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The characteristics of inclusions in high strength structural steel were characterized by scanning electron microscopy and energy dispersive spectroscopy. The influence of Ti- alloying and Ca treatment on the composition of inclusions in the steel was investigated, and the effect of oxides on the precipitation behavior of TiN and its refining effect on the microstructure were studied. The results show that the inclusions in the steels are Al- Ti- Mg- O system with spherical or polygonal shape after adding Ti, which furtherly can be effectively modified into spherical inclusions after adding Ca. The TiOx in inclusions can be reduced by Ca treatment and Ti gradually diffuses into the surface of the inclusions, which promotes the local precipitation of TiN on the surface of the composite oxides. The amounts of fine oxides and nitrides in steel increase with the increase of Ti mass percentage. Therefore, Ca treatment and higher Ti content can promote the formation of the inclusions of composite oxide and TiN, and also delay the homogeneous nucleation time of TiN inclusions, reducing its size during solidification process of the steel. TiN with the size about 2-3??m not only can induce polygonal ferrite, but also induce acicular ferrite. Specially, the inclusions with TiN and MnS locally precipitating on the surface of composite oxides are conducive to the nucleation of interlocking acicular ferrites.     

The relationship between microstructure and stress-strain behavior in tension in high strength pipeline steel

In this paper the relationship between microstructure and stress-strain behavior in tensile test of high strength pipeline steel was investigated.The steel with polygonal ferrite-bainite(PF + B) microstructure has a "round-house" type tensile stress-strain curve with low Y/T ratio,highly uniform elongation and high n-value,which means PF + B microstructure has the best deformability(i.e.Ideal stress-strain behavior) among the four microstructures.The steel with acicular ferrite-martensite&austenite(AF + MA) microstructure has a "continuous-yielding" type tensile stress-strain curve,whose deformability is worse than that of PF + B microstructure.Both the steels of polygonal ferrite-acicular ferrite(PF + AF) and polygonal ferrite-pearlite (PF+P) microstructure have "luders elongation" type tensile stress-strain curve with high Y/T ratio,low uniform elongation and low n-value,which means PF + AF and PF + P microstructures have the worst deformability among the four microstructures.     

奥氏体状态对 Mn-Cr 齿轮钢连续冷却相变组织的影响

使用Cleeblel500热模拟试验机研究了成分(%)为：0.23C,0.74Mn,0.90Cr 齿轮钢奥氏体晶粒尺 寸和变形(真应变量0.4)对连续冷却相变组织的影响和连续转变冷却(CCT)曲线。实验结果表明,当齿轮钢 未变形时,获得完全多边形铁素体+珠光体混合组织的临界冷速为0.5~1℃/s,冷速较快时,中温相变产物 由贝氏体及针状铁素体组成;奥氏体变形时,多边形铁素体相变开始温度升高,获得完全多边形铁素体+珠光 体混合组织冷速增大,为1~2℃/s,中温相变产物没有出现贝氏体,只有针状铁素体。     

针状铁素体对含铌HRB400钢筋屈服行为的影响

对比研究成分为20MnSiV和16MnVNb的HRB400钢筋的屈服行为,在同一轧制工艺条件下,与含钒钢筋相比,含铌钢筋应力-应变曲线没有明显的屈服平台。对试验钢的化学成分、显微硬度进行测试分析,利用光学显微镜、扫描电镜和透射电镜对试验钢的微观组织进行观察。结果表明,20MnSiV试验钢组织主要为铁素体＋珠光体组织,16MnVNb的组织为等轴状铁素体＋珠光体＋针状铁素体,其中针状铁素体周围珠光体退化明显。针状铁素体的显微硬度介于珠光体与铁素体之间,其内部存在高密度位错。针状铁素体组织的大量存在是导致含铌HRB400钢筋无屈服平台的原因。     

钛稀土复合处理对C--Mn钢粗晶热影响区组织及韧性的影响

利用Gleeble-1500D热模拟机进行焊接热影响区热循环模拟实验,研究了在焊接热输入为65 kJ·cm-1时稀土单独处理和钛稀土复合处理对C-Mn钢粗晶热影响区组织及冲击韧性的影响,并利用扫描电镜观察和分析了实验钢中的夹杂物和冲击断口形貌,利用光镜观察了热循环模拟后实验钢中的微观组织.实验结果表明:稀土单独处理和钛稀土复合处理的试样微观组织分别主要是晶界铁素体+块状铁素体+针状铁素体和晶界铁素体+晶内针状铁素体.经稀土单独处理的试样中夹杂物为La₂O₂S+锰铝硅酸盐+MnS复合夹杂;钛稀土复合处理的试样中的夹杂主要是La₂O₂S+TiO_x+锰铝硅酸盐+MnS复合夹杂.钛稀土复合处理钢中的复合夹杂更细小,有利于形成细小的晶内针状铁素体.钛稀土复合处理极大地改善了实验钢的焊接热影响区低温冲击韧性,比稀土单独处理对试样的冲击性能提升效果更好.      

Effect of Aluminum and Titanium Treatment on Non-Metallic Inclusions and Microstructures of CGHAZ in HSLA Steel

The Effect of A1 and Ti treatment on non-metallic inclusions and microstructures of coarse-grain HAZ in HSLA stee1 was investigated in this paper based on experiments and thermodynamic calculations.The results showed that the inclusions in A1 treated steel were mainly aluminum oxides and titanium nitrides which could not promote the formation of acicular ferrite microstructures.Microstructure of coarse-grain HAZ in A1 treated steels consists of heavy grain boundary ferrite and ferrite side plate.The inclusions in Ti treated steel were A1,Ti,Mg,Ca composite oxides with size in the range of 0.5-3μm and titanium nitrides with size less than 0.3μm.Ti composite oxide could promote the formation of acicular ferrite and microstructures of coarse-grain HAZ in Ti treated steel consists of grain boundary ferrite,small amounts of ferrite side plate and large amounts of intragranular acicular ferrite.The size of grain boundaries ferrite was increased and the amount of ferrite side plate was decreased with the increase of soaking time at the peak temperature.The amount of grain boundary ferrite and the size of acicular ferrite were also increased with the increase of cooling rate during ferrite phase formation.     

Effect of Magnesium on Inclusion Formation in TiKilled Steels and Microstructural Evolution in Welding Induced CoarseGrained Heat Affected Zone

 Effects of Mg on the chemical component and size distribution of Ti bearing inclusions favored grain refinement of the welding induced coarse grained heat affected zone (CGHAZ), with enhanced impact toughness in Ti killed steels, which were examined based on experimental observations and thermodynamic calculations. The results indicated that the chemical constituents of the inclusions gradually varied from the Ti O+Ti Mg O compound oxide to the Ti Mg O+MgO compound oxide and the single phase MgO, as the Mg content increased from 0002 3% to 0006%. A trace addition of Mg (approximately 0002%) led to the refinement of Ti bearing inclusions by creating the Ti Mg O compound oxide and provided favorable size distribution of the inclusions for acicular ferrite transformation with a high nucleation rate in the CGHAZ, and a high volume fraction of acicular ferrite was obtained in the CGHAZ with enhanced impact toughness. Otherwise, a high content of Mg (approximately 0006%) produced a single phase MgO, which was impotent to nucleate an acicular ferrite, and a microstructure comprised of a ferrite side plate and a grain boundary ferrite developed in the CGHAZ. The experimental results were confirmed by thermodynamic calculations.     

Effect of Magnesium on Inclusion Formation in Ti-Killed Steels and Microstructurai Evolution in Welding Induced Coarse-Grained Heat Affected Zone

Effects of Mg on the chemical component and size distribution of Ti-bearing inclusions favored grain refinement of the welding induced coarse-grained heat affected zone (CGHAZ),with enhanced impact toughness in Ti-killed steels,which were examined based on experimental observations and thermodynamic calculations.The results indicated that the chemical constituents of the inclusions gradually varied from the Ti-O+Ti-Mg-O compound oxide to the Ti-Mg-O+ MgO compound oxide and the single-phase MgO,as the Mg content increased from 0.002 3% to 0.006%.A trace addition of Mg (approximately 0.002 %) led to the refinement of Ti-bearing inclusions by creating the Ti-Mg-O compound oxide and provided favorable size distribution of the inclusions for acicular ferrite transformation with a high nucleation rate in the CGHAZ,and a high volume fraction of acicular ferrite was obtained in the CGHAZ with enhanced impact toughness.Otherwise,a high content of Mg (approximately 0.006%) produced a single-phase MgO,which was impotent to nucleate an acicular ferrite,and a microstructure comprised of a ferrite side plate and a grain boundary ferrite developed in the CGHAZ.The experimental results were confirmed by thermodynamic calculations.     

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。     

含有上贝氏体的ER8车轮钢的裂纹扩展行为

研究不同含量的上贝氏体对ER8车轮钢裂纹扩展行为的影响。利用激光共聚焦显微镜（LSCM）和扫描电镜（SEM）对ER8车轮钢的显微组织和裂纹扩展路径进行了研究。实验结果表明:ER8车轮钢中的组织除了有铁素体和珠光体,还存在上贝氏体;裂纹穿过上贝氏体和珠光体扩展,最终停止在珠光体区域;与珠光体组织相比,裂纹在上贝氏体中的扩展路径更曲折。利用扫描电镜（SEM）对ER8车轮钢的裂纹扩展变形进行原位观察。实验结果表明:含有80%上贝氏体的ER8车轮钢拉伸时,组织变形过程主要以铁素体和上贝氏体为主,裂纹在上贝氏体和珠光体中连续扩展,伴随着珠光体的变形;而含有50%上贝氏体的ER8车轮钢拉伸时,组织变形过程主要以铁素体和珠光体为主,并且上贝氏体对铁素体和珠光体的变形起到阻碍作用。上贝氏体能够有效地阻止裂纹扩展,在偏转裂纹路径和延缓裂纹扩展方面起着重要作用;并且对铁素体和珠光体的变形起到阻碍作用。      

含铌抗大变形管线钢奥氏体的连续冷却转变

The CCT behaviors of two bearing Nb polygonal ferrite-bainite high strength and high-deformability pipeline steels were studied in undeformed condition, The static CCT curves were constructed. The static CCT curves, microstructures and microhardness of two experimental steels were compared. It was found that microstructures of these steels contain polygonal ferrite, pearlite, bainite as cooling rate from 0.0278 to 42.5�桤s-1; Addition of Nb in the steel retards polygonal ferrite and granular bainite transformation, suppresses ferrite growth and refine ferrite grain, makes transformation line of bainite right shift, narrows the range of cooling rate of ferrite transformation, raises start temperature of ferrite and banite transformation; ferrite transformation zone is narrowed and the bainite transformation zone is expanded with increasing of Nb.     

Effect of inclusions on toughness and microstructures in simulated coarse-grain heat-affected zones of Al/Ti deoxidised and Nb/V microalloyed steels

To explore the effect of inclusions in the coarse-grain heat-affected zone (CGHAZ), four groups were designed using the ‘Al/Ti deoxidised?+?Nb/V microalloyed’ technical route. The toughness of the CGHAZ of Al–Ti–V–N steel was greatly promoted by the presence of polygonal ferrite (PF) after high heat input rather than the traditionally used acicular ferrite (AF). Furthermore, micron-sized inclusions in AF or PF were analysed, and the results indicated that the TiN and V (CN) particles attached on the Ti/Al oxide inclusions induced the nucleation of AF and PF. That can be concluded that the nucleation mechanism of PF is similar to that of AF. In addition, smaller micron- and nanoscale-size inclusions observed by transmission electron microscopy could not induce the nucleation of AF and PF because of the low heterogeneous nucleation energy. Nevertheless, these inclusions can have a drag effect on grain boundary migration.     

铌微合金化对高铁车轮钢奥氏体形核和长大的影响

 针对碳质量分数为0.47%中碳高铁车轮钢,研究了铌微合金化对前驱体为铁素体-珠光体的组织发生奥氏体逆相变的影响。结果表明,铁素体-珠光体钢的逆相变是一个由碳原子扩散控制的过程,奥氏体优先在珠光体内的铁素体与渗碳体（α/Fe3C）片层界面处形核,并且沿平行于珠光体片层方向的长大速率比垂直于珠光体片层方向更快。含铌车轮钢细化的珠光体组织可以提高奥氏体的形核率,有利于细化奥氏体晶粒。随着再加热温度的提高,含铌车轮钢的奥氏体混晶温度（960 ℃）比不含铌的钢高80 ℃,因此通过铌微合金化可扩大再加热奥氏体化温度窗口。结合Thermal-Calc热力学计算和透射电镜分析,铌在中碳钢中主要以析出物的形式存在,析出钉扎作用是其细化奥氏体晶粒、推迟混晶现象出现的主要机制。     

Effects of Microstructure on CVN Impact Toughness in Thermomechanically Processed High Strength Microalloyed Steel

Investigation on the correlation between microstructure and CVN impact toughness is of practical importance for the microstructure design of high strength microalloyed steels. In this work, three steels with characteristic microstructures were produced by cooling path control, i.e., steel A with granular bainite (GB), steel B with polygonal ferrite (PF) and martensite-austenite (M-A) constituent, and steel C with the mixture of bainitic ferrite (BF), acicular ferrite (AF), and M-A constituent. Under the same alloy composition and controlled rolling, similar ductile-to-brittle transition temperatures were obtained for the three steels. Steel A achieved the highest upper shelf energy (USE), while large variation of impact absorbed energy has been observed in the ductile-to-brittle transition region. With apparently large-sized PF and M-A constituent, steel B shows the lowest USE and delamination phenomenon in the ductile-to-brittle transition region. Steel C exhibits an extended upper shelf region, intermediate USE, and the fastest decrease of impact absorbed energy in the ductile-to-brittle transition region. The detailed CVN impact behavior is studied and then linked to the microstructural features.     

稀土处理C-Mn钢显微组织和夹杂物演化

对稀土处理C-Mn钢的夹杂物和显微组织进行分析,统计稀土处理C-Mn钢中针状铁素体形核核心尺寸,并将稀土处理钢在不同温度下淬火,研究稀土夹杂物生成和长大过程.实验结果表明:C-Mn钢加入少量稀土后钢中夹杂物从MnS＋硅铝酸盐夹杂转变为La₂O₂S＋LaAlO₃＋MnS＋硅铝酸盐夹杂,尺寸得到细化,显微组织也从马氏体＋贝氏体组织变成侧板条铁素体、针状铁素体和块状铁素体组织;稀土处理C-Mn钢中针状铁素体有效形核核心的尺寸集中在1~4μm,主要是在钢液中形成,冷却和凝固过程形成的数量较少;稀土夹杂物在钢液温度和冷却及凝固过程容易碰撞黏合长大,上浮从钢液中去除,MnS能在稀土夹杂物颗粒间析出.      

Isochronal Phase Transformations of Low‐Carbon High Strength Low Alloy Steel upon Continuous Cooling

Aimed to acquire optimum comprehensive properties for the oil and gas pipeline steels, thermal treatment should be controlled to achieve ideal microstructures. Effects of cooling rates on transformation kinetics and microstructures of the low‐carbon high strength low alloy (HSLA) steel were investigated to obtain an optimized thermal treatment technology. Dilatometric measurements, light microscopy, scanning electron microscopy, and transmission electron microscopy were employed in present work. The transformed microstructures contained polygonal ferrite + pearlite, acicular ferrite (AF), and bainitic ferrite (BF) due to the cooling rates increasing from 5 to 3000°C min^?1, in present investigated HSLA steel. The result shows that, the increase of cooling rate accelerates AF transformation and refines the steel's matrix. The morphology of martensite/austenite structures transformed from islands in AF to films in BF with the increase of cooling rate.     

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.      

Mg处理高钢级管线钢焊接热影响区晶内铁素体形核机制研究

采用热模拟技术,EBSD技术和透射电子显微镜对镁处理高钢级管线钢的焊接热影响区(HAZ)晶内铁素体(IGF)的形核现象和机制进行了试验研究。结果表明:镁处理钢中形成大量的Al、Ti、Mg复合氧化物夹杂,其颗粒大小为0.5~3μm。在粗晶热影响区(CGHAZ)中,含Mg复合氧化物具有促进晶内针状铁素体形核的能力。对Mg处理高钢级管线钢焊接热影响区晶内铁素体的形核机制进行了探讨。     

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。      

Ni含量对控轧控冷船舶用Nb-Ti微合金化NiCr钢组织和性能的影响

研究了0.31%Ni和0.88%Ni二种控轧控冷Nb-Ti微合金化NiCr钢的组织和性能。结果表明,船舶用钢控轧控冷获得粒状贝氏体、上贝氏体、针状铁素体、多边形铁素体及少量珠光体等组成的复合组织。控轧控冷造成铁素体晶粒尺寸细化,细小M-A岛增多。二种钢均获得较高的抗拉强度、屈服强度、伸长率和硬度,0.88Ni-0.32Cr钢性能优于0.31Ni-0.33Cr钢。船舶用钢-80℃试样纵向冲击功都在200J以上,0.88Ni-0.32Cr钢甚至超过了300J。该钢中最佳的Ni含量为0.88%Ni。由于控轧控冷造成了铁素体细晶强化、M-A岛复合强化、析出强化和位错强化,合金元素镍有效的提高了船舶钢的低温冲击韧性。