硼在低碳贝氏体钢中作用的实验研究

对不同成分的低碳贝氏体钢的组织、性能及冷却曲线进行了研究,分析了硼对低碳贝氏体钢组织、性能的影响.结果表明,硼使铁素体、珠光体转变点下降,CCT冷却曲线右移;含硼低碳贝氏体钢更易得到均匀的贝氏体组织,硼对强度的贡献作用很大;在一般工程应用中室温不预热条件下,含硼低碳贝氏体钢焊接不产生冷裂纹。同时简单探讨了冷却速率对硼淬透性的影响及含硼钢冲击韧性波动的原因。     

JG670DB高强钢星形裂纹控制与探讨

对低碳贝氏体高强钢生产中出现的星形裂纹进行了研究,阐述了引起裂纹的主要因素,并提出了改进措施,使得高强钢裂纹改判率大幅下降。     

铬和铝元素对低碳贝氏体钢组织和性能影响

 低碳贝氏体钢通常需要添加一定量合金元素来提升性能,为了研究合金元素铬和铝在低碳贝氏体钢中的作用,以Fe-C-Si-Mn-Mo系贝氏体钢为基础,设计了单独添加铬元素和复合添加Cr+Al元素的3种低碳贝氏体钢,研究了铬和铝的添加对连续冷却处理低碳贝氏体钢显微组织、力学性能及贝氏体相变的影响规律。结果表明,连续冷却条件下,铬可以促进低碳贝氏体钢相变趋向于更低的温度区间进行,细化贝氏体组织,从而提高强度;铝可以促进贝氏体相变动力学,但对低碳贝氏体钢意义不大。同时,添加铝会使低碳贝氏体钢组织粗化,导致强度和伸长率同时下降。综合来看,复合添加铬和铝的优化效果不如单独添加铬,单独添加铬的低碳贝氏体钢强度达到1 623 MPa,伸长率为10.5%,结果可以为低碳贝氏体钢成分设计提供依据。     

中低碳空冷贝氏体钢的冲击磨损性能

研究了4种碳含理分别为0.15%、0.18%、0.23%和0.30％的空冷贝氏体钢的冲击磨损性能,并用扫描电镜观察了磨损表面的貌特征。结果发现,随着碳含量的提高,冲击磨损速度降低,碳含量分别为0.18%,0.23%和0.30%的3种贝氏体钢的冲击磨损速率相近,前3种低碳空冷贝氏体钢的磨损表面除了有磨损犁沟外,还存在唇状裂纹,碳含量越低,磨损表面越粗糙,所研究的4种贝氏体钢中,当抗拉强度1550MPa,容易形成穿透性裂纹。     

钒微合金化低碳贝氏体钢的连续冷却相变特性

 采用热膨胀法测定6种不同成分低碳贝氏体钢的连续冷却转变(CCT)曲线。CCT曲线表明,加入微量硼能使含钒低碳贝氏体钢在大于03℃/s的冷速下获得贝氏体组织,而V-N微合金化的低碳贝氏体获得全贝氏体的临界冷速要高于V-B钢,且贝氏体转变的开始温度也要较V-B钢高20℃左右。在含钒、氮低碳贝氏体钢中加入钼、铬将会促进钢的贝氏体相变,但钼的作用要优于铬;钼、铬的加入可使含钒、氮低碳贝氏体钢的贝氏体转变温度降低至少30℃,且贝氏体组织得到了细化,钢的维氏硬度也提高了HV10~30。     

回火对低碳贝氏体钢组织和性能的影响

研究了(250~500)℃×30 min回火热处理对低碳贝氏体钢组织和性能的影响。结果表明,TMCP状态试验钢的组织为粒状贝氏体、板条贝氏体和针状铁素体。回火温度升高,粒状贝氏体增加,板条贝氏体和针状铁素体减少,组织逐渐粗化。350℃回火时,试验钢的屈服强度(Rt0.5)为735~765 MPa,抗拉强度(Rm)为845~865 MPa,屈强比为0.87~0.88,-20℃冲击功为218~257 J,强韧性匹配最佳。300~400℃回火时,裂纹形成能(E1)、韧性裂纹扩展能(E2)及脆性裂纹扩展能(E3)+脆性裂纹扩展止裂能(E4)最大,止裂性能最佳。     

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。     

汽车前轴用低碳Fe-Mn-B贝氏体钢

低碳Fe-Mn-B贝氏体钢的材料基础性能和低碳Fe-Mn-B贝氏体钢前轴的疲劳性能试验和装车试验表明,低碳Fe-Mn-B贝氏体钢可替代42CrMo钢制造汽车前轴,经济效益显著.     

经济型铁素体/贝氏体高扩孔钢的组织与性能

 通过TMCP工艺实验,研究了Si、Mn含量对低碳Si Mn钢显微组织、力学及成形性能的影响,探讨了铁素体/贝氏体双相钢(FB钢)在扩孔过程中的裂纹形成及扩展行为。研究结果表明,增加Si含量,实验钢中等轴铁素体的体积分数增加,扩孔性能得到改善;而增加Mn含量,实验钢的强度和韧性显著提高,但塑性和扩孔性能有所下降。FB钢中的裂纹扩展主要是以微孔聚集机制进行,当遇到贝氏体时,裂纹通过铁素体 贝氏体相界面并剪断铁素体进行扩展。合理选择Si、Mn含量和TMCP工艺参数,可以获得690 MPa级的经济型热轧FB高扩孔钢,扩孔率达到了95%,综合性能较好。     

DB590钢焊接冷裂纹敏感性的研究

超低碳贝氏体钢是具有高强度高韧性的新型钢种，它的合金元素含量少，含碳量又低，具有较好的焊接性能。采用插销试验研究了ＤＢ５９０钢焊接冷裂纹敏感性，同时用扫描电镜分析该钢插销试样的冷裂纹断口形貌。试验表明该钢具有优良的抗冷裂性能。     

New bainite kinetics of high strength low alloy steel in fast cooling process

Based on Kolmgorov-Johnson-Mehl-Avrami analysis, a new bainite kinetics of high strength low alloy steel in fast cooling process was developed by utilizing different experimental methods.Upper bainite transformation morphological evolutions at a cooling rate of 8.3 K/s were directly observed by laser scan-ning confocal microscopy.This qualitative analysis suggests that bainite packet is more suitable to give a one-dimensional growth model if it is considered as a transformation unit.The nucleation rate of bainite packets in fast cooling process is assumed to give an a priori item.One-dimensional growth model with constant growth rate which is assumed as a function of cooling rate is adopted as well.Thus, the devel-oped new bainite kinetics is simple in expression and contains an adjustable parameter and an empirical pa-rameter.Experimental results show upper bainite and lower bainite transformations in fast cooling proces-ses.Their referential phase volume fractions are calculated by the expanded lever rule on the first deriva-tive dilatometer curves.For the similar transformation mechanisms, upper bainite and lower bainite are considered to give the same kinetics.With considering the Nakamura′s equation, the bainite kinetics is fit-ted with experimental data.Results show that bainite volume fractions and bainite transformation rates can be expressed precisely by the newly developed bainite kinetics.     

AM对低碳贝氏体钢等温相变和显微组织的影响

摘要：设计了马氏体起始相变温度（Ms）以上和以下5个不同温度等温淬火实验,研究了Ms以上和以下温度等温淬火对低碳贝氏体钢组织和相变动力学的影响。结果表明,试样在Ms以下等温淬火时,保温前生成的先马氏体（AM）显著缩短了等温贝氏体相变孕育期,加速贝氏体形核,细化贝氏体组织。然而,Ms以下等温淬火时,总的等温贝氏体相变动力学与先马氏体的体积分数（fAM）有很大关系,当fAM较低时,AM的形成缩短了贝氏体相变孕育期,加速了贝氏体相变,当fAM过高时,又阻碍贝氏体相变,延长贝氏体总的相变时间。最后,采用Austin Rickett(AR)和Johnson Mehl Avrami Kolgomorov(JMAK)动力学模型对等温贝氏体相变动力学进行分析,结果表明,与AR模型相比,JMAK模型更适用于本研究的实验结果。     

含有上贝氏体的ER8车轮钢的裂纹扩展行为

研究不同含量的上贝氏体对ER8车轮钢裂纹扩展行为的影响。利用激光共聚焦显微镜（LSCM）和扫描电镜（SEM）对ER8车轮钢的显微组织和裂纹扩展路径进行了研究。实验结果表明:ER8车轮钢中的组织除了有铁素体和珠光体,还存在上贝氏体;裂纹穿过上贝氏体和珠光体扩展,最终停止在珠光体区域;与珠光体组织相比,裂纹在上贝氏体中的扩展路径更曲折。利用扫描电镜（SEM）对ER8车轮钢的裂纹扩展变形进行原位观察。实验结果表明:含有80%上贝氏体的ER8车轮钢拉伸时,组织变形过程主要以铁素体和上贝氏体为主,裂纹在上贝氏体和珠光体中连续扩展,伴随着珠光体的变形;而含有50%上贝氏体的ER8车轮钢拉伸时,组织变形过程主要以铁素体和珠光体为主,并且上贝氏体对铁素体和珠光体的变形起到阻碍作用。上贝氏体能够有效地阻止裂纹扩展,在偏转裂纹路径和延缓裂纹扩展方面起着重要作用;并且对铁素体和珠光体的变形起到阻碍作用。      

纳米贝氏体钢相变加速技术开发进展

摘要：纳米贝氏体的成功开发使得常规条件下对钢铁材料组织的纳米级细化成为可能,然而奥氏体中低温转变的热动力学条件限制了纳米贝氏体的相变速率,阻碍了纳米贝氏体钢的合金范围拓展和大规模工程应用。梳理了近期国内外学者针对这一问题开发的纳米贝氏体相变加速技术,综述了化学成分、预相变、预变形、强磁场等条件下贝氏体相变加速方面的进展。综合分析表明,针对贝氏体相变需充分考虑贝氏体形核以及长大2个过程。纳米贝氏体合金和工艺的设计需充分考虑各因素对2个过程的不同影响,充分优化贝氏体相变动力学和微观组织。复合相变加速技术可以成为纳米贝氏体钢开发的新方向。     

Mechanical properties of 0.40 pct C-Ni-Cr-Mo high strength steel having a mixed structure of martensite and bainite

A study has been systematically made of the effect of bainite on the mechanical properties of a commercial Japanese 0.40 pct C-Ni-Cr-Mo high strength steel (AISI 4340 type) having a mixed structure of martensite and bainite. Isothermal transformation of lower bainite at 593 K, which appeared in acicular form and partitioned prior austenite grains, in association with tempered marprovided provided a better combination of strength and fracture ductility, improving true notch tensile strength (TNTS) and fracture appearance transition temperature (FATT) in Charpy impact tests. This occurred regardless of the volume fraction of lower bainite present and/or the tempering conditions employed to create a difference in strength between the two phases. Upper bainite which was isothermally transformed at 673 K appeared as masses that filled prior austenite grains and had a very detrimental effect on the strength and fracture ductility of the steel. Significant damage occurred to TNTS and FATT, irrespective of the volume fraction of upper bainite present and/or the tempering conditions employed when the upper bainite was associated with tempered martensite. However, when the above two types of bainite appeared in the same size, shape, and distribution within tempered martensite approximately equalized to the strength of the bainite, a similar trend or a marked similarity was observed between the tensile properties of the mixed structures and the volume fraction of bainite. From the above results, it is assumed that the mechanical properties of high strength steels having a mixed structure of martensite and bainite are affected more strongly by the size, shape, and distribution of bainite within martensite than by the difference in strength between martensite and bainite or by the type of mixed bainite present. The remarkable effects of the size, shape, and distribution of bainite within martensite on the mechanical properties of the steel are briefly discussed in terms of the modified law of mixtures, metallographic examinations, and the analyses of stress-strain diagrams.     

Microstructure deformation mechanism of SEM in- situ tension in high- strength anti- seismic rebars

To study the effect of different tissues on the performance of high- strength anti- seismic rebars, the law of its microstructure deformation behavior was obtained. The microstructures of three kinds of 500MPa high- strength anti- seismic rebars with different structural features were analyzed, which is mainly pearlite and ferrite, pearlite, ferrite and a small amount of bainite, as well as pearlite, ferrite and a large amount of bainite, respectively. The in- situ tension tests were used to investigate and study the polyphase microstructure deformation, polyphase microstructure coordination deformation mechanism and fracture mechanism. The results indicate that the ferrite and pearlite are deformed obviously in the test steels mainly with ferrite and pearlite. The ferrite is firstly deformed, however, the reason for unobvious deformation in pearlite may be attributed to the hindered effect caused by hard phase bainite. As the amount of deformation increases, the pearlite breaks finally. In the test steels which mainly composed of ferrite, pearlite and a small amount of bainite, the bainite does not substantially deform at the initial stage, while it impedes the deformation of ferrite and pearlite with only a certain degree of deformation. In the test steels which mainly composed of ferrite, a small amount of pearlite and a large amount of bainite, the initial deformation mainly begins in ferrite deformation, while the pearlite deformation is not obvious because of its low content. With the increase in deformation, the deformation of bainite becomes more and more obvious. When it reaches a certain extent, pearlite begins to deform and finally gets fracture.     

低,中碳合金钢中的马氏体与贝氏体形态

低，中碳合金钢中的马氏体除局部区域因成分偏析呈孪晶亚结构外，主要是位错亚结构外，主要是位错亚结构的板条马氏体。低碳合金钢的中温转变组织主要有三类，即粒状组织，上贝氏体和下贝低体。其中上贝氏体又分为粒状贝氏体，准上贝氏体和曲型上贝氏体；下贝氏又有准下贝氏，变态下贝氏体和典型下贝氏体。中碳合金钢的中温转变组织只有上，下贝氏体。其中上贝氏体又分为准上贝氏体和典型上贝氏体，而下贝氏体则包括准下贝氏体，...     

Bainite Transformation of Low-carbon and Boron-containing Steel under Continuous Cooling

The effects of deformation temperature and strain on bainite transformation of low carbon steel and boroncontaining steel were investigated under continuous cooling conditions by means of dilatometric measurement and microstructure observation.The results show that with decreasing the deformation temperature from 1 000to 800 ℃and increasing strains,bainite start temperature for boron-containing low carbon steel increases,whereas it decreases for low carbon steel under the same condition.The bainite microstructures are easily obtained for boron-containing steel deformed at different temperatures and different strains compared with plain low carbon steel.With increasing the continuous cooling rate,the bainite start temperature under deformed condition is about 20 ℃ higher than that under undeformed condition for boron-containing steel,but it changes slightly when the cooling rate is 20℃/s or more.