用自动冲击机研究300M钢韧脆转变

北京航空航天大学研制的自动冲击机,可以重演试样冲击破坏过程,绘制、显示及打印冲力-时间、力-位移及能量-时间曲线。利用该设备对300M钢冲击功进行分解,自动快速地分析出材料受冲击后的屈服载荷、最大载荷、最大载荷之前消耗的冲击能量E_1(裂纹形成功)及最大载荷后消耗的冲击能量E_p(裂纹扩展功),以此绘制出E_1和E_p随试验温度变化的曲线,研究300M钢韧脆转变过程,确定转变温度。与常用的韧脆转变判据相比较,,用E_p或E_1作为韧脆转变判据,不仅方法简单、而且使韧脆转变温度的物理意义明确。     

船用低温钢的冲击断裂行为及韧脆转变温度曲线分析

为比较拟合韧脆转变温度曲线各方法的优劣,确定船用低温钢韧脆转变温度,研究其冲击断裂行为,在20℃至–196℃系列温度下对试验钢进行Charpy冲击试验,并对其金相组织和断口进行分析。结果表明:使用Boltzmann函数拟合韧脆转变温度曲线的物理意义明确;船用低温钢韧脆转变温度为(–97±5)℃;试验温度高于韧脆转变温度时,裂纹形核功及延性裂纹扩展阻力变化不明显,但裂纹脆性扩展的阻力和裂纹失稳后的止裂能力随温度下降有较明显的降低;试验温度低于韧脆转变温度后,裂纹形核功及延性裂纹扩展阻力随温度降低迅速减小;试验钢的有效晶粒为(3.1±0.4)μm,细小的有效晶粒尺寸,是保证其低温韧性良好,韧脆转变温度低的主要原因。     

10Ni5CrMoV钢低温冲击断裂行为研究

采用示波冲击试验方法，研究了１０Ｎｉ５ＣｒＭｏＶ钢在冲击断裂过程中各部分能量与温度的关系。在２０℃～－１００℃温度范围内，裂纹形成功（Ｅｉ）基本不变，裂纹扩展功（Ｅｐ）显示与总冲击功相一致的转变特征。在上平台，１０Ｎｉ５ＣｒＭｏＶ钢具有高的裂纹扩展功，Ｅｐ＞１００Ｊ；在转折区，钢的韧脆转变平缓。试验结果表明，Ｅｐ＝Ｅｉ对应的温度可作为韧脆转折温度。本试验钢的韧脆转折温度低达－８５℃，具有优良的低温韧性。     

两种钢夏比V型冲击试验裂纹形成能量与扩展能量之间的关系

采用仪器化冲击试验方法对两种承压设备用钢Q245R钢和13MnNiMoR钢进行系列温度下的夏比V型冲击试验,对比研究了两种钢裂纹形成能量W_i与裂纹扩展能量W_p之间的关系。结果表明:两种钢在韧脆转变K_(V2)-t曲线的上平台以及紧邻转变区的温度范围内,裂纹形成能量W_i不随温度变化而变化,基本恒定,但13MnNiMoR钢的值高于Q245R钢的;材料的韧脆转变,始于裂纹扩展能量W_p转变,其是主导材料由韧向脆的关键。     

PA6/POE-g-MAH共混体系缺口冲击断裂机理研究

研究了PA6/POE-g-MAH共混体系缺口冲击断裂的裂纹萌生、裂纹扩展、冲击断面形貌及紧邻断面下方截面上的相形态.结果显示:随着POE-g-MAH质量分数增加,PA6/POE-g-MAH共混体系缺口冲击断裂发生脆韧转变,裂纹源由"中心辐射型"转变为"线型",裂纹扩展形貌由岩石状脆性断裂特征转变为具有横纹形貌的韧性断裂特征.在紧邻韧性断面下方的截面上可观察到网状形貌,可能是由被刻蚀掉的POE-g-MAH和冲击时基体微观破坏共同组成.在脆性断裂的截面上则无明显的网状形貌.PA6/POE-g-MAH共混体系的断面及截面形貌变化与其脆韧转变的逾渗行为完全对应.DSC分析认为POE-g-MAH提高POE-g-MAH/PA6共混物的缺口冲击韧性与其对PA6晶体结构的改变没有关系.     

高强度桥梁用宽厚板断裂韧性分析

利用示波冲击试验及断口分析的方法对500MPa级桥梁用钢的断裂韧性进行了研究。结果表明：随着温度的降低,冲击总能量Wt和裂纹扩展能量Wp均在减小,裂纹形成能量Wi变化不明显,试样钢的韧一脆转变温度约在-40℃左右。随着温度的降低,材料的断裂方式由最初的韧性断裂转变为胞】生断裂,断裂机理由微孔聚集的韧窝断裂转变为穿晶解理断裂。     

13Cr11Ni2W2MoV马氏体热强不锈钢的韧-脆转变及脆化机理

13Cr11Ni2W2MoV马氏体热强不锈钢用于制备航天火工品构件时,服役温度低至-196℃,需其具有良好的低温冲击韧性.为此本实验研究了13Cr11Ni2W2MoV不锈钢在-150～100℃的夏比冲击性能.采用光学显微镜、扫描电子显微镜和透射电镜分析其显微组织及冲击断口形貌,结合冲击能量及脆性断面率确定了韧-脆转变温度(DBTT),分析了韧-脆转变规律.结果表明:13Cr11Ni2W2MoV不锈钢的DBTT为-35.5℃.温度由100℃降低到-150℃,13Cr11Ni2W2MoV不锈钢的冲击吸收功由180 J降低至30 J.断口放射区主要表现为由撕裂棱和解理面共存的准解理断裂模式,随着温度降低,放射区解理台阶的高度减小,撕裂棱的宽度变窄.纤维区及剪切唇区表现为韧性断裂模式,断口以韧窝为主,随温度降低韧窝的数量及深度减少.裂纹萌生能量及稳定裂纹扩展过程中吸收的能量随温度降低显著下降,裂纹扩展的难度变低,因此发生了韧-脆转变.韧-脆转变的可能原因为低温下位错难以产生和滑动.     

示波冲击试验评价正火12Cr1MoV钢回火脆化敏感性

采用示波冲击试验及断口形貌分析技术，研究了正火１２Ｃｒ１ＭｏＶ钢回火试样的夏比冲击断裂过程及能量消耗，提出了采用裂纹扩展功与萌生功之比做为衡量回火脆化敏感性及一般材料韧脆断裂状态的性能指标，该指标与冲击断口形貌特征有较好的对应关系。文中还对正火１２Ｃｒ１ＭｏＶ钢的回火脆化敏感性进行了评价。     

25Mn钢冲击性能的研究

为研究25Mn钢不同状态的冲击性能的差异，采用示波冲击试验、硬度测定、显微组织观察和冲击断口的SEM形貌分析等方法，分别对轧制态、正火和淬火＋回火的试样进行了测定。结果表明，用示波冲击试验能得到不同变形和断裂阶段载荷、变形及能量消耗的变化。如淬火＋回火态的变形抗力和变形能力都较高，但其总冲击功仅比正火态平均高6J，可却使其材料的裂纹扩展功平均提高16．78J。分析冲击试样的裂纹形成功和裂纹扩展功，以及断口形貌可以判断材料的韧脆性。     

试样厚度对夏比冲击试验结果的影响

通过不同温度下的夏比摆锤冲击试验对非标准小尺寸V型缺口冲击试样的冲击吸收能量和侧膨胀值进行了分析,并结合力-位移曲线,研究了试样厚度对冲击试验结果的影响。结果表明:当试验温度高于韧脆转变温度时,冲击吸收能量与试样的横截面积有关,因此与厚度呈线性关系;而低于韧脆转变温度时,冲击吸收能量与试样厚度之间没有明显关系;试样的侧膨胀值、剪切断面率与厚度之间没有直接联系。随着试样厚度的减小,不稳定裂纹扩展起始力越来越小,从而导致冲击吸收能量减小。厚度越大试样吸收的能量越多,冲击过程中所受到的最大力也越大。     

Impact Energy of Functionally Graded Steels with Crack Divider Configuration

Functionally graded steels were produced via electroslag remelting process using the primary electrodes of plain carbon and austenitic stainless steels. Charpy impact energy of as-prepared specimens was measured in the form of crack divider. The obtained results show that the impact energy of the specimens depends on the type and the volume fraction of the present phases. Based on the rule of mixtures, a mathematical model, which correlates the impact energy of functionally graded steels to the impact energ...     

管线钢冲击吸收功测量的尺寸效应

对20钢、16Mn钢和X70钢不同宽度试样在-80～40℃范围内进行夏比冲击试验,研究了非标准尺寸试样冲击功与标准试样冲击功之间的关系,比较了大小试样韧脆转变温度的不同;把试验结果与ASTM标准、BS标准进行对比,不同尺寸试样的韧脆转变温度漂移程度相差很大。并对上平台冲击功的换算公式做了修正。     

THE INFLUENCE OF TEST TEMPERATURE ON IMPACT FATIGUE CRACK GROWTH BEHAVIOR IN QUENCHED AND TEMPERED Cr-Mo ALLOY STEELS WITH DIFFERENT PRIOR AUSTENITE GRAIN SIZES

Abstract— Impact fatigue tests were carried out using a rotating-disk type impact fatigue testing machine. The influence of prior austenite grain size, ductile-brittle transition temperature and test temperature on impact fatigue crack growth rate was investigated by means of fracture mechanics and fractography in quenched and tempered Cr-Mo alloy steel in which the prior austenite grain size was varied from 8–3 to 25-4 μm. The results in impact fatigue tests were compared to those under non-impact conditions. The crack growth rates associated with striation formation were insensitive to the change in prior austenite grain size, ductile-brittle transition temperature and test temperature regardless of impact and non-impact fatigue. When the material was in the brittle condition, impact fatigue gave rise to a transition from striation formation to intergranular and cleavage cracking. Such a transition will result in the acceleration of crack growth rate. The Paris Law exponent values in impact fatigue were reasonably expressed by the ratio of test temperature to ductile-brittle transition temperature.     

Prediction of ductile-brittle transition for ductile crack growth in reactor pressure-vessel steels

We have investigated the local stress-strain state at the crack tip using the finite-element method in a geometrically nonlinear formulation (with account of the variations in the crack tip blunting) for both a stationary crack and a crack growing by a ductile mechanism. Combined with the criterion of brittle fracture, the derived relationships governing the generation of the stress-strain state at the tips of stationary and growing cracks allowed us to explain the ductile-brittle transition for reactor pressure-vessel steels. We propose a technique for predicting the value of the ductile crack extension up to the instant of the ductile-brittle transition depending on the test temperature, and a procedure for calculating fracture toughness taking into account ductile crack extension. The calculations for predicting the ductile-brittle transition are made as applied to reactor pressure-vessel steel 15Kh2MFA. Analysis is made of the results obtained and available experimental data. Various approaches to the interpretation of the ductile-brittle transition are discussed. TsNII KM “Prometei,” St. Petersburg, Russia. Translated from Problemy Prochnosti, No. 6, pp. 5–22, November–December, 1999.     

The influence of stored energy on crack arrest of BS 4360 50B structural steel

Dynamic crack initiation in BS 4360 50B steel specimens has been achieved by testing the steel with a brittle superimposed Hardex 450 weld bead. The effect of this brittle weld has been shown to move the ductile-brittle transition temperature for the underlying steel from conventional values of approximately −60°C to higher values of the order of −35 to −40°C. The extent by which the transition temperature is raised is shown to be dependent upon the stored energy present in the tested structure. The results confirm that the problem of arresting a running crack in structural steels is not solely a property of the material under test but depends upon the total strain energy stored in the system.     

An efficient method for estimating from sparse data the parameters of the impact energy variation in the ductile-brittle transition region

An efficient method is proposed for estimating from sparse data the parameters of the systematic variation of the Charpy impact energy in the ductile-brittle transition region of low-carbon weld steels. The parameter estimates are practically unbiased and with a very good precision even in the case of very large scatter of the absorbed impact energy. Furthermore, the parameter estimates determining the shape of the transition curve are not affected by its location along the temperature axis. The method is robust regarding the temperature corresponding to a specified impact energy level. Thus, for different type of scatter of the impact toughness and different lengths of the scatter intervals, the estimates of the temperature corresponding to a specified impact energy vary in narrow limits. The transition temperature corresponding to a specified impact energy level is estimated with a very good precision, which is important for quantifying the deterioration of properties due to embrittlement.     

两种焊接工艺对焊接接头冲击韧度的影响

针对对接焊缝金属的冲击吸收功低于熔敷焊接接头中的熔敷金属的冲击吸收功的现象,分别从材料的力学性能和显微组织方面进行探讨。结果表明:对接焊缝金属中的屈氏体含量高于熔敷金属中的含量,组织较粗大,从而使得对接焊缝金属容易形成裂纹,致使相同温度下对接焊缝金属与熔敷金属相比其冲击吸收功较低,韧性-脆性转变温度较高。     

PA6/POE-g-MAH共混物在缺口冲击与缺口拉伸实验中的脆韧转变

用缺口冲击和缺口拉伸实验研究PA6/POE-g-MAH共混物的脆韧转变。结果显示,POE-g-MAH含量对共混物脆韧转变的影响主要是POE-g-MAH含量对裂尖局部应变速率的影响。在缺口冲击和缺口拉伸实验中,随着POE-g-MAH含量增加,裂尖附近参与变形的范围增大,导致局部应变速率降低。当局部应变速率降低至某临界值时,材料的断裂发生脆韧转变。在缺口拉伸实验中,随着拉伸速度增加,PA6/POE-g-MAH共混物发生脆韧转变的POE-g-MAH含量增加。这可能是拉伸速度与POE-g-MAH含量对PA6/POE-g-MAH共混物裂尖局部应变速率共同影响的结果。