SPAH钢的高温氧化行为

SPAH钢在热轧过程中氧化不仅会影响到产品的表面质量还会影响到材料的收得率.在热轧温度范围733～1 333 K,对该钢进行了热轧试验,利用扫描电子显微镜、能谱分析和X射线衍射等方式研究了其高温氧化行为.研究表明,当温度低于833 K时,钢的高温氧化非常轻微.在钢的温度低于1 133 K时,其表面氧化膜均比较致密.如果温度超过1 133 K,所形成的氧化膜松而脆,而且此时随着温度的升高,表面氧化速率显著增加.进一步数值分析表明,提高轧制过程中的冷却速率或提高轧制速度可以减少表面氧化.     

中温低张应力下磷在2．25Cr-1Mo钢中的晶界偏聚研究

采用俄歇电子能谱仪(AES)研究了在520 ℃,40 MPa的张应力下2.25Cr-1Mo钢中磷元素的晶界偏聚行为.经检测发现磷在晶界处发生了明显的非平衡晶界偏聚现象,其临界时间为0.5 h,此时磷原子的偏聚量为14.82%(原子百分比).根据徐庭栋的中温低张应力引起的非平衡晶界偏聚理论模型进行分析,发现张应力使磷-空位复合体的扩散系数增加了1个数量级,使磷原子的扩散系数降低了4个数量级,且俄歇试样的断口形貌与晶界磷原子的偏聚结果相一致.     

一种高氮钢的高温力学性能和组织演变规律

6Cr21Mn10MoVNbN合金是重型发动机用高氮钢.采用Gleeble1500热模拟、金相分析、扫描电镜、XRD和理论分析相结合的方法研究了该合金的高温变形特性.微观结构分析表明,变形温度和应变速率对该合金微观组织的演变有很大的影响.合金在850,950,1050℃经历相同的变形量后,合金晶粒尺寸相差不大.但当温度升至1150℃,变形后合金晶粒尺寸迅速增大,此类变化主要是由于温度升高使合金中铬的碳化物快速溶解和转化所致.     

A method to study interface diffusion of arsenic into a Nb-Ti microalloyed low carbon steel

A novel diffusion couple method was used to investigate the interface diffusion of arsenic into a Nb-Ti microalloyed low carbon steel and its effects on phase transformation at the interface. It is discovered that the content of arsenic has great effect on grain growth and phase transformation at high temperature. When the arsenic content is no more than 1wt%, there is no obvious grain growth and no obvious ferrite transitional region formed at the diffusion interface. However, when the arsenic content is no less than 5wt%, the grain grows very rapidly. In addition, the arsenic-enriched ferrite transitional layer forms at the diffusion interface in the hot-rolling process, which results from a slower diffusion rate of arsenic atoms than that of carbon in ferrite.     

Experimental determination of mechanical properties and short-time creep of AISI 304 stainless steel at elevated temperatures

The high temperature properties of AISI 304 stainless steel were studied. Basic data about the employed experimental equipment, testing procedures, and specimen geometry were given. The experimental setup was used to obtain stress-strain diagrams from tensile tests at room temperature as well as several elevated temperatures. Furthermore, the specimens were subjected to short-time creep tests at various temperatures. Stress levels for creep testing were established as a percentage of yield stress. The results indicate that at lowered temperatures and lower stress levels, AISI 304 stainless steel can be used as a sufficiently creep resistant material.     

正火过程中V--N微合金化钢的第二相行为

采用物理化学相分析、高分辨透射电镜等手段研究V-N微合金化钢在正火过程中第二相行为,并进行相应的理论计算,讨论该行为对材料性能产生的影响.正火加热保温过程中,V-N钢有约32.9%的V( C,N)未溶解,阻止奥氏体晶粒长大.在正火冷却过程中,未溶解的V( C,N)诱导晶内铁素体形核,细化铁素体晶粒,而溶解的V( C,N)重新析出,起到析出强化作用. V( C,N)析出相行为的变化导致材料力学性能的改变.与热轧态V-N钢相比,正火态V-N钢细晶强化贡献值增加31 MPa,而析出强化贡献值减少45 MPa.     

5 Cr9 Si3钢的高温变形行为及流变应力异常变化机理

通过不同热加工参数下的热压缩试验,研究了新型阀门钢5Cr9Si3的高温变形行为.5Cr9Si3钢在850~900℃和1000~1100℃温度区间内峰值应力分别随温度的升高而减小,而在900~1000℃温度区间内出现峰值应力随温度升高而增大的异常现象.进一步的微观组织及相结构演化分析表明：5Cr9Si3钢在900~1000℃温度区间内发生了由铁素体向奥氏体的转变,产生奥氏体相变强化;同时,随着变形温度的提高,碳化物的回溶造成碳元素和铬元素对5Cr9Si3基体固溶强化效果增强.相变强化和固溶强化是导致5Cr9Si3在900~1000℃温度区间内流变应力异常变化的主要原因.     

CSP微合金高强度钢研究

在热模拟实验机上进行不同变形工艺的试验,研究了不同变形工艺参数对CSP生产线生产的一种微合金高强度钢组织和性能的影响.结果表明,通过优化道次变形量、变形速度、变形温度和冷却速率等工艺参数,可获得微合金高强度钢产品.     

含钛微合金钢的高温热塑性及断裂机理

运用Gleeble 1500热模拟机对600~1350益温度范围内SS400B钢加入钛后的高温力学性能进行测试,对断口形貌及低倍组织进行扫描电镜观察,研究其断裂机理及影响因素。利用热力学软件Factsage对不同钛含量条件下第二相粒子的析出情况进行计算分析。结果表明,在实验温度范围内测试试样的断面收缩率均超过了45%;在高温区生成的铝钛氧化物可作为塑坑的形核核心,促进延性断裂的发生;同时由于铝钛氧化物、氮化钛的生成,降低了对钢塑性有害的氮化铝生成;沿晶铁素体和沿晶渗碳体的生成恶化钢的塑性,促进沿晶脆性断裂的发生。     

Nucleation and three-dimensional morphology of intragranular ferrite in a vanadium microalloyed steel

The formation of intragranular ferrite at inclusions was analyzed by SEM-EDX in a vanadium microalloyed steel with an excess amount of sulfur. The precipitation of MnS at aluminum oxides may result in Mn depletion, which, in turn, promotes the formation of intragranular ferrite. The morphology of intragranular ferrite changed with undercooling. At higher temperatures intragranular ferrite is nearly equiaxed whereas it is plate-like at lower temperatures.     

低碳钢烘烤硬化中C元素晶界的偏聚

针对低碳钢,测试了不同预变形量下的烘烤硬化性能;采用电子背散射衍射及电子探针技术分别分析了低碳烘烤硬化钢板的晶界特征和晶界元素偏聚。结果表明,随着预变形量不断增加,烘烤硬化值不断增大;钢中小角度晶界不断增多,但总体上大角度晶界还是占主导地位。退火态和不同预变形量下的烘烤态均存在碳元素在晶界处偏聚的现象,锰元素没有晶界偏聚。     

Ultrafine microstructure in microalloyed steel by a new thermomechnical process

Low carbon microalloyed steel containing 0.062% C, 2.34% Mn,0.044% Nb, 0.029% Ti, 0.032% V in mass fraction and small amount of B was prepared in laboratory. Slabs of the steel were rolled into plates of 6mm in thickness followed by accelerated cooling. The plates possess very high yield strength and reasonable ductility, and the yield ratio is about 0.8. Ultra-fine ferrite structure with micrometer dimension was observed in the surface layer of the plates. Moreover, the effect of the finishing rolling temperature on the final microstructure and formation mechanism of ultra-fine ferrite as well as the γ→α transformation behavior of the steel was discussed.     

淮南煤焦结构及其高温气化反应性研究

采用FTIR、TG/DTA和比表面分析对淮南煤焦进行研究,考察了成焦条件对淮南煤焦的物理、化学结构及其CO2气化反应性的影响.结果表明,随着热解温度的升高,煤焦中的碳含量增加、氢含量降低、孔容减小,煤焦与CO2的气化反应性降低;在热解温度相同的条件下,与快速热解煤焦相比,慢速热解煤焦的碳含量较高、氢含量较低、孔容和比表面积较小、与CO2的气化反应性较低.     

中温大变形量下磷在2．25Cr1Mo钢中的晶界偏聚

采用AES法对中温大变形量下2.25Cr1Mo钢中磷的晶界偏聚现象进行试验研究.通过试验得到磷的晶界偏聚动力学曲线,并对其偏聚规律进行分析.结果表明,磷的晶界偏聚特征是非平衡晶界偏聚,在偏聚的动力学过程中,磷出现了2个偏聚峰值.     

氧化铝基耐火材料的高温耐磨性

采用新研制的高温耐磨性实验装置,测定了五种氧化铝基耐火制品的高温耐磨性能. 结果表明:当材料处于弹性变形阶段时,随温度的升高,磨损体积变化不明显;当温度继续升高,材料达到塑性变形阶段时,磨损体积大幅度减小. 以高硬度矿物相为主晶相的耐火制品更耐磨,但材料的烧结程度对耐磨性的影响更显著,对于具有同样主矿物相的材料,烧结程度越好,耐磨性也越好. 高温下材料中产生低熔点液相时,缓冲了磨损,其作用超过矿物相硬度对耐磨性的影响. 材料的磨损体积与其高温抗折强度紧密相关,在脆性变形阶段,高温抗折强度越高,磨损体积越小;在塑性变形阶段,材料的磨损体积和高温抗折强度均显著降低.     

含铌微合金钢的再结晶组织演化模拟

建立了热轧时流变应力、回复、再结晶及析出的物理冶金模型,用于计算轧制时位错密度变化、再结晶形核、再结晶晶粒长大以及粒子析出等. 结果表明,模型对含铌微合金钢在不同的热轧形变条件下模拟结果与实验值符合较好,可以有效预测在不同热轧形变条件下的再结晶体积分数与再结晶晶粒大小. 模型包含基本冶金现象的描述,原则上通过调整材料基本参数,可以运用于不同的钢种.     

高温动态拉伸下NG TiAl弹塑性行为的数值模拟

基于率相关的晶体塑性理论,发展了更为合理的同时考虑位错滑移和形变孪晶作用、并计及温度影响的TiAl单晶本构模型.在此基础上,建立了能够反映晶粒随机取向的多晶有限元模型,对不同温度(室温～840℃)不同拉伸应变率(0.001～1 350/s)下NG TiAl的弹塑性力学行为进行了模拟.结果显示,模拟得到的应力应变曲线与试验结果基本一致,能够比较好地模拟NG TiAl在不同温度和应变率下的材料响应.还考察了形变孪晶对塑性变形的影响,结果表明孪晶为NG TiAl重要的变形方式之一;动态条件下孪晶的体积分数增大,从而提高了NG TiAl的塑性变形;而温度对孪晶体积分数演化的影响不明显.     

Ductile fracture behavior of TA15 titanium alloy at elevated temperatures

To better understand the fracture behavior of TA15 titanium alloy during hot forming, three groups of experiments were conducted to investigate the influence of deformation temperature, strain rate, initial microstructure, and stress triaxiality on the fracture behavior of TA15 titanium alloy. The microstructure and fracture surface of the alloy were observed by scanning electronic microscopy to analyze the potential fracture mechanisms under the experimental deformation conditions. The experimental results indicate that the fracture strain increases with increasing deformation temperature, decreasing strain rate, and decreasing stress triaxiality. Fracture is mainly caused by the nucleation, growth, and coalescence of microvoids because of the breakdown of compatibility requirements at the α/β interface. In the equiaxed microstructure, the fracture strain decreases with decreasing volume fraction of the primary α-phase (α_p) and increasing α/β-interface length. In the bimodal microstructure, the fracture strain is mainly affected by α-lamella width.     

High-temperature properties and microstructure of Mo microalloyed ultra-high-strength steel

The high-temperature mechanical properties and microstructure of forging billets of C-Si-Mn-Cr and C-Si-Mn-Cr-Mo ultra-high-strength cold-rolled steels (tensile strength≥1000 MPa, elongation≥10%) were studied. Through the comparison of reduction in area and hot deformation resistance at 600–1300°C, the Mo-containing steel was found to possess a higher strength and a better plasticity than the Mo-free one. The equilibrium phase diagram and atom fraction of Mo in different phases at different temperatures were calculated by Thermo-Calc software (TCW). The results analyzed by using transmission electron microscopy and TCW show that precipitates in the Mo-containing steel are primarily M₂₃C₆, which promote pearlite formation. The experimental data also show that a lower ductility point existing in the Mo-free steel at 850°C is eliminated in the Mo-containing one. This is mainly due to the segregation of Mo at grain boundaries investigated by electron probe microanalysis (EPMA), which improves the strength of grain boundaries.     

X60钢在不同温度下的CO2腐蚀行为

为了研究腐蚀因素与腐蚀速率的关系，通过在NACE溶液（5％NaCl＋0.5％CH3COOH）中进行饱和CO2浸泡腐蚀实验，利用失重法、电子显微镜（SEM）和数码相机等方法研究了X60管线钢在30、60和90℃温度条件下的腐蚀行为，研究结果表明，X60钢在90℃条件下的腐蚀速率比在30和60℃条件下高一个数量级，为12.8858mm／a,在30℃时，试样表面无明显点蚀特征，在60℃条件下试样表面仅仅出现点蚀，其余部分平整，而在90℃条件下试样表面不仅出现严重的台地腐蚀而且出现线蚀槽，腐蚀严重。在60℃条件下，点蚀周围富集Cl-，说明Cl-在坑内富集，是引起点蚀成核的主要原因。