【作者】 王刚；

【导师】 郭幼丹；

【作者基本信息】 集美大学 ， 船舶与海洋工程， 2015， 硕士

【摘要】 长期以来螺旋桨的选材多为铜合金,然而其材料强度严重制约着船舶向着大型化、高速化方向发展,加上铜合金耐海水中硫化物腐蚀的能力有限,因此,这些对于螺旋桨的选材及制作工艺提出了更高的要求。本文螺旋桨选材为SAF2507双相不锈钢,这种材料具有铁素体-奥氏体两相组织,合金化程度很高,腐蚀性能极佳,其PRE值(耐点腐蚀能力当量)高达42,完全可以应用于海水环境中。针对选用的SAF2507双相不锈钢,如何通过正确、合理的热成形工艺来提高材料的强度等力学性能,改善材料的微观结构成为亟待解决的问题,这也是本文的主要研究内容。为制定出SAF2507双相不锈钢最佳的热成形工艺参数,本文进行了一系列实验研究和理论分析。首先我们将试样置于不同的热成形工艺条件下(如温度、冷却速度等参数变化)进行处理,之后进行试样的拉伸、冲击和显微硬度实验,分析热成形工艺参数对于材料力学性能的影响；材料热成形前后的显微结构和合金元素的变化通过扫描电镜与能谱仪测试得到,用于比较热成形对于材料微观组织结构、相比例以及合金元素的影响,另外分析了有害相σ相对于材料冲击性能的影响。最后,在热模拟试验机上进行材料CCT曲线的绘制,得到材料的CCT曲线所反映出来的特性和前面的实验数据相吻合。SAF2507双相不锈钢热成形温度应在1050℃以上,低于此温度将会析出有害相；应以较快的冷却速率通过600℃～1000℃区域,冷却速率越小,材料中铁素体分解就越完全,有害相析出也越多,材料显微硬度也随之升高,材料易发生脆性断裂。材料热成形温度达到1100℃,冷却速率大于30℃时,微观组织中无有害相的析出,铁素体-奥氏体两相比例接近1：1,同时晶粒得到细化,大幅提高了材料强度,热成形后材料所形成的渐变微观结构使其具备优良的抗冲击性能,同时具备较好的韧性。通过合理的热成形工艺处理后的材料强度可达1200MPa,延伸率在40%以上更多还原

【Abstract】 For a long time, propeller materials are copper alloy, however the strength of this material severely restricts the development of ship with large-scale and high-speed, combined with the ability of corrosion sulfide in sea-water resistance of copper alloy is limited. Therefore, for the material and production process of the propeller put forward higher requirements. In this paper,the propeller selection is SAF2507 duplex stainless steel, this material has a ferrite-austenite organization, high degree of alloying, excellent corrosion resistance-including the ability of resistance to local corrosion/, the PRE value up to 42, can be used in the seawater environment.To the SAF2507 duplex stainless steel, how to use the correct and reasonable hot forming technology to improve the mechanical properties such as strength of the material, to improve the microstructure of materials become a problem to be solved, this is also the main research content of this article.To make out the best hot forming process parameters for SAF2507 duplex stainless steel,this paper conducted a series of experimental study and theoretical analysis. At first, we put the sample under the condition of different hot forming process parameters-parameter such as temperature, cooling speed changes/ for processing, then sample tensile, impact and micro hardness test, Analysis of hot forming process parameters for the influence of material mechanical properties and mechanical behavior; before and after hot forming, the microstructure of materials and the change of alloy elements is obtained by scanning electron microscopy and spectrometer, used to compare the influence of hot forming for material microstructure, phase ratio and alloy elements, at last analyzed the influence of the harmful phase relative to the material impact. Finally, on a hot simulation experiment machine for material CCT curve drawing, get the CCT curve of material, the characteristics of CCT curve coincide with the experimental data.Hot forming temperature of SAF2507 duplex stainless steel shall be above 10503, lower than the temperature will have harmful phase precipitation; the cooling rate should be faster to through the area of 600 3~10003, the smaller the cooling rate, more ferrite will decomposes in the material, and more harmful phase will precipitate, micro hardness of this materials will also increase, materials prone to brittle fracture. When the temperature of hot forming up to 1100,the cooling rate greater than 303/s, no harmful phase precipitate, ferrite and austenite ratio is close to 1:1, Grain size refinement at the same time, significantly improves the strength of this material, after hot forming the gradient material microstructure make it possess excellent shock resistance, and good toughness. Through reasonable hot forming process, the material strength can up to 1200 MPa, elongation is more than 40%.更多还原