WO2018041089A1 - 一种磷化性能和成形性能优良的冷轧高强度钢板及其制造方法 - Google Patents

一种磷化性能和成形性能优良的冷轧高强度钢板及其制造方法 Download PDF

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WO2018041089A1
WO2018041089A1 PCT/CN2017/099421 CN2017099421W WO2018041089A1 WO 2018041089 A1 WO2018041089 A1 WO 2018041089A1 CN 2017099421 W CN2017099421 W CN 2017099421W WO 2018041089 A1 WO2018041089 A1 WO 2018041089A1
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steel sheet
cold
phosphating
strength steel
rolled high
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PCT/CN2017/099421
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English (en)
French (fr)
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周澍
钟勇
金鑫焱
王利
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宝山钢铁股份有限公司
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Priority to EP17845391.6A priority Critical patent/EP3508606B1/en
Priority to KR1020197005612A priority patent/KR102203836B1/ko
Priority to JP2019511410A priority patent/JP6696047B2/ja
Priority to US16/328,991 priority patent/US11505844B2/en
Publication of WO2018041089A1 publication Critical patent/WO2018041089A1/zh

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    • C22C32/001—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides
    • C22C32/0015—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ with only oxides with only single oxides as main non-metallic constituents
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the invention belongs to the field of cold-rolled high-strength steel, and particularly relates to a cold-rolled high-strength steel plate excellent in phosphating performance and forming property and a manufacturing method thereof.
  • the temperature dew point of the temperature region of B: 800 ⁇ B ⁇ 900) is -10 ° C or higher, and electrolytic pickling is performed in an aqueous solution containing sulfuric acid after continuous annealing, and a high-strength steel sheet disclosed in Chinese Patent No. CN103140597A and its manufacture
  • the method is similar, but the dew point of the atmosphere is set to be below -40 ° C when the temperature in the annealing furnace is above 750 ° C.
  • Both of the above patents use a pickling process after annealing, which not only increases the production cost, but also reduces the production efficiency, and the pickling process itself and the acid liquid waste treatment also have an adverse effect on the environment.
  • a high-strength steel sheet disclosed in Chinese Patent No. CN103124799A and a method for producing the same the main point of which is that the dew point of the atmosphere in a temperature range of 820 ° C or more and 1000 ° C or less in the annealing furnace during the soaking process is -45 ° C or less, and The dew point of the atmosphere in the temperature range of the annealing furnace at a temperature of 750 ° C or higher during the cooling process is -45 ° C or lower.
  • the reducing ability in the atmosphere is enhanced, and the oxide of an oxidizable element such as Si or Mn which undergoes selective surface oxidation on the surface of the steel sheet can be reduced.
  • it is technically difficult to continuously control the dew point of the atmosphere below -45 °C which not only has high requirements on the production equipment and production technology level, but also has no advantage in production cost.
  • the Si content is in the range of 0.01 to 0.5%, but the Mn content is relatively high, reaching 3.6 to 8.0%, which not only fails to fully utilize the strengthening and toughening effect of the inexpensive Si element, but also has a high Mn content which has reached the special steel.
  • the scope on the one hand, is disadvantageous in terms of cost, and on the other hand, it brings about a large number of technical problems in the production of steel making, continuous casting and subsequent heat treatment.
  • Chinese patent CN102666923A discloses a high-strength cold-rolled steel sheet and a method for producing the same, which comprises C: 0.05-0.3%, Si: 0.6-3.0%, Mn: 1.0-3.0%, P ⁇ 0.1%, S ⁇ 0.05%. Al: 0.01 to 1%, N ⁇ 0.01%, and the balance is Fe and unavoidable impurities.
  • the oxygen concentration is controlled to achieve oxidation treatment before annealing.
  • the steel sheet is first heated in an atmosphere having an oxygen concentration of 1000 ppm or more until the steel sheet temperature reaches 630 ° C or higher, and then the steel sheet is heated for a second time in an atmosphere having an oxygen concentration of less than 1000 ppm until the steel sheet temperature reaches 700 ⁇ .
  • the surface of the steel sheet was formed to have an oxidation amount of 0.1 g/m 2 or more, and then annealed at a dew point of -25 ° C or lower and 1 to 10% H 2 -N 2 in a reducing atmosphere.
  • an oxidation treatment process is added before annealing, and it is necessary to equip the production line with corresponding devices to simultaneously control the heating temperature and the oxygen concentration, and the operation is difficult.
  • An object of the present invention is to provide a cold-rolled high-strength steel sheet excellent in phosphating performance and formability, and a method for producing the same, which has good phosphating property and formability, and has a ferrite, martensite and a room temperature structure at room temperature.
  • the multiphase structure of retained austenite, tensile strength ⁇ 1180MPa, elongation ⁇ 14%, is suitable for the manufacture of automotive structural parts and safety parts.
  • the oxide particles have an average diameter of 50 to 200 nm, and the average pitch ⁇ between the oxide particles satisfies the following relationship:
  • [Si] is the content % of Si in the steel
  • [Mn] is the content % of Mn in the steel
  • d is the diameter of the oxide particles in units of nm.
  • the oxide particles are at least one of silicon oxide, manganese silicate, iron silicate, and ferromanganese silicate.
  • the steel sheet contains at least one of Cr 0.01 to 1%, Mo 0.01 to 0.5%, and Ni 0.01 to 2.0%.
  • the steel sheet contains at least one of Ti 0.005 to 0.5%, Nb 0.005 to 0.5%, and V 0.005 to 0.5%.
  • the room temperature structure of the cold-rolled high-strength steel sheet excellent in phosphating performance and formability of the present invention has a multiphase structure of ferrite, martensite and retained austenite, wherein the retained austenite content is not less than 5%.
  • the cold-rolled high-strength steel sheet has a tensile strength of ⁇ 1180 MPa and an elongation of ⁇ 14%.
  • composition design of the present invention is a composition design of the present invention:
  • the controlled C content of the present invention is 0.15 to 0.25%.
  • Si It has an effect of improving strength and improving formability of steel, and is added in a large amount in the present invention. However, when Si is excessively added, the embrittlement of the steel sheet becomes remarkable, and cracks are likely to occur at the end portion of the steel sheet during cold rolling, which hinders production efficiency. Therefore, the present invention controls the Si content to be 1.50 to 2.50%.
  • Mn increases the stability of austenite, and at the same time reduces the critical cooling temperature and the martensite transformation temperature Ms during steel quenching, and improves the hardenability of the steel sheet. Further, Mn is a solid solution strengthening element and is advantageous for improving the strength of the steel sheet. Therefore, it is necessary to add a large amount in the present invention, but an excessively high Mn content causes cracking of the slab in the continuous casting process and affects the weldability of the steel material. Therefore, the present invention controls the Mn content to be 2.00 to 3.00%.
  • P In the present invention, it is an impurity element, which deteriorates the weldability, increases the cold brittleness of the steel, and lowers the plasticity of the steel. Therefore, it is necessary to control P to be 0.02% or less.
  • Al It is added for the deoxidation of molten steel.
  • the present invention controls the Al content to be 0.03 to 0.06%.
  • N is an impurity contained in crude steel, and N and Al combine with AlN particles, which affects the ductility and thermoplasticity of the steel sheet. Therefore, it is desirable to control the N content to 0.01% or less in the steel making process as much as possible.
  • Cr contributes to the refinement of austenite grains, and at the same time, improves the hardenability of the steel sheet and improves the strength of the steel. Therefore, in order to achieve high strength, Cr can be appropriately added. However, it is not preferable to be too high. When the Cr content exceeds 1.0%, the cost of the steel sheet is increased and the weldability is deteriorated. Therefore, in the present invention, the content of Cr is controlled to be 0.01 to 1.0%.
  • Mo Improves the hardenability of the steel sheet and further increases the strength of the steel sheet. In order to ensure the hardenability of the steel sheet, Mo can be added as appropriate. However, when the Mo content is more than 0.5%, the plasticity of the steel sheet is remarkably lowered, and the production cost is increased. Therefore, in the present invention, the range of the Mo content is controlled to be 0.01 to 0.5%.
  • Ni:Ni is similar to that of Mo, and is also an element for improving the hardenability of the steel sheet.
  • Ni may be added in an appropriate amount.
  • the Ni content should not be too high. When the Ni content exceeds 2.0%, the production cost of the steel sheet is increased. Therefore, the Ni content is controlled to be 0.01 to 2.0%.
  • Ti forms precipitates with C, S, and N to effectively increase the strength and toughness of the steel sheet.
  • the Ti content needs to be 0.005% or more.
  • the Ti content in the present invention is designed to be 0.005 to 0.05%.
  • Nb Strengthens steel by precipitation strengthening, while preventing the growth of austenite grains, refining crystal grains, and improving strength and elongation.
  • the Nb content is less than 0.005%, the above effects cannot be obtained.
  • the content of Nb exceeds 0.1%, the precipitation strengthening acts excessively, resulting in a decrease in formability and an increase in manufacturing cost. Therefore, in the present invention, the control range of the Nb content is 0.005 to 0.1%.
  • V:V The effect of V:V is similar to that of Nb, which can form carbides and increase the strength of steel.
  • the V content is less than 0.005%, the precipitation strengthening effect is not remarkable.
  • the V content is more than 0.1%, the precipitation strengthening effect excessively acts, resulting in a decrease in formability of the steel sheet.
  • the V content is controlled to be 0.005 to 0.1%.
  • the surface layer of the cold-rolled high-strength steel sheet of the present invention has an inner oxide layer having a thickness of 1 to 5 ⁇ m, and the inner oxide layer contains oxide particles, and the oxide particles are one of Si oxide and Si, Mn composite oxide or A variety of characteristics of the internal oxide layer of a certain thickness of the surface layer of the steel sheet of the present invention are necessary, which is inextricably linked with the high Si and Mn contents in the steel sheet, and ensures that the Si element is not concentrated on the surface of the steel sheet to form an oxide of Si, thereby oxidizing.
  • the reaction is converted from external oxidation to internal oxidation, thereby improving the phosphating performance of the steel sheet.
  • the thickness of the inner oxide layer, the size of the oxide particles and the density of the oxide particles in the surface layer of the cold-rolled high-strength steel sheet of the present invention directly affect the effect of the inner oxide layer on the surface state of the steel sheet, and the oxide density can pass through the average spacing of the oxide particles.
  • ⁇ expression which is related to Si, Mn content and oxide particle diameter: the average pitch ⁇ between oxide particles satisfies the following relationship:
  • [Si] is the Si element content in the steel
  • [Mn] is the Mn element content in the steel
  • d is the oxide particle diameter in nm.
  • the inner oxide layer cannot prevent Si from enriching the surface of the steel sheet, and a large amount of oxide particles are still formed on the surface of the steel sheet, and external oxidation cannot be obtained. Effective inhibition, and the oxide particles on the surface of the steel plate will seriously hinder the uniform reaction of the phosphating process, causing problems such as surface yellow rust, poor phosphating, and large phosphating crystal size.
  • the thickness of the inner oxide layer is >5 ⁇ m, the average diameter of the Si oxide particles is >200 nm, and the average spacing ⁇ A, the internal oxidation is too strong, which has a significant influence on the toughness and the forming property of the steel sheet surface. Therefore, in order to ensure the steel sheet has good properties.
  • the phosphating performance the thickness of the oxide layer in the surface layer of the steel sheet is 1 to 5 ⁇ m, the average diameter of the oxide particles is controlled to 50 to 200 nm, and the average spacing ⁇ between the oxide particles is controlled between A and B.
  • the room temperature structure of the cold-rolled high-strength steel sheet of the present invention contains retained austenite, and the retained austenite content is not less than 5%.
  • the retained austenite content is ⁇ 5%, the TRIP effect is not significant, and the strength and formability of the steel sheet cannot be ensured. Therefore, it is desirable to ensure that the retained austenite content in the room temperature tissue is ⁇ 5%.
  • the invention also provides a method for manufacturing the cold-rolled high-strength steel sheet excellent in the phosphating property and the forming property, comprising the following steps:
  • the hot rolled coil is unrolled, pickled and cold rolled, the pickling speed is ⁇ 150m/min, and the cold rolling reduction is 40-80%, and the hardened strip is obtained;
  • the obtained hard strip steel is unrolled, cleaned, heated to a soaking temperature of 790 to 920 ° C, and kept for 30 to 200 s, wherein the heating rate is 1 to 20 ° C / s, and the atmosphere of the heating section and the holding section is N 2 -H 2 mixed gas, wherein the H 2 content is 0.5 to 20%, and the dew point of the annealing atmosphere is -25 to 10 ° C;
  • the temperature for reheating the slab is 1210 to 1270 ° C, and the coiling temperature is 450 to 550 ° C.
  • the soaking temperature in the step 4) is 810 to 870 °C.
  • the dew point of the annealing atmosphere in the step 4) is -10 to 5 °C.
  • the reheating temperature of the slab is 1170-1300 ° C, preferably 1210-1270 ° C. If the heating temperature is too high, the slab is over-fired, and the grain structure in the slab is coarse, resulting in hot workability. Decrease, and ultra-high temperature will cause serious decarburization on the surface of the slab; if the heating temperature is too low, the slab is descaled by high-pressure water and after the initial rolling, the finishing temperature is too low, which will cause the deformation resistance of the blank to be too large.
  • the holding time is set to 0.5 ⁇ 4h. If the holding time exceeds 4h, the grain structure in the slab will be coarse and the surface of the slab will be decarburized seriously. If the holding time is less than 0.5h, the internal temperature of the slab is not yet Evenly.
  • the invention needs to control the finish rolling temperature to be above 850 ° C to complete the hot rolling of the slab. If the finishing temperature is too low, the slab deformation resistance is too high, and it is difficult to produce the steel plate of the required thickness specification and the plate shape is poor.
  • the coiling of the hot rolled sheet is carried out at 400 to 700 ° C, and the coiling temperature is preferably 450 to 550 ° C. If the coiling temperature is too high, the scale of the steel sheet on the surface of the steel sheet is too thick to be pickled, and if the coiling temperature is too low, the hot coil strength is high, which makes it difficult to cold-roll and affects production efficiency.
  • the pickling speed is ⁇ 150 m/min during pickling. If the pickling speed is too fast, the scale on the surface of the steel sheet cannot be completely removed, and surface defects are easily formed.
  • the hot-rolled steel sheet after pickling is cold-rolled and deformed to a predetermined thickness, and the cold rolling reduction is 40 to 80%.
  • the large cold rolling reduction can increase the austenite formation rate in the subsequent annealing process, which contributes to the improvement.
  • the uniformity of the annealed steel sheet improves the ductility of the steel sheet. However, if the amount of cold rolling reduction is too large, the deformation resistance of the material due to work hardening is very high, making it extremely difficult to prepare a cold-rolled steel sheet having a predetermined thickness and a good plate shape.
  • the soaking temperature is controlled at 790-920 ° C, and the soaking time is 30-200 s.
  • the selection of soaking temperature and soaking time mainly considers the influence on the microstructure and properties of the strip substrate and the surface layer of the steel sheet.
  • the effect of the thickness of the oxide layer, and the selection of the rapid cooling temperature, the reheating temperature and the reheating holding time, is to ensure the content of retained austenite in the steel sheet to achieve the best forming properties.
  • the average temperature is When the degree is lower than 790 ° C and the soaking time is lower than 30 s, the austenitizing of the cold-rolled steel sheet is insufficient, the austenite structure is not uniform, and a sufficient amount of retained austenite cannot be formed after the subsequent annealing process and the austenite Insufficient stability of the body results in insufficient final elongation of the steel sheet.
  • the soaking temperature is higher than 920 °C and the soaking time is longer than 200 s, the austenite transformation occurs in the matrix of the steel sheet after soaking, and the austenite stability is reduced, so that the retained austenite content in the steel sheet matrix after annealing is reduced.
  • the thickness of the inner oxide layer formed on the surface layer of the steel sheet after annealing is greater than 5 ⁇ m, which affects the toughness and formability of the steel sheet.
  • the invention controls the rapid cooling temperature at 200-300 ° C and the cooling speed ⁇ 30 ° C / s to ensure a certain amount of martensite structure is produced in the steel plate.
  • the martensite critical cooling rate is 30 ° C / s, therefore, in order to ensure that only martensite transformation occurs during the cooling process, the cooling rate is not less than 30 ° C / s.
  • the rapid cooling temperature is lower than 200 °C, all austenite transformation occurs, no residual austenite is formed in the steel room temperature structure, and if the rapid cooling temperature is higher than 300 °C, the amount of martensite formation is less, and then During the reheating process, the driving force of the carbon content in the martensite to diffuse into the austenite is insufficient, resulting in insufficient austenite stability.
  • the residual austenite content in the steel sheet at room temperature is less than 5%, which affects the forming of the steel sheet. Sex.
  • the reheating temperature of the present invention is controlled at 350 to 450 ° C, and the reheating time is 60 to 250 s. If the reheating temperature is lower than 350 ° C and the reheating time is less than 60 s, the residual austenite stabilization process of the steel sheet is insufficient, and the residual austenite content in the structure at room temperature is less than 5%, if the reheating temperature is higher than 450 ° C and When the reheating time is higher than 250 s, the steel sheet undergoes significant temper softening, and the martensite strength decreases, which lowers the strength of the steel sheet.
  • a mixed gas of N 2 -H 2 is used, wherein the H 2 content is 0.5-20%, and the purpose is to reduce iron oxide on the surface of the steel strip.
  • the dew point of the annealing atmosphere is -25 to 10 ° C, preferably -10 to 5 ° C. In the above dew point range, the annealing atmosphere is reductive to Fe, and thus the iron oxide is reduced. If the dew point of the annealing atmosphere is lower than -25 ° C, the above annealing atmosphere is still oxidized to the Si element in the matrix, and Si in the matrix will form a continuous dense oxide film on the surface of the strip to affect the phosphating performance.
  • the dew point of the annealing atmosphere is higher than 10 ° C, the oxygen potential in the annealing atmosphere is too high, and the ability of O atoms to diffuse into the steel substrate is increased.
  • the formation of the inner oxide layer in the surface layer of the steel sheet such as Si and Mn is too thick, affecting the steel sheet. Strength and formability, at the same time, Si and Mn begin to form enrichment on the surface of the steel sheet, which deteriorates the phosphating performance of the steel sheet.
  • the inner layer of the cold-rolled high-strength steel sheet of the present invention has an inner oxide layer which is made of iron and has a thickness of 1 to 5 ⁇ m and contains oxide particles, and the inner oxide layer prevents elements such as Si and Mn from being turned toward the steel sheet.
  • the enrichment of the surface makes the oxidation reaction of the above elements not occur on the surface of the steel sheet, and changes from external oxidation to internal oxidation.
  • the surface of the steel sheet is free of Si and Mn elements, thereby improving the phosphating performance of the steel sheet and ensuring the high Si content. Excellent phosphating performance of rolled high strength steel sheets.
  • the room temperature structure of the cold-rolled high-strength steel sheet of the present invention contains retained austenite. During the deformation process, a certain amount of retained austenite undergoes phase transformation to martensite, and a TRIP effect occurs to ensure that the steel sheet has a strength of 1180 MPa. At the same time, it has good formability.
  • the selection of the soaking temperature and the soaking time mainly considers the influence on the microstructure and properties of the strip substrate, and the influence on the thickness of the oxide layer in the surface layer of the steel sheet, and the rapid cooling temperature, the reheating temperature and The selection of reheating and holding time is to ensure the content of retained austenite in the steel sheet to achieve the best forming performance.
  • the annealing atmosphere of the heating section and the soaking section is selected from a mixed gas of N 2 -H 2 , wherein the content of H 2 is 0.5-20%, and the iron oxide on the surface of the strip is reduced, and the dew point of the annealing atmosphere is -25 ⁇ 10°C, within the dew point range, the selected annealing atmosphere is all reductive to Fe. Therefore, the iron oxide is reduced, and the external oxidation and enrichment of oxidizable elements such as Si and Mn on the surface of the steel sheet is inhibited. This was converted into internal oxidation and an inner oxide layer of 1 to 5 ⁇ m was formed in the surface layer.
  • the invention can be completed on the existing high-strength steel continuous annealing production line without major adjustment, and has a good application prospect in automobile structural parts, and is particularly suitable for manufacturing complicated shapes, forming properties and corrosion resistance. Both require higher vehicle structural components and safety components such as door impact bars, bumpers and B-pillars.
  • 1 is a schematic view showing an inner oxide layer on the surface of a cold-rolled high-strength steel sheet of the present invention, wherein 1 is a steel sheet, 2 is an inner oxide layer, and 3 is an oxide particle.
  • 2 is a cross-sectional scanning electron microscope backscattered electron image of a cold-rolled high-strength steel sheet according to an embodiment of the present invention, wherein 1 is a steel sheet, and 2 is an inner oxide layer of a surface layer of the steel sheet.
  • FIG. 3 is a secondary electron image of a surface scanning electron microscope after phosphating treatment of a cold-rolled high-strength steel sheet according to an embodiment of the present invention.
  • Fig. 5 is a SEM secondary electron image of the cold-rolled high-strength steel sheet of Comparative Example 1 after phosphating treatment.
  • Table 1 lists the mass percentages (%) of the respective chemical elements of Examples 1 to 16 and Comparative Examples 1 to 5, and the balance is Fe.
  • the steel material having the composition shown in Table 1 is smelted and cast to form a slab, and the slab is heated at a heating temperature of 1250 ° C. After the holding time is 1 h, hot rolling is performed, and finish rolling is completed at a finishing temperature of 900 ° C or higher.
  • the thickness of the hot rolled steel sheet is about 2.5 mm.
  • the hot rolled steel sheet was taken up at 500 ° C, and subjected to pickling and cold rolling, the cold rolling reduction was 52%, and the final thickness of the rolled hard strip was 1.2 mm.
  • the obtained hard-rolled steel strip was unrolled, cleaned, annealed, annealed in the examples and comparative examples, and the atmospheric conditions are shown in Table 2, and then the mechanical properties and residual austenite content of the cold-rolled high-strength steel sheet after annealing were The thickness of the oxide layer in the surface layer, the average diameter of the oxide particles, the average pitch, and the phosphating performance were evaluated. The evaluation results are shown in Table 3.
  • the dew point of Comparative Example 1 is -40 ° C, which is much lower than the design lower limit of the present invention, and no surface oxide layer is formed on the surface (see FIG. 4 ), and Si and Mn are concentrated on the surface of the steel sheet, so After the phosphating of the steel plate, only phosphating crystals are locally present on the surface and the crystal size is coarse, and most of the surface is covered with no phosphating crystal, and the phosphating performance is poor, as shown in FIG.
  • Comparative Example 2 While the rapid cooling temperature of Comparative Example 2 is 100 ° C, all austenite is transformed into martensite and no retained austenite remains. Therefore, the strength of the steel sheet is high and the elongation is low.
  • the soaking temperature of Comparative Example 3 was 755 ° C, which was lower than the design requirement of 790 ° C, and its austenite during soaking The bulking is insufficient, and a sufficient amount of retained austenite cannot be stabilized during subsequent cooling and heating, and therefore, the strength and elongation of the material are both low.
  • the tensile test method was as follows: JIS No. 5 tensile test specimen was used, and the tensile direction was perpendicular to the rolling direction.
  • Residual austenite content test method A sample of 15 ⁇ 15 mm size was cut from the steel plate, and after grinding and polishing, XRD quantitative test was performed.
  • the sections of the steel plate were sampled, and after grinding and polishing, the cross-sectional morphology of all the steel sheets was observed at 5000 times under a scanning electron microscope.
  • Method for determining the average diameter and average spacing of oxide particles in an oxide layer sampling along the section of the steel plate, after grinding and polishing, using a scanning electron microscope to randomly observe 10 fields of view at 10,000 times, and using image software to average the average diameter and average spacing of the oxide particles. statistics.
  • the evaluation method of phosphating performance of steel plate the annealed steel plate is subjected to degreasing, water washing, surface conditioning, water washing, followed by phosphating, then washed and dried, and 500 fields of phosphating steel plate are randomly observed by scanning electron microscopy, and 5 fields of view are used.
  • the image software counts the uncovered area of the phosphate film. If the uncovered area is less than 20% and the phosphating crystal size is less than 10 ⁇ m, it is judged that the phosphating performance is good (OK), and conversely, the phosphating performance is judged to be poor (NG).

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Abstract

一种冷轧钢板（1）及其制造方法。钢板（1）的化学成分重量百分比为：C 0.15～0.25％，Si 1.50～2.50％，Mn 2.00～3.00％，P≤0.02％，S≤0.01％，Al 0.03～0.06％，N≤0.01％，其余为Fe及杂质，表层具有厚度为1～5μm的内氧化层（2），表面无Si、Mn元素富集，具有良好的磷化性能和成形性，抗拉强度≥1180MPa，延伸率≥14％，具有铁素体、马氏体以及残余奥氏体的复相组织，残余奥氏体含量不低于5％。连续退火过程中露点在-25～10℃，使外氧化转为内氧化。

Description

一种磷化性能和成形性能优良的冷轧高强度钢板及其制造方法 技术领域
本发明属于冷轧高强钢领域，具体涉及一种磷化性能和成形性能优良的冷轧高强度钢板及其制造方法。
背景技术
近年来，随着环保法和碰撞法规的要求越来越高，汽车上开始大量使用强度在590～980MPa级别的高强度冷轧钢板替代传统汽车用钢，从而实现车身零件的高强减薄，达到节能减重、提高安全性和降低制造成本的目的。
为进一步提升车身轻量化效果，材料强度需进一步提高，即强度达到1180MPa以上，然而，随着强度的增加，钢板的成形性逐渐劣化，因此，期望开发兼具有高强度和高成形性的钢板。
通常，钢板在汽车上使用之前需要进行涂装，而在涂装前需要进行磷化处理，使钢板表面形成磷化膜，正常的磷化膜具有均匀致密，磷化结晶细小的特点，可改善涂层附着力，增强电泳效果，提高零件涂装后的耐蚀性，因此，磷化的好坏直接决定了涂装质量和汽车的耐蚀性，进而影响着钢板在汽车上的应用。
为同时提高钢板的强度和成形性，通常会在钢中加入一定量的Si，然而，高Si成分设计的钢板在连续退火时，Si元素会在钢板表面富集形成Si的氧化物，该氧化物在磷化过程中阻碍了磷化过程的均匀反应，引发磷化覆盖不良，磷化结晶尺寸粗大等问题，从而导致了钢板的磷化性能恶化，涂装质量和耐蚀性不过关，严重限制了高Si成分设计的钢板在汽车上的应用。因此，改善高Si成分设计的冷轧高强度钢板在使用过程中的磷化涂装性能一直是主要问题。
中国专利CN103154297A公开了一种高强度冷轧钢板及其制造方法，钢板中含有C：0.01～0.18％、Si：0.4～2.0％、Mn：1.0～3.0％、P：0.005～0.060％、S≤0.01％、Al：0.001～1.0％、N≤0.01％且其余为Fe和不可避免的杂质，对该钢板进行连续退火时，控制加热炉温度为A℃以上且B℃以下(A：600≤A≤780， B：800≤B≤900)的温度区域的气氛露点为-10℃以上，并且，在连续退火后在含有硫酸的水溶液中进行电解酸洗，中国专利CN103140597A公开的一种高强度钢板及其制造方法与其类似，但退火炉内温度在750℃以上时气氛露点的设定为-40℃以下。上述两个专利均在退火后采用了酸洗工序，不仅增加了生产成本、降低了生产效率，并且，酸洗工序本身及酸液废液处理对环境也存在不利影响。
中国专利CN103124799A公开的一种高强度钢板及其制造方法，其要点为：使均热过程中退火炉内温度为820℃以上且1000℃以下的温度区域的气氛露点为-45℃以下，并且，使冷却过程中退火炉内温度为750℃以上的温度区域的气氛露点为-45℃以下。通过该种处理，气氛中的还原能力增强，并且可以使在钢板表面上发生选择性表面氧化后的Si、Mn等易氧化性元素的氧化物还原。然而，实际连续退火生产时，将气氛露点连续稳定控制在-45℃以下技术难度较大，不仅对生产装备和生产技术水平有很高的要求，生产成本方面也不具备优势。
中国专利CN104508155A公开了一种高强度钢板及其制造方法，钢板的化学成分以质量百分数％计含有C：0.03～0.35％、Si：0.01～0.5％、Mn：3.6～8.0％、Al：0.01～1.0％、P≤0.10％、S≤0.010％且余量为Fe和不可避免的杂质，对该钢板进行连续退火时，退火炉内，设定钢板的最高温度为600～750℃，时间为30秒～10分钟，将气氛中的露点设定为-10℃以上。该方法中Si含量在0.01～0.5％的范围内，但Mn含量较高，达到3.6～8.0％，不仅无法充分利用廉价Si元素的强韧化作用，而且较高的Mn含量已经达到特殊钢的范畴，一方面在成本方面不利，另一方面也会带来炼钢、连铸和后续热处理生产的大量技术问题。
中国专利CN102666923A公开了一种高强度冷轧钢板及其制造方法，钢板中含有C：0.05～0.3％、Si：0.6～3.0％、Mn：1.0～3.0％、P≤0.1％、S≤0.05％、Al：0.01～1％、N≤0.01％且其余为Fe和不可避免的杂质，对该钢板进行连续退火时，控制氧浓度，实现在退火前的氧化处理。在氧浓度为1000ppm以上的气氛下对钢板进行第一次加热，直至钢板温度达到630℃以上，接着，在氧浓度低于1000ppm的气氛下对钢板进行第二次加热，直至钢板温度达到700～800℃，使得钢板表面形成0.1g/m2以上的氧化量，接着，利用露点为-25℃以下，1～10％H2-N2的还原性气氛进行退火。该制造方法中，在退火前增加了氧化处理工序，需要产线配备相应装置同时控制加热温度和氧浓度，操作难度较大，现 有大多数连续退火产线不具备此类功能，而且，利用高含氧量的气氛实现钢板表面的非选择性氧化，氧化反应程度对气氛非常敏感，反应均匀性难以保证，易出现氧化层厚度及氧化程度的不均，后续通过还原反应生成还原铁层也容易发生厚度不均，导致产品磷化性能不良。
发明内容
本发明的目的在于提供一种磷化性能和成形性能优良的冷轧高强度钢板及其制造方法，该钢板具有良好的磷化性能和成形性，室温组织为具有铁素体、马氏体以及残余奥氏体的复相组织，抗拉强度≥1180MPa，延伸率≥14％，适用于制造汽车结构件和安全件。
为达到上述目的，本发明提供的技术方案如下：
一种磷化性能和成形性能优良的冷轧高强度钢板，其化学成分按重量百分比含有：C 0.15～0.25％，Si 1.50～2.50％，Mn 2.00～3.00％，P≤0.02％，S≤0.01％，Al 0.03～0.06％，N≤0.01％，其余为Fe和不可避免的杂质元素，所述钢板表层存在厚度为1～5μm的内氧化层，所述内氧化层以铁为基体，该基体中含有氧化物颗粒，所述氧化物颗粒为Si氧化物、Si与Mn的复合氧化物中的至少一种，表面无Si、Mn元素富集；
所述氧化物颗粒的平均直径为50～200nm，氧化物颗粒间的平均间距λ满足下述关系：
A＝0.247×(0.94×[Si]+0.68×[Mn])1/2×d
B＝1.382×(0.94×[Si]+0.68×[Mn])1/2×d
A≤λ≤B
其中，[Si]为钢中Si的含量％；[Mn]为钢中Mn的含量％；d为氧化物颗粒直径，单位nm。
优选地，所述氧化物颗粒为氧化硅、硅酸锰、硅酸铁以及硅酸锰铁中的至少一种。
进一步，所述的钢板含有Cr 0.01～1％，Mo 0.01～0.5％和Ni 0.01～2.0％中的至少一种。
又进一步，所述的钢板含有Ti 0.005～0.5％，Nb 0.005～0.5％和V 0.005～0.5％中的至少一种。
本发明所述磷化性能和成形性能优良的冷轧高强度钢板的室温组织具有铁素体、马氏体以及残余奥氏体的复相组织，其中，残余奥氏体含量不低于5％，该冷轧高强度钢板的抗拉强度≥1180MPa，延伸率≥14％。
在本发明的成分设计中：
C：是钢中为了确保强度而必需的固溶强化元素，是奥氏体稳定化元素。C含量过低时，残余奥氏体的含量不足且材料强度偏低，而C含量过高时，钢材的焊接性能显著恶化，因此，本发明控制C含量为0.15～0.25％。
Si：具有提高强度同时改善钢材成形性的作用，本发明中大量添加。但过量添加Si，钢板脆化变得显著，冷轧时易在钢板端部产生裂纹，阻碍生产效率。因此，本发明控制Si含量为1.50～2.50％。
Mn：增加了奥氏体的稳定性，同时降低了钢淬火时的临界冷却温度以及马氏体转变温度Ms，提高钢板的淬透性。此外，Mn是固溶强化元素，对提高钢板的强度有利，因此，需要在本发明中大量添加，但过高的Mn含量会导致连铸工序中钢坯裂纹产生，且影响钢材的焊接性能。因此，本发明控制Mn含量为2.00～3.00％。
P：在本发明中是杂质元素，使得焊接性能变差，增加钢的冷脆性，降低了钢的塑性，因此，需要控制P在0.02％以下。
S：同样作为杂质元素，使得焊接性能变差，降低钢的塑性，因此，需要控制S在0.01％以下。
Al：是为了钢水的脱氧而添加的。Al含量过低时，无法达到脱氧的目的，而Al含量过高，脱氧效果饱和。因此，本发明控制Al含量在0.03～0.06％。
N：是粗钢中含有的杂质，N与Al结合AlN颗粒，影响钢板的延展性和热塑性。因此，期望尽可能在炼钢工序将N含量控制在0.01％以下。
Cr：有助于奥氏体晶粒的细化，同时，提高钢板的淬透性，提高钢的强度。因此，为达到高强度，可适当添加Cr。但不宜过高，当Cr含量超过1.0％时，钢板的成本提高，焊接性能变差，因此，在本发明中，将Cr的含量控制在0.01～1.0％。
Mo：可提高钢板的淬透性，进而提高钢板的强度。为保证钢板的淬透性， 可适当添加Mo。然而，当Mo含量高于0.5％时，钢板的塑性明显下降，且生产成本提高，因此，本发明中将Mo含量的范围控制在0.01～0.5％。
Ni：Ni的作用与Mo类似，同样为提高钢板淬透性的元素。为保证抗拉强度达到1180MPa以上，可适量添加Ni。但Ni含量不宜过高，当Ni含量超过2.0％时，钢板的生产成本提高，因此，控制Ni的含量在0.01～2.0％。
Ti：Ti与C、S、N形成析出物而有效地提高钢板的强度和韧性。为达到上述效果，Ti含量需要在0.005％以上。另一方面，如果Ti含量超过0.05％，再增加其含量，对于钢的改善效果并不显著。因此，本发明中的Ti含量设计为0.005～0.05％。
Nb：通过析出强化而对钢进行强化，同时阻止奥氏体晶粒的长大，细化晶粒，同时提高强度和延伸率。当Nb含量小于0.005％时，无法达到上述的效果，但当Nb的含量超过0.1％时，析出强化过度发挥作用，导致成形性下降，同时，增加制造成本。因此，在本发明中，Nb含量的控制范围为0.005～0.1％。
V：V的作用与Nb类似，可形成碳化物，提高钢的强度。当V含量小于0.005％时，析出强化效果不显著。然而，当V含量大于0.1％时，析出强化效果过度发挥作用，导致钢板成形性下降。为此，在本发明中，V含量控制在0.005～0.1％。
本发明的冷轧高强钢板表层存在厚度在1～5μm的内氧化层，该内氧化层含有氧化物颗粒，所述氧化物颗粒为Si氧化物以及Si、Mn复合氧化物之中的一种或多种，本发明钢板表层一定厚度的内氧化层特征是必需的，其与钢板中的高Si、Mn含量有着必然的联系，保证了Si元素不在钢板表面富集形成Si的氧化物，使氧化反应由外氧化转变为内氧化，从而改善了钢板的磷化性能。
本发明冷轧高强钢板表层的内氧化层的厚度、氧化物颗粒的尺寸和氧化物粒子密度会直接影响内氧化层改善钢板表面状态作用的发挥，而氧化物密度可以通过氧化物颗粒的平均间距λ表达，其与Si、Mn含量以及氧化物颗粒直径的关系为：氧化物颗粒间的平均间距λ满足下述关系：
A＝0.247×(0.94×[Si]+0.68×[Mn])1/2×d
B＝1.382×(0.94×[Si]+0.68×[Mn])1/2×d
A≤λ≤B
其中，[Si]为钢中的Si元素含量，[Mn]为钢中的Mn元素含量，d为氧化物颗粒直径，单位nm。当内氧化层厚度<1μm，Si氧化物颗粒平均直径＜50nm以及平均间距λ>B时，内氧化层无法阻止Si向钢板表面富集，钢板表面仍形成大量的氧化物颗粒，外氧化无法得到有效抑制，而钢板表面的氧化物颗粒将严重阻碍磷化过程的均匀反应，造成表面黄锈，磷化不良，磷化结晶尺寸粗大等问题。
而当内氧化层厚度＞5μm，Si氧化物颗粒平均直径＞200nm以及平均间距λ<A时，内氧化作用过于强烈，对钢板表面的韧性和成形性能有显著影响，因此，为保证钢板具有良好的磷化性能，钢板表层内氧化层的厚度为1～5μm，氧化物颗粒平均直径控制在50～200nm，氧化物颗粒间的平均间距λ控制在A与B之间。
本发明所述冷轧高强钢板的室温组织包含残余奥氏体，残余奥氏体含量不小于5％。在变形过程中，一定量的残余奥氏体发生相变转变为马氏体，发生TRIP效应，保证钢板在具有1180MPa强度的同时具有良好的成形性能。当残余奥氏体含量＜5％时，其TRIP效应不显著，钢板的强度和成形性无法保证。因此，期望保证室温组织中的残余奥氏体含量≥5％。
本发明还提供了该磷化性能和成形性能优良的冷轧高强度钢板的制造方法，包括以下步骤：
1)冶炼、铸造
按照上述化学成分冶炼和浇铸后制成板坯；
2)热轧、卷取
将板坯加热到1170～1300℃，保温0.5～4h，轧制，终轧温度≥850℃；卷取，卷取温度为400～700℃，获得热轧卷；
3)酸洗、冷轧
将热轧卷开卷，进行酸洗及冷轧，酸洗速度≤150m/min，冷轧压下量为40～80％，获得轧硬带钢；
4)连续退火
将获得的轧硬带钢开卷、清洗，加热至均热温度790～920℃，保温30～200s，其中，加热速率为1～20℃/s，加热段和保温段的气氛采用N2-H2混合气体，其 中H2含量为0.5～20％，退火气氛的露点为-25～10℃；；
之后快冷至200～300℃，冷却速度≥30℃/s；
然后再加热至350～450℃，保温60～250s，获得具有优良磷化性能和成形性的冷轧高强度钢板。
优选地，步骤2)中进行热轧时，对板坯再加热的温度为1210～1270℃，卷取温度为450～550℃。
又，步骤4)中的均热温度为810～870℃。
进一步，步骤4)中退火气氛的露点为-10～5℃。
本发明的制造工艺设计的理由如下：
本发明在热轧时，对板坯的再加热温度为1170～1300℃，优选1210～1270℃，加热温度过高，会造成板坯过烧，板坯内晶粒组织粗大导致其热加工性能降低，并且超高温会引起板坯表面严重脱碳；加热温度过低，板坯经高压水除鳞和初轧后，精轧温度过低，会造成坯料变形抗力过大。在热轧时，保温时间设为0.5～4h，若保温时间超过4h，会造成板坯内晶粒组织粗大同时板坯表面脱碳严重，若保温时间低于0.5h，则板坯内部温度尚未均匀。
本发明需要控制终轧温度在850℃以上，完成对铸坯的热轧，终轧温度过低会造成板坯变形抗力过高，从而难以生产出所需厚度规格的钢板且板形不良。
本发明在400～700℃进行热轧板的卷取，优选卷取温度为450～550℃。若卷取温度过高，则钢板表面的氧化铁皮生成过厚，难于酸洗，而如果卷取温度过低，则热卷强度偏高，难于冷轧，影响生产效率。
本发明在酸洗时，酸洗速度≤150m/min，若酸洗速度过快，钢板表面的氧化皮无法完全去除，易形成表面缺陷。将酸洗后的热轧钢板冷轧变形至规定厚度，冷轧压下量为40～80％，大的冷轧压下量可以在后续退火过程中提高奥氏体形成速率，有助于提高退火钢板的组织均匀性，从而提高钢板的延展性。但如果冷轧压下量过大，会因加工硬化导致材料的变形抗力非常高，使得制备规定厚度和良好板型的冷轧钢板变得异常困难。
本发明在退火过程中，均热温度控制在790～920℃，均热时间在30～200s，均热温度及均热时间的选取主要考虑对带钢基体组织和性能的影响以及对钢板表层内氧化层厚度的影响，而快冷温度，再加热温度以及再加热保温时间的选取则希望保证钢板中残余奥氏体的含量，以达到最佳的成形性能。如果均热温 度低于790℃、均热时间低于30s，冷轧钢板的奥氏体化不充分，奥氏体组织不均匀，在随后的退火工艺后，无法形成足够量的残余奥氏体且奥氏体的稳定性不足，导致钢板最终的延伸率不足。当均热温度高于920℃、均热时间长于200s时，均热处理后钢板基体组织发生完全奥氏体相变，奥氏体稳定性降低，从而使得退火后钢板基体中残余奥氏体含量减少，同时退火后钢板表层形成的内氧化层厚度大于5μm，影响钢板的韧性和成形性。
本发明在快冷阶段，控制快冷温度在200～300℃，冷却速度≥30℃/s，保证钢板中生产一定量的马氏体组织。本发明的成分设计中，马氏体临界冷却速度为30℃/s，因此，为保证冷却过程中仅发生马氏体相变，冷却速度不小于30℃/s。如果快冷温度低于200℃，奥氏体全部发生马氏体转变，钢板室温组织中无残余奥氏体生成，而如果快冷温度高于300℃，则马氏体生成量较少，随后的再加热过程中，马氏体中碳含量向奥氏体中扩散的驱动力不足，导致奥氏体的稳定性不足，室温下钢板中残余奥氏体的含量小于5％，影响钢板的成形性。
本发明的再加热温度控制在350～450℃，再加热时间在60～250s。如果再加热温度低于350℃和再加热时间低于60s，钢板残余奥氏体稳定化过程不充分，室温下组织中的残余奥氏体含量小于5％，如果再加热温度高于450℃和再加热时间高于250s，钢板发生显著的回火软化，马氏体强度下降，则会使钢板的强度下降。
本发明在加热及均热段的退火气氛选用N2-H2混合气体，其中H2含量为0.5～20％，目的是还原带钢表面的氧化铁。退火气氛的露点为-25～10℃，优选-10～5℃，在上述露点范围内，退火气氛对Fe都是还原性的，因此会把氧化铁还原。若退火气氛露点低于-25℃，则上述退火气氛对基体中的Si元素依然是氧化的，基体中的Si会在带钢表面形成连续致密的氧化物薄膜影响磷化性能。若退火气氛露点高于10℃，则退火气氛中的氧势过高，O原子向带钢基体扩散的能力加大，在钢板表层Si和Mn等合金元素形成内氧化层过厚，影响钢板的强度和成形性，同时，Si和Mn又开始在钢板表面形成富集，使得钢板的磷化性能恶化。
与现有技术相比，本发明的有益效果：
1)本发明的冷轧高强度钢板表层存在内氧化层，该内氧化层以铁为基体，厚度为1～5μm，含有氧化物颗粒，该内氧化层阻止了Si、Mn等元素向钢板表 面富集，使得上述元素的氧化反应不在钢板表面发生，由外氧化转变为内氧化，该钢板表面无Si、Mn元素富集，从而改善了钢板的磷化性能，保证了高Si含量的冷轧高强钢板的优异的磷化性能。
2)本发明的冷轧高强钢板的室温组织包含残余奥氏体，在变形过程中，一定量的残余奥氏体发生相变转变为马氏体，发生TRIP效应，保证钢板在具有1180MPa强度的同时具有良好的成形性能。
3)本发明在退火过程中，均热温度及均热时间的选取主要考虑对带钢基体组织和性能的影响，以及对钢板表层内氧化层厚度的影响，而快冷温度，再加热温度以及再加热保温时间的选取则希望保证钢板中残余奥氏体的含量，以达到最佳的成形性能。
4)本发明在退火过程中，加热段及均热段的退火气氛选用N2-H2混合气体，其中H2含量为0.5～20％，还原带钢表面的氧化铁，退火气氛的露点为-25～10℃，在该露点范围内，选用的退火气氛对Fe都是还原性的，因此，会将氧化铁还原，抑制了Si、Mn等易氧化元素在钢板表面的外氧化富集，使其转化成内氧化并在表层形成了1～5μm的内氧化层。
5)本发明可以在现有高强钢连续退火生产线上完成，无需做较大调整，在汽车结构件中将具有很好的应用前景，特别适合于制造形状较为复杂、对成形性能和耐蚀性能都要求较高的车辆结构件和安全件，如车门防撞杆、保险杠及B柱等。
附图说明
图1为本发明冷轧高强度钢板表面内氧化层的示意图，其中，1为钢板，2为内氧化层，3为氧化物颗粒。
图2为本发明实施例的冷轧高强钢板的截面扫描电镜背散射电子像，其中1为钢板，2为钢板表层的内氧化层。
图3为本发明实施例的冷轧高强度钢板经过磷化处理后表面扫描电镜二次电子像。
图4为对比例1的冷轧高强钢板的截面扫描电镜背散射电子像。
图5为对比例1的冷轧高强度钢板经过磷化处理后表面扫描电镜二次电子像。
具体实施方式
下面将结合附图说明和具体的实施例对本发明进一步的解释和说明，然而该解释和说明并不对本发明的技术方案构成不当限定。
实施例和对比例
本发明实施例1～16的磷化性能和成形性能优良的冷轧高强度钢板和对比例1～5的钢板采用下述步骤制得：
表1列出了实施例1～16和对比例1～5的各化学元素的质量百分比(％)，其余为Fe。
将具有表1所示成分的钢料经冶炼和浇铸后制成板坯，在1250℃加热温度下加热板坯，保温时间1h后进行热轧，在900℃以上的终轧温度下完成精轧，热轧钢板的厚度约为2.5mm。将所述热轧钢板在500℃下卷取，并进行酸洗和冷轧，冷轧压下量为52％，轧硬带钢的最终厚度为1.2mm。
将所获得的轧硬带钢开卷、清洗，进行退火，实施例和对比例的退火工艺、气氛条件参见表2，然后对退火后的冷轧高强度钢板的力学性能，残余奥氏体含量，表层内氧化层厚度，氧化物颗粒平均直径，平均间距以及磷化性能进行评价，评价结果参见表3。
从表3可以看出，经本发明的退火工艺配合，所有实施例的抗拉强度均在1180MPa以上，且延伸率在14％以上，其室温组织中残余奥氏体含量不低于5％，成形性良好，同时，通过控制退火气氛的露点，钢板表层存在1～5μm的内氧化层，内氧化层特征参见图1～2，经磷化处理后，磷化结晶均匀覆盖在钢板表面，且尺寸尺寸小于10μm，覆盖面积达到80％以上，磷化性能优良，参见图3。
结合表2和表3可知，对比例1的露点为-40℃，远低于本发明的设计下限，其表面无内氧化层生成(参见图4)，Si和Mn在钢板表面富集，因此，钢板磷化后，表面仅局部存在磷化结晶且结晶尺寸粗大，且大部分表面无磷化结晶覆盖，磷化性能不良，如图5所示。
而对比例2的快冷温度为100℃，奥氏体全部转变为马氏体，无残余奥氏体保留，因此，钢板的强度偏高，延伸率偏低。
对比例3的均热温度为755℃，低于设计要求的790℃，其均热过程中奥氏 体化不充分，在随后的冷却和在加热过程中无法稳定足够量的残余奥氏体，因此，材料的强度和延伸率均偏低。
对比例4则由于采用了超出本发明设计上限的露点，钢板表面的内氧化层偏厚，影响了材料抗拉强度和延伸率，同时，过高的露点使得Si和Mn元素重新在钢板表面富集，钢板的磷化性能又开始变差。
结合表1和表3可知，对比例5的Si含量偏低，其延伸率无法达到14％。这是由于Si含量未达到设计下限，因此，在退火过程中，残余奥氏体的含量不足，致使其延伸率偏低。
拉伸试验方法为：采用JIS5号拉伸试样，拉伸方向垂直于轧制方向。
残余奥氏体含量测试方法：从钢板上切取15×15mm尺寸的试样，经过研磨和抛光后，进行XRD定量测试。
沿钢板截面取样，经过研磨和抛光后，在扫描电镜下以5000倍观察所有试样钢板的截面形貌。
氧化层中氧化物粒子平均直径和平均间距测定方法：沿钢板截面取样，经过研磨和抛光后，使用扫描电镜以10000倍随机观察10个视野，并用图像软件对氧化物颗粒平均直径和平均间距进行统计。
钢板磷化性能评价方法：将退火钢板依次经过脱脂、水洗、表调、水洗后进行磷化，之后再水洗、干燥，使用扫描电镜以500倍对磷化后的钢板随机观察5个视野，并用图像软件对磷化膜的未覆盖面积进行统计。若未覆盖面积不足20％且磷化结晶尺寸小于10μm，则判断磷化性能良好(OK)，反之，则判断磷化性能较差(NG)。
需要注意的是，以上列举的仅为本发明的具体实施例，显然本发明不限于以上实施例，随之有着许多的类似变化。本领域的技术人员如果从本发明公开的内容直接导出或联想到的所有变化，均应属于本发明的保护范围。
表1
编号 C Si Mn P S Al N Cr Mo Ti Nb V
A 0.16 1.6 2.5 0.009 0.003 0.045 0.0057 0.5 — 0.02 — —
B 0.23 1.5 2.9 0.015 0.004 0.033 0.0037 — 0.1 — 0.03 —
C 0.18 1.7 2.5 0.01 0.006 0.04 0.0065 0.2 0.15 — — 0.05
D 0.2 1.8 2.3 0.008 0.007 0.052 0.0043 — 0.2 0.015 0.015 —
E 0.14 1.2 2.3 0.011 0.002 0.032 0.0023 — 0.05 — 0.015 0.025
表2
Figure PCTCN2017099421-appb-000001
表3
Figure PCTCN2017099421-appb-000002

Claims (9)

  1. 一种磷化性能和成形性能优良的冷轧高强度钢板，其化学成分重量百分比含有：C 0.15～0.25％，Si 1.50～2.50％，Mn 2.00～3.00％，P≤0.02％，S≤0.01％，Al 0.03～0.06％，N≤0.01％，其余为Fe和不可避免的杂质元素，所述钢板表层存在厚度为1～5μm的内氧化层，所述内氧化层以铁为基体，该基体中含有氧化物颗粒，所述氧化物颗粒为Si氧化物、Si与Mn的复合氧化物中的至少一种，表面无Si、Mn元素富集；
    所述氧化物颗粒的平均直径为50～200nm，氧化物颗粒间的平均间距λ满足下述关系：
    A＝0.247×(0.94×[Si]+0.68×[Mn])1/2×d
    B＝1.382×(0.94×[Si]+0.68×[Mn])1/2×d
    A≤λ≤B
    其中，[Si]为钢中Si的含量％；[Mn]为钢中Mn的含量％；d为氧化物颗粒直径，单位nm。
  2. 根据权利要求1所述的磷化性能和成形性能优良的冷轧高强度钢板，其特征在于，所述的钢板还含有：Cr 0.01～1.0％，Mo 0.01～0.5％和Ni 0.01～2.0％中的至少一种。
  3. 根据权利要求1所述的磷化性能和成形性能优良的冷轧高强度钢板，其特征在于，所述的钢板还含有：Ti 0.005～0.05％，Nb 0.005～0.1％和V 0.005～0.1％中的至少一种。
  4. 根据权利要求1～3任一项所述的磷化性能和成形性能优良的冷轧高强度钢板，其特征在于，所述氧化物颗粒为氧化硅、硅酸锰、硅酸铁和硅酸锰铁中的至少一种。
  5. 根据权利要求1所述的磷化性能和成形性能优良的冷轧高强度钢板，其特征在于，所述磷化性能和成形性能优良的冷轧高强度钢板的室温组织具有铁素体、马氏体以及残余奥氏体的复相组织；其中，残余奥氏体含量不低于5％。
  6. 根据权利要求1所述的磷化性能和成形性能优良的冷轧高强度钢板，其特征在于，该冷轧高强度钢板的抗拉强度≥1180MPa，延伸率≥14％。
  7. 根据权利要求1～6任一项所述磷化性能和成形性能优良的冷轧高强度钢板的制造方法，包括以下步骤：
    1)冶炼、铸造
    按照所述化学成分冶炼和浇铸后制成板坯；
    2)热轧、卷取
    将板坯加热到1170～1300℃，保温0.5～4h，轧制，终轧温度≥850℃；卷取，卷取温度为400～700℃，获得热轧卷；
    3)酸洗、冷轧
    将热轧卷开卷，进行酸洗及冷轧，酸洗速度≤150m/min，冷轧压下量为40～80％，获得轧硬带钢；
    4)连续退火
    将获得的轧硬带钢开卷、清洗，加热至均热温度790～920℃，保温30～200s，其中，加热速率为1～20℃/s，加热段和保温段的气氛采用N2-H2混合气体，其中H2含量为0.5～20％，退火气氛的露点为-25～10℃；
    之后快冷至200～300℃，冷却速度≥30℃/s；
    然后再加热至350～450℃，保温60～250s，获得具有优良磷化性能和成形性的冷轧高强度钢板。
  8. 根据权利要求7所述的磷化性能和成形性能优良的冷轧高强度钢板的制造方法，其特征在于，步骤2)中进行热轧时，对板坯再加热的温度为1210～1270℃，卷取温度为450～550℃。
  9. 根据权利要求7或8所述的磷化性能和成形性能优良的冷轧高强度钢板的制造方法，其特征在于，步骤4)中的均热温度为810～870℃，退火气氛的露点为-10～5℃。
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