Inclusion and its deformation behavior in 304 stainless steel

Non-metallic inclusion is the main reason for the presence of surface defects in cold-rolled steel strip. In this study,the composition,morphology,and size of the non-metallic inclusion in hot-rolled 304 stainless steel strips are analyzed. Cold-rolled 304 stainless steel strips with different cold-rolling reduction have been prepared,and the morphology and size of inclusion in these cold-rolled strips are also analyzed. Furthermore,the deformation behavior of a non-metallic inclusion during the cold-rolling process is studied. The results showthat Ca O-SiO2-MgO-Al2O3,a kind of brittle compound oxide,is the main type of inclusion in hot-rolled 304 stainless steel strips.During the cold-rolling process,ductile deformation of this type of inclusion is not obvious,where large inclusions are crushed,and the average size of inclusions in cold-rolled strips decreased while the cold-rolling reduction increased.     

On the hot tensile deformation behavior of an AISI 316LN stainless steel

The hot deformation characteristics of AISI 316LN stainless steel were studied in the temperature range of 1123–1323 K and strain rate range of 10⁻⁴–10⁻¹s⁻¹ by carrying out tensile tests. The flow stress, ultimate tensile stress and percentage elongation were found to be strongly dependent on the temperature and strain rate. The critical strain required for the initiation of dynamic recrystallisation and peak strain were determined at each condition and their variation with temperature and strain rate studied. The deformation behavior was analyzed using a generic model for high temperature deformation and deformation parameters were computed. The variation of the true activation energy with strain for rate controlled high temperature tensile deformation was obtained. Microstructural studies were carried out on tested samples and the results of all the above studies are presented.     

Microstructural changes during heating of super duplex stainless steel and its thermal deformation behavior

Microstructural changes during heating of highly alloyed Cr26Ni7 type super duplex stainless steel( SDSS2607) and its thermal deformation behavior were investigated. At different heating rates,the mechanism of phase transition from γ phase to δ phase and grow th modes of δ phase differed. Variations in microstructures for ascast SDSS2607 during heat preservation at 1 220 ℃ indicated two kinds of transformations from γ phase to δ phase.In-situ observations of microstructural changes during the tensile process at 1 050 ℃ showed a mutual coordination betw een γ and δ phases. When the true strain increased,the mutual coordination between γ and δ phases was damaged. Subsequently,cracks nucleated at the γ/δ interface. With the increase in temperature,the strength of ascast SDSS2607 decreased while its plasticity increased. Its thermoplasticity was poor,and the reduction in area of tensile specimens was less than 80%. When the deformation strain of hot compression increased,the stable deformation zone in the heat processing maps enlarged gradually. Moreover,the unstable deformation zones were extended.     

超级奥氏体不锈钢的高温变形行为

 为了研究超级奥氏体不锈钢Cr20Ni24Mo6N钢的高温变形行为,采用Gleeble热模拟试验机进行了等温压缩试验,建立了合金的热加工图。结果表明,当变形温度为1 000～1 200 ℃时,Cr20Ni24Mo6N钢的流变曲线表现出典型的“加工硬化＋动态再结晶软化”特点;Cr20Ni24Mo6N钢的热激活能[Q]为678.656 kJ/mol。通过加工图与微观组织综合分析得出,超级奥氏体不锈钢Cr20Ni24Mo6N的合适热加工工艺为,应变速率10 s－1左右,应变量0.5～0.8,变形温度1 150～1 200 ℃。     

薄带连铸AISI304不锈钢中铁素体行为

为了确定薄带连铸AISI304不锈钢凝固过程中残留铁素体的生成及转变行为,采用彩色金相、电解侵蚀、电子背散射衍射分析技术及X射线衍射分析等研究手段对双辊薄带连铸AISI304不锈钢凝固组织及残留铁素体特征进行了研究.结果表明AISI304不锈钢薄带的凝固组织由表层胞状晶区、中间柱状晶区和中心等轴晶区三部分组成.薄带表层胞状晶区内残留铁素体呈棒状,柱状晶区的残留铁素体形态为鱼骨状,中心等轴晶区的残留铁素体呈弯曲的树枝状;薄带的表层胞状晶区残留铁素体的质量分数为4.6%～6.6%,柱状晶区内的残留铁素体质量分数为3.6%～3.7%,中心等轴晶区内的残留铁素体质量分数为11.27%～11.34%;残留铁素体沿着厚度方向呈现\     

变形对亚稳态奥氏体不锈钢低温敏化的影响

采用扫描电镜(SEM)、X射线衍射分析(XRD)及透射电镜(TEM)研究了不同形变量下的亚稳态不锈钢(AISI 304)经过低温敏化处理(380 ℃、240 h的真空热处理)后组织的变化。通过双循环电化学动电位活化技术(DL-EPR)对敏化态的试样进行敏化度(DOS)测试,并用电化学阻抗谱表征了不同试样的耐腐蚀性能。结果表明,随着变形量的增加,低温敏化试样的敏化度递增,材料的耐腐蚀性能下降,当变形量达到40%时,敏化度达到71%。经过DL-EPR测试后,试样奥氏体晶粒和大部分晶界完好,马氏体区域是主要腐蚀区域,腐蚀模式为穿晶腐蚀。马氏体板条和基体中的滑移带是碳化物容易形核的位置。     

含4.35%铜抗菌不锈钢的热变形行为

含铜奥氏体不锈钢具有优异的抗菌性能而广泛应用在食品加工、医疗等领域,然而铜的加入会显著影响不锈钢的加工性能。用Gleeble-3800热模拟试验机对含铜4.35%奥氏体抗菌不锈钢进行了单道次等温热压缩试验,研究了不锈钢在变形温度为900～1 150℃、应变速率为0.01～10 s^-1和变形量为50%下的高温变形行为,构建了反映其材料特性的本构方程,使用金相显微镜观察了热变形后的微观组织,分析了各变形工艺下的微观组织演化规律,为含铜不锈钢的加工成型工艺及组织优化提供了理论参考。结果表明,4.35%Cu-304L钢的流动应力对变形工艺是敏感的,应力随着变形温度的升高和应变速率的降低而减小。采用得到的应力应变曲线建立了一种基于Arrhenius的5阶多项式拟合的应变补偿本构模型,根据此模型计算了相关系数R和平均相对误差AARE分别为0.972和9.03%,这表明所构建模型可以准确地反映含铜不锈钢的流动行为。结合微观组织发现较高的温度和较快的应变速率有利于再结晶的发生,由于0.01 s^-1低应变速率提供的变形能低,在变形温度为1 100℃、应变速率为...     

面内双轴循环载荷下304不锈钢的力学行为

为研究面内双轴载荷下304不锈钢材料的力学行为,运用有限元方法对十字形试样尺寸进行了设计与优化,在自主设计的面内双轴疲劳试验系统上对304不锈钢进行了单轴拉伸、双轴比例加载和非比例圆路径下的力学试验。结果表明,比例加载条件下304不锈钢的棘轮应变累积最小,圆路径下材料的棘轮应变最大,而单轴加载的棘轮应变累积介于比例载荷与圆路径之间。进入棘轮应变稳定增长阶段,圆路径对应的棘轮应变率高于单轴与比例加载,说明圆路径使304不锈钢的损伤失效进程加速。     

抗晶间腐蚀奥氏体不锈钢的晶界工程

Sensitization by chromium depletion due to chromium carbide precipitation at grain boundaries in austenitic stainless steels can not be prevented perfectly only by previous conventional techniques, such as reduction of carbon content, stabilization-treatment, local solution-heat-treatment, etc. Recent studies on grain boundary structure have revealed that the sensitization depends strongly on grain boundary character and atomic structure, and that low energy grain boundaries such a~ coincidence-site-lattice (CSL) boundaries have strong resistance to intergranular corrosion. The concept of grain boundary design and control has been developed as grain boundary engineering (GBE). GBEed materials are characterized by high frequencies of CSL boundaries which are resistant to intergranular deterioration of materials, such as intergranular corrosion. A thermomechanical treatment was tried to improve the resistance to the sensitization by GBE. A type 304 austenitic stainless steel was cold-rolled and solution-heat-treated, and then sensitization-heat-treated. The grain boundary character distribution was examined by orientation imaging microscopy (OIM). The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation (EPR) and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction The frequency of CSL boundaries indicated a maximum at the small reduction. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanical-treated specimen than in the base material. A high density of annealing twins were observed in the thermomechanical-treated specimen. The results suggdst that the therrmomechanical treatment can introduce low energy segments in the grain boundary network by annealing twins and can arrest the percolation of intergranular corrosion from the surface. The effects of carbon content and other minor elements on optimization in grain boundary character distribution (GBCD) and thermomechanical parameters were also examined during GBE.     

304不锈钢在模拟压水堆一回路水中高温电化学腐蚀行为

通过模拟压水堆一回路水环境,研究了氯离子浓度和溶解氧对304不锈钢高温电化学腐蚀行为的影响.动电位极化曲线结果表明,氯离子浓度主要影响高电位下的二次钝化效应,低电位下影响效果不明显,结合X射线光电子能谱对氧化膜元素成分的分析发现二次钝化效应与氧化膜中Fe/Cr元素含量比密切相关.电化学阻抗谱和扫描电镜结果表明,随着氯离子浓度增加,氧化膜阻抗逐渐降低,表面外层氧化物颗粒和间隙逐渐增大,耐腐蚀性能降低.随着溶解氧含量的升高,304自腐蚀电位逐渐升高,钝化电流密度降低,钝化区间缩小,表面氧化膜阻抗逐渐增加.     

冷轧硅脱氧304不锈钢中氧化物夹杂的演变行为

 为实现固态钢基体内夹杂物在冷轧过程中的控制,将硅脱氧304不锈钢热轧板经多道次冷轧至不同的厚度,利用扫描电子显微镜对试样内夹杂物在冷轧过程中的演变行为进行了研究。结果表明,硅脱氧304不锈钢内夹杂物的类型主要为低熔点SiO2-CaO-MnO-Al2O3,其在热轧板内的形貌为大尺寸长条状。冷轧时,这些长度为2.0～23.0 μm的长条状氧化物夹杂发生断裂,形成多个1.0～3.0 μm小尺寸夹杂物。随着冷轧压下量的增加,断裂后形成的夹杂物尺寸逐渐减小。但当夹杂物尺寸降低至约0.5 μm时,夹杂物不再发生断裂。同时,断裂后形成的小尺寸夹杂物之间的距离与夹杂物的初始尺寸无关,由冷轧板的伸长率决定。     

模拟地热水环境中304不锈钢管材的结垢与腐蚀电化学行为

基于地热水输送过程中金属管道材料出现的腐蚀结垢问题,研究了模拟地热水(我国中部平原地热水的环境条件)中304不锈钢管材的结垢和电化学腐蚀行为.结果表明,304不锈钢管在模拟地热水环境中的结垢过程分为结晶成核和晶核生长两个阶段,结晶成核阶段消耗结垢离子的速度比晶核生长阶段更快,304不锈钢管道表面结垢层的微观形貌为不规则的\     

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.     

Grain growth behaviour of an AISI 422 martensitic stainless steel after hot deformation process

The metadynamic softening behaviour and grain size refinement of an AISI 422 martensitic stainless steel in the temperature range of 950–1150°C was investigated by double-hit compression tests. The deformed specimens were held at deformation temperature with delay times of 5–300?s after achieving a strain of 0.3. Based on the experimental results, a model was established for estimation of a softening fraction at different deformation parameters, and the softening fraction was compared with a recrystallised fraction. A major deviation was observed at the beginning of interpass time denoting a significant contribution of recovery to the fractional softening (FS). However, by increasing the time and temperature, the difference between the FS and recrystallised fraction is reduced. The finer grain size was achieved by prior fine pre-austenite grain and lower secondary deformation temperature. The initial grain size of 53?µm decreased down to 32 and 19?µm at the deformation temperatures of 1020 and 940°C, respectively. The austenite grains have considerable growth at a temperature higher than 1020°C, while the grain coarsening is negligible at lower deformation temperatures.     

含铈304不锈钢夹杂物改性及耐腐蚀性能优化

 通过在304不锈钢中加入不同含量的铈,研究了铈处理前后钢中夹杂物的变化,并借助于腐蚀失重试验及电化学试验,分析了不同含量的铈处理后钢中夹杂物性质变化对304不锈钢耐腐蚀性能的影响。研究结果表明,未加铈的不锈钢中主要为MnS夹杂及复合氧化物夹杂,夹杂物的平均尺寸为8.6 μm,而钢的自腐蚀电位仅为-348.52 mV。加入稀土铈后,夹杂物逐渐改性成球状或椭球状的含铈夹杂物,平均尺寸有所降低,而不锈钢耐腐蚀性则有所提高。当铈质量分数达到0.012%时,钢中MnS夹杂全部改性成球状含铈夹杂,不锈钢自腐蚀电位高达-311.25 mV,耐腐蚀性能最好。继续增加稀土铈含量,钢中夹杂物的形状变得不规则,尺寸也有所增加,导致不锈钢耐腐蚀性能降低。     

Effect of heat treatment on the behavior ofδ-ferrite in B410D martensitic stainless steel

The morphology and the evolution ofδ-ferrite existing in B410D slabs,hot-rolled plates,annealed plates and quenched plates were studied through metallographic observation.Results show thatδ-ferrite forms during the solidification process and that it easily grows and increases in quantity during high temperature annealing.Band-shapedδ-ferrite in hotrolled plates is difficult to be eliminated by conventional heat treatment and hard to recrystallize.     

The effects of cold working on sensitization and intergranular corrosion behavior of AISI 304 stainless steel

The effects of prior cold rolling of up to an 80 pct reduction in thickness on the sensitization-desensitization behavior of Type AISI 304 stainless steel and its susceptibility to intergranular corrosion have been studied by electrochemical potentiokinetic reactivation (EPR) and Strauss-test methods. The results indicate that the prior deformation accelerated the sensitization as compared to the undeformed stainless steel. The deformed Type 304 stainless steel experienced desensitization at higher temperatures and times, and it was found to be enhanced by increased cold deformation. This could be attributed to the increased long-range chromium diffusion, possibly brought on by increasing pipe diffusion and vacancies. The role of the deformation-induced martensite (DIM) and texture, introduced by uniaxial cold rolling, on the sensitization-desensitization kinetics has also been discussed. This study could not reveal any systematic relationship between texture and the degree of sensitization (DOS) obtained. The effect of DIM on DOS seems to be pronounced at 500 °C when the steel retained significant amounts of DIM; however, the retained DIM is insignificant at higher sensitization times and temperatures.     

Research on martensitic transformation of 304 stainless steel

采用光学显微镜、扫描电镜、磁性测量和力学分析等手段,研究了304奥氏体不锈钢形变过程中发生开裂的原因,研究发现开裂是由于形变过程中发生了马氏体相变,导致塑性变差引起的,开裂处的磁性率达到了22.9%。发生马氏体转变的原因是由于w（Ni）低于标准下限,其组织稳定性下降,在形变过程中诱发了马氏体转变。     

316L不锈钢动态再结晶行为

在Gleeble-1500热模拟试验机上,通过高温压缩实验对316L不锈钢的动态再结晶行为进行了系统研究.结果表明:316L不锈钢热变形加工硬化倾向性较大,在真应力应变曲线上没有出现明显的应力峰值σ_p;316L不锈钢在热变形过程中发生了动态再结晶,但只是在局部区域观察到了动态再结晶晶粒.对动态再结晶的实验数据进行拟合,得到316L不锈钢的热激活能和热变形方程,并给出了发生动态再结晶的临界应变和临界应力以及Zener-Hollomon参数和稳态应力的关系.