控轧控冷工艺对X100管线钢组织和性能的影响

通过实验室φ350 mm 4辊轧机对V-Nb-Wi微合金化X100管线钢(%:0.057C、1.84Mn、0.25Mo)进行控轧控冷试验。结果表明,在1 100℃始轧,800～900℃终轧,100～400℃终冷温度下,X100钢的组织为针状铁素体+粒状贝氏体-下贝氏体。降低终轧温度可细化组织,提高钢的强度;降低终冷温度可提高钢的强度,但使钢的韧性降低。X100管线钢的最佳轧制工艺为终轧温度850℃,终冷温度200℃。     

不同终轧温度下36Mn2V钢的连续冷却转变规律

采用Gleeble-1500热模拟机,测定了36Mn2V钢经四种终轧温度变形后的连续冷却膨胀曲线,结合金相-硬度法,获得了该钢种的连续冷却转变曲线.结果表明:随冷却速度的增大,实验钢的γ/α相变开始温度逐渐降低,贝氏体相变开始温度先升高到一个平台,随冷却速度的进一步增加又降低,晶粒细化;随终轧温度的降低,实验钢的动态连续冷却转变曲线整体向左上方移动,网状铁素体和晶内铁素体明显减少,晶粒略有细化;经四种温度终轧后以3℃.s-1的冷速冷却到室温的四个试样中,唯独950℃终轧的试样中未观察到贝氏体.      

盘螺钢贝氏体组织的产生原因及控制

分析了利用高速线材生产线轧制小规格螺纹钢的生产过程中,钢中贝氏体组织产生的原因,并提出了相应的控制措施。分析认为,盘螺钢中锰含量偏高及轧后冷却速度过快是产生贝氏体的主要原因。通过降低轧制温度和吐丝温度,最大限度地提高奥氏体的晶粒度级别,促进过冷奥氏体向铁素体、珠光体转变;根据季节环境等客观条件的不同,适当提高或降低Mn含量及轧后冷却速度;控制钢中Nb含量≤0.04%等,可保证盘螺钢具有良好的F+P或F+P+少量B组织,从而获得优良的力学性能。     

热连轧E36船板钢连续冷却相变行为

通过热模拟试验机模拟了20 mm E36船板钢(%:0.15C、0.38Si、1.56Mn、0.011P、0.002S、0.04Nb、0.06V、0.02Ti、0.037Als)经1 080℃和830～890℃分别以变形速率1 s^-1变形30%的双道次轧制及冷却过程,测得连续冷却转变曲线,并研究终轧温度和轧后冷却速度(5～25℃/s)对该钢相变和组织的影响。结果表明,随着冷却速度的增加,相变开始温度降低,珠光体的体积分数减小,贝氏体的体积分数增大;随着终轧温度的降低,相变开始温度升高;铁素体晶粒随冷却速度的增加和终轧温度的降低而细化。     

Nb对热轧低碳贝氏体钢组织与性能的影响

为开发600MPa级热轧贝氏体钢,设计了两种钢种成分,以C-Si-Mn系贝氏体钢为基础,添加一定合金元素Nb,经冶炼、轧制后进行组织观察、析出沉淀分析以及性能测试试验,研究Nb元素在热轧贝氏体钢中的作用。结果表明,添加0.025wt%的Nb,能细化贝氏体板条,贝氏体板条短小,有利于提高钢的强度与韧性。弥散的含Nb碳氮化物颗粒析出,起到析出强化作用,提高钢的强度。Nb明显改善低碳高强贝氏体钢的综合性能。     

Nb对C-Si-Mn-Cr双相钢相变规律、组织和性能的影响

  根据C Si Mn Cr和C Si Mn Cr Nb实验钢的相变规律,在实验室进行了控轧控冷实验研究,分析了微合金元素Nb对高强度热轧双相钢相变规律、组织和性能的影响。实验结果表明,Nb可显著推迟铁素体和珠光体转变,并显著降低铁素体开始转变温度,但对铁素体终止转变温度和贝氏体转变温度区间基本没有影响。经Nb微合金化后,实验钢的屈服强度和抗拉强度增幅均在100 MPa以上,屈服强度的增幅高于抗拉强度,且在强度大幅度升高的同时,伸长率下降并不明显,表明Nb的细晶强化作用对提高中温卷取热轧双相钢强度级别的效果明显。     

低碳锰铌钢控制轧制及轧后快冷复相组织的强度及断裂行为

本文研究了06MnNb钢中Mn、Nb含量,加热温度、轧制制度,轧后冷却等工艺因素与轧后组织性能的关系。采用低的加热温度、适合的轧制制度、轧后在780～600℃之间以每秒17℃冷速间断快冷,在06MnNb钢13mm厚的板带上既提高钢的屈服强度,又降低钢的脆性转化温度,并得到细小的针状铁素体(d<4μm),细小的M/A岛及少量粒状贝氏体的复合组织。研究了各类组织在断裂中对裂纹形成及裂纹扩展的作用;分析了各类组织对强度和低温韧性的作用。     

超高强铁素体/贝氏体双相钢的控轧控冷实验研究

在实验室Φ450 mm轧机上进行了铁素体/贝氏体双相钢（/%:0.22C,0.47Si,2.50Mn,0.05Al,0.02Nb,0.41 Cu）终轧800～860℃的控轧控冷实验。结果表明,实验钢经控轧控冷后,获得以铁素体/贝氏体双相组织为主并含有少量残余奥氏体+马氏体的复相组织。降低终轧温度、加快冷却速度可使铁素体晶粒细化。800℃终轧后层流冷却到560℃,然后空冷到室温的实验钢组织中残余奥氏体含量为11.4%,对强度和韧性的良好匹配贡献很大,其力学性能为:抗拉强度（R_m）1131MPa ,屈强比(R_p0.2/R_m)0.61,伸长率(A₅₀)16%,强塑积(Rm×A₅₀)18096 MPa·%     

终轧温度对含铌低Si-Mn系热轧双相钢组织与性能的影响

采用TEM、SEM技术和光学显微分析等方法,研究了终轧温度对Si-Mn系热轧双相钢组织与力学性能的影响。试验结果表明,随着终轧温度降低,铁素体晶粒尺寸减小且大小差异性增加,马氏体体积分数下降,贝氏体体积分数升高。当终轧温度为860℃时,强化相主要为马氏体,抗拉强度较高且屈强比低,第二相主要成分为Nb(C、N)且尺寸较大;当终轧温度为743℃时,强化相主要为贝氏体,屈服强度较高且塑性较好,第二相主要成分为复合碳氮化合物Nb(Ti)CN且尺寸较小。综合分析表明,合理控制终轧温度可使热轧双相钢获得不同比例的强化相和不同成分的第二相,从而控制其力学性能。     

超高强铁素体/贝氏体双相钢的控轧控冷

通过实验室热轧机组的控轧控冷试验,研究了控轧控冷参数对超高强铁素体/贝氏体双相钢组织性能的影响。结果表明,采用不同温度终轧,轧后不同方式冷却,抗拉强度几乎都在1 000MPa以上,屈强比在0.54～0.62之间,伸长率在13%～17%之间。铁素体晶粒随终轧温度降低和冷却速度加快而细化;终冷温度降低,贝氏体量增多。经800℃终轧后层流冷却至560℃左右空冷,由于铁素体晶粒细化,组织中大量的粒状贝氏体、无碳化物贝氏体、少量的孪晶马氏体以及残余奥氏体的存在使抗拉强度达1 130MPa,伸长率达16%,强塑积达到18 080MPa.%的最高值。控轧控冷获得以铁素体/贝氏体双相组织为主并含有少量残余奥氏体+马氏体的复相组织,使试验钢具有了优异的力学性能。     

Influence of Nb on Microstructure and Property of Low-Carbon Mn-Series air-cooled Bainitic Steel

 The effect of Nb on the microstructure evolution of low carbon Mn series air cooling bainitic steels has been discussed in this paper by using Gleeble 1500D, SEM, and TEM observation. The results show that: The amount of grain boundary allotriomorphic ferrites is relatively higher in non-Nb bearing steel than Nb-bearing steel under same deformation conditions. And the ferrites in Nb bearing steel are more finer. With the decreasing of finishing rolling temperature (FRT), the particles of Nb(CN) precipitating in Nb bearing steel are smaller and more dispersive. The properties of the Nb bearing steel is higher than that of non-Nb bearing steel at same FRT, and it is suggested that the toughness of Nb Micro-alloyed steel will be improved more effectively than that of non-Nb bearing steel with the decreasing of FRT.     

Effect of alloying elements on the microstructure‐property relationship in thermomechanically processed C‐Mn‐Si TRIP steels

The effect of additions of Nb, Al and Mo to Fe‐C‐Mn‐Si TRIP steel on the final microstructure and mechanical properties after simulated thermomechanical processing (TMP) has been studied. The laboratory simulations of discontinuous cooling during TMP were performed using a hot rolling mill. All samples were characterised using optical microscopy and image analysis. The volume fraction of retained austenite was ascertained using a heat tinting technique and X‐ray diffraction measurements. Room temperature mechanical properties were determined by a tensile test. From this a comprehensive understanding of the structural aspect of the bainite transformation in these types of TRIP steels has been developed. The results have shown that the final microstructures of thermomechanically processed TRIP steels comprise ~ 50 % of polygonal ferrite, 7 ‐12 % of retained austenite, non‐carbide bainitic structure and martensite. All steels exhibited a good combination of ultimate tensile strength and total elongation. The microstructure‐property examination revealed the relationship between the composition of TRIP steels and their mechanical properties. It has been shown that the addition of Mo to the C‐Si‐Mn‐Nb TRIP steel increases the ultimate tensile strength up to 1020 MPa. The stability of the retained austenite of the Nb‐Mo steel was degraded, which led to a decrease in the elongation (24 %). The results have demonstrated that the addition of Al to C‐Si‐Mn‐Nb steel leads to a good combination of strength (~ 940 MPa) and elongation (~ 30 %) due to the formation of refined acicular ferrite and granular bainite structure with ~7 ‐ 8 % of stable retained austenite. Furthermore, it has been found that the addition of Al increases the volume fraction of bainitic ferrite laths. The investigations have shown an interesting result that, in the Nb‐Mo‐Al steel, Al has a more pronounced effect on the microstructure in comparison with Mo. It has been found that the bainitic structure of the Nb‐Mo‐Al steel appears to be more granular than in the Nb‐Mo steel. Moreover, the volume fraction of the retained austenite increased (12 %) with decreasing bainitic ferrite content. The results have demonstrated that this steel has the best mechanical properties (1100 MPa and 28 % elongation). It has been concluded that the combined effect of Nb, Mo, and Al addition on the dispersion of the bainite, martensite and retained austenite in the ferrite matrix and the morphology of these phases is different than effect of Nb, Mo and Al, separately.     

微合金成分对低碳贝氏体钢强度的影响

采用不同V、Cr含量,结合Nb、Ti、Mo等微合金化的成分设计,控轧控冷、离线回火工艺生产了30 mm厚度规格的低碳贝氏体钢板,钢板的组织为粒状贝氏体、少量针状铁素体以及少量多边形铁素体,钢板的力学性能满足交货需要.使用透射电镜结合能谱仪分析了钢板的析出相情况,结果表明钢板的析出相主要是Nb、Ti的碳氮化物,析出相含有微乎其微的V,而没有Cr;Nb、Ti通过析出对钢板起到析出强化作用,V、Cr在钢中起固溶强化作用,对强度贡献较小.     

热变形对钒、氮合金钢77B性能的影响

 对未微合金化高碳钢77B和V、N微合金化高碳钢钢77B进行了620℃盐浴等温和920℃热变形后再进行620℃等温处理。结果表明：盐浴等温后微合金化钢比未微合金化钢77B强度显著增加,韧性略有下降, V（CN）的沉淀析出提高了组织的强度,但对珠光体团几乎无细化作用;经热变形等温处理后,两种试验钢的强度和韧性与盐浴等温相比,均得到了有效提高,加V、N的77B钢珠光体团发生了显著的细化,计算表明这与大量V(CN)形变诱导析出抑制奥氏体再结晶有关。     

高强集装箱用钢AQ700MC的开发

在实验室研制的Mn-Nb-B系高强集装箱用钢AQ700MC属于新一代多用途钢铁材料,是一种具有高强度和良好韧塑性配合的热轧低碳贝氏体钢.阐述了该钢的合金设计思想,对其组织结构与性能之间的关系进行了分析,旨在为工业化生产提供参考.     

Nb对C38+N2非调质钢组织和力学性能的影响

针对曲轴用新型铁素体+珠光体型非调质钢C38+N2锻件组织中铁素体含量往往难以达到用户要求的问题,研究了微量Nb元素(质量分数为0.022％)对其锻造后组织和力学性能的影响规律.结果表明,C38+N2钢中添加微量Nb能够细化晶粒和锻后组织,显著地提高组织中的铁素体含量,模拟曲轴锻造后组织中的铁素体体积分数可达到20％,...     

Mn-Series Low-Carbon Air-Cooled Bainitic Steel Containing Niobium of 0.02%

 A new hot-rolled low carbon air-cooling bainitic steel containing 0.02%Nb has been developed based on alloying design of the grain boundary allotriomorphic ferrite (FGBA)/ granular bainite (BG) duplex steel.The as-rolled microstructure and mechanical properties of 0.02%Nb bainitic steel were investigated by tensile test, X-ray diffraction(XRD),Optical Microscopy (OM), scanning electron microscopy (SEM) ,and Transmission electron microscopy(TEM). The results show that (1) The addition of 0.02% niobium improves the strength obviously without sacrificing toughness of the FGBA/BG steel. Compared with Non-Nb FGBA/ BG steel, 0.02% Nb increases the tensile strength and yield strength about 20% (From 780Mpa to 937Mpa)and 17%(From 557Mpa to 650Mpa) respectively, remaining 18% elongation and 83J Akv. (2) Small addition of Nb(0.02%) not only refines the allotriomorphic ferrite grain but also promotes the nucleation of intragranular ferrite, both of which in turn contribute to the refinement of granular bainite cluster including its ferrite platelets and M-A islands. Compared with Non-Nb steel, the volume fraction of M-A island in 0.02%Nb steel increases from 21% to 31%, and the average size of M-A island decreases from 1.2μm to 0.95um.(3)There is hardly any Nb(C,N) has been observed in 0.02%Nb steel. It is suggested that the strengthening effect of 0.02%Nb can be mainly attributed to the influence of the segregation of Nb to γ/α phase boundaries(solute drag-like effect) on the phase transformation rather than the precipitation strengthening of Nb(C,N).     

Si-Cr-Nb高强钢轨钢的研制

在实验室将Si-C-Nb钢轨钢与UIC900A、U71Mn等钢轨钢进行了对比试验研究.各钢种的力学性能测定和热模拟试验表明,Si-Cr-Nb钢轨钢具有良好的强韧性,适合于全长淬火,具有较好的焊接性能.     

铜含量对超高强度低碳贝氏体钢力学性能的影响

实验用低碳贝氏体钢(%:0.042～0.045C、1.43～1.47Mn、1.0～2.5Cu、0.29～0.30Mo、0.025~0.029Nb、0.011~0.018Ti,0.0013~0.0023B)由50 kg真空感应炉冶炼。实验结果表明,随铜含量由1.0%增加至 2.5%,8-Cu在钢中沉淀速度加快,峰值硬度增大;随Cu%的增加,轧后直接淬火(DQ)钢的屈服强度由865 MPa增 至918 MPa, DQ+500℃回火钢的屈服强度由935 MPa增至1140 MPa,但1.0%~2.5%Cu DQ+500 ℃回火钢的抗 拉强度和冲击韧性均比DQ态钢有所降低。     

超低碳贝氏体钢及其焊接特性

超低碳贝氏体（ULCB）钢采用极低的碳含量，充分利用Mn,Mo,Nb,Ni,Ti,B等元素的合金化作用，通过ULCB组织最高的强韧性及优良的低温韧性。由于ULCB钢碳含量极低，焊接性优良，焊接热影响区（HAZ）韧性明显,裂纹敏感性显著降低。ULCB钢焊接时，焊缝金属是焊接接头的薄弱环节，研制开发超低碳贝氏体焊接材料是实现ULCB钢焊接的关键环节。