控轧控冷工艺对高强度锚杆钢组织和性能的影响

随着矿井深度的增加,对锚杆支护强韧性的要求越来越高,为了应对这一情况,需要研发出更高强度的锚杆钢。利用锚杆钢研究了轧制工艺、冷却工艺与珠光体、铁素体相比例,析出相析出行为及力学性能的关系。研究结果表明,在中轧后、精轧前采用适当水冷+回复段处理的复合工艺可使晶粒更细小、组织更均匀。对超高强度锚杆钢进行热压缩变形试验,由热模拟试验结果确定相转变温度为A_c1=737 ℃、A_c3=886 ℃。最终筛选出入精轧温度为810 ℃、回复段温度为800 ℃时,可获得的晶粒尺寸达4 μm,珠光体体积分数为66.8%,铁素体体积分数为33.2%,珠光体片层间距达200 nm;另外调整V、Cr、N等析出以提高锚杆钢的强韧性,较低的回复温度有利于细小、弥散、V(C/N)析出相的析出,V(C/N)的析出可进一步改善锚杆钢的力学性能。由该控轧控冷工艺轧制的锚杆钢屈服强度为780 MPa、抗拉强度为930 MPa、硬度为291HV、伸长率为20%。     

控轧控冷工艺对高强度锚杆钢组织和性能的影响

随着矿井深度的增加,对锚杆支护强韧性的要求越来越高,为了应对这一情况,需要研发出更高强度的锚杆钢。利用锚杆钢研究了轧制工艺、冷却工艺与珠光体、铁素体相比例,析出相析出行为及力学性能的关系。研究结果表明,在中轧后、精轧前采用适当水冷+回复段处理的复合工艺可使晶粒更细小、组织更均匀。对超高强度锚杆钢进行热压缩变形试验,由热模拟试验结果确定相转变温度为A_c1=737 ℃、A_c3=886 ℃。最终筛选出入精轧温度为810 ℃、回复段温度为800 ℃时,可获得的晶粒尺寸达4 μm,珠光体体积分数为66.8%,铁素体体积分数为33.2%,珠光体片层间距达200 nm;另外调整V、Cr、N等析出以提高锚杆钢的强韧性,较低的回复温度有利于细小、弥散、V(C/N)析出相的析出,V(C/N)的析出可进一步改善锚杆钢的力学性能。由该控轧控冷工艺轧制的锚杆钢屈服强度为780 MPa、抗拉强度为930 MPa、硬度为291HV、伸长率为20%。     

热轧窄带65Mn钢珠光体组织与性能的窄范围控制

为制定65Mn窄范围质量控制工艺参数,利用OM、SEM、拉伸试验机及洛氏硬度仪等,研究热轧窄带65Mn钢的终轧温度、终轧后冷速下以及卷取后冷速对珠光体组织及力学性能的影响。结果表明:在其他工艺参数相同的情况下,随着终轧温度的提高、终轧后冷却速率的减缓和卷取后冷却速率的加快,热轧窄带65Mn钢珠光体球团尺寸和片层间距不断增大、片层变厚、抗拉强度及硬度均逐渐降低,当终轧温度大于960℃、终轧后冷却速率小于5.58℃/s及卷取后冷却速率小于0.1℃/s时,其抗拉强度小于900 MPa。     

降低武钢CSP低碳酸洗钢SAPH370屈强比的实践

屈强比偏高是CSP低碳产品的共性问题。为降低CSP低碳酸洗钢SAPH370的屈强比,采取了不同轧制工艺(终轧温度FT7、卷取温度CT和冷却方式)进行试验,对不同工艺下的低碳酸洗钢的力学性能、晶粒尺寸和相组成进行了对比分析。结果表明:SAPH370钢采用终轧温度(FT7)为860℃、卷取温度(CT)600℃、后段快速冷却的工艺,在满足强度要求的前提下,屈强比可降低到0.8以下。观察到铁素体晶粒粗化、珠光体弥散分布。分析表明:CSP采用后段快冷工艺与传统热连轧的两段冷却工艺相当,有利于获得合适的铁素体晶粒度和弥散分布的珠光体。     

汽车裂解连杆用高强度非调质钢组织和性能的研究

采用金相显微镜、扫描电镜和透射电镜等分析方法, 研究了Rm≥1 000 MPa、ReL≥750 MPa的高强度非调质钢的组织和性能.结果表明:材料为铁素体-珠光体组织,铁素体呈网状分布;珠光体片层间距对强度的影响较大,当片层间距从207 nm减少到171 nm时,屈服强度从 820 MPa上升到840 MPa;其析出第...     

轧后冷却工艺对高强度汽车发动机裂解连杆用钢组织和性能的影响

采用金相显微镜、扫描电镜和透射电镜等分析方法,研究了轧后冷却工艺对高强度汽车发动机裂解连杆用微合金非调质中碳钢的组织和性能的影响。结果表明,提高轧后冷却速度有利于钢中珠光体比例的增加,降低铁素体晶粒尺寸和减少珠光体片层间距;钢中的第二相沉淀析出相主要是弥散分布在铁素体基体中的(V,Ti)(C,N)复合相,粒度在30~170 nm,随着轧后冷却速度的增加而减小;而其屈服强度随轧后冷却速度的增加而提高,在高的冷却速度下,其屈服强度达到770 MPa,其中析出相对屈服强度的贡献达到174 MPa。     

钒对中碳非调质钢组织性能的影响

利用金相显微镜、透射电镜及物理化学相分析等方法研究4种不同钒含量的中碳非调质钢锻后空冷下的微观组织参数与材料力学性能的定量关系.结果表明:随着V含量的增加,铁素体体积分数增多且晶粒尺寸减小,珠光体片层间距变细,直径小于10 nm的析出相粒子占比增加.当V质量分数增至0.2％时材料的韧性急剧降低.材料硬度随V质量分数的增加而增大且铁素体与珠光体的显微硬度比值增大,但材料的屈服强度并不完全取决于铁素体;在Hall-Patch公式、固溶元素强化系数和Ashby-Orowan模型等理论的基础上结合相关文献的实验数据,建立了一个普遍适用于V微合金化中碳非调质钢屈服强度的预测方程.     

轧制工艺对高强度建筑钢板组织和屈强比的影响

针对鄂钢生产的部分高强度建筑钢板出现屈强比超标的现象,采用金相显微镜,扫描电镜和万能试验机测试了不同轧制工艺的钢板组织和性能,分析了轧制工艺对组织和性能的影响,找出了部分钢板屈强比超标的原因。结果表明,减少轧制道次,增大道次压下率,造成晶粒细化,而珠光体百分比和片层间距基本不变,是钢板的屈服强度升高的主要原因,从而导致了钢板屈强比超过标准。因此,保持适当轧制道次,优化轧制工艺以获得优良的性能。     

Effects of TMCP Parameters on the Microstructure and Mechanical Properties of Nb-Bearing Spring Steel

The effects of TMCP parameters,such as finish rolling temperature and cooling rate on the microstructure and mechanical properties of Nb-bearing spring steel were investigated by thermal simulation,quantitative metallography and tensile test.And the precipitation in Nb-bearing spring steel was analysis by electron microscopy.Experimental results indicate that the higher finish rolling temperature or the more rapid cooling rate in a given range,the less the proeutectoid ferrite content and the thinner the interlamellar spacing is.Reasonably higher finish rolling temperature followed by properly higher cooling rate is suggested to improve the mechanical properties of Nb-bearing spring steel.Micro-addition of niobium decreases the proeutectoid ferrite content and the interlamellar spacing and leads to forming degenerated pearlite.The precipitation of size range ～20-50 nm in Nb-bearing spring steel occurred at the lamellar ferrite of pearlite and the proeutectoid ferrite.     

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％.     

Pearlite spheroidization by thermomechanical treatment of directly charged thin slabs

Considering coarse initial austenite grain and the reduced thickness of directly charged thin slabs, a modified thermomechanical treatment was carried out on an unalloyed engineering steel with 0.66% C. For the laboratory simulation to determine the microstructural and mechanical properties a continuous casting simulator linked with the hot deformation simulator (Wumsi) were used. The aim of these tests was to study the process of the strain induced spheroidization of lamellar pearlite in order to improve the cold deformability of the steel, taking account of the particular conditions of direct charging. By the Variation of hot rolling deformation schedules, the influence of austenite grain size, pearlite interlamellar spacing as well as strain and strain temperature were investigated. The spheroidization process was mostly influenced by the strain applied just after finished pearlite transformation. Improving both strength and ductility by increasing fraction of spheroidized pearlite was supported by a smaller pearlite interlamellar spacing before deformation. A coarse austenite grain hardly affects the spheroidization process and brings about no impairment of mechanical properties, which makes this processing particularly attractive for direct charging of thin slabs. Moreover, a finely spheroidized pearlite exerts structural similarities to a tempered martensite, concerning distribution, shape and size of the cementite, accordingly leading to comparable mechanical properties. This justifies such modified hot rolling to be accepted as a potential substitution for the conventional post-rolling quench and tempering of high carbon steel products.     

Influence of microstructure on fatigue crack initiation in fully pearlitic steels

The effect of microstructure on the fatigue crack initiation of fully pearlitic steels was studied through independent variation of the prior austenite grain size, pearlite colony size, and the pearlite interlamellar spacing. Increasing yield strength (controlled by decreasing the pearlite interlamellar spacing) was seen to increase the smooth and notched-bar crack initiation endurance limit. Grain and colony size variations, at constant yield strength, were seen to exhibit no effect on crack initiation. Scanning Electron Microscopy revealed smooth-bar cracks to have initiated at surface inclusions. The influence of the pearlite interlamellar spacing, reflecting a change in the effective slip length, and the differences between notched and smooth-bar fatigue specimens for studying the effects of microstructure on crack initiation are discussed. Formerly with Carnegie-Mellon University     

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Influence of finish rolling temperature on the metallographic structure, mechanical properties and precipitation behavior of the second phase particles was studied by means of optical microscopy, scanning electron microscopy, transmission electron microscopy and other test equipments. The results show that the metallographic structures of high strength steels for container with different finish rolling temperatures are composed of ferrite and a little pearlite and the grain size grades of ferrite are both 13.0. Compared with the one with finish rolling temperature of 890 ??, the yield strength and tensile strength of the one with finish rolling temperature of 850 ?? increase by 32 MPa and 26 MPa respectively. The results of theoretical calculation and observation by TEM show that the higher strength of the one with finish rolling temperature of 850 ?? mainly is due to the higher nucleation rate of second phase particles, more precipitation amount and smaller particle spacing, which makes precipitation strengthening effect more significant.     

形变对共析钢连续冷却过程中珠光体相变的影响

摘要：为掌握形变对共析钢连续冷却过程中珠光体相变的影响,研究了共析钢在720～920℃温度范围内进行形变后,在连续冷却过程中奥氏体向珠光体相变的规律,建立了相变时的过冷度和珠光体片层间距的相互关系,并预测了试验钢的力学性能。结果表明：形变储存能促进共析钢在50℃/s高冷速下发生珠光体相变,形成片层间距为129～187 nm的超细片层珠光体,抗拉强度达到近1000MPa,且随着形变温度提高,形变储存能减小,珠光体相变温度降低,珠光体片层间距减小,屈服强度和抗拉强度提高。     

轧制与冷却工艺对X65薄规格管线钢组织与性能的影响

系统研究了控轧及控轧控冷工艺对9.5mm薄规格X65管线钢组织和性能的影响。结果表明:控轧控冷生产的钢的强度、韧性及微观组织整体优于控轧型X65管线钢。对于控轧工艺,降低轧制温度,晶粒细化,强度提高至550MPa,屈强比有增大趋势(0.90～0.95),但韧性较差;轧后配合水冷,通过优化冷却温度和精轧开轧厚度,组织明显细化,混晶程度和带状组织均改善,强度提高至580～620MPa,-20℃冲击韧性稳定在130～150J,屈强比稳定在0.83～0.9。无论是控轧工艺还是控轧控冷工艺,仅通过降低轧制温度、冷却温度对钢的强度提高幅度有限。     

The effect of morphology on the strength of pearlite

The effects of various morphological features on the strength of high-purity pearlite were studied. A continuous-cooling mode of transformation from different austenitizing temperatures was used to produce variations in average nodule diameter and minimum interlamellar spacing. It was found that, for a constant transformation temperature, nodule size was directly related to prior austenite grain size. On the other hand, minimum interlamellar spacing is controlled by transformation temperature, independent of prior austenite grain size and nodule size. Both the yield strength and fracture stress of pearlite was found to be inversely proportional to interlamellar spacing and independent of prior austenite grain size and nodule size.     

The effect of morphology on the strength of pearlite

The effects of various morphological features on the strength of high-purity pearlite were studied. A continuous-cooling mode of transformation from different austenitizing temperatures was used to produce variations in average nodule diameter and minimum interlamellar spacing. It was found that, for a constant transformation temperature, nodule size was directly related to prior austenite grain size. On the other hand, minimum interlamellar spacing is controlled by transformation temperature, independent of prior austenite grain size and nodule size. Both the yield strength and fracture stress of pearlite was found to be inversely proportional to interlamellar spacing and independent of prior austenite grain size and nodule size.     

Controlled Rolling and Controlled Cooling Technology of Ultra-High Strength Steel with 700 Mpa Grade

With Gleeble-1500 system, the influences of rolling temperature, finishing tempera ture and cooling rate on the mechanical properties of two ultra-high strength steels were analyzed. The microstructure of the hot rolled specimens was observed by optical microscope, TEM and SEM. The TRIP of HSLA steels was studied. The results show that the yield stress of 700 MPa can be reached for two steels. The controlled rolling and controlled cooling technology has different effects on two sleds, but it is rational to adopt finishing temperature 800℃ for both of them. The microstructure of the steels is mainly bainite, and the influence factors ofmechanical properties are the size of bainite, and the size, distribution, composition and morphology of secondary phases. The deformation of high molybdenum steels at a high temperature with a high cooling rate would promote TRIP.     

TMCP工艺对高性能桥梁钢Q370qE-HPS组织性能的影响研究

为了研究TMCP工艺对Q370q E-HPS高性能桥梁钢组织和性能的影响,达到替代正火工艺的目的,对终轧温度、开冷温度、返红温度及冷却速率等TMCP关键工艺参数与组织、力学性能的关系进行分析。结果表明:采用两阶段控轧控冷工艺生产Q370q E-HPS钢时,随终轧温度升高、开冷温度降低、返红温度升高及冷却速度降低,铁素体晶粒尺寸增大,珠光体含量增加,屈强比降低。通过工艺参数优化,可获得合适尺寸和体积分数的铁素体和珠光体,实现Q370q E-HPS钢良好的强韧性匹配和较低的屈强比。