回火温度对1Cr15Ni4Mo3N钢组织和性能的影响

研究了回火温度对1Cr15Ni4Mo3N钢组织和性能的影响.结果表明,组织中具有高密度位错的板条马氏体及与基体共格的细小沉淀相M2C是该钢具有高强度的主要原因.470℃左右回火强度达到峰值,冲击韧性处于低谷.     

回火温度对含钒ULCB钢组织及析出的影响

利用热模拟技术并结合SEM和TEM分析方法,研究了含钒超低碳贝氏体钢(ULCB)在轧后快速加热回火过程中不同回火温度对其组织、显微硬度及析出行为的影响.结果表明:未经回火的试验钢组织为板条贝氏体+粒状贝氏体;经高温回火后,组织中出现了多边形铁素体,随回火温度的增加,板条贝氏体数量减少,多边形铁素体数量增加.在600℃以下回火时,析出相主要是沿位错析出;在600℃以上时,以晶界析出和沿位错线析出两种方式存在.高的加热速率、较短的保温时间不利于位错的回复消失以及碳元素和钒元素的扩散,故随回火温度的增加,析出相的数量增多,但尺寸变化不明显.基体中存在两种尺寸的纳米级析出相:一种是只含有V,尺寸在15～20 nm的V(C,N);另一种含有V、Cr两种元素,尺寸在10 nm以下具有面心立方结构的(V,Cr)(C,N)复合析出相.当回火温度为600℃时,试验钢具有最高的硬度值,332 HV.试验钢硬度的变化是回火后贝氏体组织粗化、位错亚结构的回复软化以及第二相析出的强化机制综合作用的结果.     

回火温度对2Cr13钢疲劳强度的影响

通过对2Cr13钢进行拉伸试验,比较了2Cr13钢调质处理时在两种不同回火温度下的疲劳强度.结果表明,与970℃淬火 710℃回火工艺相比,2Cr13钢在970℃淬火 640℃回火后的疲劳强度提高,塑性降低.     

高温回火热处理对9Cr-1Mo钢焊缝组织韧性的影响

以ESAB公司的三种9Cr-1Mo焊条的焊缝金属为研究对象,以Formastor-D全自动热膨胀记录仪分析了焊缝金属的连续冷却曲线,用MTS试验机分析了焊缝组织的断裂韧性.研究结果表明,Cr、Ni、C和Mn等元素导致OK1和OK3的Ms点应比OK2的低,奥氏体稳定性升高.710℃高温回火处理后,OK2焊缝组织的韧性较高.回火组织中碳化物沿晶界或相界析出使裂纹扩展更加容易从而使9Cr-1Mo焊缝组织的韧性降低.     

奥氏体变形对22CrSH齿轮钢连续冷却相变的影响

为了研究奥氏体变形对22CrSH齿轮钢连续冷却相变的影响,在Gleeble 1500热模拟机上,将22CrSH钢在950℃变形0.4及未变形处理,然后连续冷却.利用膨胀曲线、光学显微镜、透射显微镜,结合各种腐蚀方法,分析了22CrSH钢相变行为及相变组织.研究表明:奥氏体变形使多边形铁素体加珠光体混合组织的临界冷速增大;当奥氏体变形及降低冷速时,大量的晶界仿晶型铁素体占据了奥氏体晶界,贝氏体相变向针状铁素体相变转变;变形使奥氏体在中温相变区稳定性增加,室温组织中M/A岛的数量增多.     

回火温度对0Cr16Ni5Mo马氏体不锈钢组织和性能的影响

通过光学显微镜(OM)、扫描电镜(SEM)、X射线衍射分析(XRD)和力学性能测试,研究了回火温度对0Cr16Ni5Mo马氏体不锈钢组织和性能的影响。结果表明,试验钢在450—700℃温度区间回火处理后的组织均为回火马氏体+残余奥氏体+δ-铁素体,随着回火温度的升高,韧化相残余奥氏体含量先增加后降低,在600℃其含量达到最大值29.8%。其强度则随着回火温度的升高先降低然后回升,在600℃回火后强度最低,而伸长率变化趋势与强度相反;不同温度回火后的冲击断口均呈韧窝状,撕裂棱清晰可见,断裂方式均为韧性断裂。     

回火温度对16Co14Ni10Cr2Mo钢断裂韧度和抗应力腐蚀性能的影响

研究了回火温度对１６Ｃｏ１４Ｎｉ１０Ｃｒｔ２Ｍｏ钢断裂韧度ＫＩＣ和抗应力腐蚀性能ＫＩＳＣＣ的影响。发现５１０℃以下回火ＫＩＣ和冲击值ａｋ的变化一致，都表面出回火马氏体脆性，但在回火脆性区内ＫＩＣ不降低。在二次硬化峰之前ＫＩＳＣＣ值很低，这是二次硬化钢不能在硬化峰之前回火使用的重要原因。     

淬火温度对5CrW2Si钢组织与性能的影响

研究了５ＣｒＷ２Ｓｉ钢经正火加调质预处理后，在不同淬火温度下的显微组织，测定了其σｂ，Ｋ１ｃ和等力学性能。给出了显微组织与性能的关系，确定了５ＣｒＷ２Ｓｉ钢最佳强韬性的热处理工艺。     

一次回火温度对烧结NdFeB永磁材料组织和性能的影响

探讨了880~900℃、910~930℃、940~960℃温度区间下1h回火处理对Nd30Dy3.5Al0.2B1合金显微组织和磁性能的影响。研究表明,温度低于910℃时,晶界富Nd带过厚且积聚,主相体积分数小,矫顽力、磁能积低;温度高于930℃时,晶粒尺寸过大,晶界面积变小,晶界富Nd带加厚,矫顽力、磁能积均下降;910~930℃时晶粒尺寸趋向均匀,晶界富Nd带呈薄层状分布,磁性能最佳。     

回火温度对MC3钢碳化物析出及力学性能的影响

由于工作环境的恶劣性,冷轧辊在工作过程中常会发生断辊.为使冷轧辊用MC3钢获得良好的强韧性匹配,避免断辊的发生,本文采用扫描电子显微镜、X射线衍射仪、能谱分析仪等研究了不同回火温度对冷轧辊用MC3钢显微组织和力学性能的影响.研究表明:经550-750℃回火处理的MC3钢组织均为回火索氏体组织,随着回火温度的升高,析出的...     

Reverted austenite in PH 13-8 Mo maraging steels

The mechanical properties of maraging steels are strongly influenced by the presence of reverted austenite. In this study, the morphology and chemical composition of reverted austenite in a corrosion resistant maraging steel was characterized using transmission electron microscopy (TEM) and atom probe tomography (APT). Two types of austenite, i.e. granular and elongated, are present after aging at 575 °C, whereby the content of the latter increases during aging. The investigations revealed that the austenite phase is enriched in Ni, which prevents the transformation to martensite during cooling. Inside and next to the austenitc areas, Mo and Cr-rich carbides, which form during the aging treatment, were found. Various aging treatments were performed to obtain the activation energy for the formation of reverted austenite. Additionally, the experimental data are compared with thermodynamic and kinetic simulations. Based on these results and the chemical composition changes of the phases, a model for the formation of reverted austenite is presented. It is concluded that precipitation of B2-ordered NiAl and formation of reverted austenite take place simultaneously during aging and that dissolution of precipitates is not essential for the initial formation of reverted austenite.     

2.47 GPa grade ultra-strong 15Co-12Ni secondary hardening steel with superior ductility and fracture toughness

This study investigated the effect of multi-step heat treatment on the microstructure, mechanical properties and fracture behavior of thick 15 Co-12 Ni secondary hardening steel. As-quenched sample was found to have elongated prior austenite grain(PAG) and coarse lenticular martensitic structure. On the other hand, heat-treated sample was observed to have fine lenticular martensitic structure due to fine PAG size and a lot of nano-sized carbides. Also, after heat treatment, nano-scale reverted austenite film was formed at the martensite interfaces. The heat-treated sample showed 2.47 GPa superior tensile strength and superior elongation of about 12 %. The high strength was mainly due to fine block size and high number density of nano-sized carbides. The average value of plane strain fracture toughness(KIC) was 29.3 MPa m1/2, which indicated a good fracture toughness even with the high tensile strength. The tensile fracture surface was observed to have ductile fracture mode(cup-and-cone) and the formation of about ~1 μm ultra-fine dimples. In addition to this, nano-sized carbides were observed within the dimples.The findings suggested that the nano-sized carbide had a positive effect not only on the strength but also on the ductility of the alloy. The fractured surface after toughness test, also showed ductile fracture mode with a lot of dimples. Based on the above results, correlation among microstructural evolution,deformation and fracture mechanisms along the heat-treatment was also discussed.     

Austenitizing treatment influence on the electrochemical corrosion behavior of 0.3C-14Cr-3Mo martensitic stainless steel

Effects of austenitizing treatment temperatures on aqueous corrosion properties of martensitic stainless steels were investigated by electrochemical tests (potentiodynamic test, potentiostatic test and electrochemical impedance spectroscopy), and surface analyses (optical microscopy and XRD). The results of potentiodynamic test revealed that the breakdown potential increased with the increased austenitizing temperature, indicating increased relative resistance to initiation of localized corrosion. EIS measurements showed that MSS3 (1030 °C) exhibits larger polarization resistance value than MSS1 (970 °C) and MSS2 (1000 °C) at passive and breakdown states. This was caused by decreasing the amount of Cr-rich M₂₃C₆ carbide which acts as preferential sites for pitting corrosion.     

On pinning effect of austenite grain growth in Mg-containing low-carbon steel

ABSTRACT

The pinning effect of adding the microalloying element Mg on the growth of austenite grain for low-carbon steel was investigated in this study. The grain growth pinning behaviour of austenite was observed in situ at high temperature using a high-temperature confocal scanning laser microscope at 1573?K for 300?s. The average austenite grain size was calculated using optical micrograph Leica software. In situ observation showed that the finely dispersed Mg inclusions can inhibit the boundary migration of austenite grains. MgO–MnS is the most effective inclusions for pinning of austenite grain boundaries in Mg-containing SS400, and the ratios of inclusion on austenite grain boundaries to the total inclusion are 43%. In addition, the increase in Mg addition reduces the grain mobility.     

23Cr-14Ni高氮奥氏体不锈钢σ相析出行为EI北大核心CSCD

采用经验公式、热力学计算方法、Gleeble热/力模拟实验技术,结合光学显微镜、扫描电镜及透射电镜分析,研究了23Cr-14Ni高氮奥氏体不锈钢中σ相的析出行为。结果表明,23Cr-14Ni高氮奥氏体不锈钢中σ相可在960~1030℃析出,高于1050℃溶解。σ相析出具有异常快速的动力学特征,在经过1030℃保温1 min固溶处理后,σ相可直接从奥氏体晶界快速析出,析出先于碳氮化物相。σ相析出动力学行为及相对碳氮化物的析出次序和传统奥氏体不锈钢显著不同。铬、锰、钼元素含量较高且钼元素在晶界处偏聚提高了σ相平衡析出温度,是加速σ相析出的主要原因。     

The role of retained austenite in hydrogen embrittlement of supermartensitic stainless steel

Retained austenite may play a role in the hydrogen embrittlement process because austenite has much higher hydrogen solubility than martensite has. The effect of the retained austenite on hydrogen cracking was investigated by tensile testing of standard round bar specimens that had been heat treated in order to achieve different levels of retained austenite. A significant effect of the retained austenite was observed. Samples with high amounts of retained austenite experienced a much higher reduction in ductility after hydrogen charging than samples with low amounts of retained austenite. In order to explain this effect, the hydrogen solubility of samples containing different levels of austenite and precipitates was measured. This was achieved by charging the samples to saturation in an electrolyte and performing hydrogen analysis.     

The effect of stress relaxation loading cycles on the creep behaviour of 2.25Cr-1Mo pressure vessel steel

This paper investigates the effects of repeated stress relaxation loadings and post stress relaxation creep to assess the stress relaxation-creep interaction and microstructural evolution of 2.25Cr-1Mo steel. Prior to creep testing, the microstructure of the material subjected to stress relaxation exhibited a structure which was non-conservative in predicting the remaining creep life of the material. The results obtained in the test program showed that the damage due to the effects of stress relaxation was crucial and had a significant effect on the creep life of this material. The study has also shown that the extent of metallurgical degradation, due to stress relaxation, may not be evident through microstructural assessment. Consequently, established life assessment procedures may not represent conservative estimates of remaining life because the microstructural indicators of damage, due to stress relaxation, are not evident.The effects of stress relaxation on the creep properties of ferritic pressure vessel steel are life limiting for critical high temperature power generation plant. In this study a comprehensive test program has been undertaken to assess the interaction of stress relaxation with creep and microstructural evolution in 2.25Cr-1Mo steel.     

Deformation behavior and the Portevin-Le Chatelier effect in a modified 18Cr-8Ni stainless steel

Mechanical behavior and microstructural evolution of a 2.5%W + 0.4%Nb + 0.3%V + 0.17%N modified 18Cr-8Ni austenitic steel was studied in the temperature interval 410-740 °C at initial strain rates ranging from 6.7 × 10⁻⁶ to 1.3 × 10⁻² s⁻¹. The Portevin-Le Chatelier (PLC) effect attributed to dynamic strain aging (DSA) was found to occur in the temperature range 530-680 °C. The PLC effect is manifested in the form of serrated (jerky) flow and planar slip. DSA increases yield strength, σ_0.2, and ultimate tensile strength, σ_UTS, in comparison with conventional SUS304 steel due to the additional alloying that provides the formations of the clouds of solutes around the dislocations that exert the solute drag force.     

Constitutive modelling for high temperature behavior of 1Cr12Ni3Mo2VNbN martensitic steel

The deformation behavior of 1Cr12Ni3Mo2VNbN martensitic steel in the temperature range of 1253 and 1453 K and the strain rate range of 0.01 and 10 s⁻¹ are investigated by isothermal compression tests on a Gleeble 1500 thermal-mechanics simulator. Most of the stress-strain curves exhibit a single peak stress, after which the stress gradually decreases until a steady state stress occurs, indicating a typical dynamic recrystallization (DRX) behavior of the steel under the deformation conditions. The experimental data are employed to develop constitutive equations on the basis of the Arrhenius-type equation. In the constitutive equations, the effect of the strain on the deformation behavior is incorporated and the effects of the deformation temperature and strain rate are represented by the Zener-Holloman parameter. The flow stress predicted by the constitutive equations shows good agreement with the experimental stress, which validates the efficiency of the constitutive equations in describing the deformation behavior of the material.