TWI491741B - High strength steel sheet and method for manufacturing the same - Google Patents
High strength steel sheet and method for manufacturing the same Download PDFInfo
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本發明係關於即便在Si含有量多之情況,仍具有優異之化成處理性及電著塗裝後之耐蝕性的高強度鋼板及其製造方法。The present invention relates to a high-strength steel sheet having excellent chemical conversion treatability and corrosion resistance after electrocoating even when the Si content is large, and a method for producing the same.
近年來,從汽車之燃料費提高及提升汽車之衝突安全性的觀點而言,係利用車體材料之高強度化而尋求薄壁化,車體本身之輕量化且高強度化的需求日漸提高。因此,高強度鋼板對汽車之應用正被提倡中。In recent years, from the viewpoint of improving the fuel cost of automobiles and improving the safety of conflicts between automobiles, the use of the strength of the vehicle body material has been sought to reduce the thickness of the vehicle body, and the demand for lightweight and high strength of the vehicle body has been increasing. . Therefore, the application of high-strength steel sheets to automobiles is being promoted.
一般而言,汽車用鋼板係經塗裝而使用,作為該塗裝之前處理,係施行稱作磷酸鹽處理的化成處理。鋼板之化成處理係用以確保塗裝後之耐蝕性的重要處理之一。In general, a steel sheet for automobiles is used for coating, and as a treatment before the coating, a chemical conversion treatment called phosphate treatment is performed. The chemical conversion treatment of the steel sheet is one of important treatments for ensuring the corrosion resistance after coating.
為了提高鋼板之強度、延展性,Si之添加係為有效。然而,於連續退火時,即便在Fe之氧化不會發生(將Fe氧化物還原)的還原性N2 +H2 氣體環境中進行退火之情況,Si仍會氧化,而於鋼板最表層形成Si氧化物(SiO2 )。由於該SiO2 會阻礙化成處理中化成皮膜的生成反應,故會形成化成皮膜未生成之微小區域(以下亦稱為空孔),而降低化成處理性。In order to increase the strength and ductility of the steel sheet, the addition of Si is effective. However, in the case of continuous annealing, even in the case where the oxidation of Fe does not occur (reduction of Fe oxide) in the environment of reducing N 2 + H 2 gas, Si is oxidized, and Si is formed on the outermost layer of the steel sheet. Oxide (SiO 2 ). Since this SiO 2 inhibits the formation reaction of the chemical conversion film in the chemical conversion treatment, a minute region (hereinafter also referred to as a void) in which the chemical conversion film is not formed is formed, and the chemical conversion processability is lowered.
作為改善含高Si鋼板之化成處理性的習知技術,專利文獻1中揭示有使用電鍍法於鋼板上形成20~1500mg/m2 之鐵被覆層的方法。然而,該方法需要另外增設電鍍設備,而有步驟增加且成本亦增高之問題。As a conventional technique for improving the chemical conversion treatment property of a high-Si steel sheet, Patent Document 1 discloses a method of forming an iron coating layer of 20 to 1500 mg/m 2 on a steel sheet by an electroplating method. However, this method requires an additional plating apparatus, and there are problems in that steps are increased and costs are also increased.
又,專利文獻2中係規定Mn/Si比率、專利文獻3中則藉由添加Ni而提升磷酸處理性。然而,其效果係依存於鋼板中之Si含有量,對於Si含有量高的鋼板,需要更進一步的改善。Further, in Patent Document 2, the Mn/Si ratio is defined, and in Patent Document 3, the phosphoric acid treatability is improved by the addition of Ni. However, the effect depends on the Si content in the steel sheet, and further improvement is required for a steel sheet having a high Si content.
此外,專利文獻4中揭示一種方法,其藉由將退火時之露點定為-25~0℃,在鋼板基板表面起深1μm以內,形成由含Si氧化物所構成之內部氧化層,俾使鋼板表面長度10μm中所佔之含Si氧化物的比例為80%以下。然而,專利文獻4所記載之方法的情況,係以控制露點的區域為爐內整體為前提,因此露點之控制性困難,而難以進行穩定操作。又,在不安定的露點控制之基礎下進行退火之情況,形成於鋼板之內部氧化物的分佈狀態會觀察到偏差,會有在鋼板長度方向或寬度方向發生化成處理性之不均(整體或一部分有空孔)之虞。此外,在提升化成處理性之情況,因為化成處理皮膜之正下方存在有含Si氧化物,故有電著塗裝後之耐蝕性不佳的問題。Further, Patent Document 4 discloses a method of forming an internal oxide layer composed of a Si-containing oxide by setting the dew point during annealing to -25 to 0 ° C to a depth of 1 μm on the surface of the steel sheet substrate. The proportion of the Si-containing oxide in the surface length of the steel sheet of 10 μm was 80% or less. However, in the case of the method described in Patent Document 4, it is assumed that the region where the dew point is controlled is the entire furnace, and therefore the controllability of the dew point is difficult, and it is difficult to perform stable operation. Further, when the annealing is performed under the control of the unstable dew point, the distribution of the internal oxide formed in the steel sheet is observed to be uneven, and the processing property in the longitudinal direction or the width direction of the steel sheet may be uneven (integral or Part of it has a hole). Further, in the case where the chemical conversion treatment property is improved, since the Si-containing oxide is present directly under the chemical conversion treatment film, there is a problem that the corrosion resistance after the electrocoating is poor.
又,專利文獻5中,係記載在氧化性環境中使鋼板溫度到達350~650℃,於鋼板表面形成氧化膜,之後再於還原性環境中加熱至再結晶溫度並冷卻之方法。然而,該方法中,因為氧化之方法,形成於鋼板表面之氧化皮膜的厚度發生差異,會有無法充分進行氧化,或者氧化皮膜變得過厚,在之後的還原性環境中,於退火中發生氧化膜之殘留或剝離,而使表面性狀惡化之情況。其實施例中雖記載在大氣中進行氧化之技術,但具有大氣中之氧化生成厚的氧化物而使得其後之還原困難,或者需要高氫濃度之還原環境等問題。Further, Patent Document 5 describes a method in which an steel sheet is heated to a recrystallization temperature in a reducing environment by cooling the steel sheet to an evaporation temperature of 350 to 650 ° C in an oxidizing atmosphere. However, in this method, the thickness of the oxide film formed on the surface of the steel sheet differs depending on the method of oxidation, and oxidation may not be sufficiently performed, or the oxide film may become too thick, and may occur in annealing in a subsequent reducing environment. The surface of the oxide film is deteriorated or peeled off. In the examples, the technique of performing oxidation in the atmosphere is described, but there is a problem that oxidation in the atmosphere generates a thick oxide to make subsequent reduction difficult, or a reduction environment having a high hydrogen concentration is required.
此外,專利文獻6中記載一種方法,其係對以質量%計含有Si 0.1%以上及/或Mn 1.0%以上之冷軋鋼板,以鋼板溫度400℃以上且鐵的氧化環境下,於鋼板表面形成氧化膜,其後,於鐵的還原環境下將上述鋼板表面之氧化膜予以還原之方法。具體而言,係於400℃以上,使用空氣比0.93以上且1.10以下之直火爐將鋼板表面之Fe氧化後,在將Fe氧化物還原之N2 +H2 氣體環境下退火,藉此抑制會使化成處理性劣化之SiO2 於最表面之氧化,並於最表面形成Fe之氧化層的方法。專利文獻6中並未具體記載直火爐的加熱溫度,但在含有較多Si(大約0.6%以上)之情況,較Fe更容易氧化之Si之氧化量變多,Fe之氧化會受到抑制,或者Fe之氧化本身會變得過少。其結果,會有還原後之表面Fe還原層的形成不充分,或還原後之鋼板表面存在SiO2 而發生化成皮膜的空孔之情況。Further, Patent Document 6 describes a method of using a cold-rolled steel sheet containing 0.1% or more of Si and/or 1.0% or more of Mn by mass%, at a steel sheet temperature of 400 ° C or more and an oxidizing atmosphere of iron on the surface of the steel sheet. An oxide film is formed, and then the oxide film on the surface of the steel sheet is reduced in a reducing atmosphere of iron. Specifically, at 400 ° C or higher, the Fe on the surface of the steel sheet is oxidized using a direct fire furnace having an air ratio of 0.93 or more and 1.10 or less, and then annealed in a N 2 +H 2 gas atmosphere in which Fe oxide is reduced, thereby suppressing the reaction. A method of forming oxidized layer of Fe on the outermost surface by oxidizing SiO 2 which is deteriorated in handleability to the outermost surface. Patent Document 6 does not specifically describe the heating temperature of the direct fire furnace. However, when Si is contained in a large amount (about 0.6% or more), the amount of oxidation of Si which is more likely to be oxidized than Fe is increased, and oxidation of Fe is suppressed, or Fe is suppressed. The oxidation itself will become too small. As a result, the formation of the surface Fe reduction layer after reduction may be insufficient, or SiO 2 may be present on the surface of the reduced steel sheet to form a pore of the film.
[專利文獻1]日本專利特開平5-320952號公報[Patent Document 1] Japanese Patent Laid-Open No. Hei 5-320952
[專利文獻2]日本專利特開2004-323969號公報[Patent Document 2] Japanese Patent Laid-Open Publication No. 2004-323969
[專利文獻3]日本專利特開平6-10096號公報[Patent Document 3] Japanese Patent Laid-Open No. Hei 6-10096
[專利文獻4]日本專利特開2003-113441號公報[Patent Document 4] Japanese Patent Laid-Open Publication No. 2003-113441
[專利文獻5]日本專利特開昭55-145122號公報[Patent Document 5] Japanese Patent Laid-Open No. 55-145122
[專利文獻6]日本專利特開2006-45615號公報[Patent Document 6] Japanese Patent Laid-Open Publication No. 2006-45615
本發明係有鑑於上述情況,目的在於提供即便在Si含有量多之情況,仍具有優異之化成處理性及電著塗裝後之耐蝕性的高強度鋼板及其製造方法。In view of the above, it is an object of the present invention to provide a high-strength steel sheet having excellent chemical conversion treatability and corrosion resistance after electrocoating even when the Si content is large, and a method for producing the same.
習知技術中,係單純藉由使退火爐內整體之水蒸氣分壓或氧分壓上升而使露點或氧濃度提高,以使鋼板之內部過度氧化,因此,如上所述,會有露點或氧化控制性方面之問題,或者會於化成處理性方面發生不均,或使電著塗裝後之耐蝕性劣化等,會發生各種問題。因此,本發明人等檢討以習知思想中未被採取的嶄新方法來解決問題。結果發現,藉由對可能成為電著塗裝後之耐蝕性劣化起點的鋼板表層之組織、構造來進行高度控制,可獲得化成處理性及電著塗裝後之耐蝕性優異之高強度鋼板。具體而言,係在加熱過程中限定為加熱爐內溫度:A℃以上且B℃以下(A:600≦A≦780,B:800≦B≦900)之溫度區域中,以環境之露點成為-10℃以上之方式進行控制,退火而進行化成處理。藉由進行此種處理,可選擇性地控制表面氧化,抑制表面濃化,而可獲得化成處理性及電著塗裝後之耐蝕性優異之高強度鋼板。另外,化成處理性優異係指具有化成處理後不具空孔、不均之外觀。In the prior art, the dew point or the oxygen concentration is increased by simply increasing the partial pressure of water vapor or the partial pressure of oxygen in the annealing furnace to excessively oxidize the inside of the steel sheet. Therefore, as described above, there is a dew point or The problem of oxidation control property may cause various problems such as unevenness in chemical conversion treatment, deterioration of corrosion resistance after electrocoating, and the like. Therefore, the present inventors reviewed a new method that was not taken in the conventional idea to solve the problem. As a result, it has been found that high-strength steel sheets having excellent chemical conversion properties and corrosion resistance after electrocoating can be obtained by highly controlling the structure and structure of the surface layer of the steel sheet which may become the starting point of corrosion resistance after electrocoating. Specifically, in the heating process, the temperature in the heating furnace is limited to a temperature range of A ° C or more and B ° C or less (A: 600 ≦ A ≦ 780, B: 800 ≦ B ≦ 900), and the dew point of the environment becomes Controlled by -10 ° C or more, and annealed to carry out a chemical conversion treatment. By performing such a treatment, surface oxidation can be selectively controlled, and surface concentration can be suppressed, and a high-strength steel sheet excellent in chemical conversion treatability and corrosion resistance after electrocoating can be obtained. Further, the excellent chemical conversion property means an appearance which has no voids and is uneven after the chemical conversion treatment.
另外,藉由以上之方法所獲得的高強度鋼板,係於從鋼板表面起100μm以內之鋼板表層部,以每單面0.010~0.50g/m2 形成從Fe、Si、Mn、Al、P進而B、Nb、Ti、Cr、Mo、Cu、Ni中選擇之至少1種以上的氧化物,再從鋼板表面起10μm為止之區域中,成為從粒界起1μm以內之基底鐵粒內析出結晶性Si、Mn系氧化物之組織、構造。藉此可實現電著塗裝後之耐蝕性的劣化,使得化成處理性優異。In addition, the high-strength steel sheet obtained by the above method is formed from the surface layer portion of the steel sheet within 100 μm from the surface of the steel sheet, and is formed of Fe, Si, Mn, Al, and P at a ratio of 0.010 to 0.50 g/m 2 per one side. B, Nb, Ti, Cr, Mo, Cu, and Ni are at least one or more oxides selected from the surface of the steel sheet, and crystallinity is precipitated in the base iron particles within 1 μm from the grain boundary. The structure and structure of Si and Mn-based oxides. Thereby, deterioration of corrosion resistance after electrocoating can be achieved, and the chemical conversion treatability is excellent.
本發明係根據上述發現而完成者,其特徵如下。The present invention has been completed based on the above findings and is characterized as follows.
[1]一種高強度鋼板之製造方法,係在對以質量%含有C:0.01~0.18%、Si:0.4~2.0%、Mn:1.0~3.0%、Al:0.001~1.0%、P:0.005~0.060%、S≦0.01%,其餘部分為Fe及不可避免之雜質所構成的鋼板施行連續退火時,於加熱過程中,在加熱爐內溫度:A℃以上且B℃以下之溫度區域,以環境之露點:-10℃以上進行。其中,A:600≦A≦780,B:800≦B≦900。[1] A method for producing a high-strength steel sheet, comprising C: 0.01 to 0.18%, Si: 0.4 to 2.0%, Mn: 1.0 to 3.0%, Al: 0.001 to 1.0%, and P: 0.005 in mass%. 0.060%, S≦0.01%, and the rest of the steel sheet consisting of Fe and unavoidable impurities is subjected to continuous annealing. During the heating process, the temperature in the heating furnace is above A°C and below B°C. Dew point: above -10 °C. Among them, A: 600≦A≦780, B:800≦B≦900.
[2]如上述[1]之高強度鋼板之製造方法,其中,上述鋼板之成分組成係以質量%進一步含有從以下元素中所選擇之1種以上的元素;B:0.001~0.005%、Nb:0.005~0.05%、Ti:0.005~0.05%、Cr:0.001~1.0%、Mo:0.05~1.0%、Cu:0.05~1.0%、Ni:0.05~1.0%。[2] The method for producing a high-strength steel sheet according to the above [1], wherein the component composition of the steel sheet further contains one or more elements selected from the following elements in mass%; B: 0.001 to 0.005%, Nb : 0.005 to 0.05%, Ti: 0.005 to 0.05%, Cr: 0.001 to 1.0%, Mo: 0.05 to 1.0%, Cu: 0.05 to 1.0%, and Ni: 0.05 to 1.0%.
[3]如上述[1]或[2]之高強度鋼板之製造方法,其中,在進行上述連續退火後,在含有硫酸之水溶液中進行電解酸洗。[3] The method for producing a high-strength steel sheet according to [1] or [2] above, wherein after the continuous annealing, electrolytic pickling is performed in an aqueous solution containing sulfuric acid.
[4]一種高強度鋼板,係利用上述[1]至[3]中任一項之製造方法所製造,於從鋼板表面起100μm以內之鋼板表層部,以每單面0.010~0.50g/m2 形成從Fe、Si、Mn、Al、P、B、Nb、Ti、Cr、Mo、Cu、Ni中所選擇之至少1種以上的氧化物,並進一步於鋼板表面起10μm以內之區域,在鋼板結晶粒界1μm以內之晶粒內,存在有結晶性Si、Mn系氧化物。[4] A high-strength steel sheet produced by the production method according to any one of the above [1] to [3], wherein the surface layer portion of the steel sheet within 100 μm from the surface of the steel sheet is 0.010 to 0.50 g/m per one side. (2) forming at least one or more oxides selected from the group consisting of Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu, and Ni, and further forming a region within 10 μm of the surface of the steel sheet. Crystalline Si and Mn-based oxides are present in the crystal grains within 1 μm of the crystal grain boundary of the steel sheet.
另外,本發明中,高強度係指拉伸強度TS為340MPa以上。又,本發明之高強度鋼板係包含冷軋鋼板與熱軋鋼板之任一者。Further, in the present invention, the high strength means that the tensile strength TS is 340 MPa or more. Moreover, the high-strength steel sheet according to the present invention includes either a cold-rolled steel sheet or a hot-rolled steel sheet.
根據本發明,即便在Si含有量多之情況,仍可獲得具有優異化成處理性及電著塗裝後耐蝕性之高強度鋼板。According to the present invention, even when the Si content is large, a high-strength steel sheet having excellent chemical conversion properties and corrosion resistance after electrocoating can be obtained.
以下,針對本發明具體進行說明。另外,以下說明中,鋼成分組成之各元素的含有量單位係「質量%」,以下只要未特別限制,均以「%」表示。Hereinafter, the present invention will be specifically described. In addition, in the following description, the content unit of each element of the steel component composition is "% by mass", and unless otherwise specified, it is represented by "%".
首先,針對屬於本發明最重要之要件的決定鋼板表面構造之退火環境條件進行說明。First, the annealing environment conditions for determining the surface structure of the steel sheet, which are the most important requirements of the present invention, will be described.
在退火爐內之加熱過程中,於加熱爐內溫度:A℃以上且B℃以下(A:600≦A≦780,B:800≦B≦900)之限定溫度區域中,以環境之露點為-10℃以上之方式進行控制,予以連續退火後再進行化成處理,藉此,使鋼板表層10μm以內之內部適量地存在易氧化性元素(Si、Mn)等之氧化物(以下亦稱為內部氧化),可抑制使退火後之化成處理性劣化的鋼中Si、Mn等在鋼板表層發生選擇性地表面氧化之情況(以下亦稱為表面濃化)。In the heating process in the annealing furnace, in the temperature range of the heating furnace: A ° C or more and B ° C or less (A: 600 ≦ A ≦ 780, B: 800 ≦ B ≦ 900), the ambient dew point is In the case of -10 ° C or more, the film is continuously annealed and then subjected to a chemical conversion treatment, whereby an oxide such as an easily oxidizable element (Si, Mn) is present in an amount of 10 μm or less in the surface layer of the steel sheet (hereinafter also referred to as internal Oxidation) suppresses the selective surface oxidation of Si, Mn, or the like in the steel sheet surface layer in the steel which deteriorates the processability after annealing (hereinafter also referred to as surface concentration).
將下限溫度A定為600≦A≦780之理由如下。在低於600℃之溫度區域中即便不實施露點控制、不形成內部氧化,由於原本就是表面濃化少的溫度區域,因此不會阻礙化成處理性。又,在不控制露點並升溫至超過780℃之溫度的情況,由於表面濃化多,故氧之內部擴散受到阻礙,不易發生內部氧化。因此,必須至少從780℃以下之溫度區域控制為-10℃以上之露點。由上所述,A之容許範圍為A:600≦A≦780,根據上述理由,於該範圍內,A較佳係為儘可能低的值。The reason why the lower limit temperature A is set to 600 ≦ A ≦ 780 is as follows. In the temperature range of less than 600 ° C, even if the dew point control is not performed and internal oxidation is not formed, since it is originally a temperature region where the surface concentration is small, the formation processability is not inhibited. Further, when the dew point is not controlled and the temperature is raised to a temperature exceeding 780 ° C, since the surface is concentrated, the internal diffusion of oxygen is inhibited, and internal oxidation is less likely to occur. Therefore, it is necessary to control the dew point of at least -10 ° C from at least a temperature region of 780 ° C or less. From the above, the allowable range of A is A: 600 ≦ A ≦ 780. For the above reasons, A is preferably as low as possible within this range.
將上限溫度B定為800≦B≦900之理由如下。藉由形成內部氧化,使減少鋼板表層10μm以內之內部的易氧化性元素(Si、Mn等)的固溶量之區域(以下稱為缺乏層)形成,抑制易氧化性元素從鋼中向表面擴散。為了形成該內部氧化,並形成用以抑制表面濃化所充足的缺乏層,必須將B定在800≦B≦900。當低於800℃之情況,無法充分形成內部氧化。又,若超過900℃,則內部氧化之形成量過剩,會成為電著塗裝後之耐蝕性劣化的起點。The reason why the upper limit temperature B is set to 800 ≦ B ≦ 900 is as follows. By forming internal oxidation, a region (hereinafter referred to as a lacking layer) which reduces the amount of solid solution of an easily oxidizable element (Si, Mn, etc.) within 10 μm of the surface layer of the steel sheet is formed, and the oxidizable element is suppressed from the steel to the surface. diffusion. In order to form the internal oxidation and form a lacking layer sufficient to suppress surface enrichment, B must be set at 800 ≦ B ≦ 900. When it is lower than 800 ° C, internal oxidation cannot be sufficiently formed. Moreover, when it exceeds 900 °C, the amount of formation of internal oxidation is excessive, and it becomes a starting point of deterioration of corrosion resistance after electrocoating.
將A℃以上且B℃以下之溫度區域的露點定為-10℃以上之理由如下。藉由使露點上升,可使由H2 O之分解所生成的O2 位能上升,而促進內部氧化。在低於-10℃之溫度區域中,內部氧化之形成量少。又,露點之上限並未特別規定,但若超過90℃,則Fe之氧化量變多,有退火爐壁或輥劣化之虞,因此較佳為90℃以下。The reason why the dew point of the temperature range of A ° C or more and B ° C or less is set to -10 ° C or more is as follows. By raising the dew point, the O 2 position generated by the decomposition of H 2 O can be increased to promote internal oxidation. In the temperature region below -10 ° C, the amount of internal oxidation formed is small. Further, the upper limit of the dew point is not particularly limited. However, if it exceeds 90 ° C, the amount of oxidation of Fe increases, and the annealing furnace wall or the roll deteriorates. Therefore, it is preferably 90 ° C or lower.
其次,針對本發明對象之高強度鋼板的鋼成分組成進行說明。Next, the steel component composition of the high-strength steel sheet to which the present invention is applied will be described.
C:0.01~0.18%C: 0.01~0.18%
C係作為鋼組織而形成麻田散鐵等,藉此使加工性提升。因此,需要0.01%以上。另一方面,若超過0.18%,則延伸度降低,材質劣化,甚至使熔接性劣化。因此,C量係定為0.01%以上且0.18%以下。The C system forms a granulated iron or the like as a steel structure, thereby improving workability. Therefore, 0.01% or more is required. On the other hand, when it exceeds 0.18%, the elongation is lowered, the material is deteriorated, and the weldability is deteriorated. Therefore, the amount of C is set to be 0.01% or more and 0.18% or less.
Si:0.4~2.0%Si: 0.4~2.0%
Si係使鋼強化並提高延伸度,係用以獲得良好材質之有效元素,而為了獲得本發明目的之強度,需要0.4%以上。若Si未滿0.4%,則無法獲得本發明適用範圍之強度,化成處理性則不成問題。另一方面,若超過2.0%,則鋼之強化能力或延伸度提升效果飽和。此外,化成處理性之改善變得困難。因此,Si量係定為0.4%以上且2.0%以下。The Si system strengthens the steel and increases the elongation, and is used to obtain an effective element of a good material, and 0.4% or more is required in order to obtain the strength of the object of the present invention. If Si is less than 0.4%, the strength of the application range of the present invention cannot be obtained, and the chemical conversion processability is not a problem. On the other hand, if it exceeds 2.0%, the steel reinforcing ability or the elongation improving effect is saturated. In addition, improvement in chemical conversion process becomes difficult. Therefore, the amount of Si is set to be 0.4% or more and 2.0% or less.
Mn:1.0~3.0%Mn: 1.0~3.0%
Mn係鋼高強度化之有效元素。為了確保機械特性與強度,必須含有1.0%以上。另一方面,若超過3.0%,則難以確保熔接性或強度與延展性之平衡。因此,Mn量係定為1.0%以上且3.0%以下。An effective element for increasing the strength of Mn-based steel. In order to ensure mechanical properties and strength, it must be 1.0% or more. On the other hand, when it exceeds 3.0%, it is difficult to ensure the balance of weldability or strength and ductility. Therefore, the amount of Mn is set to be 1.0% or more and 3.0% or less.
Al:0.001~1.0%Al: 0.001~1.0%
Al係以熔鋼之脫酸作為目的而添加。0.001%以上可獲得熔鋼之脫酸效果。另一方面,若超過1.0%,則會導致成本增加。此外,Al之表面濃化會變多,化成處理性之改善變得困難。因此,Al量係定為0.001%以上且1.0%以下。Al is added for the purpose of deacidification of molten steel. The deacidification effect of the molten steel can be obtained by 0.001% or more. On the other hand, if it exceeds 1.0%, the cost will increase. Further, the surface concentration of Al is increased, and it becomes difficult to improve the processability. Therefore, the amount of Al is set to be 0.001% or more and 1.0% or less.
P:0.005~0.060%以下P: 0.005~0.060% or less
P係不可避免地含有之元素之一,若欲使其未滿0.005%,則有成本增加之顧慮,因此定為0.005%以上。另一方面,若P含有超過0.060%,則熔接性會劣化。此外,化成處理性之劣化變得激烈,即便利用本發明,仍難以提昇化成處理性。因此,P量係定為0.005%以上且0.060%以下。P is one of the elements inevitably contained, and if it is intended to be less than 0.005%, there is a concern that the cost increases, so it is 0.005% or more. On the other hand, when P contains more than 0.060%, the weldability may deteriorate. Further, the deterioration of the chemical conversion treatment property is fierce, and even with the present invention, it is difficult to improve the chemical conversion processability. Therefore, the amount of P is set to be 0.005% or more and 0.060% or less.
S≦0.01%S≦0.01%
S係不可避免地含有之元素之一。下限並無規定,若大量地含有,則熔接性與耐蝕性會劣化,因此定為0.01%以下。The S system inevitably contains one of the elements. The lower limit is not specified. When it is contained in a large amount, the weldability and the corrosion resistance are deteriorated, so that it is made 0.01% or less.
另外,為了控制強度與延展性之平衡,亦可視需要添加從B:0.001~0.005%、Nb:0.005~0.05%、Ti:0.005~0.05%、Cr:0.001~1.0%、Mo:0.05~1.0%、Cu:0.05~1.0%、Ni:0.05~1.0%中所選擇之1種以上的元素。In addition, in order to control the balance between strength and ductility, it is also possible to add from B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.05%, Cr: 0.001 to 1.0%, Mo: 0.05 to 1.0%. , Cu: 0.05 to 1.0%, and Ni: 0.05 to 1.0% of one or more selected elements.
添加該等元素之情況的適當添加量之限定理由如下。The reason for the appropriate addition amount in the case of adding these elements is as follows.
B:0.001~0.005%B: 0.001~0.005%
B若未滿0.001%則難以獲得淬火促進效果。另一方面,若超過0.005%,則化成處理性會劣化。因此,在含有之情況,B量係定為0.001%以上且0.005%以下。If B is less than 0.001%, it is difficult to obtain a quenching promoting effect. On the other hand, when it exceeds 0.005%, the chemical conversion processability will deteriorate. Therefore, in the case of being contained, the amount of B is set to be 0.001% or more and 0.005% or less.
Nb:0.005~0.05%Nb: 0.005~0.05%
Nb若未滿0.005%,則難以獲得強度調整之效果。另一方面,若超過0.05%,則會導致成本增加。因此,在含有之情況,Nb量係定為0.005%以上且0.05%以下。If Nb is less than 0.005%, it is difficult to obtain the effect of strength adjustment. On the other hand, if it exceeds 0.05%, the cost will increase. Therefore, in the case of being contained, the amount of Nb is set to be 0.005% or more and 0.05% or less.
Ti:0.005~0.05%Ti: 0.005~0.05%
Ti若未滿0.005%,則難以獲得強度調整之效果。另一方面,若超過0.05%,則會導致化成處理性劣化。因此,在含有之情況,Ti量係定為0.005%以上且0.05%以下。If Ti is less than 0.005%, it is difficult to obtain the effect of strength adjustment. On the other hand, when it exceeds 0.05%, the chemical conversion treatability deteriorates. Therefore, in the case of being contained, the amount of Ti is set to be 0.005% or more and 0.05% or less.
Cr:0.001~1.0%Cr: 0.001~1.0%
Cr若未滿0.001%,則難以獲得淬火促進效果。另一方面,若超過1.0%,則Cr會發生表面濃化,因而使熔接性劣化。因此,在含有之情況,Cr量係定為0.001%以上且1.0%以下。If Cr is less than 0.001%, it is difficult to obtain a quenching promoting effect. On the other hand, when it exceeds 1.0%, surface-concentration of Cr will occur, and the weldability will deteriorate. Therefore, in the case of being contained, the amount of Cr is set to be 0.001% or more and 1.0% or less.
Mo:0.05~1.0%Mo: 0.05~1.0%
Mo若未滿0.05%,則難以獲得強度調整之效果。另一方面,若超過1.0%,則會導致成本增加。因此,在含有之情況,Mo量係定為0.05%以上且1.0%以下。If Mo is less than 0.05%, it is difficult to obtain the effect of strength adjustment. On the other hand, if it exceeds 1.0%, the cost will increase. Therefore, in the case of being contained, the amount of Mo is set to be 0.05% or more and 1.0% or less.
Cu:0.05~1.0%Cu: 0.05~1.0%
Cu若未滿0.05%,則難以獲得殘留γ相形成促進效果。另一方面,若超過1.0%,則會導致成本增加。因此,在含有之情況,Cu量係定為0.05%以上且1.0%以下。When Cu is less than 0.05%, it is difficult to obtain a residual γ phase formation promoting effect. On the other hand, if it exceeds 1.0%, the cost will increase. Therefore, in the case of being contained, the amount of Cu is set to be 0.05% or more and 1.0% or less.
Ni:0.05~1.0%Ni: 0.05~1.0%
Ni若未滿0.05%,則難以獲得殘留γ相形成促進效果。另一方面,若超過1.0%,則會導致成本增加。因此,在含有之情況,Ni量係定為0.05%以上且1.0%以下。If Ni is less than 0.05%, it is difficult to obtain a residual γ phase formation promoting effect. On the other hand, if it exceeds 1.0%, the cost will increase. Therefore, in the case of being contained, the amount of Ni is set to be 0.05% or more and 1.0% or less.
上述以外之其餘部分係Fe及不可避免之雜質。The rest of the above is Fe and unavoidable impurities.
其次,針對本發明之高強度鋼板之製造方法與其限定理由進行說明。Next, the method for producing the high-strength steel sheet of the present invention and the reasons for its limitation will be described.
例如,在將具有上述化學成分之鋼予以熱軋後,進行冷軋,接著於連續式退火設備中進行退火後,進行化成處理。另外,此時,本發明中在退火時之加熱過程中,係將加熱爐內溫度:A℃以上且B℃以下(A:600≦A≦780,B:800≦B≦900)之溫度區域以環境之露點:-10℃以上進行。此係於本發明中最重要的要件。藉由如此在退火步驟中控制露點(亦即環境中氧分壓),提高氧位能,在正要對屬於易氧化性元素的Si或Mn等進行化成處理前,預先進行內部氧化,使鋼板表層部之Si、Mn之活動(activity)降低。然後,抑制該等元素之外部氧化,結果可改善化成處理性。又,上述中,亦有於熱軋結束後不施行冷軋而直接進行退火之情況。For example, after the steel having the above chemical composition is hot rolled, cold rolling is performed, followed by annealing in a continuous annealing apparatus, and then chemical conversion treatment is performed. Further, at this time, in the heating process during annealing in the present invention, the temperature in the heating furnace is a temperature range of A ° C or more and B ° C or less (A: 600 ≦ A ≦ 780, B: 800 ≦ B ≦ 900). Take the environment dew point: -10 °C or more. This is the most important requirement in the present invention. By controlling the dew point (that is, the oxygen partial pressure in the environment) in the annealing step to increase the oxygen potential energy, the internal oxidation is performed in advance before the chemical treatment of the Si or Mn which is an oxidizable element is performed. The activity of Si and Mn in the surface layer is lowered. Then, external oxidation of the elements is suppressed, and as a result, chemical conversion treatability can be improved. Further, in the above, there is a case where the cold rolling is performed without performing cold rolling after the completion of the hot rolling.
可以一般進行之條件進行。It can be carried out under normal conditions.
較佳係於熱軋後進行酸洗處理。利用酸洗步驟,將表面所生成之黑皮鏽去除,接著進行冷軋。另外,酸洗條件並無特別限定。It is preferred to carry out a pickling treatment after hot rolling. The black rust generated on the surface is removed by the pickling step, followed by cold rolling. Further, the pickling conditions are not particularly limited.
較佳係以40%以上且80%以下之軋縮率進行。若軋縮率未滿40%,則再結晶溫度會低溫化,因此機械特性容易劣化。另一方面,若軋縮率超過80%,則屬於高強度鋼板,故不僅會提高輥軋成本,退火時之表面濃化情形亦會增加,因此有化成處理性劣化之情況。It is preferably carried out at a reduction ratio of 40% or more and 80% or less. When the rolling reduction ratio is less than 40%, the recrystallization temperature is lowered, and thus the mechanical properties are easily deteriorated. On the other hand, when the rolling reduction ratio exceeds 80%, it belongs to a high-strength steel sheet, so that not only the rolling cost but also the surface concentration during annealing is increased, and thus the chemical conversion property is deteriorated.
對於經冷軋之鋼板或經熱軋之鋼板進行退火,接著施行化成處理。The cold-rolled steel sheet or the hot-rolled steel sheet is annealed, followed by a chemical conversion treatment.
在退火爐中係進行以前段之加熱帶將鋼板加熱至既定溫度之加熱步驟,並進行以後段之均熱帶於既定溫度下保持既定時間之均熱步驟。接著,進行冷卻步驟。In the annealing furnace, a heating step of heating the steel sheet to a predetermined temperature is carried out in the previous stage, and a soaking step of maintaining the tempering temperature in the subsequent stage at a predetermined temperature for a predetermined time is performed. Next, a cooling step is performed.
另外,如上所述,在加熱爐內溫度:A℃以上且B℃以下(A:600≦A≦780,B:800≦B≦900)之溫度區域以環境之露點成為-10℃以上之方式進行控制,進行退火。A℃以上且B℃以下之區域以外的退火爐內環境之露點並無特別限定,較佳為-50℃~-10℃。Further, as described above, in the temperature range of the heating furnace: A ° C or more and B ° C or less (A: 600 ≦ A ≦ 780, B: 800 ≦ B ≦ 900), the dew point of the environment becomes -10 ° C or more. Control is performed and annealing is performed. The dew point of the atmosphere in the annealing furnace other than the region of A ° C or more and B ° C or less is not particularly limited, but is preferably -50 ° C to -10 ° C.
退火爐內之氣體成分係由氮、氫及不可避免之雜質所構成。只要為不損及本發明效果者,亦可含有其他氣體成分。若退火爐內環境之氫濃度未滿1體積%,則無法獲得還原所帶來之活性化效果,化成處理性劣化。上限並無特別規定,若超過50體積%則會增加成本,且效果飽和。因此,氫濃度以1體積%以上且50體積%以下為佳。另外,退火爐內之氣體成分除了氫氣以外係由氮氣與不可避免之雜質氣體所構成。只要為不損及本發明效果者,亦可含有其他氣體成分。The gas component in the annealing furnace is composed of nitrogen, hydrogen, and unavoidable impurities. Any gas component may be contained as long as it does not impair the effects of the present invention. When the hydrogen concentration in the atmosphere in the annealing furnace is less than 1% by volume, the activation effect by reduction cannot be obtained, and the chemical conversion treatment property is deteriorated. The upper limit is not specifically defined, and if it exceeds 50% by volume, the cost is increased and the effect is saturated. Therefore, the hydrogen concentration is preferably 1% by volume or more and 50% by volume or less. Further, the gas component in the annealing furnace is composed of nitrogen gas and an unavoidable impurity gas in addition to hydrogen gas. Any gas component may be contained as long as it does not impair the effects of the present invention.
從750℃以上之溫度區域冷卻後,亦可視需要進行淬火、回火。其條件並無特別限定,但回火較佳係於150~400℃之溫度下進行。因若未滿150℃會有延伸度劣化之傾向,若超過400℃,則有硬度降低之傾向。After cooling from a temperature range of 750 ° C or higher, quenching and tempering may be performed as needed. The conditions are not particularly limited, but the tempering is preferably carried out at a temperature of from 150 to 400 °C. If the temperature is less than 150 ° C, the elongation tends to deteriorate, and if it exceeds 400 ° C, the hardness tends to decrease.
本發明中,即便未實施電解酸洗,仍可確保良好的化成處理性,但較佳係將退火時不可避免地產生之微量表面濃化物去除,而為了確保更良好的化成處理性,較佳係進行電解酸洗。In the present invention, even if electrolytic pickling is not performed, good chemical conversion treatability can be ensured, but it is preferred to remove a small amount of surface concentrate which is inevitably generated during annealing, and it is preferable to ensure better chemical conversion treatability. It is subjected to electrolytic pickling.
電解酸洗之條件並無特別限定,為了有效率地將退火後形成之不可避免地發生表面濃化之Si或Mn的氧化物去除,較佳係為電流密度1A/dm2 以上之交流電。交流電之理由在於,若將鋼板維持保持為陰極,則酸洗效果小,反之,若鋼板維持保持為陽極,則電解時溶出之Fe會累積於酸洗液中,酸洗液中之Fe濃度增大,若附著於鋼板表面則會發生乾燥污垢等之問題。The conditions of the electrolytic pickling are not particularly limited, and it is preferably an alternating current having a current density of 1 A/dm 2 or more in order to efficiently remove oxides of Si or Mn which are inevitably formed on the surface after annealing. The reason for the alternating current is that if the steel sheet is maintained at the cathode, the pickling effect is small. On the other hand, if the steel sheet is maintained at the anode, the Fe eluted during the electrolysis is accumulated in the pickling liquid, and the Fe concentration in the pickling liquid is increased. If it is attached to the surface of the steel sheet, problems such as drying of the dirt may occur.
此外,使用於電解酸洗之酸洗液並無特別限定,硝酸與氫氟酸對設備之腐蝕性強,於操作上必須特別注意,因此較不佳。又,鹽酸可能從陰極產生氯氣,較不佳。因此,若考慮腐蝕性與環境,較佳係使用硫酸。硫酸濃度較佳為5質量%以上且20質量%以下。若硫酸濃度未滿5質量%,則導電率降低,因此電解時之電解槽電壓(bath voltage)上升,有電源負荷增大之情況。另一方面,於超過20質量%之情況,因帶出效應(drag-out)所造成之損失大,成本上會有問題。Further, the pickling liquid used for electrolytic pickling is not particularly limited, and nitric acid and hydrofluoric acid are highly corrosive to equipment, and must be handled with particular care, and thus are not preferable. Also, hydrochloric acid may generate chlorine gas from the cathode, which is less preferred. Therefore, in consideration of corrosiveness and environment, it is preferred to use sulfuric acid. The sulfuric acid concentration is preferably 5% by mass or more and 20% by mass or less. When the sulfuric acid concentration is less than 5% by mass, the electrical conductivity is lowered. Therefore, the cell voltage at the time of electrolysis is increased, and the power supply load is increased. On the other hand, in the case of more than 20% by mass, the loss due to the drag-out is large, and there is a problem in cost.
電解液之溫度較佳為40℃以上且70℃以下。由於連續電解所造成之發熱會使浴溫上升,因此若未滿40℃會有酸洗效果降低之情況。又,有難以維持在未滿40℃之溫度的情況。又,從電解槽之內襯的耐久性之觀點而言,溫度超過70℃較為不佳。The temperature of the electrolytic solution is preferably 40 ° C or more and 70 ° C or less. Since the heat generated by continuous electrolysis causes the bath temperature to rise, if the temperature is less than 40 ° C, the pickling effect may be lowered. Moreover, it is difficult to maintain the temperature below 40 °C. Further, from the viewpoint of the durability of the inner liner of the electrolytic cell, the temperature exceeding 70 ° C is not preferable.
由上可獲得本發明之高強度鋼板。The high strength steel sheet of the present invention can be obtained from the above.
另外,如下所述,鋼板表面之構造係具有特徵。In addition, as described below, the structure of the surface of the steel sheet has characteristics.
從鋼板表面起100μm以內之鋼板表層部中,每單面係形成有合計0.010~0.50g/m2 之從Fe、Si、Mn、Al、P、進而B、Nb、Ti、Cr、Mo、Cu、Ni中所選擇之至少1種以上的氧化物。又,從鋼板表面起10μm為止之區域中,於粒界起1μm以內之基底鐵粒內係存在有結晶性Si、Mn系複合氧化物。In the surface layer portion of the steel sheet within 100 μm from the surface of the steel sheet, a total of 0.010 to 0.50 g/m 2 is formed from Fe, Si, Mn, Al, P, further B, Nb, Ti, Cr, Mo, Cu. At least one or more oxides selected from Ni. Further, in the region from the surface of the steel sheet of 10 μm, crystalline Si or Mn-based composite oxide is present in the base iron particles within 1 μm from the grain boundary.
於鋼中添加有Si及大量Mn之高強度鋼板中,為了滿足電著塗裝後之耐蝕性,必須更高度地控制可能成為腐蝕破裂等之起點的鋼板表層之組織、構造。因此,本發明中,首先,為了確保化成處理性,在退火步驟中為了提高氧位能係如上述般進行露點控制。其結果,藉由提高氧位能,屬於易氧化性元素之Si或Mn等係在正要化成處理前預先發生內部氧化,於鋼板表層部之Si、Mn的活動降低。然後,該等元素之外部氧化受到抑制,結果改善了化成處理性及電著塗裝後之耐蝕性。此外,此改善效果係使從鋼板表面起100μm以內之鋼板表層部中,每單面存在有0.010g/m2 以上之從Fe、Si、Mn、Al、P、進而B、Nb、Ti、Cr、Mo、Cu、Ni中所選擇之至少1種以上的氧化物。另一方面,若存在超過0.50g/m2 ,該效果則飽和,因此上限定為0.50g/m2 。In the high-strength steel sheet in which Si and a large amount of Mn are added to the steel, in order to satisfy the corrosion resistance after electrocoating, it is necessary to more highly control the structure and structure of the surface layer of the steel sheet which may become a starting point of corrosion cracking or the like. Therefore, in the present invention, first, in order to ensure chemical conversion treatability, dew point control is performed in order to increase the oxygen level in the annealing step as described above. As a result, by increasing the oxygen potential energy, Si or Mn which is an oxidizable element is internally oxidized before the chemical conversion treatment, and the activity of Si and Mn in the surface layer portion of the steel sheet is lowered. Then, the external oxidation of the elements is suppressed, and as a result, the chemical conversion treatability and the corrosion resistance after electrocoating are improved. In addition, in the surface layer portion of the steel sheet within 100 μm from the surface of the steel sheet, there are 0.010 g/m 2 or more of Fe, Si, Mn, Al, P, further B, Nb, Ti, Cr per one side. At least one or more oxides selected from the group consisting of Mo, Cu, and Ni. On the other hand, if more than 0.50 g/m 2 is present , the effect is saturated, so the upper limit is 0.50 g/m 2 .
又,當內部氧化物僅存在於粒界而不存在於粒內之情況,雖可抑制鋼中易氧化性元素之粒界擴散,但有無法充分抑制粒內擴散之情況。因此,本發明中係如上述,藉由在加熱爐內溫度:A℃以上且B℃以下(A:600≦A≦780,B:800≦B≦900)之溫度區域中,以環境之露點為-10℃以上之方式進行控制,不僅在粒界,在粒內亦發生內部氧化。具體而言,係於鋼板表層起10μm以內之區域,在粒界1μm以內之基底鐵粒內,使結晶性Si、Mn系複合氧化物存在。藉由於基底鐵粒內存在氧化物,氧化物附近之基底鐵粒內之固溶Si、Mn之量減少。其結果,可抑制Si、Mn之粒內擴散所造成的往表面之濃化。Further, when the internal oxide exists only in the grain boundary and does not exist in the grain, the grain boundary diffusion of the oxidizable element in the steel can be suppressed, but the intragranular diffusion cannot be sufficiently suppressed. Therefore, in the present invention, as described above, in the temperature range of the heating furnace: A ° C or more and B ° C or less (A: 600 ≦ A ≦ 780, B: 800 ≦ B ≦ 900), the environmental dew point Controlled at a temperature above -10 ° C, internal oxidation occurs not only in the grain boundaries but also in the grains. Specifically, in the region of the steel sheet surface layer within 10 μm, the crystalline Si and Mn-based composite oxide are present in the base iron particles within 1 μm of the grain boundary. Due to the presence of oxides in the base iron particles, the amount of solid solution Si and Mn in the base iron particles in the vicinity of the oxide is reduced. As a result, it is possible to suppress the concentration of the surface to be diffused by the intragranular diffusion of Si and Mn.
另外,本發明之製造方法所得之高強度鋼板的鋼板表面構造雖係如上述,但例如使上述氧化物在從鋼板表面起超過100μm之區域成長,亦無問題。又,在從鋼板表面起超過10μm之區域中,於離粒界1μm以上之基底鐵粒內使結晶性Si、Mn系複合氧化物存在,亦無問題。In addition, although the surface structure of the steel sheet of the high-strength steel sheet obtained by the production method of the present invention is as described above, for example, the oxide is grown in a region exceeding 100 μm from the surface of the steel sheet, and there is no problem. In addition, in the region of more than 10 μm from the surface of the steel sheet, the crystalline Si or Mn-based composite oxide is present in the base iron particles having a grain boundary of 1 μm or more, and there is no problem.
以下,根據實施例具體說明本發明。Hereinafter, the present invention will be specifically described based on examples.
將表1所示之鋼組成所構成的熱軋鋼板予以酸洗,去除黑皮鏽後,進行冷軋,獲得厚度1.0mm之冷軋鋼板。另外,一部分係未實施冷軋,亦準備去除黑皮鏽後之熱軋鋼板(厚度2.0mm)。The hot-rolled steel sheet having the steel composition shown in Table 1 was pickled to remove black rust, and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.0 mm. In addition, some of them were not subjected to cold rolling, and were also prepared to remove hot-rolled steel sheets (thickness: 2.0 mm) after black rust.
其次,將上述所得之冷軋鋼板及熱軋鋼板裝入連續退火設備。退火設備中,係如表2所示,控制加熱爐內溫度與露點並通板進行退火後,於水淬火後進行300℃×140秒之回火。接著,於40℃、5質量%之硫酸水溶液中,以表2所示之電流密度條件,將樣品以陽極、陰極之順序,以各3秒之交流電進行電解酸洗,獲得樣品。另外,上述控制露點之區域以外的退火爐之露點係以-35℃為基本。又,環境之氣體成分係由氮氣與氫氣及不可避免的雜質氣體所構成,露點係將環境中之水分予以除濕或吸收去除而進行控制。環境中之氫濃度係以10體積%為基本。Next, the cold-rolled steel sheet and the hot-rolled steel sheet obtained above were placed in a continuous annealing apparatus. In the annealing equipment, as shown in Table 2, the temperature and the dew point in the heating furnace were controlled and annealed through a plate, and then tempered at 300 ° C for 140 seconds after water quenching. Next, the sample was subjected to electrolytic pickling in the order of the anode and the cathode in the order of the anode and the cathode at 40 ° C and a 5 mass % sulfuric acid aqueous solution under the current density conditions shown in Table 2 to obtain a sample. Further, the dew point of the annealing furnace other than the above-mentioned area for controlling the dew point is based on -35 °C. Further, the environmental gas component is composed of nitrogen gas, hydrogen gas, and unavoidable impurity gas, and the dew point is controlled by dehumidifying or absorbing and removing moisture in the environment. The concentration of hydrogen in the environment is based on 10% by volume.
對於所得之樣品,根據JIS Z 2241金屬材料拉伸試驗方法測定TS、El。又,對所得之樣品調查化成處理性及耐蝕性。測定存在於鋼板表層正下方至100μm為止之鋼板表層部的氧化物之量(內部氧化量)。測定方法及評估基準如下所示。For the obtained sample, TS and El were measured in accordance with JIS Z 2241 Metallic Material Tensile Test Method. Further, the obtained samples were investigated for chemical conversion properties and corrosion resistance. The amount of oxide (internal oxidation amount) of the surface layer portion of the steel sheet which was present immediately below the surface layer of the steel sheet to 100 μm was measured. The measurement method and evaluation criteria are as follows.
化成處理性之評估方法記載如下。The evaluation method of the chemical conversion treatment is described below.
化成處理液係使用日本PARKERIZING(股)製之化成處理液(Parbond L3080(註冊商標)),以下述方法施行化成處理。For the chemical conversion treatment liquid, a chemical conversion treatment liquid (Parbond L3080 (registered trademark)) manufactured by Japan PARKERIZING Co., Ltd. was used, and the chemical conversion treatment was carried out in the following manner.
以日本PARKERIZING(股)製之脫脂液Fine Cleaner(註冊商標)脫脂後,進行水洗,接著以日本PARKERIZING(股)製之表面調整液Prepan Z(註冊商標)進行30秒之表面調整,於43℃之化成處理液(Parbond L3080)中浸漬120秒後,進行水洗並以溫風乾燥。After degreasing with the degreasing liquid Fine Cleaner (registered trademark) manufactured by Japan PARKERIZING Co., Ltd., it was washed with water, and then subjected to surface conditioning of Prepan Z (registered trademark) manufactured by Japan PARKERIZING Co., Ltd. for 30 seconds at 43 ° C. After immersing in the chemical conversion liquid (Parbond L3080) for 120 seconds, it was washed with water and dried with warm air.
將化成處理後之樣品利用掃瞄型電子顯微鏡(SEM)以倍率500倍隨機觀察5視野,利用影像處理測定化成處理皮膜之空孔面積率,利用空孔面積率進行以下之評估。○為合格等級。The sample after the chemical conversion treatment was randomly observed with a scanning electron microscope (SEM) at a magnification of 500 times, and the area of the pores of the chemical conversion treatment film was measured by image processing, and the following evaluation was performed using the pore area ratio. ○ is a qualified level.
○:10%以下○: 10% or less
╳:超過10%╳: More than 10%
從上述方法所得之經化成處理的樣品中切出尺寸70mm×150mm之試驗片,以Nippon Paint(股)製之PN-150G(註冊商標)進行陽離子電著塗裝(硬化條件:170℃×20分鐘,膜厚25μm)。其後,將端部與不進行評估之側的面以A1膠帶進行密封,以切刀橫切至到達基底鐵(橫切角度60°),作為樣品。A test piece having a size of 70 mm × 150 mm was cut out from the chemically-treated sample obtained by the above method, and cationic electrocoating was carried out using PN-150G (registered trademark) manufactured by Nippon Paint Co., Ltd. (hardening condition: 170 ° C × 20 Minutes, film thickness 25 μm). Thereafter, the end portion and the side on which the evaluation was not performed were sealed with an A1 tape, and the cutter was transversely cut to reach the base iron (transverse angle of 60°) as a sample.
其次,將樣品於5質量%NaCl水溶液(55℃)中浸漬240小時後取出,水洗並乾燥後,將橫切部進行膠帶剝離,測定剝離寬度,進行以下之評估。○為合格等級。Next, the sample was immersed in a 5% by mass aqueous NaCl solution (55 ° C) for 240 hours, and then taken out, washed with water, and dried. Then, the cross-section was subjected to tape peeling, and the peeling width was measured, and the following evaluation was performed. ○ is a qualified level.
○:剝離寬度係單側未滿2.5mm○: peeling width is less than 2.5 mm on one side
╳:剝離寬度係單側2.5mm以上╳: peeling width is more than 2.5mm on one side
加工性係在相對於輥軋方向90°之方向,從試料採取JIS5號拉伸試驗片,依據JIS Z 2241之規定,以十字頭(crosshead)速度固定10mm/min,進行拉伸試驗,測定拉伸強度(TS/MPa)與延伸度(El%),當TS未滿650MPa之情況,TS×El≧22000者為良好,TS×El<22000者為不良。當TS為650MPa以上且900MPa之情況,TS×El≧20000者為良好,TS×El<20000者為不良。當TS為900MPa以上之情況,TS×El≧18000者為良好,TS×El<18000者為不良。The workability was measured in the direction of 90° with respect to the rolling direction, and the JIS No. 5 tensile test piece was taken from the sample, and the tensile test was carried out at a crosshead speed of 10 mm/min in accordance with JIS Z 2241. Stretching strength (TS/MPa) and elongation (El%). When TS is less than 650 MPa, TS × El ≧ 22,000 is good, and TS × El < 2 2,000 is bad. When TS is 650 MPa or more and 900 MPa, TS × El ≧ 20000 is good, and TS × El < 2000 is bad. When TS is 900 MPa or more, TS × El ≧ 18000 is good, and TS × El < 18000 is bad.
內部氧化量係利用「脈衝爐熔融-紅外線吸收法」測定。惟,由於必須扣除素材(亦即實施退火前之高強度鋼板)中所含之氧量,故本發明中,係將連續退火後之高強度鋼板的兩面之表層部研磨100μm以上,測定鋼中氧濃度,以該測定值作為素材所含之氧量OH,並且測定連續退火後之高強度鋼板的板厚方向整體之鋼中氧濃度,將該測定值作為內部氧化後之氧量OI。使用如此所得之高強度鋼板之內部氧化後的氧量OI與素材中所含之氧量OH,算出OI與OH之差(=OI-OH),進一步以換算為單面單位面積(亦即1m2 )之量的值(g/m2 )作為內部氧化量。The internal oxidation amount is measured by "pulse furnace melting-infrared absorption method". However, since it is necessary to subtract the amount of oxygen contained in the material (that is, the high-strength steel sheet before annealing), in the present invention, the surface layer portions of both surfaces of the high-strength steel sheet after continuous annealing are polished to 100 μm or more, and the steel is measured. The oxygen concentration is determined by using the measured value as the oxygen amount OH contained in the material, and the oxygen concentration in the steel in the thickness direction of the high-strength steel sheet after continuous annealing is measured, and the measured value is taken as the oxygen amount OI after the internal oxidation. Using the oxygen content OI after internal oxidation of the high-strength steel sheet thus obtained and the amount of oxygen OH contained in the material, the difference between OI and OH (=OI-OH) is calculated, and further converted into a single-sided unit area (that is, 1 m). 2 ) The amount of the amount (g/m 2 ) is taken as the internal oxidation amount.
將以上所得之結果與製造條件一起示於表2。The results obtained above are shown in Table 2 together with the production conditions.
由表2可知,本發明法所製造之高強度鋼板,雖係大量含有Si、Mn等之易氧化性元素的高強度鋼板,但化成處理性、電著塗裝後之耐蝕性、加工性優異。As can be seen from Table 2, the high-strength steel sheet produced by the method of the present invention is a high-strength steel sheet containing a large amount of easily oxidizable elements such as Si or Mn, but has excellent chemical conversion properties and corrosion resistance and workability after electrocoating. .
另一方面,比較例中,化成處理性、電著塗裝後之耐蝕性、加工性係有任一者以上不佳。On the other hand, in the comparative example, the chemical conversion treatment property, the corrosion resistance after the electrocoating, and the workability are not preferable.
本發明之高強度鋼板係化成處理性、耐蝕性、加工性優異,可利用作為用以使汽車車體本身輕量化且高強度化之表面處理鋼板。又,除了汽車之外,亦可做成對素材鋼板賦予防鏽性之表面處理鋼板,應用於家電、建材領域等之廣泛領域。The high-strength steel sheet of the present invention is excellent in chemical conversion treatability, corrosion resistance, and workability, and can be used as a surface-treated steel sheet for reducing the weight and height of the automobile body itself. In addition to the automobile, the surface-treated steel sheet which imparts rust resistance to the material steel sheet can be used in a wide range of fields such as home appliances and building materials.
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TWI302571B (en) * | 2005-10-14 | 2008-11-01 | Nippon Steel Corp | A method for continuous annealing and hot-dip plating of silicon-containing steel sheet and an apparatus for carrying out the same |
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