热处理对双相不锈钢焊接应力及其组织与性能的影响

发布时间：2018-04-10 01:18

  本文选题：双相不锈钢　切入点：焊接　出处：《兰州理工大学》2017年硕士论文

【摘要】：双相不锈钢发展至今,因其具有良好的抗氧化性、力学性能及耐腐蚀性能,越来越多的应用到油田平台、远洋航海、化工工业等领域。特别是在化工工业领域,良好的耐氯化物腐蚀性能使双相不锈钢不仅在酸类、聚合物等产品中得到使用,更被广泛的应用到了压力容器、反应器、热交换器等设备之中。SAF2205双相不锈钢作为最常用的双相不锈钢,因其具有良好的耐腐蚀性能以及焊接性能,常采用气体保护钨极氩弧焊(GTAW)、手工电弧焊(SMAW)以及埋弧自动焊(SAW)等方法进行焊接。但在焊接过程中,因为焊接热循环的存在,导致了析出相以及焊接应力的产生,影响了焊接接头的性能。为此,研究不同焊接方法及热处理工艺对SAF2205双相不锈钢焊接接头各项性能的影响,对于其在实际生产中的应用具有一定的理论和实际意义。本文采用GTAW和SMAW两种不同的焊接方法,前期通过对比两种焊接方法对SAF2205双相不锈钢各项性能影响的优劣,分析不同焊接方法对焊接接头的力学性能及耐腐蚀性能的影响;后期对焊接试件进行退火热处理,通过对比不同退火温度及保温时间后焊接接头力学性能及耐腐蚀性能,研究了热处理对两种不同焊接方法焊接接头的应力消除效果、力学性能的改变及对耐腐蚀性能的影响,得到如下几条主要结论:(1)GTAW和SMAW两种焊接方法对试样焊缝区抗拉强度及抗弯强度的影响不大,且均高于母材。但焊缝区的冲击韧性均低于母材,且SMAW明显低于GTAW。金相试验表明,焊缝区晶粒粗大是引起其冲击韧性降低的主要原因。(2)GTAW和SMAW两种焊接方法焊缝区有着比母材更优良的耐腐蚀性能。这是因为焊缝区具有良好的相比例。(3)试样经热处理后的试验结果表明,在规定的退火温度及保温时间内,拉伸强度和抗弯强度均没有明显的变化;冲击试验结果表明,过高的热处理温度使焊缝及热影响区的冲击吸收功降低。因此,退火温度不宜超过350℃。(4)焊接试样热处理后的耐腐蚀试验表明,试样的腐蚀速率随退火温度的提高以及保温时间的延长而增加;在较低的280℃退火时,保温时间对试样的腐蚀速率影响不大。(5)焊接所产生的应力主要集中在焊缝热影响区。在280℃去应力退火,焊接应力随保温时间的延长而下降。试验表明,保温6h焊接应力下降7.7%,保温12h焊接应力下降14.5%。
[Abstract]:Dual-phase stainless steel has been widely used in oil platform, ocean navigation, chemical industry and so on because of its good oxidation resistance, mechanical properties and corrosion resistance.Especially in the field of chemical industry, because of its good corrosion resistance to chloride, duplex stainless steel is not only used in acid, polymer and other products, but also widely used in pressure vessels and reactors.As the most commonly used duplex stainless steel, the. SAF2205 duplex stainless steel has good corrosion resistance and welding performance.Gas shielded argon tungsten arc welding (GTAW), manual arc welding (SMAW) and submerged arc welding (SAW) are often used for welding.However, in the welding process, due to the existence of welding thermal cycle, the precipitate phase and the welding stress are produced, which affects the performance of the welded joint.Therefore, it is of theoretical and practical significance to study the effects of different welding methods and heat treatment processes on the properties of SAF2205 duplex stainless steel welded joints.In this paper, two different welding methods, GTAW and SMAW, are used to analyze the effects of different welding methods on the mechanical properties and corrosion resistance of the welded joints by comparing the advantages and disadvantages of the two welding methods on the properties of SAF2205 duplex stainless steel.The stress relief effect of heat treatment on two different welding methods was studied by comparing the mechanical properties and corrosion resistance of welded joints after different annealing temperatures and holding time.With the change of mechanical properties and the effect on corrosion resistance, the main conclusions are as follows: (1) GTAW and SMAW welding methods have little effect on tensile strength and bending strength of weld zone, and both of them are higher than base metal.However, the impact toughness of weld zone is lower than that of base metal, and SMAW is obviously lower than that of GTAW.The results of metallographic test show that the coarse grain size in the weld zone is the main reason for the decrease of impact toughness. The weld zone has better corrosion resistance than the base metal by the two welding methods, I. e., GTAW and SMAW.This is because the weld zone has a good phase ratio. The test results after heat treatment show that the tensile strength and bending strength of the specimen have no obvious change within the specified annealing temperature and holding time, and the impact test results show that,Too high heat treatment temperature reduces the impact absorption energy of weld and heat affected zone.Therefore, the corrosion resistance of the welded specimens after heat treatment should not exceed 350 鈩，

本文编号：1729018