X80管线钢中Nb元素析出规律的研究

采用热力学模型计算了X80管线钢在不同温度下的相组成,相析出温度及Nb元素的析出规律;研究不同Nb含量对A3温度、各相析出温度和Nb析出规律的影响。计算结果表明,X80管线钢平衡态的析出相主要为Ti,Nb的碳氮化物、合金渗碳体、MnS、AlN、M7C3和Mo的碳化物。随Nb含量的增加,A3温度升高,Nb析出相的析出温度升高,而AlN相析出温度降低;在同一温度下Nb元素的析出量随Nb含量增加而升高。     

稀土对X80管线钢中铌元素赋存状态的影响

采用真空感应炉冶炼制备添加微量稀土的X80管线钢,通过FactSage软件计算,不同温度时效处理后显微硬度的测量,结合微观组织分析,研究加热过程中稀土对铌溶解行为的影响;利用MMS-200热模拟试验机测定PTT曲线,研究稀土对铌应变诱导析出行为的影响.结果表明,稀土微合金促进X80管线钢奥氏体中铌溶解,抑制奥氏体中铌应变诱导析出,但稀土微合金增加了铌元素在铁素体中沉淀析出量,理论上可部分替代钢中的钒元素.     

卷取温度对X80管线钢析出行为与性能的影响

观察了不同卷取温度下X80管线钢中析出物的情况,并结合其组织性能对比可知:在实验情况下,480℃卷取时,有大量细小弥散的Nb、V的碳氮化物析出物,起到了较好的析出强化作用.     

连铸过程铌钛微合金钢中第二相复合析出模型

针对连铸过程铌钛微合金钢中第二相在固液两相区和奥氏体内的复合析出行为,通过近似处理建立了多元第二相复合析出的热力学模型,并利用模型研究了X80,E36,J55钢中第二相的析出行为。结果表明:在凝固过程不同的Ti/N摩尔比对液相中Ti,C,N元素的变化影响显著,先析出的第二相对后析出的第二相影响显著,成分高低的差异不但导致第二相析出量的不同,而且也导致析出相种类的不同,碳氮化物在析出的过程中C,N元素摩尔分数的变化受析出温度和钢中元素含量的影响。     

铌对高钢级管线钢中第二相析出与奥氏体晶粒长大行为的影响

基于双亚点阵模型,计算了两种不同铌含量的高钢级管线钢在不同温度下Nb、Ti和Al的析出量,测定了不同加热温度和保温时间下奥氏体晶粒尺寸,建立两种钢奥氏体晶粒长大模型.发现Nb含量增加提高了其全固溶温度,并且温降过程中Nb析出量显著增多,在晶界两边析出的细小碳氮化物对奥氏体晶粒长大有显著的阴碍作用.高铌钢加热温度为1250℃时奥氏体晶粒显著粗化,预测模型也不同于1050~1200℃的模型,但相同保温温度下晶粒尺寸明显小于低铌实验钢.通过数据拟合计算出高铌钢的长大激活能远远高于低铌钢,再次证明高Nb的管线钢在1200℃以下能够有效地细化奥氏体晶粒,预测模型与实验值吻合较好.     

X—52管线钢连铸坯高温变形试样中碳,氮化物的析出和钢的高温延性

测试了３Ｘ－５２钢连铸坯试件的高温延性。变形试样中主要在三类碳，氮化物析出：高温下析出的块状粗大ＴｉＮ析出物。９５０￣９００℃沿晶界和在晶粒基体内部析出的微细动态析出产物；依附在ＴｉＮ颗粒上生长的复合析出物。与不含钛的含铌钢相比，Ｘ－５２钢试样在８５０℃￣Ａｒ３温度之间没有出现进一步的延性降低，γ→Ｐ转变温度的提高，减轻了其在第Ⅲ脆性温度区的脆性程度。     

钒含量对稀土处理X80管线钢微观组织和析出相的影响

针对国内某X80管线钢的抗腐蚀问题,在加入稀土（0.02%）处理后,设计三种不同钒含量（0.05%、0.10%、0.15%）的试验钢,通过光学显微镜(OM)、扫描电镜（SEM）、Thermo-Calc热力学软件、Fatesage7.0热力学软件、透射电子显微镜-能谱仪(TEM-EDS)等试验仪器对钢中组织和夹杂物的观察分析,论述了稀土在钢中对针状铁素体的生成机理。通过热力学计算,研究不同钒含量梯度对试验钢微观组织和析出相的影响。通过电化学技术检测了不同钒含量试验钢在（3.5%）NaCl溶液中抗腐蚀性能。结果表明：稀土可以变质夹杂物,诱导针状铁素体的形成。钒可以细化晶粒,从而起到细晶强化的作用。通过透射电镜观察,析出相的数量和平均尺寸都随着钒含量的增加而增加,有效起到钉扎作用,从而提高钢的强度。通过极化曲线和交流阻抗曲线看出,试验钢的抗腐蚀性能随着钒含量的增加先增强后减弱。钒促进铁素体的形成,晶粒过细反而导致抗腐蚀性能减弱。     

X80管线钢精炼过程中夹杂物行为研究

研究了国内某厂生产X80管线钢精炼过程中夹杂物的转变.BOF出钢阶段加铝脱氧,钢中夹杂物以伴有极少量MgO的Al2O3为主;LF过程采用高碱度高还原性渣精炼,钢中Al2O3夹杂物向钙铝酸盐和CaO-MgO-Al2O3复合夹杂物转变,平均成分靠近低熔点区;RH真空处理后,夹杂物中Al2O3和MgO的含量减少,CaO含量增加,夹杂物成分分布较为分散;钙处理后,钢中CaO-MgO-Al2O3复合夹杂比例明显减少,CaO与CaS比例明显增加,夹杂物平均成分已经远离低熔点区,达到了高品质管线钢的冶炼效果.     

钛合金改善X80管线钢中硫化物析出的研究

管线钢中的 MnS 对管线钢的韧性、焊接性能、应力腐蚀断裂等性能都有着不可忽视的影响.以不同 S 含量的 X80 管线钢为研究对象,通过加入不同的 Ti 含量控制 MnS 的生成,使其生成 Ti4 C2 S2 .运用 Factsage 软件模拟计算,探讨了 Ti 含量对 MnS 析出的影响,计算得到了不同 S 含量下 Ti4 C2 S2 析出时的临界 Ti 含量.在实验室条件下,制作了不同 Ti、S 含量下的试样,采用 SEM、EDS 观察不同条件下试样中夹杂物的形貌、尺寸和成分变化.研究表明,管线钢中加入 Ti 合金可以使 MnS 转化生成 Ti4 C2 S2 ,且 随 钢 中 S 含 量 的 提 高 其 要 求 转 化 生 成Ti4 C2 S2 的 Ti 含量也需提高.     

X80管线钢生产过程纯净度控制

介绍了采用铁水脱硫预处理、复吹转炉、LF精炼、RH精炼、板坯连铸工艺开发X80管线钢的过程。采用该工艺生产的X80管线钢钢水成品[C]≤0.05%[,P]≤0.012%[,S]≤0.0022%[,N]≤0.005%,T[O]≤30×10-6,[H]≤2.5×10-6,钢中的A、B类夹杂物控制在1.5级以下,C、D类夹杂物能控制在0.5级以下,管线钢洁净度完全满足用户要求。     

Austenitization Behaviors of X80 Pipeline Steels With High Nb and Micro-Ti Treatment

 The austenitization behaviors of two high Nb-containing X80 pipeline steels with different Ti contents, including the dissolution of microalloying precipitates and the austenite grain growth behaviors, were investigated by using physical-chemical phase analysis method and optimal microstructure observation. The results illustrate that most Nb can be dissolved into austenite during the soaking at 1180℃, but very little amount of Ti can be dissolved. It is found that during soaking, the austenite grain growth rate is initially high, and then it decreases after 1h soaking; moreover, the austenite grains grow up more rapidly at temperatures above 1180℃ than at temperatures below 1180℃. It is shown that the steel with 0.016%Ti content has a larger austenite grain size than the steel with 0.012%Ti under the same soaking conditions, which has been explained by considering the particle size distribution.     

Precipitation Behavior and Its Strengthening Effect of X100 Pipeline Steel

 Using TEM, electron diffraction, EDX analysis and physicochemical phase analysis, the morphology, crystal structure, size distribution and chemical composition of precipitates in the microstructure of high strength Nb-microalloyed X100 pipeline steel were investigated, and the strengthening effect of precipitation was quantitatively calculated with Ashby-Orowan correction model. The precipitates obtained in X100 pipeline steel can be divided into two kinds: “complex” and “single” particles by morphology. The EDX analysis of single precipitates reveals that the chemical composition matches well with particle dimensions, especially the Nb/Ti ratio regularly reduces with the increase of particle size. The yield strength increments in the way of precipitation strengthening of X100 pipeline steel reached about 52MPa, which suggests that the precipitation strengthening is not the dominative strengthening mechanism for X100 pipeline steel.     

Austenitization Behaviors of X80 Pipeline Steel With High Nb and Trace Ti Treatment

The austenitization behaviors of two high niobium-containing X80 pipeline steels with different titanium contents, including the dissolution of microalloying precipitates and the austenite grain growth, were investigated by using physical-chemical phase analysis method and microstructural observation. The results illustrated that most niobium could be dissolved into austenite during soaking at 1180℃, whereas little amount of titanium could be dissolved. It was found that during soaking, the austenite grain growth rate was initially high, and then decreased after soaking for 1 h; moreover, the austenite grains grew up more rapidly at temperatures above 1180℃ than below 1180℃. The results show that the steel with titanium content of 0.016% has a larger austenite grain size than that with titanium content of 0.012% under the same soaking conditions, which is explained by considering the particle size distribution.     

X80高级别管线钢的洁净度

针对莱芜钢铁集团120 t顶底复吹转炉(脱磷)→120 t顶底复吹转炉(脱碳)→LF→RH→CC试生产X80管线钢的生产工艺,采取示踪剂示踪、系统取样、综合分析的方法,对LF精炼前后、RH精炼前后,中间包和铸坯中总氧、氮、显微夹杂物和铸坯中大型夹杂物的变化进行了系统的研究。研究结果表明,铸坯中总氧含量平均为8×10-6,氮含量平均为58×10-6(质量分数,下同),96%的显微夹杂物的尺寸小于2μm,平均为2.50个/mm2,大型夹杂物平均为2.23 mg/10 kg。铸坯中氮含量较高,精炼过程夹杂物变性效果较差。     

抗大变形管线钢X80轧制工艺研究

为提高抗大变形管线钢X80的力学性能,在鞍钢5500宽厚板生产线上对其轧制工艺进行了研究。结果表明,提高板坯加热温度及保温时间可改善产品抗拉强度;适当调整弛豫时间,保证钢板入水温度及优化轧制力、轧制道次,可有效控制钢板显微组织,提高产品的均匀延伸率。     

高级别厚规格X80管线钢研制开发

介绍了采用低碳成分设计和TMCP工艺开发X80钢级石油输送管用热轧卷板的关键控制技术和工艺路线。通过低碳多合金强化等微合金化的成分设计、控制钢水的纯净度和板坯的偏析,采用合理的两阶段控制轧制及控制冷却工艺,可以得到针状铁素体＋贝氏体组织。检测指标表明：强度指标和低温韧性等各项力学性能良好,满足中石油＂西二线＂管道工程用热轧卷板技术条件,制管后管体取样各项指标良好。     

Effect of Nb on Mechanical Properties of HAZ for High-Nb X80 Pipeline Steels

The mechanical properties of heat affected zone (HAZ) of two commercial high-Nb X80 grade pipeline steels with different alloy elements were investigated using thermal simulation performed on a Gleeble-3500 thermal simulator. The results showed that the high-Nb steels have excellent weldability. Embrittlement regions appear in coarse grain heat affected zone (CGHAZ) and intercritically heat affected zone (ICHAZ); Softening region appears in fine-grain heat affected zone (FGHAZ), and the strength here was even lower than 555 MPa as required in the standard. Meanwhile, with the increase of heat input, the strength and the toughness of HAZ of steel with high Nb, C and lower alloy decrease notably. Therefore, take into account the welding procedure during manufacture of weld pipe, suitable amount of alloy elements, such as Cr, Ni, Cu, Mo and so on, is necessary for high Nb X80 heavy-thick steel plate.