连铸方坯形状及截面尺寸的分析研究

论述了连铸方坯对不同产品用途、规格所需的压缩比,分析了矩形连铸坯截面优于方形坯;指出优化截面尺寸,选择近终形截面连铸是发展方向。     

压下率和退火温度对SPCC冷轧钢带组织与性能的影响

对不同压下率生产的不同规格冷轧钢带,在不同温度下进行模拟罩式退火试验。讨论了压下率和温度对SPCC钢带组织与性能的影响。结果表明,在同一退火温度下,压下率为76%时晶粒尺寸最小;当压下率低于64%时,即使退火温度达到800℃,晶粒仍为拉长形;不同厚度规格冷轧板的屈强比随退火温度升高明显降低;厚度小于0.3 mm钢带最优的退火温度确定为675-700℃。     

Concerning the influence of pre-heat treatments on the grain size stability of microalloyed carburising steels

Abstract

The production of case hardened parts involves a number of heat treatment steps with different influences on the grain size stability. Microalloyed steels in particular, which are expected to be very stable, tend to react quite sensitive to additional heat treatments. The object of the project, summarised in this paper, was to carry out a basic preliminary study to evaluate the precipitation behaviour during different heat treatments and their value for the microalloyed steels in case hardening treatments. However, the essential condition for this is sufficient alloying of the steels. In this work, it was possible to derive a simple heat treatment that restores the grain size stability for sufficiently alloyed steels.     

FATIGUE LIVES FOR INDUCTION HARDENED SHAFTS MATERIALS ACCORDING TO THE ENVIRONMENTAL TEMPERATURES

Rotary bending fatigue tests were carried out with two kinds of materials, S43C and S50C, using the front engine and front drive shaft （FF shaft） of vehicle. The specimens were induction hardened about 1.0mm depth from the specimen surface, and the hardness value on the surface was about HRC56-60. The tested environment temperatures were -30, 25 and 80℃ in order to look over effect of the induction hardening and the environmental temperatures on the fatigue characteristics. The fatigue limit of induction hardened specimens increased more about 45% than non-hardened specimens showing that the endurances of S43C and S50C were 98.1 and 107.9MPa in non-hardened samples, 147.1 and 156.9MPa in hardened samplesrespectably. The maximum tensile and compressive stress on the small circular defect was about ＋250 and -450MPa respectively when circular defect is situated on top and bottom. The fatigue life increased 80, 25 and -30℃ in order regardless of hardening. In comparison of the fatigue lives on the basis of tested result at 25℃, the fatigue lives of non-hardened specimens decreased about 35%, but that of hardened specimens decreased about only 5% at 80℃ more than at 25℃. And fatigue life of non-hardened and hardened specimens were about 110% and 120% higher at -30℃ than that of 25℃. Based on the result of stress distribution near the defect, the tensile and compressive stress repeatedly generated by load direction were the largest on the small circular defect due to the stress concentration.     

缺口几何尺寸对钢材疲劳强度的影响

研究了缺口零件的疲劳行为,表明缺口的几何尺寸对零件疲劳强度有明显的影响。从钝缺口样品的研究得到了几何尺寸的影响是通过改变缺口处的应力梯度来实现的,其值可以用线弹性断裂力学进行估算。缺口尺寸对疲劳强度的影响能用几何尺寸因素进行解释,而当缺口逐渐变得尖锐时,在某一个极限范围内塑性区域应变开始对裂纹萌生起重要作用,这时的疲劳强度比用几何尺寸影响来预测的值要低。这种情况下的缺口样品疲劳强度该方法不再适用,则需用其它方法进行估算。     

TWIP钢中晶粒尺寸对TWIP效应的影响

冷轧TWIP钢经1073,1173,1273和1373K固溶处理10min后,得到了晶粒尺寸分别为7,13,30和63μm的奥氏体组织.拉伸实验表明,随着晶粒尺寸的增加,加工硬化速率(dσ/dε)与真应变(ε)的变化关系由2阶段变为3阶段.当晶粒尺寸大于30μm时,加工硬化速率与真应变关系中的第2阶段对应的应变长度随着晶粒尺寸的增加而迅速增加.当真应变为0—0.2时,加工硬化指数随真应变的增加而迅速增加;在随后的变形中,与上述4个晶粒尺寸对应的试样的加工硬化指数分别稳定在0.47,0.53,0.56和0.68.OM和TEM观察显示,随晶粒尺寸的增大,变形过程中形变孪晶数量增多.对于较大晶粒尺寸的试样,形变孪晶在拉伸变形过程中形核的临界应力较低,随变形量增加,形变孪晶可持续形成,使其加工硬化能力增加,从而增大了TWIP效应;相反,晶粒尺寸减小使变形过程中的形变孪晶形核临界应力增大,抑制形变孪晶的产生,从而减小了TWIP效应.     

10CrNi3MoV钢低匹配对接接头的拉伸疲劳性能

通过余高削平的10CrNi3MoV钢低匹配对接接头的拉伸和脉动拉伸疲劳试验,研究了匹配比对高强钢对接接头力学性能的影响,给出了匹配比与削平对接接头疲劳强度及寿命的关系方程.结果表明,随匹配比降低,削平对接接头抗拉强度、断后伸长率和疲劳强度降低,但匹配比对接头抗拉强度影响较小,对断后伸长率和疲劳强度影响较大;由于焊缝冶金强化和力学强化效应的作用,接头抗拉强度和疲劳强度远高于焊缝熔敷金属本身.匹配比过低的焊接结构缺少满足需要的塑性储备,以接头断裂模式为标准,进行了匹配比下限值的初步界定.     

TWIP钢Fe-23Mn-2Al-0.2C的组织及拉伸变形机制

研究了TWIP钢Fe-23Mn-2Al-0.2C固溶处理后的组织演变和拉伸变形行为,并对其变形机制进行了探讨。结果表明:随固溶温度升高,实验钢的晶粒尺寸逐渐增大,屈服强度和抗拉强度均降低,伸长率增大,强塑积先增大后减小,在900℃时达到最高;实验钢的拉伸变形呈现连续屈服,同时随固溶温度升高,加工硬化速率(dσ/dε)与真应变(ε)的变化关系由2阶段变为3阶段。通过OM和TEM观察显示,随着晶粒尺寸的增加,变形过程中形变孪晶数量增多,孪晶诱导塑性(TWIP)效应增大。     

玻璃态Cu29Zr32Ti15Al5Ni19在纳米压入过程中的压痕尺寸效应及应变硬化现象

利用纳米压痕技术对高熵非晶合金Cu₂₉Zr₃₂Ti₁₅Al₅Ni₁₉分别在载荷控制模式、连续刚度模式和循环加载模式下进行了研究。该合金在纳米压入过程中会发生Pop-in现象,且载荷大小比加载速率对Pop-in现象的影响更大。当载荷超过40mN时,即使采用高达5mN/s的加载速率仍然可以观察到Pop-in现象。该合金存在压痕尺寸效应,其测试纳米硬度随载荷的增大而下降,其Meyer指数(n)小于2。压入过程中的能量耗散分数(E_d)在54%-60%之间变化。循环加载测试结果显示该合金加工硬化效应明显。     

Low cycle fatigue life: Dependence on test mode

Fatigue hardening and softening in materials result in different lives in low cycle fatigue, depending on the test mode. The problem is discussed based on the cyclic stress-strain relation, and a suitable testing mode is suggested for the design of structural parts, which are subjected to either constant load or constant displacement fatigue.     

石墨形态对铸铁热疲劳性能的影响

主要研究了石墨形态对铸铁热疲劳性能的影响,为高速列车制动盘的合理选材提供依据。试验结果表明:蠕墨铸铁的耐热疲劳性能最好,球墨铸铁次之,灰铸铁最差。     

Fatigue behaviour of A356 aluminium alloy for automotive wheels

Abstract

The low cycle fatigue (LCF), high cycle fatigue (HCF), microstructure and tensile properties of a low pressure cast A356 aluminium alloy wheel were investigated with T6 heat treatment. The cast microstructure of the alloy significantly influenced the low and high cycle fatigue behaviours. The rim region of the cast aluminium alloy wheel showed higher low and high cycle fatigue strength compared with the spoke region; this difference is thought to be caused by the higher cooling rate of the rim region during casting. The microstructure of the spoke region of the alloy wheel consisted of a dendrite structure with primary α-phase and frequently dispersed large eutectic phases, which led to partial brittle fracture and lower fatigue life with less fatigue plastic strain.     

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通过常规疲劳试验和超声疲劳试验测试模具钢107周次疲劳性能和108超高周次疲劳性能,对模具钢超高周疲劳试样断口进行了分析。将两种不同频率下模具钢试样的疲劳性能进行对比探讨模具钢的频率效应,将20 k Hz频率下两种不同尺寸试样的疲劳性能进行对比探讨模具钢的尺寸效应。结果表明:20 k Hz和130 Hz下模具钢107周次的疲劳极限相差9%,不同尺寸的两种圆弧形试样108周次下的疲劳极限相差16%。     

表面处理对球墨铸铁接触疲劳性能的影响

本文研究了激光微熔处理和高频感应加热淬火对球墨铸铁表面组织、接触疲劳强度和接触疲劳破坏过程的影响。结果表明,激光处理和高频淬火均可提高球铁的接触疲劳强度,但其接触疲劳破坏过程和形式却不同,前者是由于硬化层与基体间裂纹扩展造成大块深层剥落,后者则是表层裂纹在油楔作用下造成小块浅层脱落。     

铸态锰钢的加工硬化性能

采用压缩试验方法,就合金元素对铸态锰钢的加工硬化性能的影响作了系统试验;试验结果表明,锰含量的降低,奥氏体的稳定性下降,因而铸态锰钢的加工硬化能力提高,适宜的N、Cr含量及N/Cr比使铸态锰钢的加工硬化能力显著提高,并对铸态锰钢的加工硬化机理作了重点分析探讨。     

等温淬火温度对40CrMnSiMoVA超高强度钢微观组织与疲劳性能的影响

研究了４０ＣｒＭｎＳｉＭｏＶＡ钢等温淬火温度对元件轴向拉伸疲劳性能的影响。研究表明，３００℃等温淬火可降低材料对应力集中的敏感性，提高４０ＣｒＭｎＳｉＭｏＶＡ钢制复杂零件的疲劳性能。     

孪晶铜中孪晶尺寸对疲劳位错组态的影响

对孪晶铜进行塑性应变幅控制下的疲劳实验,研究了不同宽度的孪晶内疲劳位错组态及演化过程．结果表明,孪晶宽度不同时,孪晶内的疲劳位错组态不同．当孪晶宽度大于1μm时,孪晶内疲劳位错组态与单晶中情况类似;孪晶宽度介于1μm到200nm之间时,位错形成类PSBs结构;孪晶宽度介于200nm到20nm之间时,孪晶内只能形成一些位错碎片;孪晶宽度小于20nm时,孪晶内没有稳定的晶格位错存在．     

A study of several factors governing the fatigue limits of austempered ductile cast iron with various microstructures

The effects the leading factors bearing on fatigue limits were investigated with three kinds of ductile iron specimens various microstructures. As a result of examination, the fatigue limits in relationship to hardness and tensile strength, the expected higher improvement for fatigue limits in the case of the high strength specimens that experienced austempering treatment are not observed in comparison with the specimens treated with stress relief treatment. The estimated maximum defect size is one of the important parameters in predicting and evaluating fatigue limits for three different heat-treated ductile cast irons. Also, a quantitative relationship can be established between the fatigue limit and maximum defect size. Moreover, it is possible to explain the difference in fatigue limits in the three ductile cast irons by application of the rates of non-propagating crack which connects the adjacent graphite nodules before it stops.     

高频淬火态新型叶片钢的疲劳性能

对一种新型叶片钢在室温大气、80℃22%NaCl溶液和95℃水蒸汽中进行腐蚀疲劳试验,测定了此钢在不同腐蚀环境下的拉压疲劳S-N曲线,利用金相显微镜和显微硬度计分析了显微组织和显微硬度的分布,用扫描电镜分析了疲劳断口。结果表明,80℃22%NaCl溶液和95℃水蒸汽分别使新型叶片钢的疲劳极限比室温大气下的疲劳极限降低了32.60%和11.84%。疲劳源都位于试样表面。80℃22%NaCl溶液中的腐蚀疲劳断口没有明显的疲劳辉纹,室温大气和95℃水蒸汽中的疲劳断口都出现了疲劳辉纹,后者的疲劳断口还出现了大量的解理裂纹。