Carbide and Nitride Precipitation in High Temperature TensiledSpecimens and Hot Ductility of Nb-and Ti-ContainingSteel CC Slabs

Hot ductility of the Nb- and Ti-containing line-pipe steel CC slab specimens were measured under the sirain rate of 1 x 10-3/s. Three types of precipitates were found in the fractured specimens. One was the block-shaped coarse TiN particles precipitated at high temperature. Another type was the fine dynamic precipitation products precipitated at 950～900℃ which caused remarkable ductility reduction of the steel. The third type was the co-existed precipitates formed by fine Nb precipitates nucleating and growing on TiN paricles. Compared with Nb-containing steel which contains no Ti, there was no ductility drop for Nb- and Ti-containing steel at temperature between 850℃ and Ar3 and, the γ→α transformation inside the grain matrixes proceeded faster, which both improved the ductility of the steel in the low ductility temperature Region Ⅲ.     

X60管线钢连铸过程碳、氮化物的析出热力学研究

连铸工艺中不同温度区间内析出的碳化物、氮化物对钢的高温力学性能有重要影响。基于规则溶液理论对X60管线钢在液相、凝固过程及奥氏体相3个阶段析出的微合金元素碳化物、氮化物进行热力学分析与计算,研究析出物的析出相阶段、析出温度及析出顺序,探讨固—液两相阶段由于溶质元素富集而导致析出物溶度积增大、增大析出可能性的因素。计算结果表明：TiN在高温固—液两相区中开始析出,析出温度为1 781 K,奥氏体相区第二相析出物为NbC,NbN,AlN,TiC。     

中温压力容器钢12CrMo的高温塑性研究

通过热模拟试验对中温压力容器钢12CrMo连铸坯的高温塑性进行研究。在不同的变形温度下采用10-3s-1的应变速率对试样进行拉伸变形,测量拉伸断口的面缩率,并对拉伸断口的显微组织和析出物进行分析。结果表明,当变形温度高于900℃时,试样在拉伸过程中发生动态再结晶,其面缩率大于85%,表现出优良的高温塑性;当变形温度为850℃时,有大量细小的AlN在12CrMo钢中弥散析出,其尺寸约为10 nm;当变形温度降至800℃时,大量的先共析铁素体沿奥氏体晶界析出,形成网状结构,试样面缩率降至36%,12CrMo钢的高温塑性显著下降。     

温度、应变率和晶粒对Mn18Cr18N钢高温塑性的影响

通过拉伸热模拟试验研究了温度、应变率和晶粒尺寸对Mn18Cr18N高氮奥氏体不锈钢高温塑性的影响。结果表明：在800℃~1 200℃温度范围内,Mn18Cr18N高氮奥氏体不锈钢的塑性随温度升高而升高,1 200℃时达到最好,然后开始下降;应变率通过再结晶的作用而影响塑性;当温度低于1100℃时,细晶粒尺寸材料的塑性优于粗晶粒尺寸,而温度高于1 100℃时中等晶粒尺寸材料塑性最好。     

Prediction of Hot Ductility of Low-Carbon Steels Based on BP Network

The purpose of the research is to obtain an effective method to predict the hot ductility of low-carbon steels, which will be a reference to evaluate the crack sensitivity of steels. Several sub-networks modeled from BP network were constructed for different temperature use, and the measured reduction of area (AR) of 12 kinds of low-carbon steels under the temperature of 600 to 1000 ℃ were processed as training samples. The result of software simulation shows that the model established is relatively effective for predicting the hot ductility of steels.     

Longitudinal surface cracks on continuous casting slabs of P and Cu containing container steel

The fact that the amount of the mold flux components differs at different locations on the cracking surface indicates that the longitudinal surface cracks are initially formed in the mold and are enlarged in the secondary cooling zone. Based on the hot ductility measurement of two typical container used steels, it is known that the steels are in severe embrittlement state in the temperature range of 825-775℃. By means of increasing Cr/Ni plating thickness on the upper part of the mold, reducing mold heat flux, adopting new secondary cooling pattern, etc., the occurrence of the surface longitudinal cracks on the steel CC (continuous casting) slabs has been significantly reduced.     

关于连铸坯热送热装的探讨

本文简要介绍了目前世界上(如日本等国)使用连铸坯热送热装的发展现状.初步探讨和分析了实现连铸坯热送热装的几个关键问题,提出了在我国尽快实现这个新工艺的初步设想。     

典型钢框架结构节点的动态力学性能与延性分析

采用ABAQUS有限元软件分析了典型钢框架节点(狗骨式节点、端板螺栓连接节点和T型钢连接节点)抗倒塌性能,通过改变冲击荷载大小得到节点的荷载-位移曲线关系,从而得到节点的动态力学性能。分析结果表明,对于不同类型节点,在冲击荷载作用下均未形成悬索机构,且翼缘削弱部分和螺栓连接是梁柱子结构中的薄弱环节。提出了采用节点延性系数评估连续倒塌过程中节点延性的方法,定义不同类型节点结构动力荷载下的极限转动能力θmax与结构开始形成悬链线效应所达到的转角(θc)比值为节点延性系数。当节点延性系数大于1.0时,表示该节点结构能够形成悬链线效应,进入悬索作用阶段;延性系数越大,结构的安全储备越大。节点延性系数可以用于结构抗连续倒塌设计,评估结构是否考虑悬链线效应,以便对结构进行经济、合理的设计。     

3Cr2W8V热挤压模具钢的热处理工艺分析

介绍了3Cr2W8V钢热挤压模具使用条件及失效特征,分析了该模具热处理工艺,并提出了工艺改进方案,可以有效延长热挤压模具使用寿命.实际应用表明,模具使用寿命可从2 000件提高到7 000件左右.     

Hot ductility behavior of V-N and V-Nb microalloyed steels

The hot ductility of V-N and V-Nb microalloyed steels was investigated on a Gleeble-1500 thermomechanical simulator, and the results were compared with those of V and Nb microalloyed steels. A ductility trough is found in both the steels in the temperature range of 700 to 1050°C. Compared to the V steel, the V-N steel has a wider and deeper ductility trough with the increase of N content, due to the in-creased precipitation of V(C, N) in the steel. Above 930°C, when 0.047wt% V is added to the 0.028wt% Nb-containing steel, the ductility becomes worse, owing to the rise of the onset dynamic recrystallization temperature. However, the ductility gets better at 800 to 930°C be-cause of the coarsening of precipitates in austenite. With the improvement in ductility, the fracture mechanism is changed from intergranular to high ductile fracture in the temperature range of 800 to 1050°C.