310S钢焊接热影响区粗晶区晶粒细化的研究

发布时间：2018-10-17 10:05

【摘要】：310S奥氏体耐热不锈钢用于高放废物储置罐材料,在焊接高放废物储置罐时焊接热影响区粗晶区(CGHAZ)的晶粒粗化严重,导致其力学性能的降低。为了满足高放废物储置罐焊接热影响区粗晶区的强度和韧性的要求,通过微合金化的方法抑制晶粒的长大。本论文利用金相显微镜、扫描观察、透射电子显微镜,sysweld软件等对储置罐用310S钢的CGHAZ区的组织和力学性能进行了系统的研究。论文主要内容如下:1.310S钢自熔焊数值模拟基于sysweld软件建立了焊接热源模型,模拟了实际的单道自熔焊实验,提取得到了CGHAZ区的焊接热循环曲线,模拟的焊接温度场与实验测得的温度场吻合、焊接热源参数选取的合理,建立的焊接热源模型可靠,为下一步的测定CGHAZ的力学性能奠定基础。2.310S钢相组成及其析出相研究基于Thermo-Calc热力学计算软件计算了310S钢的相组成、合金元素对相组成的影响,为制定310S钢合理的含铝范围以及为后续的固溶工艺奠定了基础,同时也为该材料的焊接热影响区的温度选择提供了参考。计算结果表明,随着Al含量的变化,310S钢的组织保持不变,但AlN析出相的数量发生变化,并且AlN析出相由二次析出转变为一次析出。随着Nb含量的增加,310S钢的固相线开始下降。MX相和Z相的含量逐渐增加。3.不同Al、Nb含量的310S钢BM和CGHAZ区的微观组织及析出相研究通过对含Al和含Nb钢的组织观察。发现粗晶区的奥氏体晶粒尺寸和母材的大致相当。说明Al和Nb元素都对粗晶区奥氏体晶粒有抑制长大的作用。随Al含量的增加,AlN析出相逐渐增多。且Al含量越多的310S钢,在经过铸造、锻造、热轧后,残存了一次AlN相并且其颗粒尺寸比较粗大,对材料的力学性能产生损害。当Al含量为1.38%时,310S钢中析出了δ-铁素体。在铸造过程中,Al会优先进入δ-铁素体中,减少了AlN相的含量。随着Nb含量的增加,MX相有所增加,抑制粗晶区奥氏体晶粒长大的能力有所增加。4.Al、Nb含量对310S钢力学性能的影响研究发现AlN在拉伸变形过程中,会阻止晶粒的变形,当Al含量较高时(1.38%),δ-铁素体沿拉伸方向延展,会起到“硬相”的作用,从而增加了材料的塑性。由于AlN和δ-铁素体的显微硬度都高于奥氏体基体,会降低310S钢的韧性。MX相在310S钢中对拉伸影响不明显,三种含Nb钢的母材和粗晶区的抗拉强度大致相当。对冲击功造成的影响比较大,随Nb含量的增加,冲击功不断降低。焊接热循环前后,0Nb钢冲击功明显下降,而对同种成分的含Nb钢来说,母材和粗晶区冲击强度大致相当。
[Abstract]:310s austenitic heat-resistant stainless steel is used for high level radioactive waste storage tank material. The coarse grain coarsening of (CGHAZ) in heat affected zone (HAZ) is serious, which results in the decrease of mechanical properties. In order to meet the requirement of strength and toughness of coarse grain zone in heat affected zone (HAZ) of high level radioactive waste storage tank, grain growth was restrained by microalloying. In this paper, the microstructure and mechanical properties of 310S steel for storage tank in CGHAZ region were systematically studied by metallographic microscope, scanning observation, transmission electron microscope and sysweld software. The main contents of this paper are as follows: 1.The welding heat source model based on sysweld software is established by numerical simulation of self-fusion welding of steel, and the welding heat cycle curve of CGHAZ region is obtained by simulating the actual experiment of single-pass self-fusion welding. The simulated welding temperature field coincides with the measured temperature field, the welding heat source parameters are selected reasonably, and the welding heat source model is reliable. The phase composition and precipitates of 2.310S steel were studied. The phase composition and the effect of alloying elements on the phase composition of 310S steel were calculated based on Thermo-Calc thermodynamics calculation software. It lays a foundation for the formulation of reasonable range of aluminum in 310S steel and for the subsequent solid solution process, and also provides a reference for the selection of the temperature of the welding heat affected zone of the material. The results show that with the change of Al content, the microstructure of 310S steel remains unchanged, but the number of AlN precipitates changes, and the precipitation phase of AlN changes from secondary precipitation to primary precipitation. With the increase of Nb content, the solid line of 310S steel began to decrease, and the contents of MX phase and Z phase increased gradually. The microstructure and precipitate phase of 310s steel BM and CGHAZ with different Al,Nb content were studied by observing the microstructure of the steel containing Al and Nb. It is found that the grain size of austenite in the coarse grain region is approximately the same as that of the base metal. The results show that both Al and Nb can inhibit the growth of austenite grains in coarse grain region. With the increase of Al content, the precipitate phase of AlN increases gradually. After casting, forging and hot rolling, the 310S steel with more Al content has a residual AlN phase and its particle size is relatively large, which causes damage to the mechanical properties of the material. When Al content is 1.38, 未 -ferrite is precipitated in 310S steel. In the process of casting, Al will preferentially enter 未-ferrite, reducing the content of AlN phase. With the increase of Nb content, the MX phase increases, and the ability of inhibiting austenite grain growth in coarse grain region increases. 4. The effect of AlN content on mechanical properties of 310S steel is studied. It is found that AlN can prevent the grain from deforming during tensile deformation. When the content of Al is high (1.38%), 未 -ferrite extends along the tensile direction, which will play the role of "hard phase", thus increasing the plasticity of the material. Because the microhardness of AlN and 未 -ferrite is higher than that of austenitic matrix, the toughness of 310S steel will be reduced. The tensile strength of the three kinds of Nb containing steels is similar to that of the base metal and coarse grain zone, and the effect of MX phase on tensile strength is not obvious in 310S steel. The impact on the impact work is great. With the increase of Nb content, the impact work decreases. Before and after welding thermal cycling, the impact energy of 0Nb steel decreases obviously, but for the same composition of Nb steel, the impact strength of base metal and coarse grain region is about the same.
【学位授予单位】：沈阳理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.11

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