HTP工艺超低碳贝氏体钢Q620CFD中厚板的开发

研究了超低碳贝氏体钢Q620CFD在HTP工艺条件下轧态、回火态的组织与力学性能;与同级别低Nb钢板进行了变形抗力热模拟对比试验。结果表明,二次开轧温度和轧后回火工艺对该钢的组织、性能和析出物的形态数量有明显影响;采用HTP工艺可以有效降低其控轧生产时的轧制负荷。     

回火温度对轧后直接水淬15CrMoV钢组织和力学性能的影响

试验用钢15CrMoV(%:0.15C、0.29Si、0.57Mn、1.01 Cr、0.37Mo、0.24V)16 mm板材的终轧温度为900～950℃,轧后在880～900℃水淬,并经670～800℃回火。结果表明,试验钢在线淬火后的组织为马氏体+贝氏体,随回火温度升高,钢中碳化物析出量增加,贝氏体板条束逐渐合并和减少,最终转化为碳化物+多边形铁素体组织;在730～780℃回火,15CrMoV钢具有良好的综合力学性能,抗拉强度680～760 MPa,冲击功55～130 J。     

HTP工艺生产的700 MPa级中厚板的组织与性能

 研究了高Nb超低碳贝氏体钢在HTP工艺条件下轧态、回火态的组织与力学性能。采用的合金成分（质量分数）为：C 0.05%、Mn 1.85%、Nb 0.1%左右,其余合金元素有Cu、Ni、Cr、B等。进行了热模拟研究、实验室冶炼轧制和工业试制。试验结果表明,第二阶段开轧温度、冷却速度和轧后高温回火工艺对钢的组织、析出物的形态和数量有明显影响。采用合适的HTP工艺与轧后高温回火相结合,能够生产出屈服强度达到700 MPa级别的高强度、高韧性钢板。     

800MPa级含钨低碳贝氏体钢的实验研究

采用金相及硬度测量并结合透射电子显微镜观察,研究了800MPa级含钨低碳贝氏体钢轧态及回火态组织和性能的变化.结果表明,实验钢的屈服强度、抗拉强度均随钨的质量分数的提高而提高;回火后试样的冲击值和延伸率都较轧态有所提高;添加钨后,钢板组织为板条贝氏体和少量粒状贝氏体的复合组织;当钨含量高于0.4%,回火温度在550～600℃范围内时,在板条间和位错上析出大量细小的含Nb、W、Ti碳化物,提高了钢板强度;当钨含量低于0.3%时,钨的固溶强化机制作用明显.     

超高强韧油井管合金设计与高强韧机制

 为了揭示1 000 MPa级低碳加铌钒钛微合金钢的高强韧机制,研究了S1(w(C)=0.09%)与S2(w(C)=0.17%)两种合金成分的油井管钢成分-工艺-组织-性能关系。试验表明,两种成分试验钢经水淬后的组织分别为板条贝氏体加少量马氏体和马氏体加少量贝氏体的复相组织。两种成分钢经过450~600 ℃、30 min的中温回火后,组织中均出现碳化物析出,且S1试验钢回火后的屈服强度基本不变,抗拉强度下降了约70 MPa,S2试验钢回火后的屈服强度与抗拉强度迅速升高170 MPa左右。溶度积公式的计算结果表明,两种钢的水淬组织中铌、钛元素析出彻底且析出物的体积分数都很小,因此回火铁素体基体中的VC析出强化对S1试验钢回火后屈服强度保持不变以及S2试验钢回火后屈服、抗拉强度提高起到重要作用。     

回火温度对Mo-V-Ti钢组织与性能的影响

为了研究回火温度、析出相对含Mo-V-Ti钢组织与性能的影响,试验采用550 mm轧机对含Mo-V-Ti钢轧制后进行完全淬火,然后在630~710℃不同的温度下进行回火。结果表明,高温回火后,钢的组织由回火索氏体和少量贝氏体组成,组织中发生回复和再结晶,钢的强韧性匹配发生变化。在670℃以下回火时产生的析出相主要为Ti、V和Mo复合的碳氮化合物和V、Mo复合的碳氮化合物,随着回火温度的提高,产生了新的析出相Fe、Mn和Mo及V合金渗碳体,析出相对钢的强韧性有重要影响。     

低碳贝氏体钢的回火转变及内耗研究

针对低碳贝氏体钢,采用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射和内耗手段分析了600℃回火过程中的显微组织变化,测试了回火后的屈服强度。结果表明,试验钢轧制态的显微组织是板条贝氏体与粒状贝氏体的混合组织,有少量Mo_2C和NbC析出。随着回火时间延长,贝氏体板条的宽度不断增大,板条内部形成较多不同取向的胞状结构,有些板条逐步演化为多边形状,粒状贝氏体不断吞噬板条贝氏体,使显微组织中粒状贝氏体增多且粗化;Mo_2C和NbC析出物进一步增多,贝氏体铁素体中的位错密度不断降低;内耗-温度谱中Snoek峰值不断降低,表面处的SKK峰值先降低后升高,心部的SKK峰值先降低后变化不大;屈服强度呈现先提高后降低的趋势。     

回火温度对800 MPa级低碳贝氏体钢组织及性能的影响

对采用TMCP工艺轧制的800 MPa低碳贝氏体钢进行不同温度的回火试验,分析了不同回火温度对800MPa级低碳贝氏体钢的组织及性能的影响。结果表明:回火过程是板条贝氏体的熟化过程,随着回火温度的升高,强度降低,而冲击韧性得到改善。     

热处理工艺对100mm特厚07MnCrMoVR水电钢板组织性能的影响

对07MnCrMoR水电钢板的淬透性曲线进行了测定,利用淬火机和热处理炉对100 mm厚试验钢板进行了淬火和回火试验,并对试验钢进行了组织观察和力学性能测定。结果表明,随着试验钢距水冷端的距离增大,淬火组织由马氏体转变为粒状贝氏体,距离端部50 mm处转变为铁素体和粒状贝氏体的混合组织。试验钢板利用淬火机淬火后得到板条贝氏体+粒状贝氏体+先共析铁素体,回火后转变为铁素体+粒状贝氏体,同时大量的碳化物在铁素体基体和晶界处析出。试验钢最合理的热处理工艺为930℃ 30min水冷淬火,660℃ 60min空冷回火。     

非调质型15万m~3石油储备罐体用610MPa高强度钢板轧制和热处理工艺研究与实践

主要采用热模拟技术研究了不同终轧工艺和不同回火温度对石油储备罐体用高强度钢板JGR610E显微组织的影响,并利用金相和萃取复型等分析方法对不同工艺下的显微结构和碳化物进行了分析。结果表明,JGR610E钢在860℃左右终轧温度、20℃/s冷却速度下可以获得板条状低碳贝氏体组织,经过620℃回火后得到具有良好强韧性能的板条贝氏体和针状铁素体混合组织,其析出相主要有两类,尺寸在300 nm左右的为含有Fe和Mn的MxCy型碳化物,尺寸范围在50～100 nm的为含有Ti和Nb的MC型碳化物,且在该回火温度下,有大量的尺寸范围在几个纳米至十几个纳米尺寸的Ti(CN)析出。     

Morphology and properties of low-carbon bainite

Morphology of low-carbon bainite in commercial-grade high-tensile-strength steels in both isothermal transformation and continuous cooling transformation is lathlike ferrite elongated in the 〈11l〉_b direction. Based on carbide distribution, three types of bainites are classified: Type I, is carbide-free, Type II has fine carbide platelets lying between laths, and Type III has carbides parallel to a specific ferrite plane. At the initial stage of transformation, upper bainitic ferrite forms a subunit elongated in the [−101]f which is nearly parallel to the [lll]_b direction with the cross section a parallelogram shape. Coalescence of the subunit yields the lathlike bainite with the [−101]_f growth direction and the habit plane between (232)_f and (lll)_f. Cementite particles precipitate on the sidewise growth tips of the Type II bainitic ferrite subunit. This results in the cementite platelet aligning parallel to a specific ferrite plane in the laths after coalescence. These morphologies of bainites are the same in various kinds of low-carbon high-strength steels. The lowest brittle-ductile transition temperature and the highest strength were obtained either by Type III bainite or bainite/martensite duplex structure because of the crack path limited by fine unit microstructure. It should also be noted that the tempered duplex structure has higher strength than the tempered martensite in the tempering temperature range between 200 °C and 500 °C. In the case of controlled rolling, the accelerated cooling afterward produces a complex structure comprised of ferrite, cementite, and martensite as well as BI-type bainite. Type I bainite in this structure is refined by controlled rolling and plays a very important role in improving the strength and toughness of low-carbon steels. This paper is based on a presentation made in the symposium “International Conference on Bainite” presented at the 1988 World Materials Congress in Chicago, IL, on September 26 and 27, 1988, under the auspices of the ASM INTERNATIONAL Phase Transformations Committee and the TMS Ferrous Metallurgy Committee.     

Strain tempering of bainite

In the present investigation the strain tempering of bainite has been carried out with (EN 24) a medium carbon low alloy steel. The specimens were austenitized at 850°C and isothermally transformed at 300°, 360°, and 400°C to produce bainite, strained and tempered in the range 100° to 400°C. The bainite formed at 360°C has been specifically examined by thermomagnetic analysis to confirm quantitatively the solution of ∈ carbide. Thermomagnetic analysis has shown that the carbide phase in bainite formed even at 360°C is a mixture of ∈ carbide and cementite. It has been found that with lowering of bainite transformation temperature, the strain tempering treatment results in higher strength consistent with good ductility. The present investigation favors the carbon dislocation trapping model for the mechanism of strain tempering of bainite, similar to that proposed for the strain tempering of martensite.     

C-Mn-Cr-Nb系低合金钢抗氢致开裂性能

 研究了一种低C、低Mn、高Cr和高Nb低合金钢经控轧控冷及轧后回火处理后性能与组织的变化,并对试验钢进行了抗氢致开裂(HIC)试验。结果表明：与轧态相比,回火处理后试验钢的力学性能有较大提高,600℃左右回火后屈服强度由轧态519MPa增加到626MPa,抗拉强度由653MPa增加到705MPa,且韧性基本未降低,回火处理后组织仍以针状铁素体为主,回火后M/A岛尺寸减少。此外,轧态与回火态钢均能满足抗HIC试验衡量标准,回火处理后抗HIC性能优异。降低Mn质量分数能显著提高低合金钢抗HIC性能,提高Cr质量分数和Nb质量分数能有效强化低Mn钢的强度。     

调质工艺对汽车大梁钢700L组织性能的影响

摘 要: 通过金属摆锤冲击和显微硬度试验,采用OM、SEM、TEM等表征手段,研究了不同调质工艺对700L汽车大梁钢组织和力学性能的影响。结果表明,随着淬火温度的提高,粒状贝氏体(GB)组织有所减少,板条状贝氏体铁素体(BF)数量逐渐变多,板条宽度增加,铁素体基体及边界上的白色析出物数量增多;随着回火温度的提高,块状铁素体有所长大,马奥岛组织和残余奥氏体分解现象明显,且出现了数量较少的等轴状铁素体,回火析出物数量增多,回火温度超过600 ℃后粒子出现粗化长大现象。低温冲击功在不同淬火与回火条件下均表现为上下波动的状态,这主要与第二相粒子及基体组织规律性的变化有关;试验钢在经600 ℃回火后具有最佳低温冲击韧性,其主要原因是钢基体中存在数量较多的具有高密度位错的贝氏体铁素体(BF)与尺寸合适、分布均匀的第二相纳米粒子。     

空冷高硅中碳低合金钢的组织与性能

研究了高硅中碳低合金钢空冷态和空冷+回火态的显微组织和力学性能.试验钢在860℃保温0.5h奥氏体化后空冷处理,随后分别在250℃和400℃保温1h回火.结果表明:试验钢空冷后组织为贝氏体/马氏体和残余奥氏体的混合组织,硬度约为41 HRC;而250℃回火后组织变化不大,硬度明显升高,约为49 HRC,韧性明显增加,由44 J/cm2增加到66 J/cm2,抗拉强度、屈服强度和延伸率明显下降.回火温度进一步增加对力学性能影响不大.     

HB400级高强度准贝氏体耐磨钢板的组织与性能

研究了热轧、低温回火和热轧、正火、低温回火及轧态不同温度回火工艺对新型HB400级高强度准贝氏体耐磨钢板的组织和力学性能及耐磨性能的影响。结果表明，2种状态下耐磨板的组织由贝氏体铁索体(BF)和残余奥氏体(AR)组成，具有良好的强韧性及耐磨性能。低温回火可以改善耐磨钢板的韧性。新型耐磨钢板具有较强的回火抗力。用准贝氏体钢生产高强度耐磨板具有生产工艺简单，成本低廉等特点。     

Study of TRIP-Aided Bainitic Ferritic Steels Produced by Hot Press Forming

A study is reported to produce high strength ductile steels by controlled cooling following hot press forming, instead of quenching, as is practiced in the traditional press hardened steels. Heat treatments of several specially designed low carbon steels were carried out by interrupting the fast cooling from the austenization temperature at temperatures between T ₀ and Ms and then cooling in controlled rates to room temperature. The effect of the interrupt temperature and the cooling rate afterward on the microstructures and tensile properties was studied. The microstructures were characterized using dilatometry, optical microscopy, X-ray diffraction, and TEM. A multi-phase microstructure including bainite, martensite, and retained austenite was obtained in the simulated hot press forming process. Volume fraction bainite was found to increase with an increase in interrupt temperature and a decrease in cooling rate. Structure–property correlations of the studied steels heat treated at different conditions were developed. Improved tensile properties were obtained by controlling the interrupt temperature and cooling rate which produced an optimum bainite content of 60 to 75 pct and retained austenite. Unfortunately, the bainite in the simulated samples was not completely carbide free even though the steels contained about 1.6 wt pct of Si.     

钢铁结构材料的组织细化

采用组织超细化提高钢铁结构材料的强细性和使用寿命是上个世纪90年代中期以来的发展趋势。介绍了我国973第一批项目之一“新一代钢铁材料重大基础研究”的主要5种超细化方法，适用于不同强度和显微组织的钢类：具有铁素体 珠光体(F P)的碳素或低合金钢，采用强力轧制和形变诱导铁素体相交(DIFT)技术；在薄板坯连铸连轧现代流程下，采用第二相(析出相)的纳米化控制；具有低碳贝氏体或针状铁素体的微合金钢采用形变诱导析出(DIP)和中温相交控制；采用调质处理的合金结构钢，应用新的合金设计思路以提高界面温度，增加氢陷阱和二次硬化路线，快速超细晶热处理的综合技术；发展无碳化物贝／马组织和富碳残奥薄膜以做到中低温回火合结钢的强韧化优良配合。     

Bainitic chromium-tungsten steels with 3 Pct chromium

Previous work on 3Cr-1.5MoV (nominally Fe-3Cr-2.5Mo-0.25V-0.1C), 2.25Cr-2W (Fe-2.25Cr-2W-0.1C), and 2.25Cr-2WV (Fe-2.25Cr-2W-0.25V-0.1C) steels indicated that the impact toughness of these steels depended on the microstructure of the bainite formed during continuous cooling from the austenitization temperature. Microstructures formed during continuous cooling can differ from classical upper and lower bainite formed during isothermal transformation. Two types of nonclassical microstructures were observed depending on the cooling rate: carbide-free acicular bainite at rapid cooling rates and granular bainite at slower cooling rates. The Charpy impact toughness of the acicular ferrite was considerably better than for the granular bainite. It was postulated that alloying to improve the hardenability of the steel would promote the formation of acicular bainite, just as increasing the cooling rate does. To test this, chromium and tungsten were added to the 2.25Cr-2W and 2.25Cr-2WV steel compositions to increase their hardenability. Charpy testing indicated that the new 3Cr-W and 3Cr-WV steels had improved impact toughness, as demonstrated by lower ductile-brittle transition temperatures and higher upper-shelf energies. This improvement occurred with less tempering than was necessary to achieve similar toughness for the 2.25Cr steels and for high-chromium (9 to 12 pct Cr) Cr-W and Cr-Mo steels.