Development of Nb-V-Ti Hot-Rolled High Strength Steel With Fine Ferrite and Precipitation Strengthening

A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature (DBTT) lower than-70℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800 ℃ is rational, and coiling temperature is between 400 and 500℃. The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.     

CSP热轧低碳钢的强化机制研究

研究了CSP热轧低碳SPHC钢的微观组织、第二相粒子的析出及其对强度的影响,对马钢CSP生产的SPHC钢和常规热轧工艺的SPHC钢进行了屈服强度比较.结果表明,马钢SPHC钢的实测值比计算值高42MPa,常规工艺生产的SPHC钢实测值与计算值比较接近.对马钢SPHC钢进行透射电镜观察,观察到其中存在纳米级的、亚微米级的和微米级的3种尺寸级别的第二相粒子,马钢SPHC钢沉淀强化的强度增量为40 MPa.     

薄板坯连铸连轧低碳微合金高强度钢的力学性能与组织控制

利用薄板坯连铸连轧工艺和控轧与控冷工艺,生产了低碳微合金高强度钢.利用光学显微镜、扫描电子显微镜(SEM)和透射电子显微镜(TEM)分析了该钢的微观组织结构.该钢主要由精细的针状铁素体、粒状贝氏体和多边形铁素体组成.铁素体和贝氏体组织中存在由位错形成的胞状亚结构,这有利于品粒细化.薄板坯连铸连轧工艺生产的低碳微合金高强度钢具有良好的综合力学性能.其屈服强度达到了600 MPa级,伸长率大于20%.     

含钒低合金高强钢的沉淀析出行为

介绍了含钒低合金高强钢沉淀析出的形成,分析了碳氮化钒的一般析出、相间析出和纤维状析出的典型形貌、析出模型等,给出了最新的研究现状,探讨了含钒低合金高强钢的应用前景。     

High Strength High Carbon Low Alloy Pearlite-Ferrite-Tempered Martensite Steels

High strength multiphase steels have been developed consisting of combination of pearlite, tempered martensite and small amount of ferrite, by suitable heat treatment of a high carbon low alloy rail steel (0.7 % C). The desired microstructure has been obtained by holding fully homogenized steel in pearlitic range for small durations followed by water quenching and subsequent tempering at 773 K for 18 h. Variation in mechanical properties has been studied with the change in volume fraction of different phases. Yield strength, ultimate tensile strength and elongation are observed to be in the range of 500–1,000 MPa, 900–1,185 MPa and up to 16.8 %, respectively. Continuous and discontinuous yielding along with substantial work hardening has been explained as a function of tempered martensite content.     

铜沉淀在低合金高强度钢中的特性

1　简介低合金高强度 ( HSL A)钢 ,如海洋结构用钢HSL A- 1 0 0 ,要求强度、韧性与焊接性等综合性能。为达到这些性能 ,需在低碳钢中添加几种合金元素 ,加铜就是为了通过时效硬化来提高强度。几种参考文献中均讨论过时效期间铜沉淀的特性及强化机理。在时效初始阶段形成粘着性微细体心立方沉淀物。随着时效时间的延长 ,体心立方相转化成非粘着性面心立方铜沉淀物。当粘着性沉淀达到一个临界值 (～ 2 .4mm)时 ,出现了峰值强度。铜沉淀的量、大小和形态可影响含铜钢时效后的性能。目前 ,已试图研究等温时效期间和连续冷却过程中铜沉淀的特…     

新型高强度铜微合金材料的研究与开发

本文以提高铜管材的抗拉强度为主要内容,针对以磷脱氧铜为基体添加微量元素的铜微合金进行了机械性能等方面的分析,得出部分结论,仅供参考。     

低碳微合金钢中超细组织的热稳定性分析

研究了经过新开发的弛豫-析出控制相变RPC技术得到的钢板在650℃等温回火过程中组织与性能的演变,并与经过930℃保温1h后再淬火（RQ）工艺处理后的钢板进行了对比。回火前两种钢板均为贝氏体和少量马氏体的复合组织,经过RPC处理后的钢板回火0．5h后,金相尺度下的组织没有明显变化,但硬度下降较快,在1～7h的回火过程中组织中局部区域出现板条合并现象,此阶段硬度值变化不明显,7h之后某些区域组织的板条特征趋于消失,出现了少量的多边形铁素体,硬度开始明显下降,回火20h后,大约一半的组织转化成了多边形铁素体。而经过RQ处理后的钢板回火前硬度虽然较低,但回火过程中软化速度极快,板条组织很快消失,最终获得全部的多边形铁素体组织。结果表明超细组织的热稳定性取决于其加热历史。     

低碳微合金钢中的晶内铁素体及组织控制

回顾和评述了晶内铁素体的发现、发展及其与组织控制的关系.介绍了晶内铁素体的形核机制和影响晶内铁素体形成的因素,讨论了晶内铁素体的三维形态和长大动力学,并从以上几方面分析了晶内铁素体对低碳微合金钢组织细化的重要作用和影响.     

微合金高碳硬线钢的研制

通过实验室研究与酒钢现场生产工艺相结合,对微合金高碳钢在中小型转炉条件下的生产技术进行了研究。试验表明,改进工艺后钢中ω（TO）平均降低至0．0038％,显微夹杂物数量降低了78％,大颗粒夹杂物数量降低了65%。铌微合金化处理后高碳钢线材的力学性能得到了改善。酒钢应用新工艺生产了铌微合金高碳硬线钢2980t,拉拔正常且钢丝性能优良。     

EAF-CSP流程钛微合金化高强钢板的组织和性能研究

珠钢采用Ti微合金化技术在EAF—CSP流程上成功地开发出屈服强度为450～700MPa的高强度热轧钢板。系统地研究了试验钢的组织和性能．并分析了组织与性能的关系。结果表明，随钛含量增加或成品厚度减薄钢板的屈服强度显著提高，最高达到695MPa；钛的质量分数低于0．024％时对屈服强度影响不大；当钛的质量分数低于0．045％时．钢板屈服强度的提高主要来自于晶粒细化，而当钛的质量分数大于0．045％后，钢板强度的进一步提高来自于沉淀强化。     

钛微合金化高强钢的研究与发展

简要回顾了国内外钛微合金化高强钢的发展历程,详细论述了700 MPa以上级别钛微合金化高强钢的研发现状,着重阐述了钛微合金化高强钢中纳米碳化物析出行为(形变诱导析出与相间析出)的研究现状,并分析了钛微合金化技术的发展趋势,旨在进一步完善钛微合金化物理冶金学理论,为钛微合金化高强钢的发展和工业应用提供一定的指导。     

V-N微合金化高强度厚板的研制

对比了V-N微合金化和V微合金化钢的强化效果，确认钢中增加N含量能有效提高V的析出强化与细晶强化能力，对钢的各项性能都不会产生不利影响。采用V-N微合金化和控制轧制工艺试制了60、70mm厚板，产品性能到达了Q390E钢的质量要求。     

含Nb-Ti低碳钢的析出与细晶强化效应研究

采用控轧控冷(TMCP)工艺制备的0.013%Nb-0.013%Ti钢和C-Mn钢性能对比显示,添加微量Nb-Ti明显提高了钢的强度和冲击韧性,原因是微量Nb-Ti细化了铁素体晶粒并得到更高体积分数的弥散分布(Nb,Ti)(C,N)析出颗粒。用Hall-Petch晶粒尺寸强化和Ashby-Orowan弥散强化模型计算铁素体晶粒尺寸、析出颗粒尺寸和体积分数等微观组织变量对强度的量化贡献,结果表明,Nb-Ti钢的主要强化机理为细晶强化和弥散强化,而降低韧脆转变温度的主要机理是晶粒细化和微合金碳氮化物析出降低了钢中的自由氮含量。     

Effects of Coiling Temperature on Strength,Yield Ratio and Precipitation Behaviors of Hot Rolled High Strength Microalloyed Steel for Cold Forming

Various hot rolling schedules were applied to a Nb,V,Ti contained HSLA steel.Coiling temperature had crucial effects on not only yield strength,but also yield ratio and precipitation behavior.600Mpa yield strength is achieved when coiled at 450℃,which is 100Mpa higher than those coiled at 570℃.However,the low coiling temperature had adverse effect to increase yield ratio,which increased from 0.78 to 0.88 as coiling temperature dropped from 570℃ to 450℃.High resolution SEM analysis shows that sizes of Nb,V,Ti precipitates are affected by coiling temperature.Coarse (Nb,Ti)(C,N) precipitates up to 5μm are observed at higher coiling temperature and to decrease tensile strength,where high coiling temperature corresponds to low cooling rate.With strong cooling and coiling capacity of Shasteel’s 1450mm width hot rolling mill,these results indicate that strength and formability of the steel can be balanced when coiling temperature has been optimized.Alloying and microalloying costs can be reduced by efficiently utilizing the capacity of rolling mill.Alumina inclusions are found to act as nucleus for Nb,V,Ti precipitates,contributing to coarsening of precipitates.     

低碳高强度Q620D结构钢研制

通过合理的组织、成分设计,并根据成分特点及钢种级别确定了合理的冶炼及加热工艺,轧制及热处理工序采用TMCP(Thermo mechanical Controlled Process)+回火工艺,成功开发了Q620D级低合金高强度结构钢板。该钢种组织以贝氏体为主,还有少量针状铁素体,晶粒细小,具有较高的强度和优良的冲击韧性。     

低碳钒氮微合金钢中V(C,N)在奥氏体中的析出动力学

控制VN在奥氏体中的有效析出是利用VN诱导晶内铁素体细化铁素体晶粒的关键技术。采用应力松弛方法研究了低碳钒氮微合金钢中V(C,N)在奥氏体区的等温析出行为。结果表明：试验钢的析出-温度-时间曲线(PTT)呈典型的C形,本试验条件下析出开始时间最短的“鼻子”温度为870℃左右。钢中的碳、氮含量以及变形量对PTT曲线有较大影响,它们增加均使C曲线向左移,特别是氮含量对V(C,N)析出的影响最显著。在碳含量约为0．10％的试验钢中,当氮含量从0．0036％增加到0．0140％时,可使870℃的析出开始时间从400s缩短到70s左右。     

Precipitates and Hydrogen Permeation Behavior in Vanadium-Bearing Microalloyed Low Carbon Steel

The precipitates and hydrogen permeation behavior were studied in the low carbon steel for enameling.During the preparation of samples,Ti containing and Ti free in vanadium-bearing microalloyed low carbon steel heating at 750℃ for 3 h,were adopted after cold-rolling.It was found that the a large number of fine VC,TiC,TiN and Ti 4 C 2 S 2 precipitates were in samples of Vanadium-bearing microalloyed low carbon steel with Ti element.And fine VC,Fe 3 C and MnS precipitates were in steels without Ti element.So the numbers of precipitates in the former is more bigger than the later.The activation energies for hydrogen diffusion in both samples are 26.5 and 23.7 kJ/mol,respectively.But at 25℃,the effective diffusion coefficients in the samples for Ti containing and Ti free in Vanadium-bearing microalloyed low carbon steel were measured as 2.71×10-6 and 4.22×10-6 cm 2 /s,respectively.No fishscaling defect occurred in the former and heavy fishscaling defect in the later.     

Investigation of Austenitization in Low Carbon Microalloyed Steel During Continuous Heating

Dilatation associated with the formation of austenite from ferrite–pearlite was calculated from equilibrium phase fraction and composition. Linear thermal expansion coefficient of ferrite required for the calculation was determined by iteration of dilatation data. A good match was obtained between the calculated and experimental dilatation curves. The calculated dilatation data were used to identify the stages of austenite formation: pearlite dissolution followed by ferrite to austenite transformation which is gradual at first before becoming rapid.     

铌微合金化高碳钢的连续冷却转变

在Geeble-1500热／力模拟试验机上测定了铌微合金化高碳钢与普通高碳钢变形后的连续冷却转变曲线，分析比较了它们的组织演变规律。实验结果表明，与普通高碳钢相比，含铌高碳钢的转变温度较高，A P两相区的温度范围较大(在所测定的冷速下，温度范围均在100℃以上)，且在相同冷速下，先共析铁素体的数量明显增多，而奥氏体晶粒较小。在本实验条件下，当冷速大于10℃／s时，含铌高碳钢转变后的珠光体片层间距较小；在冷速大于30℃／s时，其基体中出现贝氏体组织。