High Nitrogen Austenitic Stainless Steels Manufactured by Nitrogen Gas Alloying and Adding Nitrided Ferroalloys

A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe-Cr-Mn-Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 0.69% in 18Crl8Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel-free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 0.81%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 um. After homogenization of the hot rolled plate at 1 150℃ × 1 h followed by water quenching, the microstructure consisted of homogeneous austenite.

Fabrication of high nitrogen austenitic stainless steels with excellent mechanical and pitting corrosion properties

A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then the stainless steel pipes were welded on the surface of an electrode with low nitrogen content to prepare a compound electrode. Using Si3N4 as a nitrogen alloying source, the silicon contents in the ingots were prone to be out of the specification range, the electric current fluctuated greatly and the surface qualities of the ingots were poor. The surface qualities of the ingots were improved with FeCrN as a nitrogen alloying source. The sound and compact macrostructure ingot with the maximum nitrogen content of 1.21wt% can be obtained. The 18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical ductile-brittle transition behavior and excellent pitting corrosion resistance properties.

Development of Fe-Cr-Ni-Mn-N High-Alloyed Powder Processed by Mechanical Alloying

The present work shows the research results of phase formation in obtaining high-alloy powder of Fe-Cr-Ni-Mn-N by mechanochemical synthesis in various gas atmospheres.

Development of nitrogen-alloyed stainless steel sheet products in Baosteel

Nitrogen plays a vitally important role for improving properties for stainless steels in many aspects.In this paper,the physical metallurgy behavior and the beneficial effects of nitrogen on corrosion resistance and other mechanical properties of stainless steels were summarised.Based on nitrogen alloying,various stainless steel products,such as austenitic,duplex and martensitic staniless steels were developed with enhanced properties,such as corrosion resistance,mechanical strength and weldability,among other things.

Improvement of the Corrosion Resistance of High Alloyed Austenitic Cr-Ni-Mo Stainless Steels by Solution Nitriding

Characteristic features of austenitic steel grades combine a good corrosion resistance with a low hardness, wear resistance and scratch resistance. An interesting possibility for improving the wear behaviour of these steels without loss of their corrosion resistance lies in enriching the near surface region with nitrogen. The process of a solution nitriding allows the rise of the solution of nitrogen in the solid phase. On this state nitrogen increases the corrosion resistance and the tribilogical load-bearing capacity. The aim of the study was, to investigate the improvement of the pitting corrosion behaviour by solution nitriding. A special topic was to observe the effect of nitrogen by different molybdenum content. So austenitic stainless steels (18% Cr, 12% Ni, Mo gradation between 0.06 to 3.6%) had been solution nitrided. The samples could be prepared with various surface content of nitrogen from 0.04 to 0.45% with a step-by-step grinding. The susceptibility against pitting corrosion of these samples had been tested by determination of the stable pitting potential in 0.5M and 1M NaCl at 25°C. For the investigated steel composition and the used corrosion system there is no influence of molybdenum on the effectiveness of nitrogen. The influence of nitrogen to all of the determined parameters can be described well by PRE = Cr + 3,3 * Mo + 25 *N. XPS analysis of the sample surfaces support the results of the pitting corrosion tests.Additionally surface investigations with an acid elektolyte (0,1M HC1 + 0,4M NaCl) were performed. In this case the passivation effective nitrogen content increases markedly with rising molybdenum concentration of the steel. Obviously an interaction of Mo and N is connected with a strongly acid electrolyte.

高氮不锈钢光丝同轴激光增材组织与性能研究

为研究光丝同轴激光增材技术在制备高氮不锈钢块体材料中的应用潜力,采用直径1.2 mm、氮含量为0.71 wt.%的高氮钢丝材,通过光丝同轴激光增材技术进行多道多层增材试验。利用工业CT扫描、氮含量分析、组织形貌观察、物相分析及力学性能测试等方法,对增材块体的内部质量、氮含量、微观组织及力学性能进行了系统研究。结果表明,增材块体中存在少量未熔合缺陷,主要分布在底部,且一般出现于每一层的前两道附近,等效直径主要分布于200~300μm。内部存在大量细小孔洞状低密度缺陷,其体积占比为0.073%,其中约90%的等效直径区间为1.5~7.5μm。中部和顶部的氮含量都在0.66 wt.%以上,氮损失均低于7.5%;底部氮含量降至0.58 wt.%,氮损失为19%。物相分析表明,增材块体主要为奥氏体γ-Fe相,通过SEM和EDS可发现基体材料中存在少量α-Fe枝晶和Mn的氧化物。金相观察发现,增材块体主要由细小的柱状晶和等轴晶组成。增材块体底部力学性能较好,中部各向异性较小。其增材方向上的硬度分布为315~355 HV,且底部明显高于中部和顶部。块体中部增材方向抗拉强度875 MPa,屈服强度为679 MPa,延伸率为50%;行进方向抗拉强度为908 MPa,屈服强度为685 MPa,延伸率为34%。此外,块体底部行进方向的抗拉强度为997 MPa,屈服强度为770 MPa,延伸率为43%。本研究证实了光丝同轴激光增材技术制备高氮不锈钢块体材料的可行性,为高氮不锈钢增材制造技术的开发和应用提供了重要的理论依据和技术支持。

加压电渣重熔装备与工艺技术开发

加压电渣重熔是目前工业化制备高氮钢和高氮合金最为有效的生产路线,是当今电渣冶金领域的研究热点和前沿技术。介绍了加压电渣重熔成套设备、工艺技术发展和主要产品特点。对当前加压电渣炉装备中氮化合金加料系统和水-气动态平衡系统等核心部件进行综述;针对加压电渣重熔生产中的工艺难点,阐述了氮化合金增氮和气相增氮技术的机理和方法、新型高效发热精炼重熔渣系开发及元素精准控制等新工艺技术发展。近年来,随着国内新建的系列国产化中试规模加压电渣炉的应用和系列高氮钢产品的成功研制,我国在加压电渣重熔成套装备的自主研制和工艺技术开发上取得的较大突破,并逐步向国际先进水平迈进。同时,深入开展工业级加压电渣重熔成套装备的自主研制和工艺技术研发,保障我国航空、航天和军工等领域高端高品质特殊钢和特种合金等急需的关键材料制备,是我国发展现代电渣冶金技术的重要方向。

Research and Practice of Production Technology for High Performance Low Alloy Steels in WISCO

The product system of high strength low alloy steels (HSLA) produced by Wuhan Iron and Steel (Group) Corporation (WISCO) was presented.A series of high performance structural steels have been developed for important construction projects around the world in different areas,such as bridge,pressure vessel,pipe line,shipbuilding,architecture,machinery and railway wagons.In order to promote the development of large heat input welding steel,high grade thick pipeline steel and long span bridge steel,a lot of advanced production technologies have been achieved through intensive investigation,such as the control of high purity,high homogenization and free defects in steel slabs,the rules of high melting point particle formation and distribution in micro and nano scale during steel production,and the TMCP technology for ultra low carbon bainite steel for medium and heavy plates.WISCO will carry on research and application of economic and weather-resistant steels and promote the developing and producing technologies of HSLA steel.

钢丝热镀锌-10%铝-3%镁-稀土合金镀层工艺

介绍了高碳钢丝热镀锌-10%铝-3%镁-稀土合金镀层工艺。给出合金成分质量分数要求:铝9.0%~12.5%,镁3%~3.5%,稀土0.03%~0.30%。助镀剂中氯化物质量浓度5~15 g/L;硼化物质量浓度30~80 g/L,表面活性剂体积分数2 ml/L。助镀剂温度60~70℃,合金液温度465~470℃。氮气抹拭保证氮气温度250~255℃,压力不小于0.02 MPa,根据钢丝走线速度调节氮气流量和压力。试生产产品镀层和表面质量符合标准要求。

油页岩干馏废水中高氨氮回收处理技术

油页岩干馏废水中氨氮浓度均值在4000 mg/L,属于高氨氮废水,为了寻求适合油页岩干馏工艺特点的废水处理方案,分析了该废水水质特点,开展空气吹脱法和蒸汽汽提法对比工艺分析。结果表明:空气吹脱法为传统脱氮工艺,需补充大量碳源和碱度,污水处理厂运行成本极高,同时造成氨氮资源浪费;蒸汽汽提法结合干馏工艺特点,将废水中的氨氮提炼浓缩为15%以上浓氨水,再应用到干馏工艺的脱硫单元,实现污染物质在系统内部再利用。

热力学计算在高氮奥氏体不锈钢研究中的应用

采用Thermo-Calc软件,计算了碳、铬、锰、镍元素和压力因素对22Cr高氮奥氏体不锈钢氮溶解度、凝固过程中相转变以及析出相的影响,并对设计的新型高氮奥氏体不锈钢组织及析出相进行了研究。结果表明:铬元素主要增加液态钢的氮溶解度,增加0.1%(质量分数)的碳即能显著增大奥氏体不锈钢在高温凝固时的最小氮溶解度。锰元素既增加液态钢中的饱和氮溶解度,又增加凝固初期的最小氮溶解度。适当的锰含量能扩大并稳定奥氏体相区,避免"铁素体阱"的出现。少量的镍含量既增加奥氏体不锈钢高温凝固时的最小氮溶解度,缩小高温δ铁素体存在的温度区间,也能使钢在室温下有完全的奥氏体组织。加压冶炼能有效促进氮溶解度。新型高氮奥氏体不锈钢的析出相主要为Cr23C6,Cr2N。采用热力学计算工具可以对高氮奥氏体不锈钢的冶炼、组织控制、热处理和热加工提供科学的指导。

用机械合金化法制备含氮不锈钢粉末

采用机械合金化法(MA)分别在N_2气氛和氨水介质中利用高能球磨进行了含氮不锈钢粉末的制备，探讨了MA法对含氮不锈钢粉末性能的影响．结果表明，随球磨时间延长，粉末含氮量升高，接近高氮不锈钢氮含量，且颗粒不断细化，球磨10h的粉末粒度可达到1．878μm．

高氮钢的研究和发展

介绍了一种综合性能优异的新钢种─—高氮钢，详细讨论了钢中氮的作用，并综述了其熔制方法、应用前景和研究方向。

高氮奥氏体钢粉末的合成及其致密化工艺

采用机械合金化和高压气雾化两种工艺分别合成了近球形粉末,随后通过粉末注射成形技术制备了0Cr17Mn11Mo3N高氮奥氏体钢材料。用X射线衍射、扫描电镜、拉伸试验等手段研究了粉末和块状材料的结构及性能。结果表明:两种粉末球形度好,颗粒细小,装载量和烧结活性较高,都能够较好满足后续粉末注射成形工艺要求。机械合金化粉末最佳致密化条件是采用真空脱氧+氮气烧结方式,在0.1 MPa氮气压力下于1260℃烧结120 min,烧结体相对密度97.90%,氮含量1.02 mass%,经过1150℃×90 min固溶处理后屈服强度、抗拉强度、伸长率、断面收缩率、维氏硬度分别高达627 MPa、965 MPa、11.3%、16.7%、312HV;高压气雾化粉末最佳致密化条件为0.1 MPa氮气压力下1300℃烧结120 min,烧结体相对密度98.33%,氮含量0.78mass%,经固溶处理后屈服强度、抗拉强度、伸长率、断面收缩率、维氏硬度也分别达到580 MPa、885 MPa、26.0%、29.1%、222HV。由于氮在奥氏体中的强化作用,0Cr17Mn11Mo3N高氮奥氏体钢的强度、硬度等远高于传统注射成形316L奥氏体不锈钢。

高氮钢的基础研究及应用进展

介绍了高氮钢结构特点的最新研究,高氮钢平衡相图的进展及其在高氮钢成分设计方面的应用;概括了氮在钢液中的溶解度公式和高氮钢熔炼过程中的关键问题;分析了氮在奥氏体钢、铁素体钢和双相不锈钢中的作用,即氮在不牺牲强度的同时不仅提高了钢的韧性,且改善了钢的抗腐蚀性能;并列举了一些典型的高氮钢的用途。

氮含量对超细晶奥氏体不锈钢组织和性能的影响

通过机械合金化和放电等离子烧结技术制备超细晶奥氏体不锈钢,分析其组织与性能,研究了氮含量对该不锈钢组织和性能的影响。结果表明,随氮含量的增加,烧结试样中马氏体越来越少。氮具有稳定奥氏体的作用,当氮含量为1.2%时,试样基体转化为单一奥氏体相。制得试样晶粒均细小且均匀,尺寸都达到纳米级,氮含量为1.2%的试样,晶粒尺寸最小,只有100 nm。表明采用机械合金化方法结合等离子烧结技术成功制备了纳米级奥氏体不锈钢。氮的加入还能显著提高奥氏体不锈钢的硬度、耐磨性和抗拉强度。

超细晶高氮奥氏体不锈钢的制备及其性能

通过机械合金化和放电等离子烧结技术制备超细晶高氮奥氏体不锈钢，用X射线衍射仪和透射电镜、能谱仪对粉体及烧结试样进行了表征，对其进行了力学性能试验。结果表明：在球磨的过程中，粉末中的氮化物逐渐消失，烧结试样基体为奥氏体；烧结试样氮含量1．19％，其晶粒尺寸为50～100nm，氮元素在试样基体内分布均匀；制备的超细晶高氮奥氏体不锈钢硬度、抗拉强度均超过普通的304奥氏体不锈钢，耐腐蚀性能比304奥氏体不锈钢更加优良。

机械合金化制备超细晶高氮奥氏体不锈钢粉末的探讨

研究了不同球磨时间对粉末颗粒度、晶粒度和相组成的影响,以及真空退火、添加过程控制剂(PCA)对球磨后粉末的相组成和形貌的影响。结果表明,随着球磨时间的增加,粉末的颗粒度及晶粒度均不断减小。真空退火处理可以使球磨后的粉末奥氏体化程度大大提高,过程控制剂的加入,可以使球磨后的粉末颗粒均匀化,细小化。氮氧分析表明,在球磨过程中氮基本上没有流失。

铝、钛、钒和铌对中碳钢奥氏体晶粒度的影响

对6炉微合金化高氮L45钢进行了长时间(1800s)加热时和快速(50℃/s)短时间(5s)加热时奥氏体晶粒长大试验。测定了奥氏体晶粒平均截线长度。在萃取复型透射电镜照片上利用图象分析仪测定了1、3和6钢样中微细析出相的尺寸分布。利用透射电镜能谱仪分析了微细析出相的化学成分。还探讨了铝及微合金化元素钛、钒和铌与加热温度对高氮中碳钢奥氏体晶粒度的影响机制。

先进钢铁材料技术的进展

钢铁材料是不断发展的先进材料 ,它依然是本世纪的主要结构材料。先进钢铁材料具有环境友好、性能优良、资源节约、成本低廉的特征。从钢铁材料理论进展出发 ,结合市场的需求 ,论述了微合金化钢、超细晶粒钢、氮合金化不锈钢、高质量特殊钢、钢材组织性能预报和材料信息化技术等重要的先进钢铁材料技术进展。