Effect of stabilizing elements Nb and Ti on the microstructure and properties of low carbon ferritic stainless steel

The effect of stabilizing elements, such as Nb and Ti, on the microstructure and properties of low carbon ferritic stainless steel （FSS） has been investigated. The results of the Thermo-calc simulation have shown that the interstitial elements, such as C and N, may be completely stabilized by the addition of Nb and Ti. With the increase of Nb and Ti contents ,the α ＋ γ two phases gradually transfer to a single α-phase under a high temperature condition ,and the content of the carbide M23 C6 gradually decreases. The microstructure has indicated that the combined addition of Nb and Ti can promote the recrystallization of the band structure and form more uniform equiaxed grains. Also, with the increase of Nb and Ti contents,the elongation, the r-value and the corrosion resistance of cold-rolled and annealed sheets are improved prominently. In comparison with the effect of Ti ,the addition of Nb is more beneficial to the increase of r-value and the corrosion resistance.

Prevention of burn-on defect on surface of hydroturbine blade casting of ultra-low-carbon refining stainless steel

The burn-on sand is common surface defect encountered in CO2 -cured silicate-bonded sand casting of hydroturbine blade of ultra-low-carbon martensitic stainless steel,its feature,causes and prevention measures are presented in this paper.Experiments showed that the burn-on defect is caused by oxidization of chromium in the molten steel at high temperature and can be effectively eliminated by using chromium-corundum coating.

Development and application of fluorine-free mold powder for low carbon steel

Fluorine in mold powder is known as harmful to human health and the environment. Being the advocate of green production, Baosteel developed an environmentally friendly mold powder without fluorine. The main problem of fluorine-free flux film is small heat resistance and thus the heat transfer intensity of the mold is too large, which to some extent hinders the increase of the casting speed. With the heat flow simulation equipment, controlling precipitation of crystal in flux and solidification temperature properly, fluorine-free mold powder for low carbon steel,which substitutes F with B203 ,was successfully developed and applied in industrial production. The production results show that, by using boronic fluorine-free mold powder,the boron increment in molten steel is less than 1.3ppm for conventional aluminium killed low carbon steel.

Influence of cold deformation on microstructure,mechanical properties,and corrosion resistance of high-sulfur free-cutting 316LS stainless steel

In this study,the influence of plastic deformation produced by cold rolling at reduction ratios ranging from 10% to 80% on the microstructure,mechanical properties,and pitting corrosion behavior of high-sulfur freecutting 316 LS austenitic stainless steel was investigated. The results indicate that slipping is the predominant effect and that sulfide inclusions extend along the rolling direction during the cold deformation of 316 LS. The strong austenite stability of 316 LS results in the formation of only a small quantity of deformation-induced martensite. The experimental results reveal that the strength,hardness,and yield ratio increased with increases in the reduction ratio,mainly due to work hardening,whereas the elongation decreased drastically,due to the combined effect of the work hardening and brittleness caused by the numerous sulfide inclusions. Electrochemically active sites on the surface of316 LS increased with an increased reduction ratio,which caused an increased current fluctuation in the passive zone. This also caused the breakdown potential（ E_b） near the pitting zone to exhibit a gradual increase in the zigzag current shift to the left on the polarization curves. The E_b of 316 LS decreased with increases in the reduction ratio,mainly due to the extended sulfide inclusions,the increased dislocation density,and the deformation-induced martensite content.

Advanced manufacturing technologies of large martensitic stainless steel castings with ultra low carbon and high cleanliness

The key manufacturing technologies associated with composition, microstructure, mechanical properties, casting quality and key process control for large martensitic stainless steel castings are involved in this paper. The achievements fully satisfeid the technical requirements of the large 700 MW stainless steel hydraulic turbine runner for the Three Gorges Hydropower Station, and become the major technical support for the design and manufacture of the largest 700 MW hydraulic turbine generator unit in the world developed through our own efforts. The characteristics of a new high yield to tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel with ultra low carbon and high cleanliness are also described. Over the next ten years, the large martensitic stainless steel castings and advanced manufacturing technologies will see a huge demand in clean energy industry such as nuclear power, hydraulic power at home and abroad. Therefore, the new high yield o tensile strength (R p0.2/R m ) ratio and high obdurability martensitic stainless steel materials, the fast and flexible manufacturing technologies of large size castings, and new environment friendly sustainable process will face new challenges and opportunities.

Effect of Mn on the microstructure and property of 13Cr stainless steel

Mn is a weak element for austenite formation and its effect on martensitic stainless steel is seldom researched. The microstructure and property of 13Cr martensitic stainless steel with varied Mn content and low carbon content were studied. The research demonstrates that Mn enlarges the austenitic zone at a high temperature and increases the strength and hardness of martensitic stainless steel. Following the addition of Mn,the corrosion resistance property of low carbon 13Cr stainless steel only decreases slightly. The strength and hardness of low carbon 13Cr stainless steel containing Mn is similar to that of high carbon 13Cr stainless steel.

温度和应变幅对亚稳奥氏体不锈钢S321低周疲劳行为的影响

在室温和650℃的环境下对S321、S321H不锈钢进行了0.5%、0.7%、0.9%应变幅下的低周疲劳试验,并在室温下对S321和S321H开展了多个寿命点的疲劳加载历史试验,结合X射线衍射定量分析测算形变诱发马氏体的含量。结果表明:形变诱发马氏体的生成会导致奥氏体钢持续循环硬化,室温下合金在初次硬化后继续二次硬化,而在650℃下没有形变诱发马氏体生成,合金在初次硬化后进入循环稳定阶段。循环过程中,碳含量越低,形变诱发马氏体含量越多,合金的循环硬化程度更高。两种温度下,两种材料的疲劳寿命在低应变幅下都相差不大,应变幅越大,两种材料的疲劳寿命相差越大,因此,可以考虑服役条件为低应变幅时使用S321不锈钢代替S321H不锈钢。

马氏体板条细化机制及其对马氏体钢力学性能的影响

以00Cr11Ni4Mo低碳马氏体不锈钢为研究对象,研究一次正火、循环正火、正火+回火处理对其组织和性能的影响,分析马氏体板条细化对低碳马氏体钢力学性能的影响,并阐明马氏体板条的细化机制。结果表明,采用一次正火温度为900℃的热处理工艺得到的屈服强度、极限抗拉强度、延伸率分别为961 MPa、1093 MPa、20.7%,综合力学性能最佳;随着正火温度的升高,马氏体板条粗化,其极限抗拉强度和屈服强度下降,塑性呈先上升后下降的趋势。循环正火热处理并没有达到提高材料强度的效果,对塑性的改善也有限。正火+回火热处理工艺细化了马氏体板条,但并未提高材料的强度。通过马氏体板条细化来提高材料强度具有一定的局限性,需要综合考虑更多影响材料强塑性的因素。

不同冶炼工艺对J409L低碳氮不锈钢纯净度的影响

通过气体分析仪、X荧光法、金相显微镜、扫描电镜及能谱仪对比分析了一步法(AOD+LF)和二步法(AOD+VOD+LF)工艺冶炼J409L低碳氮不锈钢各工序全氧含量、炉渣组分、夹杂物的控制情况。结果表明:一步法工艺冶炼的J409L在LF精炼过程、连铸中包试样的T[O]均较高;Al脱氧能力明显较强,二步法VOD工序具有更良好的脱氧效果;一步法冶炼炉渣组分的SiO_(2)含量偏高,Ti收得率偏低;不同冶炼工艺生产J409L,连铸中包钢液的夹杂物类型一致,均为Ti氧化物包裹Al-Si氧化物的复合夹杂物。

华龙一号主管道电渣锭成分偏析控制

华龙一号核电主管道采用X2CrNiMo 18.12(控氮)超低碳奥氏体不锈钢制造,该钢种碳含量低,铬、镍含量高且范围窄,尤其是N含量控制难度大,对质量要求苛刻;同时主管道锭型达到百吨级,易产生成分偏析,通过对大型主管道电渣锭成分偏析的分析与研究,阐述了大型单相电渣锭成分均匀性的控制方法,并取得了良好的效果。

Microstructure and Mechanical Properties of a Dissimilar Friction Stir Weld between Austenitic Stainless Steel and Low Carbon Steel

Dissimilar fusion welding of austenitic stainless steels to carbon steels has some metallurgical and technical problems. It was suggested that the solid-state nature of friction stir welding （FSW） can overcome these problems and produce a sound weld with reliable mechanical properties. In this study, plates of 304 stainless steel and st37 steel were welded together by FSW at tool rotational speed of 600 r/rain and welding speed of 50 ram/rain. In the stir zone （SZ） of 304 stainless steel, the results showed a refined grain structure with some features of metadynamic recrystallization. In the SZ of st37 steel, the hot deformation of material in the austenite region produced small austenite grains. These grains transformed to fine ferrite and pearlite by cooling the material after FSW. The production of fine grains increased the hardness and tensile strength in the SZ of both sides with respect to their base metals （BMs）.

Effect of Free-cutting Additives on Machining Characteristics of Austenitic Stainless Steels

The machinability tests were conducted by using a YD-21 dynamometer on a CA6161A lathe.The experiments were conducted to determine the effect of free-cutting additives on machining characteristics of austenitic stainless steels.The conventional austenitic stainless steel 1Cr18Ni9Ti（steel A） and the free cutting austenitic stainless steel（steel B） were prepared.The results have shown that machinable inclusions were composed of MnS and CuO,and they might be also Ti4C2S2.The presence of Bi in the inclusion was detected by the atom map and electro-probe microanalysis（EPMA）,which might be one of the most important factors to improve the machinability of austenitic stainless steels.The cutting forces for steel B were lower than those of steel A at various cutting speeds;the abrasion depth of the flank of the tool for steel B was less than that of the steel A under the same cutting conditions.The machinability of austenitic stainless steel was visibly improved by adding free-cutting additives,such as S,Cu and Bi.Ultimate tensile,yield strength,and total elongation values of the free cutting austenitic stainless steel were improved due to the addition of these free-cutting additives.

Analysis on composition and inclusions of ballpoint pen tip steel

Ballpoint pen tip steel, a super free-cutting stainless steel, exhibits excellent corrosion resistance and good machining properties. In this study, inductively coupled plasma spectroscopy, metallographic microscopy, and scanning electron microscopy were used to determine the elemental contents in five ballpoint pen tips and their components, morphologies, and inclusion distributions. The results showed that the steels were all S–Pb–Te super free-cutting ferritic stainless steel. The free-cutting phases in the steels were mainly Mn S, Pb, and small amounts of Pb Te. Mn S inclusions were in the form of chain distributions, and the aspect ratio of each size inclusion in the chain was small. The stress concentration effect could substantially reduce the cutting force when the material was machined. Some of the Pb was distributed evenly in the steel matrix as fine particles（1–2 μm）, and the rest of the Pb was distributed at the middle or at both ends of the Mn S inclusions. The Pb plays a role in lubrication and melting embrittlement, which substantially increases the cutting performance. Pb Te was also usually distributed in the middle and at both ends of the Mn S inclusions, and Te could convert the sulfides into spindles, thereby improving the cutting performance of the steel.

Current Situation and Development of Refractories for Clean Steel Production

The low cost and high efficient clean steels metallur- gy has been focused much attention in China. Among the factors affecting the cleanliness and consequent quali- ty of steel products, refractories are one of the key fac- tors. Meanwhile the restriction of resource, energy and environment is getting stronger, thus the improvement of refractories becontes much more important. In this paper, refractories selection principle Jbr clean steel production according to their thermodynamic features was ex- plained; refractories for tundLsh and flow control in con- tinuous casting, which play important roles in prohibi- ring secondary contamination of molten steel, were intro- duced. Moreover, new development of low-carbon and carbon-free refractory materials was also described.

不同补焊次数下ZG06Cr13Ni4Mo的组织演变规律

为了明确不同补焊次数下ZG06Gr13Ni4Mo马氏体不锈钢补焊区显微组织的演变规律,采用钨极气体保护电弧焊(Gas tungsten arc wel-ding,GTAW焊)对40 mm厚ZG06Gr13Ni4Mo板进行一次、二次补焊,每次补焊完成后进行600℃下2 h的回火。分别采用OM、SEM、EBSD和TEM检测母材和不同补焊次数下补焊区的显微组织变化,研究补焊区域的组织演变规律。结果表明:补焊区的物相主要由马氏体和少量逆变奥氏体组成,逆变奥氏体以细条状分布在马氏体边界及基体内。补焊区中逆变奥氏体的含量随补焊次数的增加而增多,而且焊缝区逆变奥氏体的含量大于热影响区。此外,补焊区的晶粒有细化的趋势,相对于母材,一次及二次焊缝区的晶粒尺寸细化了45.2%和61.9%,焊缝区的晶粒尺寸比热影响区分别细化了40.8%和48.3%,逆变奥氏体的大小约为马氏体的50.0%。补焊区域织构的取向由铸件的〈101〉转变为各向异性,小角度晶界减少,大角度晶界增多。随补焊次数增加,补焊接头的硬度、抗拉强度逐渐下降,塑性得到改善。

原始铸态组织对Cr13Ni4Mo钢逆变奥氏体形成的影响

采用扫描电子显微镜、X射线衍射分析仪、电子背散射衍射研究了原始铸态组织对Cr13Ni4Mo马氏体不锈钢回火过程中逆变奥氏体形成的影响。浇注厚度为40mm、60mm、80mm的阶梯形铸件,以获得凝固速度不同的原始等轴晶铸态组织,经正火+二次回火处理后,随铸件厚度的减小,组织中逆变奥氏体的含量增加,Cr13Ni4Mo钢的抗拉强度和伸长率均提高。采用定向凝固方法,改变下拉速度为1μm/s、5μm/s和50μm/s,以获得原始柱状晶铸态组织,结果发现随着下拉速度的提高,定向生长的柱状晶细化,逆变奥氏体的含量增多,Cr13Ni4Mo钢的抗拉强度和强塑积增大。Cr13Ni4Mo钢综合力学性能的提高源于细晶强化和逆变奥氏体TRIP效应的双重效果。

445J2超纯铁素体不锈钢和316L超低碳奥氏体不锈钢在溴化锂溶液的点蚀分析

445J2铁素体不锈钢由于高的导热率、低的热膨胀系数以及良好的耐蚀性能使得其作为溴冷机中一些部件的良好候选材料,本文采用电化学测试方法对比研究了445J2超纯铁素体不锈钢(/%:0.01C,22.5Cr,1.9Mo,0.27Nb,0.20Ti,0.09Al,0.36Cu,0.015P,0.001S,0.015N)和316L奥氏体不锈钢(/%:0.002C,16.8Cr,10.19Ni,2.02Mo,0.025P,0.0008S)在20~60℃0.1~1M的溴化锂溶液中的点蚀行为,并采用扫描电镜(SEM)和能谱分析仪(EDS)对电化学结果进行表征。结果表明,随着LiBr温度和浓度的升高,两种钢腐蚀电流密度增大,点蚀电位降低,耐点蚀性变差;氧化物和硫化物夹杂会引起两种钢的点蚀;高含量的Cr以及Mo、Ti、Nb、Al等合金元素使445J2钢具有优异的耐点蚀性能。

低碳高硫易切削钢基体显微组织对切削性能的影响

研究180 mm×240 mm方坯轧制后不同显微组织对低碳高硫易切削钢切削性能的影响,控制合适的显微组织以提高低碳高硫易切削钢的切削性能。低碳高硫易切削钢显微组织由铁素体、珠光体和硫化物组成,但铁素体和珠光体所占比例直接影响材料的切削性能,调整碳含量是改变两种组织比例的有效手段。试验通过调整1215钢不同的碳含量,并对碳含量不同的材料分别进行切削试验,分析显微组织差别对切削性能的影响。结果表明:钢中珠光体体积分数15%~20%时,切削性能最佳,此时钢中C质量分数为0.12%。

新型铁路信号继电器重锤片的研制

重锤片是铁路信号继电器磁路系统衔铁组件中的一个零件,在继电器的机械负载和磁路平衡中起着配重的作用,用于保证继电器衔铁可靠落下。通过对比原重锤片的结构尺寸及材料,结合新工艺技术对重锤片的结构尺寸及材料重新研制,主要从重锤片研制的设计输入、理论计算、实物验证等内容,并对重锤片研制前后的实物进行对比分析。新型重锤片的成功研制将提高重锤片零件的防腐性能及应用环境,彻底取消电镀工序对环境质量的影响,同时提高零件的生产效率,缩短产品的生产周期。

低加热速率下ZG06Cr13Ni4Mo低碳马氏体不锈钢回火过程的相变研究

利用热膨胀仪、透射电子显微镜(TEM),X射线能谱仪(EDX),X射线衍射仪(XRD)等对ZG06Cr13Ni4Mo在0.05℃/s低加热速率下回火过程中逆变奥氏体的产生机理进行了研究.结果表明:低加热速率下ZG06Cr13Ni4Mo在A_s—A_f区间回火产生的逆变奥氏体中富集了奥氏体化元素Ni,且不含高密度位错,马氏体向逆变奥氏体的转变是扩散型相变,高于600℃回火得到的逆变奥氏体不稳定,在随后冷却过程中部分发生马氏体转变,一次回火在620℃时能得到最大量的逆变奥氏体;620—660℃一次回火生成的逆变奥氏体在冷却过程中产生大量弥散分布的马氏体,增加了600℃二次回火时逆变奥氏体的形核位置,使二次回火后逆变奥氏体含量显著增加。