氮气加压熔炼高氮钢技术的研究进展

在综述氮气加压熔炼高氮钢技术的基础上，指出了大熔池法（BSB）适合于工业化大规模制备高氮钢；并基于国内几十年来电渣冶金技术的丰富经验，提出了采用电弧渣重熔（ASR）和加压电弧渣重熔（ASRP）技术生产高氮钢是目前较为可行的技术方案。     

抚顺特钢高强钢及超高强度钢发展现状

基于国内特殊钢冶炼高强钢技术的发展及现状、对抚顺特钢生产的高强钢、超高强度钢及超高强度不锈钢特殊冶炼技术工艺进行简要分析研究.简要介绍了目前抚顺特钢超高强度钢领域典型新材料特殊熔炼技术和制备工艺流程,分析讨论了高品质特殊钢目前工业化生产技术瓶颈及发展现状.     

钒氮钢中铁素体等温形核规律的试验研究

采用Geeble 3500热模拟试验机，对比研究了钒氮钢、钒钢的等温相变特征。结果表明，在相变过程中，钒氮钢中铁素体形核总量和晶内铁素体形核数量都明显高于钒钢，分析认为，这与钒氮钢中V（C，N）的析出造成了铁素体形核位置的改变，同时也增加了形核位置密度有关，尝试用一种新的形核方式对此进行了描述。     

凝固过程重轨钢中MnS粒子形核与长大动力学分析

利用经典形核理论和扩散控制长大模型计算分析了重轨钢中MnS粒子析出的动力学行为,计算结果表明,MnS粒子在重轨钢凝固过程以均匀形核和晶界形核为主,主要在凝固末期析出。在设定的重轨钢成分下,计算出MnS的有效形核温度为1 634K,即Mn、S实际浓度积等于平衡浓度积。降低S的质量分数小于5.0×10-5能够推迟MnS接近固相线析出,而对MnS的长大半径影响较小;提高冷却速率从0.14K/s到1.45K/s,连铸坯内柱状晶区中MnS的长大半径比中心等轴晶区的大1个数量级,但对MnS的析出时机无影响。S元素是MnS在凝固过程中粗化长大的控制性环节,在凝固过程冷却速率对MnS粒子长大半径起着决定性的作用。     

高品质特殊钢关键生产技术

介绍了21世纪国际上以轴承钢为代表的特殊钢发展新趋势,分析了国内外轴承钢产品质量的差距和问题,重点介绍了近几年国内在转炉高碳脱磷低氧钢冶炼、降低还原势的炉外精炼工艺、大型夹杂物来源与控制、超低钛钢冶炼和大方坯连铸凝固末端凸辊压下等高品质特殊钢冶炼技术的发展状况和研究成果。     

Cr12N高氮钢冶炼过程中氮的控制

在高温高压反应釜内冶炼Cr12N高氮钢,通过试验发现,在Cr12N的熔炼过程中,随着压力的提高,钢中的氮含量不断增加,钢锭中得到的固相中氮的饱和溶解度和Chipman等人的热力学模型计算得到的氮的饱和溶解度有一定的偏差,为了修正这个偏差,引进了Burton-Prim-Slichter方程,修正后得到液相中氮的饱和溶解度的修正值和计算值吻合得很好。计算了在Cr12N的冶炼过程中,防止气泡析出所需要的最小凝固压力为2.84 MPa,通过试验发现,在高的凝固压力下,钢锭的致密性和缩孔现象得到明显改善。     

Mn18Cr18N高氮奥氏体不锈钢的冶炼工艺

为了研究Mn18Cr18N高氮奥氏体不锈钢的冶炼工艺,采用加压感应炉+保护气氛电渣重熔工艺进行Mn18Cr18N高氮奥氏体不锈钢的冶炼工艺试验,冶炼过程中采用氮化合金与加压氮气渗入相结合的方法增氮。结果表明,随着氮气分压的增加,钢中氮质量分数随之增大;当冶炼过程中氮气分压提高0.03 MPa时,能够成功抑制皮下气泡的生产;试验钢经保护气氛电渣重熔后,钢中夹杂物会普遍降低,主要为细小的方形TiN夹杂。     

特殊钢冶炼配料及合金化计算模型

分析了特殊钢冶炼中人工调整钢液成分计算公式的缺点,建立了高精度基本计算模型以及特殊钢冶炼中装炉配料、合金化、钢液量估算、超规格元素成分调整和元素回收率确定等常见问题的相应计算模型和程序模块,最后举例说明了该计算程序的主要运行特点.     

特殊钢的连铸

特殊钢一般含有一定的合金元素,冷却凝固状态不同于普通碳素钢,在连铸坯中更易产生成分 和组织偏析,和表面裂纹等缺陷。所以冶炼特殊钢时应提高钢水的纯洁度,减少夹杂物含量和改善夹杂物形 态,连铸时采用钢液二次氧化和污染,以减少铸坯低过热度(10～15℃)浇注和保护浇铸技术,防止成分和组 织偏析,提高铸坯表面质量和内部致密度。叙述了连铸保护浇铸技术,中间包冶金,电磁搅拌、凝固末端轻压 下特殊钢连铸专用覆盖剂、保护渣和自动化技术。讨论了特殊钢连铸工艺参数,存在的问题和对策。     

基于双亚点阵模型对H13钢中初生碳氮化物的研究

实验证明H13钢中存在三类初生碳氮化物，包括富V和C的（V_x，Mo_1-x）（C_y，N_1-y）、富Ti和N的（Ti_x，V_1-x）（C_y，N_1-y）及富V和C的（Ti_x，V_1-x）（C_y，N_1-y），部分存在形核核心.基于双亚点阵模型和凝固偏析模型分析计算H13钢凝固过程中元素含量变化，考虑初生碳氮化物中元素间的相互作用，根据三类碳氮化物中合金元素含量和C/N比值不同，对各碳氮化物的生成自由能进行分析.理论研究指出富Ti和N的（Ti_x，V_1-x）（C_y，N_1-y）在固相率为0.90时即可生成，而富V和C的（Ti_x，V_1-x）（C_y，N_1-y）在固相率大于0.96才可生成，两类碳氮化物的临界生成固相率f_P均随固溶Ti和N含量的增加而减小.（V_x，Mo_1-x）（C_y，N_1-y）的临界生成固相率与x值密切相关，x减小时f_P降低，粒子尺寸增加，实验与理论分析吻合良好.根据错配度分析氧化物和碳氮化物对H13钢中初生碳氮化物异质形核的作用.      

含氮不锈钢凝固模式及显微组织研究

研究了四种不同N含量的18Mn18Cr N不锈钢的凝固模式、显微组织和元素分布.结果表明:N含量影响18Mn18Cr N合金系的凝固模式和显微组织.氮的质量分数由0.07%增加至0.72%时,实验钢的凝固模式由F模式转变为A模式,显微组织由铁素体和奥氏体魏氏两相组织转变为铁素体和奥氏体两相组织以及单相奥氏体组织.N含量影响奥氏体相形貌,随N含量增加,奥氏体由板条状、针状转变为枝晶间和等轴状.枝晶间和等轴状奥氏体晶粒中存在褶皱形貌,且随着氮含量增加,褶皱数量增多.褶皱的产生与凝固过程中奥氏体相内部Fe、Mn、Cr元素的偏析有关,且该凝固偏析被保留至室温组织中.      

The effect of quenching on the solidification structure and transformation behavior of stainless steel welds

Weld solidification structure of three different types of stainless steel,i.e., 310 austenitic, 309 and 304 semiaustenitic, and 430 ferritic, was investigated. Welds of each material were made without any quenching, with water quenching, and with liquid-tin quenching during welding. The weld micro-structure obtained was explained with the help of the pseudobinary phase diagrams for Fe-Cr-Ni and Fe-Cr-C systems. It was found that, due to the postsolidification 5 → γ phase transformation in 309 and 304 stainless steels and the rapid homogenization of microsegregation in 430 stainless steel, their weld solidification structure could not be observed unless quenched from the solidification range with liquid tin. Moreover, the formation of acicular austenite, and hence, martensite, at the grain boundaries of 430 stainless steel welds was eliminated completely when quenched with liquid tin. The weld solidification structure of 310 stainless steel, on the other hand, was essentially unaffected by quenching. Based upon the observations made, the weld microstructure of these stainless steels was summarized. The effect of cooling rate on the formation of primary austenite in 309 stainless steel welds was discussed. Finally, a simple method for determining the relationship between the secondary dendrite arm spacing and the solidification time, based on welding speeds and weld pool configurations, was suggested.     

冷轧变形量对高氮奥氏体不锈钢Mnl7Crl9N0.6组织和性能的影响

对感应炉-电渣重熔冶炼的节镍型高氮奥氏体不锈钢Mn17Cr19N0.6的3mm热轧板进行变形量10%～60%的冷轧及拉伸实验。结合金相组织观察及XRD物相分析,研究高氮奥氏体不锈钢冷变形过程中微观组织变化规律,得出结论:在冷轧过程中,随着变形量的增加,实验钢中晶粒的形状由块状到压扁拉长状,滑移从单滑移为主到交滑移,孪晶最终被分割破碎。实验钢在不同冷轧变形量后的组织均为单一的奥氏体相,并没有出现其他相,实验钢在冷变形过程中没有发生马氏体转变,因此,实验钢在冷轧过程中没有通过相变强化,以形变强化为主,抗拉强度从冷轧变形量为10%时的1045 MPa升高至变形量为60%时的1880MPa,因此通过冷变形可以制备出不同强度级别且组织为单一奥氏体的特种材料。     

稀土元素在铁素体不锈钢中的作用和应用前景

铁素体不锈钢(11%～30%Cr)的抗点蚀、抗应力腐蚀和抗高温氧化性能均优于奥氏体不锈钢。但普通铁素体不锈钢晶间腐蚀敏感性较高,塑性和韧性较低,焊接裂纹倾向较大。经分析得出,铁素体不锈钢加稀土元素可改善钢的凝固组织,影响碳、氮化物析出形态,细化晶粒,改变钢中硫化物形态和夹杂物成分,从而改善钢的横向韧性、焊接性能和疲劳性能。因此,稀土元素在铁素体不锈钢中的应用研究工作有广阔的前景。     

超级贝氏体钢的现状和进展

超级贝氏体钢的基本合金元素为C-Mn-Si,通过300～500℃低温相变得到超细贝氏体、马氏体和残余奥氏体组织。为减小临界冷却速度、促进贝氏体转变,部分超级贝氏体钢中添加Cr、Ni、Mo等合金元素,并降低C、Mn含量以改善钢材的焊接性能。超级贝氏体钢具有超高强度和良好的塑性,其屈服和抗拉强度分别达～1 200MPa和1 600～1 700 MPa,总伸长率为～15%。新一代超级贝氏体钢的屈服强度可达1 300 MPa以上,抗拉强度超过1 700 MPa。     

Calculation of solidification-related thermophysical properties for steels

Special algorithms have been developed to calculate important solidification-related thermophysical properties: enthalpy and enthalpy-related data (i.e., specific and latent heat), density, and thermal conductivity for low-alloyed and stainless steels. The algorithms are heavily based on the use of earlier developed phase transformation models, an interdendritic solidification model (IDS), and an austenite decomposition model (ADC), which solve, as a function of temperature, the phase fractions and compositions needed in these calculations. As a result, the thermophysical properties can be calculated at any temperature, from 1600 °C to 25 °C, taking into account the discontinuities caused by special phase transformations (i.e., ferritic, austenitic and peritectic solidification, ferrite/austenite transformation, and austenite decomposition to various structures) influenced by the steel grade and the cooling conditions.     

Microstructural modification of austenitic stainless steels by rapid solidification

The microstructural modifications in three austenitic stainless steels (types 308, 310, and 312) were evaluated after rapid solidification. These three steels are commonly used weld filler metals. Two methods of rapid solidification were investigated, autogenous laser welding and arc-hammer splat quenching. The structure of 310 stainless steel was found to be 100 pct austenite, and did not vary over the range of conditions studied. On the contrary, the structures of types 308 and 312 steels were very sensitive to the cooling rates and solidification conditions. With the highest cooling rates, the type 308 structure was fully austenitic while the type 312 structure was fully ferritic. At lower cooling rates, the structures were duplex ferrite plus austenite. The results were interpreted in terms of faster kinetics of solidification of austenite compared to ferrite under the conditions examined. A comparison of the structures produced by the two rapid solidification techniques indicated the cooling rates are comparable.     

Concept of a new high‐strength austenitic stainless steel

The concept of combined addition of C and N, as persued in previous work on martensitic steels, is transferred to austenitic stainless steels in order to gain highest phase stability. Thermodynamic calculations with special respect to the influence of temperature and interstitial content (C, N or C + N) were studied in the FeCrMnNC‐system. Promising compositions like Fe‐13Cr‐17Mn and Fe‐13Cr‐21Mn revealed an extended austenitic phase field. Some appropriate alloys were investigated with regard to their microscopic and electron structure. The concentration of free electrons in the austenite as the origin of phase stabilitiy increased in the order of C, N, C + N being added. Thus, the metallic character of interatomic bonding is enhanced, which entails short range atomic order. Hence, the substitutional alloy content can be minimized.     

Rapid solidification of a droplet-processed stainless steel

Individual powder particles of a droplet-processed and rapidly solidified 303 stainless steel are characterized in terms of microstructure and composition variations within the solidification structure using scanning transmission electron microscopy (STEM). Fcc is found to be the crystallization phase in powder particles larger than about 70 micron diameter, and bcc is the crystallization phase in the smaller powder particles. An important difference in partitioning behavior between these two crystal structures of this alloy is found in that solute elements are more completely trapped in the bcc structures. Massive solidification of bcc structures is found to produce supersaturated solid solutions which are retained to ambient temperatures in the smallest powder particles. Calculated liquid-to-crystal nucleation temperatures for fcc and bcc show a tendency for bcc nucleation at the large liquid supercoolings which are likely to occur in smaller droplets. The importance of small droplet sizes in rapid solidification processes is stressed. Formerly with Massachusetts Institute of Technology, Cambridge, MA.     

Heat transfer during Nd: Yag pulsed laser welding and its effect on solidification structure of austenitic stainless steels

Theoretical and experimental investigations were carried out to determine the effect of process parameters on weld metal microstructures of austenitic stainless steels during pulsed laser welding. Laser welds made on four austenitic stainless steels at different power levels and scanning speeds were considered. A transient heat transfer model that takes into account fluid flow in the weld pool was employed to simulate thermal cycles and cooling rates experienced by the material under various welding conditions. The weld metal thermal cycles and cooling rates are related to features of the solidification structure. For the conditions investigated, the observed fusion zone structure ranged from duplex austenite (γ)+ferrite (δ) to fully austenitic or fully ferritic. Unlike welding with a continuous wave laser, pulsed laser welding results in thermal cycling from multiple melting and solidification cycles in the fusion zone, causing significant post-solidification solid-state transformation to occur. There was microstructural evidence of significant recrystallization in the fusion zone structure that can be explained on the basis of the thermal cycles. The present investigation clearly demonstrated the potential of the computational model to provide detailed information regarding the heat transfer conditions experienced during welding.