氧化物冶金在大线能量焊接用钢中的应用

 为了分析氧化物冶金钢中不同类型夹杂物的形核能力及其对大线能量焊接性能的提升效果，对Ti Ca、Ti Mg试验钢进行了模拟焊接热循环并利用氧化物冶金技术实现了不同钢种的工业化生产。结果表明，在1 400 ℃峰值温度等温30 s后，Ti Mg复合夹杂物可有效钉扎奥氏体晶界移动，并在后续冷却过程中作为形核质点诱导针状铁素体形核。为了保持氧化物冶金技术所需的氧含量，建立了转炉Si Mn预脱氧加Ti Mg脱氧的优化工艺路线。采用新技术冶炼的钢种具有200 kJ/cm气电立焊性能。-40 ℃下HAZ冲击韧性达到200 J，焊接接头内观察到大量针状铁素体板条组织。     

氧化物冶金工艺对EH36钢HAZ组织性能的影响

设计了Ti- Ca和Ti- Mg两种氧化物冶金脱氧工艺的EH36实验钢来考察粗晶热影响区的组织性能和冲击韧性。结果表明，两种处理工艺的实验钢热模拟后的焊接热影响区内都有大量细小的晶内针状铁素体产生；与Ti- Ca脱氧工艺相比，采用Ti- Mg脱氧工艺的实验钢，焊接热影响区中针状组织更加明显，夹杂物的类型也更加复杂，同时Ti- Mg复合脱氧工艺在焊接热循环中能够更好地钉扎奥氏体晶界。-40℃的冲击数据表明，Ti- Mg脱氧工艺处理后的实验钢HAZ冲击性能优于Ti- Ca处理工艺。     

镁处理对船体钢组织细化作用的高温原位分析

 船体钢经镁处理后其焊接热影响区性能显著提升。为进一步弄清镁的作用机制,采用高温激光共聚焦显微镜原位观察传统船体钢和镁处理船体钢在升降温过程中显微组织的演变过程,并对不同保温时间下钢组织在连续冷却过程中的相变进行研究。通过对比发现,镁处理船体钢在升温过程中因微细夹杂物粒子的钉扎作用使得奥氏体晶粒尺寸并未发生粗化,并且在冷却过程中奥氏体晶粒内部出现大量夹杂物诱发的针状铁素体,使钢组织得到进一步细化,而夹杂物这种诱发晶内针状铁素体的能力则呈现出随保温时间延长而逐渐增强的规律。与此同时,夹杂物数量及分布情况的统计也为上述结果提供了有力佐证。     

外加镁系氧化物粒子在钢铁材料制备中的进展

镁系氧化物粒子(MgO和MgO·Al₂O₃)在钢液中具有良好的分布特征，在适当的条件下向钢液加入镁系氧化物粒子可以改性和细化夹杂物、细化奥氏体晶粒和诱导晶内铁素体形核，最终实现钢材性能的优化。从镁系氧化物粒子的加入方法、对夹杂物的影响、对奥氏体晶粒的钉扎作用、诱导铁素体形核机理、对力学性能的影响5个方面进行总结。结果表明，降低密度差和润湿角粒子或结合强反应元素有利于提高收得率，粉末预分散法结合外场搅拌有利于进一步提升粒子在钢液中的均匀性；合理的镁系氧化物粒子加入量(质量分数)为0.01%～0.03%,夹杂物平均尺寸控制在1～2μm,可以将夹杂物改性为MgO·Al₂O₃或MgS;外加镁系氧化物有利于细化奥氏体晶粒、改善硫化物分布和提高针状铁素体比例，当其加入量为0.05%时，针状铁素体联锁最优，奥氏体晶粒最小；当超微镁系氧化物粒子的加入量为0.05%左右时钢铁材料的力学性能最优，屈服强度、抗拉强度、冲击韧性显著提高。     

奥氏体化温度对Ti–Zr处理钢中针状铁素体转变的影响

Ti、Zr的复合氧化物可以有效诱导针状铁素体形核,从而细化晶粒。为了研究Ti–Zr处理钢中针状铁素体转变机理,使用25 kg真空感应炉中熔炼试验所需钢种,向低合金钢中添加了质量分数为0.038%钛和0.008%锆。利用高温激光共聚焦显微镜原位观察了奥氏体化温度对针状铁素体转变行为的变化,使用扫描电镜观察了Ti–Zr处理钢种的夹杂物成分和针状铁素体在夹杂物表面形核,使用光学显微镜观察不同奥氏体化温度下的微观组织变化差异。结果表明,随着奥氏体化温度从1250 ℃增加至1400 ℃,奥氏体晶粒尺寸从125.6 μm 增加至279.8 μm,针状铁素体开始转变温度和侧板条铁素体开始转变温度先增加,在1350 ℃条件下达到最大值,后又降低,针状铁素体的体积分数由39.6%增加至83.6%;Ti–Zr处理钢中核心为Zr–Ti–O,外部为Al–Ti–Zr–O的氧化物为核心表面析出MnS的复合氧化物主要集中在1.5～3 μm,可以有效促进针状铁素体形核,贫Mn区和夹杂物与铁素体之间的良好晶格关系为该型夹杂物能够促进针状铁素体形核机理。奥氏体晶粒尺寸的增加导致多边形铁素形核位点的减少和针状铁素体的形核空间的增加,钛锆复合处理形成大量的有效诱发针状铁素体形核的夹杂物,这共同导致了针状铁素体体积分数增加。      

含钛可焊接海洋结构用钢

1　前言本文研究了弥散于钢中细小的钛—氧化物颗粒对热影响区 ( HAZ)韧性的改善作用。在 HAZ内 ,奥氏体到铁素体的转变过程中 ,针状铁素体(晶内铁素体片 ,IFP)以 Ti-氧化物颗粒为核径向长大而且粗大的奥氏体晶粒得到有效细化。钛一氧钢中没有明显的局部脆化区 ,因为 Ti-氧化物颗粒即使在温度超过 1 40 0℃区域化学成分也能保持稳定。因此在整个热影响区包括在熔合线附近其组织也能得到细化。认为 IFP的形成能够阻止对韧性有害的晶界形核铁素体板条 ( FSP)的生长 ,结果得到较细小的晶粒尺寸。通过增加 Ti-氧化物颗粒的数量即增加 IF…     

镁处理对钢中夹杂物以及HAZ组织和性能的影响

 近年来镁处理的氧化物冶金技术研究非常活跃,为了总结镁处理氧化物冶金研究的最新成果,综述了镁处理对钢中夹杂物以及HAZ组织和性能的影响研究。通过镁处理形成的微米级含镁氧化物和硫化物复合夹杂物可以诱导晶内针状铁素体析出;镁处理过程中形成的纳米析出物,通过对奥氏体晶界的钉扎作用可以抑制原奥氏体晶粒长大,钉扎粒子多为300 nm以下的TiN、在MgO表面析出TiN形成的MgO+TiN复合夹杂和镁的氧化物或硫化物及其复合夹杂物。这两种氧化物冶金作用机理都有助于提高厚钢板的大线能量焊接热影响区的低温冲击韧性。镁处理可以同时对钢中氧化物和硫化物进行改性,改变了硫化物的组成和形态,生成以含镁夹杂物为核心,外围包裹MnS的复合夹杂物抑制了树枝状MnS的生成,促进钢中生成细小、球状分布的MnS夹杂物,进而改善钢的可加工性能;并且形成的含镁复合夹杂物之间的作用力约为Al₂O₃夹杂物之间作用力的1/10,作用距离约为Al₂O₃夹杂物最大作用距离的2/5,呈现弥散分布状态。     

Al、Ti处理对低合金钢焊接粗晶区组织的影响

研究了Al、Ti处理对低合金钢焊接粗晶区组织的影响.研究发现:用Al处理时,钢中形成的夹杂物为Al的氧化物和细小的TiN.Al的氧化物和TiN不能促进晶内铁素体的形成,焊接粗晶区主要由粗大的晶界铁素体和平行排列的侧板条铁素体组成.用Ti处理时,钢中形成大量的Al、Ti、Mg、Ca复合氧化物夹杂,其颗粒大小为0.5～3.0 μm,同时还有一定量细小的Ti的氮化物.复合Ti的氧化物具有促进晶内针状铁素体形核的能力,焊接粗晶区主要由晶界铁素体、少量的侧板条铁素体和大量的晶内针状铁素体组成.随焊接热循环高温保温时间增长,晶界铁素体粗大,侧板条铁素体数量减少.相变区的冷却速度减慢,晶界铁素体数量增多,针状铁素体的尺寸显著增大.     

Ti、V、Nb元素对DH36焊接热影响区显微组织的影响

结合Ti、V、Nb元素对焊接热影响区微观组织的影响,添加不同微合金元素,进行实验室真空冶炼-轧制DH36高强船板钢。利用Gleeble3500试验机,针对加入不同微合金元素的DH36船板钢进行线能量为50 k J/cm和100 k J/cm的焊接热模拟试验,研究微合金元素V、Ti、Nb对焊接热影响区组织性能的影响。结果表明,在DH36焊接热影响区中,Ti生成了氧化物,该氧化物诱发了针状铁素体,钉扎了奥氏体晶界,而V、Nb并未生成夹杂物。     

Ti-Mg复合脱氧对钢热影响区组织和冲击性能的影响

利用Gleeble-1500热模拟试验机进行焊接热模拟实验,研究16Mn钢经微Ti和Ti-Mg处理后焊接热影响区组织及冲击性能的变化,并利用扫描电镜和能谱分析法观察和分析实验钢的夹杂与冲击断口形貌.Ti和Ti-Mg复合处理试样的热影响区显微组织分别主要是晶界块状铁素体+晶界侧板条铁素体和晶内针状铁素体+晶界块状铁素体.经Ti处理后钢中夹杂物主要为5μm左右的TiO_x+MnS复合夹杂,经Ti-Mg复合脱氧后钢中夹杂物主要为2μm左右Ti-Mg-O+MnS组成的复合夹杂,且后者明显细化了钢中夹杂物尺寸.Ti-Mg复合脱氧试样中存在大量细小夹杂颗粒,一方面可钉扎裂纹,另一方面诱导形成了使大量针状铁素体,大焊接热输入条件下Ti-Mg复合脱氧试样热影响区冲击韧性明显强于单独Ti处理的试样.      

Toughness improvement by Zr addition in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels

The effect of Zr addition on the microstructure and impact toughness in the coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels subjected to 100?kJ?cm^-1 heat input was investigated. The second- phase particles were mainly Al–Ti complex oxides and (Ti,Nb)N precipitates in Zr-free steel, whereas lots of finer Zr–Al–Ti complex oxides and (Al,Ti,Nb)N precipitates were formed in Zr-bearing steel because of Zr addition. These finer oxides and precipitates effectively restricted the austenite grain growth by pinning effect during welding thermal cycle, and smaller and more uniform prior austenite grains were obtained in CGHAZ of Zr-bearing steel. Furthermore, more acicular ferrite grains nucleated on Zr–Al–Ti complex oxides, inducing formation of fine-grained microstructure in CGHAZ of Zr-bearing steel. The toughness improvement in CGHAZ of Zr-bearing steel with dimple fracture surface was attributed to the grain refinement by pinning effect and acicular ferrite formation.     

微合金化控轧控冷钢筋纵向金相组织研究

 对微合金化控轧控冷钢筋的纵向金相组织进行了研究,并分析了不同成分试验钢纵向“条带”组织的差异及形成原因。研究结果表明：偏析元素（P、Si、Mn等）在轧制过程中沿轧制方向呈条状分布,是20MnSi、20MnSiV钢产生带状组织的原因。铌及其碳氮化物的溶质拖曳和“钉扎”作用,使20MnSiNb钢的奥氏体未再结晶轧制温度提高到1050℃,在冷却过程中,先共析铁素体在形变奥氏体晶界和内部变形带均匀析出,随后沿形变奥氏体晶界（在先共析铁素体与奥氏体的界面上）生成珠光体带,最后在形变奥氏体晶粒内部形成贝氏体条。研究条件下优势形核点的排序为：形变奥氏体晶界和形变奥氏体晶内变形带、偏析元素和夹杂、再结晶奥氏体晶界。     

大线能量焊接用船体结构钢的研究进展

介绍了大线能量焊接在船舶建造中的应用,对比了船体结构钢与其它钢种对大线能量焊接适应性的不同要求。针对大线能量焊接热影响区韧性下降问题,提出了目前提高热影响区韧性的主要措施。指出降低碳当量、细化热影响区奥氏体晶粒尺寸、利用有益氧化物诱导晶内铁素体析出是提高船体结构钢大线能量焊接适应性的有效途径。介绍了鞍钢在热影响区组织调控技术和氧化物诱导机理研究等方面取得的成果。     

Austenitization during intercritical annealing of an Fe-C-Si-Mn dual-phase steel

Partial austenitization during the intercritical annealing of an Fe-2.2 pct Si-1.8 pct Mn-0.04 pct C steel has been investigated on four kinds of starting microstructures. It has been found that austenite formation during the annealing can be interpreted in terms of a carbon diffusion-limited growth process. The preferential growth of austenite along the ferrite grain boundaries was explained by the rapid carbon supply from the dissolving carbide particles to the growing fronts of austenite particles along the newly formed austenite grain boundaries on the prior ferrite grain boundaries. The preferential austenitization along the grain boundaries proceeded rapidly, but the austenite growth became slowed down after the ferrite grain boundaries were site-saturated with austenite particles. When the ferrite grain boundaries were site-saturated with austenite particles in a coarse-grained structure, the austenite particles grew by the mode of Widmanstätten side plate rather than by the normal growth mode of planar interface displacement.     

变形晶界对低碳钢显微组织的影响

对不同温度下变形和变形后再加热到奥氏体区的低碳钢SS400的显微组织进行了研究，结果表明：变形使奥氏体和铁素体晶界呈锯齿状，锯齿状的奥氏体晶界优先成为铁素体的形核位置，锯齿状的铁素体晶界有利于铁素体再结晶核心的形成。     

A New Route for Identification of Precipitates on Austenite Grain Boundary in an Nb-V-Ti Microalloyed Steel

 The precipitates on austenite grain boundaries in an Nb-V-Ti microalloyed steel have been investigated by transmission electron microscope (TEM) examination of carbon extraction replica. The replica was prepared from specimen etched with saturated picric solution rather than Nital which is conventionally used. Then particles on both grain boundaries and triple point of grain boundaries were clearly observed and identified as (Nb,Ti)(C,N) particles. In case of conventional way, it is difficult to determine the location of particles with respect to austenite grain boundaries. The number of particles observed in new way developed was greatly reduced compared with that found in replica prepared by the conventional way, which may be caused by the dissolution of partial precipitates during the etching with longer time and at higher temperature involved in new way. Despite this, the new way developed provides an effective way to determine the precipitate particles on austenite grain boundaries.     

Austenite Grain Growth and the Surface Quality of Continuously Cast Steel

Austenite grain growth does not only play an important role in determining the mechanical properties of steel, but certain surface defects encountered in the continuous casting industry have also been attributed to the formation of large austenite grains. Earlier research has seen innovative experimentation, the development of metallographic techniques to determine austenite grain size and the building of mathematical models to simulate the conditions pertaining to austenite grain growth during the continuous casting of steel. Oscillation marks and depressions in the meniscus region of the continuously casting mold lead to retarded cooling of the strand surface, which in turn results in the formation of coarse austenite grains, but little is known about the mechanism and rate of formation of these large austenite grains. Relevant earlier research will be briefly reviewed to put into context our recent in situ observations of the delta-ferrite to austenite phase transition. We have confirmed earlier evidence that very large delta-ferrite grains are formed very quickly in the single-phase region and that these large delta-ferrite grains are transformed to large austenite grains at low cooling rates. At the higher cooling rates relevant to the early stages of the solidification of steel in a continuously cast mold, delta-ferrite transforms to austenite by an apparently massive type of transformation mechanism. Large austenite grains then form very quickly from this massive type of microstructure and on further cooling, austenite transforms to thin ferrite allotriomorphs on austenite grain boundaries, followed by Widmanstätten plate growth, with almost no regard to the cooling rate. This observation is important because it is now well established that the presence of a thin ferrite film on austenite grain boundaries is the main cause of reduction in hot ductility. Moreover, this reduction in ductility is exacerbated by the presence of large austenite grains.     

钒氮钢中晶粒细化研究

 采用Gleeble 3500热模拟试验机，在相同工艺条件下，对比研究了钒氮钢、钒钢以及碳锰钢的晶粒细化效果。结果表明，钒氮钢的晶粒细化效果最显著，铁素体的晶粒尺寸可达61 μm，这主要与在奥氏体区中析出的V(C，N)有关。奥氏体区析出的V(C，N)，不但可抑制奥氏体晶粒长大，同时还可以作为铁素体的形核核心，诱导晶内铁素体形成，大大增加铁素体形核率，从而提高了相变细化的比率。     

Ultrafine Grained Austenite in a Low Carbon Vanadium Microalloyed Steel

 Ultrafine austenite grains with average size of 2 μm were successfully obtained by combining thermo-mechanical control process followed by reheating in a vanadium microalloyed steel. The mixed microstructure transformed from pancaked austenite formed during controlled rolling has a higher density of high angle boundaries, compared to that transformed from equiaxial austenite. It contributes to increasing nucleation density of austenite grain during the reheating process. A certain volume fraction of undissolved nano-sized (Ti,V)C particles, which are formed during the controlled rolling process and/or the reheating process, effectively inhibit austenite grain growth and consequently refine austenite grain size significantly. The critical grain size of austenite calculated by Gladman model agrees well with the experimental result.     

Quantitative geometric characterization of high carbon martensite

Quantitative stereology was applied to study the transformation behavior and the microgeometry of athermally transformed martensite for two austenite grain sizes in Fe-1.4 wt pct C-0.02 wt pct P alloy and commercial 01 tool steel. The effects of prior austenite grain boundaries and the existing martensite plates on the nucleation of martensite were studied and each was found to play different roles during the transformation. Autocatalytic nucleation was found to be less than that for a burst transformation. Prior austenite grain boundaries were found to have a strong influence on the initial nucleation of martensite. Plate thickness was constant during the transformation except for coarsegrained 01 tool steel after ～60 pct transformation. The plate radius decreased slowly with fraction transformed and was found to be independent of the mean free path in austenite initially, but decreases with the decreasing mean free path in the later stages.