JP2009041103A - Austenitic stainless steel for component of exhaust gas re-circulation system, and manufacturing method therefor - Google Patents
Austenitic stainless steel for component of exhaust gas re-circulation system, and manufacturing method therefor Download PDFInfo
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Abstract
Description
本発明は、自動車のエンジンの排気側から分岐して吸気側の間に配置される排気ガス再循環系部品に用いられるオーステナイト系ステンレス鋼およびその製造方法に関するものである。 The present invention relates to an austenitic stainless steel used for exhaust gas recirculation system parts branched from an exhaust side of an automobile engine and disposed between intake sides, and a method of manufacturing the same.
自動車用ディーゼルエンジンにおいて、近年厳しくなってきた排気ガス規制をクリアするために、排気ガスの一部を吸気側に還流させる、排気ガス再循環（Ｅｘｈａｕｓｔ Ｇａｓ Ｒｅｃｉｒｃｕｌａｔｉｏｎ、通称「ＥＧＲ」と呼ばれる）の系統を設置して、燃焼温度を低く抑えてＮＯｘの生成を抑制する方法が採られてきている。
この排気ガス再循環系には、排気ガス流路用パイプ類、チャンバー類、ＥＧＲバルブ部品、冷却器（ＥＧＲクーラー）部品、種々センサー部品などの多くの用途に金属材料が使用されている。ＥＧＲ経路においては、特にＥＧＲクーラーを通過した再循環ガスが冷却されることによって、再循環ガス中の水分が凝縮して凝縮水となる。この凝縮水には、燃料中に含まれる硫黄分が濃縮されて主に硫酸水の環境となる。
このような硫酸環境の凝縮水が部分的に滞留すると、その部分で金属材料の腐食が促進されて、最終的にはパイプ等のガス流路の金属材料に腐食による貫通孔が開き、再循環ガスが漏洩したり、薄肉の金属材料を用いた部品においては、腐食による部品の折損、脱落が起こったりする恐れがある。
従来、排気ガス再循環系においては、耐硫酸腐食性を得るために、ステンレス鋼の部品が使用されてきており、ＥＧＲバルブ部品には耐硫酸腐食性の優れたオーステナイト系ステンレス鋳鋼が提案されている（例えば、特許文献１参照）。この提案はオーステナイト系ステンレス鋳鋼の組成を最適化することによって広範囲の硫酸濃度の硫酸水中で優れた耐硫酸腐食性を示すという点で優れたものである。
In this exhaust gas recirculation system, metal materials are used in many applications such as exhaust gas flow pipes, chambers, EGR valve parts, cooler (EGR cooler) parts, and various sensor parts. In the EGR path, in particular, when the recirculated gas that has passed through the EGR cooler is cooled, the water in the recirculated gas is condensed and becomes condensed water. In this condensed water, the sulfur content contained in the fuel is concentrated and becomes an environment of mainly sulfuric acid water.
When the condensed water in such a sulfuric acid environment partially accumulates, corrosion of the metal material is promoted at that portion, and finally, a through-hole due to corrosion opens in the metal material of the gas flow path such as a pipe and recirculates. There is a risk that gas leaks or parts using thin metal materials break or drop off due to corrosion.
Conventionally, in exhaust gas recirculation systems, stainless steel parts have been used to obtain sulfuric acid corrosion resistance, and austenitic stainless cast steel having excellent sulfuric acid corrosion resistance has been proposed for EGR valve parts. (For example, refer to Patent Document 1). This proposal is excellent in that it shows excellent sulfuric acid corrosion resistance in sulfuric acid water in a wide range of sulfuric acid concentrations by optimizing the composition of the austenitic stainless cast steel.
上述した特許文献１に開示されるステンレス鋳鋼からなる部品は、ＳＣＳ１３、ＳＣＳ１６のようなＪＩＳに規定される一般のステンレス鋳鋼に比べると良好な耐硫酸腐食性を有するものの、さらに厳しい排ガス規制によってＥＧＲ流路を通過する再循環ガス流量の増加すると、さらに良好な耐硫酸腐食性が要求されることになる。また、鋳鋼では製造不可能な薄肉部品への使用も考えると必ずしも十分とは言えない。
本発明の目的は、薄肉化が可能な圧延加工ができ、かつ、さらに良好な耐硫酸腐食性を具備した排ガス再循環系部品用オーステナイト系ステンレス鋼を提供することである。
The parts made of cast stainless steel disclosed in Patent Document 1 described above have better sulfuric acid corrosion resistance than ordinary cast stainless steels defined by JIS such as SCS13 and SCS16, but are more strict by exhaust gas regulations. When the flow rate of the recirculation gas passing through the flow path is increased, even better sulfuric acid corrosion resistance is required. In addition, it is not always sufficient when considering use for thin parts that cannot be manufactured with cast steel.
An object of the present invention is to provide an austenitic stainless steel for exhaust gas recirculation system parts that can be rolled to enable thinning, and further has excellent sulfuric acid corrosion resistance.
本発明者は、硫酸腐食環境が厳しい排ガス再循環系部品の材質として、圧延可能なオーステナイト系ステンレス鋼に着目し、その合金系と合金元素量を最適化することによって低濃度から高濃度までの広範囲の硫酸水に対して優れた耐食性が得られることを見いだし本発明に到達した。
すなわち本発明は、質量％でＣ：０．２５％以下、Ｓｉ：２．０％以下、Ｍｎ：２．０％以下、Ｃｒ：１２〜２０％、Ｎｉ：８〜１４％、Ｍｏ：０．１〜４％、Ｗ：２％以下（０を含む）で、かつ（Ｍｏ＋０．５Ｗ）：０．１〜４％、Ｃｕ：０．５〜３％、Ｎｂ：０．０３〜１．５％、残部は実質的にＦｅでなり、粒子状のＮｂ炭化物が分散した金属組織を有する排ガス再循環系部品用オーステナイト系ステンレス鋼である。
好ましくは質量％濃度２０〜９６％の硫酸に６０℃で５時間浸漬した後の腐食減量が１００ｇ／（ｍ２・ｈ）以下である排ガス再循環系部品用オーステナイト系ステンレス鋼である。
また本発明は、質量％でＣ：０．２５％以下、Ｓｉ：２．０％以下、Ｍｎ：２．０％以下、Ｃｒ：１２〜２０％、Ｎｉ：８〜１４％、Ｍｏ：０．１〜４％、Ｗ：２％以下（０を含む）で、かつ（Ｍｏ＋０．５Ｗ）：０．１〜４％、Ｃｕ：０．５〜３％、Ｎｂ：０．０３〜１．５％、残部は実質的にＦｅでなる圧延用素材を熱間圧延と冷間圧延とを少なくとも１回以上行い、厚さ２ｍｍ以下の帯材とする工程を含む排ガス再循環系部品用オーステナイト系ステンレス鋼の製造方法である。
The present inventor has focused on austenitic stainless steel that can be rolled as a material for exhaust gas recirculation parts with severe sulfuric acid corrosive environments, and has optimized the alloy system and the amount of alloy elements from low to high concentrations. The inventors have found that excellent corrosion resistance can be obtained with respect to a wide range of sulfuric acid water, and have reached the present invention.
That is, in the present invention, by mass, C: 0.25% or less, Si: 2.0% or less, Mn: 2.0% or less, Cr: 12-20%, Ni: 8-14%, Mo: 0.00. 1-4%, W: 2% or less (including 0), and (Mo + 0.5W): 0.1-4%, Cu: 0.5-3%, Nb: 0.03-1.5% The balance is austenitic stainless steel for exhaust gas recirculation system parts having a metal structure that is substantially made of Fe and in which particulate Nb carbides are dispersed.
Preferably, it is an austenitic stainless steel for exhaust gas recirculation system parts having a weight loss of corrosion of 100 g / (m 2 · h) or less after being immersed in sulfuric acid having a mass% concentration of 20 to 96% at 60 ° C. for 5 hours.
Moreover, this invention is C: 0.25% or less, Si: 2.0% or less, Mn: 2.0% or less, Cr: 12-20%, Ni: 8-14%, Mo: 0.1% by mass%. 1-4%, W: 2% or less (including 0), and (Mo + 0.5W): 0.1-4%, Cu: 0.5-3%, Nb: 0.03-1.5% The balance is austenitic stainless steel for exhaust gas recirculation system parts including a step of performing a hot rolling and a cold rolling at least once on a material for rolling consisting essentially of Fe to form a strip having a thickness of 2 mm or less. It is a manufacturing method.
本発明の排ガス再循環系部品用オーステナイト系ステンレス鋼は耐酸化性だけでなく、耐硫酸腐食性が優れているため、排ガス再循環系の部品の寿命を大幅に改善する効果を得ることができ、これを用いてなる排ガス再循環系部品は薄肉化による軽量化と長寿命化の効果を奏するものである。 Since the austenitic stainless steel for exhaust gas recirculation system parts of the present invention is excellent not only in oxidation resistance but also in sulfuric acid corrosion resistance, it is possible to obtain the effect of greatly improving the life of exhaust gas recirculation system parts. The exhaust gas recirculation system parts using this have the effect of reducing the weight and extending the service life by reducing the thickness.
上述したように本発明の重要な特徴は耐酸化性および良好な耐硫酸腐食性を併せもった最適組成にある。
以下に各元素の作用について説明する。なお、各元素の含有量は質量％として記す。
ＣはＣｒ等と結びついて炭化物を形成し、結晶粒粗大化を防止する作用があり、少量添加が必要である。しかし、過度の添加は多量の炭化物形成による冷間加工性の低下およびマトリックス中のＣｒの欠乏を招き耐硫酸腐食性を低下させるため０．２５％以下に限定する。好ましいＣの上限は０．１５％であり、更に好ましくは０．０８％である。
As described above, an important feature of the present invention is an optimum composition that combines oxidation resistance and good sulfuric acid corrosion resistance.
The operation of each element will be described below. In addition, content of each element is described as mass%.
C combines with Cr and the like to form carbides and has the effect of preventing crystal grain coarsening, and a small amount needs to be added. However, excessive addition causes a decrease in cold workability due to the formation of a large amount of carbide and a deficiency of Cr in the matrix, so that the sulfuric acid corrosion resistance is lowered. Therefore, it is limited to 0.25% or less. The upper limit of C is preferably 0.15%, more preferably 0.08%.
Ｓｉは溶湯に対して強力な脱酸作用を発揮するほか、鋳造性を向上させる作用がある。また、Ｓｉは硫酸水に対して大きく耐食性を向上させる作用を有する。またＳｉＯ２は酸化被膜と母材の中間に形成され、酸化被膜の剥離を阻止する。これらの理由でＳｉを添加するが、過度の添加は耐酸化性の低下を招くためＳｉは２．０％以下とした。好ましいＳｉ含有量の下限は０．１％である。また、好ましいＳｉの上限は１．５％である。
ＭｎはＳｉと同じく脱酸作用を発揮するほか、鋳造性を向上させる作用があるが、過度の添加は耐酸化性の低下を招くためＭｎは２．０％以下とした。好ましいＭｎ含有量の下限は０．１％である。また、好ましいＭｎの上限は１．５％である。
Si exhibits a strong deoxidizing action on the molten metal and has an effect of improving castability. Moreover, Si has the effect | action which improves a corrosion resistance largely with respect to sulfuric acid water. SiO 2 is formed between the oxide film and the base material, and prevents the oxide film from peeling off. For these reasons, Si is added. However, excessive addition causes a decrease in oxidation resistance, so Si was made 2.0% or less. The lower limit of the preferred Si content is 0.1%. A preferable upper limit of Si is 1.5%.
Mn exhibits a deoxidizing effect similar to Si, and has an effect of improving castability. However, excessive addition causes a decrease in oxidation resistance, so Mn is set to 2.0% or less. The minimum of preferable Mn content is 0.1%. A preferable upper limit of Mn is 1.5%.
Ｃｒはマトリックス中に存在することにより高温において材料表面にＣｒ２Ｏ３被膜を形成し耐酸化性を向上させるだけでなく、表面に不動態皮膜を形成させることによって硫酸水等の酸に対する耐食性を向上させるために非常に有効な元素である。硫酸に対する耐食性および高温での耐酸化性を付与させるためには、下限を１２％以上とすることが必要である。しかし、過度の添加はマトリックスをオーステナイト単相組織ではなく、オーステナイトとフェライトの２相組織に変化させて熱間加工性を低下させる。従って、Ｃｒの含有量を１２〜２０％とした。好ましくは１６〜２０％である。
Ｎｉは硫酸水中での耐食性を向上させるのに有効な元素であるだけでなく、マトリックスをオーステナイト単相組織にして熱間加工性を向上させるのに必要な元素である。Ｎｉは８％より少ないとオーステナイト組織を安定に維持できず、良好な耐硫酸腐食性も得られず、一方１４％を超えて添加すると特性向上の割りに高価になるので、Ｎｉは８〜１４％とした。好ましくは８．５〜１１％である。
The presence of Cr in the matrix not only improves the oxidation resistance by forming a Cr 2 O 3 film on the surface of the material at high temperatures, but also provides a corrosion resistance to acids such as sulfuric acid by forming a passive film on the surface. It is a very effective element to improve. In order to impart corrosion resistance to sulfuric acid and oxidation resistance at high temperatures, the lower limit must be 12% or more. However, excessive addition changes the matrix to a two-phase structure of austenite and ferrite instead of an austenite single-phase structure, thereby reducing hot workability. Therefore, the content of Cr is set to 12 to 20%. Preferably it is 16 to 20%.
Ni is not only an element effective for improving the corrosion resistance in sulfuric acid water, but also an element necessary for improving the hot workability by making the matrix into an austenite single phase structure. If Ni is less than 8%, the austenite structure cannot be stably maintained, and good sulfuric acid corrosion resistance cannot be obtained. On the other hand, if Ni is added in excess of 14%, it becomes expensive for improving the characteristics. %. Preferably it is 8.5 to 11%.
ＭｏはＣｒの不動態化皮膜を安定化させて耐硫酸腐食性を向上させる効果がある。Ｗも同様の効果があるが、単独添加では効果が低く、Ｗを添加する場合はＭｏとともに添加する。Ｍｏは０．１％より少ないと効果がなく、一方４％より多く添加するとフェライト相を生成しやすくなるため、オーステナイト単相のマトリックス組織を維持できなくなり熱間加工性が低下するため、Ｍｏは０．１〜４％とした。好ましくは、０．１〜１．５％である。
ＷはＭｏと共に添加する場合はＭｏ当量で同量（原子濃度で同量）添加、すなわち質量％でＷ量の１／２添加するが、無添加でもよいことから、Ｗは２％以下とした。
Ｍｏ＋０．５ＷはＭｏ、Ｗをともに添加する場合のＭｏ当量を表しており、Ｍｏ当量がＭｏ単独添加の場合の範囲であればよいことから、０．１〜４％とした。好ましくは、０．１〜１．５％である。
Mo has an effect of stabilizing the passivation film of Cr and improving the resistance to sulfuric acid corrosion. W has the same effect, but the effect is low when it is added alone, and when W is added, it is added together with Mo. If Mo is less than 0.1%, there is no effect. On the other hand, if it is added more than 4%, a ferrite phase is likely to be formed, so that the matrix structure of the austenite single phase cannot be maintained and hot workability is reduced. It was set to 0.1 to 4%. Preferably, it is 0.1 to 1.5%.
When W is added together with Mo, it is added in the same amount as Mo equivalent (same amount in atomic concentration), that is, ½% of W amount is added in mass%, but it may not be added, so W was set to 2% or less. .
Mo + 0.5W represents the Mo equivalent when Mo and W are added together, and the Mo equivalent may be in the range when Mo alone is added, so the content was set to 0.1 to 4%. Preferably, it is 0.1 to 1.5%.
Ｃｕは耐硫酸腐食性を大幅に向上させる有効な元素であり、かつオーステナイト相を安定化して熱間加工性を改善する効果を有する。Ｃｕは０．５％より少ないと十分な耐硫酸腐食性が得られず、一方３％を超えて添加すると熱間加工時に表面にＣｕが濃化して熱間加工性を低下させる恐れがあることから、Ｃｕは０．５〜３％とした。好ましくは、１％〜３％である。
ＮｂはＣと結びついて炭化物を形成し、オーステナイト相のマトリックス中の固溶Ｃを低下させて耐食性を向上させるだけでなく、Ｎｂ炭化物がオーステナイト結晶粒界をピン止めすることで結晶粒を微細化して熱間および冷間加工性を向上させる効果を有する。Ｎｂは０．０３％より少ないと効果が十分でなく、一方、１．５％を越えて添加するとＮｂ炭化物が粗大化して逆に熱間加工性を低下させることから、Ｎｂは０．０３〜１．５％とした。好ましくは、０．０３〜１．０％である。
Cu is an effective element that greatly improves the resistance to sulfuric acid corrosion, and has an effect of improving the hot workability by stabilizing the austenite phase. When Cu is less than 0.5%, sufficient sulfuric acid corrosion resistance cannot be obtained. On the other hand, when Cu is added in excess of 3%, Cu may be concentrated on the surface during hot working, which may reduce hot workability. Therefore, Cu was 0.5 to 3%. Preferably, it is 1% to 3%.
Nb combines with C to form carbides and not only lowers the solid solution C in the austenite phase matrix to improve corrosion resistance, but also Nb carbides refine the grains by pinning austenite grain boundaries. This has the effect of improving hot and cold workability. If Nb is less than 0.03%, the effect is not sufficient. On the other hand, if added over 1.5%, Nb carbides coarsen and conversely reduce hot workability. 1.5%. Preferably, it is 0.03 to 1.0%.
なお、本発明では以下の元素は下記の範囲内で本発明鋼に含まれても良い。
Ａｌ≦０．１％、Ｐ≦０．０４％、Ｖ≦０．５％、Ｔａ≦０．５％、Ｃａ≦０．０２％、Ｃｏ≦２％、Ｂ≦０．０１％、Ｎ≦０．０５％
In the present invention, the following elements may be included in the steel of the present invention within the following range.
Al ≦ 0.1%, P ≦ 0.04%, V ≦ 0.5%, Ta ≦ 0.5%, Ca ≦ 0.02%, Co ≦ 2%, B ≦ 0.01%, N ≦ 0 .05%
次に本発明鋼の組織について説明する。
本発明の排ガス再循環系部品用オーステナイト系ステンレス鋼の組織はオーステナイト相からなるマトリックス中に粒子状のＮｂ炭化物が分散したものである。オーステナイト相はＮｉを多く含むことから耐硫酸腐食性に対して好ましい組織である。
また、Ｎｂ炭化物は、鋳造後に行う例えば熱間鍛造等の熱間塑性加工により、粒子状に分断されたものが分散することによって、熱間圧延と冷間圧延の工程中にオーステナイト結晶粒界をピン止めして結晶粒の微細化に有効に作用する。
粒子状に分散していないとオーステナイト結晶粒のピン止め効果が不均一となり、結晶粒微細化が均一に起こらないため、熱間加工性、冷間加工性が低下するだけでなく、均一な耐硫酸腐食性も得られにくくなるので、Ｎｂ炭化物は粒子状に分散する必要がある。
この場合、Ｎｂ炭化物粒子の最大サイズは０．１μｍ〜１５μｍの範囲内であれば良い。過度にＮｂ炭化物粒子が粗大化すると、冷間圧延工程にて割れ等の問題が生じる場合がある。また、過度にＮｂ炭化物粒子が微細であると上記のピン止め効果が得にくくなる。
なお、典型的な粒子状のＮｂ炭化物の存在形態を示すと、例えば図１および図２に示すように固溶化処理を行った再結晶組織中に単独で存在するものや、複数個のＮｂ炭化物粒子が連なっているものがある。何れの顕微鏡写真も粒子状のＮｂ炭化物が分散した金属組織である。
Next, the structure of the steel of the present invention will be described.
The structure of the austenitic stainless steel for exhaust gas recirculation system parts of the present invention is such that particulate Nb carbide is dispersed in a matrix composed of an austenitic phase. Since the austenite phase contains a large amount of Ni, it is a preferred structure for sulfuric acid corrosion resistance.
In addition, Nb carbide is dispersed in the form of particles by hot plastic working such as hot forging performed after casting, thereby dispersing austenite grain boundaries during the hot rolling and cold rolling processes. It works effectively for pinning and crystal grain refinement.
If not dispersed in the form of particles, the pinning effect of the austenite crystal grains becomes non-uniform, and the refinement of the crystal grains does not occur uniformly. Therefore, not only the hot workability and the cold workability are lowered, but also uniform resistance Since it becomes difficult to obtain sulfuric acid corrosivity, Nb carbides must be dispersed in the form of particles.
In this case, the maximum size of the Nb carbide particles may be in the range of 0.1 μm to 15 μm. If the Nb carbide particles are excessively coarse, problems such as cracks may occur in the cold rolling process. Further, if the Nb carbide particles are excessively fine, it is difficult to obtain the above pinning effect.
In addition, when the typical form of the particulate Nb carbide is shown, for example, as shown in FIG. 1 and FIG. 2, it exists alone in the recrystallized structure subjected to the solution treatment, or a plurality of Nb carbides. Some particles are connected. Each micrograph is a metal structure in which particulate Nb carbide is dispersed.
以上、説明する本発明の組成を有するオーステナイト系ステンレス鋼は、硫酸腐食環境が厳しい排ガス再循環系部品を模試する環境である、質量％濃度２０〜９６％の硫酸に６０℃で５時間浸漬した後の腐食減量が１００ｇ／（ｍ２・ｈ）以下とすることができる。
以上、説明する本発明の組成を有するオーステナイト系ステンレス鋼は、耐硫酸腐食性が良好であるため、より薄肉化して使用することが可能である。薄肉化する手段として、熱間圧延と冷間圧延を少なくとも行うことが好ましい。熱間圧延または冷間圧延の圧延素材は鋳造した鋼塊でもよいし、鋳造した鋼塊を鍛造した鋼片でもよい。圧延によって鋳鋼では製造しづらい２ｍｍ以下の厚さに仕上げることが容易に可能である。
As described above, the austenitic stainless steel having the composition of the present invention described above is immersed in sulfuric acid having a mass% concentration of 20 to 96% for 5 hours at 60 ° C., which is an environment for testing exhaust gas recirculation system parts having severe sulfuric acid corrosion environment. The subsequent corrosion weight loss can be 100 g / (m 2 · h) or less.
As described above, since the austenitic stainless steel having the composition of the present invention to be described has good resistance to sulfuric acid corrosion, it can be used after being made thinner. As means for thinning, it is preferable to perform at least hot rolling and cold rolling. The rolled material for hot rolling or cold rolling may be a cast steel ingot or a steel piece forged from the cast steel ingot. It is possible to easily finish the cast steel to a thickness of 2 mm or less, which is difficult to manufacture with cast steel.
以下の実施例で本発明を更に詳しく説明する。
真空溶解により、表１に示す組成のオーステナイト系ステンレス鋼の１０ｋｇインゴットを溶製した。表１中の合金Ｎｏ．１〜４は本発明合金、合金Ｎｏ．１１、Ｎｏ．１２は比較に用いた従来オーステナイト系ステンレス鋼である。
そして、上記のインゴットを鍛造および熱間圧延によって厚さ２０ｍｍの板材に加工した後、１０５０℃×３０分保持後、水冷の溶体化処理を施した。
The following examples further illustrate the present invention.
An austenitic stainless steel 10 kg ingot having the composition shown in Table 1 was melted by vacuum melting. Alloy No. 1 in Table 1 1-4 are alloys according to the present invention, alloy no. 11, no. 12 is a conventional austenitic stainless steel used for comparison.
And after processing said ingot into a 20-mm-thick board | plate material by forging and hot rolling, after hold | maintaining 1050 degreeC x 30 minutes, the solution treatment of water cooling was performed.
本発明合金Ｎｏ．１〜４、比較合金Ｎｏ．１１、Ｎｏ．１２の厚さ２０ｍｍの板材より直径１０ｍｍ、長さ２０ｍｍの円柱状試験片を採取し、６０℃の質量％濃度２０％、４０％、６０％、８０％、９６％の硫酸中に５時間浸漬した後の腐食減量を測定し、耐硫酸腐食性を評価した。
また、本発明合金Ｎｏ．１〜４、比較合金Ｎｏ．１１、Ｎｏ．１２の板材より直径１０ｍｍ、長さ２０ｍｍの円柱状試験片を採取し、９００℃の大気中で１００時間加熱した後の酸化増量を測定し、耐酸化性を評価した。
これらの評価結果を表２に示すが、本発明合金Ｎｏ．１〜４は何れも比較合金Ｎｏ．１１、Ｎｏ．１２に比べて、硫酸水中での腐食減量が大幅に少なく、かつ高温大気中での酸化増量が少ない。したがって、本発明合金は、良好な耐硫酸腐食性と耐酸化性を兼備していることがわかる。
Invention alloy No. 1-4, comparative alloy no. 11, no. A cylindrical test piece having a diameter of 10 mm and a length of 20 mm was taken from a plate material having a thickness of 12 mm and immersed in sulfuric acid at a mass concentration of 60%, 20%, 40%, 60%, 80% and 96% for 5 hours. The corrosion weight loss after the measurement was measured, and the sulfuric acid corrosion resistance was evaluated.
In addition, the alloy No. of the present invention. 1-4, comparative alloy no. 11, no. Cylindrical test pieces having a diameter of 10 mm and a length of 20 mm were collected from 12 plate materials, and the oxidation increase after heating in the atmosphere at 900 ° C. for 100 hours was measured to evaluate the oxidation resistance.
These evaluation results are shown in Table 2. 1 to 4 are all comparative alloy Nos. 11, no. Compared to 12, the corrosion weight loss in sulfuric acid water is significantly less, and the oxidation gain in high temperature air is less. Therefore, it can be seen that the alloy of the present invention has both good sulfuric acid corrosion resistance and oxidation resistance.
さらに排気ガス再循環系の薄肉部品に適用できるかを確認するため、冷間加工を行い、厚さ０．５ｍｍに圧延加工を行った。その結果、割れ等の問題もなく冷間加工が行えた。
この結果から、本発明の排ガス再循環系部品用オーステナイト系ステンレス鋼は、薄肉化が可能な熱間圧延および冷間圧延による圧延加工ができ、かつ、さらに良好な耐硫酸腐食性を具備するものであることが確認された。
Further, in order to confirm whether it can be applied to a thin-walled part of an exhaust gas recirculation system, cold working was performed, and rolling was performed to a thickness of 0.5 mm. As a result, cold working was possible without problems such as cracking.
From this result, the austenitic stainless steel for exhaust gas recirculation system parts of the present invention can be rolled by hot rolling and cold rolling capable of thinning, and further has excellent sulfuric acid corrosion resistance. It was confirmed that.
また、本発明の排ガス再循環系部品用オーステナイト系ステンレス鋼Ｎｏ．１の熱間圧延後、溶体化処理したものの断面顕微鏡写真を図１に示し、冷間圧延後、溶体化処理したものの断面顕微鏡写真を図２に示す。
図１および図２から、本発明の再循環系部品用オーステナイト系ステンレス鋼は、マトリックスは再結晶したオーステナイト単相組織からなり、最大サイズが１５μｍ以下の粒子状のＮｂ炭化物が分散した金属組織を有することがわかる。このような組織を得ることによって安定した耐硫酸腐食性を得ることができる。
なお、熱間圧延後の金属組織および冷間圧延後の金属組織も観察したが、その金属組織は、圧延組織中に粒子状のＮｂ炭化物が分散した金属組織であり、Ｎｏ．２〜Ｎｏ．４の本発明鋼の金属組織も同様であった。
In addition, austenitic stainless steel No. 1 for exhaust gas recirculation system parts of the present invention. FIG. 1 shows a cross-sectional photomicrograph of the solution treated after the hot rolling 1 and FIG. 2 shows a cross-sectional photo of the solution treated after the cold rolling.
From FIG. 1 and FIG. 2, the austenitic stainless steel for recirculation system parts of the present invention has a matrix composed of a recrystallized austenite single phase structure and a metal structure in which particulate Nb carbide having a maximum size of 15 μm or less is dispersed. You can see that By obtaining such a structure, stable sulfuric acid corrosion resistance can be obtained.
The metal structure after hot rolling and the metal structure after cold rolling were also observed. The metal structure was a metal structure in which particulate Nb carbides were dispersed in the rolled structure. 2-No. The metal structure of steel No. 4 of the present invention was the same.
本発明合金は、広範囲の濃度の硫酸水環境での耐腐食性に優れ、かつ高温大気中での耐酸化性が良好であることから、これらの特性を兼備することが要求される排ガス再循環系部品に適用することができる。 The alloy of the present invention has excellent corrosion resistance in a wide range of sulfuric acid environments and good oxidation resistance in high-temperature air, so exhaust gas recirculation is required to combine these characteristics. It can be applied to system parts.
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2012133574A1 (en) * | 2011-03-29 | 2012-10-04 | 新日鐵住金ステンレス株式会社 | Highly corrosion-resistant austenite stainless steel well-suited to brazing |
| JP2013199661A (en) * | 2012-03-23 | 2013-10-03 | Nisshin Steel Co Ltd | Austenitic stainless steel for member of exhaust gas flow channel |
| JP2015189990A (en) * | 2014-03-27 | 2015-11-02 | 日新製鋼株式会社 | Austenitic stainless steel for exhaust gas flow passage member excellent in corrosion resistance, particularly having improved sensitization property |
| WO2018117488A1 (en) * | 2016-12-23 | 2018-06-28 | 주식회사 포스코 | Austenitic stainless steel with excellent sulfuric acid corrosion resistance |
| KR20180073879A (en) * | 2016-12-23 | 2018-07-03 | 주식회사 포스코 | Austenitic stainless steel having excellent hot workability and corrosion resistance and method of manufacturing the same |
| KR20200057441A (en) * | 2018-11-16 | 2020-05-26 | 주식회사 포스코 | Austenitic stainless steel with excellent resistance to stress corrosion cracking and surfuric acid dew point corrosion |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2012133574A1 (en) * | 2011-03-29 | 2012-10-04 | 新日鐵住金ステンレス株式会社 | Highly corrosion-resistant austenite stainless steel well-suited to brazing |
| JP2013199661A (en) * | 2012-03-23 | 2013-10-03 | Nisshin Steel Co Ltd | Austenitic stainless steel for member of exhaust gas flow channel |
| JP2015189990A (en) * | 2014-03-27 | 2015-11-02 | 日新製鋼株式会社 | Austenitic stainless steel for exhaust gas flow passage member excellent in corrosion resistance, particularly having improved sensitization property |
| WO2018117488A1 (en) * | 2016-12-23 | 2018-06-28 | 주식회사 포스코 | Austenitic stainless steel with excellent sulfuric acid corrosion resistance |
| KR20180073879A (en) * | 2016-12-23 | 2018-07-03 | 주식회사 포스코 | Austenitic stainless steel having excellent hot workability and corrosion resistance and method of manufacturing the same |
| KR101903173B1 (en) * | 2016-12-23 | 2018-10-01 | 주식회사 포스코 | Austenitic stainless steel having excellent hot workability and corrosion resistance and method of manufacturing the same |
| KR20200057441A (en) * | 2018-11-16 | 2020-05-26 | 주식회사 포스코 | Austenitic stainless steel with excellent resistance to stress corrosion cracking and surfuric acid dew point corrosion |
| KR102143076B1 (en) * | 2018-11-16 | 2020-08-10 | 주식회사 포스코 | Austenitic stainless steel with excellent resistance to stress corrosion cracking and surfuric acid dew point corrosion |
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