The direction of tensile strain and the “roping” phenomenon in ferritic stainless steels

Recent observations that rolling direction surface striations are generated by tensile elongation transverse to the rolling direction have cast doubt on the validity of the plastic buckling model for roping in ferritic stainless steels. Moreover, these observations are seemingly incompatible with the transverse cross section undulations which characterize the roping morphology. To clarify this situation, detailed profilometric evaluations have been performed on roping prone type 434 stainless steel strip elongated at angles of 0, 30, 45, 60 and 90 deg to the rolling direction. In all cases, light surface striations were produced parallel to the rolling direction. However, the amplitude of the characteristic cross section undulation was quite dependent on the tensile strain axis orientation. The undulation or corrugation amplitude was greatest for tensile elongation in the rolling direction and decreased as the tensile axis diverged from the rolling direction to a point where noundulations were apparent for the case of tensile elongation transverse to the rolling direction. Thus, it is concluded that the acceptibility of the plastic buckling model is not called to question by the results of tensile elongation transverse to the rolling direction and that roping, in the general sense, is not developed by such transverse elongation. The compatibility of the plastic buckling model with observed corrugation development upon 45 deg extension is demonstrated.     

Anisotropic plastic flow in ferritic stainless steels and the “roping” phenomenon

The recent papers of Chao and Takechi, Kato, Sunami and Nakayama are discussed relative to the “roping” morphology and the textures commonly observed in ferritic stainless steels prone to “roping”. The anisotropic plastic flow associated with textures having [110] and [112J rolling directions is reviewed and a transverse plastic buckling mechanism is proposed as being consistent with “roping” morphology and texture combinations. It is proposed that longitudinal bands with a strong (001) [110] (or similar) texture surrounded by material with a (111) [11άcr2] (or similar) texture will undergo plastic buckling under transverse compressive stresses that result from the texture mix and elongation in the rolling direction. The mechanism predicts amaximum ratio of sheet thickness to corrugation width of about 0.43 for buckling with “clamped ends” and about 0.86 for buckling with “hinged ends”. Profile measurements of 430 and 434 stainless steel sheets pulled to 15 pct in the rolling direction show ratios generally under 0.4. Furthermore, the mechanism predicts that aminimum plastic elongation of 0.4 pct is required in the rolling direction to initiate buckling or “roping”. Profile measurements are presented showing that the “roping” corrugations do not develop until 1.5 to 2.0 pct plastic elongation in the rolling direction. Formerly with Allegheny Ludlum Industries, Inc., Brackenridge, Pa.     

The fracture and shear band formation in an AlCuLiMgZr alloy

The tensile properties of an Al3.2Cu1.6Li1.1Mg0.3Zr alloy with different cold rolling before peak aging were studied. The strength of the material reaches a maximum with a moderate reduction in thickness by rolling. For heavily cold rolled and aged alloy, when tensile tested in the transverse direction, both the strength and elongation are higher than in the longitudinal direction. When tested in the longitudinal direction, two sets of shear bands formed in the specimen and wedge type tensile fractures were observed to occur along the shear bands irrespective of the change in width/thickness ratio of the specimens. When tested in the transverse direction, the fracture was intergranular “woody” type, and no shear bands were observed. An explanation based on the assumption of the {110} 〈001〉 texture development in the alloy with the rolling operation was given to rationalize satisfactorily all the observations in this study.     

Influence of elastic and plastic anisotropy on the flow behavior in a duplex stainless steel

The load partitioning between two phases in a cold-rolled duplex stainless steel has been experimentally studied in situ by X-ray diffraction, for different loading directions. It was found that the load partitioning between the two phases is dependent on the loading direction. For loading in the rolling direction, both phases deform plastically to the same degree, while more plastic deformation occurs in the austenitic phase during loading in the transverse direction. For loading in the 45-deg direction, more plastic deformation occurs in the ferritic phase. The strong crystallographic texture in the ferritic phase makes the material anisotropic, with a higher stiffness and yield strength in the transverse direction compared to the rolling direction. The measured texture was used as input to theoretical predictions of both elastic and plastic anisotropy. The plastic anisotropy was predicted by assuming intragranular slip as the main deformation mechanism. The predicted anisotropic material properties were then used in finite-element simulations to study the flow behavior of the material in different directions. The predicted flow behavior was found to be in good agreement with the experimentally observed load partitioning between the phases for loading in the rolling and transverse directions. However, the yield strength of the ferritic phase during loading in the 45-deg direction was found to be lower than what was predicted. The reason for this is the difference in slip characteristics in different sample directions, because of the morphological texture.     

In-Plane Anisotropy in Mechanical Behavior and Microstructural Evolution of Commercially Pure Titanium in Tensile and Cyclic Loading

Tensile and cyclic deformation behavior of three samples oriented at 0, 45, and 90 deg to the rolling direction in the rolling direction–transverse direction (RD–TD) plane of cold-rolled and annealed plate of commercially pure titanium is studied in the present investigation. The sample along the RD (R0) shows the highest strength but lowest ductility in monotonic tension. Although ultimate tensile strength (UTS) and elongation of samples along 45 and 90 deg to the RD (R45 and R90, respectively) are similar, the former has significantly higher yield strength than the latter, indicating different strain-hardening behavior. It is found that the R90 sample exhibits the highest monotonic ductility as well as fatigue life. This is attributed to a higher propensity for twinning in this sample with the presence of multiple variants and twin intersections. Cyclic life is also influenced by the high tendency for detwinning of contraction twins in this orientation. Elastoplastic self-consistent (EPSC) simulations of one-cycle tension-compression load reversal indicate that the activity of pyramidal 〈c + a〉 slip and extension twinning oscillates during cyclic loading that builds up damage in a cumulative manner, leading to failure in fatigue.     

Fatigue Strength of Conventionally Cast Tool Steels and its Dependence of Carbide Microstructure

The axial fatigue strength at two million cycles was experimentally determined for two conventionally cast tool steels and successfully compared with results from a fatigue limit model. Specimens were tested both in the rolling and transverse direction and showed large differences in fatigue properties due to the segregated carbide microstructure. Rolling direction specimens experienced higher fatigue strength than the transverse direction specimens. This is due to smaller carbides present in the load affected cross section of the rolling direction fatigue test bars compared to the cross section of the transverse direction fatigue test bars. Fractographic analysis of failed specimens showed that large carbides had caused fatigue failure, which was also predicted by the model. Measured size distributions of carbides and inclusions were used as input data in the model. The probability that at least one particle will be present in the material volume having a size larger than the threshold value for crack propagation was calculated.     

冷加工对316L不锈钢力学行为和组织的影响

采用室温拉伸及硬度测试研究了不同的冷变形量对316L不锈钢室温力学性能及硬度的影响,并通过OM、TEM对冷变形后组织结构的观察,分析讨论了不同变形后力学性能及硬度的变化机制.结果表明,冷变形使材料的强度和硬度得到大幅度提高,但塑性有所降低.冷变形量为25％时,钢的屈服强度可达到745 MPa,同时伸长率达到19.3％.随冷变形量的不同,该钢加工硬化能力不同.变形量低于2.5％时,强度、硬度增加的速度较快,而变形量高于约2.5％后,强度、硬度增加的速度却相对较小,其原因是变形机制不同.另外,冷变形后钢的屈服强度与硬度有着相似的变化规律,由此提出了由冷变形后硬度变化预测冷变形后拉伸屈服强度的方程.     

Effect of Rare Earth Cerium on Yield Strength Anisotropy of Al-Li Alloy Sheet and Its Theoretical Prediction

Traceadditionofrareearthinto 2 0 90Al Lialloyisoneofthemeasurestoimproveitslowductilityandtoughness .Al Lialloysheetwithstrongcrystallo graphictexturehasbeenknowntohaveunusuallyhigheryieldstrengthanisotropythanconventionalalu minumalloys[1～3] .However ,ithasnotbeennormallyrecognizedsofarabouttheeffectofceriumonthisanisotropyofAl Lialloy .Someinvestigationsonheat treatableAl Lialloysshowthattheyieldstrengthanisotropyof 2 0 90sheetalloyisdefinitelyassociatedwiththevolumefractionofT1precipita…     

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The stainless steel/iron chips core cladding bar was hot-rolled by using recycling iron scrap. The interface of the metals and the influence of rolling pass, rolling temperature, graphite additive on properties of stainless steel/iron chips core cladding bar were analyzed by optical microscope, SEM, EDS and micro hardness tester. The experimental results show that element diffusion occurs at the interface after six passes rolling and the width of diffusion zone is about 70-80??m. The Fe of carbon steel diffuses into stainless steel and the Cr, Ni, Mn of stainless steel diffuse into carbon steel which makes micro hardness of carbon steel near the interface increase obviously. The bonding strength between stainless steel and iron chips core increases with increasing of rolling passes and it is 355MPa after six passes rolling. The tensile strength and elongation of the cladding bar increase with increasing of rolling temperature and they are 470MPa and 32% at 1150??, 500MPa and 35% at 1250??. The composition of iron chips core is improved by adding graphite powder. With the increasing of the graphite in iron chips, the tensile strength of cladding bar increase, but decrease for elongation. White reticular secondary cementite is appearing when the graphite is 1. 0% and the tensile strength is up to 736. 5MPa, the elongation decrease to 16%. The tensile fracture shows brittle fracture morphology.