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。     

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.     

Through-thickness fracture of a Ti-V-N plate steel

The effects of microstructure on through-thickness fracture properties of a Ti-V-N plate steel have been determined directly by through-thickness tensile tests and indirectly by studying delamination fractures in longitudinal tensile and Charpy tests. The initiation of ductile fracture is primarily controlled by inclusions, but overall ductility is influenced by microstructure such that the tensile fracture strain is higher for ferrite-pearlite microstructures than for ferrite-bainite or ferrite-martensite. The cleavage fracture stress is lower for steels which have been rolled belowAr ₃ and contain deformed ferrite than for steels finish rolled aboveAr ₃. Measurements of true stress and true strain for fracture initiation qualitatively fit a model which assumes cleavage fracture occurs at a critical stress, ductile rupture at a critical strain, and a transition fracture mode comprising ductile initiation followed by cleavage. Formerly Visiting Research Fellow, Metals Technology Laboratories, CANMET, Ottawa, ON, Canada Formerly Research Scientist, Metals Technology Laboratories, CANMET     

Through-thickness fracture of a Ti-V-N plate steel

The effects of microstructure on through-thickness fracture properties of a Ti-V-N plate steel have been determined directly by through-thickness tensile tests and indirectly by studying delamination fractures in longitudinal tensile and Charpy tests. The initiation of ductile fracture is primarily controlled by inclusions, but overall ductility is influenced by microstructure such that the tensile fracture strain is higher for ferrite-pearlite microstructures than for ferrite-bainite or ferrite-martensite. The cleavage fracture stress is lower for steels which have been rolled belowAr ₃ and contain deformed ferrite than for steels finish rolled aboveAr ₃. Measurements of true stress and true strain for fracture initiation qualitatively fit a model which assumes cleavage fracture occurs at a critical stress, ductile rupture at a critical strain, and a transition fracture mode comprising ductile initiation followed by cleavage. Formerly Visiting Research Fellow, Metals Technology Laboratories, CANMET, Ottawa, ON, Canada Formerly Research Scientist, Metals Technology Laboratories, CANMET     

A rationalization of tensile ductility and fracture in Alpha-Beta Ti-Mn alloys

Void nucleation and growth were studied in equiaxed α-gb Ti-Mn alloys, containing 1.8, 3.9, 5.8, and 8.0 wt pct Mn, in an attempt to understand why ductility tended to remain relatively constant, as both yield strength and fracture strength increased with increasing Mn content. In addition, measurements of volume fraction of voids,/,, and average void diameter,d _v, in the minimum neck section were made to determine whether catastrophic void coalescence was a possible mechanism of fracture. The values of_v andd _v at fracture were obtained by linear extrapolation of log_v andd _v vs true strain. These data indicated that the average distance between voids in the minimum neck section for Ti-3.9 Mn which contained the largest/, was most likely too large to permit catastrophic void coalescence to take place. These results supported earlier^1,2,3 and current observations that fracture occurred, during tensile straining, when a critical relationship was reached between void length and the fracture stress corrected for necking, σ_fc. It was shown that the changes in this critical relationship with both microconstituent size and volume fraction of phases were balanced by a change in void growth rate to critical size, with the result that strain to fracture remained nearly constant.     

Hydrogen induced ductility losses in austenitic stainless steel welds

The effect of hydrogen on the tensile behavior of austenitic stainless steel welds was studied in two AISI 300 series alloys and two nitrogen strengthened alloys. The microstructure of these welds typically contained several percent ferrite in an austenite matrix. Hydrogen was found to reduce the ductility of all welds; however, the severity of ductility loss increased with increasing tendency to deform via a planar slip mode. In materials exhibiting large degrees of slip planarity, 304L and 308L, hydrogen changed the fracture mode from dimple rupture to a mixed mode of ductile and brittle fracture associated with the austenite-ferrite interface. The two alloys, 22-13-5 and 309S, which tend to deform by cross slip mechanisms, showed smaller losses in ductility even though hydrogen assisted the ductile rupture process by aiding void growth and coalescence, without changing the fracture mode. Varying the amount of ferrite from approximately one to 10 pct had no significant effect on performance in hydrogen.