20g钢珠光体球化后拉伸断裂过程组织变化

采用现场金相显微镜对珠光体球化的20g钢拉伸过程进行了原位观察,用扫描电镜分析变形组织及裂纹。结果表明：珠光体发生球化的20g钢在拉伸过程中,在某些晶粒内部首先发生变形,产生大量的滑移带,并在晶界处产生塞积。随后其它部分晶粒转动,形成对变形有利的取向,各晶粒协调变形。拉伸过程中,裂纹首先产生于试样边缘的珠光体组织。试件内部,微裂纹空洞在铁素体和珠光体的晶界处萌生,由于应力集中,产生扩展连接,呈穿晶和沿晶断裂。     

Analysis on the deformation and fracture behavior of carbon steel by in situ tensile test

1. IntroductionIn materials science, the emphasis is on the under-lying relationship between the microstructure andproperties of materials. Materials science and engi-neering has since long times aimed to develop the accu-rate relationship between the pro…     

等离子喷焊ZrC增强铁基喷焊层Q345复合板的制备

对Q345钢板进行等离子喷焊表面处理,通过正交实验优化了Q345表面处理的最佳工艺参数,优化的喷焊工艺为电流60 A、焊枪行走速度20 mm/min、送粉量为35％、离子气流量为1.2～1.4 L/min、保护气流量为10～12 L/min.结果表明,Q345基板的组织正常,为珠光体+铁素体组织,热影响区处金相组织仍为...     

Characteristics of retained austenite in TRIP steels with bainitic ferrite matrix

Heat treatment process for producing cold rolled transformation induced plasticity-aided (TRIP-aided) steels with bainitic ferrite matrix was adopted. Characteristics of retained austenite (RA) in such TRIP steels were investigated. SEM and OM determination results showed that the stable austenite retained at room temperature were mainly located between laths and some of them inside the coarse ferrite. The grains were uniformly distributed in heat treated steel matrix and the regularly dispersed RA represented to be triangular morphology. XRD analysis indicated that RA content in matrix was not less than 10%, and TEM testified that RA inside the matrix were formed at the prior austenite boundaries and represented to be single or twin crystals. The ductile fracture originated from the boundaries of martensite islands from RA and ferrite. The cracks propagated along grain boundaries and some passed through the large ferrite grains and induced transgranular fracture.     

合金元素Mo对冷轧双相钢组织的影响

分析Mo微合金冷轧双相钢和普通C-Mn冷轧双相钢在不同双相热处理工艺下微观结构,讨论Mo对冷轧双相钢组织变化规律的影响。实验结果表明：当两种双相钢以1700℃／s冷却时,均获得了铁素体、马氏体双相组织,马氏体均匀分布在铁素体基体上,随着加热温度的升高,普通C-Mn双相钢得到的马氏体体积分数多。当以5．4℃／s冷却时,Mo微合金双相钢得到的马氏体体积分数多;当加热到820℃保温结束后以5．4℃／s的速率冷却时,普通C-Mn钢的组织组成相为铁素体、珠光体、马氏体;Mo微合金钢的组织组成相为铁素体、贝氏体、马氏体;Mo对铁素体晶粒的细化作用不明显。     

关于钢的珠光体分解

一般认为，珠光体转变得到铁素体和渗碳体的机械混合物，而且存在领先相．应用系统科学的理论和方法，研究了钢中珠光体共析分解机制，否定了领先相的存在．认为，过冷奥氏体的珠光体转变以及所谓“相同沉淀”都是铁素体和碳化物两相的共析共生的分解过程，设计了新的转变模型．实验表明，珠光体分解在奥氏体晶界形核，铁素体和渗碳体具有位向关系．明确指出，钢中的珠光体和“相间沉淀”产物都是共析铁素体和共析碳化物构成的整合组织．     

高速车轮钢断裂韧性与组织结构的关系

以CLSOD车轮钢为研究对象,对断裂韧性水平不同的试样断口进行显微组织分析,研究组织中晶粒尺寸、铁素体含量、珠光体片层间距对材料断裂韧性的影响。结果表明,车轮钢断裂韧性随着平均晶粒尺寸、5％最大平均晶粒尺寸的增大而降低,晶粒越均匀,断裂韧性越高;断裂韧性起初随铁素体含量的增加而增大,达到一个峰值后随着铁素体含量的增加而减小;在珠光体片层间距为0．13-0．16μm的范围内,断裂韧性与珠光体片层间距的相关性不大。     

珠光体基球铁在拉伸过程中的变形与断裂行为

通过对珠光体基球铁裂纹萌生和扩展过程的观察，深入探讨了珠光体在球铁拉伸断裂过程中的变形与破坏行为。研究认为，珠光体基球铁拉伸断裂规律为；石墨球和基体脱离，基体塑变，裂纹萌生，裂纹扩展，解理破坏；断裂方式为正断裂穿晶断裂。其韧脆性取决于珠光体的形态与细化程度。     

断口—倾斜面的扫描电镜观察

本文提出了采用断口—倾斜面金相试样在扫描电镜中直接观察断口形态、裂纹扩展以及显微组织之间相互关系的实验方法;介绍了这种断口—倾斜面金相试样的制作过程,以及运用这一实验技术研究钢中细小析出相与微裂纹作用的典型实例。     

High performance low cost steels with ultrafine grained and multi-phased microstructure

Ultrafine grained ferrite was obtained through tempering cold rolled martensite with an average grain size of 200―400 nm in a low carbon and a microalloyed steel. Thermal and mechanical stability of the two steels was studied. Due to the pinning effect of microalloyed precipitates on the movement of dislocations and grain boundaries, the recrystallization and grain growth rate were retarded, and the thermal stability of ultrafine grained microstructure was improved. The ultrafine grained ferritic steel was ...     

Surface nanostructure formation mechanism of 45 steel induced by supersonic fine particles pombarding

By means of supersonic fine particles bombarding (SFPB),a nanostructured surface layer up to 15 μm was fabricated on a 45 steel plate with ferrite and pearlite phases. To reveal the grain refinement mechanism of SFPB-treated 45 steel,microstructure features of various sections in the treated surface were systematically characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Grain size increases with an increase of depth from the treated surface...     

铸态QT550-7球墨铸铁制备及组织研究

为了研究铸态QT550-7球墨铸铁组织,铁液凝固过程及石墨球化机理,用回炉铁、生铁、废碳钢、球化剂、孕育剂等材料,采用双联熔炼法制备了球墨铸铁.经测试,化学成分和力学性能满足QT550-7球墨铸铁要求,球墨铸铁组织由铁素体＋珠光体＋球状石墨组成,凝固过程为糊状凝固.     

高速客车转向架构架焊接接头组织与力学性能

采用混合气体保护焊焊接方法对进口S355J2W钢和国产09CuPCrNi-A钢两种耐候钢通过焊接机器人单面焊双面成型的方式进行自动焊接实验,通过拉伸、硬度和金相检验试验方法对得到的焊接接头显微组织和力学性能进行了分析研究。结果表明,两种钢材焊接接头抗拉强度均优于母材,具有良好的力学强度,能够满足国产化技术要求。两种钢的焊接接头焊缝组织类似,S355J2W钢焊缝主要为粗大板条状和块状铁素体加先共析铁素体,含少量珠光体和粒状贝氏体;09CuPCrNi-A钢焊缝主要为条状和针状铁素体加先共析铁素体,含少量珠光体和粒状贝氏体。     

热处理对Zr-4合金显微组织和拉伸性能的影响

为探讨不同显微组织对核燃料包壳管Zr-4合金力学性能的影响,对Zr-4合金进行了再结晶退火,960℃、4min淬火,960℃、4min淬火＋400℃、18h回火的工艺处理,并分析了Zr-4合金的显微组织和拉伸性能.试验结果表明：再结晶退火态的Zr-4合金组织为等轴α晶;拉伸断裂形式呈韧性断裂,断口以韧窝为主,韧窝底部不存在第二相粒子;经960℃、4min淬火后,显微组织为板条状马氏体,抗拉强度达到635MPa,断口形式属于脆性断裂;回火后显微组织与淬火后相同.     

中碳钢楔横轧轧制过程及组织性能研究

采用有限元方法对两种不同温度下三辊楔横轧中碳钢棒材的轧制过程进行了数值分析,分析了轧件横截面上温度及等效应变的分布规律,并通过实验研究分析测定了截面上不同位置处的显微组织及硬度分布。结果表明：轧件等效应变等值面在轧件横截面上呈环状分布,由心部向外变形程度逐渐增大;轧制过程中轧件内部存在明显的温升,大约在轧件1/2半径处温升最明显;轧件典型组织为珠光体与先共析铁素体,且从心部到表层组织逐渐变细。同时发现轧件外表层有产生脱碳,其组织为铁素体。     

Dynamic Fracture of Ti-5553 Alloy in Taylor Impact Test

The dynamic fracture behavior of a new near-beta Ti-5Al-5Mo-5V-3Cr~(-1)Fe(Ti-5553)alloy under a high strain rate loading was investigated systemically using the Taylor impact test,over the impact velocity ranging from156 ms~(-1) to 256 ms~(-1).An optical microscope(OM)and a scanning electron microscope(SEM)were used to characterize the microstructure evolution.The experimental results have demonstrated that the velocity from deformation to fracture is 256 ms~(-1) for the alloy with anα+βduplex microstructure including more primaryαphase,while the velocity is 234 ms~(-1) for the alloy with a duplex microstructure including less primaryα phase.From the impact fracture morphologies,smooth and smeared surfaces and ductile dimple areas can be observed.The failure mode of the titanium alloy with both microstructures is adiabatic shear banding.According to the fracture analysis,the ductile fracture area with the dimple area in the alloy with much more primaryαphase were more than that with less primaryαphase.Compared to the duplex microstructure with less primaryα phase,Ti-5553 alloy with more primaryαphase exhibited a better capability to resist an adiabatic shear damage.     

65Mn钢大塑性变形后的组织与力学性能

在650℃下对65Mn钢进行了C方式的等径弯曲通道变形(Equal Channel AngularPressing,简称ECAP)研究。重复挤压时试样沿轴线旋转180°再装入模具。通过光学及透射显微镜研究发现:ECAP变形后65Mn钢的累积等效真应变达到5左右,片层状的珠光体组织演变成了超细的渗碳体颗粒均匀分布于亚微晶铁素体基体组织中;变形5道次后铁素体基体为均匀的等轴晶,平均晶粒尺寸约为0.3μm。65Mn钢经ECAP变形后,硬度明显提高。     

Microstructural Features During Strain Induced Ferrite Transformation in 08 and 20Mn Steels

The microstructure evolution during strain induced ferrite transformation was followed in thermal-simulation tests of clean 08 and 20Mn steels. The influences of carbon equivalence and initial austenite grain size on ferrite grain refinement and the volume frac- tion of ferrite during straining were inspected. The results revealed that the accelerating effect of ferrite transformation by strain was increased as the carbon equivalence decreased. However, finer ferrite grains were obtained at higher carbon content. At strain of -1 .5 ferrite grains less than 3 μm and 2 μm can be obtained in 08 and 20Mn steels respectively. Whereas the ferrite grain refinement in 08 steel was due to both effects of strain induced transformation and ferrite dynamic recrystallization, that in 20Mn was mainly due to st fain induced transformation. Heavy strain can produce fine ferrite grains in coarse austenite grained 08 steel, but it would lead to band microstructure in coarse austenite grained 20Mn.     

Microstructure analysis of microwave sintered ferrous PM alloys

The properties and microstructure of microwave and conventional sintered Fe-2Cu-0.6C powder metallurgy (PM) alloys were investigated. The experimental results show that microwave sintered alloy has the better properties (sintered density 7.20 g/cm³, Rockwell hardness 75 HRB, tensile strength 413.90 MPa and elongation 6.0%), compared with the conventional sintered counterpart. Detailed analyses by using optical microscopy and scanning electron microscopy (SEM) reveal that microwave sintered sample has finer microstructure with small, rounded and uniformly distributed pores, and also demonstrate the presence of more flaky and granular pearlite in the microwave sintered body, both of which account for the property improvement. SEM images on the fracture morphology indicate that a mixed mode containing ductile and brittle fracture is presented in microwave sintered alloy, in contrast with the brittle fracture in conventional sintered counterpart. Funded by the National Science and Technology Development Program (No.2004-09ZD)     

Metal magnetic memory signals from surface of low-carbon steel and low-carbon alloyed steel

In order to investigate the regularity of metal magnetic signals of ferromagnetic materials under the effect of applied load, the static tensile test of Q235 steel and 18CrNiWA steel plate specimens were conducted and metal magnetic memory signals of specimens were measured during the test process. The influencing factors of metal magnetic memory signals and the relationship between axial applied load and signals were analyzed. The fracture and microstructure of the specimens were observed. The results show that the magnetic signals corresponding to the measured points change linearly approximately with increasing axial load. The microstructure of Q235 steel is ferrite and perlite, whereas that of 18CrNiWA steel is bainite and low-carbon martensite. The fracture of these two kinds of specimens is ductile rupture; carbon content of specimen materials and dislocation glide give much contribution to the characteristics of magnetic curves.