WO2017107778A1 - 一种大线能量焊接热影响区韧性优异的厚钢板及其制造方法 - Google Patents

一种大线能量焊接热影响区韧性优异的厚钢板及其制造方法 Download PDF

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WO2017107778A1
WO2017107778A1 PCT/CN2016/109024 CN2016109024W WO2017107778A1 WO 2017107778 A1 WO2017107778 A1 WO 2017107778A1 CN 2016109024 W CN2016109024 W CN 2016109024W WO 2017107778 A1 WO2017107778 A1 WO 2017107778A1
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steel plate
welding
affected zone
toughness
steel
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PCT/CN2016/109024
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English (en)
French (fr)
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杨健
高珊
马志刚
王睿之
张才毅
王俊凯
徐国栋
王毓男
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宝山钢铁股份有限公司
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Priority to EP16877589.8A priority Critical patent/EP3395985B1/en
Priority to US16/062,880 priority patent/US10837089B2/en
Publication of WO2017107778A1 publication Critical patent/WO2017107778A1/zh

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Definitions

  • the invention belongs to the field of steel metallurgy and steel materials, and particularly relates to a thick steel plate with excellent toughness in a heat affected zone of a large-line energy welding and a manufacturing method thereof, the steel plate has a thickness of 50-70 mm, and the tensile strength of the base material is ⁇ 510 MPa, and the welding line is performed.
  • the welding energy is 200-400kJ/cm.
  • the average Charpy impact energy of the steel plate in the welding heat affected zone is above 100J at -40 °C, and the base material thickness is 1/2 average Charpy impact energy at -40 °C. Above 46J. It can be applied to welded structural materials in the fields of shipbuilding, construction, offshore platforms, bridges, pressure vessels and oil and gas pipelines.
  • the microstructure of the steel is destroyed, the austenite grains grow significantly, and the coarse-grained heat affected zone is formed, which reduces the toughness of the welded heat affected zone.
  • the structure causing embrittlement in the coarse-grained heat-affected zone is coarse grain boundary ferrite, side slab ferrite and upper bainite formed during cooling, and pearlite formed in the vicinity of grain boundary ferrite, A carbide island-shaped MA component formed between the slats of the side slab ferrite.
  • a certain amount of Ti and N are added to the composition design of the steel material, and TiN particles can be used to suppress deterioration of toughness in the heat affected zone of the weld.
  • Line energy can be increased to 50kJ/cm.
  • the temperature of the heat affected zone is welded. Up to 1400 ° C, TiN particles will partially solidify or grow, and the effect of suppressing grain growth in the heat affected zone will partially disappear, which will lead to deterioration of toughness in the heat affected zone of the weld. Therefore, it is difficult to improve the large-line energy welding performance of the thick steel plate by using only the steel material of the fine particle TiN.
  • titanium oxides can also increase the toughness of the heat affected zone of the large-line energy welding of steel. This is because the oxide of titanium is stable at high temperatures and is less likely to solidify. At the same time, the oxide of titanium can act as the nucleation core of ferrite, refine the ferrite grains, and form acicular ferrite structure with large dip grains. It is beneficial to improve the heat affected zone of the weld. toughness. See Japanese Patent JP517300 "Manufacturing Method for Steel Resin for the Resilience of Heat-affected Parts of the Handle".
  • titanium oxide there are two major problems in the presence of titanium oxide in a small amount and difficulty in dispersion in steel. If it is desired to increase the amount of titanium oxide by increasing the titanium content in the steel, it tends to result in the formation of large titanium oxide inclusions. When the size of the titanium oxide particles is more than 5 ⁇ m, the impact toughness of the base material and the heat affected zone of the weld will be lowered. Therefore, in the large-line energy welding process where the welding line energy is greater than 200 kJ/cm, it is still difficult to improve the toughness of the welded heat affected zone by the oxide of titanium alone.
  • the object of the present invention is to provide a thick steel plate with excellent toughness in a heat-affected zone of a large-line energy welding and a manufacturing method thereof, the thick steel plate has a thickness of 50 to 70 mm, the tensile strength of the base material is ⁇ 510 MPa, and the energy of the welding line is 200 ⁇ . Under the welding condition of 400kJ/cm, it has good impact toughness in the weld heat affected zone with v E -40 ⁇ 100J, and the average 1:1 aging impact energy of the base metal plate thickness at -40 °C is above 46J.
  • a thick steel plate with excellent toughness in a heat-affected zone of large-line energy welding the mass percentage of which is: C: 0.05-0.08%, Si: 0.10-0.30%, Mn: 1.2-1.6%, P ⁇ 0.02%, S : 0.002 to 0.008%, B: 0.0005 to 0.005%, Ni: 0.20 to 0.40%, Cu: 0.15 to 0.3%, Ti: 0.005 to 0.03%, Al: 0.003 to 0.03%, Ca: 0.001 to 0.005%, REM ⁇ 0.01%, Zr ⁇ 0.01%, N: 0.001-0.006%, the rest are Fe and inevitable impurities; and, at the same time, satisfy:
  • the effective S amount in steel S-0.8Ca-0.34REM-0.35Zr;
  • Effective S amount in steel 0.0006 ⁇ 0.005%
  • the proportion of CaO+Al 2 O 3 +MnS+TiN composite inclusions in the steel plate is ⁇ 12%.
  • the chemical composition of the steel further contains one or more elements of Nb ⁇ 0.03% or Cr ⁇ 0.2%, in terms of mass percentage.
  • the method for manufacturing a thick steel plate excellent in toughness of a large-line energy welding heat-affected zone includes the following steps:
  • the chemical composition percentage of steel is: C: 0.05-0.08%, Si: 0.10-0.30%, Mn: 1.2-1.6%, P ⁇ 0.02%, S: 0.002 ⁇ 0.008%, B: 0.0005 to 0.005%, Ni: 0.20 to 0.40%, Cu: 0.15 to 0.3%, Ti: 0.005 to 0.03%, Al: 0.003 to 0.03%, Ca: 0.001 to 0.005%, and REM ⁇ 0.01% , Zr ⁇ 0.01%, N: 0.001 to 0.006%, the rest is Fe and inevitable impurities; and, at the same time, it is required to satisfy:
  • the effective S amount in steel S-0.8Ca-0.34REM-0.35Zr;
  • Effective S amount in steel 0.0006 ⁇ 0.005%
  • the slab is heated to 1050 ⁇ 1250 ° C, the initial rolling temperature is higher than 930 ° C, the cumulative reduction ratio is greater than 30%; the finishing rolling temperature is less than 930 ° C, the cumulative reduction ratio is greater than 30%;
  • the chemical composition of the steel further contains one or more elements of Nb ⁇ 0.03% or Cr ⁇ 0.2%, in terms of mass percentage.
  • C is an element that increases the strength of steel.
  • the lower limit of the C content is 0.05%.
  • excessive addition of C results in a decrease in toughness of the base material and the heat affected zone of the weld, and the upper limit of the C content is 0.08%.
  • Si is an element required in the pre-deoxidation process of steelmaking, and can function as a reinforcing base material, so the lower limit of the Si content is 0.1%. However, if the Si content is too high above 0.3%, the toughness of the base metal will be lowered, and in the process of large-line energy welding, the island martensite-austenite component will be promoted. Generated, significantly reducing the toughness of the weld heat affected zone.
  • the Si content ranges from 0.10 to 0.30%.
  • Mn can improve the strength of the base material by solid solution strengthening, and can also act as a pre-deoxidation element.
  • MnS precipitates on the surface of the oxide inclusion, and a Mn-depleted layer is formed around the inclusion, which can effectively promote the intra-crystalline needle shape.
  • the lower limit of Mn is 1.2%.
  • too high Mn will cause center segregation of the slab, and at the same time lead to hardening and MA formation in the heat affected zone of the large-line energy welding, and reduce the toughness of the weld heat affected zone, so the upper limit of Mn is controlled to be 1.6%.
  • Ni can increase the strength and toughness of the base material, and the lower limit is 0.2%. However, due to its high price, the upper limit is 0.4% due to cost constraints.
  • Cu can improve the strength and toughness of the base material, and the lower limit is 0.15%. However, if the Cu content is too high, it will cause hot brittleness, and the upper limit of Cu is 0.3%.
  • Ti by forming Ti 2 O 3 particles, can promote the formation of intragranular ferrite.
  • the combination of Ti and N to form TiN particles can pin the austenite grain growth, refine the microstructure of the base material and the heat affected zone, and improve the toughness.
  • Such TiN particles are easily precipitated on the surface of the CaO+Al 2 O 3 oxide particles, and since the TiN and the ferrite have a small lattice mismatch, the acicular ferrite can be induced to grow on the surface thereof. Therefore, as a beneficial element, the lower limit of the Ti content is 0.005%.
  • the upper limit of the Ti content is 0.03%.
  • the lower limit is 0.001%. However, if the content exceeds 0.006%, the formation of solid solution N will be caused, and the toughness of the base material and the heat affected zone of the weld will be lowered.
  • Ti/N 1 ⁇ Ti / N ⁇ 6.
  • Ti/N the ratio of which is 1 ⁇ Ti / N ⁇ 6.
  • Ti/N the number of TiN particles will decrease sharply, and a sufficient amount of TiN particles cannot be formed, which inhibits the growth of austenite grains during the welding of large-line energy and reduces the toughness of the heat affected zone.
  • Ti/N is greater than 6, the TiN particles are coarsened, and the excess Ti is easily combined with C to form coarse TiC particles. These coarse particles may be used as the starting point of crack initiation, which reduces the base metal and the heat affected zone of the weld. Impact toughness.
  • the upper limit of the Al content is 0.03%.
  • maintaining a certain Al content in the steel can improve the cleanliness of the molten steel, reduce the total oxygen content in the steel, and thereby improve the impact toughness of the steel, so the lower limit of the Al content is 0.003%.
  • the addition of Ca can improve the morphology of sulfides, and the oxides and sulfides of Ca can also promote the growth of intragranular ferrite.
  • the combination of CaO and Al 2 O 3 can form inclusions with low melting point and improve the morphology of the inclusions.
  • the inclusions have a high sulfur capacity, which is favorable for promoting the precipitation of MnS on the surface thereof, and at the same time promoting the precipitation of TiN.
  • the Ca content in the steel is less than 0.001%, the ratio of (Ca+REM+Zr)/Al in the steel cannot satisfy the requirement of 0.11 or more, and the ratio of the CaO+Al 2 O 3 +MnS+TiN composite inclusions cannot be satisfied.
  • the impact toughness of the weld heat affected zone is reduced. If the Ca content is more than 0.005%, the effect of Ca is already saturated, while increasing the evaporation loss and oxidation loss of Ca. Therefore, the range of the Ca content is reasonable: 0.001 to 0.005%.
  • REM and Zr can improve the morphology of the sulfide, while the oxides and sulfides of REM and Zr can inhibit the growth of austenite grains during the thermal cycle of the weld.
  • the content of REM and Zr is more than 0.01%, inclusions having a partial particle diameter of more than 5 ⁇ m are formed, and the impact toughness of the base material and the heat affected zone of the weld is lowered.
  • the lower limit of the B content is 0.0005%.
  • the hardenability is remarkably increased, and the toughness and ductility of the base material are lowered, and the upper limit is 0.005%.
  • S in the process of adding Ca and/or RE and Zr, sulfide particles are precipitated with Ca and/or RE and Zr. It is also possible to promote the precipitation of MnS on the oxide particles, particularly on the surface of CaO + Al 2 O 3 . Thereby, the formation of intragranular ferrite is promoted, and the lower limit thereof is 0.002%. However, if the content is too high, it will cause center segregation of the slab. In addition, when the S content exceeds 0.008%, a part of coarse sulfide will be formed, and these coarse sulfides will serve as a starting point for crack formation, and the impact toughness of the base material and the heat affected zone of the weld will be lowered. Therefore, the upper limit of the S content is 0.008%.
  • the effective S amount in the controlled steel S-0.8Ca-0.34REM-0.35Zr.
  • the effective S amount in the steel is less than 0.0006, the requirement for large-scale precipitation of MnS cannot be satisfied.
  • the CaO+Al 2 O 3 +MnS+TiN composite in the steel The proportion of inclusions will not meet the requirement of 12% or more. Since the number of acicular ferrite formed on the surface of the CaO+Al 2 O 3 +MnS+TiN composite inclusion is reduced, the impact toughness of the heat affected zone of the large-line energy welding is greatly reduced.
  • the effective S amount is more than 0.005%, the number of elemental MnS inclusions will increase sharply and the size will be significantly increased. This large-sized MnS inclusion will extend along the rolling direction during rolling, which will greatly reduce the steel. Lateral impact performance. Therefore, the effective S amount control range in steel is 0.0006 to 0.005%.
  • the invention determines the composition of the inclusions by SEM-EDS, and after the sample is ground and mirror polished, the inclusions are observed and analyzed by SEM, and the composition of each sample inclusion is the analysis result of 10 arbitrary inclusions. average value.
  • the SEM was used to observe 50 consecutively selected fields of view at 1000x magnification, and the observed field of view was greater than 0.27 mm 2 .
  • the areal density of the inclusions is a calculation of the number of inclusions observed and the area of the field of view.
  • the ratio of the amount of certain inclusions is the ratio of the areal density of the inclusions to the areal density of all types of inclusions.
  • P which is an impurity element in steel, should be reduced as much as possible. If the content is too high, it will lead to center segregation and reduce the toughness of the weld heat affected zone.
  • the upper limit of P is 0.02%.
  • Nb can refine the structure of steel and improve strength and toughness. However, if the content is too high, the toughness of the weld heat affected zone will be lowered, and the upper limit is 0.03%.
  • Cr can improve the hardenability of steel. For thick steel plates, improving the hardenability can compensate for the strength loss caused by the thickness, increase the strength of the central portion of the plate thickness, and improve the uniformity of performance in the thickness direction.
  • Cr and Mn are too high, a low-melting Cr-Mn composite oxide is formed, and surface cracks are easily formed during hot rolling, and the weldability of the steel is also affected. Therefore, the upper limit of the Cr content is 0.2%.
  • the invention is in a rolling and cooling process:
  • the heating temperature before rolling is less than 1050 ° C, the carbonitride of Nb cannot be completely dissolved.
  • the heating temperature is greater than 1250 ° C, it will cause the growth of austenite grains.
  • the initial rolling temperature is higher than 930 ° C, and the cumulative reduction ratio is more than 30%, because recrystallization occurs above this temperature, and austenite grains can be refined.
  • the cumulative reduction ratio is less than 30%, the coarse austenite grains formed during the heating process remain, which reduces the toughness of the base material.
  • the finishing rolling temperature is less than 930 ° C, and the cumulative reduction ratio is more than 30%, because at such a temperature, austenite does not recrystallize, and dislocations formed during rolling can be used as ferrite nucleation.
  • the core works.
  • the cumulative reduction ratio is less than 30%, the number of dislocations formed is small, which is insufficient to induce nucleation of acicular ferrite.
  • the water is cooled to a final cooling temperature of 300 to 550 ° C at a cooling rate of 2 to 30 ° C / s, because:
  • the cooling rate is less than 2 ° C / s, the strength of the base metal cannot meet the requirements.
  • the cooling rate is greater than 30 ° C / s, the toughness of the base material will be lowered.
  • the final cooling temperature is greater than 550 ° C, the strength of the base material cannot meet the requirements.
  • the final cooling temperature is less than 300 ° C, the toughness of the base material is lowered.
  • the invention adopts suitable composition design and inclusion control technology to control the effective S amount in the steel by controlling the Ti/N ratio and the ratio of (Ca+REM+Zr)/Al in the steel, and controlling the CaO+Al in the steel plate.
  • the proportion of 2 O 3 +MnS+TiN composite inclusions can promote the growth of intragranular acicular ferrite on the surface of these inclusions during solidification and phase transformation, or inhibit austenite during large-line energy welding.
  • the growth of the grain improves the large-line energy welding performance of the thick steel plate.
  • the thickness of the manufactured steel plate is 50-70mm, the tensile strength of the base metal is ⁇ 510MPa, and the welding heat-affected zone has a good large-line energy of v E -40 ⁇ 100J under the welding condition of welding line energy of 200-400kJ/cm.
  • Table 1 shows the chemical composition, Ti/N ratio and (Ca + REM + Zr) / Al ratio of the examples and comparative examples of the present invention.
  • Table 2 shows the mechanical properties, inclusion characteristics, and impact toughness of the weld heat affected zone of the examples and comparative examples of the present invention.
  • the slab is obtained by smelting, refining and continuous casting, and then the slab is heated to 1050 ° C ⁇ 1250 ° C, the initial rolling temperature is 1000 ⁇ 1150 ° C, the cumulative reduction rate is 50%; the finishing rolling temperature is 700 ⁇ 850 ° C, cumulative The reduction ratio is 53 to 67% by weight; after finish rolling, it is water-cooled to a final cooling temperature of 300 to 550 ° C at a cooling rate of 3 to 10 ° C / s.
  • Gas-electric vertical welding is used for one-time welding of steel plates of different thicknesses, and the welding line energy is 200-400 kJ/cm.
  • the impact sample was taken on the fusion line of the 1/2 part of the plate thickness, and the V-shaped notch was introduced for the impact toughness test.
  • the Charpy impact test of the three samples was carried out at -40 ° C, and the heat affected zone was punched.
  • the data on the toughness is the average of three measurements.
  • the aging impact sample data is the average of three measurements.
  • the chemical composition range determined according to the present invention is subjected to composition control, and the Ti/N ratio is controlled to be 1 ⁇ Ti / N ⁇ 6, and the ratio of (Ca + REM + Zr) / Al ⁇ 0.11, the effective S amount in steel is 0.0006-0.005%; in addition, the proportion of CaO+Al 2 O 3 +MnS+TiN composite inclusions in the control steel plate is ⁇ 12%.
  • Comparative Examples 1 and 2 the Al content was more than 0.03%, the (Ca+REM+Zr)/Al ratio was less than 0.11, the effective S amount of Comparative Example 1 was less than 0.0006%, and the effective S amount of Comparative Example 2 was more than 0.005%. Further, the ratio of the amount of CaO + Al 2 O 3 + MnS + TiN composite type inclusions in Comparative Example 1 was less than 12%.
  • Table 2 lists the tensile properties, impact toughness, aging impact, and impact toughness of the base material in the examples and comparative examples.
  • the yield strength, tensile strength and section shrinkage of the base metal are the average of the two test data.
  • the base metal, aging impact and weld heat affected zone -40 ° C Charpy impact energy are the average of the three test data.
  • the base material thickness at 1/2 ° C was 1/2 of the average Charpy impact energy of 46 J or more.
  • the effective S content was too high, the aging impact performance of the sheet thickness of 1/2 was remarkably lowered.
  • the invention adopts a suitable composition design, and controls the effective S amount in the steel by controlling the Ti/N ratio and the (Ca+REM+Zr)/Al ratio in the steel, and simultaneously controls the CaO+Al 2 O 3 +MnS in the steel plate.
  • the proportion of +TiN composite inclusions which promotes the growth of intragranular acicular ferrite on the surface of these inclusions during solidification and phase transformation, or inhibits the growth of austenite grains during large-line energy welding. Improve the large-line energy welding performance of thick steel plates.
  • the thickness of the manufactured steel plate is 50-70mm, the tensile strength of the base metal is ⁇ 510MPa, and the welding heat affected zone has a good large-line energy of v E -40 ⁇ 100J under the welding condition of welding line energy of 200-400kJ/cm.
  • the welding performance, at the same time, the base material thickness at 1/2 °C 1/2 average Charpy aging impact work is above 46J. .
  • the invention can be used in the manufacturing process of thick steel plates such as shipbuilding, construction, offshore platforms, bridges, pressure vessels and oil and natural gas pipelines, and is used for improving the large-line energy welding performance of thick steel plates.

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Abstract

一种大线能量焊接热影响区韧性优异的厚钢板及其制造方法，包括冶炼、精炼、连铸、轧制、冷却等步骤；并且钢板化学成分满足1≤Ti/N≤6，(Ca+REM+Zr)/Al≥0.11；钢中有效S量＝S-0.8Ca-0.34REM-0.35Zr，钢中有效S量：0.0006～0.005％；可形成微细弥散分布的夹杂物，钢板中CaO+Al 2O 3+MnS+TiN复合型夹杂的数量比例≥12％。对于钢板板厚50～70mm，母材抗拉强度≥510MPa，进行焊接线能量为200～400kJ/cm的焊接，钢板焊接热影响区在-40℃下的平均夏比冲击功在100J以上，同时-40℃下的母材板厚1/2平均夏比时效冲击功在46J以上。

Description

一种大线能量焊接热影响区韧性优异的厚钢板及其制造方法 技术领域
本发明属于钢铁冶金和钢铁材料领域，特别涉及一种大线能量焊接热影响区韧性优异的厚钢板及其制造方法，该钢板板厚50～70mm，母材抗拉强度≥510MPa，进行焊接线能量为200～400kJ/cm的焊接，钢板的焊接热影响区在-40℃下的平均夏比冲击功在100J以上，同时-40℃下的母材板厚1/2平均夏比时效冲击功在46J以上。可以应用于造船、建筑、海洋平台、桥梁、压力容器和石油天然气管线等领域的焊接结构材料。
背景技术
对于造船、建筑、压力容器、石油天然气管线及海洋平台等领域，提高厚钢板的大线能量焊接性能，可以提高焊接效率、缩短制造工时，降低制造成本，因此改善厚钢板的焊接热影响区韧性已成为越来越迫切的要求。
经大线能量焊接后，钢材的组织结构遭到破坏，奥氏体晶粒明显长大，形成粗晶热影响区，降低了焊接热影响区的韧性。在粗晶热影响区导致脆化的组织是冷却过程中形成的粗大的晶界铁素体、侧板条铁素体和上贝氏体，以及在晶界铁素体近傍形成的珠光体、在侧板条铁素体的板条间形成的碳化物岛状M-A组元等。随着旧奥氏体晶粒粒径的增加，晶界铁素体和侧板条铁素体等尺寸也相应增大，焊接热影响区的夏比冲击功将显著降低。
在大线能量焊接条件下，为了改善厚钢板焊接热影响区的低温韧性，前人进行了大量的研究工作。
如日本专利JP5116890公开的“大入热溶接用高张力钢材制品制造方法”，在其钢材的成分设计中，添加一定量的Ti、N，利用TiN粒子可以抑制焊接热影响区韧性的劣化，焊接线能量可以提高到50kJ/cm。但是当焊接线能量达到200kJ/cm以上时，在焊接过程中，焊接热影响区的温度 将高达1400℃，TiN粒子将部分发生固溶或者长大，其抑制焊接热影响区晶粒长大的作用将部分消失，这样将导致焊接热影响区韧性劣化。因此，仅仅利用微细粒子TiN的钢材，难以提高厚钢板的大线能量焊接性能。
利用钛的氧化物也可以提高钢材大线能量焊接热影响区的韧性。这是因为钛的氧化物在高温下稳定，不易发生固溶。同时钛的氧化物可以作为铁素体的形核核心发挥作用，细化铁素体晶粒，并且形成相互间具有大倾角晶粒的针状铁素体组织，有利于改善焊接热影响区的韧性。参见日本专利JP517300“溶接継手熱影響部靭性のすぐれた鋼材の製造法”。
但是，钛氧化物存在数量较少和在钢中难以弥散分布两大问题。如果希望通过提高钢中的钛含量来提高钛氧化物的数量，势必导致大型钛氧化物夹杂的形成。当钛氧化物粒子的尺寸大于5μm时，将降低母材和焊接热影响区的冲击韧性。因此在焊接线能量大于200kJ/cm的大线能量焊接过程中，单靠钛的氧化物仍然难以改善焊接热影响区的韧性。
发明内容
本发明的目的是提供一种大线能量焊接热影响区韧性优异的厚钢板及其制造方法，该厚钢板板厚为50～70mm，母材抗拉强度≥510MPa；在焊接线能量为200～400kJ/cm焊接条件下，具有vE-40≥100J良好的焊接热影响区冲击韧性，同时-40℃下的母材板厚1/2平均夏比时效冲击功在46J以上。
为达到上述目的，本发明的技术方案是：
一种大线能量焊接热影响区韧性优异的厚钢板，其化学成分的质量百分比为：C：0.05～0.08％，Si：0.10～0.30％，Mn：1.2～1.6％，P≤0.02％，S：0.002～0.008％，B：0.0005～0.005％，Ni：0.20～0.40％，Cu：0.15～0.3％，Ti：0.005～0.03％，Al：0.003～0.03％，Ca：0.001～0.005％，REM≤0.01％，Zr≤0.01％，N：0.001～0.006％，其余为Fe和不可避免杂质；并且，同时满足：
1≤Ti/N≤6，(Ca+REM+Zr)/Al≥0.11；
钢中有效S量＝S-0.8Ca-0.34REM-0.35Zr；
钢中有效S量：0.0006～0.005％；
钢板中CaO+Al2O3+MnS+TiN复合型夹杂的数量比例≥12％。
进一步，钢的化学成分还含有Nb≤0.03％或Cr≤0.2％中一种以上元素，以质量百分比计。
本发明的大线能量焊接热影响区韧性优异的厚钢板的制造方法，包括如下步骤：
1)冶炼、精炼和连铸
按下述成分冶炼、精炼、连铸成坯，钢的化学成分质量百分比为：C：0.05～0.08％，Si：0.10～0.30％，Mn：1.2～1.6％，P≤0.02％，S：0.002～0.008％，B：0.0005～0.005％，Ni：0.20～0.40％，Cu：0.15～0.3％，Ti：0.005～0.03％，Al：0.003～0.03％，Ca：0.001～0.005％，REM≤0.01％，Zr≤0.01％，N：0.001～0.006％，其余为Fe和不可避免杂质；并且，需同时满足：
1≤Ti/N≤6，(Ca+REM+Zr)/Al≥0.11；
钢中有效S量＝S-0.8Ca-0.34REM-0.35Zr；
钢中有效S量：0.0006～0.005％；
控制钢板中CaO+Al2O3+MnS+TiN复合型夹杂的数量比例≥12％；
2)轧制
将铸坯加热到1050～1250℃，初轧温度高于930℃，累计压下率大于30％；精轧温度小于930℃，累计压下率大于30％；
3)冷却
以2～30℃/s的冷却速率水冷至终冷温度300～550℃。
进一步，钢的化学成分还含有Nb≤0.03％或Cr≤0.2％中一种以上元素，以质量百分比计。
在本发明钢的成分设计中：
C，是增加钢材强度的元素。对于控轧控冷的TMCP工艺而言，为了稳定地保持特定强度，C含量的下限为0.05％。但是过量地添加C，将导致母材和焊接热影响区的韧性降低，C含量的上限为0.08％。
Si，是炼钢预脱氧过程中所需要的元素，并且可以起到强化母材的作用，因此Si含量的下限为0.1％。但是Si含量过高超过0.3％时，会降低母材的韧性，同时在大线能量焊接过程中，将促进岛状马氏体-奥氏体组元的 生成，显著降低焊接热影响区韧性。Si含量范围为0.10～0.30％。
Mn，可以通过固溶强化提高母材的强度，又可以作为预脱氧元素发挥作用；同时MnS在氧化物夹杂表面析出，在该夹杂物的周围形成贫Mn层，可以有效地促进晶内针状铁素体的生成，Mn的下限值为1.2％。但是过高的Mn将导致板坯的中心偏析，同时会导致大线能量焊接热影响区的硬化和MA生成，降低焊接热影响区的韧性，所以Mn的上限值控制为1.6％。
Ni，可以提高母材的强度和韧性，其下限为0.2％。但是由于其价格昂贵，鉴于成本的限制，其上限为0.4％。
Cu，可以提高母材的强度和韧性，其下限为0.15％。但是Cu含量过高，将导致热态脆性，Cu的上限为0.3％。
Ti，通过形成Ti2O3粒子，可以促进晶内铁素体的生成。同时Ti与N结合生成TiN粒子可以钉扎奥氏体晶粒的长大，使母材和焊接热影响区组织细化，提高韧性。这种TiN粒子容易在CaO+Al2O3氧化物粒子的表面析出，由于TiN与铁素体具有较小的晶格错配度，可以诱导针状铁素体在其表面生长。所以作为有益元素，Ti含量的下限为0.005％。但是Ti含量过高时，将形成粗大的氮化物，或者促使TiC的生成，降低母材和焊接热影响区的韧性，所以Ti含量上限为0.03％。
N，可以形成微细的Ti氮化物，在大线能量焊接过程中，可以有效地抑制奥氏体晶粒的长大。同时这种TiN粒子容易在CaO+Al2O3氧化物粒子的表面析出，由于TiN与铁素体具有较小的晶格错配度，可以诱导针状铁素体在其表面生长。所以作为有益元素，其下限为0.001％。但是其含量超过0.006％，将导致固溶N的形成，降低母材和焊接热影响区的韧性。
同时，要保持钢材中具有合适的Ti/N比，其比值为1≤Ti/N≤6。当Ti/N小于1时，TiN粒子的数量将会急剧降低，不能形成足够数量的TiN粒子，抑制大线能量焊接过程中奥氏体晶粒的长大，降低了焊接热影响区的韧性。当Ti/N大于6时，TiN粒子粗大化，同时过剩的Ti容易与C结合生成粗大的TiC粒子，这些粗大的粒子都有可能作为裂纹发生的起点，降低了母材和焊接热影响区的冲击韧性。
Al，当钢中Al含量太高时，容易生成簇状氧化铝夹杂，不利于微细 弥散分布夹杂物的生成。因此，Al含量的上限为0.03％。同时，钢中保持一定的Al含量，可以提高钢液的洁净度，降低钢中的全氧含量，从而提高钢材的冲击韧性，因此Al含量的下限为0.003％。
Ca，添加Ca可以改善硫化物的形态，Ca的氧化物和硫化物还可以促进晶内铁素体的生长。CaO和Al2O3结合可以形成低熔点的夹杂物，改善夹杂物的形貌。这种夹杂物具有较高的硫容量，有利于促进MnS在其表面析出，同时又可以促进TiN的析出。当钢中Ca含量小于0.001％时，钢中的(Ca+REM+Zr)/Al的比值不能满足大于等于0.11的要求，CaO+Al2O3+MnS+TiN复合型夹杂的数量比例不能满足大于等于12％的要求。降低了焊接热影响区的冲击韧性。如果Ca含量大于0.005％，Ca的作用已经饱和，同时增加了Ca的蒸发损失和氧化损失。因此Ca含量合理的范围是：0.001～0.005％。
REM和Zr，REM和Zr的添加可以改善硫化物的形态，同时REM和Zr的氧化物和硫化物可以抑制焊接热循环过程中奥氏体晶粒的长大。但是，当REM和Zr的含量大于0.01％，将生成部分粒径大于5μm的夹杂物，降低母材和焊接热影响区的冲击韧性。
B，通过形成BN，可以促进晶内铁素体的生长；作为固溶B，在焊接后的冷却过程中偏析于奥氏体晶界，抑制晶界铁素体的生成。为了提高焊接热影响区的冲击韧性，B含量的下限是0.0005％。但是B含量过高时将导致淬透性显著上升，降低母材的韧性和延性，其上限是0.005％。
S，在Ca和/或RE、Zr的添加过程中，与Ca和/或RE、Zr形成硫化物粒子析出。还可以促进MnS在氧化物粒子上，特别是在CaO+Al2O3表面析出。从而促进晶内铁素体的形成，其下限为0.002％。但是，其含量过高，将导致板坯的中心偏析。另外，当S含量超过0.008％时，将会形成部分粗大的硫化物，这些粗大的硫化物将会作为裂纹形成的起点，降低母材和焊接热影响区的冲击韧性。因此，S含量的上限为0.008％。
本发明通过大量研究发现：
控制钢中的有效S量＝S-0.8Ca-0.34REM-0.35Zr，当钢中有效S量小于0.0006时，不能满足MnS大量析出的要求，钢中CaO+Al2O3+MnS+TiN复合夹杂物的数量比例将不能满足大于等于12％的要求。由于在 CaO+Al2O3+MnS+TiN复合夹杂物表面形成的针状铁素体的数量减少，大线能量焊接热影响区的冲击韧性将大幅度降低。当有效S量大于0.005％时，将会导致单质MnS夹杂物的数量急剧增加，尺寸显著长大，这种大型MnS夹杂物在轧制过程中沿着轧向延伸，将大幅度地降低钢材的横向冲击性能。因此，钢中有效S量控制范围是0.0006～0.005％。
上述公式中的含量均以实际数值计入，不包括％。
本发明确定夹杂物的成分利用SEM-EDS进行测量，对于样品进行研磨和镜面抛光之后，利用SEM对于夹杂物进行观察与分析，每个样品夹杂物的成份是对于10个任意选取夹杂物分析结果的平均值。
利用SEM在1000倍的倍率下对于50个连续选取视场进行观察，所观察的视场面积大于0.27mm2。夹杂物的面密度是所观察的夹杂物数量和视场面积的计算结果。某种夹杂物的数量比例是该种夹杂物的面密度和所有种类夹杂物的面密度的比值。
P，是钢中的杂质元素，应尽量降低。其含量过高，将导致中心偏析，降低焊接热影响区的韧性，P的上限为0.02％。
Nb，可以细化钢材的组织，提高强度和韧性。但是含量过高将降低焊接热影响区的韧性，其上限是0.03％。
Cr，可以提高钢的淬透性。对于厚钢板而言，提高淬透性可以弥补厚度带来的强度损失，提高板厚中心区域的强度，改善厚度方向上性能的均匀性。但是太高的Cr和Mn同时加入时，会形成低熔点的Cr-Mn复合氧化物，在热轧过程中容易形成表面裂纹，同时还会影响钢材的焊接性能。因此Cr含量上限为0.2％。
本发明在轧制和冷却工艺中：
轧制前的加热温度小于1050℃时，Nb的碳氮化物不能完全固溶。当加热温度大于1250℃时，将导致奥氏体晶粒的长大。
初轧温度高于930℃，累计压下率大于30％，因为在此温度以上，发生再结晶，可以细化奥氏体晶粒。当累计压下率小于30％时，加热过程中所形成的粗大奥氏体晶粒还会残存，降低了母材的韧性。
精轧温度小于930℃，累计压下率大于30％，因为在这样的温度下，奥氏体不发生再结晶，轧制过程中所形成的位错，可以作为铁素体形核的 核心起作用。当累计压下率小于30％时，所形成的位错较少，不足以诱发针状铁素体的形核。
精轧之后以2～30℃/s的冷却速率水冷至终冷温度300～550℃，这是因为：
当冷却速率小于2℃/s时，母材强度不能满足要求。当冷却速率大于30℃/s时，将降低母材的韧性。当终冷温度大于550℃时，母材的强度不能满足要求。当终冷温度小于300℃时，将降低母材的韧性。
本发明的有益效果：
本发明采取合适的成分设计和夹杂物控制技术，通过对于钢中Ti/N比值和(Ca+REM+Zr)/Al比值进行合理控制，控制钢中有效S量，同时控制钢板中CaO+Al2O3+MnS+TiN复合型夹杂的数量比例，可以在凝固和相变过程中，在这些夹杂物表面促进晶内针状铁素体的生长，或者抑制大线能量焊接过程中奥氏体晶粒的长大，改善厚钢板的大线能量焊接性能。所制造的钢板厚度规格为50～70mm，母材抗拉强度≥510MPa，在焊接线能量为200～400kJ/cm的焊接条件下，焊接热影响区具有vE-40≥100J良好的大线能量焊接性能，同时-40℃下的母材板厚1/2平均夏比时效冲击功在46J以上。。
具体实施方式
下面结合实施例对本发明做进一步说明。
表1是本发明实施例和对比例的化学成分，Ti/N比值和(Ca+REM+Zr)/Al比值。表2是本发明实施例和对比例的母材力学性能、夹杂物特性和焊接热影响区冲击韧性。
通过冶炼、精炼和连铸得到铸坯，然后将铸坯加热到1050℃～1250℃，初轧温度为1000～1150℃，累计压下率为50％；精轧温度为700～850℃，累计压下率为53～67％％；精轧之后以3～10℃/s的冷却速率水冷至终冷温度300～550℃。
采用气电立焊对于不同厚度的钢板实施一道次焊接，焊接线能量为200～400kJ/cm。在板厚1/2部的熔合线上取冲击试样，导入V型切口进行冲击韧性检测，在-40℃下进行三个样品的夏比冲击试验，焊接热影响区冲 击韧性的数据是三次测量结果的平均值。
对于板厚1/2部取时效冲击试样，5％应变量，在-40℃下进行三个样品的夏比冲击试验，时效冲击试样数据是三次测量结果的平均值。
由表1和表2可见，实施例中根据本发明所确定的化学成分范围进行成分控制，并且控制Ti/N比值为1≤Ti/N≤6，(Ca+REM+Zr)/Al比值≥0.11，钢中有效S量为0.0006～0.005％；另外，控制钢板中CaO+Al2O3+MnS+TiN复合型夹杂的数量比例≥12％。
在对比例1和2中，Al含量大于0.03％，(Ca+REM+Zr)/Al比值小于0.11，对比例1的有效S量小于0.0006％，对比例2的有效S量大于0.005％。此外，在对比例1中的CaO+Al2O3+MnS+TiN复合型夹杂的数量比例小于12％。
表2列出了实施例和对比例中母材的拉伸性能，冲击韧性，时效冲击以及焊接热影响区的冲击韧性。母材的屈服强度、抗拉强度和断面收缩率为两个测试数据的平均值，母材，时效冲击和焊接热影响区-40℃夏比冲击功是三个测试数据的平均值。
从表中数据可以看出，实施例和对比例的母材力学性能没有明显的差异，都能满足所制造钢板的厚度规格为50～70mm，母材抗拉强度≥510MPa的要求。在焊接线能量为200～400kJ/cm的条件下，对于焊接热影响区-40℃夏比冲击功进行了测试，实施例1～5的值分别是108、125、115、120、170(J)，对比例1、2的值是11、17(J)。实施例焊接热影响区的冲击韧性大幅度改善，可以满足200～400kJ/cm大线能量焊接的要求。
另外，所有实施例-40℃下的母材板厚1/2平均夏比时效冲击功在46J以上。对比例2由于有效S含量过高，板厚1/2的时效冲击性能显著降低。
本发明采取合适的成分设计，通过对于钢中Ti/N比值和(Ca+REM+Zr)/Al比值进行合理控制，控制钢中有效S量，同时控制钢板中CaO+Al2O3+MnS+TiN复合型夹杂的数量比例，这样可以在凝固和相变过程中在这些夹杂物表面促进晶内针状铁素体的生长，或者抑制大线能量焊接过程中奥氏体晶粒的长大，改善厚钢板的大线能量焊接性能。所制造的钢板的厚度规格为50～70mm，母材抗拉强度≥510MPa，在焊接线能量为200～400kJ/cm焊接条件下，焊接热影响区具有vE-40≥100J良好的大线能 量焊接性能，同时-40℃下的母材板厚1/2平均夏比时效冲击功在46J以上。。本发明可用于造船、建筑、海洋平台、桥梁、压力容器和石油天然气管线等厚钢板的制造过程中，用于改善厚钢板的大线能量焊接性能。
Figure PCTCN2016109024-appb-000001
Figure PCTCN2016109024-appb-000002

Claims (6)

  1. 一种大线能量焊接热影响区韧性优异的厚钢板，其化学成分质量百分比为：
    C：0.05～0.08％，
    Si：0.10～0.30％，
    Mn：1.2～1.6％，
    P≤0.02％，
    S：0.002～0.008％，
    B：0.0005～0.005％
    Ni：0.20～0.40％，
    Cu：0.15～0.3％，
    Ti：0.005～0.03％，
    Al：0.003～0.03％，
    Ca：0.001～0.005％，
    REM≤0.01％，
    Zr≤0.01％，
    N：0.001～0.006％，
    其余为Fe和不可避免杂质；并且，需同时满足：
    1≤Ti/N≤6，(Ca+REM+Zr)/Al≥0.11；
    钢中有效S量＝S-0.8Ca-0.34REM-0.35Zr；
    钢中有效S量：0.0006～0.005％；
    钢板中CaO+Al2O3+MnS+TiN复合型夹杂的数量比例≥12％。
  2. 如权利要求1所述的大线能量焊接热影响区韧性优异的厚钢板，其特征是，钢的化学成分还含有Nb≤0.03％或Cr≤0.2％中一种以上元素，以质量百分比计。
  3. 如权利要求1或2所述的大线能量焊接热影响区韧性优异的厚钢板，其特征是，板厚50～70mm，母材抗拉强度≥510MPa，在焊接线能量为200～400kJ/cm焊接条件下，钢板焊接热影响区在-40℃下的平均夏比冲击功在100J以上，同时-40℃下的母材板厚1/2平均夏比时效冲击功在 46J以上。
  4. 一种大线能量焊接热影响区韧性优异的厚钢板的制造方法，其特征是，包括如下步骤：
    1)冶炼、精炼和连铸
    按下述成分冶炼、精炼、连铸成坯，钢的化学成分质量百分比为：C：0.05～0.08％，Si：0.10～0.30％，Mn：1.2～1.6％，P≤0.02％，S：0.002～0.008％，B：0.0005～0.005％，Ni：0.20～0.40％，Cu：0.15～0.3％，Ti：0.005～0.03％，Al：0.003～0.03％，Ca：0.001～0.005％，REM≤0.01％，Zr≤0.01％，N：0.001～0.006％，其余为Fe和不可避免杂质；并且，需同时满足：1≤Ti/N≤6，(Ca+REM+Zr)/Al≥0.11；钢中有效S量＝S-0.8Ca-0.34REM-0.35Zr；钢中有效S量：0.0006～0.005％；控制钢板中CaO+Al2O3+MnS+TiN复合型夹杂的数量比例≥12％；
    2)轧制
    将铸坯加热到1050～1250℃，初轧温度高于930℃，累计压下率大于30％；精轧温度小于930℃，累计压下率大于30％；
    3)冷却
    以2～30℃/s的冷却速率水冷至终冷温度300～550℃。
  5. 如权利要求4所述的大线能量焊接热影响区韧性优异的厚钢板的制造方法，其特征是，所述厚钢板的化学成分还含有Nb≤0.03％或Cr≤0.2％中一种以上元素，以质量百分比计。
  6. 如权利要求4或5所述的大线能量焊接热影响区韧性优异的厚钢板的制造方法，其特征是，所述厚钢板的板厚为50～70mm，母材抗拉强度≥510MPa，在焊接线能量为200～400kJ/cm焊接条件下，钢板焊接热影响区在-40℃下的平均夏比冲击功在100J以上，同时-40℃下的母材板厚1/2平均夏比时效冲击功在46J以上。
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