The Influence of Abnormal Segregation Band on Mechanical Properties of Hot Rolled Ferrite/Pearlite Steel Plate

In order to further reveal the influence of abnormal segregation band on mechanical properties of hot rolled ferrite/pearlite steel plate, especially on laminated tensile fracture, the experimental method of delamination tension was adopted. In this paper, the thin tensile samples with 3 mm thickness from the surface, 1/4 positions and center along the thickness orientation of test plate were measured, also the relationship between microstructure and mechanical properties was probed. The results show that the center region of hot rolled ferrite/pearlite steel plate exists granular bainite and ferrite mixed grains, which leads to lower plasticity and toughness of this region. During the tensile process, microcracks are generated and extended at the center of steel plate due to the inconsistency of deformation and fracture on the adjacent structures, finally leading to laminated fracture of steel plate.

Predication of Plastic Flow Characteristics in Ferrite/Pearlite Steel Using a Fern Unit Cell Method

The flow stress of ferrite/pearlite steel under uni-axial tension was simulated with finite element method (FEM) by applying commercial software MARC/MENTAT. Flow stress curves of ferrite/pearlite steels were calculated based on unit cell model. The effects of volume fraction, distribution and the aspect ratio of pearlite on tensile properties have been investigated.

Surface Ferrite Grain Refinement and Mechanical Properties of Low Carbon Steel Plates

Considering the specialities of the steel plate production, the TMCP study has been carried out with Gleeble 2000 tester to explore the possibility of fine grained ferrite in the low carbon steel plates with the chemical composition of C 0.13--0.18, Si 0.12-0.18, Mn 0.50-0. 65, P 0. 010-0. 025, and S 0. 005-0. 028. The plates with thickness of 8. 7 mm in which the ferrite grain size is smaller than 8μm have been produced by special de- formation process in the laboratory. Furthermore, the trial production of special plain carbon steel plates of 16-25 mm in thickness and 2 000- 2 800 mm in width with fine grained ferrite has been successfully carried out in the Shougang Steel Plate Rolling Plant. The ferrite grain size is 5.5-7μm in the surface layers and 9.5-15μm in the central layer respectively. The yield strength is 320- 360 MPa, tensile strength is 440-520 MPa and the elongation is 25%- 34 %. It is very important for the rolling plants to improve the low carbon steel plates＇ mechanical properties. The results show that the ferrite grains in the surface layer can be refined effectively by the appropriate rolling process, and the strength can be also increased.

Characteristic of Near-surface Microstructure and Its Effects on the Torsion Performance of Cold Drawn Pearlitic Steel Wires for Bridge Cables

The characteristic of near-surface microstructure and its effects on the torsion performance of cold-drawn pearlitic steel wires for bridge cables were investigated by focused ion beam-scanning electron microscope,transmission electron microscopy and differential scanning calorimetry.The samples with similar tensile strength before and after hot-dip galvanizing process are,respectively,characterized as delaminated and non-delaminated in torsion test which indicates that the tensile strength is independent of the toughness value(i e,reduction area and torsion ability).It is interesting to find that there exists submicron granular ferrite on near-surface of the wires,which can be attributed to dislocation rearrangement and sub-grains rotation during cold drawing and hot-dip galvanizing process.And their distribution can suggest homogeneousness of deformation degree to a certain extent:the closer to the surface of their distribution,the more homogeneous deformation of the wires.There is a close relationship between the thermal stability of the cementite layer and distribution of granular ferrite:differential scanning calorimetry(DSC)analysis shows that the sample is accompanied by submicron granular ferrite which is located closer to the surface has higher thermal stability under galvanizing temperature(450°C).A new mechanism of the torsion delamination of pearlitic steel wires is discussed in terms of the thermal stability of the cementite layer and distribution of granular ferrite.

Hydrogen-assisted fracture features of a high strength ferrite-pearlite steel

Up to now, the exact reason of hydrogen-induced fracture for ferrite-pearlite(FP) steel is still not fully understood. This study presents detail observations of the feature beneath the fracture surface with the aim to reveal the hydrogen-induced cracking initiation and propagation processes. Slow strain rate tensile(SSRT) testing shows that the FP steel is sensitive to hydrogen embrittlement(HE). Focused ion beam(FIB)was used to prepare samples for TEM observations after HE fracture. The corresponding fractographic morphologies of hydrogen charged specimen exhibit intergranular(IG) and quasi-cleavage(QC) fracture feature. Pearlite colony, ferrite/pearlite(F/P) boundary and the adjacent ferrite matrix are found to be responsible for the initial HE fracture and the subsequent propagation. With increasing of the stress intensity factor, fracture mode is found to change from mixed IG and QC to entire QC feature which only occurs at the ferrite matrix. No crack is observed at the ferrite/cementite(F/C) interface. This may be mainly due to the limited pearlite lamella size and relatively low interface energy.

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. Iso-work 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%.

高性能特厚板的研发

现有特厚板强度较低,低温韧性较差。研发了一种碳质量分数为0.065%的120 mm特厚钢板。研究了轧制加热温度和非再结晶区轧制总压下率对钢板奥氏体晶粒尺寸、显微组织和力学性能的影响。结果表明:在1200℃以下加热的钢板奥氏体晶粒长大不明显;在1250℃加热的钢板奥氏体晶粒平均尺寸为111μm,最大为295μm;随着非再结晶区轧制总压下率的增大,钢板铁素体增多,组织细化。通过控制加热温度和非再结晶区轧制总压下率试制的120 mm厚钢板屈服强度大于390 MPa,抗拉强度大于510 MPa,-60℃冲击吸收能量大于200 J,表面和表面以下50 mm处韧-脆转变温度低于-80℃。

436L铁素体不锈钢换热板片的成形过程及分析

针对436L铁素体不锈钢换热板片冲压成形的开裂问题,通过Dynaform数值模拟分析和冲压成形试验,对两种典型波纹结构换热板片的成形特征进行研究,分析其成形过程中的成形极限和减薄率的演变规律,研究板片厚度和波纹参数(波纹法向节距)对裂纹位置及开裂程度的影响,探讨波纹法向节距对减薄率的影响。结果表明,436L铁素体不锈钢换热板片的开裂和减薄同时受板厚及波纹参数的影响。对于浅波纹换热板片(波纹深度2 mm),易开裂处为波纹的波峰圆角顶部,板厚增加对开裂倾向和减薄率影响显著,每增加0.1 mm板材厚度,波峰圆角处最大减薄率可降低约2.6%,此时,能够安全成形的最大减薄率为18.9%,最小成形板厚为0.6 mm。而对于深波纹换热板片(波纹深度2.6 mm),易开裂处为波纹的波峰圆角两侧和波峰圆角顶部,此时,板厚增加对开裂倾向和减薄率影响较小,每增加0.1 mm板材厚度,波峰圆角处最大减薄率仅降低约1.4%,需通过增大波纹法向节距满足成形质量要求。

Effect of Mg addition on formation of intragranular acicular ferrite in heat-affected zone of steel plate after high-heat-input welding

The effects of Mg content, inclusion size, and austenite grain size on the intragranular acicular ferrite （IAF） nucleation in heat-affected zone of steel plate after high-heat-input welding of 400 kJ/cm were investigated by welding simulation and observation using a scanning electron microscope equipped with an energy dispersive spectrometer and an optical microscope. The IAFs are observed in steel with Mg addition, and the volume fraction of IAF is as high as 55.4% in the steel containing 0.0027 mass% Mg. The MgO-Al2O3-Ti2O3-MnS inclusions with size around 2 μm are effective nucleation sites for IAF, whereas Al2O3-MnS inclusions are impotent to nucleate the acicular ferrite. The prior-austenite grain （PAG） size distribution in low Mg steel is similar to that in steel without Mg addition. The austenite grain with size about 200 μm is favorable for the IAF formation. In the steel with high Mg content of 0.0099%, the growth of PAG is greatly inhibited, and PAG sizes are smaller than 100 μm. Therefore, the nucleation of IAF can hardly be observed.

变形温度对45#精冲钢组织演变的影响

利用热模拟单道次压缩实验研究了45#钢在不同温度变形过程中微观组织的演变规律。通过对变形过程中组织形貌的观察和应力-应变曲线的分析,讨论了变形过程中的相变行为和软化过程。结果显示,实验钢在热变形过程发生铁素体(DIF)和珠光体(DIP)两种形变诱导相变,Ar3温度以上变形时,主要发生形变诱导铁素体相变,伴随少量珠光体生成,并且随着变形温度的降低铁素体增加,珠光体略微降低;Ar3温度以下变形时,形变诱导珠光体逐渐取代铁素体,且随温度的变化趋势相反。低温变形时,形变诱导相变是软化的主要原因,高温变形时主要发生动态再结晶,导致软化,并且动态再结晶的软化作用要比形变诱导相变的好。

铁素体/珠光体组织对管线钢中氢扩散行为的影响

长距离管道输送是氢气输送的重要发展方向之一。氢在管线钢的扩散和局部聚集导致材料力学性能下降,在外界作用下引发脆性失效。因此,氢在管线钢材中的扩散和富集是评价管线钢相容性与判断管道升级可行性的重要参考依据。以三种不同等级的管线钢(X52,X65,X70)共22种材料为研究对象,结合图像处理技术与基于材料内铁素体/珠光体组织结构的连续介质数值计算,推算长期服役后结构内部氢的扩散和富集。考虑到铁素体和珠光体组织中的氢扩散速率与晶界的扩散阻碍作用,通过对比量化不同铁素体/珠光体的结构分布和组织取向下氢质量浓度和扩散通量的差异,分析铁素体/珠光体组织对管线钢中氢的扩散和富集作用,为长距离输氢管道材料选用提供技术参考。

超高强抗震钢筋弯曲断裂原因

超高强抗震钢筋在进行弯曲试验时发生断裂。采用宏观观察、化学成分分析、扫描电镜分析、金相检验、中心偏析检验等方法,对弯曲试样断裂的原因进行分析。结果表明:热轧前加热温度较高,变形后奥氏体晶粒长大,使得珠光体团尺寸增大、珠光体含量增多;冷却缓慢导致网状铁素体沿奥氏体晶界析出,使材料的塑性和韧性下降,最终导致试样在弯曲试验时发生断裂。

铁素体钢薄板对接焊缝相控阵超声检测标准分析

为推动相控阵超声检测技术在核电厂铁素体钢薄板对接焊缝上的工程应用,对国、内外适用于铁素体钢薄板对接焊缝相控阵超声检测技术标准的主要内容进行了分析,ISO 13588—2019、DL/T 1718—2017和NB/T 47013.15—2021比较适合作为核电厂薄板对接焊缝相控阵超声检测的参考标准,核电厂铁素体钢薄板对接焊缝相控阵超声检测应用可参考NB/T 47013.3—2015检测灵敏度和验收标准要求。该结论可为核电厂铁素体钢薄板对接焊缝相控阵超声检测技术的工程应用提供参考。

焊接参数对409L热轧板拼焊接头组织的影响

使用太钢不锈冷轧厂的焊接机组对10 mm厚的409L热轧板进行了焊接试验,将坡口间隙分别设置为1 mm、2 mm、3 mm、4 mm,焊接参数随之微调,焊后对焊接接头进行金相组织分析。结果表明:坡口间隙从1 mm调整至4 mm,焊接参数变化不大,热输入增加了约17%。这四组焊接参数的焊接HAZ宽度差别不大,高热输入下焊接HAZ的晶粒粗化程度略有增加;坡口间隙为1 mm时,焊缝下半部分出现了未熔合缺陷,会严重影响焊接接头的力学性能,导致过线时开裂,甚至发生断带事故。

普通C-Mn钢超细晶中厚板的带状组织

采用Gleeble2000热模拟试验机研究了普通C-Mn钢的再结晶规律,在实验室轧机上进行了C-Mn钢超细晶中板的轧制,并且在首钢中厚板厂工业轧机上进行了超细晶中厚板的工业试制,研究了工艺条件对中厚板带状组织的影响,分析了带状组织产生的机理.研究结果表明,在靠近静态相变温度Ara附近的未再结晶区进行大变形量轧制(形变诱导相变),不仅可以使板材的铁素体晶粒细化甚至获得超细晶组织,而且普通C-Mn钢中厚板中的带状组织减轻1～2级;降低精轧开轧温度有利于减轻板材的带状组织;在未再结晶区控轧有利于减轻板材的带状组织;随着未再结晶区形变量增加,板材的带状组织减弱.

薄板坯连铸连轧65Mn钢的热轧组织与力学性能

利用光学显微镜,扫描电子显微镜（SEM）,透射电子显微镜（TEM）和拉伸试验机,硬度仪分析薄板坯连铸连轧工艺CSP生产的高碳高强度钢65Mn的热轧板微观组织与力学性能。该钢主要由珠光体和少量多边形铁素体组成,珠光体片层间距在0.2-0.5μm之间。该钢的平均屈服强度为489MPa,硬度为HRC22.3,伸长率达到18%;没有明显的C和Mn元素偏析,力学性能分布均匀。通过与传统连铸工艺生产的65Mn钢热轧组织与力学性能对比,CSP工艺生产的65Mn钢的组织更加细小,性能更加优良和均匀。

管线钢的研究进展

根据材料的显微组织将管线钢分为四种类型,即铁素体-珠光体管线钢、针状铁素体管线钢、贝氏体-马氏体管线钢和回火索氏体管线钢;并以此为线索介绍了该四类管线钢的化学成分、显微组织和性能,综述了管线钢的发展历程。

超细晶粒钢的显微组织

分析了以普碳钢成分生产的超细晶粒钢的显微组织。结果表明:工业生产的超细晶粒钢的显微组织由铁素体和珠光体组成,铁素体的晶粒尺寸为4～5μm,组织中珠光体所占体积分数较低。珠光体中渗碳体以短棒状或颗粒状存在,细小的铁素体晶粒使晶粒内的位错塞积密度减少,有利于提高钢的强度和韧性。

VN合金化对20MnSiV钢筋钢组织的影响

对比研究了VN合金化和Fe-V合金化的 2 0MnSiV钢筋钢的显微组织和钒析出物。结果表明 :用VN合金化的 2 0MnSiV钢筋钢的铁素体量较多 ,珠光体量较少 ;钒析出物的量明显较多。预计用VN合金生产的2 0MnSiV钢筋钢将具有较高的屈服强度和较低的冲击转变温度。

控轧控冷参数对含铌微合金钢组织的影响

利用Gleeble-1500型热模拟试验机研究了含铌微合金钢在不同控轧控冷参数下组织的变化规律。结果表明：低温变形由于引发了形变诱导铁素体相变,对珠光体转变的促进作用更加明显；珠光体片层间距随变形温度的升高而减小,并且随冷却速率增加明显减小；高温变形扩大了贝氏体相变的冷速区间,低温变形由于引发形变诱导铁素体相变,对贝氏体相变起到了抑制作用。