不同组织低碳微合金钢力学化学效应的研究

发布时间：2018-01-30 11:27

本文关键词： 低碳微合金钢腐蚀组织力学化学效应　出处：《北京科技大学》2015年博士论文　论文类型：学位论文

【摘要】：低碳微合金耐候钢具有较好的力学性能、耐蚀性和经济的生产成本等特点,作为结构钢的一种,一般都要承受一定应力,并在一定腐蚀环境中服役,因而,既要考虑其力学性能,又要考虑其腐蚀行为,即外加应力作用时的腐蚀行为——力学化学效应。目前关于力学化学效应的研究还不够完善且存在一定的问题,关于材料组织对力学化学效应的影响还未见报道。因此,本论文设计了一种低碳微合金耐候钢,通过热处理得到成分相同的三种不同显微组织：贝氏体组织(B)、铁素体贝氏体组织(FBDP)、铁素体珠光体组织(FPDP),并以具有这三种不同显微组织的低碳微合金钢为研究对象,对其力学化学效应机理进行了研究。本研究对于发展高性能耐候钢、预测材料的服役安全和指导工程选材有重要意义。通过研究无外加应力作用时组织对低碳微合金钢腐蚀行为的影响发现,显微组织的改变可以影响材料整体的热力学稳定性：B钢的热力学稳定性最高FPDP钢的次之,FBDP钢的最差；三种不同相的热力学稳定性顺序也各不相同：P的热力学稳定性最高,B的次之,F的最差。B钢属于均匀腐蚀,其腐蚀表面粗糙度最小；FBDP钢和FPDP钢属于择优腐蚀,FPDP钢的表面粗糙度大于FBDP钢的表面粗糙度。显微组织对低碳微合金钢长期的腐蚀速率没有明显影响。 FBDP钢在3.5mass%NaCl溶液中的浸泡初期,腐蚀优先在铁素体内部及铁素体晶界处开始,铁素体相作为电偶腐蚀阳极比贝氏体更加容易腐蚀。FBDP钢腐蚀表面的表面粗糙度主要是由两相的择优腐蚀造成的,其大小决定于其显微组织中各相的体积分数及两相的高度差。本论文提出了一种可靠的腐蚀模型用于描述多相钢中各相的腐蚀行为,并利用参数KG对双相钢中两相间的电偶腐蚀行为进行评价。研究表明,造成FBDP钢中贝氏体组织(BFBDP)伏打电位(自腐蚀电位)较高、耐腐蚀性能较好的原因是由于C元素在BFBDP中的富集。在外加弹性应力作用时,B钢、FBDP钢对力学化学效应不敏感；FPDP钢的力学化学效应最显著且随外加应力的增大而增大。低碳微合金钢在0.5mass%NaCl溶液中浸泡时,其腐蚀过程的电化学反应机理、腐蚀产物膜的成分和物相及其生成过程不受材料的显微组织及外加应力的影响。在外加弹性应力作用下,B钢的自腐蚀电位变化不明显,FPDP钢的自腐蚀电位会随着外加弹性应力的增大而负移。腐蚀产物膜的破裂是造成低碳微合金钢力学化学效应的本质原因。腐蚀产物膜的破裂与试样表面的蠕变、试样内部不均匀蠕变行为有关,当试样应(蠕)变导致的试样表面积的增大量大于新生腐蚀产物膜对新增表面的覆盖量时,试样表面的腐蚀产物膜将出现开裂现象。随着外加弹性应力的增加,FPDP钢中珠光体组织(PFPDP)的腐蚀速率先增大后减小。应力对FPDP钢腐蚀过程中腐蚀溶质的扩散过程及FPDP钢中两相的电偶腐蚀的影响共同决定了FPDP钢中两相的力学化学效应。在外加应力作用下FPDP钢中两相的伏打电位差会增加,导致两相的电偶腐蚀趋势增大,腐蚀表面的粗糙度也随之增大。
[Abstract]:Good mechanical properties of low carbon microalloyed steel, corrosion resistance and economic cost, as a kind of structural steel, usually under stress, and service, and in a certain corrosive environment, should not only consider the mechanical properties, but also consider the corrosion behavior, which should be applied: effect of mechanical and chemical corrosion behavior of force. The current research on the mechanochemical effect is still not perfect and there are some problems about the influence of microstructure on the mechanical and chemical effect has not been reported. Therefore, this paper designed a kind of low carbon micro alloy steel, three different microstructures of the same composition by heat treatment: bainite (B), ferrite bainite (FBDP), ferrite pearlite (FPDP), and with the low carbon has three different microstructures of microalloyed steel as the research object, the mechanics and chemistry This study is of great significance for the development of high performance weathering steel, the prediction of the service safety of the materials and the guidance of the material selection.
By studying the effects of no external stresses on Microstructure of low carbon microalloyed steel corrosion behavior, microstructure change can affect the thermodynamic stability of the whole material: the highest FPDP steel B steel the thermodynamic stability of FBDP steel is the worst; three kinds of different thermal phase stability order is also different P: the thermodynamic stability is the highest, the second is B, F is the worst.B steel is uniform corrosion, the corrosion of the minimum surface roughness; FBDP steel and FPDP steel is preferred corrosion, FPDP steel surface rough surface degree of roughness was higher than that of FBDP steel. The microstructure of low carbon microalloyed steel for corrosion the rate has no obvious influence.
The early immersion of FBDP steel in 3.5mass%NaCl solution, corrosion preferentially in the ferrite and ferrite grain boundaries, ferrite phase as the anode surface galvanic corrosion Bibeishi body more prone to corrosion corrosion of.FBDP steel surface roughness is mainly caused by the preferential etching phase, the height difference of which depends on the volume fraction and the two phase of each phase in the microstructure. This paper proposes a reliable corrosion model is used to describe the corrosion behavior of each phase of the multiphase steel, evaluated by the KG parameters of the galvanic corrosion behavior of two phases in dual phase steels. The research shows that resulted in FBDP steel bainite (BFBDP) potential (Ecorr) high resistance to corrosion, good performance is due to the enrichment of BFBDP in the C element.
The external elastic stress, B steel, FBDP steel is not sensitive to chemical mechanical effect; increasing effect of mechanical and chemical FPDP steel is the most significant and with applied stress increases. Low carbon microalloyed steel immersed in 0.5mass%NaCl solution, the electrochemical reaction mechanism of the corrosion process, corrosion products and components the membrane phase and its formation process is not affected by the microstructure of the material and applied stress. The external elastic stress of B steel, the corrosion potential did not change significantly, the corrosion potential of FPDP steel will increase along with the elastic stress and negative shift. Rupture of corrosion products film is the essential reason due to the low carbon microalloyed steel. The effect of mechanical and chemical corrosion product film rupture and surface creep, the creep behavior of specimen is not uniform, when the specimen should be changed to sample (creep) surface area increases the corrosion product film is higher than that of the new freshmen When the surface coverage is increased, the corrosion product film on the surface of the specimen will appear cracking.
With the increase of the external elastic stress of pearlite in steel FPDP (PFPDP) the corrosion rate increased firstly and then decreased. Effects of galvanic corrosion of two-phase force diffusion process and FPDP steel on Corrosion of FPDP steel corrosion in the process of solute in determines the effect of mechanical and chemical phase in FPDP steel. In the external phase V in FPDP steel under the force of potential difference will increase, resulting in the increase of galvanic corrosion tendency of two-phase corrosion, the surface roughness increases.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.1

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