铸态超级双相不锈钢S32750热加工性能

 为研究热变形参数对铸态超级双相不锈钢S32750热变形行为和显微组织的影响,运用Gleeble-3800热模拟试验机对S32750进行不同温度和应变速率下的高温拉伸和压缩试验。结果表明,S32750在1000~1200℃范围内具有较好的热塑性。在变形温度较低、应变速率较低时,流变曲线表现出不同于单相不锈钢的“类屈服平台”特征;当应变速率较高或变形温度较高、应变速率较低时,流变曲线为典型的动态再结晶特征。微观组织演变显示,铁素体和奥氏体两相都发生动态再结晶,且铁素体的再结晶先于奥氏体。降低应变速率,提高变形温度,可促进动态再结晶发生。基于热变形动力学模型建立了本构方程,表观应力指数为3.99,热变形激活能为393.75kJ/mol。S32750的高温软化机制与Zener-Hollomon(Z)参数有关,随Z参数增加,热变形峰值应力增加。     

铸态超级双相不锈钢S32750热变形行为及组织演变

通过Gleeble-3800热压缩实验研究了铸态超级双相不锈钢S32750(/%:0. 017C,0.53Si,0.93Mn,0.023P,0.001S,25.58Cr,7.00Ni,4.03Mo,0.28N)在变形温度为950～1200℃、应变速率为0.1～25/s、真应变为1条件下的热变形行为与组织演变规律。结果表明,超级双相不锈钢S32750热变形行为受变形温度和应变速率的影响明显。在950～1050℃、0.1/s变形时,流变曲线表现出"类屈服平台"特征;当变形温度为1100～1200或应变速率为10/s、25/s时,流变曲线为典型的动态再结晶特征。对其微观组织进行观察发现,铁素体在各变形条件下均发生动态再结晶;奥氏体在950℃和1200℃时基本不受应变速率影响,前者发生动态回复,后者发生动态再结晶。而在1050℃时,受应变速率影响较大:小应变速率下(0.1/s)下发生动态回复,大应变速率下(10/s)发生动态再结晶。     

固溶处理对S32707特超级双相不锈钢析出相、组织及性能影响

通过Thermo-Calc热力学计算、OM和FE-SEM观察、力学性能和腐蚀性能试验对不同固溶温度下的特超级双相不锈钢进行分析和研究。结果表明:σ相和非平衡氮化物是固溶水冷组织中的主要析出相,当固溶温度低于1050 ℃时,σ相优先沿双相界面析出,显著降低双相不锈钢的冲击韧性;当固溶温度高于1100 ℃,非平衡氮化物开始在铁素体晶粒内部析出,且随着固溶温度的升高,非平衡氮化物析出数量增加。这是由于固溶水冷过程中氮在铁素体中的溶解度快速降低,过饱和的氮来不及扩散到相邻奥氏体中,只能以氮化物的形式析出。随固溶温度升高,铁素体含量增加,奥氏体含量降低,实验钢的强度增加,冲击韧性降低。在1080～1120 ℃之间固溶时,双相比例接近1∶1,S32707特超级双相不锈钢具有优良的综合力学性能和耐晶间腐蚀性能。      

双相不锈钢热老化前后拉伸变形行为的电子背散射衍射表征

通过电子背散射衍射实验分析方法,研究变形量和热老化因素对双相不锈钢的拉伸性能、相边界、局部应变分布、重位点阵特殊晶界和取向分布的影响.研究结果表明:热老化后,双相不锈钢的强度提高,韧性降低;在大变形条件下铁素体晶粒内小角度晶界的数量和密度略有增加;热老化材料的铁素体的塑性变形和局部应变能力下降,大变形破坏初始奥氏体和铁素体以及Σ3孪晶边界的分布.      

冷轧退火温度对301L织构和晶界特征的影响

 利用电子背散射衍射技术,研究了冷轧后亚稳态奥氏体不锈钢301L的退火织构和晶界特征,分析了不同冷轧退火温度对织构和晶界特征的影响。结果表明,冷轧退火后奥氏体不锈钢301L的织构主要由Copper{112}<111>,Brass{110}<112>,Goss{110}<001>和S{123}<634>组成,并且随着退火温度的升高,织构强度逐渐减弱,重位点阵晶界Σ3晶界含量明显增加,其他重位点阵晶界含量没有明显变化。     

时效对超级双相不锈钢析出相演变的影响

通过在850℃时效处理研究了S32750超级双相不锈钢析出相的析出行为。采用Thermo-Calc热力学软件预测析出相及相组成,采用OM,FE-SEM和EDS对S32750超级双相不锈钢铸坯不同时效状态下的样品进行全面分析,利用K-J-M-A模型进行σ相析出动力学拟合。实验结果表明：850℃时效过程中,σ相优先在铁素体内部和双相晶界处析出,直至铁素体相耗尽;σ相的析出动力学控速环节主要是：初始阶段形核控速和时效40 min后的元素扩散控速;除σ相外,时效过程中还会析出χ相和Cr2N相。其中χ相属于亚稳定相,主要在时效前期析出,随着时效时间的延长最终转化成σ相。     

固溶处理对超级双相不锈钢S32750组织和性能的影响

研究了950～1 200℃60 min水冷的固溶处理对超级双相不锈钢S32750(/%:0.02C、0.49Si、1.03Mn、0.026S、0.001P、25.01 Cr、7.03Ni、3.80Mo、0.29N)12 mm板的组织、力学性能和耐蚀性的影响。结果表明,随固溶温度升高,钢中铁素体相增加,奥氏体相减少;在950℃加热时铁素体中析出大量σ-相,使钢的性能恶化,在1 050～1 100℃固溶处理后,钢中铁素体相和奥氏体相各占50%, S32750钢具有较好的综合力学性能和优良的耐蚀性能。     

电渣重熔超级双相不锈钢用炉渣性能研究

针对S32750超级双相不锈钢电渣重熔生产工艺,研制开发了超级双相不锈钢电渣重熔结晶器用渣系;通过现场试验证明,该渣系导热系数小,熔炼过程中稳定性和润滑性好,渣系的熔化温度在1348-1422℃,四元碱度(CaO+MgO)/(SiO_(2 )+Al_2O_3)为1.31-2.28,1500℃时黏度为0.024-0.033 Pa·s,电导率为0.243-0.292Ω~(-1)·cm~(-1),可满足S32750超级双相不锈钢电渣重熔生产要求。     

提高双相不锈钢热塑性的实践

在国外双相不锈钢管的制造是通过热挤压的方法。而国内绝大多数制管企业采用两辊斜轧穿孔的方法来获得毛管,由于变形剧烈,对钢的热塑性要求甚高,为了适应这种情况,必须提高双相不锈钢热塑性。本文介绍了添加微量元素、铁素体控制等方法而获得的效果,即使超级双相不锈钢S32750在1180℃?1200℃ Gleeble热模拟试验,其断面收缩率也高达97%,热塑性大大提高,可顺利通过热穿孔。     

2205双相不锈钢连铸坯加热过程组织转变

对2205双相不锈钢连铸坯试样在1 220、1 240、1 260、1 280℃保温10、20、30和40 min进行加热处理,通过光学显微镜和铁素体仪试验分析2205双相不锈钢的组织和铁素体含量随保温时间和加热温度的变化情况.结果表明,2205双相不锈钢连铸坯试样在相同的保温时间下,随着加热温度的升高,铁素体含量逐渐增加,1 260℃时奥氏体晶粒明显变得粗大;在相同的加热温度下,随着保温时间的延长,铁素体的含量逐渐减少.     

铌对高钢级管线钢中第二相析出与奥氏体晶粒长大行为的影响

基于双亚点阵模型,计算了两种不同铌含量的高钢级管线钢在不同温度下Nb、Ti和Al的析出量,测定了不同加热温度和保温时间下奥氏体晶粒尺寸,建立两种钢奥氏体晶粒长大模型.发现Nb含量增加提高了其全固溶温度,并且温降过程中Nb析出量显著增多,在晶界两边析出的细小碳氮化物对奥氏体晶粒长大有显著的阴碍作用.高铌钢加热温度为1250℃时奥氏体晶粒显著粗化,预测模型也不同于1050~1200℃的模型,但相同保温温度下晶粒尺寸明显小于低铌实验钢.通过数据拟合计算出高铌钢的长大激活能远远高于低铌钢,再次证明高Nb的管线钢在1200℃以下能够有效地细化奥氏体晶粒,预测模型与实验值吻合较好.      

超细晶粒钢及其力学性能特征

探索了在新一代钢中获得超细晶粒的方法。通过低温轧制和应变诱导铁素体相变，可以在碳素结构钢中获得晶粒尺寸小于5μm的超细晶粒，屈服强度大于400MPa。采用应变诱导铁素体相变可以在微合金钢中得到晶粒尺寸为1μm的超细晶粒。低碳微合金钢的屈服强度达到了600MPa，超低碳微合金钢的屈服强度超过了800MPa。采用微合金化和循环热处理可以在合金结构钢中获得2μm的奥氏体晶粒，1500MPa级抗拉强度下改善了耐延迟断裂性能。     

Ferrite recrystallization and austenite formation in cold-rolled intercritically annealed steel

The recrystallization of ferrite and austenite formation during intercritical annealing were studied in a 0.08C-1.45Mn-0.21Si steel by light and transmission electron microscopy. Normalized specimens were cold rolled 25 and 50 pct and annealed between 650 °C and 760 °C. Recrystallization of the 50 pct deformed ferrite was complete within 30 seconds at 760 °C. Austenite formation initiated concurrently with the ferrite recrystallization and continued beyond complete recrystallization of the ferrite matrix. The recrystallization of the deformed ferrite and the spheroidization of the cementite in the deformed pearlite strongly influence the formation and distribution of austenite produced by intercritical annealing. Austenite forms first at the grain boundaries of unrecrystallized and elongated ferrite grains and the spheroidized cementite colonies associated with ferrite grain boundaries. Spheroidized cementite particles dispersed within recrystallized ferrite grains by deformation and annealing phenomena were the sites for later austenite formation.     

Effects of Initial Structure and Reversion Temperature on Austenite Nucleation Site in Pearlite and Ferrite–Pearlite

Austenite nucleation sites were investigated in near-eutectoid 0.8 mass pct C steel and hypoeutectoid 0.4 mass pct C steel samples with full pearlite and ferrite–pearlite initial structures, respectively. In particular, the prior austenite grain size had been coarsened to compare grain boundaries in the hierarchical pearlite structure, i.e., the low-angle pearlite colony and high-angle block boundaries with ferrite/pearlite interfaces in the austenite nucleation ability. When the full pearlite in 0.8 mass pct C steel underwent reversion at a relatively low temperature, austenite grains preferentially formed at pearlite block boundaries. Consequently, when the full pearlite with the coarse block structure underwent reversion just above the eutectoid temperature, the reversion took a long time due to the low nucleation density. However, austenite grains densely formed at the pearlite colony boundaries as well, as the reversion temperature became sufficiently high. On the other hand, when ferrite–pearlite in the 0.4 mass pct C steel underwent reversion to austenite, the ferrite/pearlite interface acted as a more preferential austenite nucleation site than the pearlite block boundary even in the case of low-temperature reversion. From these results, it can be concluded that the preferential austenite nucleation site in carbon steels is in the following order: ferrite/pearlite interface?>?pearlite block?>?colony boundaries. In addition, orientation analysis results revealed that ferrite restricts the austenite nucleation more strongly than pearlitic ferrite does, which contributes to the preferential nucleation at ferrite/pearlite interfaces. This suggests that austenite grains formed at a ferrite/pearlite interface tend to have an identical orientation even under high-temperature reversion. Therefore, it is thought that the activation of austenite nucleation within pearlite by increasing the reversion temperature may be effective for rapid austenitization and the grain refinement of austenite structure after the completion of reversion in carbon steels.     

晶界位向对硅钢立方/旋转立方取向双晶轧制取向变化的影响

晶界和{100}柱状晶在硅钢生产过程中对织构的遗传和演变有关键作用,因此本文利用晶体塑性有限元方法进行立方和旋转立方取向双晶在晶界不同位向时晶体取向演变的全场模拟.模拟显示,三种晶界位向下,晶界都具有诱发晶内产生S形状形变不均匀和缓解局部形变不均匀区取向转动的特点,立方和旋转立方取向双晶在带有剪切作用的轧制条件下都显示明显的取向稳定性.GB上RD(表示晶界垂直于轧向)晶界位向时,旋转立方取向晶粒优先在晶界中心位置发生取向转动,而立方取向则优先在远离晶界的端部发生取向转动.GB上TD(表示晶界垂直于横向)的晶界位向下,其晶界阻碍作用最小,双晶内产生的取向漫散度大,织构强度较低;除绕TD转动外,也具有复杂的绕RD、ND的取向转动.GB上ND(表示晶界垂直于法向)的晶界位向下,取向转动与GB上RD时相近,但有少量取向绕ND转动.     

双辊铸轧Cr12钢的热处理工艺对深冲性和抗皱性的影响

将双辊铸轧Cr12钢薄板于1 000℃固溶,再采用炉冷和水淬两种方式冷却至室温,分别获得了多边形铁素体和板条马氏体两种组织,再经过相同冷轧和退火工艺,得到了两种成品板.经拉伸试验测定,水淬板的深冲性和抗皱性均强于炉冷板.组织分析发现:热处理后,水淬板内马氏体板块明显细小于炉冷板内铁素体晶粒;冷轧后,水淬板内板块间界演变...     

奥氏体变形及冷却速率对低碳贝氏体组织中大角晶界分布的影响

使用电子背散射衍射技术研究了低C高Mn高Nb成分设计下,非再结晶奥氏体变形及加速冷却速率对低碳贝氏体组织取向差特征和大角晶界分布的影响.结果表明,与原奥氏体晶粒内部的相变组织相比,原奥氏体晶界附近具有更高的大角晶界密度,非再结晶区奥氏体变形及快速冷却都有利于提高共格相变的驱动力、弱化变体选择以及有效增加大角晶界密度.此外,非再结晶区的大变形除了可充分压扁奥氏体晶粒和增加单位面积的奥氏体晶界密度外,还导致奥氏体晶界上细小的非共格转变铁素体晶粒生成,且这些铁素体晶粒与相邻组织表现出大取向差.      

Analysis of texture evolution in channel die compression—I. Effects of grain interaction

The effect of grain interactions on deformation patterns and texture evolution is examined by the finite element method for a particular set of grains deformed in channel die compression. The material behavior within each element is determined from a slip based constitutive formulation that fully accounts for finite deformations and lattice rotations with deformation. Compatibility and equilibrium are enforced across the grain boundaries, and grain boundary sliding is not permitted. In order to make the analyses numerically tractable, an idealized two-dimensional geometric model is used to model the deformation in the longitudinal-transverse plane; and the strains are assumed to be uniform through the compression direction. Boundary conditions simulating homogeneous plane-strain compression are applied to the model region. The results reveal complex deformation patterns arising from grain interactions. The analyses also show that the crystallographic texture and the spread of orientations within a grain depend not only on the orientations of the neighboring grains, but also on the constraints provided by grains located several grains away.     

热处理对高强大梁钢冲击吸收功的影响分析

为了研究热处理工艺对高强大梁钢冲击性能的影响，采用扫描电镜、透射电镜和EBSD等方法对700L不同热处理工艺后的冲击性能进行了研究。结果显示，热处理工艺对700L的冲击性能影响显著。在低于400 ℃退火时，冲击性能较原板有所提高;在高于550 ℃退火时，钢板组织发生变化，晶界析出大量渗碳体，冲击性能明显恶化。原板经不同奥氏体化温度空冷处理后，850 ℃空冷后的钢板拥有最佳的冲击性能，其组织由等轴的细小铁素体与M/A岛组成。织构分析结果表明，原板拥有较强的{001}〈110〉型织构，这类型织构可能对钢板冲击性能有不利影响，经低温退火处理后，{001}〈110〉型织构强度减弱，经奥氏体化处理后织构消失。     

Fiber texture and substructural features in the caliber-rolled low-carbon steels

Caliber rolling at the recrystallization temperatures of ferrite is a new process that was developed to fabricate an ultrafine-grained microstructure for low-carbon steels. In the present investigation, the electron backscattered diffraction (EBSD) measurement was carried out to characterize thoroughly the texture and substructural features in two caliber-rolled low-carbon steels, with special attention on the effects of a phosphorus addition to the steel and the annealing treatment after rolling. Finer ferrite grains appeared in the phosphorus-added steel under the same rolling condition. The phosphorus addition caused also the stronger <110>//rolling direction (RD) fiber texture in the caliber-rolled steel bars and, hence, showed a larger average Taylor factor than the steel without phosphorus. Microband features within the ultrafine ferrite grains were characterized with both transmission electron microscopy (TEM) observation and orientation-imaging micrograph (OIM) analysis. Nearly half of the low-angle boundaries, whose kernel average misorientation was larger than 0.8 deg, were found to have the planar character and were specifically parallel to the {110} or {112} planes. In the as-rolled condition, the total volume fraction of the low-angle boundaries was 0.3 and 0.23 in the steels with and without a phosphorus addition, respectively. More {112}-type planar boundaries were observed than the {110} type boundaries in both steels. Annealing treatment increased the volume fraction and changed the type of the low-angle boundaries in both steels. Using the model proposed by Peeters et al., the critical resolved shear stress (CRSS) of the 110 and 112 slip systems was calculated by considering the contributions of both the randomly distributed dislocations and the oriented planar boundaries. We concluded that the contribution of the planar low-angle boundaries to the total CRSS was less than 2 pct. The texture features and dislocation structure in the ultrafine-grained steels influenced the mechanical behavior to some extent, in addition to the refined ferrite grains. Phosphorus added to the steels showed a larger influence on the formation of texture and the retained dislocation structure, than that on the grain refinement in the caliber-rolling process.