Strain-Induced Dissolution of Cementite in Cold-Drawn Pearlitic Steel Wires

Metallurgical and Materials Transactions A - Strain-induced dissolution of cementite is one of the most important microstructural changes undergone by a pearlitic steel wire during cold drawing,...     

冷拔珠光体钢丝帘线中织构演变的定量研究

采用精确的线材织构测定方法与取向分布函数(ODF)相结合的方法研究了不同热处理制度下冷拔珠光体钢丝中织构演变的变化规律.帘线钢盘条首先经过1223 K保温0.5 h后空冷至室温,然后在296、773、923 K3个温度下进行0.5 h的等温处理,经冷拔后获得试验样品.研究结果表明:冷拔珠光体钢丝帘线中晶粒取向主要集中在α取向线上,形成＜110＞>丝织构.主要织构组分为{001}＜110＞、{111}＜110＞、{110}＜110＞,其中{001}＜110＞织构组分的强度最大.反极图定量计算表明:296 K时,＜110＞织构组分的体积分数由表及里呈现上升趋势;而773 K时,＜110＞织构组分的体积分数由表及里先下降后升高;923 K时,＜110＞织构组分的体积分数由表及里先下降后升高,在中心层达到最大.     

Delamination of Pearlitic Steel Wires: The Defining Role of Prior-Drawing Microstructure

This article reports the occasional (< 10 pct of the actual production) delamination of pearlitic wires subjected to a drawing strain of ~ 2.5. The original wire rods which exhibited post-drawing delamination had noticeably lower axial alignment of the pearlite: 22 ± 5 pct vs 34 ± 4 pct in the nondelaminated wires. Although all wires had similar through-thickness texture and stress gradients, delaminated wires had stronger gradients in composition and higher hardness across the ferrite–cementite interface. Carbide dissolution and formation of supersaturated ferrite were clearly correlated with delamination, which could be effectively mitigated by controlled laboratory annealing at 673 K. Direct observations on samples subjected to simple shear revealed significant differences in shear localizations. These were controlled by pearlite morphology and interlamellar spacing. Prior-drawing microstructure of coarse misaligned pearlite thus emerged as a critical factor in the wire drawing-induced delamination of the pearlitic wires.     

Microstructures and Mechanical Properties of as-Drawn and Laboratory Annealed Pearlitic Steel Wires

Near eutectoid fully pearlitic wire rod (5.5 mm diameter) was taken through six stages of wire drawing (drawing strains of 0 to 2.47). The as-drawn (AD) wires were further laboratory annealed (LA) to re-austenitize and reform the pearlite. AD and LA grades, for respective wire diameters, had similar pearlite microstructure: interlamellar spacing (λ) and pearlite alignment with the wire axis. However, LA grade had lower hardness (for both phases) and slightly lower fiber texture and residual stresses in ferrite. Surprisingly, essentially identical tensile yield strengths in AD and LA wires, measured at equivalent spacing, were found. The work hardened AD had, as expected, higher torsional yield strengths and lower tensile and torsional ductilities than LA. In both wires, stronger pearlite alignment gave significantly increased torsional ductility.     

Pearlitic Transformations in an Ultrafine-Grained Hypereutectoid Steel

Common steels of both hypo- and hypereutectoid compositions form pearlitic or martensitic constituents when cooled from austenite temperature in air or in water. Here, we provide evidence that this is not the case in an ultrafine-grained hypereutectoid steel. In this system, when the grain size was reduced to a scale of 2 to 4 μm, normal pearlite could not be obtained when the steel was cooled in air; instead, nanometer-sized granular cementite and ferrite were formed in the eutectoid transformation. When the cooling rate was increased by quenching in saltwater, martensite was no longer formed; instead, fine lamellar pearlite was formed. This research indicates that these abnormal phase transformations were related to the rapid diffusion present in the ultrafine-grained steel, which changed the diffusive transformations.     

Cyclic Deformation Microstructure in Heavily Cold-Drawn Austenitic Stainless Steel

Cyclic deformation microstructure of the heavily cold-drawn austenitic stainless steel is significantly influenced by the spacing between mechanical twins introduced by prior cold drawing. Well-developed dislocation cells form between mechanical twins with the spacing larger than about 800 nm. Persistent slip band (PSB)-like structure with ladders takes place between mechanical twins spacing from 300 to 800 nm. Few dislocations occur between neighboring mechanical twins with spacing less than about 100 nm. Pre-existing mechanical twins and deformation bands segment austenitic grains, facilitating multi-slip and consequently suppressing PSB formation.     

Evolution of the Defect Structure of Pearlitic Steel in Cold Deformation

A method of microdiffraction analysis is developed in order to determine the defect structure of pearlitic steels during cold plastic deformation. The total reduction in the drawing of C86D steel coil is shown to affect the azimuthal blurring of the subreflexes in the microdiffraction pattern and the distortion of the plates in the pearlite colony.     

Texture and Microstructural Evolution in Pearlitic Steel During Triaxial Compression

This article presents the deformation behavior of high-strength pearlitic steel deformed by triaxial compression to achieve ultra-fine ferrite grain size with fragmented cementite. The consequent evolution of microstructure and texture has been studied using scanning electron microscopy, electron back-scatter diffraction, and X-ray diffraction. The synergistic effect of diffusion and deformation leads to the uniform dissolution of cementite at higher temperature. At lower temperature, significant grain refinement of ferrite phase occurs by deformation and exhibits a characteristic deformation texture. In contrast, the high-temperature deformed sample shows a weaker texture with cube component for the ferrite phase, indicating the occurrence of recrystallization. The different mechanisms responsible for the refinement of ferrite as well as the fragmentation of cementite and their interaction with each other have been analyzed. Viscoplastic self-consistent simulation was employed to understand deformation texture in the ferrite phase during triaxial compression.     

Fracture Characteristics of Fully Pearlitic Steel Wire in Tension and Torsion

The fracture characteristics of fully pearlitic steel wires with fine and randomly oriented lamellae have been investigated after tension and torsion,respectively.It is found that the predominant fracture mode under small predeformation is dimple.The analysis of the colony size and the lamellar structure near the fracture surface indicates that each dimple roots from one colony.A simulation of tensile deformation with several pearlitic colonies based on the real scanning electron microscopy(SEM)observation shows that the plastic deformation concentrates and the stress traxiality is larger at the boundaries of colonies.It demonstrates the microcracks initialize at colony boundaries.Thus,the colony size is a significant factor for fracture behaviors under small pre-deformation.On the other hand,the fracture surface is investigated after large pre-deformation via torsion.The results show that fracture characteristics vary with radius from dimples,elongated dimples to the fibrous structure.It indicates that the fracture characteristics are dependent on the pre-deformation.The fracture mode under large pre-deformation becomes an anisotropic fibrous structure instead of dimples.     

Cold-Drawn Bioabsorbable Ferrous and Ferrous Composite Wires: An Evaluation of Mechanical Strength and Fatigue Durability

Yield strengths exceeding 1 GPa with elastic strains exceeding 1 pct were measured in novel bioabsorbable wire materials comprising high-purity iron (Fe), manganese (Mn), magnesium (Mn), and zinc (Zn), which may enable the development of self-expandable, bioabsorbable, wire-based endovascular stents. The high strength of these materials is attributed to the fine microstructure and fiber textures achieved through cold drawing techniques. Bioabsorbable vascular stents comprising nutrient metal compositions may provide a means to overcome the limitations of polymer-based bioabsorbable stents such as excessive strut thickness and poor degradation rate control. Thin, 125-μm wires comprising combinations of ferrous alloys surrounding a relatively anodic nonferrous core were manufactured and tested using monotonic and cyclic techniques. The strength and durability properties are tested in air and in body temperature phosphate-buffered saline, and then they were compared with cold-drawn 316L stainless steel wire. The antiferromagnetic Fe35Mn-Mg composite wire exhibited more than 7 pct greater elasticity (1.12 pct vs 1.04 pct engineering strain), similar fatigue strength in air, an ultimate strength of more than 1.4 GPa, and a toughness exceeding 35 mJ/mm³ compared with 30 mJ/mm³ for 316L.     

高碳珠光体钢在温变形过程中的组织变化

用SEM、TEM等方法研究了一种原始组织为层片状珠光体的高碳钢在多向温变形(楔横轧)和单向温变形(压缩)条件下试样心部与表层显微组织的演变情况.结果表明,在多向温变形条件下,试样表层可获得铁素体晶粒与渗碳体颗粒尺寸均在0.3 μm以下的超微细(α θ)复相组织,心部渗碳体片虽已碎断并部分球化,但其排布形态与变形珠光体基本保持一致,而单向温变形条件下的情况则恰好相反;变形过程中试样所受应力、应变状态的不同是引起组织差异的根本原因.     

Influence of Microstructure on the Mechanical Properties of a Pearlitic Steel

Metallurgical and Materials Transactions A - The effect of austenite grain size on microstructure and mechanical properties was studied for a pearlitic steel. The best combination of ultimate...     

钛脱氧钢中针状铁素体的形成

通过实验研究了钢中加钛脱氧后针状铁素体的形成及夹杂物的变化。对实验钢的化学成分、组织变化、析出相成分、钢中氧含量及夹杂物尺寸进行了分析。实验证明,在钢中加钛处理后,钢中产生了大量的以钛氧化物或钛铝等复合氧化物为核心的针状铁素体,钢的组织明显细化,随着钛加入后孕育时间的延长,钢中夹杂物的尺寸变小,孕育时间存在最佳值。     

珠光体耐热钢顶杆焊接工艺研究

12CrMoV珠光体耐热钢顶杆在制作过程中,采用V型坡口焊条电弧焊、水平固定全位置对接接头焊接,焊接性差,焊接难度大,通过规范焊接工艺和焊接质量控制,有效避免了未焊透、夹渣、裂纹等缺陷,保证了焊接质量.     

Characteristics of Strain-Induced Ferrite in Low Carbon Steel

Itiswellknownthatthestrain inducedtrans formationfromaustenitetoferritecanleadtograinrefinement .Thushighermechanicalpropertiessuchasstrengthandductilitycanbeobtained[1,2 ] .Someresearcheshavebeencarriedoutonthenucleationofstrain inducedferriteinthepastyears .PDHodgsonetalsuggestedthattheaustenitegrainsshouldbeascoarseaspossibletodecreasenucleationatgrainbo undaries[3 ] .PJHurleyetalconsideredthatthecel lularboundaryofdislocationsuppliesthesitesfornu cleationofstrain inducedferrite[4] .Yang…     

Fine Microstructure of Bainitic Ferrite in Bainitic Steel

Asbainiticsteelspossesshighhardness ,highstrength toughness ,highwearresistanceandhighhardenability ,theacademicandengineeringcircleshavepaidcloseattentiontotheinvestigationoffinemicrostructure[1,2 ] .However ,thefinemicrostruc tureofbainiticsteelsisnotdeterminedyet .Thefinemicrostructuresofmediumandmedium highcarbonbainiticsteelswereobservedandanalyzedbyhighresolutionelectronmicroscope (HREM ) ,andthere sultsshowthatthereareretainedausteniticfilmsatdifferentlevelstructureunitboundaries .The…