成分偏析严重的12CrNi2MnCu铸钢冷脆转变特性研究

采用系列温度动态撕裂试验、断口分析和金相分析,并结合断裂力学研究了成分偏析严重的12CrNi2MnCu铸钢的冷脆转变特性.结果表明,本试验铸钢在试验温度范围内动态撕裂能普遍较低,但仍表现出冷脆转变特性.试验温度高于冷脆转变温度时,裂纹以沿脆化的一次晶晶界扩展为主,形成脆性的沿晶断裂;试验温度低于冷脆转变温度时,裂纹以在冷脆的晶内扩展为主,形成穿晶断裂.     

低碳钢冷脆特征温度的研究SCIEI

本文根据低碳钢裂缝弯曲试样的冷脆行为特征,定义了冷脆特征温度T_(4m),并阐明了相应的物理含义。同时,对在这一温度下发生的断裂韧性及止裂特性转折的力学本质进行了阐述。在上述研究基础上,对T_(pm)温度在低碳钢冷脆评定中的应用价值进行了探讨。     

超低间隙TC4-DT钛合金厚板显微组织与力学性能研究

研究了固溶+时效处理对超低间隙TC4-DT钛合金厚板显微组织和力学性能的影响。结果表明，固溶温度会显著影响TC4-DT钛合金厚板组织中初生α相和次生α相的含量及尺寸，提高固溶温度可以适当提高板材的强度及断裂韧度。固溶处理冷却速率较快时(水冷和空冷)，会析出细针状和板条状的片层组织，主要提高板材的断裂韧度。当固溶温度为945℃，且经水冷或空冷后可以获得强度-塑性-韧性匹配良好的TC4-DT钛合金厚板。     

高速重载列车车轴用钢EA4T的低温韧度

将经过高温系列回火的EA4T钢试样加工成夏比V型缺口冲击试样,通过低温系列冲击试验对EA4T钢的低温韧度进行了研究。结果表明,EA4T钢经880℃油淬,650℃回火后的冷脆转变温度为-97.37℃至-117.59℃,且在0℃至-80℃冲击时,其A_(KV)基本高于150 J,断口韧性断裂特征明显,表明EA4T钢具有良好的抗冷脆转变能力。     

韧脆转变温度曲线特点

正1韧脆转变韧脆转变温度:对体心立方晶体金属及合金或者某些密排六方晶体金属及合金当温度低于某一温度Tk时,材料由韧性状态转变为脆性状态,冲击吸收功明显下降,断裂机理由微孔聚集型变为穿晶解理,断口特征由纤维状变为结晶状,这就是低温脆性。此时的转变温度Tk称为韧脆转变温度,也称冷脆转变温度。     

THERMODYNAMICS OF THE MARTENSITIC TRANSFORMATION IN Fe-X-C SYSTEMS

Fe-X-C系马氏体相变时的△G_(Fe-X-C)~(γ→α)为:△G_(Fe-X-C)~(γ→α)=_(xFe)△G_Fe~(γ→α)+_(XC)RT×ln_(γ_C~α/γ_C~γ)+x_i△G_i~(γ→α)+△Ω~(γ→α)其中γ_C~α和γ_C~γ分别表示碳在Fe-X-C系铁素体和奥氏体内的活度系数.对Fe-Ni-C和Fe-Cr-C系所求得的M_S值和实验值很好符合.碳在Fe-X-C系的活度值及对奥氏体的强化作用主要决定Fe-X-C系的M_s值.碳是决定Fe-X-C系相变驱动力的主要元素.     

利用线型缺口冲击试验测定材料动态冷脆特征温度影响因素的研究

通过线型缺口（缺口深度α＝４ｍｍ）冲击试样在系列温度下的冲击试验，发现不管是脆性材料还是韧性材料，裂纹扩展功随温度的变化与总功随温度的变化具有一致性，即影响材料动态冷脆特征温度的主要因素是裂纹扩展功。对于脆性材料，裂纹形成功随温度的变化很小，且有成直线渐增趋势，但幅度甚微；对于韧性材料，则与上述不同，当温度超过某一温度时，裂纹形成功开始有较大上升，但其随温度的变化与总功随温度的变化没有很好的对应关     

Fe-X-C系马氏体相变热力学

Fe-X-C系马氏体相变时的△G_(Fe-X-C)~(γ→α)为:△G_(Fe-X-C)~(γ→α)=_(xFe)△G_Fe~(γ→α)+_(XC)RT×ln_(γ_C~α/γ_C~γ)+x_i△G_i~(γ→α)+△Ω~(γ→α)其中γ_C~α和γ_C~γ分别表示碳在Fe-X-C系铁素体和奥氏体内的活度系数.对Fe-Ni-C和Fe-Cr-C系所求得的M_S值和实验值很好符合.碳在Fe-X-C系的活度值及对奥氏体的强化作用主要决定Fe-X-C系的M_s值.碳是决定Fe-X-C系相变驱动力的主要元素.     

热轧Al-Mg-Mn-Er-Zr合金板材的低温冲击性能

采用夏比缺口冲击试验研究了Al-Mg-Mn-Er-Zr合金的低温冲击性能。结果表明,在-192~0 ℃试验温度范围,随着温度的升高,冲击吸收能量不断降低,而剪切断面率不断上升;Al-Mg-Mn-Er-Zr合金失效方式均以Ⅰ型断裂为主,部分表面显示Ⅱ型剪切断裂特征;在-192 ℃,断口表现出的台阶型断裂特征与Ⅰ/Ⅲ型混合载荷条件下的断裂形貌相似。     

HRB400热轧带肋钢筋冷弯断裂原因的分析

国内西北某钢厂生产的HRB400热轧带肋钢筋在冬天作业时常常出现冷弯断裂。通过扫描电镜-能谱仪(SEM-EDS)、Thermo-Calc热力学软件以及光学显微镜(OM)等,对HRB400螺纹钢冷弯断裂的原因进行了研究,论述了非金属夹杂物、磷含量、钒氮比及显微组织对钢筋断裂的影响。结果表明:试验钢断口为脆性断口;破碎状的大尺寸夹杂物可能是裂纹产生的源头;钢中P含量偏高使得韧-脆转变温度升高,且自由氮的存在加剧了该温度的进一步升高,由于西北地区冬天气温低,钢筋作业时的温度很可能低于韧-脆转变温度,使钢筋处于脆性状态;魏氏组织的存在增加了钢筋的脆性,为裂纹的扩展提供了可能性。由于国内西北、东北地区温度较低,对在西北、东北地区使用的HRB400热轧带肋钢筋应提出更高的要求,对P、S、O、N的含量应有新的标准,以满足冬天作业时使用温度高于韧-脆转变温度的需要。     

CRITICAL NOTCH(CRACK)SIZE AS A CHARACTERISTIC PARAMETER EVALUATING CRYOGENIC BRITTLENESS IN LOW CARBON STEEL

The effect of notch depth on the cryogenic fracture behavior has been studied using a low car-bon steel.An analysis was made for the fracture features at T_c~*(cryogenic brittleness-char-acteristic temperature)at which the facture load reaehes a valley value.Furthermore,accord-ing to the experimental results and engineering design practice,a concept of critical notch(crack)'size for cryogenic brittleness,a_c,as well as its limit value a_c~*,was put forward andrecommended to be a basic characteristic parameter for controlling the brittleness.Mathematical derivation was carried out to give the expression of a_c and a_c~*,the reliabilityof which was verified by the modeling tests under both static and cyclic loading conditions.     

关于金属材料断裂试验的缺口敏感性

本文在Alberto Carpinteri研究集合材料(Aggregative Materials)断裂试验缺口敏感性的基础上,得到了圆环裂纹圆柱试样的脆性系数、裂纹扩展力、极限强度破坏力的关系曲线,并将脆性系数理论推广应用于金属材料.分析表明,在满足低应力脆断的情况下,用脆性系数分析铸镁合金和中、高强钢的断裂试验是合适的.     

Influence of the notch root radius on the fracture toughness of brittle metals: Nanostructure tungsten alloy,a case study

Tungsten and tungsten-based alloys are considered to be candidate materials for next-generation nuclear fusion reactors. Unfortunately, their use in structural applications is compromised due to their inherent brittleness. To improve this crucial feature, it is necessary to accurately measure their fracture toughness as a real property independent of geometrical parameters and the method used to introduce the induced crack. This goal is the objective of this work; where the notch tip radius influence on the fracture toughness of a brittle nanostructured tungsten alloy is analyzed in depth.Three-point bending tests at room temperature were performed on four types of notch geometries in which the notch root radius was gradually reduced. The notches were introduced using four different methods: with a classical diamond disc, a diamond wire, a razor blade and an ultra-short pulsed laser. The results showed that single edge notched beam specimens overestimate the fracture toughness values and introduce some deformation into the notch root grains. However, the razor blade yields very good results with a low dispersion, but is only suitable for coarse grain materials since the size effect appears as the grain size decreases. Therefore, for nanostructured materials such as in this case, the notch root radius is still too large (several times the grain size), requiring the implementation of a new method. Very sharp single edge laser-notched beam specimens with a 5–20 nm root radius were accordingly produced by using ultra-short pulsed laser ablation. This method has been previously used on ceramics but no evidence of its use was found on metals.     

焊接热循环对T92钢组织脆化的影响

采用Gleeble—3800热模拟试验机对T92钢进行不同峰值温度的焊接热循环试验,并对试验试样进行室温冲击韧性试验.借助光学显微镜分析其微观组织,用扫描电镜观察其冲击试样断口形貌特征.结果表明,T92钢焊接加热温度在900℃以上易因奥氏体晶粒粗大导致其组织脆化,断口呈现典型的准解理形貌特征,而在900℃以下的焊接加热仍能保持较好的室温冲击韧性,断口呈现均匀细小的韧窝断口特征;T92钢中高含量的强碳、氮化物形成元素高温状态重新固溶后,在奥氏体中的扩散速度滞后于晶界的迁移速度,进而产生过饱和的室温组织是引起组织脆化的直接原因.     

Notch-sensitive fracture behavior of a silicon carbide fiber-reinforced glass-ceramic at elevated temperatures

The effect on high-temperature embrittlement of introducing a through-thickness notch in a multidirectional silicon carbide fiber-reinforced calcium-aluminosilicate glass-ceramic composite was investigated through tensile testing, microdebonding, and light and scanning electron microscopy techniques. The fracture mechanism of the composite changed from notch insensitive at room temperature to notch sensitive at elevated temperatures due to increased fiber-matrix bond strength caused by oxidation effects at interfaces exposed to the oxidative environment. Stress concentration and bending effects at the notch tip resulted in growth of the notch through fibers in a planar fashion covering the entire fracture surface. This was contrary to the case of an unnotched composite, for which two distinct fracture surface regions were observed as planar embrittlement zones at the periphery and fibrous at the center. Cracks in the notched composite were more closed relative to those in the unnotched one, except at the notch tip. Concentration of the stress at the notch tip increased the high-temperature embrittlement effect on the composite.     

20Mn2钢圆环链脆性断裂原因分析

针对20Mn2结构钢圆环链拉伸试验时出现脆性断口的现象,经断口宏微观观察、金相分析后,认为圆环链的断裂性质为沿晶脆性断裂。分析认为,出现沿晶脆断是由于回火温度过高,且圆环链加工现场受场地限制,热处理后的成品链堆放在一起,造成内部圆环链冷却速率较慢,致使Si、Mn、P等元素在奥氏体晶界偏聚富集,形成高温回火脆性。利用合金结构钢高温回火脆性的可逆性,该批圆环链经670℃保温1h重新回火后,用油快速冷却,消除了高温回火脆性,经检验完全合格。     

Mo-Si-B三元系中T2相合金制备及其室温力学性能

通过放电等离子烧结(SPS)制备T2(Mo5SiB2)相合金,并采用SEM、XRD及压痕、压缩和三点弯曲等实验对合金的微观组织和室温力学性能进行表征。结果表明:SPS法以独特的等离子活化烧结方式制备出纯度高、致密且晶粒细小的T2相合金。该合金在室温压缩下几乎没有塑性变形,抗压强度为2907MPa;维氏硬度为17.86GPa,压痕法测得的断裂韧性为3.23MPa·m1/2,与三点弯曲法测得的3.34MPa·m1/2接近,沿{001}面发生解理断裂。共价键交替排列,是T2相室温脆性、高强度、高硬度的根本原因。     

残留/逆转变奥氏体对改善高强度不锈钢-196℃超低温冲击性能的影响

采用力学性能测试、SEM和XRD等手段研究了淬火+低温回火处理的0Cr16Ni6高强度不锈钢和过时效处理的00Cr11Ni11MoTi马氏体时效不锈钢,并分析了残留/逆转变奥氏体对试验钢超低温缺口抗拉强度和冲击性能的影响。结果表明,在两种试验钢室温强韧性相近的情况下,0Cr16Ni6钢在超低温下(-196 ℃)的缺口抗拉强度和冲击性能显著优于00Cr11Ni11MoTi钢。根据冲击试样远离断口和断口附近马氏体/奥氏体衍射峰的相对强度分别定量计算的残留/逆转变奥氏体含量,发现在裂纹形成和扩展过程中0Cr16Ni6钢有接近90%的残留奥氏体通过应变诱发相变生成马氏体,显著改善了超低温韧性;而过时效00Cr11Ni11MoTi钢形成的逆转变奥氏体具有较高的稳定性,难以发生应变诱发马氏体相变,改善超低温韧性作用程度有限。     

EVALUATION OF EMBRITTLEMENT BEHAVIOR DUE TO SENSITIZATION IN A CRYOGENIC AUSTENITIC STAINLESS STEEL BY MEANS OF SMALL PUNCH AND FRACTURE TOUGHNESS TESTS

1.IntroductionStructuralmaterialsusedinlargesuperc0nductingmagnetsystemsforfuturefusionpowerreactorsarerequlredtopossesshighstrengthandfracturet0ughnessatcryogenicservicetemperatures.Theload-bearingparts0fthislargesystemarec0nstructedofheavyplatesandweldingisrequiredintheirfabrication.JN1austeniticstainlesssteelhasbeendevel0pedasoneofthecandidatecryogenicstructuralmaterials[l'2I.Althoughfullys0lu-tiontreated,JN1materialhasg00dcombinationofstrengthandtoughness,alth0ughitmaybeembrittledduet0be…     

Solute drag effects during the dynamic recrystallization of nickel

Solute drag effects during dynamic recrystallization were studied using five different nickel–sulfur alloys. The steady state stress for dynamic recrystallization, measured using hot compression tests, depends on the sulfur concentration. The experimental results are analyzed using a model that relates the steady state stress to the grain boundary mobility. At the lower temperatures, the mobilities are strongly reduced by a solute drag effect; above a transition temperature, the drag effect becomes negligible. The extent of sulfur segregation at grain boundaries during recrystallization was assessed using cryogenic tensile tests of microsamples removed from the hot compressed specimens. The fracture surfaces exhibit the characteristics of intergranular brittleness when hot compression is carried out within the “grain boundary segregation” temperature range; above the transition temperature, the fracture surfaces are purely ductile.