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.     

φ5.35mm-2100MPa桥梁用锌铝钢丝的工艺与组织性能

 为了制备更高强度级别的桥梁缆索用热镀锌铝钢丝，通过对高碳钢盘条的成分设计、低损伤拉拔技术以及热浸镀锌铝等工艺过程的优化，成功试制出?5.35 mm-2 100 MPa级桥梁缆索用热镀锌铝钢丝。设计的SWRS92Si盘条主要成分为（质量分数）：C 0.90%～0.95%，Si 0.8%～1.1%，Cr 0.20%～0.30%。试制结果表明，?13 mm-SWRS92Si盘条经铅浴处理后，珠光体层片平均尺寸从120下降至90 nm，盘条强度上升约260 MPa。经冷拉拔与热镀锌铝后，层片宽度约40 nm的珠光体层片未明显球化，可制备出2 100 MPa级直径5.35 mm的桥梁缆索用热镀锌铝钢丝。钢丝的平均抗拉强度为2 128 MPa，平均断后伸长率为5.4%，扭转圈数平均值为22圈，断口均为平断口，镀层较均匀致密；其他性能指标均优于交通部标准JT/T 1104—2016《桥梁用热镀锌铝合金钢丝》中的要求。     

Microstructural Engineering in Eutectoid Steel: A Technological Possibility?

Eutectoid wire rods were subjected to controlled thermo-mechanical processing (TMP). Both increased cooling rate and applied stress during the austenite-to-pearlite decomposition produced significant changes in the microstructure: major increases in the pearlite’s axial alignment and minor decreases in the interlamellar spacing. The pearlite alignment was correlated with changes in the ferrite crystallographic texture and the state of residual stress. Microstructural engineering, improved axial alignment of pearlite, through controlled TMP gave a fourfold increase in torsional ductility. TMP of eutectoid steel thus appears to have interesting technological possibilities.     

Optimization of mechanical properties of high-carbon pearlitic steels with Si and V additions

Systematic research has been undertaken on the effects of single and combined additions of vanadium and silicon on the mechanical properties of pearlitic steels being developed for wire rod production. Mechanical test results demonstrate that the alloy additions are beneficial to the mechanical properties of the steels, especially the tensile strength. Silicon strengthens pearlite mainly by solid-solution strengthening of the ferrite phase. Vanadium increases the strength of pearlite mainly by precipitation strengthening of the pearlitic ferrite. When added separately, these elements produce relatively greater strengthening at higher transformation temperatures. When added in combination the behavior is different, and substantial strength increments are produced at all transformation temperatures studied (550 °C to 650 °C). The addition of silicon and vanadium to very-high-carbon steels (>0.8 wt pct C) also suppresses the formation of a network of continuous grain-boundary cementite, so that these hypereutectoid materials have high strength coupled with adequate ductility for cold drawing. A wire-drawing trial showed that total drawing reductions in area of 90 pct could be obtained, leading to final tensile strengths of up to 2540 MPa in 3.3-mm-diameter wires.     

Effect of cementite morphology on pearlitic wire drawing deformation

A comparative study was conducted on the effects of lamellar cementites and globular cementites on the cold drawing process and the mechanical properties of pearlitic wire steel, with the help of metallographic microscope, scanning electron microscope, transmission electron microscope, tensile tester and hardness tester. The lamellar cementites showed the deformation capacity to some extent during the cold drawing process. As the drawing strain increased, the pearlitic wire with globular cementites evolved into the fibrous form gradually and no obvious defects were found in the microstructure. The globular cementites turned to the drawing direction without any deformation of itself during the deformation process. And micro- cracks occurred in the cementite/ferrite interface due to stress concentration caused by pinning dislocations in spherical cementites. The strength and hardness of both pearlitic wires gradually increased as the drawing strain rose. And the pearlitic wire with lamellar cementites had a higher drawing hardening rate. The ferrite <110> texture formed in both pearlitic wires during the cold drawing process. Compared with the globular pearlite, the pearlitic wire with lamellar cementites had higher ferrite <110> texture intensity. And the difference of their ferrite <110> texture intensity became bigger and bigger as the drawing strain increased.     

Pearlite in ultrahigh carbon steels: Heat treatments and mechanical properties

Two ultrahigh carbon steel (UHCS) alloys containing 1.5 and 1.8 wt pct carbon, respectively, were studied. These materials were processed into fully spheroidized microstructures and were then given heat treatments to form pearlite. The mechanical properties of the heat-treated materials were evaluated by tension tests at room temperature. Use of the hypereutectoid austenite-cementite to pearlite transformation enabled achievement of pearlitic microstructures with various interlamellar spacings. The yield strengths of the pearlitic steels are found to correlate with a predictive relation based on interlamellar spacing and pearlite colony size. Decreasing the pearlite interlamellar spacing increases the yield strength and the ultimate strength and decreases the tensile ductility. It is shown that solid solution alloying strongly influences the strength of pearlitic steels.     

合金元素钒对高碳钢丝组织与性能的影响

 钒对高碳钢丝的微观组织、力学性能及热稳定性具有显著的影响。钒元素在高碳钢中主要存在于渗碳体中,可以起到强化渗碳体的作用。添加钒元素有利于珠光体片层间距的细化,还可以增加渗碳体的热稳定性,从而抑制钢丝拉拔过程中渗碳体的分解。但在拉拔应变量较大时,富含钒的渗碳体片碎化严重,会加重钢丝在镀锌过程中的球化现象,而导致钒合金化钢丝与未添加钒元素的钢丝相比,无论镀锌与否,其扭转性能均明显下降。     

The micro structure of high carbon low alloy steel for easy drawing

For better processing performance of high carbon low alloy steel wire rod,an investigation about the influence of cementite lamellar spacing on wire ’easy drawing’ performance is completed.It is pointed out that too thin cementite lamellar spacing(<80 um) reduces the strain hardening level of wire drawing, and reduce the torsion performance of drawn wire at same time.For the wire or wire rod from industrial production,compared with the micro-structure with troostite,the micro-structure with sorbite or sorbite mixed with pearlite is more suitable to the drawing process with high reduction ratio.     

Preliminary evaluation of tensile and stress-rupture behavior of W + 24 At. Pct Re + 0.4 At. Pct HfC wire

The tensile properties of hafnium carbide-dispersed tungsten-rhenium alloy wire, W + 24 at. pct Re + 0.4 at. pct HfC (W24ReHfC), were studied from liquid nitrogen temperature (LN₂) to 1750 K and its stress-rupture behavior determined from 1144 to 1500 K. These results are compared to previous data on W + 4 at. pct Re + 0.4 at. pct HfC (W4ReHfC) and W + 0.4 at. pct HfC (WHfC) wire.[5] The room-temperature (RT) tensile strength of the W24ReHfC wire was about 3250 MPa and higher than that of the W4ReHfC (3160 MPa) and WHfC (2250 MPa) wires. The RT ductility of the W24ReHfC wire was quite high with a 50 pct reduction of area, whereas the W4ReHfC wire and the WHfC wire had RT ductilities of 28 and 2 pct, respectively. At temperatures of 1144 to 1366 K, the W24ReHfC wire had tensile strengths favorably comparable to the W4ReHfC and WHfC wires. However, above 1366 K, the W4ReHfC wire had both a greater tensile strength and stress-rupture strength than the W24ReHfC wire. The main contributions to the strengthening of the W24ReHfC wire were the fine and elongated fibrous grain microstructures and the dispersion of the HfC particles in the W-Re matrix. These properties suggested that the W24ReHfC wires hold promise as potential fiber reinforcements in composites from RT to about 1350 K.     

0.88C-1.2Si-0.75Mn-2Al高强度电缆铠装钢用盘条的试制

采用中高碳成分添加低密度元素Si、Al进行轻量化的设计思路设计了试验钢的化学成分,试验钢采用50 kg真空感应炉冶炼。利用金相显微镜、SEM扫描电镜和力学性能检测设备对试制后的Φ6 mm盘条进行了显微组织观察、珠光体片层间距的测量和屈服强度、抗拉强度、延伸率的检验。结果表明:盘条在600℃等温2 h后的金相显微组织为铁素体+珠光体的混合组织,珠光体的片层间距为(126±5) nm,屈服强度大于1 183 MPa、抗拉强度大于1 425 MPa、延伸率大于10%,其力学性能满足电缆用铠装钢的技术要求。     

82B高速线材拉拔过程中显微组织的演变分析

借助扫描电子显微镜(SEM)观察分析研究了82B线材在拉拔过程中显微组织和芯部马氏体的演变规律。分析认为:由于索氏体属于细片状珠光体,拉拔变形时,承受滑移的铁素体相不易引起应力集中;渗碳体相为细薄片层形态,也能够发生塑性变形,经过多道次的拉拔,索氏体基体变形量较大,没有出现任何裂纹。而芯部由偏析形成的马氏体,其塑性变形能力明显低于索氏体,基本无变形,在基本拉应力和附加拉应力的共同作用下,在早期拉拔时就在芯部出现裂纹,在后期拉拔过程中,裂纹沿着拉拔方向不断扩展。为减少断丝,可采用加大吹风量、扩大连铸坯、控制钢水过热度、增加电磁搅拌等工艺,来提高索氏体含量和细化渗碳体片层及预防马氏体的形成,以提高拉拔性能。     

Wrought aluminum-nickel alloys for high strength-high conductivity applications

Aluminum-Nickel alloys ranging from 0.06 pct to 6.1 pct (by wt) Ni have been developed for high strength-high conductivity applications. These alloys were produced by solidification in a permanent mold followed by homogenization, hot extrusion or hot rolling and cold drawing to wire form. This sequence of fabrication a) led to the production of fine fibrous dispersoids of NiAl₃ as part of the Al-NiAl₃ eutectic during the initial casting operation, b) permitted the retention of fine fibrous dispersiods of NiAl₃ produced during casting without any significant coarsening during processing and c) led to uniform dispersion and general alignment of these fibrous dispersoids along a given direction in the product without any measurable fiber-matrix separation, extensive fiber-fragmentation or crack production in the matrix. These alloys can be processed to wire form as easily as aluminum and when processed by the above sequence, possess very attractive combination of high strength-high electrical conductivity. Tensile strengths range from 173 N/mm² (at 0.6 pct Ni) to 241 N/mm² (at 6.1 pct Ni) in combination with corresponding conductivity values between 62 pct IACS and 55.5 pct IACS. The wires also possess attractive yield strength; for instance, the 0.2 pct off-set strength of Al-6.1 pct Ni wire is 213 N/mm². Using simple composite rules, the estimated strength and the conductivity of NiAl₃ fibers were found to be 1380 N/mm² and 18 pct IACS respectively, in these wires.     

Wrought aluminum-nickel alloys for high strength-high conductivity applications

Aluminum-Nickel alloys ranging from 0.06 pct to 6.1 pct (by wt) Ni have been developed for high strength-high conductivity applications. These alloys were produced by solidification in a permanent mold followed by homogenization, hot extrusion or hot rolling and cold drawing to wire form. This seguence of fabrication a) led to the production of fine fibrous dispersoids of NiAl₃ as part of the Al-NiAl₃ eutectic during the initial casting operation, b) permitted the retention of fine fibrous dispersiods of NiAl₃ produced during casting without any significant coarsening during processing and c) led to uniform dispersion and general alignment of these fibrous dispersoids along a given direction in the product without any measurable fiber-matrix separation, extensive fiber-fragmentation or crack production in the matrix. These alloys can be processed to wire form as easily as aluminum and when processed by the above sequence, possess very attractive combination of high strength-high electrical conductivity. Tensile strengths range from 173 N/mm² (at 0.6 pct Ni) to 241 N/mm² (at 6.1 pct Ni) in combination with corresponding conductivity values between 62 pct IACS and 55.5 pct IACS. The wires also possess attractive yield strength; for instance, the 0.2 pct off-set strength of Al-6.1 pet Ni wire is 213 N/mm². Using simple composite rules, the estimated strength and the conductivity of NiAl₃ fibers were found to be 1380 N/mm² and 18 pct IACS respectively, in these wires.     

Deformation of pearlite

Pearlite with its lamellae oriented mainly parallel to the longitudinal direction was prepared by Bolling's method of transformation in a steep temperature gradient. The Fe-0.7 pct Mn-0.9 pct C pearlite was drawn into wire and also into strip in dies designed to minimize macroscopically nonuniform deformation. Cross sections of the drawn wires and strip were examined by conventional and high-voltage transmission electron microscopy and were analyzed by quantitative metallography for a) average interlamellar spacing, b) distribution of interlamellar spacings, and c) orientation relationship between the cementite lamellae and the slip systems in the ferrite. The strength of pearlite is proportional to the reciprocal square root of the average interlamellar spacing, and the proportionality constant analogous to the Hall-Petch constant (k) is related to the strength of the cementite lamellae. If the stress for the propagation of slip through the cementite is assumed constant, a Hall-Petch type of equation can be derived for the strengthening of the pearlite against slip in the ferrite by piled-up groups of dislocations. Evidence for the plastic deformability of cementite is presented; sufficiently thin cementite plates were fully plastic. The exponential strain hardening of drawn pearlitic wires and of rolled pearlite is explained in terms of locally inhomogenous deformation revealed by the lack of fragmentation of the lamellae. This paper is based on a presentation made at a symposium on “Mechanical-Thermal Processing and Dislocation Substructure Strengthening,” held at the Annual Meeting in Las Vegas, Nevada, on February 23, 1976, under the sponsorship of the TMS/IMD Heat Treating Committee.     

ER50-6盘条拉拔开裂原因分析

低合金焊接用钢盘条在拉拔过程中有时出现劈裂现象,为找出其原因,对每一道次的钢丝取样进行金相分析,发现劈裂钢丝对应的盘条和半成品钢丝中都存在严重的横向珠光体带状偏析,且盘条的横向带状偏析与连铸坯的内部裂纹有很好的对应关系,盘条中存在的严重横向带状偏析是造成钢丝劈裂的主要原因。     

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In order to find out the differences between domestic and imported LX80B steel wire rods, intrinsic quality and mechanical properties were studied by OM, SEM, EPMA, tensile testing machine and other instruments. The results show that the quantity of brittle non-metallic inclusions of domestic steel wire rods is 5 times as many as imported steel wire rods. The serious carbon segregation in domestic steel wire rods results in delamination fracture during twisting. The oxide scales of domestic and imported steel wire rods are composed of inner layer (Fe1-yO) and outer layer (Fe3O4), yet the thickness of oxide scale for domestic ones is smaller than that of imported ones. The microstructure of domestic ones is composed of proeutectoid cementite and pearlite, while that of imported ones is mainly pearlite. The large variation of lamellar spacing of pearlite results in a large variation of mechanical properties of domestic ones.     

82B钢的微合金化-相变控制与生产实践

为了优化82B钢的成分和热轧冷却工艺,以提高82B盘条的强度,测定了80钢和82B钢的等温转变温度对相变时间、珠光体片层间距的影响以及Cr元素对82B相变温度的影响,分析了Cr合金化和相变控制对82B盘条的微观组织和抗拉强度的影响。对于82B,当温度在595～615℃相变速度最快,其转变时间为10～15s,在590～625℃可得到理想的0.10～0.20μm的珠光体片层间距;通过添加0.18%～0.24%Cr和控制热轧冷却速度,可以控制82B钢的相变温度区间和相变速度,得到均匀细片状的珠光体组织;将Φ12.5mm 82B盘条的主要成分调整为0.78%～0.84%C、0.15%～0.35%Si、0.78%～0.88%Mn和0.18%～0.24%Cr;在热轧控冷过程中,弱化水冷,强化风冷,控制82B盘条的吐丝温度为840～880℃,目标值860℃,增大82B盘条在风冷线上的冷速,提高了盘条的强度。     

Prediction of mechanical behavior of ferrite-pearlite steel

A new approach describing the flow stress of ferrite-pearlite steel has been proposed,which divided the deformation process into three stages based on whether ferrite or pearlite yielded.Isowork increment assumption was applied to describe the transfer of load between the components.The physically based model to describe ferrite was approximated with Swift's equation in order to obtain the analytic solution.The tensile strength of ferrite-pearlite had a linear relation with pearlite volume fraction,square root reciprocal of ferrite grain size and reciprocal of pearlite interlamellar spacing.Moreover,a model to calculate the tensile strength of ferrite-pearlite steel was proposed.The predicted values of tensile strength were in good agreement with experimental results when the pearlite volume fraction was less than 20％.Considering the plastic relaxation mechanisms,the internal stress was modified with pearlite volume fraction,total strain,yield stress of ferrite and pearlite when the pearlite volume fraction was more than 20％.     

大应变变形珠光体钢丝微观组织结构的研究

  采用扫描电镜（SEM）观察了以不同应变量拉拔变形后SWRH72A钢丝的显微组织变化,并测量了钢丝力学性能、磁学性能随应变量增大的变化趋势。试验结果表明,随着拉拔变形应变量的增大,珠光体片层间距逐渐减小,钢丝强度随之升高。由于变形应变量的增大,微缺陷密度升高,钢丝矫顽力Hc和剩余磁化强度Mr都随之变大。而应变量较小时,钢丝比饱和磁化强度基本不变,为227.87 emu/g。当应变量增大到2.60时,样品的比饱和磁化强度升高到233.55 emu/g,计算得知钢丝中渗碳体的质量分数由未变形状态的10.8%降至8.6%。     

高碳钢线材组织和屈服强度关系的数学模型

通过光学和扫描电子显微镜,运用定量金相技术,分析计算高碳钢(%:0.56～0.63C、0.60～0.71Mn、0.23～0.28Si)铁索体含量和珠光体片间距,建立高碳钢线材的组织和屈服强度(σ_s)之间关系的数学模型:σ_a(Pa)=104.52×10^-6+161.70(1-f_a^1/3)S^-1(m),其中fa~-铁素体的体积百分数,S-珠光体的片层间距。模型的计算值与实验值的相对误差为2.9%。