二次急冷淬火成形SAF2507双相不锈钢螺旋桨在SRB+IOB海水中的腐蚀行为

Corrosion Behaviors of SAF2507 DSS Propeller Blade by Secondary Quench Stamping in SRB+IOB Seawater

为了研究SAF2507双相不锈钢(SAF2507 DSS)螺旋桨叶片在含硫酸盐还原菌(SRB)和铁氧化菌(IOB)海水中的耐腐蚀性能,提出一种二次急冷淬火成形技术来成形SAF2507DSS螺旋桨叶片。同时根据螺旋桨叶片在不同二次急冷淬火成形温度下析出相的类型和析出规律,研究螺旋桨叶片在含SRB和IOB海水中的耐腐蚀性能。结果表明,当二次急冷淬火成形温度在700℃时,螺旋桨叶片表面析出少量的χ相;达到850℃时,χ相停止析出并完全转化成σ相,析出的σ相达到最大值;超过850℃时,析出的σ相开始急剧减少,到950℃时仅有少量的σ相析出。螺旋桨叶片在不同二次急冷淬火成形温度下,腐蚀电流密度、交流阻抗等电化学性能变化规律与螺旋桨叶片表层χ相和σ相的析出规律、以及χ相和σ相自身的耐腐蚀特征相吻合。二次急冷淬火成形温度在750~1050℃之间,螺旋桨叶片的耐腐蚀性能随热成形温度的升高呈增强-降低-增强规律变化,850℃时螺旋桨叶片的耐腐蚀性能最差。螺旋桨叶片二次急冷淬火成形后富Fe的表面特征,使得在SRB+IOB的作用下,螺旋桨叶片表面钝化膜被破坏,导致耐腐蚀性能降低。

In order to study the corrosion resistance of the SAF2507 duplex stainless steel(SAF2507 DSS)propeller blades in seawater containing sulfate-reducing bacteria(SRB)and iron oxidizing bacteria(IOB),a secondary quench stamping technology was proposed to stamping SAF2507 DSS propeller blades.The corrosion behavior of propeller blades in seawater containing SRB and IOB was studied according to the precipitated phases types and precipitation laws of the propeller blades at different secondary quench stamping temperatures.The results show that when the secondary quench stamping temperature is 700℃,a small amount of χ phases are precipitated on the surface of the propeller blades;and when it reaches 850℃,the χ phases is completely converted to theσphases,and the precipitation ofσphases reaches the peak value,and at 950℃ only a small number of σ phases are precipitated.The variation laws of the corrosion current density,Ac impedance and other electrochemical properties of propeller blades at different secondary quench stamping temperatures are consistent with precipitation law of χ phases andσphases in the surface layer of propeller blades and the corrosion resistance characteristics ofχphases and σ phases.When the secondary quench stamping temperature is between 750℃ and 1050℃,the corrosion resistance of propeller blades changes in the rule of“enhancement-reduction-enhancement”with the increase of the secondary quench stamping temperature,and the corrosion resistance of propeller blades is the worst at 850℃ in seawater containing SRB and IOB.For the surface characteristics of the rich Fe on the surface layer of propeller blade after secondary quench stamping,the surface passivation film of propeller blade is damaged in seawater containing SRB and IOB,which leads to the decrease of corrosion resistance.