【作者】 王博；

【导师】 姜茂发；

【作者基本信息】 东北大学 ， 钢铁冶金， 2008， 博士

【摘要】 耐候钢是一种成本低廉、综合性能良好的低合金结构用钢,不仅具有良好的耐大气腐蚀性能,还具有优良的力学、焊接等综合性能。目前,耐候钢向降低碳含量方向发展,并利用微合金化和组织强化等措施提高强度,既保证了焊接性,同时又获得高强度和高韧性。在此研究背景下,本论文在保证耐候性和焊接性前提下,采取降低碳含量以提高耐候钢韧性,采取增加锰、铬含量以及钒氮微合金化措施以提高耐候钢强度。分别研究了上述成分设计在非控轧控冷条件下对耐候钢强度和韧性的影响。结合相应研究手段,本文系统分析和探讨了各合金元素对耐候钢组织、力学性能以及耐腐蚀性能的影响规律和作用机理。研究成果可为设计和开发新一代耐候钢提供理论依据。力学实验表明,两组高氮—钒合金化耐候钢(锰质量分数分别为0.50%和1.31%)取得了良好的强韧化效果,屈服强度分别达到了555MPa和610MPa,并且具有较高的加工硬化性能,抗拉强度达650MPa和705MPa；塑性和韧性均满足相同强度级别耐候钢的使用要求。热力学分析证明,本实验高氮—钒成分设计(0.0320%N-0.096V和0.0358%N-0.083V)明显提高了钒的高温析出能力,钒开始析出温度达1130℃以上,85℃钒析出率达90%以上；而如果采取常规氮质量分数(0.0050%)设计,则析出温度降至1000℃以下,850℃钒的析出率低于20%。动力学分析表明,850℃终轧温度下VN完全析出时间<110s；透射电镜分析表明VN颗粒尺寸分布在20nm～300nm,达到了VN析出强化临界颗粒尺寸7.89nm；高温析出的VN颗粒起到了很好的细晶强化和沉淀强化作用,两项加和对屈服强度贡献率达70%以上。极化曲线测试和腐蚀减重实验发现,钒氮合金化能够降低耐候钢的腐蚀速率；电化学阻抗谱(EIS)测试和锈层分析实验表明：钒氮合金化耐候钢具有良好的抑制点蚀能力,腐蚀反应在钢基体表面更加均匀进行,而且锈层具有较高的电荷传导电阻,绝缘性能增强；钒氮合金化改变了铬的富集方式,铬富集区域由内锈层扩展至外锈层,这与其它实验耐候钢有所不同；钒氮合金化耐候钢锈层中α-FeOOH含量较高,α-FeOOH与γ-FeOOH比值较大,表明钒氮合金化有利于生成热力学稳定的锈层。锰质量分数增至0.93%,对耐候钢强化效果较弱,屈服强度和抗拉强度分别为345MPa和485MPa,而锰质量分数由0.50%增至1.36%,屈服强度由390MPa增至435MPa,并且获得了高加工硬化性能,抗拉强度达到600MPa,塑性和韧性亦处于较高水平,强韧化效果较好。动态热模拟实验发现锰质量分数增至1.36%,Ar3温度可降低60℃～80℃,具有较好的细化铁素体晶粒作用,并且耐候钢的淬透性明显增强,在本实验最大冷速15℃·s-1下,贝氏体体积分数接近100%。极化曲线测试和腐蚀减重实验表明,增加锰含量耐候钢腐蚀速率有小幅增加；EIS测试和锈层截面形貌显示,增加耐候钢锰质量分数,点蚀特征增强,经热力学分析认为这与锰元素具有较高的腐蚀倾向性有关；EIS测试发现增加锰含量对锈层绝缘性能没有明显影响,电子探针结果表明锰均匀分布于内外锈层中,没有发生富集现象,锈层物相分析表明锈层中α-FeOOH略有增加,而α-FeOOH与γ-FeOOH比值降低,说明锰对稳定锈层的生成没有明显影响。热模拟实验发现,耐候钢中铬质量分数由0.62%增至1.50%,Ar3温度没有明显变化,淬透性有所提升,15℃·s-1冷速下,贝氏体所占体积分数由12.8%增至23%。力学实验表明,增加铬含量对耐候钢强化作用较弱,屈服强度仅为350MPa,虽然加工硬化性能略有增强,但并未获得高抗拉强度,为460MPa；然而却获得了高塑性和高韧性；极化曲线测试与腐蚀减重实验发现,铬质量分数由0.62%增至1.50%,耐候钢腐蚀速率降低。EIS测试显示,其腐蚀反应初期具有较强的点蚀反应特征,然而点蚀反应被迅速抑制,而且阻抗模图表明有绝缘性能较好的锈层生成；电子探针分析发现,增加耐候钢铬质量分数对锈层结构没有明显影响,而锈层物相分析则表明,α-FeOOH含量显著增加,α-FeOOH与γ-FeOOH比值明显升高,说明增加铬含量加速了锈层获得稳定结构的进程。更多还原

【Abstract】 Weathering steel is one type of low alloy structural steel with good comprehensive performance and lower cost, which not only has good atmospheric corrosion resistance, but also has a well mechanical property and weldability. Untill now, in order to obtain the higher combination of strength-toughness and weldability, development of weathering steel is facing to decrease carbon content and increase strength by the method of microalloying or microstructure strengthening.According to present research, in this paper, on the basis of insuring atmospheric resistance and weldability, carbon content of weathering steel was decreased to increase toughness, at the same time, increasing Mn and Cr content, V-N microalloying were adopted to increase strength of weathering steel respectively. On the condition without TMCP, influence of above design viewpoints on strength and toughness of weathering steel were studied as well as influence and mechanisms of alloy elements on mechanical properties and corrsosion resistance of weathering steel were analyzed and discussed respectively. Those results could be provided to design and develop a new generation of weathering steel.Mechanical tests showed that, yield strength of two kinds of weathering steels with V-N alloying treatment and bearing 0.50%Mn and 1.31%Mn respectively achieved 555MPa and 610MPa, in addition, tensile strength reached 650MPa and 705MPa due to a relative high strain-hardening properties. Further, both plasticity and toughness satisfied the requirement of the high strength weathering steel.Thermodynamics analysis proved that, V-N alloying increased the precipitation performance of Vanadium at high temperature remarkably. For the weathering steels with 0.0320%N-0.096V and 0.0358%N-0.083V, initial precipitation temperature of Vanadium increased to more than 1130℃and precipitation rate of Vanadium exceeded 90% at 850℃. However, for a normal weathering steel bearing 0.0050%N, initial precipitation temperature of Vanadium was lower than 1000℃and precipitation rate of Vanadium was lower than 20% respectively at 850℃. Kinetics analysis showed that, total precipitation time of VN was lower than 110s at 850℃. TEM analysis showed, for the V-N alloying weathering steels, the grain size of VN particles was in the range of 20nm-300nm, which exceeded the critical precipitation size of 7.89nm. Precipitation strengthening and refining strengthening contributed to more than 70% of yield strength owing toVN particles precipitating at high temperature.Polarization curve test and corrosion mass lost experiment showed, the corrosion rate of weathering steel was decreased because of V-N alloying. EIS test and rust layer analysis results showed, corrosion reaction occurred on the surface of matrix more symmetrically because of pitting being suppressed by V-N alloying, furthermore, the rust layer had a relative high charge conducting resistance, which characterized that the insulating property of rust layer increased. Cr enrichment characteristic was changed by V-N alloying and Cr enrichment zone expanded from inner rust layer to outer rust layer, which was different from other experimental weathering steels. V-N alloying could accelerate to form thermodynamic stable rsut layer because of the relative highα-FeOOH content and ratio ofα-FeOOH andγ-FeOOH.When Mn mass fraction increased to 0.93%, the strengthening effect was much weak, which yield strength and tensile strength was 345MP and 485MPa respectively, however, when Mn mass fraction increased to 1.36%, the yield strength increased from 390MPa to 435MPa and tensile strength increased from 470MPa to 600MPa due to the relative high strain-hardening property, as well as comparatively high plasticity and ductility were acquired, which showed that the strengthening-toughening effect was stronger. Thermal simulation results showed that, increasing Mn mass fraction to 1.36%, Ar3 temperature decreased 60℃～80℃, accordingly, ferrite grain size was refined remarkably and the hardenability enhanced. At the highest cooling rate of 15℃·s-1 in this study, the volume fraction of bainite almostly increased to 100%. Polarization curve test and corrosion mass lost experiment showed, the corrosion rate had a slight increase with Mn content increasing. EIS test and the morphology of rust layer cross section showed, pitting characteristic increased with Mn content increasing, because Mn element has a strong corrosion tendence proved by thermodynamics analysis. EIS test showed, Mn content increase had little influence on insulating property of rust layer. EPMA results showed, there was no enrichment of Mn element in the rust layer, and Mn just distributed in inner and outer rust layer homogeneously. Phase analysis of rust layer showed, increasing Mn content, theα-FeOOH content in rust layer increased somewhat but ratio of α-FeOOH andγ-FeOOH decreased, which characterized that Mn had little effect on the formation of thermodynamic stable rsut layer.Thermal simulation results showed that, when Cr mass fraction increased from 0.62% to 1.50%, Ar3 temperature had little change but the hardenability enhanced somewhat. At the cooling rate of 15℃·s-1, the volume fraction of bainite increased to 23%. Mechanical tests showed, Cr mass fraction had a slight influence on strengthening, though strain-hardening property increased somewhat, so its yield strength and tensile strength only was 350MPa and 460MPa respectively, however, its plasticity and ductility was high. Polarization curve test and corrosion mass lost experiment showed, the corrosion rate decreased with increasing Cr mass fraction from 0.62% to 1.50%. EIS test showed, pitting was stronger at the initial stage of corrosion reaction but it was suppressed immediately, yet, the Bode plots figure showed, the rust layer with better insulating property formed. EPMA results showed, increasing Cr content had little effect on the structure of rust layer but phase analysis of rust layer revealed that,α-FeOOH content and the ratio ofα-FeOOH andγ-FeOOH increased remarkably, which characterized that the formation progress of thermodynamic stable rsut layer was accelerated.更多还原