Effect of Rare Earth Elements on Austenite Growth Dynamics of Steel 9Cr2Mo

ＥｆｆｅｃｔｏｆＲａｒｅＥａｒｔｈＥｌｅｍｅｎｔｓｏｎＡｕｓｔｅｎｉｔｅＧｒｏｗｔｈＤｙｎａｍｉｃｓｏｆＳｔｅｅｌ９Ｃｒ２ＭｏＹａｎｇＱｉｎｇｘｉａｎｇ；ＷａｎｇＡｉｒｏｎｇ；ＧａｏＭｉｎｇ；ＷｕＨａｏｑｕａｎ；ＧｕｏＴｉｅｂｏＧａｏＭｉing;Ａｂｓｔ...     

稀土对9Cr2M0钢组织和性能的影响

研究了稀土元素对9Cr2Mo钢组织和性能的影响.试验结果表明9Cr2Mo钢中添加稀土元素,可使其奥氏体晶粒细化,未溶碳化物数量增加,抗淬裂能力及回火稳定性提高.     

中锰马氏体NM500钢奥氏体晶粒长大行为

 中锰马氏体耐磨钢是一种新型的低成本高性能耐磨钢,揭示钢中奥氏体晶粒长大行为,并建立精确的预测模型,对其组织和性能的调控至关重要。利用Gleeble-3500型热模拟试验机、金相显微镜和透射电子显微镜等设备,系统研究了中锰马氏体NM500钢在不同加热温度和保温时间下的奥氏体晶粒长大行为,探讨了微合金第二相对奥氏体晶粒长大行为的影响。研究结果表明,加热温度对试验钢中奥氏体晶粒长大的影响明显大于保温时间,且试验钢中奥氏体晶粒长大行为受基体中V(C,N)粒子析出行为的影响,其可分为两个阶段。当加热温度小于950 ℃时,试验钢中存在大量未溶的纳米级球状和短棒状V(C,N)粒子,能够有效地钉扎奥氏体晶界,奥氏体晶粒长大缓慢;但当加热温度不低于950 ℃时,试验钢中V(C,N)粒子大量溶解和粗化。其中,加热温度为950 ℃、保温时间为60 min时,试验钢中V(C,N)粒子的体积分数仅为0.041%,平均粒径增大至45.78 nm。其对奥氏体晶粒的钉扎作用显著减低,且随着温度升高,原子扩散速度加快,奥氏体晶粒快速长大。基于Beck模型,建立了试验钢中奥氏体晶粒等温长大动力学模型,计算得到低温及高温阶段试验钢中奥氏体晶粒长大表观激活能分别为66.561 kg/mol和170.416 kJ/mol,且奥氏体晶粒的理论计算值与实测结果吻合较好。     

Effect of Rare Earth Composite Modification on Microstructure and Properties of a New Cast Hot-Work Die Steel

The effects of RE modification on structure and the properties of a new cast hot-work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly - distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02 %, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.     

稀土对抽油杆用钢组织和性能的影响

本文对３５Ｍｎ２ＲＥ及３５Ｍｎ２抽油杆用钢的奥氏体晶粒大小，组织状态及抗Ｎ２Ｓ应力腐蚀性能进行了分析研究。研究表明：稀土加入钢中，细化钢的奥氏体晶粒，改善钢的组织，显著延长钢的Ｈ２Ｓ应力腐蚀断裂时间。     

BVRE重轨钢奥氏体长大行为的动力学研究

以BVRE重轨钢为研究对象,通过真空冶炼、锻造和轧制工艺制备合格的重轨钢试样.在此基础上,系统研究稀土重轨钢奥氏体晶粒的长大动力学.实验结果表明,随着加热温度的提高,稀土重轨钢奥氏体晶粒呈指数关系长大;随着保温时间的延长,稀土重轨钢奥氏体晶粒长大呈抛物线规律.重轨钢中添加微量的稀土,可以明显降低不同加热条件下的奥氏体晶粒尺寸.模型计算结果表明,重轨钢的奥氏体晶粒长大公式分别为:d4.80=d4.800+ 2.82×1028texp(- 556450/RT)(不加稀土)和d5.34=d5.340 +4.52×1032texp(- 646890/RT)(稀土重轨钢).稀土主要通过晶界的偏聚机制使奥氏体晶粒长大激活能由556450J·mol-1增加到646890J·mol-1,从而抑制奥氏体晶粒尺寸的增加.     

低合金铜时效强化钢奥氏体化过程的动力学模型

通过高温金相试验,研究了一种船用低合金铜时效强化钢在不同加热温度和保温时间下的奥氏体晶粒长大行为和尺寸分布规律。结果表明:随着加热温度的升高,奥氏体晶粒尺寸逐渐增大,并且在不同的温度区间,奥氏体晶粒具有不同的长大速度。随着保温时间的延长,奥氏体晶粒也逐渐长大,但加热温度越高,奥氏体晶粒长大速度越快。各加热温度及保温时间下奥氏体晶粒尺寸呈对数正态分布,且随着加热温度升高或保温时间延长,对数正态分布曲线峰值横坐标右移,峰值频率下降。通过对试验数据进行回归分析,建立了适用于本钢种的奥氏体晶粒长大的动力学模型,模型计算值与试验值吻合较好,平均相对误差小于5%,所建立的模型具有较高的精准性和可靠性。     

超超临界机组叶片钢KT5331晶粒长大行为

通过在不同温度下等温奥氏体化,研究KT5331钢奥氏体晶粒长大行为,并探讨析出相对奥氏体晶粒长大行为的影响机理.研究表明,KT5331钢奥氏体晶粒长大可分为三个阶段：1075℃以下,由于含W和Nb的析出相钉扎作用,晶粒长大缓慢;1075℃以上,含W和Nb的析出相溶解,钉扎作用减弱,随加热温度和保温时间延长晶粒迅速长大;1225℃及以上,δ铁素体析出,晶粒尺寸随加热温度升高而急剧减小.通过拟合分别得到晶粒粗化温度以下（950~1075℃）和晶粒粗化温度以上（1100~1200℃）的晶粒长大模型.     

Effect of vanadium on the microstructure and properties of metastable austenitic stainless steel AISI 301LN

In this study,the effect of vanadium on the microstructure and properties of the metastable austenitic stainless steel AISI 301LN w as investigated. Results of the study show that the addition of vanadium can refine grains and increase the strength of AISI 301LN by solution treatment. After 60%cold-rolling reduction,the microstructure of the steel w as composed of w ork-hardened austenite bands and deformation-inducedɑ'martensite.Considerable w ork-hardening and phase transformation strengthening occurred. After cold rolling and subsequent annealing,the deformation-inducedɑ'martensite w as reversed into fine-grained austenite. The w orkhardened austenite bands underw ent recrystallization; how ever,the structure of the recrystallized austenite grains w as coarser than that of the reversed ones.Simultaneously,the strength of the experimental steels decreased w ith the increase in annealing temperature. The pinning effect of precipitates of vanadium inhibited the grow th of austenite grains.Thus,the desirable combination of strength and ductility w as obtained by grain refinement.     

不同成分系列微合金钢抗奥氏体晶粒长大能力研究

研究了ＮｂＶ－Ｖ，Ｎｂ－Ｔｉ，Ｎｂ－Ｖ－Ｔｉ三种成分系列微合金钢的抗奥氏体晶粒长大能力，以及含氮量对Ｎｂ－Ｖ－Ｔｉ微合金钢抗奥氏体晶粒长大能力的影响。试验结果表明，微合金钢中加入微量钛可大大提高钢抗奥氏体晶粒长大能力，Ｎｂ－Ｖ－Ｔｉ微合金钢中含氮量增多抗奥氏体晶粒长大能力增强，但含氮量过高会影响焊接热影响区韧性。     

大型盾构机用轴承钢奥氏体晶粒长大模型

 利用箱式电阻炉研究了加热温度为900,950,1 000,1 050,1 100,1 150 ℃,保温时间为10,30,60,90 min时大型盾构机用GCr15SiMn轴承钢的奥氏体晶粒长大规律,利用截线法统计奥氏体晶粒尺寸。试验结果表明,随着加热温度提高和保温时间延长,奥氏体晶粒尺寸和长大速率逐渐增大,加热温度的提高比保温时间的延长对奥氏体晶粒长大速率影响更大,奥氏体晶粒迅速长大的加热温度为1 000 ℃,保温时间为60 min。在已有晶粒长大模型的基础上,通过对试验数据进行线性回归,得到了描述GCr15SiMn钢奥氏体晶粒长大规律的数学模型。     

Effects of RE and Vanadium on Microalloyed Steel

The effects of RE were studied by TEM, SEM, ICP and thermal simulation methods in vanadium microalloyed steel. The content.of RE in the solid solution can reach the order of 10^-5 --10^-4 in steel. The solid solution of RE was found to reduce the stability of precipitated V (C, N ), impede the precipitation of V (C, N ) in austenite, and accelerate and refine the precipitation of V (C, N) in ferrite. The combined effect of RE and V is to delay the dynamic recrystaUization, refine the grains and second phase particles, and to promote the precipitation of V (C, N) obviously. Thus the microalloying with RE and V leads to raising the strength and toughness of steel.     

Austenite Grain Refinement and Isothermal Growth Behavior in a Low Carbon Vanadium Microalloyed Steel

The austenite grain refinement through control of the grain growth during reheating process after thermomechanical controlled process(TMCP)in a vanadium microalloyed steel was achieved.The formation of ultra-fine grained austenite was attributed to the high density of austenite nucleation at the ferrite/martensite structure and to the inhibition of austenite growth by(Ti,V)C particles at the relatively low reheating temperature.Corresponding with the precipitation behavior of(Ti,V)C with temperature,the growth behavior of austenite in the vanadium microalloyed steel could be divided into two regions.At lower reheating temperature,austenite grains grew slowly,and ultra-fine grained austenite smaller than 5μm was successfully obtained.By contrast,the austenite grains grew rapidly at high temperature due to the dissolution of(Ti,V)C particles.According to the measured and predicted results of austenite growth kinetics,two models were developed to describe the growth behavior of austenite grains in two different temperature regions,and the apparent activation energy Qappfor grain growth was estimated to be about 115 and 195kJ/mol,respectively.     

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.     

In-situ observation on austenite grain growth of a Nb microalloyed high-carbon steel

It was reported in previous studies that the growth of austenite was inhibited by the pinning effect of Nb containing precipitates and the solute dragging effect of solute Nb. The effect of Nb on austenite grain growth of high carbon steel was investigated by laser scanning confocal microscope (LSCM). Microstructure evolution during heating process of the tested steel was observed by in situ observation. The results show that even without the pinning effect of Nb containing precipitates (at high temperatures), Nb can hinder the growth of austenite grains due to the solute dragging effect of Nb. Two models were used to fit the austenite grain growth process, and the Beck growth models of Nb microalloyed high carbon steels at different heating temperatures were established. The austenite grain growth kinetics model considering the influence of heating temperature and holding time can accurately predict the austenite grain growth process of Nb microalloyed high carbon steels.     

Nb微合金化高碳钢奥氏体晶粒长大原位观察

摘要：以往研究表明Nb析出相钉扎和固溶Nb溶质拖曳作用共同阻碍奥氏体晶粒长大。采用高温共聚焦显微镜研究了Nb对一种高碳含Nb钢奥氏体晶粒长大的影响,对含Nb钢加热过程组织演变进行原位观察。结果表明,Nb在没有钉扎作用下（即高温条件下）仍能起到阻碍奥氏体晶粒长大的作用,该阻碍效果主要是固溶Nb的溶质拖曳作用引起的。采用2种模型对奥氏体晶粒长大行为进行拟合,给出了不同加热温度下Nb微合金化高碳钢的Beck长大方程,同时考虑到加热温度和保温时间的共同影响,根据原位观察结果得到实验钢的奥氏体晶粒长大动力学模型,该模型能够较准确地预测Nb微合金化高碳钢奥氏体晶粒长大行为。     

Distribution and Behaviour of Rare Earths in Laser Coating

ＴｈｅｒｅａｒｅｍａｎｙｍｅｔｈｏｄｓｏｆａｄｄｉｎｇＲＥｉｎｔｏｓｔｅｅｌｓｕｒｆａｃｅ［１］，ｏｆｗｈｉｃｈｔｈｅｄｉｆｕｓｉｏｎｐｅｎｅｔｒａｔｉｏｎｍｅｔｈｏｄｉｓａｎｅｗｏｎｅ．Ｔｈｅｌａｓｅｒｔｒｅａｔｅｄｓｕｒｆａｃｅｓｏｆｂｏｔｈｔ...     

Austenitization Behaviors of X80 Pipeline Steels With High Nb and Micro-Ti Treatment

 The austenitization behaviors of two high Nb-containing X80 pipeline steels with different Ti contents, including the dissolution of microalloying precipitates and the austenite grain growth behaviors, were investigated by using physical-chemical phase analysis method and optimal microstructure observation. The results illustrate that most Nb can be dissolved into austenite during the soaking at 1180℃, but very little amount of Ti can be dissolved. It is found that during soaking, the austenite grain growth rate is initially high, and then it decreases after 1h soaking; moreover, the austenite grains grow up more rapidly at temperatures above 1180℃ than at temperatures below 1180℃. It is shown that the steel with 0.016%Ti content has a larger austenite grain size than the steel with 0.012%Ti under the same soaking conditions, which has been explained by considering the particle size distribution.     

中厚板中间坯冷却过程中晶粒长大及控制方法

为控制中厚板中间坯长时间待温导致的晶粒长大,研究了中间强制水冷却对奥氏体组织的影响.通过对Q345B钢和含Nb-Ti钢采用1050℃变形后快冷至1050~950℃预定温度保温的热模拟方法,确定了中间坯冷却过程中的晶粒尺寸变化规律,提出了中厚板冷却过程中晶粒长大的控制方法,建立了Q345B钢和含Nb-Ti钢在中间冷却过程中的晶粒长大模型.在中间冷却过程中,Q345B钢晶粒稳定性较差,而含Nb-Ti钢晶粒稳定性良好,归因于以铌为主的析出相对奥氏体晶界的钉扎作用.中间坯的强制冷却可控制奥氏体晶粒长大,63mm厚中间坯强制冷却可有效减小平均晶粒尺寸约20μm.在实际生产中,经中间强制冷却后16 mm厚度Q345B钢板的冲击韧性提高25%~70%.     

薄板坯连铸连轧流程钛微合金钢控制轧制技术

 重点阐述了薄板坯连铸连轧流程钛微合金钢的控制轧制模式及其机理。基于应力松弛试验和双道次压缩热模拟试验,研究分析了薄板坯连铸连轧钛微合金钢的奥氏体再结晶动力学。研究结果表明,轧前铸态粗大奥氏体组织经F1高温大压下后可实现完全静态再结晶;铸坯中固析TiN粒子可以有效阻止奥氏体再结晶晶粒的长大,实现再结晶区控轧。固溶钛的溶质拖曳作用以及形变诱导析出的TiC粒子对奥氏体再结晶具有抑制作用,可以阻止奥氏体再结晶的发生,实现未再结晶区控轧。