Nb,Ti微合金钢热变形的动态模拟变形抗力模型

本文报道 Nb,Ti 微合金钢的热变形动态模拟变形抗力模型。在试验中用热加工模拟试验机进行高温压缩试验,其变形温度为1123—1423K,变形速率为0.1—60s~(-1)。结果表明,在峰值以前该钢种的流变应力数学模型为:σ=5.99.ε~(0.167)·(?)~(6.47×10~(-5)·T)·exp(4064/T)。形变激活能(Q)为444 kJ/mol,β系数为0.080。峰值应力(σ_p),临界应变(ε_c)和温度补偿应变速率参数(Z)之间的关系分别为:σ_p=12.56·lnZ-391.8;lnε_c=0.157·lnZ-7.39。     

Recrystallization/precipitation behaviour in microalloyed steels

Microalloyed high-strength low-alloy (HSLA) steels contain additions of Nb, V, Ti, or in combination, in amounts of 0.01 to 0.1 weight percent to improve mechanical properties, which are strongly dependent on the thermomechanical interaction taking place in the course of rolling mill processes. The recrystallizatian of hat-twisted austenite has been investigated in a cylindrical specimen (f 6×50 mm) machined from hat rolled plates of 0,052 wt % Niobium microalloyed steel. Continuous and interrupted torsion test were carried out in the temperature range 1123 K to 1173 K after a solution treatment of 1.5 minutes at 1423 K and torque-twist data were analysed. The various methods were discussed for obtaining results from torsion tests. The effect of precipitation kinetics was appreciated by way of connection t_p/t_p(red), where t_p is the experimental measured time for the peak stress and t_p(red) is the newly defined reduced time. The softening ratio X and time t_0.05R for start of static recrystallization were established.

The correlation between precipitation and recrystallization is presented as a graphs for chosen requirements (temperature of austenitization, carbon and niobium content and strain rate). If temperature goes below 850°C, the restoration processes are hardly suppressed, both are limited by diffusion and Nb(CN) precipitation, which are extended dynamically in the range of strains rates 10⁻² to 1 s⁻¹.

In the present paper, an attempt is made to derive the PRTT diagram and to define all mathematical equations for describing recrystallization times t_0.05R, t_0.5R, t_0.95R and t_0.05P for the start of precipitation. In real metal forming processes such as the hot rolling of plates or strips the knowledge of these parameters and results is extremely important for the the correct microstructure and sheet quality to be obtained.     

我国非调质钢的发展与应用

本文综述了我国非调质钢的研究与应用情况，内容包括显微组织参数、化学成分和热加工参数等对性能的影响及非调质钢的断裂行为、疲劳性能和可切削性。文中比较了非调质钢与调质钢在上述性能方面的差异。     

薄板坯连铸连轧工艺对铌微合金化高强度钢组织和性能的影响

首先建立薄板坯连铸连轧工艺的试验室模拟技术，并运用该模拟技术，研究薄板坯连铸连轧工艺(CSP)和传统板坯再加热工艺(TRP)两种工艺对铌微合金化高强度钢的显微组织和力学性能的影响。研究结果表明：CSP钢的晶粒细化效果不如TRP钢，两者的平均铁素体晶粒尺寸分别为8．17μm和6．30μm。在CSP试验钢板中铌的析出量较大，特别是在铁素体中细小颗粒的铌的析出物较多，沉淀强化效果较强。CSP试验钢的σ0.5和σb分别较TRP工艺低约40MPa和约25MPa，同时其低温冲击韧性较好，FATT温度较低。     

Microstructural Modelling of Nb Microalloyed Steels during Thin Slab Direct Rolling Processing

The microstructural evolution during the hot rolling of coarse grain sized austenite has been modeled considering all the microstructural mechanisms (dynamic, static and metadynamic recrystallization, strain induced precipitation) that can take place during an industrial TSDR production of three Nb microalloyed steels. Based on the results obtained from the model, processing maps have been drawn for 0.02%, 0.035% and 0.05% Nb microalloyed steels. Optimum processing conditions to exploit all the benefits of the Nb microalloying have been defined considering a final gauge thickness range between 1.5 and 12.65 mm. In addition, and facing the difficulties present in the production of thick hot strip, several alternative thermomechanical schedules are proposed, which would originate microstructures with a suitable combination of homogeneity and retained strain prior to transformation.     

N含量对Nb微合金化HRB400E钢筋组织与性能的影响

摘要：为了更好地发挥N元素在Nb微合金化钢筋中的作用,降低生产成本以及为钢筋成分设计提供理论依据。利用金相显微镜、扫描电镜、透射电镜、力学试验机对不同N含量的Nb微合金化高强抗震钢筋进行显微组织表征及力学性能测试,探究N含量对Nb微合金化钢筋的组织与力学性能的影响。研究表明,轧制过程中的奥氏体组织,随着N含量的增加,平均奥氏体晶粒有所减小;最终组织为铁素体和珠光体,随着N含量的增加,铁素体平均晶粒尺寸而减小,片层状珠光体的连续性增加,片层间距减小;析出相Nb(C,N)随着N含量的增大,沉淀析出的第二项颗粒体积分数增大,颗粒尺寸随之减小;在力学性能方面,屈服强度逐渐增加,抗拉强度先增加后减少。     

Ti-V-Nb微合金钢中的第二相粒子及其对焊接热影响区奥氏体晶粒长大的影响

利用萃取复型技术及焊接热模拟技术研究了Ti—V—Nb微合金钢及热影响区中的第二相粒子及其对HAZ区奥氏体晶粒长大的影响。研究表明，微合金钢中存在大量弥散分布的细小粒子．这些粒子是Ti、Nb、V等元素的碳氮化合物．具有很高的稳定性。在焊接热循环过程中．这些粒子能够显著地阻止奥氏体晶粒长大。焊接热循环峰值温度在1200C以下时，热影响区中的第二相粒子在热循环过程中仅发生轻微的溶解及长大，奥氏体晶粒长大程度很小，且奥氏体晶粒尺寸基本不随焊接热输入(t815)及热循环峰值温度(Tm)的变化而变化。Tm在1250C以上时，热影响区中的第二相粒子显著减少而尺寸显著增大，奥氏体晶粒尺寸随t815及Tm的增大而显著增大。     

钒微合金化H型钢表面裂纹研究与控制

分析了V微合金H型钢S450J0-T轧后表面裂纹的形成原因。结果表明,S450J0-T钢轧后裂纹主要是由于连铸过程中铸坯上细小裂纹所导致,并在轧制过程中扩展形成。通过对钢水成分进行控制以及连铸工艺进行优化,显著降低了该钢种轧后裂纹修磨率。     

铝对含钛微合金钢成分控制及夹杂物形成的影响

自主设计了不同Al含量的含钛微合金钢，采用火花源光电直读光谱仪检测了每炉钢的化学成分，分析了Al含量对试验钢中O和Ti含量的影响规律；利用OM、SEM观察了试验钢夹杂物形貌并进行了能谱分析，研究了Al含量对试验钢夹杂物形成的影响规律。研究结果表明：随着Al含量的增加，钢中Ti氧化物夹杂逐渐减少，Ti主要以TiN及TiC的形式存在，收得率得到提高；当Al质量分数大于0.033 7%时，Ti的收得率均高于90%；当Al质量分数控制在0.033 7%~0.060 6%时，脱氧效果较好，并可降低夹杂物数量、减小夹杂物的尺寸。     

铁素体—珠光体型非调质钢及其控锻控冷技术

综述了国内外铁素体－珠光体型非调质钢发展现状，探讨了锻造温度、锻造变形量、变形速率及锻后冷却速度对非调质钢强韧化的影响，指出了旨在控制先共析铁素体组织参数和沉淀硬化效应的控锻控冷新技术。为稳定锻造用铁素体－珠光体型非调质钢性能，推动其规模化生产应用，开拓了前景。