TWI503422B - Ferritic stainless steel excellent in corrosion resistance and workability - Google Patents
Ferritic stainless steel excellent in corrosion resistance and workability Download PDFInfo
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Description
本發明係關於具優異耐蝕性及加工性之肥粒鐵系不鏽鋼,其係可適宜地使用於如二次熱交換器般曝露於低pH值且存在有氯化物的環境中的部件。The present invention relates to a ferrite-based iron-based stainless steel having excellent corrosion resistance and workability, which can be suitably used for a member exposed to a low pH and in the presence of a chloride, such as a secondary heat exchanger.
本申請案係主張基於在2011年9月6日於日本提申之日本特願2011-193915號案的優先權,並將其之內容引用於此。The present application claims priority based on Japanese Patent Application No. 2011-193915, filed on Sep. 6, 2011.
在燃燒各種各樣的化石燃料所產生的廢氣中,含有來自燃料/大氣的SOx及NOx。此等成分與大氣中的氧或水蒸氣反應而產生H2 SO4 及HNO3 等,或在雲水中濕沈降,又或者是在大氣中作為氣溶膠而乾沈降。這被視為是產生酸雨的機制。酸雨係pH值為5.6以下左右的雨,分別包含各約10ppm的SO4 2- 離子及NO3 - 離子。特別係在工業區及產生火山氣體的地區來說,酸雨的pH值更低且包含許多SO4 2- 離子及NO3 - 離子。進一步,有以數ppm~100ppm的量來包含來自海鹽等的氯化物的可能性。要是附著了這樣成分的雨水,因乾燥而使得低pH化與濃縮進展,而成為嚴苛的腐蝕環境。惟,與熱交換器所暴露之廢氣會直接凝結般的環境相較,則這樣的酸雨環境係輕度的腐蝕環境。The exhaust gas generated by burning various fossil fuels contains SOx and NOx from fuel/atmosphere. These components react with oxygen or water vapor in the atmosphere to produce H 2 SO 4 , HNO 3 , etc., or wet settle in cloud water, or dry settle as an aerosol in the atmosphere. This is seen as a mechanism for acid rain. The acid rain has a pH of about 5.6 or less, and contains about 10 ppm of SO 4 2- ions and NO 3 - ions, respectively. Especially in industrial areas and areas where volcanic gases are produced, acid rain has a lower pH and contains many SO 4 2- ions and NO 3 - ions. Further, there is a possibility that the chloride derived from sea salt or the like is contained in an amount of several ppm to 100 ppm. If rainwater adhered to such a component is dried, the pH is lowered and the concentration progresses, and it becomes a severe corrosive environment. However, such an acid rain environment is a mild corrosive environment as compared with an environment in which the exhaust gas exposed to the heat exchanger directly condenses.
熱交換器係使各種各樣的燃料燃燒將產生的 熱,供給至以水為主的介質的裝置,其被使用於各種各樣的領域,從核能發電的蒸氣產生器至一般家庭的熱水器。其中,在一般家庭的瓦斯熱水器或是石油熱水器中亦為了利用其之燃燒熱來將水做成熱水而在內置在熱交換器內。習知此熱交換器為了提高熱效率,使用易加工成鰭狀結構等且傳熱性優異的銅至今。然而因為近年的環境問題,在熱水器亦要求CO2 的減量。因為這個原因,以進一步提高熱效率為目的,開發了進一步利用習知廢氣之熱的潛熱回收型熱水器。此熱水器係進一步利用使通過習知之熱交換器(一次熱交換器)後之氣體及石油燃燒所生之廢氣的熱。因為這個原因,而還具有另一個熱交換器(二次熱交換器)。通過一次熱交換器之後的廢氣約係150~200℃,且包含大量的水蒸氣。因為這個原因,就二次熱交換器來說,不單只是直接的熱,還藉由回收水蒸氣成為水滴的凝結熱也就是潛熱,來使總熱效率提升到95%以上。此潛熱回收型熱水器結構的一例,例如係揭示於專利文獻1。The heat exchanger is a device that supplies heat generated by combustion of various fuels to a water-based medium, and is used in various fields, from a steam generator for nuclear power generation to a water heater for a general household. Among them, in general household gas water heaters or oil water heaters, in order to use the combustion heat thereof to make water into hot water, it is built in the heat exchanger. Conventionally, in order to improve the heat efficiency, this heat exchanger has been used for copper which is easy to process into a fin structure and has excellent heat transfer properties. However, due to environmental problems in recent years, the reduction of CO 2 is also required in water heaters. For this reason, in order to further improve the heat efficiency, a latent heat recovery type water heater that further utilizes the heat of the conventional exhaust gas has been developed. The water heater further utilizes heat of exhaust gas generated by combustion of gas and petroleum after a conventional heat exchanger (primary heat exchanger). For this reason, there is another heat exchanger (secondary heat exchanger). The exhaust gas after passing through the primary heat exchanger is about 150 to 200 ° C and contains a large amount of water vapor. For this reason, in the case of the secondary heat exchanger, not only the direct heat but also the condensation heat of the water droplets is the latent heat of the water droplets, so that the total heat efficiency is increased to 95% or more. An example of the structure of the latent heat recovery type water heater is disclosed, for example, in Patent Document 1.
於此處,在二次熱交換器產生的凝結水係生成自廢氣,該廢氣係使城鎮氣體燃料或LPG、石油等碳氫化合物系原料燃燒所生者。因為這個原因,凝結水包含來自該廢氣成分等的硝酸根離子及硫酸根離子,而成為pH值為約3以下的弱酸性水溶液。就此低pH值的溶液來說,習知所使用的銅(在pH值為6.5以下會腐蝕)係不能使用。即便係其它的普通鋼(在pH值為約7以下會腐蝕)及鋁(在pH值為約3以下會腐蝕),在暴露於上述凝結水的環境中亦會腐蝕。因 此,現在選定在弱酸性範圍中耐蝕性優異的不鏽鋼作為二次熱交換器用之材料,在通用不鏽鋼之中主要亦係採用耐蝕性更優異的奧斯田鐵系不鏽鋼的SUS316L(18Cr-10Ni-2Mo)。SUS316L滿足應用於潛熱回收型熱水器之二次熱交換器部件所必須的耐蝕性。惟,該原料來說,大量包含價格昂貴且價格安定性係非常不安定的Ni及Mo。潛熱回收型熱水器被期待廣泛普遍的普及化,作為CO2 減量的妙策,為使此實現,迫切期望材料進一步的成本降低與良好的加工性。就二次熱交換器材料之SUS316L來說,當然期待著更低成本之替代材料的提案。又,在一般的使用環境來說雖被視作沒有耐蝕性的問題,但在妨礙不鏽鋼耐蝕性主要原因之一的海鹽粒子容易飛來的海岸附近等地區來說,即便係SUS316L亦不能否認發生腐蝕的可能性。此狀況時,就SUS316L來說,有發生應力腐蝕裂痕的可能性,該應力腐蝕裂痕係奧斯田鐵系不鏽鋼的弱點之一。Here, the condensed water generated in the secondary heat exchanger is generated from an exhaust gas which is produced by burning a municipal gas fuel, a hydrocarbon-based raw material such as LPG or petroleum. For this reason, the condensed water contains nitrate ions and sulfate ions derived from the exhaust gas component and the like, and becomes a weakly acidic aqueous solution having a pH of about 3 or less. For this low pH solution, the copper used (which corrodes below pH 6.5) cannot be used. Even other ordinary steels (corrosive at pH values below about 7) and aluminum (corrosive at pH values below about 3) can corrode in environments exposed to the above condensed water. Therefore, stainless steel which is excellent in corrosion resistance in the weakly acidic range is selected as the material for the secondary heat exchanger. Among the general-purpose stainless steels, the SUS316L (18Cr-10Ni- of the Osfield iron-based stainless steel which is more excellent in corrosion resistance is also used. 2Mo). SUS316L meets the corrosion resistance necessary for secondary heat exchanger components used in latent heat recovery water heaters. However, this raw material contains a large amount of Ni and Mo which are expensive and have a very stable price stability. A latent heat recovery type water heater is expected to be widely used in general, and as a countermeasure for CO 2 reduction, in order to achieve this, further cost reduction and good processability of materials are urgently desired. As for the SUS316L of the secondary heat exchanger material, of course, a proposal for a lower cost alternative material is expected. In addition, in the general use environment, it is considered that there is no problem of corrosion resistance. However, in areas such as the coast where sea salt particles, which are one of the main causes of corrosion resistance of stainless steel, are likely to fly, even SUS316L cannot be denied. The possibility of corrosion. In this case, in the case of SUS316L, there is a possibility that stress corrosion cracking occurs, and the stress corrosion cracking is one of the weaknesses of the Osbane iron-based stainless steel.
為了解決應用奧斯田鐵系不鏽鋼之際發生的這樣的問題,近年,嘗試進行將肥粒鐵系不鏽鋼應用於二次熱交換器部件(專利文獻2~6)。In recent years, attempts have been made to apply ferrite-grained stainless steel to secondary heat exchanger components (Patent Documents 2 to 6) in order to solve the problem of the application of the Oswego iron-based stainless steel.
專利文獻2提案將肥粒鐵系不鏽鋼作為對含硫氣體具有耐蝕性的熱交換器材料。就此肥粒鐵系不鏽鋼來說,與Nb或Ti一起添加有Mo,藉此,抑制耐蝕性的降低且可謀求高溫強度的提升。又,藉由降低Si及Al的含量,來謀求焊接性及成形性的提升。Patent Document 2 proposes a ferrite-based iron-based stainless steel as a heat exchanger material having corrosion resistance to a sulfur-containing gas. In the ferrite-based iron-based stainless steel, Mo is added together with Nb or Ti, whereby the deterioration of corrosion resistance is suppressed and the high-temperature strength can be improved. Further, by reducing the contents of Si and Al, it is possible to improve weldability and formability.
專利文獻3揭示在高溫的水蒸氣環境下發揮耐久性的肥粒鐵系不鏽鋼,高溫的水蒸氣環境係熱交換器所暴露的環境。就此肥粒鐵系不鏽鋼來說,調整成分來滿足由Cr、Mo、Si及Al的含量與使用預定溫度所導出的特定關係式。惟,由於Al添加量多,有材料變得非常硬且脆的問題。還有,設想的溫度係300~1000℃,係定為在較作為本發明之對象的潛熱回收型熱水器還要高溫之非常高溫的環境下所使用的材料。Patent Document 3 discloses an environment in which a ferrite-based iron-based stainless steel exhibiting durability in a high-temperature steam environment and a high-temperature water vapor-based heat exchanger is exposed. In the case of the ferrite-based stainless steel, the composition is adjusted to satisfy a specific relationship derived from the contents of Cr, Mo, Si, and Al and the use of a predetermined temperature. However, due to the large amount of Al added, there is a problem that the material becomes very hard and brittle. In addition, the temperature of 300 to 1000 ° C is assumed to be a material used in an environment of a very high temperature which is higher than that of the latent heat recovery type water heater which is the object of the present invention.
專利文獻4揭示具有優異焊接性的肥粒鐵系不鏽鋼,其特徵在於降低了Ti及Al的含量。Patent Document 4 discloses a ferrite-based iron-based stainless steel having excellent weldability, which is characterized in that the content of Ti and Al is lowered.
專利文獻5揭示肥粒鐵系不鏽鋼,其係適宜作為在供至焊接的熱交換器部件。就此肥粒鐵系不鏽鋼來說,調整成分使得由Nb、C及N的含量所算出的A值成為0.1以上。但是,在焊接中之熱處理時為防止結晶粒粗化一事,將Nb當作必要元素,卻沒有指出如何提升耐蝕性。Patent Document 5 discloses a ferrite-based iron-based stainless steel which is suitable as a heat exchanger member for supplying to welding. In the ferrite-based iron-based stainless steel, the composition is adjusted such that the A value calculated from the contents of Nb, C, and N is 0.1 or more. However, in order to prevent coarsening of crystal grains during heat treatment in welding, Nb is regarded as an essential element, but there is no indication of how to improve corrosion resistance.
專利文獻6揭示焊接用的肥粒鐵系不鏽鋼材及熱交換器部件。為了防止高溫焊接時的粗粒化,規定了再結晶粒所占的面積比,卻沒有指出如何提升耐蝕性。Patent Document 6 discloses a ferrite-grained stainless steel material for welding and a heat exchanger member. In order to prevent coarse graining during high-temperature welding, the area ratio of recrystallized grains is specified, but there is no indication of how to improve corrosion resistance.
又,二次熱交換器的熱交換管有必要進行彎曲加工,一部分製品來說亦利用有可撓性管。因為這個原因,對熱交換器部件要求良好的加工性。習知所使用至今的奧斯田鐵系不鏽鋼雖具有充分的加工性,但在加工性上肥粒鐵系不鏽鋼係劣於奧斯田鐵系不鏽鋼。因為這個原因,特別需求具優異加工性的材料。Further, the heat exchange tubes of the secondary heat exchanger are required to be bent, and a part of the products are also made of a flexible tube. For this reason, good processability is required for the heat exchanger components. Although the Osbane-based stainless steel used in the prior art has sufficient workability, the ferrite-based stainless steel is inferior to the Osbane-based stainless steel in processing. For this reason, materials having excellent workability are particularly required.
就習知知識來說,沒有提及在低pH值且存在有氯化物的環境中耐蝕性與加工性任一者的先行技術,不能說係充分揭露在這般的環境下可適宜地使用的肥粒鐵系不鏽鋼的狀況。As far as the prior knowledge is concerned, there is no mention of the prior art of corrosion resistance and processability in a low pH and chloride-containing environment, and it cannot be said that it is sufficiently disclosed that it can be suitably used in such an environment. The condition of the ferrite iron stainless steel.
專利文獻1:日本特開2002-106970號公報Patent Document 1: Japanese Patent Laid-Open Publication No. 2002-106970
專利文獻2:日本特開平7-292446號公報Patent Document 2: Japanese Patent Laid-Open No. Hei 7-292446
專利文獻3:日本特開2003-328088號公報Patent Document 3: Japanese Patent Laid-Open Publication No. 2003-328088
專利文獻4:日本特開2009-174046號公報Patent Document 4: Japanese Laid-Open Patent Publication No. 2009-174046
專利文獻5:日本特開2009-299182號公報Patent Document 5: Japanese Laid-Open Patent Publication No. 2009-299182
專利文獻6:日本特開2010-285683號公報。Patent Document 6: Japanese Laid-Open Patent Publication No. 2010-285683.
有鑑於這樣的事情,本發明係以提供廉價且具優異耐蝕性,並且具有良好加工性,可在上述環境中適宜地使用的肥粒鐵系不鏽鋼為目的。In view of the above, the present invention has an object of providing a ferrite-based iron-based stainless steel which is inexpensive and has excellent corrosion resistance and has good processability and can be suitably used in the above environment.
本發明人等為解決上述課題,評價在這樣的環境下之各種不鏽鋼的耐蝕性。其結果揭明了Cr、Al及Ti之含量多且特別係當該等係濃縮在鈍化膜表面的狀況時,耐蝕性特別優異。In order to solve the above problems, the inventors of the present invention evaluated the corrosion resistance of various stainless steels in such an environment. As a result, it has been revealed that the contents of Cr, Al, and Ti are large, and particularly when such a system is concentrated on the surface of the passivation film, the corrosion resistance is particularly excellent.
還有,從產生之腐蝕起始點的評價,認知到以下事項。Also, from the evaluation of the origin of corrosion generated, the following matters were recognized.
(a)藉由降低Cu及Si的含量,在作為對象的環境中的耐蝕性提升。(a) By reducing the content of Cu and Si, the corrosion resistance in the target environment is improved.
(b)進一步,藉由降低Mo及Ni的含量,加工性提升。(b) Further, workability is improved by lowering the contents of Mo and Ni.
本發明係以這樣的二次熱交換器內部為對象,專精進行在低pH值且存在氯化物的腐蝕環境中耐蝕性優異材料的檢討。其結果,開發了在為對象之環境中具優異耐蝕性及加工性的肥粒鐵系不鏽鋼。The present invention is directed to the inside of such a secondary heat exchanger, and is specialized in conducting a review of a material excellent in corrosion resistance in a corrosive environment having a low pH and a chloride. As a result, a ferrite-based iron-based stainless steel having excellent corrosion resistance and workability in a target environment has been developed.
即,本發明具有以下特徴,且係在低pH值且存在氯化物之環境中亦具有優異耐蝕性與良好加工性之肥粒鐵系不鏽鋼。That is, the present invention has the following characteristics, and is a ferrite-based iron-based stainless steel which has excellent corrosion resistance and good processability in an environment of low pH and presence of chloride.
(1)一種具優異耐蝕性及加工性之肥粒鐵系不鏽鋼,其特徵在於:以質量%計,含有C:0.030%以下、N:0.030%以下、Si:0.60%以下、Mn:0.01~0.5%、P:0.05%以下、S:0.01%以下、Cr:13~22.5%、Ni:低於0.35%、Ti:0.05~0.30%、Al:0.01~0.2%、Cu:0.5%以下,以及Mo:低於0.30%,而剩餘部份係Fe及不可避免的不純物,並且滿足下述(A)式及(B)式:(A)式:Cr+10Ti+10Al≧15;(B)式:Si+Cu≦1.1;(但是,式中之Cr、Ti、Al、Si及Cu係意指各別元素的含量(質量%))。(1) A ferrite-based iron-based stainless steel having excellent corrosion resistance and workability, characterized by containing C: 0.030% or less, N: 0.030% or less, Si: 0.60% or less, and Mn: 0.01% by mass%. 0.5%, P: 0.05% or less, S: 0.01% or less, Cr: 13 to 22.5%, Ni: less than 0.35%, Ti: 0.05 to 0.30%, Al: 0.01 to 0.2%, Cu: 0.5% or less, and Mo: less than 0.30%, and the remainder is Fe and unavoidable impurities, and satisfy the following formulas (A) and (B): (A): Cr+10Ti+10Al≧15; (B) :Si+Cu≦1.1; (However, Cr, Ti, Al, Si, and Cu in the formula means the content (% by mass) of each element).
(2)如前述第(1)項之具優異耐蝕性及加工性之肥粒鐵系不鏽鋼,其進一步含有Nb:0.05~0.50%。(2) The ferrite-based iron-based stainless steel having excellent corrosion resistance and workability as in the above item (1), further containing Nb: 0.05 to 0.50%.
(3)如前述第(1)或(2)項之具優異耐蝕性及加工性之肥粒鐵系不鏽鋼,其進一步含有Sn:0.005~1.0%。(3) The ferrite-based iron-based stainless steel having excellent corrosion resistance and workability as in the above item (1) or (2), further containing Sn: 0.005 to 1.0%.
(4)如前述第(1)~(3)項中任一項之具優異耐蝕性及加工性之肥粒鐵系不鏽鋼,其進一步含有B:0.0001~0.003%及V:0.03~1.0%中任一者或兩者元素。(4) The ferrite-based iron-based stainless steel having excellent corrosion resistance and workability according to any one of the above items (1) to (3), further comprising B: 0.0001 to 0.003% and V: 0.03 to 1.0% Either or both elements.
(5)如前述第(1)~(4)項中任一項之具優異耐蝕性及加工性之肥粒鐵系不鏽鋼,其滿足下述(B’)式以取代前述(B)式:(B’)式:Si+Cu≦0.5;(但是,式中之Si及Cu係意指各個元素的含量(質量%))。(5) The ferrite-based iron-based stainless steel having excellent corrosion resistance and workability according to any one of the above items (1) to (4), which satisfies the following formula (B') in place of the above formula (B): (B') Formula: Si + Cu ≦ 0.5; (However, Si and Cu in the formula means the content (% by mass) of each element).
(6)如前述第(1)~(5)項中任一項之具優異耐蝕性及加工性之肥粒鐵系不鏽鋼,其透過經使用酸雨的模擬液進行的腐蝕試驗所測定的平均腐蝕失重為0.4mg/cm2 以下;前述腐蝕試驗中,係使用pH值為4.5且含有10ppm之硝酸根離子、10ppm之硫酸根離子,及5ppm之氯離子的水溶液作為前述模擬液,實施乾濕反覆試驗10次循環,並測定前述乾濕反覆試驗後之質量的減少量,而獲得前述平均腐蝕失重;該前述乾濕反覆試驗係使賦有間隙的試驗片半浸漬於前述水溶液中,並在50℃下保持24小時者。(6) A ferrite-based iron-based stainless steel having excellent corrosion resistance and workability as described in any one of the above items (1) to (5), which is subjected to an average corrosion measured by a corrosion test using a simulated liquid using acid rain The weight loss is 0.4 mg/cm 2 or less; in the above corrosion test, an aqueous solution having a pH of 4.5 and containing 10 ppm of nitrate ions, 10 ppm of sulfate ions, and 5 ppm of chloride ions is used as the above-mentioned simulated liquid, and dry and wet repeating is performed. The above-mentioned average corrosion loss was obtained by measuring 10 times of the cycle and measuring the mass reduction after the dry-wet test, and the dry-wet test was performed by semi-immersing the test piece with the gap in the aqueous solution at 50 ° C. Hold for 24 hours.
(7)如前述第(6)項之具優異耐蝕性及加工性之肥粒鐵系不鏽鋼,其透過經使用燃燒廢氣之凝結水的模擬液進行的腐蝕試驗所測定的平均腐蝕失重為1.0mg/cm2 以下;前述腐蝕試驗中,係使用pH值為2.5且含有100ppm之硝酸根離子、10ppm之硫酸根離子及100ppm之氯離子的水溶液作為前述模擬液,實施乾濕反覆試驗10次循環,並測定 前述乾濕反覆試驗後之質量的減少量,而獲得前述平均腐蝕失重;該前述乾濕反覆試驗係使賦有間隙的試驗片半浸漬於前述水溶液中,並在80℃下保持24小時者。(7) The ferrite-based iron-based stainless steel having excellent corrosion resistance and workability as described in the above item (6), which has an average corrosion weight loss of 1.0 mg as measured by a corrosion test using a simulated liquid using condensed water for burning exhaust gas. /cm 2 or less; in the above corrosion test, an aqueous solution having a pH of 2.5 and containing 100 ppm of nitrate ions, 10 ppm of sulfate ions, and 100 ppm of chloride ions was used as the above-mentioned simulated liquid, and the dry-wet repeated test was carried out for 10 cycles. And determining the above-mentioned average corrosion loss by the amount of reduction after the dry-wet test, wherein the dry-wet test is semi-immersed in the aqueous solution and maintained at 80 ° C for 24 hours. .
依據本發明之態樣,可提供在例如酸雨般低pH值且存在有氯化物之環境中具有優異耐蝕性與良好加工性的肥粒鐵系不鏽鋼。又,與奧斯田鐵系不鏽鋼不同,此肥粒鐵系不鏽鋼未大量含有昂貴的Ni及Mo。特別地依據本發明適宜的態樣,作為如熱水器等等般暴露於將LNG或石油等碳氫化合物作為燃料的燃燒氣體之凝結水的環境中之機械材料亦可發揮優異的耐蝕性。According to the aspect of the present invention, it is possible to provide a ferrite-based iron-based stainless steel having excellent corrosion resistance and good processability in an environment such as acid rain-like low pH and presence of chloride. Also, unlike the Osbane iron-based stainless steel, the ferrite-based iron-based stainless steel does not contain a large amount of expensive Ni and Mo. In particular, according to a preferred aspect of the present invention, a mechanical material in an environment exposed to a condensed water of a combustion gas which uses a hydrocarbon such as LNG or petroleum as a fuel, such as a water heater, can exhibit excellent corrosion resistance.
圖1係針對耐蝕性之評價方法進行說明的圖,(a)係顯示試樣的設置狀況,(b)係顯示供於試驗之樣本的形狀,(c)係顯示C-C箭號方向的截面圖。Fig. 1 is a view for explaining a method for evaluating corrosion resistance, wherein (a) shows the setting state of the sample, (b) shows the shape of the sample for the test, and (c) shows a sectional view of the direction of the CC arrow. .
圖2係顯示在利用由酸雨之模擬液進行的腐蝕試驗所測定的平均腐蝕失重,與構成元素之關係的圖。Fig. 2 is a graph showing the relationship between the average corrosion weight loss measured by the corrosion test by the acid rain simulation liquid and the constituent elements.
圖3係顯示在利用由燃燒廢氣之凝結水的模擬液進行之腐蝕試驗所測定的平均腐蝕失重,與構成元素之關係的圖。Fig. 3 is a graph showing the relationship between the average corrosion loss and the constituent elements measured by a corrosion test using a simulated liquid of condensed water for burning exhaust gas.
圖4係顯示在實施例及比較例之結果中,在利用酸雨之模擬液進行之腐蝕試驗所測定的平均腐蝕失重,與構成元素之關係的圖。Fig. 4 is a graph showing the relationship between the average corrosion loss and the constituent elements measured by a corrosion test using a simulated liquid of acid rain in the results of the examples and the comparative examples.
圖5係顯示在實施例及比較例之結果中,在利用燃燒廢 氣之凝結水的模擬液進行之腐蝕試驗所測定的平均腐蝕失重,與構成元素之關係的圖。Figure 5 shows the use of combustion waste in the results of the examples and comparative examples. The graph of the relationship between the average corrosion weight loss measured by the corrosion test conducted by the simulated liquid of the gas condensate and the constituent elements.
以下,只要沒有特別事先說明,「%」係意指「質量%」。Hereinafter, "%" means "% by mass" unless otherwise specified.
發明人等為了提供在低pH值且存在有氯化物之環境中顯示優異耐蝕性並且具有良好加工性的肥粒鐵系不鏽鋼,進行專精研發。其結果,認知到以下的事項。The inventors have conducted specialization research and development in order to provide a ferrite-based iron-based stainless steel which exhibits excellent corrosion resistance in an environment of low pH and presence of chloride and has good processability. As a result, the following matters were recognized.
(1)進行模擬下酸雨之環境的乾濕反覆試驗,測定賦有間隙的試驗片的平均腐蝕失重。就滿足以下(A)式及(B)式的肥粒鐵系不鏽鋼來說,其結果係平均腐蝕失重為0.4mg/cm2 以下。(1) A dry-wet test was carried out to simulate an environment of acid rain, and the average corrosion weight loss of the test piece to which the gap was applied was measured. In the case of the ferrite-based iron-based stainless steel which satisfies the following formulas (A) and (B), the average corrosion weight loss is 0.4 mg/cm 2 or less.
(A)式:Cr+10Ti+10Al≧15(A): Cr+10Ti+10Al≧15
(B)式:Si+Cu≦1.1(B) Formula: Si+Cu≦1.1
(2)比較(A)式左邊之值相同的肥粒鐵系不鏽鋼與奧斯田鐵系不鏽鋼之結果,在酸雨環境下,肥粒鐵系不鏽鋼的平均腐蝕失重變得小於奧斯田鐵系不鏽鋼的平均腐蝕失重。(2) Comparing the results of the ferrite-based stainless steel with the same value on the left side of the formula (A) and the Osfield iron-based stainless steel, the average corrosion weight loss of the ferrite-based stainless steel in the acid rain environment becomes smaller than that of the Oswald iron system. The average corrosion weight loss of stainless steel.
(3)進行模擬因燃燒廢氣產生凝結水之環境的乾濕反覆試驗,測定賦有間隙的試驗片的平均腐蝕失重。就滿足以下(A)式及(B’)式的肥粒鐵系不鏽鋼來說,其結果係平均腐蝕失重為1.0mg/cm2 以下。(3) A dry-wet test was conducted to simulate an environment in which condensed water was generated by combustion exhaust gas, and the average corrosion weight loss of the test piece to which the gap was applied was measured. In the case of the ferrite-based iron-based stainless steel which satisfies the following formulas (A) and (B'), the average corrosion weight loss is 1.0 mg/cm 2 or less.
(A)式:Cr+10Ti+10Al≧15(A): Cr+10Ti+10Al≧15
(B’)式:Si+Cu≦0.5(B') formula: Si+Cu≦0.5
(4)和上述(2)相同地,比較(A)式左邊之值相同的肥粒鐵系不鏽鋼與奧斯田鐵系不鏽鋼的結果,即便係在燃燒廢氣之凝結水的環境來說,亦是肥粒鐵系不鏽鋼的平均腐蝕失重變得小於奧斯田鐵系不鏽鋼的平均腐蝕失重。(4) In the same manner as in the above (2), the result of comparing the fat iron-based stainless steel having the same value on the left side of the formula (A) with the Aostian iron-based stainless steel is even in the environment of the condensed water of the combustion exhaust gas. The average corrosion weight loss of the ferrite-based stainless steel becomes smaller than the average corrosion weight loss of the Osbane iron-based stainless steel.
(5)為評價加工性,透過拉伸試驗來測定伸長值。發現若含有Cr、Si、Cu、Mo及Ni的話,則結果係伸長值減少且加工性降低。(5) In order to evaluate the workability, the elongation value was measured by a tensile test. When Cr, Si, Cu, Mo, and Ni were contained, it was found that the elongation value was decreased and the workability was lowered.
首先,針對模擬酸雨環境的腐蝕試驗(耐蝕性的評價方法)進行說明。First, a corrosion test (method for evaluating corrosion resistance) simulating an acid rain environment will be described.
使用試劑來調製pH=4.5且含有硝酸根離子10ppm、硫酸根離子10ppm及氯離子5ppm的試驗溶液來作為酸雨的模擬液。A test solution having a pH of 4.5 and containing 10 ppm of nitrate ions, 10 ppm of sulfate ions, and 5 ppm of chloride ions was prepared using a reagent as a simulated liquid of acid rain.
對各種不鏽鋼(試樣材料)的每一種,準備3片具有如圖1(b)所示25×50mm尺寸的試驗片1。在本試驗來說,為評價間隙腐蝕,如以下般將玻璃/金屬的間隙賦予至試驗片1。在試驗片1大致中央部挖6mm的孔9。於試驗開始前將試驗片1整面以#400砂紙進行濕式研磨處理,迅速地使用特夫綸(註冊商標)製螺栓2、特夫綸(註冊商標)製螺帽3及鈦製墊圈5,將試驗片1夾入2片玻璃板4之間。透過上述來將玻璃/金屬的間隙賦予至試驗片1。For each of various stainless steels (sample materials), three test pieces 1 having a size of 25 × 50 mm as shown in Fig. 1 (b) were prepared. In this test, in order to evaluate the crevice corrosion, a gap of glass/metal was imparted to the test piece 1 as follows. Digging in the center of the test piece 1 6mm hole 9. Before the start of the test, the test piece 1 was wet-polished with #400 sandpaper, and the Teflon (registered trademark) bolt 2, the Teflon (registered trademark) nut 3, and the titanium gasket 5 were quickly used. The test piece 1 was sandwiched between two glass plates 4. The glass/metal gap was imparted to the test piece 1 by the above.
將此試驗片1設置於如圖1(a)所示般的燒杯7,填充50ml酸雨的模擬液8,使試驗片1半浸漬。將此燒杯7置入50℃的溫浴保持24小時。於此期間,模擬液8進行乾燥濃 縮。接著,從經乾燥濃縮的模擬液8中取出不鏽鋼樣本(試驗片1),輕輕地以蒸餾水洗淨。接著,再度將試驗溶液(酸雨的模擬液8)填充至新洗淨好的燒杯7中。接著,再使不鏽鋼樣本(試驗片1)半浸漬並在50℃下保持24小時。使試驗片1半浸漬在模擬液8中,接著在50℃下保持24小時,將此反覆10次(乾濕反覆試驗)。This test piece 1 was placed in a beaker 7 as shown in Fig. 1 (a), and 50 ml of acid rain simulated liquid 8 was filled, and the test piece 1 was semi-impregnated. The beaker 7 was placed in a warm bath at 50 ° C for 24 hours. During this period, the simulated liquid 8 was dried and concentrated. Shrink. Next, a stainless steel sample (test piece 1) was taken out from the dried and concentrated simulation liquid 8, and gently washed with distilled water. Next, the test solution (acid rain simulating solution 8) was again filled into the freshly washed beaker 7. Next, the stainless steel sample (test piece 1) was further semi-impregnated and kept at 50 ° C for 24 hours. The test piece 1 was half-immersed in the dummy liquid 8, and then kept at 50 ° C for 24 hours, and this was repeated 10 times (dry and dry repeated test).
還有,50℃的設定溫度係模擬在腐蝕對象物中可以推測到較高的溫度者,該腐蝕對象物係設置在下酸雨的屋外。Further, the set temperature of 50 ° C is a simulation of a higher temperature in the object to be corroded, and the object to be corroded is placed outside the acid rain.
在經過10次循環後,弄下試驗片1的鏽,利用電子天秤來測定質量。從預先測定好的試驗前之試驗片1的質量減去試驗後之試驗片1的質量來求得腐蝕失重。After 10 cycles, the rust of the test piece 1 was removed, and the mass was measured using an electronic balance. The corrosion weight loss was obtained by subtracting the mass of the test piece 1 after the test from the mass of the test piece 1 before the test which was previously measured.
對3片試驗片1的每一片進行相同的乾濕反覆試驗來求得腐蝕失重。然後,求得腐蝕失重的平均值(平均腐蝕失重)。The same dry-wet test was performed on each of the three test pieces 1 to obtain corrosion loss. Then, the average value of the corrosion weight loss (average corrosion weight loss) was obtained.
使用具有表1所示組成的20種鋼作為試樣材料。還有,在表1記載的組成中,剩餘部份係鐵及不可避免的不純物。還有,於表1記載的符號*係指示為奧斯田鐵系不鏽鋼(鋼No.B9及B10)。Twenty kinds of steels having the compositions shown in Table 1 were used as the sample materials. Further, in the composition described in Table 1, the remaining portion was iron and unavoidable impurities. In addition, the symbol * shown in Table 1 is indicated by the Osbane iron-based stainless steel (steel No. B9 and B10).
將此試驗的結果顯示於表2及圖2。就平均腐蝕失重超過0.4mg/cm2 的不鏽鋼來說,判斷為往間隙外發生銹紋而外觀受損。此不鏽鋼則判定為耐蝕性差,於圖2以實心圓(●)來繪圖。又,平均腐蝕失重為0.4mg/cm2 以下之不鏽鋼則判定為耐蝕性優異,於圖2以空心圓(○)來繪圖。The results of this test are shown in Table 2 and Figure 2. In the case of stainless steel having an average corrosion loss of more than 0.4 mg/cm 2 , it was judged that rust was formed outside the gap and the appearance was impaired. This stainless steel was judged to have poor corrosion resistance and was drawn in a solid circle (•) in Fig. 2 . Further, stainless steel having an average corrosion loss of 0.4 mg/cm 2 or less was judged to be excellent in corrosion resistance, and was drawn in a hollow circle (○) in Fig. 2 .
發現到當以含有Cr之肥粒鐵系不鏽鋼為基材並提高Cr、Al或Ti之含量的狀況時,任一狀況下平均腐蝕失重都會改善。而且,了解到當令增加Cr含量造成的效果令為1時,則增加Al與Ti的含量造成的效果分別是10左右(Cr造成之效果的10倍左右)。It has been found that when the iron-based stainless steel containing Cr is used as a base material and the content of Cr, Al or Ti is increased, the average corrosion weight loss is improved in either case. Further, it is understood that when the effect of increasing the Cr content is set to 1, the effect of increasing the content of Al and Ti is about 10 (about 10 times that of Cr).
又,發現到Si與Cu兩者會使肥粒鐵系不鏽鋼的平均腐蝕失重増加。亦弄清楚此Si與Cu的貢獻率幾乎係相等的。Further, it was found that both Si and Cu increased the average corrosion weight loss of the ferrite-based iron-based stainless steel. It is also clear that the contribution rate of this Si and Cu is almost equal.
因此,透過Cr+10Ti+10Al及Si+Cu這2個參數來對賦有間隙的試驗片的平均腐蝕失重係受到什麼樣的影響來進行評價。Therefore, the influence of the average corrosion loss on the test piece to which the gap is applied is evaluated by the two parameters of Cr+10Ti+10Al and Si+Cu.
如表2及圖2所示般,就滿足以下(A)式及(B)式的肥粒鐵系不鏽鋼來說,其之結果顯示平均腐蝕失重係0.4mg/cm2 以下。As shown in Table 2 and Fig. 2, the ferrite-based iron-based stainless steel which satisfies the following formulas (A) and (B) has an average corrosion weight loss of 0.4 mg/cm 2 or less.
(A)式:Cr+10Ti+10Al≧15(A): Cr+10Ti+10Al≧15
(B)式:Si+Cu≦1.1(B) Formula: Si+Cu≦1.1
還有,在滿足(A)式但未滿足(B)式的狀況時,結果變成平均腐蝕失重超過0.4mg/cm2 。Further, when the condition of the formula (A) was satisfied but the formula (B) was not satisfied, the result was that the average corrosion loss was more than 0.4 mg/cm 2 .
另一方面,在如鋼No.B9及B10的奧斯田鐵系不鏽鋼來說,即便滿足(A)式及(B)式,結果變成平均腐蝕失重超過0.4mg/cm2 。這被認為是因為奧斯田鐵系不鏽鋼的鈍化膜比肥粒鐵系不鏽鋼的鈍化膜還要不安定的緣故。On the other hand, in the Osbane-based stainless steel such as Steel No. B9 and B10, even if the formulas (A) and (B) are satisfied, the average corrosion loss is more than 0.4 mg/cm 2 . This is considered to be because the passivation film of the Osbane iron stainless steel is more unstable than the passivation film of the ferrite iron stainless steel.
如此這般,揭明了在低pH值且存在指定比率以上之氯離子的溶液中,就乾濕反覆的環境來說,滿足以下(A)式及(B)式的肥粒鐵系不鏽鋼具有優異的耐蝕性。In this way, it has been revealed that in a solution having a low pH and a chloride ion having a specified ratio or more, in the dry-wet environment, the following ferrite-based stainless steels satisfying the following formulas (A) and (B) are excellent. Corrosion resistance.
(A)式:Cr+10Ti+10Al≧15(A): Cr+10Ti+10Al≧15
(B)式:Si+Cu≦1.1(B) Formula: Si+Cu≦1.1
於此處,式中的Cr、Ti、Al、Si及Cu係意指各別元素的含量(質量%)。Here, the Cr, Ti, Al, Si, and Cu systems in the formula mean the content (% by mass) of each element.
滿足Cr+10Ti+10Al≧15((A)式)時,本試驗條件下之賦有間隙的試驗片平均腐蝕失重變少的理由,被認為係如以下。When Cr+10Ti+10Al≧15 (formula (A)) is satisfied, the reason why the average corrosion loss of the test piece having a gap under the test conditions is small is considered to be as follows.
在本試驗中針對平均腐蝕失重係0.4mg/cm2 以下的樣本,以AES來分析試驗後的鈍化膜。其之結果,在表面皮膜確認到Al及Ti與Cr一起濃縮。推定在乾濕反覆試驗中,透過硝酸根離子的還原反應,Al與Ti在表面皮膜中被濃縮/氧化,而耐蝕性提高。由此看來,從結果上來看,可認為在本試驗環境中之平均腐蝕失重係以Cr+10Ti+10Al所示的指標來表示。In this test, the passivation film after the test was analyzed by AES for a sample having an average corrosion weight loss of 0.4 mg/cm 2 or less. As a result, it was confirmed that Al and Ti were concentrated together with Cr on the surface film. It is presumed that in the dry-wet repeat test, Al and Ti are concentrated/oxidized in the surface film by the reduction reaction of nitrate ions, and the corrosion resistance is improved. From this point of view, from the results, it can be considered that the average corrosion weight loss in this test environment is expressed by the index indicated by Cr+10Ti+10Al.
滿足Si+Cu≦1.1((B)式)時,平均腐蝕失重變少的理由被認為係如以下。When Si+Cu≦1.1 ((B)) is satisfied, the reason why the average corrosion weight loss is small is considered to be as follows.
Cu通常係使活性溶解速度降低並提高耐蝕性的元素,但一旦產生腐蝕的狀況時,鋼中的Cu會溶出。特別係在本試驗環境般成為氧化劑之硝酸根離子多的環境中,溶出的Cu離子則成為Cu2+ 。推定此Cu2+ 成為氧化劑而促進陰極反應,因此腐蝕速度增大,而腐蝕深度變深。Cu is usually an element which lowers the active dissolution rate and improves the corrosion resistance, but when corrosion occurs, Cu in the steel is eluted. In particular, in an environment where the amount of nitrate ions of the oxidant is large in the test environment, the eluted Cu ions become Cu 2+ . It is presumed that this Cu 2+ acts as an oxidant to promote the cathode reaction, so the corrosion rate increases and the corrosion depth becomes deep.
在上述試驗液(模擬液)中以賦有間隙的試驗片來實施乾濕反覆試驗的狀況時,在含有Si的試樣材料來說,確認到在以氣液界面為中心有Si氧化物的析出。又,確認到在此Si氧化物之析出物的附近發生腐蝕。發生腐蝕的理由被認為係,在 析出物與試樣材料之間產生的間隙成為腐蝕的起始點,而促進間隙腐蝕的緣故。進一步推定因為此時在環境中存在有Cu2+ ,而會更加速腐蝕。In the case where the dry-and-wet test was carried out in the test piece (simulation liquid) in which the gap was applied, it was confirmed that the sample material containing Si had a precipitation of Si oxide around the gas-liquid interface. . Further, it was confirmed that corrosion occurred in the vicinity of the precipitate of the Si oxide. The reason why corrosion occurs is considered to be that the gap generated between the precipitate and the sample material becomes the starting point of corrosion and promotes crevice corrosion. It is further presumed that since Cu 2+ is present in the environment at this time, corrosion is more accelerated.
還有,如前述般,就奧斯田鐵系不鏽鋼來說,即便滿足(A)式及(B)式,結果平均腐蝕失重還是超過0.4mg/cm2 。這被認為是因為與肥粒鐵系不鏽鋼相比,通用奧斯田鐵系不鏽鋼鈍化膜不安定的緣故。Further, as described above, in the case of the Osbane iron-based stainless steel, even if the formulas (A) and (B) are satisfied, the average corrosion weight loss is more than 0.4 mg/cm 2 . This is considered to be because the general Aostian iron-based stainless steel passivation film is unstable compared to the ferrite-based iron-based stainless steel.
此外,奧斯田鐵系不鏽鋼,MnS等水溶性介在物的量多於肥粒鐵系不鏽鋼。因為這個原因,在酸雨之模擬液中的溶解速度大,而此事亦被推定為腐蝕失重大的原因的1個。In addition, Osbane iron-based stainless steel, MnS and other water-soluble mediators are more than the ferrite-based iron-based stainless steel. For this reason, the dissolution rate in the simulated solution of acid rain is large, and this matter is also presumed to be one of the causes of the major corrosion loss.
(A)式左邊之Cr+10Ti+10Al的值,較理想的係17以上,更理想的係18以上。又,(B)式左邊之Si+Cu的值,較理想的係0.90以下,更理想的係0.70以下。The value of Cr+10Ti+10Al on the left side of the formula (A) is preferably 17 or more, and more preferably 18 or more. Further, the value of Si+Cu on the left side of the formula (B) is preferably 0.90 or less, more preferably 0.70 or less.
其次,評價在更嚴苛的腐蝕環境,即,在由燃燒廢氣產生之凝結水中的耐蝕性。Secondly, the corrosion resistance in the more severe corrosive environment, that is, in the condensed water produced by the combustion exhaust gas, was evaluated.
如同先前說明的,從一般的LNG或石油的燃燒廢氣產生的凝結水係含有硝酸根離子及硫酸根離子且顯示pH=3以下的酸性。又,就二次熱交換器來說,在其使用時,從一次熱交換器送入150~200℃的廢氣,而在停止時返回到室溫。如此這般在150~200℃的環境與室溫的環境下反覆。As described earlier, the condensed water generated from the combustion gas of general LNG or petroleum contains nitrate ions and sulfate ions and exhibits acidity of pH=3 or less. Further, in the case of the secondary heat exchanger, at the time of use, the exhaust gas of 150 to 200 ° C is fed from the primary heat exchanger, and returns to room temperature when it is stopped. This is repeated in an environment of 150 to 200 ° C and a room temperature environment.
又,與酸雨環境相比較,因為暴露在廢氣直接凝結而產生之凝結水中,硝酸根離子NO3 - 及硫酸根離子SO4 2- 的濃度高。因為這個原因,使用試劑來調整pH=2.5且含有硝酸根離子100ppm、硫酸根離子10ppm及氯離子(Cl- )100ppm之試驗溶 液來作為凝結水的模擬液。Further, compared with the acid rain environment, the concentration of the nitrate ion NO 3 - and the sulfate ion SO 4 2- is high because it is exposed to the condensed water generated by the direct condensation of the exhaust gas. For this reason, a reagent containing pH of 2.5 and containing 100 ppm of nitrate ions, 10 ppm of sulfate ions, and 100 ppm of chloride ions (Cl - ) was used as a simulating solution of condensed water.
凝結水之模擬液的組成係模擬由LNG的燃燒廢氣而產生的凝結水者。就Cl- 離子來說,實際凝結水中之氯離子濃度為數ppm。惟,設想在海濱環境等腐蝕性高的環境中的運轉狀況而將氯離子濃度設定為偏高。The composition of the condensate simulating liquid simulates the condensate produced by the combustion exhaust gas of LNG. In the case of Cl - ions, the concentration of chloride ions in the actual condensed water is several ppm. However, it is assumed that the chlorine ion concentration is set to be high in an environment in a corrosive environment such as a seashore environment.
對各種不鏽鋼(試樣材料)的每一種,準備3片具有如圖1(b)所示25×50mm尺寸的試驗片1。因為二次熱交換器結構複雜,而特別擔心間隙腐蝕。因此,在本試驗來說,為了有目的地引起間隙腐蝕,如以下般將玻璃/金屬間隙賦予至試驗片1。在試驗片1大致中央部挖6mm的孔9。於試驗開始前將試驗片1整面以#400砂紙進行濕式研磨處理,迅速地使用特夫綸(註冊商標)製螺栓2、特夫綸(註冊商標)製螺帽3及鈦製墊圈5,將試驗片1夾入2片玻璃板4之間。透過上述來將玻璃/金屬的間隙賦予至試驗片1。For each of various stainless steels (sample materials), three test pieces 1 having a size of 25 × 50 mm as shown in Fig. 1 (b) were prepared. Because of the complexity of the secondary heat exchanger structure, there is a particular concern about crevice corrosion. Therefore, in this test, in order to cause crevice corrosion intentionally, a glass/metal gap was imparted to the test piece 1 as follows. Digging in the center of the test piece 1 6mm hole 9. Before the start of the test, the test piece 1 was wet-polished with #400 sandpaper, and the Teflon (registered trademark) bolt 2, the Teflon (registered trademark) nut 3, and the titanium gasket 5 were quickly used. The test piece 1 was sandwiched between two glass plates 4. The glass/metal gap was imparted to the test piece 1 by the above.
將此試驗片1設置於如圖1(a)所示般的燒杯7,填充50ml燃燒廢氣之凝結水的模擬液8,使試驗片1半浸漬。將此燒杯7置入80℃的溫浴保持24小時。於此期間,模擬液8進行乾燥濃縮,而完全地乾燥。接著,取出經完全乾燥之不鏽鋼樣本(試驗片1),輕輕地以蒸餾水洗淨。接著,再度將試驗溶液(燃燒廢氣的凝結水模擬液8)填充至新洗淨好的燒杯7中。接著,再使不鏽鋼樣本(試驗片1)半浸漬並在80℃下保持24小時。使試驗片1半浸漬在模擬液8中,接著在80℃下保持24小時,將此反覆10次循環(乾濕反覆試驗)。This test piece 1 was placed in a beaker 7 as shown in Fig. 1 (a), and 50 ml of the simulated liquid 8 of the condensed water of the combustion exhaust gas was filled, and the test piece 1 was semi-impregnated. The beaker 7 was placed in a warm bath at 80 ° C for 24 hours. During this time, the simulated liquid 8 was dried and concentrated, and completely dried. Next, the completely dried stainless steel sample (test piece 1) was taken out and gently washed with distilled water. Next, the test solution (condensed water simulating liquid 8 of the combustion exhaust gas) was again filled into the freshly washed beaker 7. Next, the stainless steel sample (test piece 1) was further semi-impregnated and kept at 80 ° C for 24 hours. The test piece 1 was half-immersed in the simulation liquid 8, and then kept at 80 ° C for 24 hours, and this was repeated for 10 cycles (dry and dry repeated test).
還有,將溫度設定於80℃的理由係顯示於以下。廢氣的 溫度係150~200℃。惟,因產生凝縮水而溫度降低。又,因與產生的凝縮水接觸而可以想見實際的部件溫度變得更為低溫。因為這個原因,為了較100℃低且使腐蝕加速而瞄準相對較高的溫度而設定在80℃。Further, the reason why the temperature is set to 80 ° C is shown below. Exhaust gas The temperature is 150~200 °C. However, the temperature is lowered due to the generation of condensed water. Further, it is conceivable that the actual component temperature becomes lower due to contact with the generated condensed water. For this reason, it is set at 80 ° C in order to be slower than 100 ° C and to accelerate the corrosion while aiming at a relatively high temperature.
在經過10次循環後,弄下試驗片1的鏽,利用電子天秤來測定質量。從預先測定好的試驗前之試驗片1的質量減去試驗後之試驗片1的質量來求得腐蝕失重。After 10 cycles, the rust of the test piece 1 was removed, and the mass was measured using an electronic balance. The corrosion weight loss was obtained by subtracting the mass of the test piece 1 after the test from the mass of the test piece 1 before the test which was previously measured.
對3片試驗片1的每一片進行相同的乾濕反覆試驗來求得腐蝕失重。然後,求得腐蝕失重的平均值(平均腐蝕失重)。The same dry-wet test was performed on each of the three test pieces 1 to obtain corrosion loss. Then, the average value of the corrosion weight loss (average corrosion weight loss) was obtained.
作為試樣材料,使用具有於表1所示之組成的20種鋼。As the sample material, 20 kinds of steels having the compositions shown in Table 1 were used.
將此試驗的結果顯示於表2及圖3。就平均腐蝕失重超過1.0mg/cm2 的不鏽鋼來說,判斷為在長期來說在間隙部會達到穿孔。此不鏽鋼則判定為耐蝕性差,於圖3以實心圓(●)來繪圖。又,平均腐蝕失重為1.0mg/cm2 以下之不鏽鋼則判定為耐蝕性優異,於圖3以空心圓(○)來繪圖。發現到當以含有Cr之肥粒鐵系不鏽鋼為基材並提高Cr、Al或Ti含量之狀況時,任一狀況下平均腐蝕失重都會改善。而且,了解到令增加Cr含量造成的效果為1時,則增加Al與Ti的含量造成的效果分別是10左右(Cr造成之效果的10倍左右)。The results of this test are shown in Table 2 and Figure 3. In the case of stainless steel having an average corrosion loss of more than 1.0 mg/cm 2 , it was judged that perforation was reached in the gap portion in the long term. This stainless steel was judged to have poor corrosion resistance and was drawn in a solid circle (•) in Fig. 3 . Further, stainless steel having an average corrosion weight loss of 1.0 mg/cm 2 or less was judged to be excellent in corrosion resistance, and was drawn in a hollow circle (○) in Fig. 3 . It has been found that when the iron-based stainless steel containing Cr is used as a substrate and the Cr, Al or Ti content is increased, the average corrosion weight loss is improved in either case. Further, it is understood that when the effect of increasing the Cr content is 1, the effect of increasing the content of Al and Ti is about 10 (about 10 times that of Cr).
又,發現到Si與Cu兩者會使肥粒鐵系不鏽鋼的平均腐蝕失重増加。亦弄清楚此Si與Cu的貢獻率幾乎係相等的。Further, it was found that both Si and Cu increased the average corrosion weight loss of the ferrite-based iron-based stainless steel. It is also clear that the contribution rate of this Si and Cu is almost equal.
因此,透過Cr+10Ti+10Al及Si+Cu這2個參數,針對賦有間隙的試驗片的平均腐蝕失重係受到什麼樣的影響來進 行評價。Therefore, through the two parameters of Cr+10Ti+10Al and Si+Cu, what is the effect on the average corrosion weight loss of the test piece with gaps? Evaluation.
如表2及圖3所示般,就滿足(A)式及(B’)式的肥粒鐵系不鏽鋼來說,其之結果顯示平均腐蝕失重係1.0mg/cm2 以下。As shown in Table 2 and FIG. 3, the ferrite-based iron-based stainless steel satisfying the formulas (A) and (B') showed an average corrosion weight loss of 1.0 mg/cm 2 or less.
(A)式:Cr+10Ti+10Al≧15(A): Cr+10Ti+10Al≧15
(B’)式:Si+Cu≦0.5(B') formula: Si+Cu≦0.5
還有,在滿足(A)式但未滿足(B’)式的狀況時,結果變成平均腐蝕失重超過1.0mg/cm2 。Further, when the condition of the formula (A) was satisfied but the formula (B') was not satisfied, the result was that the average corrosion weight loss exceeded 1.0 mg/cm 2 .
另一方面,通用的奧斯田鐵系不鏽鋼,雖滿足(A)式但未滿足(B’)式。因為這個原因,結果變成平均腐蝕失重超過1.0mg/cm2 。On the other hand, the general Osbane iron-based stainless steel satisfies the (A) formula but does not satisfy the (B') formula. For this reason, the result becomes an average corrosion loss of more than 1.0 mg/cm 2 .
如此這般,揭明了在低pH值且存在指定比率以上之硝酸根離子與硫酸根離子的溶液中,就乾濕反覆的環境來說,滿足以下(A)式及(B’)式的肥粒鐵系不鏽鋼具有優異的耐蝕性。In this way, it is revealed that in the solution of nitrate ions and sulfate ions having a low pH value and a predetermined ratio or more, the following formula (A) and (B') are satisfied in the dry and wet environment. Granular iron stainless steel has excellent corrosion resistance.
(A)式:Cr+10Ti+10Al≧15(A): Cr+10Ti+10Al≧15
(B’)式:Si+Cu≦0.5(B') formula: Si+Cu≦0.5
於此處,式中的Cr、Ti、Al、Si及Cu係意指各別元素的含量(質量%)。Here, the Cr, Ti, Al, Si, and Cu systems in the formula mean the content (% by mass) of each element.
當滿足Cr+10Ti+10Al≧15((A)式)時,本試驗條件下之賦有間隙的試驗片的平均腐蝕失重變少的理由,被認為係如以下。When Cr+10Ti+10Al≧15 ((A) formula) is satisfied, the reason why the average corrosion weight loss of the test piece with a gap under the test conditions is small is considered to be as follows.
在本試驗中針對平均腐蝕失重係1.0mg/cm2 以下的樣本,以AES來分析試驗後的鈍化膜。其之結果在表面皮膜確認到Al及Ti與Cr一起濃縮。推定在乾濕反覆試驗中,透過硝 酸根離子的還原反應,在表面皮膜中Al與Ti被濃縮/氧化,而耐蝕性提高。由此看來,從結果上來看,可認為在本試驗環境中之平均腐蝕失重係以Cr+10Ti+10Al所示的指標來表示。In this test, the passivation film after the test was analyzed by AES for a sample having an average corrosion weight loss of 1.0 mg/cm 2 or less. As a result, it was confirmed in the surface film that Al and Ti were concentrated together with Cr. It is presumed that in the dry-wet repeat test, Al and Ti are concentrated/oxidized in the surface film by the reduction reaction of nitrate ions, and the corrosion resistance is improved. From this point of view, from the results, it can be considered that the average corrosion weight loss in this test environment is expressed by the index indicated by Cr+10Ti+10Al.
滿足Si+Cu≦0.5((B’)式)時,平均腐蝕失重變少的理由被認為係如以下。When Si+Cu≦0.5 ((B')) is satisfied, the reason why the average corrosion weight loss is small is considered to be as follows.
Cu通常係使活性溶解速度降低並提高耐蝕性的元素,但在一旦產生腐蝕的狀況時,鋼中的Cu會溶出。特別係在本試驗環境般成為氧化劑之硝酸根離子多的環境中,溶出的Cu離子則成為Cu2+ 。推定此Cu2+ 成為氧化劑而促進陰極反應,因此腐蝕速度增大,而腐蝕深度變深。Cu is usually an element which lowers the active dissolution rate and improves the corrosion resistance, but in the case where corrosion occurs, Cu in the steel is eluted. In particular, in an environment where the amount of nitrate ions of the oxidant is large in the test environment, the eluted Cu ions become Cu 2+ . It is presumed that this Cu 2+ acts as an oxidant to promote the cathode reaction, so the corrosion rate increases and the corrosion depth becomes deep.
在上述試驗液(模擬液)中以賦有間隙的試驗片來實施乾濕反覆試驗的狀況時,在含有Si的試樣材料來說,確認到在以氣液界面為中心有Si氧化物的析出。又,確認到在此Si氧化物之析出物的附近發生腐蝕。發生腐蝕的理由被認為係,在析出物與試樣材料之間產生的間隙係成為腐蝕的起始點,而促進間隙腐蝕的緣故。進一步,推定此時因為在環境中存在Cu2+ ,腐蝕被更加速。In the case where the dry-and-wet test was carried out in the test piece (simulation liquid) in which the gap was applied, it was confirmed that the sample material containing Si had a precipitation of Si oxide around the gas-liquid interface. . Further, it was confirmed that corrosion occurred in the vicinity of the precipitate of the Si oxide. The reason why corrosion occurs is considered to be that the gap generated between the precipitate and the sample material becomes the starting point of corrosion and promotes crevice corrosion. Further, it is presumed that corrosion is more accelerated at this time because of the presence of Cu 2+ in the environment.
還有,如前述般,就奧斯田鐵系不鏽鋼來說,即便滿足Cr+10Ti+10Al((A)式),結果平均腐蝕失重還是超過1.0mg/cm2 。在通用奧斯田鐵系不鏽鋼來說,因其之煉鋼條件,Si及Cu之含量必然地變高,大體來說Si+Cu之值都不會為0.5以下者。因為這個原因,而可想見平均腐蝕失重會變大。Further, as described above, in the case of the Osbane iron-based stainless steel, even if Cr+10Ti+10Al ((A) formula) is satisfied, the average corrosion weight loss is more than 1.0 mg/cm 2 . In the general Osbane iron-based stainless steel, the content of Si and Cu is inevitably high due to the steelmaking conditions, and the value of Si+Cu is generally not less than 0.5. For this reason, it is conceivable that the average corrosion weight loss will become larger.
進一步,奧斯田鐵系不鏽鋼MnS等水溶性介在物的量係多於肥粒鐵系不鏽鋼。因為這個原因,在凝結液之模擬液中 的溶解速度大,而此事亦被推定為腐蝕失重大的原因的1個。Further, the amount of water-soluble intermediaries such as Osbane iron-based stainless steel MnS is more than that of ferrite-based iron-based stainless steel. For this reason, in the simulated liquid of the condensate The dissolution rate is large, and this matter is also presumed to be one of the causes of the loss of corrosion.
(A)式左邊之Cr+10Ti+10Al的值,較理想的係17以上,更理想的係18以上。又,(B’)式左邊之Si+Cu的值,較理想的係低於0.35,更理想的係低於0.20。The value of Cr+10Ti+10Al on the left side of the formula (A) is preferably 17 or more, and more preferably 18 or more. Further, the value of Si+Cu on the left side of the (B') formula is preferably less than 0.35, more preferably less than 0.20.
又,為了亦可對應於熱交換器之管等複雜形狀的用途,以伸長值高者為理想的。因此,在冷延、退火及酸洗後將表面經研磨後的材料加工成於JIS13號B規定的形狀,來製作試驗片。使用此試驗片來實施拉伸試驗。Further, in order to cope with a complicated shape such as a tube of a heat exchanger, it is preferable to have a high elongation value. Therefore, after cold rolling, annealing, and pickling, the surface-polished material was processed into a shape defined by JIS No. 13 B to prepare a test piece. This test piece was used to carry out a tensile test.
於此試驗之結果中,伸長值為32%以上之不鏽鋼係判定為加工性良好。將所獲得之結果顯示於表2。Cu及Si兩者,為提升不鏽鋼的拉伸強度,Si+Cu之值必須為1.1以下。進一步,Ni及Mo兩者,為提升拉伸強度,Mo及Ni的含量皆以低者為理想的。還有,伸長值較理想係為34%以上。As a result of the test, the stainless steel having an elongation value of 32% or more was judged to have good workability. The results obtained are shown in Table 2. For both Cu and Si, in order to increase the tensile strength of stainless steel, the value of Si+Cu must be 1.1 or less. Further, both Ni and Mo are preferable in order to increase the tensile strength, and the contents of Mo and Ni are both low. Further, the elongation value is preferably 34% or more.
針對上述組成之詳細規定,於以下進行說明。The detailed regulations of the above composition will be described below.
Cr係在確保不鏽鋼之耐蝕性上最為重要的元素。為了維持鈍態,至少需要13%的Cr。要是使Cr量增加,耐蝕性雖提升,但加工性及製造性卻降低。因為這個原因,令Cr量之上限為22.5%。Cr量理想的係14.5~22.0%,較理想的係16.0~20.0%。Cr is the most important element in ensuring the corrosion resistance of stainless steel. In order to maintain a passive state, at least 13% of Cr is required. If the amount of Cr is increased, the corrosion resistance is improved, but the workability and manufacturability are lowered. For this reason, the upper limit of the amount of Cr is 22.5%. The ideal amount of Cr is 14.5-22.0%, and the ideal system is 16.0~20.0%.
一般來說Ti係在肥粒鐵系不鏽鋼的熔接部中,透過固定C及N來抑制晶界腐蝕並使加工性提升。因為這個原因,Ti係非常重要的元素。進一步,在作為本實施形態之對象的腐蝕環境中,Ti在耐蝕性上係重要的元素。Ti與氧的親和力非常強。於是,本發明者認知到以下事項。In general, Ti is used in the welded portion of the ferrite-based iron-based stainless steel to suppress the grain boundary corrosion by fixing C and N, and to improve the workability. For this reason, Ti is a very important element. Further, in the corrosive environment which is the object of the present embodiment, Ti is an element which is important in corrosion resistance. Ti has a very strong affinity with oxygen. Thus, the inventors recognized the following matters.
在作為包含硝酸根離子之本實施形態之對象的腐蝕環境來說,Ti會與Cr一起形成不鏽鋼的表面被覆。因這個原因,Ti對於抑制孔蝕發生係非常有效。In the corrosive environment which is the object of the present embodiment containing nitrate ions, Ti forms a surface coating of stainless steel together with Cr. For this reason, Ti is very effective in suppressing pitting corrosion.
為使皮膜形成,及使用Ti作為安定化元素來使C及N固定,需要Ti量係C與N的合計量(C+N)的4倍以上。然而,由於過量的添加會成為製造時表面瑕疵的原因,令Ti量的範圍為0.05~0.3%,較理想係令為0.08~0.2%。In order to form a film and to fix C and N by using Ti as a stabilizing element, it is necessary to have four times or more of the total amount (C+N) of the Ti amount system C and N. However, since excessive addition may cause surface flaws during production, the amount of Ti ranges from 0.05 to 0.3%, and is preferably from 0.08 to 0.2%.
Al作為脫氧元素係重要的,又,亦有控制非金屬介在物之組成並使組織微細化的效果。進一步,在作為本實施形態之對象的腐蝕環境中,在耐蝕性來說,Al係重要的元素。與Ti相同地,Al與氧的親和力非常強。不過,本發明人認知到以下事項。Al is important as a deoxidizing element system, and it also has an effect of controlling the composition of the non-metal intervening substance and making the structure fine. Further, in the corrosive environment which is the object of the present embodiment, Al is an important element in terms of corrosion resistance. Like Ti, Al has a very strong affinity for oxygen. However, the inventors recognized the following matters.
在作為包含硝酸根離子之本實施形態之對象的腐蝕環境來說,Al係與Cr一起形成不鏽鋼的表面被覆。因為這個原因,Al對抑制孔蝕發生係非常有效。In the corrosive environment which is the object of the present embodiment including the nitrate ion, the Al system forms a surface coating of stainless steel together with Cr. For this reason, Al is very effective in suppressing pitting corrosion.
惟,要是過量添加的話,則會招致非金屬介在物的粗化,亦有成為製品瑕疵產生的起始點之虞。因此,令Al量的下限值為0.01%且Al量之上限值為0.20%。Al量較理想係0.03%~0.10%。However, if it is added in excess, it will lead to the roughening of the non-metallic media, and it will become the starting point for the production of the product. Therefore, the lower limit of the amount of Al is 0.01% and the upper limit of the amount of Al is 0.20%. The amount of Al is preferably 0.03% to 0.10%.
Cu係作為來自原料之不可避免的不純物,以0.01%以上的量來包含。但是,在作為本實施形態之對象的環境中,由於Cu會促進腐蝕而係不理想的。其理由係推定為,如前所述在一旦腐蝕開始的狀況時,溶出的Cu離子會促進陰極反應的緣故。因此,Cu量越少越理想,故令Cu量之範圍為0.5%以 下。Cu量較理想係0.25%以下。The Cu system is contained in an amount of 0.01% or more as an unavoidable impurity derived from a raw material. However, in the environment which is the object of the present embodiment, it is not preferable because Cu promotes corrosion. The reason for this is presumed to be that, as described above, when the corrosion starts, the eluted Cu ions promote the cathode reaction. Therefore, the smaller the amount of Cu, the more ideal, so the amount of Cu is in the range of 0.5%. under. The amount of Cu is preferably less than 0.25%.
Si係作為脫氧劑不可避地混入的元素。一般來說,Si對耐蝕性及耐氧化性亦係有效的。惟,在作為本實施形態之對象的環境中,Si係有促進腐蝕進行的作用。進一步,過度添加會使加工性及製造性降低。因此,令Si量的上限為0.60%。Si量較理想係低於0.2%。又,極度地降低會招致成本的增加,因此Si量以0.05%以上為理想的。The Si system is an element that is inevitably mixed as a deoxidizer. In general, Si is also effective for corrosion resistance and oxidation resistance. However, in the environment which is the object of the present embodiment, the Si system has an effect of promoting corrosion. Further, excessive addition causes a decrease in workability and manufacturability. Therefore, the upper limit of the amount of Si is made 0.60%. The amount of Si is less than 0.2%. Further, the extreme reduction causes an increase in cost, and therefore the amount of Si is preferably 0.05% or more.
Ni雖非係必須的,但可抑制活性溶解速度。惟,過量的添加會使加工性降低,且不單係使肥粒鐵組織不安定亦使成本惡化。因為這個原因,令Ni量低於0.35%。Ni量,理想的係0.05%以上且低於0.25%。Ni is not essential but inhibits the rate of active dissolution. However, excessive addition causes a decrease in workability, and the cost is not only caused by the instability of the ferrite and iron structure. For this reason, the amount of Ni is less than 0.35%. The amount of Ni is preferably 0.05% or more and less than 0.25%.
Mo雖非必須的,作為來自原料之不可避免的不純物以0.01%以上的量被包含。一般來說,據稱Mo係提高鈍化膜的回復效果。惟,在作為本實施形態之對象的環境中來說,對耐蝕性提升的貢獻小。另一方面,Mo係使加工性降低且成本亦惡化。因此,Mo量以少者為理想的,故令Mo量之範圍為低於0.30%。Mo量理想的係0.20%以下,進一步,較理想的係0.10%以下。Although Mo is not essential, it is contained in an amount of 0.01% or more as an unavoidable impurity derived from a raw material. In general, it is said that Mo improves the recovery effect of the passivation film. However, in the environment which is the object of the present embodiment, the contribution to the improvement of corrosion resistance is small. On the other hand, Mo is degraded in workability and the cost is also deteriorated. Therefore, the amount of Mo is preferably as small as possible, so that the amount of Mo is less than 0.30%. The amount of Mo is preferably 0.20% or less, and more preferably 0.10% or less.
進一步,針對在本實施形態中所規定之其他化學成分,於以下進行詳細說明。Further, other chemical components defined in the present embodiment will be described in detail below.
C係有強度提升以及,透過與安定化元素的組合而抑制結晶粒粗化的效果。惟,C會使熔接部的耐晶界腐蝕性及加工性降低。就高純度的肥粒鐵系不鏽鋼來說,因為有必要使C的含量降低,令C量的上限為0.030%。由於過度地降低會使精煉成 本惡化,C量較理想的係0.002~0.020%。The C system has an effect of increasing the strength and suppressing coarsening of crystal grains by a combination with a stabilizer element. However, C deteriorates the intergranular corrosion resistance and workability of the welded portion. In the case of high-purity ferrite-based stainless steel, since it is necessary to lower the content of C, the upper limit of the amount of C is 0.030%. Refining due to excessive reduction This deterioration, the amount of C is ideally 0.002~0.020%.
因為N與C同樣地使耐晶界腐蝕性及加工性降低,有必要使N的含量降低。因為這個原因,令N量的上限為0.030%。但是過度地使降低會使精煉成本惡化,故N量較理想的係0.002~0.020%。In the same manner as N, the intergranular corrosion resistance and the workability are deteriorated, and it is necessary to lower the content of N. For this reason, the upper limit of the amount of N is 0.030%. However, excessive reduction causes the refining cost to deteriorate, so the amount of N is preferably 0.002 to 0.020%.
Mn作為脫氧元素係重要的元素。惟,要是過量地添加Mn,則變得易於生成會成為腐蝕起始點的MnS,又,會使肥粒鐵組織不安定化。因為這個原因,令Mn的含量為0.01~0.5%。Mn量較理想的係0.05~0.3%。Mn is an important element of the deoxidizing element system. However, if Mn is excessively added, it becomes easy to generate MnS which will become a corrosion initiation point, and the ferrite iron structure will be unstable. For this reason, the content of Mn is 0.01 to 0.5%. The amount of Mn is 0.05 to 0.3% of the ideal system.
P不僅係使熔接性及加工性降低,且使晶界腐蝕容易產生。因為這個原因,而有必要將P量抑制為低的。因此,令P含量為0.05%以下。P量較理想的係0.001~0.04%。P not only reduces weldability and workability, but also causes grain boundary corrosion to occur easily. For this reason, it is necessary to suppress the amount of P to be low. Therefore, the P content is made 0.05% or less. The amount of P is preferably 0.001 to 0.04%.
因為S係使前述的CaS及MnS等會成為腐蝕起始點的水溶性介在物生成,而有必要使S量降低。因此令S量為0.01%以下。但是過度的降低會招致成本的惡化,故S量較理想係0.0001~0.006%。Since the S system causes the above-described CaS and MnS to form a water-soluble intervening substance at the corrosion initiation point, it is necessary to lower the amount of S. Therefore, the amount of S is made 0.01% or less. However, excessive reduction will lead to cost deterioration, so the amount of S is more than 0.0001 to 0.006%.
Nb係與Ti相同地,固定C及N並抑制熔接部的晶界腐蝕而使加工性提升。因為這個原因,Nb係非常重要的元素。為此,以令Nb量為C與N之合計量(C+N)的8倍以上為理想的。但是過量的添加係會使加工性降低,故當添加的狀況時,以令Nb量為0.05~0.5%為宜。Nb量較理想的係0.1~0.3%。Similarly to Ti, the Nb system fixes C and N and suppresses grain boundary corrosion of the welded portion to improve workability. For this reason, Nb is a very important element. Therefore, it is preferable to make the amount of Nb 8 times or more of the total amount of C and N (C+N). However, excessive addition causes a decrease in workability, so when the state of addition is made, it is preferable to make the amount of Nb 0.05 to 0.5%. The amount of Nb is preferably 0.1 to 0.3%.
為確保耐銹紋性而可因應需要來添加Sn。為了抑制腐蝕速度Sn係重要的元素。惟,過量的添加係會使製造性及成本惡化,故令Sn量的範圍為0.005~1.0%。Sn量較理想的係 0.05~0.5%。To ensure rust resistance, Sn can be added as needed. In order to suppress the corrosion rate, Sn is an important element. However, excessive addition causes deterioration in manufacturability and cost, so the amount of Sn is in the range of 0.005 to 1.0%. The ideal amount of Sn 0.05~0.5%.
B因為係對改善二次加工脆性有效的晶界強化元素,可因應需要添加。惟,過度的添加會固溶強化肥粒鐵而成為延展性降低的原因。因此令B量的下限為0.0001%且令B量的上限為0.003%。B量較想的係0.0002~0.0020%。B can be added as needed because it is a grain boundary strengthening element effective for improving secondary processing brittleness. However, excessive addition will solidify and strengthen the ferrite and cause the ductility to decrease. Therefore, the lower limit of the amount of B is 0.0001% and the upper limit of the amount of B is 0.003%. The amount of B is more than 0.0002~0.0020%.
V會改善耐銹性及耐間隙腐蝕性。由於添加V來代替Cr及Mo的話亦可獲得優異的加工性,亦可因應需要來添加V。但是,V的過度添加會使加工性降低並且使耐蝕性提升的效果亦會飽和。因為這個原因,令V量的下限為0.03%且令V量的上限為1.0%。V量較理想的係0.05~0.50%。V will improve rust resistance and crevice corrosion resistance. Excellent workability can be obtained by adding V instead of Cr and Mo, and V can be added as needed. However, excessive addition of V causes a decrease in workability and an effect of improving corrosion resistance. For this reason, the lower limit of the amount of V is 0.03% and the upper limit of the amount of V is 1.0%. The ideal amount of V is 0.05~0.50%.
以通常製造高純度肥粒鐵系不鏽鋼的方法來製造具有表3及4所示之化學組成的鋼。還有,表3及4之化學組成的剩餘部份係鐵及不可避免的不純物。又,於表4記載的符號*係指示為奧斯田鐵系不鏽鋼(鋼No.B9及B10)。Steel having the chemical compositions shown in Tables 3 and 4 was produced by a method of generally producing high-purity ferrite-based stainless steel. Also, the remainder of the chemical composition of Tables 3 and 4 is iron and unavoidable impurities. Moreover, the symbol * shown in Table 4 is indicated by the Osbane iron-based stainless steel (steel No. B9 and B10).
詳細地說,首先進行真空熔製,接著製造厚40mm的鑄塊。將此鑄塊以熱軋延來軋延成4mm厚。其後,基於各個再結晶行為,在900~1000℃的溫度下進行1分鐘的熱處理。接著,磨削除去銹皮。進一步透過冷軋延來製造厚1.0mm的鋼板。對於此鋼板,基於各個再結晶行為在900~1000℃的溫度下施行1分鐘的熱處理(最終退火)。In detail, vacuum melting was first performed, followed by production of an ingot having a thickness of 40 mm. The ingot was rolled to a thickness of 4 mm by hot rolling. Thereafter, heat treatment was performed for 1 minute at a temperature of 900 to 1000 ° C based on each recrystallization behavior. Next, the scale is removed by grinding. Further, a steel plate having a thickness of 1.0 mm was produced by cold rolling. For this steel sheet, heat treatment (final annealing) was performed for 1 minute at a temperature of 900 to 1000 ° C based on each recrystallization behavior.
還有,當製造奧斯田鐵系不鏽鋼的狀況時,令熱處理溫度為1100℃。Further, when the condition of the Osbane iron-based stainless steel was produced, the heat treatment temperature was 1,100 °C.
以與前述相同的條件來進行乾濕反覆試驗。The dry-wet test was carried out under the same conditions as described above.
模擬相對較緩和的腐蝕環境的試驗溶液(酸雨的模擬液)8係含有硝酸根離子10ppm、硫酸根離子10ppm及氯離子5ppm且令pH值為4.5。The test solution (acid rain simulating solution) 8 which simulates a relatively mild corrosive environment contains 10 ppm of nitrate ions, 10 ppm of sulfate ions, and 5 ppm of chloride ions, and has a pH of 4.5.
針對各種不鏽鋼(試樣材料)的每一種,準備3片具有於圖1(b)所示25×50mm之尺寸的試驗片1。就本試驗來說,為了評價間隙腐蝕,如以下進行,將玻璃/金屬的間隙賦予至試驗片1。於試驗片1的大致中央部挖6mm的孔9。於試驗開始前將試驗片1的整面以#400砂紙來進行濕式研磨處理,迅速使用地特夫綸(註冊商標)製螺栓2、特夫綸(註冊商標)製螺帽3及鈦製墊圈5來將試驗片1夾入2片玻璃板4之間。透過上述來將玻璃/金屬的間隙賦予至試驗片1。For each of various stainless steels (sample materials), three test pieces 1 having a size of 25 × 50 mm as shown in Fig. 1 (b) were prepared. For the purpose of this test, in order to evaluate the crevice corrosion, a glass/metal gap was imparted to the test piece 1 as follows. Digging in the approximate central portion of the test piece 1 6mm hole 9. The entire surface of the test piece 1 was wet-polished by #400 sandpaper before the start of the test, and the bolts of the Teflon (registered trademark), the nut 3 of the Teflon (registered trademark), and the titanium were quickly used. The gasket 5 is used to sandwich the test piece 1 between the two glass plates 4. The glass/metal gap was imparted to the test piece 1 by the above.
將此試驗片1設置於圖1(a)所示的燒杯7中,填充50ml酸雨的模擬液8使半浸漬。將此燒杯7置入50℃的溫浴中保持24小時。接著,自經乾燥濃縮的模擬液中取出不鏽鋼樣本(試驗片1),輕輕地以蒸餾水洗淨。接著,再度將試驗溶液(酸雨的模擬液8)填充至新洗淨好的燒杯7中。接著,再使不鏽鋼樣本(試驗片1)半浸漬並於50℃下保持24小時。使試驗片1半浸漬在模擬液中,接著在50℃下保持24小時,將此反覆10次循環(乾濕反覆試驗)。This test piece 1 was placed in the beaker 7 shown in Fig. 1 (a), and 50 ml of acid rain simulated liquid 8 was filled to be semi-impregnated. The beaker 7 was placed in a warm bath at 50 ° C for 24 hours. Next, a stainless steel sample (test piece 1) was taken out from the dried and concentrated simulation liquid, and gently washed with distilled water. Next, the test solution (acid rain simulating solution 8) was again filled into the freshly washed beaker 7. Next, the stainless steel sample (test piece 1) was further semi-impregnated and kept at 50 ° C for 24 hours. The test piece 1 was half-immersed in a simulating liquid, followed by maintaining at 50 ° C for 24 hours, and this was repeated for 10 cycles (dry and dry repeated test).
在經過10次循環後,弄下試驗片1的鏽,以電子天秤來測定質量。自預先測定好之試驗前之試驗片1的質量減去試驗後之試驗片1的質量來求得腐蝕失重。After 10 cycles, the rust of the test piece 1 was taken out, and the mass was measured by an electronic balance. The corrosion weight loss was determined from the mass of the test piece 1 before the test which was measured in advance and the mass of the test piece 1 after the test.
對3片試驗片1的每一片,進行相同的乾濕反覆試驗,來 求得腐蝕失重。然後,求得腐蝕失重的平均值(平均腐蝕失重)。將所獲得之平均腐蝕失重記載於表5及6的「腐蝕失重1」欄。The same dry and wet repeated test was performed on each of the three test pieces 1. Get the weight loss of corrosion. Then, the average value of the corrosion weight loss (average corrosion weight loss) was obtained. The average corrosion loss obtained is described in the "corrosion loss 1" column of Tables 5 and 6.
模擬嚴苛腐蝕環境之試驗溶液(燃燒廢氣之凝結水的模擬液)8係含有硝酸根離子(NO3- )100ppm、硫酸根離子(SO4 2- )10ppm及氯離子(Cl- )100ppm,並令pH值為2.5。The test solution for simulating a harsh corrosive environment (simulation of condensate for combustion exhaust gas) 8 series contains nitrate ions (NO 3- ) 100 ppm, sulfate ions (SO 4 2- ) 10 ppm, and chloride ions (Cl - ) 100 ppm. And let the pH of 2.5.
針對各種不鏽鋼(試樣材料)的每一種,準備3片如圖1(b)所示之具有25×50mm尺寸的試驗片1。For each of various stainless steels (sample materials), three test pieces 1 having a size of 25 × 50 mm as shown in Fig. 1 (b) were prepared.
除使用凝結水的模擬液,及令保持溫度為80℃以外,與經使用酸雨之模擬液的試驗相同地進行腐蝕試驗來求得平均腐蝕失重。將所獲得之平均腐蝕失重記載在表5及6的「腐蝕失重2」欄。The average corrosion loss was obtained by performing a corrosion test in the same manner as the test using the acid rain simulation liquid except that the simulation liquid using the condensed water was used and the holding temperature was maintained at 80 °C. The average corrosion loss obtained is shown in the "corrosion loss 2" column of Tables 5 and 6.
在與前述相同的條件下來進行拉伸試驗。在冷軋延、退火及酸洗之後將表面經研磨後的材料加工成IS13B中所規定的形狀來製作試驗片。使用此試驗片來實施拉伸試驗。The tensile test was carried out under the same conditions as described above. After the cold rolling, annealing, and pickling, the surface-polished material was processed into a shape specified in IS13B to prepare a test piece. This test piece was used to carry out a tensile test.
將所獲得的試驗結果顯示於表5及6。
表3~5的No.A1~A25係本發明例,而No.B1~B13則為比較例。不合在本實施形態所規定之範圍的數值以底線來強調。Nos. A1 to A25 of Tables 3 to 5 are examples of the present invention, and Nos. B1 to B13 are comparative examples. The numerical values that do not fall within the range defined by the present embodiment are emphasized by the bottom line.
將對經賦予間隙後的試驗片1,經使用酸雨的模擬液進行乾濕反覆試驗的結果顯示於表5、6及圖4。The test results of the test piece 1 to which the gap was applied were subjected to a dry-wet test using a simulated liquid using acid rain are shown in Tables 5, 6 and 4.
No.A1~A25係含有在本實施形態中所規定之範圍量的成分並且滿足以下(A)式及(B)式。任一者的平均腐蝕失重都成為0.4mg/cm2 以下。No. A1 to A25 contain the components in the range specified in the present embodiment and satisfy the following formulas (A) and (B). The average corrosion weight loss of either of them was 0.4 mg/cm 2 or less.
(A)式:Cr+10Ti+10Al≧15(A): Cr+10Ti+10Al≧15
(B)式:Si+Cu≦1.1(B) Formula: Si+Cu≦1.1
就(A)式左邊之值為17以上且(B)式左邊之值為0.70以下之例來說,結果係平均腐蝕失重變小為0.30mg/cm2 。In the case where the value on the left side of the formula (A) is 17 or more and the value on the left side of the formula (B) is 0.70 or less, the average corrosion weight loss is reduced to 0.30 mg/cm 2 .
另一方面,就未滿足(A)式或(B)式之例,以及元素含量不合在本實施形態中所規定之範圍的例來說,結果係平均腐蝕失重超過0.40mg/cm2 。On the other hand, in the case where the formula (A) or the formula (B) is not satisfied, and the element content is not in the range specified in the embodiment, the average corrosion loss is more than 0.40 mg/cm 2 .
對經賦予間隙後的試驗片1經使用自燃燒廢氣產生之凝結水的模擬液進行乾濕反覆試驗,將結果顯示於表5、6及圖5。The test piece 1 to which the gap was applied was subjected to a dry-wet test using a simulated liquid using condensed water generated from the combustion exhaust gas, and the results are shown in Tables 5, 6 and 5.
No.A1~A20係含有本實施形態中所規定之範圍量的成分並且滿足以下(A)式及(B’)式。任一者平均腐蝕失重皆成為1.0mg/cm2 以下。No. A1 to A20 contain the components in the range specified in the present embodiment and satisfy the following formulas (A) and (B'). The average corrosion weight loss of either of them was 1.0 mg/cm 2 or less.
(A)式:Cr+10Ti+10Al≧15(A): Cr+10Ti+10Al≧15
(B’)式:Si+Cu≦0.5(B') formula: Si+Cu≦0.5
就(A)式左邊之值為17以上且(B’)式左邊之值低於0.35的 例來說,平均腐蝕失重為小的0.7mg/cm2 。In the case where the value on the left side of the formula (A) is 17 or more and the value on the left side of the (B') formula is less than 0.35, the average corrosion weight loss is 0.7 mg/cm 2 which is small.
進一步,就(A)式左邊之值為18以上且(B’)式左邊之值低於0.20之例來說,顯示平均腐蝕失重係0.5mg/cm2 以下且耐蝕性極為優異的結果。Further, in the case where the value on the left side of the formula (A) is 18 or more and the value on the left side of the (B') formula is less than 0.20, the average corrosion loss is 0.5 mg/cm 2 or less, and the corrosion resistance is extremely excellent.
另一方面,就未滿足(A)式與(B’)式之一者或兩者的例來說,結果任一者平均腐蝕失重皆超過1.0mg/cm2 。On the other hand, in the case where one of the formulas (A) and (B') or both were not satisfied, the average corrosion loss of either of the results exceeded 1.0 mg/cm 2 .
又,拉伸試驗的結果,滿足在本實施形態中所規定之必要條件之例,任一者皆達成32%以上的伸長。進一步,就(B)式左邊之值(Si+Cu)為0.25以下,此外,不含有Mo且Ni量低於0.35%的例來說,伸長值成為34%以上,結果變成加工性非常優異。Further, as a result of the tensile test, an example of the requirements specified in the present embodiment was satisfied, and either of them achieved an elongation of 32% or more. Further, the value (Si+Cu) on the left side of the formula (B) is 0.25 or less, and in the case where Mo is not contained and the amount of Ni is less than 0.35%, the elongation value is 34% or more, and as a result, the workability is extremely excellent.
從以上的結果,揭明了透過本實施形態可提供具有優異耐蝕性及良好加工性的肥粒鐵系不鏽鋼。還有,所謂耐蝕性意指的係因酸雨造成的腐蝕環境或是由在二次熱交換器中之自燃燒廢氣產生的凝結水造成的腐蝕環境中的耐蝕性。From the above results, it has been revealed that the ferrite-based iron-based stainless steel having excellent corrosion resistance and good processability can be provided by the present embodiment. Further, the term "corrosion resistance" means a corrosion environment caused by acid rain or corrosion in a corrosive environment caused by condensed water generated from a combustion exhaust gas in a secondary heat exchanger.
本實施形態,可應用於在因酸雨造成之損害多的地區中在屋外所使用的材料。具體來說,可應用於在各種熱交換器、酸雨環境中之屋外外部裝飾材料、建材、屋頂材料、屋外設備類、貯水/貯熱水槽、家電製品、浴缸、廚房用具以及其它屋外/屋內之一般用途。又,熱交換器用材料,特別係可應用於潛熱回收型熱水器之二次熱交換器用材料。具體來說,不僅係外殼及隔板,亦可應用於如熱交換管般需要加工性的材料。進一步,二次熱交換器用材料不僅係暴露在碳氫 化合物燃料的燃燒廢氣中,亦暴露在包含大量硝酸根離子與硫酸根離子的低pH值溶液中。就此狀態來說,乾濕會反覆進行。本實施形態亦可應用於暴露於這樣的環境中的材料。This embodiment can be applied to materials used outdoors in areas where there is much damage due to acid rain. Specifically, it can be applied to exterior heat and exterior materials in various heat exchangers, acid rain environments, building materials, roofing materials, outdoor equipment, water storage/storage sinks, home appliances, bathtubs, kitchen appliances, and other outdoor/households. General purpose. Further, the material for the heat exchanger is particularly applicable to a material for a secondary heat exchanger of a latent heat recovery type water heater. Specifically, it is not only a case and a separator, but also a material which requires workability like a heat exchange tube. Further, the material for the secondary heat exchanger is not only exposed to hydrocarbons The combustion exhaust gas of the compound fuel is also exposed to a low pH solution containing a large amount of nitrate ions and sulfate ions. In this state, wet and dry will be repeated. This embodiment can also be applied to materials exposed to such an environment.
1‧‧‧試驗片1‧‧‧Test piece
2‧‧‧特夫綸(註冊商標)製螺栓2‧‧‧Teflon (registered trademark) bolts
3‧‧‧特夫綸(註冊商標)製螺帽3‧‧‧Teflon (registered trademark) nuts
4‧‧‧玻璃板4‧‧‧ glass plate
5‧‧‧鈦製墊圈5‧‧‧Titanium washers
7‧‧‧燒杯7‧‧‧ beaker
8‧‧‧模擬液(酸雨的模擬液或燃燒廢氣之凝結水的模擬液)8‧‧‧Simulation fluid (simulation of acid rain or condensate of combustion exhaust gas)
9‧‧‧孔9‧‧‧ hole
圖1係針對耐蝕性之評價方法進行說明的圖,(a)係顯示試樣的設置狀況,(b)係顯示供於試驗之樣本的形狀,(c)係顯示C-C箭號方向的截面圖。Fig. 1 is a view for explaining a method for evaluating corrosion resistance, wherein (a) shows the setting state of the sample, (b) shows the shape of the sample for the test, and (c) shows a sectional view of the direction of the CC arrow. .
圖2係顯示在利用由酸雨之模擬液進行的腐蝕試驗所測定的平均腐蝕失重,與構成元素之關係的圖。Fig. 2 is a graph showing the relationship between the average corrosion weight loss measured by the corrosion test by the acid rain simulation liquid and the constituent elements.
圖3係顯示在利用由燃燒廢氣之凝結水的模擬液進行之腐蝕試驗所測定的平均腐蝕失重,與構成元素之關係的圖。Fig. 3 is a graph showing the relationship between the average corrosion loss and the constituent elements measured by a corrosion test using a simulated liquid of condensed water for burning exhaust gas.
圖4係顯示在實施例及比較例之結果中,在利用酸雨之模擬液進行之腐蝕試驗所測定的平均腐蝕失重,與構成元素之關係的圖。Fig. 4 is a graph showing the relationship between the average corrosion loss and the constituent elements measured by a corrosion test using a simulated liquid of acid rain in the results of the examples and the comparative examples.
圖5係顯示在實施例及比較例之結果中,在利用燃燒廢氣之凝結水的模擬液進行之腐蝕試驗所測定的平均腐蝕失重,與構成元素之關係的圖。Fig. 5 is a graph showing the relationship between the average corrosion loss and the constituent elements measured by a corrosion test using a simulated liquid of condensed water for burning exhaust gas in the results of the examples and the comparative examples.
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