Nb-V微合金化低钼型Q345耐火钢的开发

 为了推动耐火钢的市场应用,采用低碳、低钼(约0.2%)及铌、钒、钛的复合微合金化成分设计,成功开发出低成本Q345耐火钢。采用Formastor-Digital全自动相变测试仪测定了试验钢的连续冷却转变(CCT)曲线,利用Gleeble-1500热模拟试验机研究了变形后不同冷却工艺对试验钢组织及硬度的影响,并采用SEM、EBSD、TEM和物理化学相分析等手段对热轧及600 ℃高温拉伸试样基体组织及纳米第二相进行了详细表征,定量分析了试验钢室温及高温下的强度机制。结果表明,轧后760~780 ℃开始层流冷却、终冷温度为400~600 ℃,试验钢获得铁素体+贝氏体组织。经600 ℃高温拉伸后,试验钢中MC相的质量分数及处于18 nm以下的粒子质量百分比相对于热轧态试样分别提高了16.4%、9.8%,这些新析出的纳米级粒子在高温下起到了良好的沉淀强化作用,一定程度弥补了高温下因剪切模量下降和细晶强化失效导致的高温屈服强度的损失;固溶、沉淀强化为Q345耐火钢主要的高温强化方式。     

建筑结构用新型抗震耐火钢Q420FRE的开发

新型耐火钢除了要求具有等同或优于普通建筑钢的室温力学性能和良好焊接性能,还需要保证耐火性能和良好抗震性能,并拥有比传统耐火钢成本更低的特点。南钢基于实验室试验的结果,设计了低Mo新型耐火钢的化学成分和轧制工艺,试制了不同厚度规格的Q420FRE耐火钢,其各项性能均优于标准对同级别耐火钢的要求。600℃高温强度达到室温强度的70%,280 MPa恒载荷下的耐火极限温度约为700℃,模拟二次火灾高温强度仍超过280 MPa,屈强比0.83,具有良好的耐火及抗震性能。     

低Mo耐火建筑用钢Q345FRE开发试验研究

综合考虑合金元素对耐火建筑用钢高温力学性能的作用,在实验室采用500 kg多功能真空感应炉完成低Mo成分体系Q345FRE耐火钢热轧基料的制备,使用550 mm热轧实验机组完成15 mm厚度耐火建筑用钢板的轧制和冷却。比较轧后水冷和空冷两种工艺,常温力学性能均满足GB/T 28415—2012《耐火结构用钢板及钢带》标准要求。轧后空冷钢板的高温性能未满足国标要求,而轧后水冷钢板的高温性能满足国标要求,主要原因为水冷钢板高温组织相比空冷显著细化。通过合适的成分设计、轧制和冷却工艺,实现了15 mm厚度耐火建筑用钢Q345FRE的成功试验开发。     

复合微合金化对SiMn3型贝氏体钢力学性能的影响

研究了用少量Ｍｏ，微量Ｖ，Ｂ，Ｒｅ进行复合微合金化，对低碳ＳｉＭｎ３型贝氏体高强钢力学性能的影响。结果表明，复合微合金化可显著提高其空冷状态的韧性，明显改善低温韧性，并可显著提高回火抗力和高温回火后的强度。     

钒对耐火钢显微组织及高温性能的影响

 通常采用控轧控冷方式生产耐火钢Mo-Nb复合合金化。采用电子显微镜、相分析和三维原子探针等方法,研究了不同热轧工艺条件下钒对含钒耐火钢的室温和600 ℃拉伸性能的影响,探讨了微观组织与力学性能之间的关系。结果表明,添加钒后能形成细小弥散分布的析出物,配合控制贝氏体比例后能有效地提高室温和高温力学性能;钒在热轧态耐火钢中主要固溶于先共析铁素体内,再加热至600 ℃时热轧态被“隐藏”的钒存在明显的析出,进一步提高了含钒耐火钢的高温性能。     

钒对低钼耐火钢组织及性能的影响

采用扫描、透射电镜对不同钒含量的低钼耐火钢的组织进行分析,确定出热轧状态的组织为先共析铁素体、粒状组织/粒状贝氏体.同时还发现V的析出物在热轧钢中主要固溶于铁素体基体内,600 ℃重新加热时以细小的V(C,N)弥散析出,从而起到高温析出强化的作用.     

钢结构建筑用耐火钢的研究

在实验室研究基础上提出一种经济型耐火钢成分设计,研究结果表明：具有细小多边形铁素体＋珠光体＋粒状贝氏体混合组织的该钢种具有良好的高温力学性能、良好的低温韧性,满足了建筑用耐火钢的性能要求。     

60kg级低屈强比耐火钢的实验研究

对一种低屈强比建筑用耐火钢进行实验研究，介绍了实验钢的化学成分、实验工艺、力学性能等，重点论述了合金元素、组织等对钢的屈强比、高温强度的影响。结果表明，该钢具有良好的综合机械性能．组织为铁素体基体加贝氏体第二相．因此获得低的屈强比。合金元素Cr、Mo、Nb等的加入有效地提高了钢的高温性能。     

高韧性桥梁钢Q420qD的开发

为了满足桥梁钢Q420qD高强、高韧性的要求,采用低碳、铌、钒、钛微合金化成分设计方案,应用铁水预处理、自动化炼钢控制钢水洁净度,采用电磁搅拌及重压下等工艺手段保证铸坯质量,利用新一代TMCP工艺,控制钢板的组织细化和均匀,保证产品的综合力学性能。通过力学性能的测试和组织检测,开发钢种屈服强度在450~510 MPa,抗拉强度在560~640 MPa,伸长率在21%~25%,－20 ℃冲击功全部在200 J以上,屈强比全部小于0.85,Ⅱ级探伤全部合格;在Gleeble3500试验机上测定了钢种的动态CCT曲线,为制定控轧控冷工艺提供理论基础;应用透射对析出物的分析表明,析出强化贡献量占全部强度的15%以下,强化机制以固溶强化、细晶强化和贝氏体相变强化为主。     

复合微合金化低碳SiMn3型贝氏体钢焊接裂纹敏感性的研究

用铁研试验法,研究了符合我国资源特点的复合微合金化低碳ＳｉＭｎ３型贝氏体高强钢的焊接裂纹敏感性。结果表明,该类钢即使在不预热的条件下施焊,也不会出现冷裂纹。这与其ＨＡＺ过热区具有板条贝氏体加低碳马氏体混合组织有关。     

Microstructure and Mechanical Properties of Precipitation Strengthened Fire Resistant Steel Containing High Nb and Low Mo

Through the thermo-mechanical control process(TMCP),a high Nb low Mo fire resistant steel with the yield strength(YS)of 521 MPa at room temperature(RT)and 360 MPa at elevated temperature(ET)of 600 ℃was developed based on MX(M=Nb,V,Mo;X=C,N)precipitation strengthening.A series of tensile and constant load tests were conducted to study the mechanical properties at ET.The dynamic continuous cooling transformation(CCT)as well as precipitation behavior of microalloy carbonitride was investigated by means of thermal simulator and electron microscopy approaches.Results showed that the failure temperature of tested steel was determined as 653 ℃,and the granular bainite was obtained when the cooling rate was higher than 10 ℃/s.In the rolled state,a certain amount of M/A islands was observed.During heating from RT to ET,M/A islands disappeared,and cementites and high dense compound precipitates(Nb,Mo,V)C with size of less than 10 nm precipitated in ferrite at ET(600 ℃),which resulted in precipitation strengthening at ET.     

Effect of Hot Rolling Practice on Microstructure and Mechanical Properties of Fire-Resistant Steel

Trials to develop a C-Mn-Mo-Nb type fire-resistant steel have been carried out by adopting recrystallization rolling (RCR) + air cooling (AC),two-stage rolling (TSR) + AC and RCR + water cooling (WC).Both RCR and TSR followed by AC resulted in polygonal ferrite (F) + pearlite (P) microstructure,while F + bainite (B) microstructure was formed by RCR + WC.The plates with F+P microstructure show tensile strengths ≥490MPa,while those with F+B exhibit tensile strengths ≥590MPa.All the plates show favorable low yield ratios ≤ 0.75,good charpy v-notch impact property >101J at 0℃ and satisfactory high temperature strength (≥2/3 of room temperature yield strength retained at 600℃).     

耐火钢的性能及工艺研究

测定了耐火钢的CCT曲线,研究了耐火钢的性能,包括室温和高温拉伸性能、系列温度下的冲击性能、应变时效性能等;探讨了终轧温度、冷却速度、回火对耐火钢性能的影响.结果表明:试验钢的综合性能完全满足了设计指标的要求,生产工艺的研究工作为耐火钢的工业生产提供了有益的参考.     

Influence of Mo Content on Microstructure and Mechanical Properties of Fire-Resistant Construction Steel

In order to ensure fire-resistant property of the steel under the condition of the least molybdenum content,effects of molybdenum on microstructure and properties of the fire-resistant construction steel,specially on high temperature strength were investigated.The results show that the room temperature and high temperature strength of the steel is enhanced due to increased Mo content but the impact toughness deteriorates at the same time.The fraction of bainite in the microstructure increases with increasing Mo content while the fractions of polygonal ferrite and pearlite decrease.Comparing with the steel of adding Nb alone,it was obvious that combined addition of Mo and Nb could provide better effect in high temperature strengthening.Addition of 0.25mass% Mo in the steel containing Nb could meet fire-resistant requirements of the construction steel and provide better economical effectiveness.     

微钛处理对钒微合金钢组织与力学性能的影响

在承钢1780热连轧生产线上,轧制了钒微合金钢及钒钛复合微合金化钢,研究了微钛处理对钒微合金化钢微观组织与力学性能的影响.试验结果表明,钒微合金钢经微钛处理后生成了少量TiN析出物,其数量较少,晶粒细化效果有限;由于钛与氮的优先结合,减少了与钒结合的氮含量,降低了钒的析出量,导致微钛处理的钒微合金钢抗拉强度降低约54 ...     

Microstructures and Mechanical Properties of a New Low Carbon Bainitic Weathering Steel

A low carbon bainitic weathering steel with Cu-P alloying was developed.The mechanical properties and hot-rolled microstructures of the new steel at different finishing temperatures were investigated.Cu-P alloying produced strong solution strengthening,delayed the transformation of austenite to bainite,thereby increased the amount of M/A islands.The interaction of phosphorous and copper atoms with dislocations inhibited the recovery process and the formation of subgrains.Low temperature rolling promoted the formation of bainite plates and reduced the size of M/A island,which were beneficial to improving the low temperature impact toughness of phosphorus-bearing low carbon bainitic steel.