2 is realized, but the , weldability is degraded, while when the weldability is compensated by controlling the addition of alloying elements as compared with the steel sheet A as in ~he steel sheets C and F, it is difficult to obtain high strength steel sheets having TS of not less than 80 kgf/mm2 ~loreover, when the steel sheet with an extra thickness of not less than 50 mm is rolled by the conventional rolling process, the final rolling temperature exceeds 900C, so that high toughness at low temperature is not obtained.
As apparent from the above, the conventional 80 kgf/mm2 class steel (steel sheet ~) has high strength and toughness, is high in the crack susceptibility in the welding, has a crack preventing temperature as high ~ ~ g~ 4 O~
as 75C in Y-opening crack weld test (JIS ~3158) representing a low-temperature weld cracking property, and is high in the hardenability of weld heat-affected portion. On the other hand, the steels of A 710A
05 defined in ASTM standard (steel sheets A and B) are low in the weld crack susceptibility and high in the toughness, but the strength thereof is limited to 60 kgf/mm2 class at an e~tra thickness of not less than 50 mm.
It is an object of the invention to provide Cu precipitation hardening type high ~trength steels which have e~cellent weldability and low-temperature toughness and can realize high strength (TS: 80 kgf/mm2) at a thickness of not less than 50 ~m.
The invention consists in the following main points:
(1) the C amount is reduced to a range of 0.01-0.10 wt%
for improving the weldability in high strength, high toughness steel;
_0-193,019 METHOD OF MANUFACTURING
EXTRA-THICK, HIGH STRENGTH STEEL SHEETS
This invention relates to a method of manufac-turing extra-thick ('50 mm), high strength steel sheets having excellent weldability and low-temperature toughness, which are used as a material for large size 05 industrial machines, welded steel pipes, ocean structures, bridges, pressure vessels and so on.
The conventional high strength steel sheets have a high carbon equivalent for ensuring the high strength, so that thèy are generally high in the susceptibility to weld cracking. Further, there are high strength steel sheets having improved crack susceptibility by reducing C amount, but their strength is limited to 60 kgf/mm2 class (tensile s-trength:
60-70 kgf/mm2).
Moreover, in the steels standardized in ASTM-A 710, A 736 and described in U.S. Patent Specifica-tion No. 3692514, the strength is attempted to be made high by utilizing Cu precipitation hardening, but these steels are a component system of low carbon equivalent considering the weldability. In only this component system, it is difficult to ob-tain high strength steel sheets having a tensile strength of not less than 80 kgf/mm2 at an extra thickness of not less -than 50 mm.
In the aforementioned conventional high , ~-~9~
strength steel sheets, steel corresponding to A 710A
defined in ASTM standard is steel sheets A and B as shown in the following Tables 1 and 2, which are good in the weldability but poor in the strength. In the 05 same tables, steel sheet E is a known example attempting high strength by adding B, but the strength is still insufficient at an extra thickness of not less than 100 mm.
Furthermore, there are some examples attempting o high strength by making the alloying higher than the case of the steel sheet A as in steel sheets C, D and F
showing known examples. In the steel sheet D, tensile strength (TS) of 80 kgf/mm2 is realized, but the , weldability is degraded, while when the weldability is compensated by controlling the addition of alloying elements as compared with the steel sheet A as in ~he steel sheets C and F, it is difficult to obtain high strength steel sheets having TS of not less than 80 kgf/mm2 ~loreover, when the steel sheet with an extra thickness of not less than 50 mm is rolled by the conventional rolling process, the final rolling temperature exceeds 900C, so that high toughness at low temperature is not obtained.
As apparent from the above, the conventional 80 kgf/mm2 class steel (steel sheet ~) has high strength and toughness, is high in the crack susceptibility in the welding, has a crack preventing temperature as high ~ ~ g~ 4 O~
as 75C in Y-opening crack weld test (JIS ~3158) representing a low-temperature weld cracking property, and is high in the hardenability of weld heat-affected portion. On the other hand, the steels of A 710A
05 defined in ASTM standard (steel sheets A and B) are low in the weld crack susceptibility and high in the toughness, but the strength thereof is limited to 60 kgf/mm2 class at an e~tra thickness of not less than 50 mm.
It is an object of the invention to provide Cu precipitation hardening type high ~trength steels which have e~cellent weldability and low-temperature toughness and can realize high strength (TS: 80 kgf/mm2) at a thickness of not less than 50 ~m.
The invention consists in the following main points:
(1) the C amount is reduced to a range of 0.01-0.10 wt%
for improving the weldability in high strength, high toughness steel;
(2) in order to ensure high strength, Cu is included in an amount of 0.7-2.0 wt% for Cu precipitation hardening, and further 0.5-2.0 wt% of Mn, 0.1-1.0 wt%
of Mo an-l 0.0005-0.0020 wt% of B are contained; and (3) the control rolling is carried out in the presence of the above Cu amount in order to prevent the degrada-tion of toughness resulted from the precipitation hardening treatment and to improve the low-te~lperature toughness.
of Mo an-l 0.0005-0.0020 wt% of B are contained; and (3) the control rolling is carried out in the presence of the above Cu amount in order to prevent the degrada-tion of toughness resulted from the precipitation hardening treatment and to improve the low-te~lperature toughness.
~ ~9~
- v According to a first ~mbodiment of the invention there is the provision of a metho~ of manufacturing an extra-thick, high strength steel sheet having excellent weldability and low-temperature to~ghness and 05 a tensile strength of not less than 80 kgf/mm2, which comprises hot rolling a slab of steel comprising 0.01-0.10 wt% o~ C, 0.05-0.60 wt% of Si, 0.5-2.0 wt% of Mn, not more than 1.0 wt% of Cr, 0.1-1.0 wt% of Mo, 0.010-0.100 wt% of Nb, 0.0005-0.0020 wt% of B, Q.7-2.0 wt%
o of Cu, 0.010-0.100 wt% of Al and, if necessary, not more than 0.0100 wt% of Ca and the balance being substantially Fe at a draft of not less than 30% within a temperature range of 900-700C, directly quenching by cooling to room temperature at an average cooling rate of not less than 1.0C/sec, and then subjecting to Cu precipitation hardening by heating to a temperature range of 500-650C.
According to a second em~odiment of the invention there is the provision of a method of manufacturing an extra-thick, high strength steel sheet having excellent weldability and low-temperature toughness and a tensile strength of not less than 80 kgf/mm2, which comprises hot rolling a slab of steel comprising 0.01-0.10 wt% of C, 0.05-0.60 wt% of Si, 0.5-Z,0 wt% of Mn, not more than 1.0 wt% of Cr, 0.1-1.0 wt% of ~o, 0.010-0..:l00 wt% oE Nb, 0.0005-0.0020 wt% of B, 0.7-2.0 wt%
of Cu, 0.010-0.100 wt% of Al and, if necessary, not more than 0.0100 wt% of Ca and the balance being ~ 9~ ~O~
substantially Fe at a draft of not less than 30% within a temperature range of 900-700C, cooling, reheating to a temperature range of 800-950C, quenching and then subjecting to Cu precipitation hardening by heating to 05 a temperature range of 500-650C.
The invention will be described with reference to the accompanying drawings, wherein:
Fig. 1 is a graph showing an influence of a draft within a temperature range of 900-700C on vTrs; and Fig. 2 is a graph showing an influence of an average cooling rate on the tensile strength in directly quenched product.
The reason why the method of the invention is specified to the above will be described b~low.
Reason on the limitation to the above chemical composition:
(1~ The amount of C is preferably not more than 0.10 wt% from a viewpoint of the weldability and low-temperature toughness. However, it is necessary to be not less than O.Ol wt% in view of the streng~h of the steel sheet. Therefore, the C amount should be within a range of 0.01-0.10 wt%, preferably 0.03-0.07 wt%.
(2) The amount o~ Si is necessary to be not less than 0.05 wt% in order to obtain high toughness and strength of the steel sheet (particularly J when it is less than 0.05 wt%, the toughness degrades). While, when the amount exceeds 0.60 wt%, the weldability and 1.~91~0~
the toughness of weld joint are degraded. Therefore, the Si amount is within a range of 0.05-0.60 wt%.
(3) Mn is necessary to be added in an amount of not less than 0.5 wt% as an element for enhancing the 05 strength and toughness of the steel sheet. Further, the amount is required to increase as the product thickness becomes thicker from 50 mm to 200 mm. However, when the amount e~ceeds 2.0 wt%, the weldability is damaged. Therefore, the Mn amount is within a range of lo 0.5-2.0 wt%.
(4) Cu is an element necessary for attaining high strength by precipitation hardening and is required to be added in an amount of not less than 0.7 wt%. While, when it e~ceeds 2.0 wt%, the low-temperature toughness S is damaged. Therefore, the Cu amount is within a range o~ 0.7-2.0 wt%.
- v According to a first ~mbodiment of the invention there is the provision of a metho~ of manufacturing an extra-thick, high strength steel sheet having excellent weldability and low-temperature to~ghness and 05 a tensile strength of not less than 80 kgf/mm2, which comprises hot rolling a slab of steel comprising 0.01-0.10 wt% o~ C, 0.05-0.60 wt% of Si, 0.5-2.0 wt% of Mn, not more than 1.0 wt% of Cr, 0.1-1.0 wt% of Mo, 0.010-0.100 wt% of Nb, 0.0005-0.0020 wt% of B, Q.7-2.0 wt%
o of Cu, 0.010-0.100 wt% of Al and, if necessary, not more than 0.0100 wt% of Ca and the balance being substantially Fe at a draft of not less than 30% within a temperature range of 900-700C, directly quenching by cooling to room temperature at an average cooling rate of not less than 1.0C/sec, and then subjecting to Cu precipitation hardening by heating to a temperature range of 500-650C.
According to a second em~odiment of the invention there is the provision of a method of manufacturing an extra-thick, high strength steel sheet having excellent weldability and low-temperature toughness and a tensile strength of not less than 80 kgf/mm2, which comprises hot rolling a slab of steel comprising 0.01-0.10 wt% of C, 0.05-0.60 wt% of Si, 0.5-Z,0 wt% of Mn, not more than 1.0 wt% of Cr, 0.1-1.0 wt% of ~o, 0.010-0..:l00 wt% oE Nb, 0.0005-0.0020 wt% of B, 0.7-2.0 wt%
of Cu, 0.010-0.100 wt% of Al and, if necessary, not more than 0.0100 wt% of Ca and the balance being ~ 9~ ~O~
substantially Fe at a draft of not less than 30% within a temperature range of 900-700C, cooling, reheating to a temperature range of 800-950C, quenching and then subjecting to Cu precipitation hardening by heating to 05 a temperature range of 500-650C.
The invention will be described with reference to the accompanying drawings, wherein:
Fig. 1 is a graph showing an influence of a draft within a temperature range of 900-700C on vTrs; and Fig. 2 is a graph showing an influence of an average cooling rate on the tensile strength in directly quenched product.
The reason why the method of the invention is specified to the above will be described b~low.
Reason on the limitation to the above chemical composition:
(1~ The amount of C is preferably not more than 0.10 wt% from a viewpoint of the weldability and low-temperature toughness. However, it is necessary to be not less than O.Ol wt% in view of the streng~h of the steel sheet. Therefore, the C amount should be within a range of 0.01-0.10 wt%, preferably 0.03-0.07 wt%.
(2) The amount o~ Si is necessary to be not less than 0.05 wt% in order to obtain high toughness and strength of the steel sheet (particularly J when it is less than 0.05 wt%, the toughness degrades). While, when the amount exceeds 0.60 wt%, the weldability and 1.~91~0~
the toughness of weld joint are degraded. Therefore, the Si amount is within a range of 0.05-0.60 wt%.
(3) Mn is necessary to be added in an amount of not less than 0.5 wt% as an element for enhancing the 05 strength and toughness of the steel sheet. Further, the amount is required to increase as the product thickness becomes thicker from 50 mm to 200 mm. However, when the amount e~ceeds 2.0 wt%, the weldability is damaged. Therefore, the Mn amount is within a range of lo 0.5-2.0 wt%.
(4) Cu is an element necessary for attaining high strength by precipitation hardening and is required to be added in an amount of not less than 0.7 wt%. While, when it e~ceeds 2.0 wt%, the low-temperature toughness S is damaged. Therefore, the Cu amount is within a range o~ 0.7-2.0 wt%.
(5) Cr is an element effective for increasing the strength, but when the amount e~ceeds 1.0 wt%, the weldability and low-temperature toughness are unfavorably dcgraded.
(6) Mo is an element efective and indispensable for increasing the strength.
The addition effect of Mo is particularly large in an amount of about 0.3-0.4 wt%, but the addition effect becomes small outside this range.
However, even when the Mo amount is larger than 1.0 wt%, the degradations of toughness at weld joint and weldability are not observed though the low-temperature ~.% 9~ 4~) toughness is somewhat degraded, but the upper limit should be not more than l.0 wt% from a viewpoint of economical reason. On the other hand, when the Mo amount is less than 0.l wt%, the strength considerably 05 decreases, so that the Mo amount is finally limited to a range of 0.l-l.0 wt%.
The addition effect of Mo is particularly large in an amount of about 0.3-0.4 wt%, but the addition effect becomes small outside this range.
However, even when the Mo amount is larger than 1.0 wt%, the degradations of toughness at weld joint and weldability are not observed though the low-temperature ~.% 9~ 4~) toughness is somewhat degraded, but the upper limit should be not more than l.0 wt% from a viewpoint of economical reason. On the other hand, when the Mo amount is less than 0.l wt%, the strength considerably 05 decreases, so that the Mo amount is finally limited to a range of 0.l-l.0 wt%.
(7) Nb is an element exhibiting a refinement action by control rolling. When the amount is less than 0.0l0 wt%, the effect is lost, while when it exceeds 0.l0 wt%, the toughness at weld joint is degraded. Therefore, the Nb amount is limited to a range of 0.0l-0.l0 wt%.
(8) Al is an element required for deoxidation and refinement of austenite. For this purpose, it is necessary to add Al in an amount of at least 0.0l0 wt%.
While, ~1hen it e~ceeds 0.l0 wt%, the cleanness in steel is unfavorably damaged. Therefore, the Al amount is within a range of 0.0l0-0.l00 wt%.
While, ~1hen it e~ceeds 0.l0 wt%, the cleanness in steel is unfavorably damaged. Therefore, the Al amount is within a range of 0.0l0-0.l00 wt%.
(9) B is an element indispensable for obtaining the steeI according to the invention. The B amount is necessary to be not less than 0.0005 wt% for increasing the strength. While, when it exceeds 0.0020 wt%, the low-temperature toughness is degraded. Therefore, the B amount is within a range of 0.0005-0.0020 wt%.
(l0) Ca may be added as an element for the form control of inclusion, if necessary, whereby the low-temperature toughness may be improved. When the amount is more than 0.0l00 wt%, the degradation of the low~
9~ 0~
temperature toughness is inversely brought about, so that the Ca amount is limited to not more than 0.0100 wt%.
The details of the rolling conditions and the heat treating conditions in the method according to the 05 invention will be des(~ribed be]ow.
(i) The final temperature at the hot rolling should be not higher than 900C. When it exceeds 900C, the crystal grains are coarsened to degrade the toughness. While, when the ~inal temperature at the lo hot rolling is lower than 70C1 the toughness is damaged, so that the lower limit is 700C. As seen from Fig. l showing a relation between fracture transition temperature (VTrS) in Charpy impact test and dra~t, in order to obtain properties superior to the prior art, the draft at such a temperature range is necessary to be not less than 30%. When the draft is less than 30%, sufficiently fine grain structure can not be obtained.
(ii) The heating temperature for Cu precipitation hardening is a range of 500-650C. When it is outside the above range, the Cu precipitation hardening action is damaged.
~ iii) When the reheating quenching is carried out after the control rolling prior to the Cu precipitation hardening (second eMbo~inlent),it is necessary that the quenching is performed from the heating temperature of 800-950C in order to refine the composition after the quenching. Further, when the quenching is directly ~`
~ ~ 9~
carried ou~ af Ler the completion o~ the control rolling (first invention), the cooling rate is not lower than 1.0C/sec. As seen from Fig. 2, this cooling rate is dependent on the thickness, but it is necessary to be 05 not lower than 2.0C/sec at a thickness of 100 mm and not lower than 1.0C/sec at a thickness ~f 200 mm.
Moreover, the reason why the thickness o~ the steel sheet is limited to not less than 50 mm is due to the fact that the products having a thickness of less o than S0 mm can sufficiently be manufactured by the application of the conventional technique.
Example In the following Table 1 are shown chemical compositions of a first steel and a second steel produced by the method of the invention and a comparative steel.
Further, the production conditions and the mechanical properties of each of these steel sheets are shown in the following Table 2.
In each steel sheet according to the invention, the steel was heated to austenite state (118QC) and rolled to a product thickness at a final temperature while maintaining a draft of 50-7~% at a temperature range of 900-800C.
Among steels H, J, L, M and N after the rolling (Eirst embodiment), the steels H and M with a thickness of 50 mm were cooled at a rate of 8.6C/sec, the steels J and N with a thickness of 100 ~ were cooled at a rate of 2.7C/sec, and the steel L with a thickness o~ 200 mm was cooled at a rate of l.2C/sec Thereafter, the Cu precipitation hardening was carried out at 570C for 3.5 hours in case of the steels H and M, for 6.5 hours in case of the steels J and N, and for os lO hours in case of the steel L.
Steels G, I and K (second e~bodiment) were reheated to 930C and cooled with water ~quenching).
Thereafter, the Cu preci.pitation hardenin~ was carried out at 570C for 3.5 hours in case of the steel C, for 6.5 hours in case of the steel I, and for lO hours in case of the steel K.
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,................................................... ...
As apparent from Tables l and 2, the excellent strength, toughness and weldability are obtained accord-ing to the first and second ~mbodiment ~f the invention.
That is, in the steels G, I and K, the high strength is 05 attained by making the Mn, Cu and Mo amounts higher and the Cr amount lower in accordance with the product thickness. Furthermore, the high toughness is also attained by holding the draft of not less than 30%
within a temperature range of 900-700C.
In the steels H, J and L having the same chemical composition as in the steels G, I and K, the steel sheets having strength and toughness higher than those of the reheated sheet (second invention~ are obtained by the direct quenching method (first invention).
Moreover, in the steel M with a thickness of 50 mm, the steel sheet having a strength of not less than 80 kgf/mm2 is obtained by adding B to the conven-tional steel (steel A~ and increasing the Mo amount and : performing the direct quenching. According to the invention, the high toughness is obtained even in the steel N containing no Ni.
As mentioned above, according to the invention, steels containing the regulated amounts of alloying elements in accordance with the thiclcness within a given chemical composition are rolled at a draft of not less than 30% within a temperature range of 900-700C
and then directly quenched to room temperature at an average cooling rate of not less than l.0C/sec, ~, ~,1 g~
whereby steels having high strength and toughness can be provided (first e~b~iment).~urthermore, the steels after the final rolling are cooled at once, reheated to a range of 950-800C, quenched and subjected to Cu 05 precipitation hardening, whereby extra-thick steel sheets having an excellent weldability and high strength and toughness with a thickness of 50-200 mm can be provided (second e~boai~ent).
(l0) Ca may be added as an element for the form control of inclusion, if necessary, whereby the low-temperature toughness may be improved. When the amount is more than 0.0l00 wt%, the degradation of the low~
9~ 0~
temperature toughness is inversely brought about, so that the Ca amount is limited to not more than 0.0100 wt%.
The details of the rolling conditions and the heat treating conditions in the method according to the 05 invention will be des(~ribed be]ow.
(i) The final temperature at the hot rolling should be not higher than 900C. When it exceeds 900C, the crystal grains are coarsened to degrade the toughness. While, when the ~inal temperature at the lo hot rolling is lower than 70C1 the toughness is damaged, so that the lower limit is 700C. As seen from Fig. l showing a relation between fracture transition temperature (VTrS) in Charpy impact test and dra~t, in order to obtain properties superior to the prior art, the draft at such a temperature range is necessary to be not less than 30%. When the draft is less than 30%, sufficiently fine grain structure can not be obtained.
(ii) The heating temperature for Cu precipitation hardening is a range of 500-650C. When it is outside the above range, the Cu precipitation hardening action is damaged.
~ iii) When the reheating quenching is carried out after the control rolling prior to the Cu precipitation hardening (second eMbo~inlent),it is necessary that the quenching is performed from the heating temperature of 800-950C in order to refine the composition after the quenching. Further, when the quenching is directly ~`
~ ~ 9~
carried ou~ af Ler the completion o~ the control rolling (first invention), the cooling rate is not lower than 1.0C/sec. As seen from Fig. 2, this cooling rate is dependent on the thickness, but it is necessary to be 05 not lower than 2.0C/sec at a thickness of 100 mm and not lower than 1.0C/sec at a thickness ~f 200 mm.
Moreover, the reason why the thickness o~ the steel sheet is limited to not less than 50 mm is due to the fact that the products having a thickness of less o than S0 mm can sufficiently be manufactured by the application of the conventional technique.
Example In the following Table 1 are shown chemical compositions of a first steel and a second steel produced by the method of the invention and a comparative steel.
Further, the production conditions and the mechanical properties of each of these steel sheets are shown in the following Table 2.
In each steel sheet according to the invention, the steel was heated to austenite state (118QC) and rolled to a product thickness at a final temperature while maintaining a draft of 50-7~% at a temperature range of 900-800C.
Among steels H, J, L, M and N after the rolling (Eirst embodiment), the steels H and M with a thickness of 50 mm were cooled at a rate of 8.6C/sec, the steels J and N with a thickness of 100 ~ were cooled at a rate of 2.7C/sec, and the steel L with a thickness o~ 200 mm was cooled at a rate of l.2C/sec Thereafter, the Cu precipitation hardening was carried out at 570C for 3.5 hours in case of the steels H and M, for 6.5 hours in case of the steels J and N, and for os lO hours in case of the steel L.
Steels G, I and K (second e~bodiment) were reheated to 930C and cooled with water ~quenching).
Thereafter, the Cu preci.pitation hardenin~ was carried out at 570C for 3.5 hours in case of the steel C, for 6.5 hours in case of the steel I, and for lO hours in case of the steel K.
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,................................................... ...
As apparent from Tables l and 2, the excellent strength, toughness and weldability are obtained accord-ing to the first and second ~mbodiment ~f the invention.
That is, in the steels G, I and K, the high strength is 05 attained by making the Mn, Cu and Mo amounts higher and the Cr amount lower in accordance with the product thickness. Furthermore, the high toughness is also attained by holding the draft of not less than 30%
within a temperature range of 900-700C.
In the steels H, J and L having the same chemical composition as in the steels G, I and K, the steel sheets having strength and toughness higher than those of the reheated sheet (second invention~ are obtained by the direct quenching method (first invention).
Moreover, in the steel M with a thickness of 50 mm, the steel sheet having a strength of not less than 80 kgf/mm2 is obtained by adding B to the conven-tional steel (steel A~ and increasing the Mo amount and : performing the direct quenching. According to the invention, the high toughness is obtained even in the steel N containing no Ni.
As mentioned above, according to the invention, steels containing the regulated amounts of alloying elements in accordance with the thiclcness within a given chemical composition are rolled at a draft of not less than 30% within a temperature range of 900-700C
and then directly quenched to room temperature at an average cooling rate of not less than l.0C/sec, ~, ~,1 g~
whereby steels having high strength and toughness can be provided (first e~b~iment).~urthermore, the steels after the final rolling are cooled at once, reheated to a range of 950-800C, quenched and subjected to Cu 05 precipitation hardening, whereby extra-thick steel sheets having an excellent weldability and high strength and toughness with a thickness of 50-200 mm can be provided (second e~boai~ent).
Claims (8)
1. A method of manufacturing an extra-thick, high strength steel sheet having excellent weldability and low-temperature toughness and a tensile strength of not less than 80 kgf/mm2, which comprises hot rolling a slab of steel comprising 0.01-0.10 wt% of C, 0.05-0.60 wt% of Si, 0.5-2.0 wt% of Mn, not more than 1.0 wt% of Cr, 0.1-1.0 wt% of Mo, 0.010-0.100 wt%
of Nb, 0.0005-0.0020 wt% of B, 0.7-2.0 wt% of Cu, 0.010-0.100 wt% of Al and the balance being substan-tially Fe at a draft pf not less than 30% within a temperature range of 900-700°C, directly quenching by cooling to room temperature at an average cooling rate of not less than 1.0°C/sec, and then subjecting to Cu precipitation hardening by heating to a temperature range of 500-650°C.
of Nb, 0.0005-0.0020 wt% of B, 0.7-2.0 wt% of Cu, 0.010-0.100 wt% of Al and the balance being substan-tially Fe at a draft pf not less than 30% within a temperature range of 900-700°C, directly quenching by cooling to room temperature at an average cooling rate of not less than 1.0°C/sec, and then subjecting to Cu precipitation hardening by heating to a temperature range of 500-650°C.
2. A method of manufacturing an extra-thick, high strength steel sheet having excellent weldability and low-temperature toughness and a tensile strength of not less than 80 kgf/mm2, which comprises hot rolling a slab of steel comprising 0.01-0.10 wt% of C, 0.05-0.60 wt% of Si, 0.5-2.0 wt% of Mn, not less than 1.0 wt% of Cr, 0.1-1.0 wt% of Mo, 0.010-0.100 wt%
of Nb, 0.0005-0.0020 wt% of B, 0.7-2.0 wt% of Cu, 0.010-0.100 wt% of Al and the balance being substan-tially Fe at a draft of not less than 30% within a temperature range of 900-700°C, cooling, reheating to a temperature range of 800-950°C, quenching and then subjecting to Cu precipitation hardening by heating to a temperature range of 500-650°C.
of Nb, 0.0005-0.0020 wt% of B, 0.7-2.0 wt% of Cu, 0.010-0.100 wt% of Al and the balance being substan-tially Fe at a draft of not less than 30% within a temperature range of 900-700°C, cooling, reheating to a temperature range of 800-950°C, quenching and then subjecting to Cu precipitation hardening by heating to a temperature range of 500-650°C.
3. The method according to claim 1 or 2, wherein said steel further contains not more than 0.0100 wt%
of Ca.
of Ca.
4. The method according to claim 1 or 2 wherein the extra-thick steel sheet manufactured has a thickness of at least 50 mm.
5. A method of manufacturing an at least 50 mm thick, high strength steel sheet having excellent weldability and low-temperature toughness and a tensile strength of not less than 80 kgf/mm , which comprises:
(a) hot rolling a slab of steel comprising 0.01-0.10 wt% of C, 0.05-0.60 wt% of Si, 0.5-2.0 wt% of Mn, not less than 1.0 wt% of Cr, 0.1-1.0 wt% of Mo, 0.010-0.100 wt% of Nb, 0.0005-0.0020 wt% of B, 0.7-2.0 wt% of Cu, 0.010-0.100 wt% of S1, 0-0.0100 w% of Ca, 0-0.94 wt% of Ni and the balance being substantially Fe, at a draft not less than 30% and at a final temperature within the range from 900 to 700°C, thereby obtaining a hot rolled steel sheet having a thickness of at least 50 mm;
(b) either (i) directly quenching the hot rolled steel sheet by cooling it to room temperature at an average cooling rate of not less than 1.0°C/sec, or (ii) cooling the hot rolled steel sheet, reheating the cooled steel sheet to a temperature of 800-950°C and quenching the reheated steel sheet; and (c) subjecting the quenched steel sheet to Cu precipitation hardening by heating it to a temperature of 500-650°C.
(a) hot rolling a slab of steel comprising 0.01-0.10 wt% of C, 0.05-0.60 wt% of Si, 0.5-2.0 wt% of Mn, not less than 1.0 wt% of Cr, 0.1-1.0 wt% of Mo, 0.010-0.100 wt% of Nb, 0.0005-0.0020 wt% of B, 0.7-2.0 wt% of Cu, 0.010-0.100 wt% of S1, 0-0.0100 w% of Ca, 0-0.94 wt% of Ni and the balance being substantially Fe, at a draft not less than 30% and at a final temperature within the range from 900 to 700°C, thereby obtaining a hot rolled steel sheet having a thickness of at least 50 mm;
(b) either (i) directly quenching the hot rolled steel sheet by cooling it to room temperature at an average cooling rate of not less than 1.0°C/sec, or (ii) cooling the hot rolled steel sheet, reheating the cooled steel sheet to a temperature of 800-950°C and quenching the reheated steel sheet; and (c) subjecting the quenched steel sheet to Cu precipitation hardening by heating it to a temperature of 500-650°C.
6. A method according to claim 5 wherein the slab is heated to austenite state and is hot rolled at a draft of 50-75% and at a final temperature within a range of 900-800°C to a thickness of 50-200 mm.
7. A method according to claim 5 or 6 wherein the hot rolled steel sheet is directly quenched according to step (b)(i) at a rate of not lower than 2.0°C/sec when the thickness is 100 mm and at a rate of not lower than 1.0°C/sec when the thickness is 200 mm.
8. A method according to claim 5 or 6 wherein the hot rolled steel sheet is cooled, reheated and quenched according to step (b)(ii).
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP193,019/85 | 1985-09-03 | ||
| JP19301985A JPS6254019A (en) | 1985-09-03 | 1985-09-03 | Manufacture of 80kg class ultrathick high tensile steel plate superior in weldability and low temperature toughness |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1291400C true CA1291400C (en) | 1991-10-29 |
Family
ID=16300822
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000517272A Expired - Lifetime CA1291400C (en) | 1985-09-03 | 1986-09-02 | Method of manufacturing extra-thick, high strength steel sheets |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS6254019A (en) |
| CA (1) | CA1291400C (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0735538B2 (en) * | 1988-07-04 | 1995-04-19 | 株式会社神戸製鋼所 | Method for manufacturing high strength and high toughness thick steel plate with excellent weldability |
| CN103352108A (en) * | 2013-06-24 | 2013-10-16 | 米云霞 | H13 molten steel cold and hot treatment process |
| CN113399948A (en) * | 2021-07-02 | 2021-09-17 | 东北大学 | Method for producing 1000MPa hydroelectric steel with thickness of more than 100mm and specification |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6059018A (en) * | 1983-08-03 | 1985-04-05 | Nippon Steel Corp | Production of cu-added steel having excellent weldability and low-temperature toughness |
| JPS60149722A (en) * | 1984-01-14 | 1985-08-07 | Nippon Steel Corp | Manufacture of cu added steel having superior toughness at low temperature in weld zone |
-
1985
- 1985-09-03 JP JP19301985A patent/JPS6254019A/en active Pending
-
1986
- 1986-09-02 CA CA000517272A patent/CA1291400C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPS6254019A (en) | 1987-03-09 |
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