Nb微合金化对Cr-Co-Ni-Mo系超高强度不锈钢腐蚀疲劳性能的影响

为探讨超高强度不锈钢的应力腐蚀开裂行为,采用Cr-Co-Ni-Mo系超高强度不锈钢为研究对象,利用OM、XRD、TEM等测试手段,结合腐蚀疲劳试验,研究了Nb微合金化对Cr-Co-Ni-Mo系超高强度不锈钢腐蚀疲劳性能的影响。结果表明,试验钢在3.5%NaCl溶液中具有一定的应力腐蚀敏感性,其应力腐蚀开裂机理为氢致开裂和阳极溶解的混合机制。Nb微合金化提高了钢的腐蚀疲劳性能,钢中添加0.11%的Nb后,钢的腐蚀疲劳强度由440 MPa提高至495 MPa,其主要原因是,Nb微合金化可以细化钢的晶粒尺寸,促进钢中不可逆氢陷阱NbC的析出,增加了钢中原奥氏体晶界总量、小角晶界所占比例、Σ3晶界数量、奥氏体体积分数等。     

高强度不锈钢应用及研究进展

高强度不锈钢因其优异的综合性能及成熟的生产工艺,已成为航空、航天、海洋、石化工程等高端制造业领域的重要材料。系统回溯高强度不锈钢的发展及应用历程,总结此类钢的强韧化机理及最新研究进展,并详细梳理了影响该钢的氢陷阱行为及氢脆抗力的主要因素。结合现有研究成果,提出了采用多种类纳米级第二相颗粒复合析出强化突破高强度不锈钢强韧性匹配极限的思路;通过调控钢中析出相及逆转变奥氏体的交互析出行为,提高后者的机械、化学稳定性,使其作为钢中裂纹及可扩散氢的双重“陷阱”,从而提高钢的裂纹及氢脆抗力。最后指出未来新型高强度不锈钢的研发须重点关注以材料基因算法、人工神经网络、机器学习为代表的“人工智能化”合金设计理念。     

开轧温度对铌微合金化热成型钢氢致延迟开裂性能的影响

通过动态充氢恒载荷、氢渗透等实验研究轧制工艺对铌合金化热成型钢的氢致延迟开裂性能的影响.随着开轧温度从1000℃降低到950℃,热成型钢的氢扩散系数降低,氢致延迟开裂性能提高,耐腐蚀性能下降.透射电镜观察发现开轧温度为1000℃时MX型析出相尺寸为30 nm;开轧温度为950℃时热成型钢的MX型析出相尺寸为5 nm左右,可以观察到直径为50 nm Cr₂C₃析出相.作为氢陷阱的纳米析出相是提高实验钢氢致延迟开裂性能的主要因素.析出相不同的原因是开轧温度为1000℃时MX型析出相发生熟化现象,进一步抑制Cr₂C₃的析出.      

强酸性氯离子环境下低合金钢的点蚀行为

 参照国际海事组织（IMO）发布的《油轮货油舱耐蚀钢性能标准》中所规定的模拟内底板试验方法,对比研究了在强酸性高氯离子浓度的环境下,传统低合金钢和耐蚀低合金钢的腐蚀速率及点蚀行为随温度变化的规律。试验结果表明,添加铜、镍元素的耐蚀低合金钢腐蚀速率较传统低合金钢最高降低了90%以上,并且具有优于传统低合金钢的抑制点蚀增殖、扩展的性能。耐蚀低合金钢表面及点蚀坑内部分布有白色颗粒,为铜元素的再沉积所致。该纯铜颗粒分布于试验钢表面可以有效提高钢的腐蚀电位,在点蚀坑内部的富集可以有效抑制点蚀坑在深度方向上的扩展。     

时效工艺对纳米相强化低合金高强度钢显微结构及力学性能的影响

纳米相强化低合金高强度钢是在普通低合金钢基础上发展起来的,由于其强度高、加工性能较好且经济适用而在汽车、船舶与海洋工程以及桥梁等基础设施建设方面有着广泛应用.时效工艺是该类钢种优化纳米相和提高其力学性能的必须之路,且对于探索纳米相强化机制等科学问题也具有重要意义.本文主要研究了时效工艺分别对纳米相强化低合金高强度钢显微结构与力学性能的影响.研究表明时效工艺对纳米相强化低合金高强度钢显微结构无显著影响,而对纳米相析出有着重要影响.较高时效温度下,时效峰较早时间出现当其硬度却相对较低.最后,对其原因进行了讨论.     

低碳高强钢中纳米析出相回火过程中的透射分析

 研究了一种800MPa级低碳高强钢中纳米析出相在回火过程中的演变规律。通过透射、高分辨电镜,并结合能谱仪系统分析了不同回火温度下析出相的形貌特征及其与基体的位相关系。研究表明,低碳高强钢中的纳米析出相主要为Nb、Ti、V、Mo等元素的碳氮化物,低温回火时主要为Nb、Ti的二元析出,高温回火后则为含Mo、V、Ti、Nb等多种元素的复合碳化物析出;钢中纳米析出相按大小分为两类,大尺寸颗粒是钢在轧制过程中形变诱导析出的,小尺寸颗粒是钢在回火过程中相变诱导析出的;同时,随回火温度的升高,钢中的析出相均慢慢长大并粗化,长大方式为典型的Oswald熟化机制;析出相与母相基体之间存在特定的取向关系,在析出的开始阶段,析出与基体的界面基本保持共格关系,析出相形状主要为球形或者类球形,随着回火温度的升高,析出逐渐长大并粗化,形状渐渐变为方形或者椭圆形,同时与基体脱离共格界面,保持的界面关系为：{100}MC∥{100}α-Fe,<100>MC∥<110>α-Fe。     

微合金化TRIP型退火马氏体钢氢渗透行为研究

通过在0.2%C-1.5%Si-2.0%Mn成分基础上进行Nb、V和Ti微合金化成分设计以及"完全奥氏体区淬火+临界区淬火至马氏体相变点以上温度配分"工艺,获得组织为退火马氏体基体+残余奥氏体的退火型马氏体TAM。对各种钢氢渗透行为的研究发现,微合金元素析出物能够显著抑制氢在钢基体中的扩散行为。Nb、V和Ti处于可比的加入水平时,Nb微合金化钢的氢扩散系数最低,为0.716×10~(-7) cm~2/s, Ti微合金化钢为1.136×10~(-7) cm~2/s,0.052%V钢为2.647×10~(-7) cm~2/s,这些值均低于参照钢。对含钒钢,随着钢中V含量增加,氢渗透时间长,产生的氢陷阱作用增强。认为Nb和Ti在高温析出粗大的碳化物对氢的抑制作用强烈,而V在低温析出的高密度细小、弥散分布的碳化物,使基体具有大量的氢陷阱,保证材料获得强的抑制氢扩散能力。     

钒钼微合金化32MnB5热成形钢的抗氢脆性能研究

在实验室条件下通过在传统32MnB5热成形钢基础上添加不同含量的V和Mo，利用慢应变速率拉伸试验来评价材料的氢脆敏感性，并结合氢渗透试验对微合金化热成形钢的抗氢脆性能变化机理进行了探讨。试验结果表明：添加V和Mo合金元素均有利于提高材料的抗氢脆性能，材料充氢后的塑性损失均出现降低。其中V与Mo复合添加相对于单一添加V样品，其原奥氏体晶粒尺寸及纳米级析出相尺寸更为细小，可以有效捕获氢原子，阻碍了氢原子的扩散，因此表现出最佳的抗氢脆性能，氢扩散系数降至7.3×10^-11 m²/s，可扩散氢浓度减少至4 100 mol/m³。     

不同热处理状态下镍基耐蚀合金析出相的定性定量分析

镍基耐蚀钢的性能,在很大程度上取决于钢中各种相的数量、组成、大小、分布状况和合金元素在晶界的分配情况。镍基耐蚀钢经过等温热处理,通常会形成碳化物相、金属间相等析出相。这些析出相在合金中的形成将导致钢的脆化,显著降低钢的塑性、韧性和耐蚀性。为了对不同热处理条件下镍基耐蚀合金析出相做定性定量分析,实验在选择好合适的电解制度后,利用电解分离方法将析出相从基体中分离。通过扫描电镜(SEM)和X射线衍射(XRD)定性研究了提取后析出相的形貌以及结构特性的变化过程;并利用Rietveld全谱拟合法计算不同析出相的组成及含量,最后还讨论了析出相含量与材料耐蚀性能间的关系。实验结果表明900 ℃时效形成的析出相最多,且析出相的含量随时间的延长呈明显上升的趋势;腐蚀性能评价结果表明析出相的含量与平均腐蚀速率存在一定的正相关,即随着析出相含量的增加,材料的平均腐蚀速率也增加,耐蚀性能减弱。     

关于钢中氢陷阱

由于钢中存在着不同类型氢陷阱，与扩散的氢原子发生相互作用、因而影响了氢的扩散行为，通过两极化方法测定的氢的渗透曲线，能间接地测定钢中氢陷阱的密度。采用一定的工艺措施，尽可能地降低钢中陷阱以使钢中的含氢量不超过某一临界值，就有利于提高材料的抗氢的应力腐蚀能潜在力。     

Hydrogen-involved tensile and cyclic deformation behavior of low-alloy pressure vessel steel

The temperature- and strain-rate-dependent tensile behavior of hydrogen-charged low-alloy pressure vessel steel ASTM A508 C1.3 has been investigated. The fatigue crack initiation and propagation behavior of the steel in high-temperature water environments has also been evaluated. It was found that hydrogen played significant roles in both tensile and cyclic deformation processes, especially in the temperature and strain-rate region of dynamic strain aging (DSA). The presence of hydrogen resulted in a distinct softening in tensile strength and a certain loss in tensile ductility in the DSA region. Remarkable degradation in fatigue crack initiation and propagation resistance in high-temperature water environments was observed in the DSA strain-rate region. Typical hydrogen-induced cracking features also appeared on the corresponding fatigue fracture surfaces. The interactions between hydrogen and DSA in tensile and cyclic deformation processes are discussed as well as their combined effects on the environmentally assisted cracking (EAC) mechanism of pressure vessel steels in high-temperature water environments.     

The significant impact of Ti content on microstructure–toughness relationship in the simulated coarse-grained heated-affected zone of high-strength low-alloy steels

This study aims to investigate the influence of Ti addition on microstructure and toughness in the simulated coarse-grained heated-affected zone (CGHAZ) of high-strength low-alloy steels. The steels with low and high Ti content respectively were subjected to 100?kJ/cm heat input welding thermal cycle. The results indicated that the second-phase particles were mainly oxide covered with MnS and fine (Ti,Nb)N precipitate in low-Ti steel, which were modified to the oxide surrounded by TiN and coarse (Ti,Nb)N precipitate in high-Ti steel. Compared with low-Ti steels, the coarser precipitates induced larger austenite grain in CGHAZ of high-Ti steel. Moreover, the wrapping of TiN decreases the ability of inclusion to promote the nucleation of acicular ferrite, resulting in lower fraction of acicular ferrite in CGHAZ of high-Ti steel. Content of martensite-austenite constituent increased in CGHAZ of high-Ti steel. They were all responsible for the degeneration in toughness in CGHAZ of high-Ti steel.     

低合金结构钢腐蚀的影响因素及其耐蚀性判据

通过对不同厂家或产线生产的相近成分和显微组织的8种低合金工程结构钢样品进行中性盐雾加速腐蚀试验,结合成分测试、微观组织分析、腐蚀产物分析及数据统计与计算拟合等方法,提出了评价低合金结构钢耐蚀性的综合耐蚀指数及其包含钢材成分、夹杂物、组织及晶粒度等多因素的数学表达式。研究结果表明,低合金工程结构钢的耐蚀性除与传统的耐蚀指数I相关外,还受钢中夹杂物、显微组织、晶粒度等多种材料因素的耦合影响,其影响程度按从大到小排序依次为耐蚀合金元素所决定的耐蚀指数I、夹杂物总量、珠光体含量和晶粒度级别。综合耐蚀指数Y可作为比耐蚀指数I指数更有效的低合金钢耐蚀性判据,具有重要的工程应用价值。      

稀土在汽车用先进高强钢中的研究现状

成分设计与优化是先进高强钢增强、增塑以及增韧的关键技术之一。随着钢质高纯化装备和技术的进步与发展,稀土元素在钢中的应用已由净化、夹杂物改性逐步向微合金化过渡。从第一代铁素体基软钢和高强低合金钢向第二代奥氏体基超高强钢,再到多相、亚稳和多尺度组织调控的第三代高强韧性钢,先进高强钢的微合金化技术一直是控制组织和性能的有效举措。稀土原子具备较大原子半径以及与O、S的高亲和力等优异特性,可从控制凝固与固态相变,影响碳元素与合金元素的扩散等多方面影响先进高强钢的组织结构,从而对其力学性能、成形性能以及耐腐蚀等服役性能产生显著影响。本文阐述了稀土元素分别在第一代、第二代和第三代典型先进高强钢中的作用机理,并展望了稀土元素在未来汽车钢中的应用前景。      

Study of the Effect of Microstructure Characteristics on Corrosion Resistance of Cold-Rolled Micro-Alloyed Sheet Steels (Hsla) of Strength Classes 340–420 for Automobile Building

Metallurgist - The effect of microstructure characteristics and also production regimes on corrosion resistance of cold rolled high-strength low-alloy steels (HSLA) grades 340 and 420 is studied....     

On the Role of Ni in Cu Precipitation in Multicomponent Steels

The nature of Cu precipitation in quench-tempered multicomponent high-strength low-alloy steels is characterized by atom probe tomography. The detected nanometer sized Ni-rich clusters act as preferential nucleation sites for Cu-rich clusters, and Ni segregation at the Cu-rich precipitate/matrix heterophase interface contribute to fast growth of Cu precipitates. Molecular dynamics simulation indicates that local Ni clustering at atomic scale significantly quickens the solute diffusion. The initial Ni composition has a profound effect on the nature of Cu precipitation.     

低合金高强度调质钢控轧控冷工艺优化

研究了低合金高强度调质钢的轧制方式及轧后冷速对调质后微观组织及力学性能的影响。结果表明:在试验条件下,试验钢采用不同轧制方式及冷速获得不同淬火加热前的初始组织及力学性能,但调质后却具有相同的微观组织和力学性能。建议低合金高强度调质钢采用一阶段的轧制方式,终轧温度应高于奥氏体部分再结晶区的上限温度,轧后采用适宜的冷速(4~15℃/s)进行加速冷却。以此工艺调质后的试验钢具有较高的均匀性,与现行TMCP工艺相比,强塑性和强韧性更为优异。     

罩式退火铌微合金化汽车钢的强化机理

 通过比较相同冷轧与罩式退火工艺下Mn-Si系和铌微合金化2种汽车用低合金高强钢的显微组织与力学性能,研究微量铌在冷轧罩式退火低合金高强钢中的强化机理。利用OM、SEM、TEM和拉伸试验机分别对2种钢的显微组织与力学性能进行了表征。对比分析表明：相对热轧板来说,2种钢冷轧退火板的铁素体晶粒和第二相析出物的尺寸都有所长大,导致了强度降低。相对Mn-Si钢而言,铌微合金化钢热轧板和冷轧退火板中的铁素体晶粒和第二相析出物尺寸更细小,细小第二相析出物的数量也更多,在相同的伸长率水平下明显提高了强度。冷轧罩式退火板的强化机理分析表明,铌微合金化低合金高强钢的主要强化方式是细晶强化和NbC的沉淀强化;研究认为添加质量分数为0.025%的铌时细晶强化更强烈。     

Development of low-cost high-strength stainless steel for new-energy bus frames

Along with strict environmental regulation,new-energy vehicles are becoming increasingly popular due to their low emissions,and they will inevitably replace existing fossil-fuel-based buses in China.To achieve a lightweight bus body,high-strength steels are commonly used for the bus frame,but these grades are susceptible to corrosion.From the perspective of "lower life-cycle cost",high-strength stainless steel is a better bus structure choice than high-strength carbon steels,since stainless steel bus frames last 10-15 years without requiring any maintenance.The low-cost high-strength stainless steels developed by Baosteel are introduced,the yield and tensile strengths of which can be controlled to within the range of 350-700 MPa and 900-1 200 MPa,respectively,and the elongation values are above 30％.Measurements of the toughness and fatigue resistance of these high-strength stainless steels and their joints indicate that the structural integrity requirements for bus frames can be met.The results of salt spray corrosion studies indicate that stainless steels will substantially increase the service life of bus frames in wet and icy winter conditions where deicing with CaC12 is necessary for road safety.The results of our investigation clearly indicate that high-strength stainless steel is a potential bus-frame material that makes it possible to achieve substantial weight savings,excellent corrosion resistance,and prolonged operational life.     

A Novel High Nitrogen Steel Powder Designed for Minimized Cr2N Precipitations

High nitrogen steels provide excellent mechanical properties and corrosion resistance but are prone to form precipitates which adversely affect the corrosion resistance and toughness. High nitrogen steel powders currently available in the market are not claimed to be precipitate free. It is critical to avoid these precipitates while retaining nitrogen in the dissolved form to realize the value of these powder alloys. However, retaining high level of dissolved nitrogen in steel powder during melt atomization process is very challenging. Instead, solid-state dissolution of nitrogen into the powder alloy followed by rapid cooling may provide a convenient approach to avoid precipitate formation compared to traditional melt processing. This study presents a solution treatment approach to achieve elevated dissolved nitrogen levels (~ 0.4 wt pct) in Fe–Mn–Cr powder alloy with negligible precipitation of nitrides. The influence of starting material, holding time, temperature and cooling rate on the resulting microstructure is presented. A fully austenite matrix with high dissolved nitrogen content resulted in powders with desired mechanical properties.