焊接热循环对钛微合金中第二相粒子的影响

利用萃取复型及金属薄膜电子显微技术对Ｔｉ微合金风及其热影响区中的第二相粒子进行了分析。结果表明,含Ｔｉ微合金钢及其热影响区中主要为ＴｉＮ,此外还有少量ＡｌＮ等。经热循环后,粒子的尺寸明显增大、数量减少。与Ｔｉ,Ｎ一比（Ｔｉ／Ｎ）较高的钢相比,Ｔｉ／Ｎ较低的钢中ＴｉＮ粒子数量较多尺寸较小,且热循环过程中ＴｉＮ粒子的溶解及粗化程度减小,对原始奥氏体晶粒长大的阻碍作用较大。     

Ti-Nb微合金钢焊接粗晶热影响区组织及韧性

利用碳萃取复型技术研究了Ti-Nb微合金钢及其模拟粗晶区(CGHAZ)中的第二相粒子,并利用OM、TEM及系列冲击试验对Ti-Nb微合金钢焊接粗晶区的组织及韧性进行了研究.研究结果表明,Ti-Nb微合金钢中含有大量的、尺寸细小的TixNb1-x(CyN1-y)粒子,粒子中Nb的相对含量在0.25～0.82之间,形状接近球形.这些粒子具有很高的稳定性,在焊接过程中这些粒子能有效地阻止奥氏体晶粒长大、抑制粗大贝氏体的形成、促进针状铁素体析出及M-A组元的分解,从而显著善低合金高强钢焊接粗晶热影响区的韧性,t8/5越大,这种改善作用越明显.     

加热工艺对微合金钢Ti、Nb固溶及奥氏体晶粒长大的影响

研究含Ti、Nb微合金钢HJ58轧制前不同加热温度和保温时间对Ti、Nb固溶量及奥氏体晶粒尺寸的影响规律,讨论微合金元素Ti、Nb的存在状态及作用机理,提出了合理的加热工艺以指导生产.     

第二相粒子对ECAP挤压的2A12铝合金晶粒细化的影响

采用等径角挤压技术对2A12铝合金在室温下进行挤压,成功制备了亚微米尺度的块体铝合金材料.挤压前材料的平均晶粒尺寸约5μm,两次挤压后,平均晶粒尺寸细化至200nm左右.合金中的Al2Cu相在挤压过程中由针状变成了块状颗粒,而Al2CuMg相在挤压过程中晶粒大小基本不变.研究发现,硬颗粒Al.2CuMg对基体α-Al有剪切和割裂作用,可以促进基体的晶粒细化过程,并初步给出了晶粒细化的模型.     

两相区回火温度对Mn-Mo系微合金钢亚稳奥氏体形成及力学性能的影响

利用X射线衍射(XRD)、热膨胀仪、电子背散射衍射(EBSD)研究了两相区回火温度对一种Mn-Mo系微合金钢亚稳奥氏体形成及力学性能的影响。结果表明:当两相区回火温度低于650℃时,实验钢的亚稳奥氏体具有较好的稳定性,其室温下的体积分数随着两相区回火温度的升高逐渐增大;当两相区回火温度高于650℃时,亚稳奥氏体的稳定性显著降低,在回火冷却过程中,部分奥氏体转变为"新鲜"马氏体,室温亚稳奥氏体体积分数随两相区回火温度升高而逐渐降低。当两相区回火温度为650℃时,钢中亚稳奥氏体具有最佳的体积分数和稳定性配合。力学测试结果表明:当两相区回火温度为650℃时,实验钢的力学性能最佳,其屈服强度为748MPa,抗拉强度为813MPa,伸长率为27.5%,-20℃和-100℃的冲击功分别为217J和117J。     

Effect of austenite grain size on isothermal bainite transformation in low carbon microalloyed steel

Abstract

The effect of austenite grain size on isothermal bainite transformation in a low carbon microalloyed steel was studied by means of optical microscopy, SEM and TEM. Two widely varying austenite grain sizes, a fine average grain size (～20 μm) and a coarse average grain size (～260 μm), were obtained by different maximum heating temperatures. The results showed that the morphology of isothermal microstructure changes from bainite without carbide precipitation to bainitic ferrite with a decrease in holding temperature. Coarse austenite grain can retard the kinetics of bainite transformation and increase the incubation time of bainite transformation by reducing the number of nucleation site, but it does not influence the nose temperature of the C curve of bainite start transformation, which is ～534°C.     

Metallographic techniques for the determination of the austenite grain size in medium-carbon microalloyed steels

Different techniques have been investigated to seek the best procedure to reveal the prior-austenite grain boundaries in three medium-carbon microalloyed steels. This study has been carried out over a wide range of temperatures (950–1250°C) and it has been found that thermal etching (TE) is the best technique to reveal the prior-austenite grain boundaries in these steels.     

Effect of nitrogen and vanadium on austenite grain growth kinetics of a low alloy steel

Austenite grain growth kinetics in a steel containing 0.4% C, 1.8% Cr with different nitrogen contents (in the range 0.0038–0.0412%) and a micralloying addition of 0.078% V were investigated. The investigations were carried out in an austenitising temperature range of 840–1200 °C for 30 min. The results of investigations showed that N promotes the grain growth of austenite. The microalloying addition of vanadium protects the austenite grain growth because of carbonitride V(C,N) precipitation and the grain boundary pinning effect of undissolved particles of V(C,N). Using a thermodynamic model, the carbonitride V(C,N) content, undissolved at the austenitising temperature was calculated. At temperatures when a coarsening and dissolution of carbonitride occurs, the austenite grains start to growth. The effect of nitrogen on the type of chord length distribution of austenite grains was analysed.     

10CrNi3MoV钢焊接热影响区组织和晶粒度研究

采用焊接热模拟技术研究了590MPa级船用高强度结构钢焊接热影响区组织和晶粒度的变化规律．研究结果表明：10CrNi3MoV钢热影响区粗晶区(CGHAZ)经峰值温度在临界相变点Ac1和Ac3温度范围二次热循环后，具有粗大组织或粗大晶粒遗传现象．焊接线能量(t8/5时间)对粗大晶粒遗传没有影响，但对粗大组织遗传具有显著影响．当t8/5较小时，能够产生粗大组织遗传．当t8/5较大时，仅仅产生粗大晶粒遗传．并且，随着t8/5值增加，产生粗大组织遗传的温度区间减小。     

The growth behavior of austenite grain in the heating process of 300M steel

The 300M steel was heated in an electric furnace at the temperatures of 850, 900, 950, 1000, 1050 °C, and holding time of 5, 10, 30, 60, 90, 120 min. The grain size of austenite was measured by using the linear intercept method on Olympus PMG3 metallographic microscope. The experimental results show that grain size of austenite increases with the increasing of heating temperature and holding time, and the grain growth model of austenite in 300M steel is in the following: d = 4.04 × 10⁶t^0.17exp( − (1.32 × 10⁵/RT)).     

Austenite grain growth modelling in weld heat affected zone of Nb/Ti microalloyed linepipe steel

Abstract

A model to predict the austenite grain size in an Nb/Ti microalloyed steel weld heat affected zone (HAZ) was developed. The present work investigates grain growth behaviour under the influence of pinning carbonitrides. The steel has been subjected to austenitising heat treatments to selected peak temperatures at various heating rates that are typical for thermal cycles in the HAZ. The effect of temperature and heating rate on the grain size is studied. A model is proposed for the dissolution of NbCN precipitates. This model has been coupled to an austenite grain growth model in the presence of pinning particles. This coupling leads to accurate prediction of the austenite grain size along the heating path simulating selected thermal profiles of the HAZ.     

Kinetic analysis of the austenitic grain growth in HSLA steel with a low carbon content

The austenitic normal grain growth of the 16MnNi4 HSLA steel has been investigated by means of the simplified kinetic model developed by Burke and Turhbull. The equation involved in the model allows the setting of a correlation between the kinetic parameters and the microstructure features of the materials. The grain growth exponent (n) has been studied to interpret the mechanism of grain growth in the samples with different heat treatments. It was noted that the kinetic n exponent value increases when the temperature decreases. The variation in the n values (from 2 until 8) has been associated with the solubility or precipitation of the different microalloyed elements presented in the HSLA steel. Also, the activation energies have been calculated obtaining different values depending on the heat treatment.     

晶粒尺寸对18Ni马氏体时效钢力学性能的影响

为解决我国某国防用高精密弹性件材料强韧性不足的问题,研究了不同尺寸的对１８Ｎｉ（１７５０ＭＰａ级）马氏体时效钢力学性能的影响。通过循环相应细化奥氏体晶粒到不同尺寸,在相同时效处理规程下进行时效处理,机械性能测试表明,晶粒细化是提高１８Ｎｉ马氏体时效钢强度和塑性伯一种有效手段。     

双电极奥氏体不锈钢焊条单弧焊工艺研究

本文研究了双电极奥氏体不锈钢焊条单弧焊电弧的静特性、焊接电流、电弧电压、焊芯间隙对双电极焊条单弧焊的工艺性能和焊缝成形的影响;通过热电偶测试技术,对双电极焊条单弧焊焊接过程中不同部位焊芯表面温升进行了测定.研究结果表明焊芯直径为φ4.0mm的双电极A102焊条,其合适焊接工艺参数为:焊接电流140～160A,电弧电压45V左右,焊条两芯间隙1.2～1.5mm,焊接板厚8mm的1Cr18Ni9Ti材料,焊缝成形良好.     

盾构刀具用5Cr5MoSiV1钢的奥氏体晶粒长大规律研究

研究了盾构刀具用5Cr5MoSiV1钢淬火时在不同的奥氏体化温度和保温时间下的奥氏体晶粒长大规律.结果表明:在1000～1150℃加热时,试验钢奥氏体的平均晶粒尺寸D-随加热温度T的升高而增大,且二者间的定量关系近似服从Arrhenius关系,合适的奥氏体化温度应选在1000℃左右;该钢在1050℃等温加热时,奥氏体晶粒随保温时间的延长近似呈抛物线关系长大,等温长大指数η接近1/2.