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℃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.     

Fe-22Mn-0.7CTWIP钢的热塑性与断裂机制

基于Gleeble-1500热力模拟试验机测定了Fe-22Mn-0.7C TWIP钢和Q235钢700~1300℃范围内的静态拉伸行为.采用光学显微镜、扫描电子显微镜、能谱仪、电子探针微区分析等技术表征两钢种不同温度下的变形特征和断口形貌.通过分析基体化学成分、相体积分数、晶粒尺寸、凝固缺陷等因素探讨TWIP钢铸态热塑性的变化规律及其影响机制.研究结果表明,Fe-22Mn-0.7C TWIP钢700~1250℃范围内的铸态抗拉强度高于Q235,而其断面收缩率低于40%,且断口均以沿枝晶间断裂方式为主.晶粒细化和控制溶质显微偏析有利于提高TWIP钢热塑性,与基体均质性改善有关.此外,增加应变速率TWIP钢拉伸强度和断面收缩率同时增大.     

新型二次硬化渗碳钢的高温塑性及热加工图

 利用Gleeble-3800热模拟试验机,对一种新型二次硬化渗碳钢C61进行了高温轴向压缩试验,测得其高温流变曲线,观察了高温变形后的显微组织,获得了该钢的热变形激活能[Q]为414.84 kJ/mol,建立了试验钢的热变形本构方程,并绘制了其热加工图。结合高温变形后的显微组织和热加工图,确定最优热变形工艺参数为变形温度范围为1 050～1 100 ℃,应变速率范围为0.1～1.0 s－1,此时试验钢组织发生了完全动态再结晶,晶粒明显细化,且对应的能量耗散效率达到峰值。     

Q345B低碳高强度钢的高温塑性

使用Gleeble3500热/力模拟机对Q345B低碳高强度钢的高温塑性进行了测定.通过透射电镜、扫描电镜及金相显微镜对析出物形貌、断口形貌和断口组织进行了观察,分析了Q345B钢的断裂机理.结果表明,在1 350~650 ℃范围内,明显存在3个区间,第Ⅰ区温度范围为熔点到1 307 ℃,断裂形式是由S、O等元素偏析引起的沿晶断裂;第Ⅱ区温度范围为1 307~920 ℃,由于动态再结晶的发生,断裂形式为穿晶塑性断裂;第Ⅲ区温度范围为920~650 ℃,断裂形式是由析出物钉扎晶界以及先共析铁素体析出引起的沿晶断裂.分析结论可为连铸生产提供理论依据.      

Effects of hydrogen on notch ductility and fracture in spheroidized AISI 1090 steel

Notched bend specimens were tested after precharging or during dynamic charging with hydrogen. In the precharged case, hydrogen was shown to decrease markedly the critical strains for the onset of sh ear instability at the notch surface and for cracking in a mode II fracture. Dynamic charging was found to produce severe degradation in the form of a mode I fracture, independent of whether prior precharging was performed. The interactions of hydrogen with macroscopic plastic flow parameters were determined. Formerly Graduate Student at The Ohio State University.     

460MPa级海洋平台用钢的高温塑性研究

通过Gleeble-1500D热模拟机来进行EQ47(460 MPa)钢的高温塑性研究,以1×10-3/s的变形速率,在600~1 350℃的温度区间内以每50℃取一间隔做一组高温塑性试验.结果表明:在907~1 270℃之间,断面收缩率均高于60%,钢的高温塑性良好,温度高于1 270℃时,断面收缩率急剧下降,第Ⅲ脆性区在667~907℃之间,在此温度区间内存在明显的塑性低谷,断面收缩率最低值为29.44%.     

Influence of sulfide inclusion on ductility and fracture behavior of resulfurized HY-80 steel

The influence of sulfide inclusions on the ductile fracture process of experimental HY-80 steels having graded sulfur levels from 50 to 500 ppm and heat-treated to different strength levels was studied with respect to mechanical properties, namely, tensile ductility and Charpy impact en-ergy. Sulfide inclusions are found to have deleterious effect on both axisymmetric ductility and Charpy impact properties, whereas the plane strain ductility was found to be less sensitive to sulfide inclusions. The effect of interaction between the inclusion and the matrix and the as-sociated stress strain distribution at the void nucleating sites, which control the fracture process by microvoid coalescence, were discussed in the light of various models to suggest a micro-mechanism of fracture. Other toughness parameters obtained from instrumented impact tests were evaluated and discussed as a function of sulfur content.     

含铌微合金的高温塑性

综述了不同温度区间含铌微合金钢的高温塑性。研究发现，随着钢中铌含量的增加，钢的高温塑性变差，最小塑性温度区移至单相r低温区；在单相r低温区，由于NbC、Nb（CN）的析出，降低了钢的塑性；在r＋a两相区，Nb对钢的塑性影响较小，钢的脆性是沿r晶界薄膜状先共析铁素体a相的析出造成的。     

Hot ductility trough elimination through single cycle of intense cooling and reheating for microalloyed steel casting

Surface transverse cracking, especially corner cracking, is prone to generate in continuously cast slabs of microalloyed steels. The method of surface structure control (SSC) was supposed to the best way to avoid the detrimental defects. However, the mechanism of improving hot ductility by SSC and the specific parameters to control the process are still unclear for the reasonable adoption in production. In the present work, the impact of cooling rate, holding temperature and holding time on austenite decomposition, and the austenite grain size before and after intense cooling were investigated by thermal simulation method. With the increase of cooling rate, it is observed that the phase is transformed from austenite?→?grain boundary film-like alltromorph ferrite?→?Widmanstätten ferrite plates (or intragranular ferrite plates)?→?bainite+martensite. Mostly important, the film-like ferrite can be eliminated through intense cooling and the following reheating, but the austenite grain size is not observed to be refined through the single γ?→?α?→?γ cycle. Even though, the reduction of area (RA) is improved drastically to over 70% in the third ductility trough, whereas the RA value is just 相似文献   

第三代汽车钢的热塑性及断裂机理

采用Gleeble-1500热模拟试验机,对第三代汽车钢(TG钢)在不同的变形温度下进行了热拉伸试验,研究其热塑性的变化运用光学显微镜和扫描电镜分析了实验钢热变形的断口形貌及断裂机理.发现实验钢的强度随温度的升高而降低,热塑性曲线分为第Ⅰ脆性区、高温塑性区和第Ⅲ脆性区三个区域,其中第Ⅲ脆性区存在两个塑性极小值.在1300~800℃时实验钢的组织为奥氏体,断裂方式为连孔延性断裂,动态再结晶使韧窝分离前发生了较大的塑性变形,断口为大而深的韧窝;750℃时实验钢沿奥氏体晶界析出铁素体,断裂方式为界面断裂,断口既存在着铁素体内聚失效形成的小的孔洞,也存在由于裂纹沿奥氏体晶界扩展形成的石块状形貌;650℃由于出现了铁素体的准解理,实验钢的塑性下降,热塑性曲线再次出现极小值.     

Fe-36Ni因瓦合金的热塑性

采用Gleeble-3800热模拟试验机研究Fe-36Ni合金在900～1200℃的热塑性行为,并用FactSage软件、扫描电镜及透射电镜等研究该合金热塑性的影响因素及作用机理.结果表明：合金中主要形成Al₂O₃+Ti₃0₅＋MnS复合夹杂,夹杂物颗粒尺寸集中分布在0.5μm以下.合金热塑性在900～1050℃受晶界滑移及动态再结晶共同影响.晶界上分布的纳米级别（<200nm）夹杂物有效钉扎晶界,抑制动态再结晶发生的同时减小晶界结合力.微米级别（>200nm）夹杂物则促进显微裂纹在晶界滑移过程中的形成和扩展,损害合金热塑性.当温度高于1050℃时,较高的变形温度使再结晶驱动力大于钉扎作用力,合金发生动态再结晶,有效提高热塑性.在1100～1200℃区间内,枝晶间裂纹的形成、晶界滑移的加剧及动态再结晶晶粒尺寸增大都降低合金热塑性.     

含铌、钒、钛EQ47海洋平台用钢的高温塑性研究

EQ47钢是最常用海洋平台用钢之一,为了生产出符合质量要求的EQ47钢,需要对EQ47钢生产工艺进行研究;钢的高温塑性可以影响铸坯的质量,为了保证铸坯质量,需要对含铌、钒、钛EQ47海洋平台用钢的高温塑性进行研究。采用Gleeble-1500D热模拟机进行高温塑性试验,分析了EQ47钢高温塑性特点,断裂机理,以及铌、钒、钛对高温塑性的影响。结果表明：钢存在2个脆性区间,即第Ⅰ脆性区间为1270-1350℃,第Ⅲ脆性区间为600-900℃;试验钢的断裂形式有穿晶断裂和沿晶断裂;钢中的铌、钒、钛及其析出物均对钢的高温塑性产生影响。     

Development of a high strength stainless steel with improved toughness and ductility

Compositional modifications have been made to the existing Cr?Mo?Co stainless steels to produce a steel (alloy B) which combines the high strength of AFC 77 with the toughness of AFC 260. This has been achieved by utilizing both the strengthening effect of grain refinement and the crack stopping ability of retained austenite. After tempering at 800° to 900°F alloy B possesses higher elongation than other high strength stainless steels due to the ease with which its retained austenite transforms under stress to martensite to delay necking. An explanation has been advanced for the anomalously low tensile yield strength that occurs in both alloy B and AFC 77 after tempering at 1000°F.     

The ductility of a HSLA steel at temperatures below 300 K

High Strength Low Alloy (HSLA) steel exhibits good ductility at low temperatures down to 77 K in both ferrite-pearlite and dual-phase structures. The instantaneous strain-rate sensitivity (m) increases with decreasing temperature and reaches a maximum at 100 K. This peak temperature is much lower than that for plain carbon steels. The post-uniform elongation, which is more sensitively dependent onm, shows only slight increase around 100 K. The effect ofm on the post-uniform elongation is probably mitigated by the increasing dependence ofm on strain rate above 180 K. The uniform elongation, normally associated with the strain hardening characteristics of the material, also shows some increase around 100 K. Therefore, both strain-hardening and strain-rate hardening are responsible for the enhanced ductility of HSLA steel around 100 K.     

Compositional effects on the creep ductility of a low alloy steel

The role which P plays in determining the creep ductility of 2.25Cr-1Mo steel is examined by notched bar creep rupture tests on high purity material selectively doped with combinations of Mn, Si and P. The impurity concentrations, hardness and grain size were carefully controlled. The ductility of as-tempered samples containing dopants was found to be higher than those without dopants; however the ductility of step cooled samples containing Mn and P was found to be lower than as-tempered samples. It is suggested that P, when segregated to the prior austenite grain boundaries, enhances the nucleation of grain boundary cavities while retarding their growth. Mechanisms for each process are proposed. Formerly a Postdoctoral Research Fellow at the University of Pennsylvania formerly a Visiting Scientist at the University of Pennsylvania Formerly a Graduate Student at the University of Pennsylvania     

Hot ductility of DSS and its microstructure observation during hot deformation

selecting several typical DSS 00Cr22Ni5Mo3N,00Cr21Ni2Mn5N and 00Cr25Ni7Mo4N as research materials,hot ductility characteristic of DSS was studied and microstructure evolution during hot compression was observed.The results show that the optimum hot ductility temperature range of DSS is 1 050~1 200℃.00Cr25Ni7Mc4N exhibits the worst hot ductility and 00Cr21Ni2Mn5N has similar hot ductility to 00Cr22Ni5Mo3N.During hot compression,austenite of DSS mainly occurs dynamic recovery,the ferrite of 00Cr22Ni5Mo3N,00Cr21Ni2Mn5N can perform dynamic recovery and recrystallization,but only dynamic recovery can be observed in the ferrite of 00Cr25Ni7Mo4N.     

Trace element effects on ductility and fracture of Ni-Cr-Ce alloys

The effect of trace additions of Ce, ranging from Oto 180 at. ppm, on the tensile behavior of a Ni-20Cr alloy is presented. For alloys without Ce a transition from ductile transgranular to brittle intergranular fracture mode is observed at high temperatures and for low strain-rate tests. Additions of Ce suppress this transition with a resulting increase in ductility. Maximum effects are observed for temperature and strain rate values where fracture in Ce-free alloys occursvia grain boundary cavitation. The reduced cavitation rate of Ce-containing alloys is suggested to be the result of an increase in both interfacial energy and grain boundary mobility. Formerly Graduate Assistant, Department of Mechanics and Materials Science, Rutgers     

Tensile strength and ductility of an HSLA-steel and a maraging steel with different microstructures

Different types of microstructure by controlled hot rolling of austenite, cold rolling of martensite, intercritical annealing and/or tempering. Analysis of strength and ductility by tensile tests.     

The microstructure and fracture of a carburized steel

The case microstructure and fracture of a coarse-grained 8620 steel carburized to 1 pet surface carbon are quite sensitive to austenitizing conditions. Reheating martensitic speci-mens below theA _cm produces in the case a refined austenitic grain size, a very fine mar-tensite, spherical carbide particles and a minimum of retained austenite and microcrack-ing. Overload fracture through the latter microstructure is transgranular and scanning electron microscopy shows both microvoid coalescence around thecarbide particles and an apparent fine cleavage in other areas. As-carburized specimens and specimens re-austenitized above theA _cm developed a case microstructure characterized by a coarse austenitic grain structure in which plate martensite with microcracks developed on cool-ing within a large amount of retained austenite. The overload fracture through this mi-crostructure followed a predominately intergranular path and effectively by-passed the retained austenite and microcracked martensite. Auger electron analysis showed that C and P were present on the intergranular fracture surfaces at concentrations above bulk, an observation consistent with literature reports of P segregation during austenitizing. This paper is based on a presentation made at a symposium on “Carburizing and Nitriding: Fundamentals, Processes and Properties” held at the Cincinnati Meeting of The Metallurgical Society of AIME, November 11 and 12, 1975 under the sponsorship of the Heat Treatment Committee.