商用飞机起落架用单真空300M钢疲劳性能控制现状及展望

根据国内商用飞机起落架用300M钢研究和生产现状,介绍了国内单真空300M钢生产工艺以及疲劳性能控制现状,分析了国产单真空300M钢疲劳强度与抗拉强度、断裂韧性的对应关系,以及疲劳起裂过程中非金属夹杂物种类、喷丸强化作用等,展望了国内商用起落架300M钢未来市场潜力及大尺寸、高性能的绿色发展方向。通过研制攻关,国内形成了商用飞机起落架300M钢单真空冶炼技术,抚顺特钢和宝武特冶已建立了单真空300M钢生产体系且具备批量供货能力。研制生产过程中还需重点关注材料的批次稳定性、纯净度及疲劳性能,加强生产过程控制,持续优化熔炼和锻造工艺,降低能耗及成本,积累数据并完善材料标准体系,同时研制Φ1 080 mm及更大锭型的单真空300M钢,在质量、标准、成本及认证等方面与国际全面接轨。     

2 000 MPa高强度钢的超高周疲劳破坏行为

通过USF-2000超声波疲劳试验机研究了500 kg真空感应炉+电渣重熔冶炼的2000 MPa高强度钢(%:0.45C、2.0Si、0.9Cr、0.001S、0.005P、0.026Al、0.001 5O、0.002 8N)在共振频率20 kHz、载荷比R=-1,共振间隙150 ms时的超高周疲劳破坏行为。结果发现,疲劳裂纹大部分起源于钢中非金属夹杂物(夹杂平均尺寸12.3μm),钢的疲劳强度和寿命随夹杂物增大而降低;内部夹杂物引起的疲劳破坏往往呈鱼眼型;随疲劳断口裂纹源夹杂物处应力场强度因子ΔK_inc的减小,钢的疲劳寿命N_f增加。     

20CrMnTi齿轮钢表面脱碳及疲劳行为研究

以20CrMnTi齿轮钢为研究对象,采用电阻炉进行不同温度下的脱碳试验,用金相法测量脱碳层厚度,研究加热温度对试验钢脱碳的影响规律;采用QBWP-6000J型简支梁旋弯疲劳实验机对试验钢进行旋弯疲劳测试,通过成组法测定试验钢的疲劳极限,绘制S-N曲线;采用扫描电镜对试验钢疲劳断口进行形貌观察,分析断裂机理;同时,对不同温度下脱碳后的试样进行旋弯疲劳测试,对比脱碳与不脱碳情况下试验钢的疲劳寿命,分析探究脱碳行为对试验钢疲劳性能的影响。结果表明,由于加热过程中氧化与脱碳行为同时存在,两者交互作用,导致全脱碳层厚度随温度增长呈现先增加后降低的趋势,750℃时全脱碳层厚度达到最大值120μm, 850℃时全脱碳层厚度达到最小值20μm,试验钢疲劳极限约为760 MPa,试验钢疲劳裂纹源主要为Al₂O₃非金属夹杂物;脱碳行为大大降低试验钢的疲劳寿命,影响试验钢疲劳性能,脱碳层越厚,疲劳寿命越低。为减小脱碳层对试验钢疲劳性能的影响,试验钢最佳热处理温度应设为850℃。     

DP980钢及DP980钢激光焊接接头的高周疲劳性能

摘要：为了研究DP980钢的高周疲劳性能,采用疲劳试验机对DP980钢和DP980钢激光焊接接头进行高周疲劳试验,得到Basquin方程,并利用光学金相显微镜和扫描电镜进行组织和断口分析。结果表明：DP980钢激光焊接接头的焊缝根部和顶部出现形状凹陷,焊接接头的质量为中等。DP980钢疲劳极限为341MPa,DP980钢激光焊接接头的疲劳极限为148MPa,激光焊接接头的疲劳极限较母材的疲劳极限降低约50%。对于DP980钢而言,铁素体/马氏体晶界是裂纹萌生的主要位置,疲劳断口为准解理断口。对于DP980钢激光焊接接头而言,疲劳裂纹源位于焊缝凹陷处,而非热影响区及母材,疲劳断口为解理断口。DP980钢和DP980钢激光焊接接头的疲劳裂纹扩展区均有明显的疲劳条带,并伴随有二次裂纹。     

AF1410钢的旋转弯曲疲劳破坏行为

 通过力学性能测试、微观组织和疲劳断口形貌的扫描电镜（SEM）分析等方法系统研究了一种双真空工艺熔炼的高纯度超高强度钢（AF1410）的高周旋转弯曲疲劳破坏特性及非金属夹杂对其疲劳性能的影响。结果表明：AF1410钢经510℃回火5h后,具有优异的综合力学性能,其旋转弯曲疲劳极限强度达到826MPa;通过疲劳断口的SEM观察,试验用AF1410钢的旋转弯曲疲劳裂纹源均起裂于试样表面的加工缺陷,如刀痕、细微缺口等,这些表面缺陷引起的应力集中是导致其疲劳开裂的主要原因;稀土元素La的加入使得高纯AF1410钢弯曲疲劳断口中出现细小圆形的含La非金属夹杂物,但该类稀土夹杂并未成为旋转弯曲疲劳断裂的裂纹源。     

XCQ16和20Mn2车轴用钢疲劳失效的微观机理

利用扫描电镜(SEM)对XCQ16和20Mn2两种车轴用钢疲劳断口和裂纹扩展断口进行分析,研究疲劳失效过程中的裂纹萌生及扩展机理.结果表明:裂纹均是从试样表面萌生,非金属夹杂和位错是主要的萌生机制;XCQ16钢在疲劳断口中部区的裂纹闭合效应大于20Mn2钢,裂纹扩展较慢;两者在裂纹扩展区的扩展机理不同,XCQ16钢属于塑性断裂,20Mn2钢属于解理断裂;在非金属夹杂上,XCQ16钢多含氧化物和硫化物的混合夹杂,20Mn2钢主要是氧化物夹杂,混合夹杂对材料的疲劳性能影响较小.     

1 500 MPa级贝氏体/马氏体复相高强度钢的疲劳特性

对于一种C-Si-Mn-Cr合金,通过900 ℃奥氏体化20 min、空冷及280 ℃和370 ℃回火2 h,获得了抗拉强度为1 500 MPa的新型贝氏体/马氏体(B/M)复相组织高强度钢.利用疲劳实验研究了B/M复相高强度钢的疲劳极限,并采用C-T试样测定了疲劳裂纹扩展速率曲线.结果表明,B/M复相高强度钢的疲劳极限超过700 MPa,疲劳裂纹门槛值约为12.7 MPa*m1/2;经370 ℃回火的B/M复相高强度钢疲劳裂纹扩展速率较280 ℃回火时低;这种钢的疲劳性能较常规调质处理的高强度钢有所改善.     

硬线钢用盘条中夹杂物的调查

通过采用扫描电镜对国内外4个钢厂硬线钢用盘条中的非金属氧化物夹杂的类型、形貌、尺寸和数量以及成分分析可知,国内外各厂家的钢帘线盘条中夹杂物的类型主要是CaO- SiO2- Al2O3- MgO- MnO,国外厂家较国内厂家盘条中非金属夹杂物的Al2O3质量分数低,SiO2质量分数高。且国外两厂中的夹杂物变形性能好,呈长条状,长宽比都大于3。应尽量减少单位面积的非金属夹杂物数量和尺寸,如先进的国外甲、乙两厂夹杂物数量的控制水平为0.111~0.154个/mm2,尺寸较小的夹杂物（小于3μm）的夹杂物数量相对国内厂家偏少。国外厂家的wT［O］和wN都控制在0.0035%以内。国外厂家控制水平相对较高,wT［O］和wN分别为0.0021%左右和0.0025%左右。     

1950MPa级弹簧钢55SiCrA疲劳断口夹杂物来源分析

采用SEM-EDS对1950 MPa级油淬火钢丝Nakamura旋转弯曲疲劳断口和弹簧疲劳断口宏观夹杂物的成分及尺寸分布进行检测,借助ASPEX Explorer自动扫描电镜对弹簧钢55SiCrA盘条显微夹杂物成分、尺寸及分布进行检测统计。通过对比发现,疲劳断口宏观夹杂物与钢中显微夹杂物成分近乎一致,表明其主要来源为脱氧产物和钢渣反应产物。并根据断口夹杂物的尺寸分布特点推测此疲劳条件下夹杂物的临界尺寸为20μm,最后指出采用夹杂物的塑性化生产工艺,借助结晶器流场优化提高铸坯表层洁净度是后续改进方向。     

10CrNiMo高强钢的低周疲劳特性

采用圆形横截面光滑试样,通过轴向不同应变幅控制的低周疲劳试验,研究了10CrNiMo高强钢的低周疲劳特性,包括循环应力-应变行为、应变-寿命特点、循环应力响应及其力学滞后现象,给出了相应的疲劳参数、循环软硬化特性及应变滞后规律.对裂纹扩展方向及试样疲劳断口的观察表明:裂纹扩展面与轴向力呈现多角度关系,裂纹萌生于试样表面,沿断口周边分布,且具有多源性;疲劳裂纹主要以锐化——钝化机制扩展.     

High cycle fatigue behavior of DP980 steel and DP980 steel laser welded joints

For the study of the DP980 steel high cycle fatigue property, high fatigue tests of DP980 steel and DP980 steel laser welded joints were carried out with fatigue testing machine, the Basquin equation was concluded. Microstructures and fractures were analyzed by optical microscope and scanning electron microscope. The results show that DP980 steel laser welding joints have the weld concavity at the welding root and top, the quality of welded joints is medium. The fatigue limit of DP980 steel is 341MPa, the fatigue limit of DP980 steel laser welded joint is 148MPa, the fatigue limit decreases by 50% compared with the fatigue limit of the base metal. For DP980 steel, the crystal boundary of the ferrite/martensite is the main location of micro cracks initiation, the fatigue fracture of DP980 steel is the quasi cleavage fracture. For DP980 steel laser welding joints, the fatigue cracks initiation is located in the weld concavity, not in the heat affected zone, the fatigue fracture is cleavage fracture. DP980 steel and DP980 steel laser welding joints crack propagation is characterized by the obviously fatigue striations coupled with secondary cracks.     

Study on exogenous inclusions in rotary bending fatigue fracture of Si- killed spring steel 55SiCr

The size, distance from surface and composition of macro inclusions in rotary bending fatigue fracture of 1950MPa- class Si- killed 55SiCr suspension spring wire were analyzed by SEM- EDS. The composition distribution of endogenous oxide inclusions in the Si- killed 55SiCr wire rod were analyzed by means of FEI Explorer 4 automated scanning electron microscope, and the results show that macro inclusions in rotary bending fatigue fracture are exogenous inclusions. The distribution characteristics of these exogenous inclusions in the continuous casting bloom were studied by wire rod solidification dendritic display method. The results show that exogenous inclusions in fatigue fracture mainly are caused by the entrapment of mold powder, erosion of tundish line and submerged entry nozzle, and these exogenous inclusions mainly concentrate at the bloom loose side corner.     

Three-dimensional Numerical Simulation and Experimental Analysis of Austenite Grain Growth Behavior in Hot Forging Processes of 300M Steel Large Components

The microstructure models were integrated into finite element (FE)code,and a three-dimensional (3D) FE analysis on the entire hot forging processes of 300M steel large components was performed to predict the distri-butions of effective strain,temperature field and austenite grain size.The simulated results show that the finest grains distribute in the maximum effective strain region because large strain induces the occurrence of dynamic re-crystallization.However,coarse macro-grains appear in the minimum effective strain region.Then,300M steel forg-ing test was performed to validate the results of FE simulation,and microstructure observations and quantitative analysis were implemented.The average relative difference between the calculated and experimental austenite grain size is 7.5 6%,implying that the present microstructure models are reasonable and can be used to analyze the hot forging processes of 300M steel.     

High- temperature fatigue property of 18CrNbTi ferritic stainless steel

In order to determine the influence of dwell time and atmosphere environment on high- temperature fatigue properties of 18CrNbTi ferritic stainless steel, the high- temperature fatigue behaviors of 18CrNbTi steel with 10s dwell time at maximum stress in argon and simulated automobile exhaust gas were investigated under axial tension- tension stress- controlled mode at 800??, and compared with its high- temperature fatigue behavior in air without dwell time. The fracture surfaces of fatigued specimens were observed with scanning electron microscope. The results show that: the fatigue limit of 18CrNbTi steel in air is 25MPa; the fatigue resistance and fatigue life of 18CrNbTi steel significantly reduce after introducing 10s dwell time; in comparison with those in argon, the fatigue resistance and fatigue life have a further decrease in the simulated automobile exhaust gas; the fatigue cracks both initiate and propagate in a transgranular mode under all testing conditions.     

16MnR 钢的高应变超低周疲劳性能

从压力容器的实际工况和抗震安全性设计出发,研究了压力容器用钢16MnR 钢的高应变超低周疲劳性能。采用横向应变控制方法,在 MTS809拉扭复合疲劳试验机上测定了试验钢应变疲劳过程中的循环应力响应特征及循环应力与应变的关系等超低周疲劳行为;通过拟合 Basquin 公式和 Coffin-Manson 公式,获得了试验钢的高应变超低周疲劳寿命预测公式。断口扫描发现,超低周疲劳下,多处裂纹萌生于试件表面,然后裂纹共同向内扩展,直到最后快速断裂。