Influence of Finish Rolling Temperature on Microstructure and Mechanical Properties of a 19Cr1.5Mo0.5W Ferritic Stainless Steel

A 444-type heat-resistant ferritic stainless steel containing 0.05 wt% Ce(rare earth element) and 2 wt%(Mo+W) was adopted as an experimental material to study the effect of finish rolling temperature on microstructure and texture evolution as well as on mechanical properties and formability.The rolling processes contain hot rolling at two different finish rolling temperatures(860℃ and 770℃) and annealing,cold rolling and subsequent annealing.It was found that the microstructures after hot rolling and annealing could be refined by lowering finish rolling temperature.The resultant microstructures after cold rolling and annealing were hereditarily refined.Lowering finish rolling temperature can weaken α-fiber texture in hotrolled or cold-rolled ferritic stainless steel strip,while γ-fiber texture in the final product was homogeneously strengthened.Additionally,enhanced mechanical property and formability in terms of strength and average plastic strain ratio could be obtained via decreasing finish rolling temperature.     

终轧温度对铁素体不锈钢织构和成形性的影响

在实验室研究了终轧温度对铁素体不锈钢显微组织、织构和成形性的影响。结果显示,随着终轧温度的降低(从940℃到800℃),冷轧退火板的组织细化,γ再结晶织构强度增加,平均塑性应变比r值增加,平面各向异性Δr值降低。终轧温度的降低显著改善了薄板的成形性能。     

Improvement of Surface Ridging Resistance of an Ultra-purified Ferritic Stainless Steel by Optimizing Hot Rolling Condition

The effects of the finisher entry temperatures(FETs) on the surface ridging behavior for an ultra-purified21%Cr ferritic stainless steel have been investigated. The results indicate that decreasing the FET facilitates the formation of in-grain shear bands in the hot rolled slab. The in-grain shear bands supplied recrystallization nucleation sites in grains during subsequent annealing through coalescence of subgrains, which is beneficial to refine the microstructures and intensify the {111}//ND textures. This effect will evolve to the final cold rolled and annealed sheet. The micro-texture analysis indicates that the formation of grain colony in the final sheet is weakened by decreasing the FET. Then, the surface ridging resistance of FSS is enhanced due to the optimizing of micro-texture distribution.     

Effect of Cerium on High-Temperature Oxidation Resistance of 00Cr17NbTi Ferritic Stainless Steel

The influence of cerium addition on the isothermal oxidation behavior of 00Cr17 NbTi ferritic stainless steel was studied at temperature up to 1,000 °C for 100 h in air. The results show that cerium additions can reduce the grain size of this ferritic stainless steel, improve the diffusion of chromium and decrease the critical concentration of chromium to form protective Cr2O3 layer. With the increasing of cerium addition, the oxide particles become smaller and this can increase the rupture strength and spalling resistance of oxide layers. The transport mechanism through the oxide layer is varied from metal transport outward from steel to principally oxygen transport inward with the increase of cerium content,which leads to the lower oxidation rate and the better scale adherence of 00Cr17 NbTi ferritic stainless steel.     

445铁素体不锈钢内胆水箱的加工性能和耐蚀性

将445铁素体不锈钢的主要化学成分、力学性能、成型性能和焊接性能等基本性能与304奥氏体不锈钢进行对比,结果表明,445不锈钢具有较好的机加工性能。采用盐雾试验及10%的NaCl溶液加速腐蚀试验等方法,对比445水箱、304水箱及两者混合搭配的内胆水箱的太阳能热水器的耐腐蚀性能。结果表明,445不锈钢耐腐蚀性稍逊于304不锈钢,在80～120℃时,445与304不锈钢均发生蒸汽腐蚀、水线腐蚀,且445不锈钢出现较为严重的点蚀现象。     

409L铁素体不锈钢的高温拉伸行为和形变组织研究

利用金相显微镜、X射线衍射仪、EPMA、拉伸试验机研究铸态409L铁素体不锈钢在高温下的力学性能和变形组织特征.结果表明,随着温度的升高,409L不锈钢的强度在300～800℃迅速下降,800～1150℃下降变缓;伸长率在1000℃时达到最大,为131.44%;断面收缩率在800℃时最大,为97.71%.409L不锈钢的再结晶温度在950℃左右.通过XRD鉴定表明,409L不锈钢中主要组成物相为铁素体、Fe-Cr系合金和游离Cr元素.EPMA结果显示,409L不锈钢中含有的黑色点状第二相颗粒主要是Ti(C、N),此种粒子可提高钢铁材料的综合性能.     

铁素体不锈钢表面皱折及其评价方法

皱折缺陷是中铬铁素体不锈钢发生较大塑性变形后容易出现的表面缺陷。这种缺陷往往破坏了不锈钢制品的外观,因此需要对制品进行研磨和抛光以消除皱折的影响。然而,额外的加工工序大幅增加了企业的生产成本,同时不可避免地造成了环境污染。那么,正确认识和评价铁素体不锈钢的表面皱折缺陷就显得非常重要。本文主要讨论界定铁素体不锈钢表面皱折缺陷,并简要介绍表面皱折缺陷的形成原因,进而厘清表面皱折缺陷的评价参数,最后针对已有测试方法存在的问题提出可供参考的解决办法。     

Effect of Mo on High-Temperature Fatigue Behavior of 15CrNbTi Ferritic Stainless Steel

In order to understand the effect of Mo element on the high-temperature fatigue behavior of 15 CrNbTi ferritic stainless steel, the stress-controlled fatigue tests have been performed for both 15 CrNbTi and 15Cr0.5MoNbTi ferritic stainless steels at 800 °C in laboratory air. The fatigue test results indicate that the fatigue resistance of 15Cr0.5MoNbTi steel is manifestly higher than that of 15 CrNbTi steel at the maximum stress below 57 MPa; the 15Cr0.5MoNbTi steel possesses a fatigue limit of 35 MPa, which is higher than that of 15 CrNbTi steel. The TEM observations reveal that the Mo element can suppress the formation of coarsened Fe3Nb3 C precipitates and result in the fatigue resistance enhancement.The dislocation networks formed during the cyclic load favor to improve the fatigue resistance of 15Cr0.5MoNbTi steel at800 °C.     

Nb、Ti对铁素体不锈钢铸态及热轧态组织、织构的影响

研究了不同Nb、Ti添加情况下铁素体不锈钢的铸坯组织特征以及热轧后板材的组织和织构.研究结果表明:Nb的添加可以明显细化铸坯组织,而Nb、Ti双稳定元素的添加强烈地促进了铸坯组织晶粒的等轴化和晶粒细化.Nb、Ti元素的加入不仅可以细化铸坯组织,同时也可以细化热轧后的板材组织,单独添加的Nb、Ti元素均可以推迟板材的再结晶过程,Ti的作用更为明显,而Nb、Ti的同时加入可明显推迟板材的再结晶过程.     

Effect of Hot Band Annealing on Forming Limit Diagrams of Ultra-Pure Ferritic Stainless Steel

In order to better understand the texture evolution, coincidence site lattice (CSL) and forming limit diagrams (FLDs) of ferritic stainless steels with and without hot band annealing, the texture evolution and CSL of ferritic stainless steels with 15% Cr content were studied by using x-ray diffraction and electron back-scattered diffraction technique. The strain hardening exponent n value, the strength coefficient K value, and Plastic strain ratio r value are the key parameters for the FLD. It was found out that the FLD_o of plane strain condition and the stretchability were mainly influenced by their n value and K value, respectively. The higher n value and K value, better was the stretchability of investigated steels. The intensity of the γ-fiber dominated by {111} 〈112〉 was improved significantly in the cold rolled and annealed sheets because of a hot band annealing treatment and the sharp increase of Σ13b CSL boundaries. The increase of the formability is attributed to the significantly increase of the r value.     

Influence of Aging Time on Microstructure and Corrosion Behavior of a Cu-Bearing 17Cr-1Si-0.5Nb Ferritic Heat-Resistant Stainless Steel

17Cr-1Si-0.5Nb-1.2Cu ferritic heat-resistant stainless steel was aged at 750 °C from 10 min to 30 h to simulate time aging and study the microstructural evolution and its effect on corrosion behavior by using optical microscopy, scanning electron microscopy, transmission electron microscopy, potentiodynamic polarization, electrochemical impedance spectroscopy, and the Mott-Schottky approach. Four types of precipitates were discovered, including ε-Cu, NbC, Fe₃Nb₃C, and Fe₂Nb-type Laves phase. The nano-sized ε-Cu phase forms first, and its fraction follows the parabolic law change and is the largest. Compared to NbC and Fe₃Nb₃C particles, the coarsening of the Laves phase is the most pronounced. The aging process is divided into three parts: early-aged (0-5 h), peak-aged (5 h), and over-aged (5-30 h). However, the corrosion resistance is reduced in the early-aged stage of 0-2 h. Further extending the aging time to 30 h, the corrosion resistance is gradually improved. This change may be related to the competitive relationship between the beneficial effects of the Cu-rich phase and the harmful effects of Nb-containing particles. The dissolved Cu on the surface becomes more effective for the suppression of the anodic dissolution by the formation of ionic compounds of chlorine, thereby reducing the deterioration of corrosion resistance caused by Nb-rich precipitation.     

304L不锈钢高温变形组织的演化

采用Gleeble-1500D热/力学模拟试验机对304 L不锈钢铸态及锻态试样进行了热压缩试验研究,工艺参数为：变形温度950℃～1 150℃、变形量0.7,变形速率0.1s-1。结果表明：铸态的峰值应力低于锻态的峰值应力,铸态组织的动态再结晶明显迟于锻态组织;铸态及锻态304L不锈钢流变应力随着温度的升高而降低;随着变形温度的升高,动态再结晶百分数增加,再结晶组织增多并趋于完全。     

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 本文通过金相和EBSD等技术,观察了不同热轧终轧温度对00Cr21Mo1铁素体不锈钢热轧态、热轧退火态、冷轧退火态织构的变化的影响情况,并分析讨论了较高终轧温度下铁素体不锈钢00Cr21Mo1塑性应变比（Rm）较低的原因。结果表明,较低的终轧温度下,00Cr21Mo1热轧态组织形变带宽度较小,受轧辊切应变而形成的{110}<001>、{110}<112>、{4 4 11}<11 11 8>织构组分强度较小,且均匀、分散,最终冷轧退火态以{111}面织构为主,塑性应变比较高。     

430铁素体不锈钢铸件脆性分析

对430铸造铁素体不锈钢的脆性进行了分析,采用金相显微组织分析、力学性能测试、冲击断口宏观和SEM等技术手段探讨了430不锈钢发生脆化的原因.结果表明:430铸造铁素体不锈钢的脆性主要是由铸造过程中马氏体的生成引起的,通过700℃热处理水冷可以显著提高430铸造铁索体不锈钢的韧性,并同时改善其抗拉强度和塑性.     

退火工艺对29Cr-4Mo超级铁素体不锈钢微观组织的影响

以冷轧态29Cr-4Mo超级铁素体不锈钢无缝钢管为研究对象,研究了不同退火工艺对29Cr-4Mo超级铁素体不锈钢无缝钢管冷轧后微观组织的影响。结果表明,29Cr-4Mo超级铁素体不锈钢夹杂物主要成分为Cr2O3·MnO·Al2O3;在900 ℃下保温30 min,晶界三角连接处和夹杂物附近率先生成了少量σ相,σ相析出的平均面积分数随时间的延长而增加,随温度的升高而减少;当温度升高至1000 ℃,保温50 min未见有σ相析出,在900~1050 ℃整个温度区间内未见有χ相析出;建立了Sellars模型下铁素体再结晶晶粒长大经验公式,通过对比分析计算值与实验值,结果显示该公式能准确预测整个退火过程中的平均晶粒尺寸大小。     

表面双尺度结构对304不锈钢的耐磨性和成形性的影响

首先利用高能喷丸工艺对304不锈钢进行表面纳米化处理,再通过退火处理在表面获得双尺度结构,从而实现耐磨性-成形性间的平衡。通过金相和X射线衍射分析来表征细化层的微观结构,通过横截面的硬度测量和耐磨性实验来表征不锈钢的耐磨性,利用杯突实验和成形极限（FLD）实验来表征不锈钢的成形性。结果表明,0.3 MPa-6 min表面喷丸可以获得平均晶粒尺寸约为36 nm,平均硬度为353 HV_0.2,形变诱发马氏体质量分数50.2%,厚度约为125 μm的细化层。表面喷丸纳米化不锈钢的耐磨性显著提高,但成形性明显下降。表面喷丸纳米化+650 ℃退火30 min可在不锈钢表面获得双尺度结构的细化层,其中粗晶部分的平均晶粒尺寸约为1~2 μm,体积比约66%;细晶部分的平均晶粒尺寸约为58 nm,体积比为34%。这种双尺度结构的表面细化层兼具高耐磨性和高成形性的特性。     

超纯铁素体不锈钢研制和生产

超纯铁素体不锈钢因碳、氮含量极低,较普通铁素体不锈钢以及马氏体不锈钢拥有更优越的耐腐蚀性、韧性及焊接性。介绍了超纯铁素体不锈钢的应用范围和发展趋势,阐述了超纯铁素体不锈钢铸件的生产工艺,并对其进行了市场预测和经济效益分析。     

不锈钢退火酸洗线引带断裂原因分析及防控措施

针对不锈钢退火酸洗线发生引带断裂事故，对断裂试样进行宏观检测、化学成分检测、金相分析和扫描电镜分析，发现J4侧因奥氏体晶界析出的铁素体相和出现沿晶裂纹是断带的根本原因，并提出了相应的防控措施。     

316L不锈钢梯度结构及其在退火中的演变

对316L不锈钢进行表面机械研磨处理（SMAT）,获得表面为纳米晶、晶粒尺寸沿厚度方向逐渐增大的梯度组织。对SMAT样品进行不同温度的真空退火,研究组织变化。结果表明：当退火温度低于0．5L（L为熔点）时,316L不锈钢经SMAT后形成的梯度组织未发生明显的变化。随着退火温度的继续增加,梯度组织发生回复和晶粒长大,但晶粒长大的速度较小。整个退火过程中,内应力和微观应变的释放在SMAT样品的深度方向诱发了机械孪生,并在纳米结构表层中引起马氏体相变。     

不锈钢／铝合金／不锈钢多层复合板的成形性能

通过拉伸实验测试了不锈钢／铝合金／不锈钢三层、五层复合板的成形性能影响参数：厚度异性系数r、应变强化指数n和屈强比σ0．2／σb，结果表明轧制复合变形量、扩散退火温度对不锈钢／铝合金／不锈钢多层复合材料的成形性能参数有较明显的影响。