焊接热影响区针状铁素体的形核长大及其对组织的细化作用

通过观察焊接热循环冷却过程中不同温度取样直接淬火后的微观组织,研究了焊接热影响区(HAZ)晶内针状铁素体(IAF)的形核长大过程,论证了针状铁素体分割原奥氏体晶粒及细化晶内组织的机理.Auger电子能谱(AES)证实,在TiOx-MnS型复合夹杂物边界附近存在贫Mn区,IAF易于在这类复合夹杂物上形核,单个复合夹杂物能...     

硫质量分数对船体钢诱发点蚀行为的影响研究

采用腐蚀浸泡的方法研究了酸性氯离子环境下S质量分数对低合金船板钢耐蚀性的影响,探讨了非金属夹杂物诱发点蚀形核的机理。结果表明,杂质元素S对钢的耐蚀性具有不利影响。随着S质量分数的增加,钢的耐点蚀性能恶化。S元素损害耐蚀性主要与钢中的非金属夹杂物有关。不同种类夹杂物诱发点蚀的机理有显著差异。单一MnS夹杂物与基体间存在缝隙,其诱导点蚀形核包括缝隙腐蚀和夹杂物溶解两个过程,MnS夹杂物是最敏感的点蚀诱发源;MXS-Al2O3复合夹杂物同样能诱发低合金钢的点蚀形核,包裹在Al2O3外层的硫化物优先发生溶解,成为腐蚀介质的通道,从而引发局部腐蚀。MnS-Al2O3夹杂物的点蚀形核能力大于CaS-Al2O3夹杂物,CaS遇到水容易发生水解并在夹杂物周边形成OH-,阻碍了坑内部的酸化,有利于抑制钢的耐局部腐蚀性能。     

Ti-B微合金化焊缝金属的韧化机制

针对 5 0 0～ 6 0 0MPa低合金高强度钢的韧化问题 ,研究了夹杂物对Ti-B微合金化焊缝金属针状铁素体形成的影响。钢中的非金属夹杂物 ,对促进晶内针状铁素体的形成 ,提高焊缝金属韧性有显著的作用。通过电镜分析 ,探讨了夹杂物的类型、成分对针状铁素体形成的作用。结果表明 ,Ti、Mn、Al、Si的复合氧化物夹杂可有效地促进针状铁素体形核 ,而MnO·SiO2 夹杂和MnS夹杂对针状铁素体形核作用不大。夹杂物对针状铁素体形核的主要用是 ,在夹杂物周围能形成一个塑性畸变区 ,这个由夹杂物与母相热膨胀系数差引起的塑性区 ,对针状铁素体的形成有一定作用     

低合金高强度钢焊缝金属中针状铁素体的微观组织

利用光学显微镜,扫描电子显微镜及EBSD(electron backscattering diffraction)分析技术对800MPa级低碳微合金高强度钢的焊缝金属进行了分析.结果表明,焊缝金属组织主要为针状铁素体和贝氏体.针状铁素体以夹杂物为核心形核,该夹杂物主要是以Al2O3为核心形成的钛氧化物.针状铁素体以夹杂物为核心多维形核呈放射状生长,仅某些方向的针状铁素体晶核迅速长大,生长方向存在取向择优.EBSD分析同样表明针状铁素体晶粒存在取向择优.观察到由同一夹杂物生长,沿同一直线方向背向生长的针状铁素体取向相同,沿不同方向生长的针状铁素体取向不同,说明其沿原奥氏体惯习面生长,并非与夹杂物共格.     

管线钢亚微米级夹杂物的控制及对抗HIC性能的影响

通过添加Ti和Ti-Mg改性剂,试制了不同夹杂物组态的X70酸性环境用管线钢。利用OM和SEM分析试验钢中夹杂物的形态、尺寸、分布与成分;根据均质形核临界形核半径讨论了钢中夹杂物的形核和长大;测试了试验钢的氢致开裂(HIC)敏感性,并讨论了夹杂物对HIC敏感性的影响。结果表明:加Ti和加Ti-Mg均可以有效的在钢中产生大量细小、弥散的氧化物核心,其中加Ti试验钢中夹杂物以Al-Ti氧化物为核心,主要为大量亚微米级夹杂物和少量大尺寸不规则氧化物;而Ti-Mg试验钢中夹杂物以Al-Mg-Ti氧化物为核心,析出MnS,不易长大,夹杂物具有细小、弥散分布的特征。两种试验钢抗HIC性能均达到欧标要求,且Ti-Mg试验钢中完全没有发现氢致裂纹,这对提升试验钢抗HIC性能的效果明显。     

CuS在针状铁素体形核过程中的作用

设计出了研究夹杂物在针状铁素体形核过程中的作用的物理模拟试验方法。研究了CuS、Al2 O3 和Al2 O3 ·CuS在针状铁素体形核过程中的作用 ,用数字式金相显微镜观察了夹杂物界面附近区域的金相显微组织变化 ,用电子探针分析仪对夹杂物界面附近微区的化学成分进行了分析。研究结果表明 ,在热循环作用下 ,CuS和Al2 O3 ·CuS能使夹杂物与金属交界面附近出现贫Mn区 ,CuS与Al2 O3 ·CuS具有诱导针状铁素体形核的能力 ;而Al2 O3 不能使夹杂物与金属交界面附近区域的化学成分发生变化 ,Al2 O3不具有诱导针状铁素体形核的能力。夹杂物表面的CuS在针状铁素体形核过程中起着重要作用     

镧对16Mn钢中夹杂物和组织的影响

在高温钼丝炉内向16Mn钢中加入不同含量镧进行脱氧。利用SEM、EDS和OM测试并研究La含量对钢中夹杂物的成分、大小分布及试验钢组织的影响,并探讨了钢中含镧夹杂物诱发晶内针状铁素体形核机制。结果表明,随钢中镧含量增加,夹杂物依次转变为LaAlO3、La2O2S和La2S3。试样经镧处理后,钢液在1600℃时保温180 s,夹杂物最为细小且弥散。钢中晶内铁素体含量随镧含量增加先增大后减小,最佳镧含量约为0.014%(质量分数)。钢中含镧夹杂物周围形成贫Mn区,促进晶内针状铁素体形核。     

低碳钢中晶内形核铁素体三维形貌的唯象研究

采用光学显微镜和扫描电镜观察了低碳钢中晶内针状铁素体的二维金相组织形貌,运用计算机软件对铁素体的三维形貌进行了重构。试验发现钢中的MnS夹杂物对晶内铁素体形核有明显的促进作用,晶内有大量铁素体组织形成,晶内形核铁素体的三维形貌呈扁长片状,许多铁素体在空间中相互连接,并有相当数量的铁素体与夹杂物相连。由此推测铁素体的晶内形核有以下3种形核方式：在原有铁素体上激发生核;在夹杂物表面上直接生核;在已经存在的铁素体和夹杂物的交汇处形核。     

奥氏体化温度对La脱氧16Mn钢组织的影响

采用光学显微镜、扫描电子显微镜等分析技术观察了La脱氧钢组织及其夹杂物的变化,研究了不同奥氏体化温度对La处理16Mn钢组织的影响。结果表明,经La处理后钢中夹杂物由原来的MnS夹杂及Si-Mn-Al复合氧化物夹杂转变为LaAlO3、La2O2S及MnS的复合夹杂物。当La含量为0.013wt%时,钢中夹杂物分布的最为细小弥散,晶内铁素体形核效果较好,钢的组织最细小。当奥氏体化温度为1200℃并保温20 min时,钢中可形成大量晶内铁素体,有利于晶内铁素体形核的最佳奥氏体晶粒尺寸约为100μm。     

夹杂物对微合金钢熔敷金属针状铁素体形核的影响

研究了微合金钢熔敷金属中夹杂物大小、尺寸分布和化学成分对针状铁素体形核的影响。结果表明，作为针状铁素体形核核心的夹杂物，其尺寸大多数位于0．2．0．6μm之间，并且是含有多种元素的复合夹杂物，具有化学成分不均匀的性质。夹杂物作为一种高能的惰性表面，降低了形核能垒，促进了针状铁素体的形核。当一个针状铁素体以夹杂物为初始核心先期形核后，又可诱发大量的相互交错的针状铁素体感应形核。     

夹杂物/析出相尺寸对晶内铁素体形核的影响

建立了铁素体在夹杂物/析出相上形核的物理模型.从相变形核热力学和动力学机理出发,研究了晶内铁索体在夹杂物/析出相上的形核过程,分析了夹杂物/析出相的尺寸、界面性质等因素对晶内铁索体相变形核的影响.结果表明,与铁素体具有较小接触角的夹杂物/析出相更有利于晶内铁素体形核.当夹杂物与基体的界面性质一定时,铁索体在夹杂物上形核的难易程度主要取决于夹杂物的尺寸(夹杂物的曲率半径),尺寸过小不利于铁索体形核,尺寸过大对形核贡献较小.对任意类型的夹杂物/析出相,给出了其计算最优尺寸的方法,计算结果与实际吻合良好.     

Role of the particle–matrix interface on the nucleation of acicular ferrite in a medium carbon microalloyed steel

The inclusions responsible for the nucleation of acicular ferrite in a medium carbon microalloyed steel have been studied using optical and transmission electron microscopy. The acicular ferrite microstructures for such studies were obtained by isothermal treatments following austenitization at 1250°C. The samples were maintained for different times at 450°C and then water quenched, permitting observation of the evolution of the microstructure. Intragranular nucleation is enhanced by the presence of MnS inclusions covered by a CuS layer leading to an improvement in the global energetic balance for the transformation. This better energetic balance is obtained by replacing a high-energy interface between inclusion and austenite with a lower energy interface between inclusion and ferrite. The result is a fully acicular microstructure.     

Effects of inclusion size and acicular ferrite on cold cracking for high-strength steel welds of YS 600 MPa grade

The influences of microstructure and inclusion on cold cracking were studied in high-strength steel welds of YS 600?MPa grade using the Y-groove test. The weld microstructure showed a mixture of acicular ferrite, bainite and predominantly martensite. Cold crack fractography identified intergranular fracture (IF) and quasi-cleavage fracture (QCF). Bainite and martensite predominated on the surface and subsurface of IF while the QCF showed inclusions that nucleated acicular ferrite. The influence of inclusions on cold cracking can be described as follows: (i) the inclusions acted as nucleation sites of QCF, (ii) the inclusions contributed to the nucleation and growth of micro-cracks and (iii) new cracks were produced from inclusions when a crack impinged on the inclusions. Inclusions smaller than 2?μm increased the cold crack resistance by contributing to the nucleation of acicular ferrite. Inclusions larger than 2?μm increased the cold crack susceptibility by inducing crack nucleation in welds.     

New insights into intragranular ferrite in a low-carbon low-alloy steel

Single and multiple nucleation events on non-metallic inclusions have been observed, leading to the intragranular formation of ferrite as a function of transformation temperature. Three-dimensional shapes have also been characterized. When the ferrite forms at elevated temperatures it is in the form of isolated idiomorphs, whereas larger undercoolings are associated with the multiple nucleation of plates emanating from the inclusions. The plates grow at a fixed orientation to the parent austenite. Nanohardness tests indicate that the idiomorphs are softer when compared with the plates. The formation of intragranular ferrite laths or plates can facilitate the attainment of fine-grained microstructures.     

钢中夹杂物与奥氏体基体热膨胀系数差异导致的热应力和应变能研究

考虑基体的屈服，对钢中的球形夹杂物和奥氏体基体之间因热膨胀系数差在降温过程中产生的热应力，应变和应变能作了理论研究。大的过冷度和热膨胀系数差异是产生大的热应力、应变和高应变能的主要原因，在现实条件下，夹杂物的Young’s模量和Poisson比的变化对上述参量产生的影响不大，主要计算了几种典型的夹杂物和奥氏体产生的热应力、应变和应变能。结果显示，即便对于极限状态的“刚性”夹杂物，热应力形成的应变能也比相变化学驱动力小1—2个数量级。     

Crystallographic analysis for acicular ferrite formation in low carbon steel weld metals

Inclusions contributing to acicular ferrite nucleation were investigated from a crystallographic point of view in low carbon low alloy steelweld metals. The samples from electro slag welding (ESW) and submerged arc welding (SAW) deposits with various cooling rates were prepared in this study. In those samples, intragranular acicular ferrite formation was observed from inclusions. The inclusions contributing to acicular ferrite formation were of multi-phase type consisting of amorphous phase, spinel type and MnS. They were surrounded by a Ti-enriched layer. It was confirmed by selected area diffraction patterns and energy-dispersive X-ray spectrometer analyses that the Ti-enriched layer was TiO. The acicular ferrite had a Baker–Nutting orientation relationship with the TiO layer on the inclusion surface. The misfit was 3.0% at the interface between the acicular ferrite and TiO. Therefore, it is considered that TiO on the inclusion surface contributes to the heterogeneous nucleation of acicular ferrite by small lattice misfit. However, themorphologies of ferrite growth which nucleated from inclusions were different in both samples. Whereas the growth of ferrites nucleated from TiO was enough in ESW, the size of nucleated ferrite in SAW was a few hundred millimetres in size. In the early stage of nucleation from TiO, ferrite had small deviation from Kurdjumov–Sachs orientation relationship (K–S relationship) in both ESW and SAW. However, there was a difference in the growth stage of ferrite. The ferrite orientations were gradually changed to fit to the K–S relationship in ESW. On the other hand, the nucleated ferrite in SAW stopped growing and the newly nucleated ferrite which had K–S relationship prior to austenite was formed adjacently because of large super cooling due to small heat input.     

Ti脱氧钢含Ti复合夹杂物诱导晶内针状铁素体的原位观察

采用高温共聚焦激光显微镜(CSLM)对含Ti复合夹杂物诱导晶内针状铁素体(IAF)进行动态原位观察,并用OM,FE-SEM,EDS和EPMA研究奥氏体晶粒尺寸和冷却速率对含Ti复合夹杂物诱导生成IAF的影响.结果表明,IAF的开始生成温度随奥氏体晶粒尺寸的增加,先升高后降低；生成IAF体积分数随冷却速率的提高显著增加,...     

B元素对药芯焊丝焊缝金属针状铁素体形成的影响

利用金相组织观察、冲击试验和热膨胀试验,研究了B元素含量变化对高强钢药芯焊丝焊缝金属中针状铁素体形成的影响,得到了不同试验温度下焊缝金属冲击吸收功. 结合透射电镜分析和分级淬火试验从热力学和动力学的角度对B元素影响机理进行了分析. 结果表明,焊缝金属组织晶界中含有自由状态的B元素具有抑制晶界铁素体形核利于针状铁素体生成的作用;N元素含量增加会降低晶界B元素含量,并提高奥氏体向铁素体转变的温度,减少针状铁素体含量;针状铁素体是在以Ti元素和Mn元素的氧化物为核心,以Cu元素和Mn元素的硫化物为外层,以BN为过渡层的复杂结构上形核并长大的;针状铁素体含量的增加有利于提高焊缝金属冲击吸收功,–60 ℃冲击吸收功最大为70 J.