TiS夹杂物对D6AC超高强度钢强韧性的影响

一般钢中加Ti可使晶粒细化,从而提高钢的强韧性。但D6AC超高强度铟中可否加Ti的问题,一直存在争论。因为加Ti后,可能生成含Ti夹杂物而使韧性降低。为了改善D6AC钢的韧性,首先需要弄清这一问题。本文系统研究了含Ti夹杂物对D6AC钢强韧性的影响,并与同一钢种中,含有常见的MnS夹杂物进行比较,得出: 1.TiS夹杂物对强度和延伸率的影响不明显; 2.TiS夹杂物对面缩率、冲击韧性和断裂韧性稍有影响; 3.TiS开裂％随应变增大而增加,但在同一应变下却低于MnS; 4.TiS夹杂物使K_(1C)值降低的幅度低于MnS,因此,D6AC钢中加Ti可以改善强韧性。     

42CrMo钢中夹杂物在裂纹成核和扩展中的作用

通过平板拉伸实验，用准动态方法观察了４２ＣｒＭｏ钢中裂纹在夹杂物上成核和扩展，得出开裂应变与夹杂物类型和尺寸的关系，裂纹成核方式是夹杂物／基体界面开裂和夹杂物自身开裂．     

碳含量对帘线钢凝固析出TiN夹杂的影响

对含碳量（质量分数）分别为0．72％、0．82％和0．95％的帘线钢凝固析出TiN夹杂进行热力学研究,结果表明：碳含量对于不同强度级别的帘线钢中TiN夹杂的析出有着明显的影响．随着帘线钢碳含量增加,凝固前沿温度逐渐降低,析出TiN夹杂所需的氮钛活度积也逐渐下降．在相同的钢液初始Ti、N含量条件下,较高碳含量的帘线钢中析出的TiN夹杂尺寸会大于较低碳含量帘线钢中析出的TiN夹杂尺寸．为了控制超高强度级别的过共析帘线钢中TiN夹杂的析出对帘线钢加工性能的有害影响,必须通过冶炼工艺进一步降低钢液中的钛、氮含量．     

Ti微合金化对3.5Ni钢低温韧性的影响

利用光学显微镜和透射电镜观察不同Ti含量3.5Ni钢试样的组织及析出物,并通过测定其-80～-120℃的夏比冲击功来研究Ti微合金化对3.5Ni钢低温韧性的影响。结果表明,与0.042Ti试样相比,0.079Ti试样在热轧态和正火＋回火态时晶粒大小相同,但其热轧态组织中珠光体细化,且正火＋回火态组织中TiN数量增多,平均尺寸约为150nm;正火＋回火处理后,0.079Ti试样在-80～-120℃的夏比冲击功为233～23J,均低于0.042Ti试样相应值（234～66J）;对于正火＋回火态试样,较粗大TiN粒子的析出是造成其低温韧性降低的主要原因。     

钢中夹杂物与韧断机理

用平板拉伸试样直接观察夹杂物在裂纹成核和扩展中的行为得出:夹杂物开裂受应变控制:夹杂物开裂方式与加载方向有关;微裂纹在夹杂物上成核后主要按基体切变方式扩展;在夹杂物偏聚区微裂纹的扩展可按碰撞方式进行,从而加速裂纹的扩展,故在冶炼上需采取措施,以避免夹杂物的集聚。     

脱氧工艺对低合金高强度钢中夹杂物的影响

通过中小转炉工业化试验,对比研究了分别以Si-Ca-Ba合金和钛线为脱氧剂的两种不同脱氧方式对低合金高强度钢中夹杂物的影响.采用氧氮分析仪、金相显微镜、扫描电镜和能谱分析对钢中全氧含量和夹杂物进行了分析.结果表明,使用Ti脱氧工艺后,显著降低了钢中全氧含量,提高了钢的洁净度.轧材中尺寸小于5μm的复合夹杂物数目多,夹杂物呈细小弥散分布,大部分夹杂物为含MnS的球形复合夹杂.钛脱氧产物对钢中的硫化物夹杂有明显的弥散作用,显著降低了硫化物、硅酸盐类夹杂的评级.     

3Cr2W8V、4Cr5MoSiVl钢热疲劳机理及热疲劳抗力的差异

对淬火、回火后的3Cr2W8V钢、4Cr5MoSiV1钢缺口板状试样,进行了50～650℃ Coffin型热疲劳试验。根据试验结果,分析了热疲劳裂纹萌生和扩展过程,以及此过程中试样上应力的变化。结果表明:试样在升温时产生塑性压缩应变,在降温时产生弹性拉伸应变,呈现出弹塑性应变循环的特征;热疲劳裂纹沿滑移线场方向,在最大应变区形核,在形核数量上,4Cr5MoSiV1钢为3Cr2W8V钢的十几倍;裂纹扩展驱动力主要受材料高温强度和组织的热循环稳定性控制,同时也受材料对拉应力松驰能力的影响;裂纹扩展阻力主要取决于热循环后的材料断裂韧性水平、强度水平和氧化腐蚀抗力的合理配合。根据以上分析结果,从机理上解释了4Cr5MoSiV1钢热疲劳抗力优于3Cr2W8V钢的原因。     

微量Ce元素对42CrMo易切削钢切削性能的影响

利用扫描电镜、能谱仪、质量分析仪和车削加工等实验方法,对比分析稀土Ce元素对42CrMo易切削钢夹杂物和切削性能的影响。结果表明：Ce元素具有显著的变质夹杂作用,加入0.013%Ce元素后,42CrMo钢中夹杂物类型由MnS和Al₂O₃为主转变为以Ce₂S₃为主,夹杂物数量增多,尺寸减小,具有较小的长径比;细小颗粒状稀土硫化物促进了切削裂纹扩展和显微空洞形成,切屑由以平螺旋屑为主转变为以C形屑为主,切削性能得到明显改善。     

碳化物粒子尺寸对缺口试样断裂行为的影响

通过对铁素体晶粒尺寸相同，碳化物粒子尺寸不同的两种低合金钢的两部缺口试样进行断裂试验，分析研究了碳化物粒子尺寸对缺式样断裂行为的影响。结果表明，在缺口试样中，解理断裂的临界事件是铁素体晶粒尺寸的裂纹扩展进入相邻晶粒，铁素体晶粒尺寸决定缺口试样的低温解理断裂行为，而碳化物粒子尺寸对其几乎没有影响，在转变温度区，碳化物粒子尺寸分布通过影响材料塑性，对其缺口韧性产生较小影响，大碳化物粒子尺寸材料缺口韧性     

82A钢凝固过程中TiN夹杂析出热力学和动力学

用热力学和动力学方法研究82A钢液凝固过程元素偏析及其对TiN夹杂析出的影响。热力学分析表明,Ti的偏析比远高于N的偏析比;凝固冷却速度从6 K/min增至600 K/min过程中,凝固冷却速度对Ti、N凝固偏析比影响不大;钢液初始Ti含量降至0.000 2%、初始氮含量为0.002%~0.004%时,在凝固末期仍有TiN夹杂析出。动力学分析表明,随着钢液凝固冷却速度的加快,凝固析出的TiN颗粒尺寸明显变小。     

Thermodynamic calculations and experiments on inclusions to be nucleation sites for intragranular ferrite in Si-Mn-Ti deoxidized steel

Microstructures and inclusions in the Si-Mn-Ti deoxidized steels after cooling in the furnace were investigated. The composition and morphology of the inclusions were analyzed using a field emission scanning electron microscope （FE-SEM） with energy dispersive X-ray spectrometry （EDS）. The kind and composition of the inclusions calculated from the thermodynamic database were in good agreement with the experimental results. There were two main kinds of inclusions formed in the Si-Mn-Ti deoxidized steels. One kind of inclusion was the manganese titanium oxide （Mn-Ti oxide）. Another kind of inclusion was the MnS inclusion with segregation points containing Ti and N. According to the thermodynamic calculation, those segregation points were TiN precipitates. The formation of intragranular ferrite （IGF） microstructures refined the grain size during the austenite-ferrite transformation. The mechanisms of IGF formation were discussed. Mn-Ti oxide inclusions with Mn-depleted zone （MDZ） were effective to be nucleation sites for IGF formation, because the MDZ increased the austenite-ferrite transformation temperature. TiN had the low misfit ratio with IGF, so the TiN precipitated on the MnS surface also promoted the formation of IGF because of decreasing interfacial energies.     

Susceptibility of two types of low-alloy hull steels to pit initiation

Four low-alloy hull steels with different alloy elements were selected. Their susceptibility to pitting corrosion was compared by means of electrochemical polarization test. The inclusions in the steels and their pitting corrosion characteristics were studied by an electron probe micro-analyzer (EPMA). The results indicate that some inclusions are the main sources of pitting corrosion. The susceptibility of nickel-chromium steel to pit initiation is less than that of manganese steel. Under the same conditions, nickelchromium steel is easier to passivate than manganese steel, and the passive films on nickel-chromium steel surface are more stable than that on manganese steel. In low-alloy steels, the higher the contents of nickel and chromium, the lower the critical passive pH value. In the same kind of steel, multi-phase inclusions containing sulfide are easier to initiate pitting corrosion than other inclusions.     

Effects of sulfur addition methods and Ca-Si treatment on the microstructure and properties of 30Mn VS

The effects of sulfur addition methods and Ca-Si treatment on the microstructure and properties of free-cutting non-quenched and tempered steel 30Mn VS were investigated by using optical microscopy, SEM and tensile test methods. The results show that sulfur addition methods influence the morphology of sulfides and the properties of 30Mn VS slightly. Ca-Si treatment is beneficial for the formation of complex sulfides which normally have oxide cores, therefore, improving the distribution of sulfides in the tested steel and enhancing its toughness. The two methods, pyrite addition during LF process and S wire feeding during VD process,slightly influence the morphology and distribution of sulfides and the properties of 30Mn VS; Ca addition not only promotes the nucleation of sulfides on the cores of calcium aluminate inclusions,but also creates modification effect on MnS, reducing the relative plasticity and hot deformability of sulfides during hot rolling process,thereby reducing the length/width value of sulfides and improving their distribution, and significantly enhancing its mechanical properties, in particular, the impact toughness increased by 30%.     

Effect of nanophase on the nucleation of intragranular ferrite in microalloyed steel

MnS, MnS+V(C, N) complex precipitates in micro-alloyed ultra-fine grained steels were precisely analyzed to investigate the grain refining mechanism. The experimental results shows that MnS, MnS+V(C, N) precipitates provide nucleation center for Intra-granular ferrite (IGF), so that refined grain remarkably. Moreover, substructures such as grain boundary, sub-boundary, distortion band, dislocation and dislocation cell in austenite increased as the deformation energy led by heavy deformation at low temperature (deformation temperature⩽800°C, deformation quantity⩾50%). As a result, V(C, N) nanophase precipitated at these substructures, which pinned and stabilized substructures. The substructures rotated and transformed into ultra-fine ferrite. 20 nm-50 nm were the best grain size range of V(C, N) as it provided nucleating center for intragranular ferrite. The grain size of V(C, N) were less than 30 nm in the microalloyed steels that with volume ratio of ultra-fine ferrite more than 80% and grain size less than 4 μm.     

Effect of Nb on the transformation kinetics of low carbon （manganese） steel during deformation of undercooled austenite

The hot compression tests using Gleeble 1500 were performed by varying the true strain up to 1.6 （80% reduction） in Nbfree and Nb-microalloyed steels. The effect of Nb addition on the transformation kinetics during deformation of undercooled austenite was investigated. It was found that as compared with Nb-free steel, the transformation incubation period of Nb-bearing steel was prolonged and the transformation kinetics curves parallelly moved to higher strain because of the solute Nb drag effect. Studies on kinetics also showed that the deformation-enhanced ferrite transformation （DEFT） of the two steels were composed of three stages, which can be expressed by the J-M-A equations individually. However, the parameter n related to the mode of nucleation and growth is somewhat different in the first and second stages of the two steels, and the same in the third stage for both the steels corresponding to the nucleation Of retained austenite.     

DDQ钢连铸坯洁净度

采用金相观测、扫描电镜、电子探针等方法,研究了某钢厂DDQ钢连铸坯的洁净度,对铸坯中夹杂物的数量、粒径、分布、形貌及组成等进行了讨论。研究结果表明,该DDQ钢连铸坯中w（O）〈14×10-6、w（N）=18×10-6,P、S含量低,没有进行钙处理及真空处理;夹杂物大部分在4μm以下,数量少且分布均匀;夹杂物纯Al2O3居多,有MnS夹杂及以Al2O3为中心的外面是MnS的复合夹杂     

Effect of Nanophase on the Nucleation of Intragranular Ferrite in Microalloyed Steel

MnS, MnS+V(C, N) complex precipitates in micro-alloyed ultra-fine grained steels were precisely analyzed to investigate the grain refining mechanism. The experimental results shows that MnS, MnS+V(C, N) precipitates provide nucleation center for Intra-granular ferrite (IGF), so that refined grain remarkably. Moreover, substructures such as grain boundary, sub-boundary, distortion band, dislocation and dislocation cell in austenite increased as the deformation energy led by heavy deformation at low temperatu...     

多道次轧制过程中超细晶粒控制

在高强度水平的基础上获得较高的韧性,控制热加工工艺实现晶粒尺寸超细化是最佳的途径之一。低碳管线钢的超细铁索体晶粒可以从相变前的超细奥氏体晶粒获得。通过优化轧制工艺使得奥氏体的动态再结晶发生在Z（Zeller-Hollomon）参数较大的工艺条件下,获得超细的奥氏体动态再结晶晶粒尺寸。然而,大的Z参数往往具有较大的动态再结晶临界应变。为了获得足够的应变积累来克服动态再结晶的临界应变,低温大变形量的变形是基本条件。提出了在多道次轧制过程中积累应变的条件以及避免混晶的技术路线,利用提出的模型对工业轧制工艺进行优化,模拟实验的结果得到了最终产品晶粒尺寸为1.5μm。     

Effect of austenitizing temperature on microstructure in 16Mn steel treated by cerium

The change of inclusions and microstructure of 16Mn steel treated by Ce were observed,and the effect of austenitizing temperature on the microstructure was also examined.The results show that the inclusions are transformed from Si-Mn-Al composite oxide and MnS into AlCeO3,Ce2O2S,and MnS composite inclusions after being treated by Ce.Plenty of intragranular ferrites are formed in 16Mn steel conraining ～0.017wt％ Ce.A large amount of intragranular acicular ferrites are formed after being austenitized for 20 min at 1473 K.The prior austenite grain size fit for the formation of intragranular acicular ferrites is about 120 μm.