具有仿晶界型铁素体/粒状贝氏体复相组织的大截面钢筋

探索了仿晶界型铁素体／粒状贝氏体复相钢用于制造热轧低碳高强度可焊钢筋的可行性与工业化前景。对不同铬含量的空冷贝氏体钢筋的组织、强韧性及可焊性等进行了对比研究。结果表明，含有0．25％铬的Mn-Si—Cr系低碳贝氏体钢在轧后空冷条件下得到含有约26％(体积分数)的仿晶界型铁素体的粒状贝氏体复相钢，其抗拉强度、屈服强度和伸长率(δ6)分别达到830MPa、560MPa和18％，实现了较好的强韧性配合，并且具有较好的可焊性。存用干制造500MPa级大截面钢筋方面具有较大的市场化优势。     

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).     

X80级高强低合金管线钢组织与冲击韧性

 为了研究准多边形铁素体/板条贝氏体/粒状贝氏体显微组织的高强低合金X80管线钢的低温韧性与冲击裂纹扩展特点，用OM、SEM、EBSD和TEM等多尺度手段进行了表征。结果表明，与针状铁素体/粒状贝氏体相比，在－60 ℃以上时，准多边形铁素体/板条贝氏体/粒状贝氏体表现出更好的阻止裂纹扩展的能力，准多边形铁素体可以分割显微组织并细化有效晶粒尺寸，增加大角度晶界比例，协调约束冲击裂纹扩展，进而提高韧性；当温度在－60 ℃以下时，这种准多边形铁素体/板条贝氏体/粒状贝氏体对裂纹扩展的协调约束作用减弱，成为显微组织的“软区”，使得材料韧性下降。     

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。     

Low-Temperature Toughening Mechanism in Thermomechanically Processed High-Strength Low-Alloy Steels

High-strength low-alloy (HSLA) steels were fabricated by varying thermomechanical processing conditions such as rolling and cooling conditions in the intercritical region, and the low-temperature toughening mechanism was investigated in terms of microstructure and the associated grain boundary characteristics. The steels acceleratedly cooled to relatively higher temperature had lower tensile strength than those acceleratedly cooled to room temperature due to the increased volume fraction of granular bainite or polygonal ferrite (PF) irrespective of rolling in the intercritical region, while the yield strength was dependent on intercritical rolling, and start and finish cooling temperatures, which affected the formation of PF and low-temperature transformation phases. The steel rolled in the intercritical region and cooled to 673 K (400 °C) provided the best combination of high yield strength and excellent low-temperature toughness because of the presence of fine PF and appropriate mixture of various low-temperature transformation phases such as granular bainite, degenerate upper bainite (DUB), lower bainite (LB), and lath martensite (LM). Despite the high yield strength, the improvement of low-temperature toughness could be explained by the reduction of overall effective grain size based on the electron backscattered diffraction (EBSD) analysis data, leading to the decrease in ductile-to-brittle transition temperature (DBTT).     

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。      

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。     

Weldability of 780 MPa Super-High Strength Heavy-Duty Truck Crossbeam Steel

 CO2-shielded welding experiments of newly developed, 780 MPa super-high strength heavy-duty truck crossbeam steel were conducted, and the microstructure, microhardness, mechanical properties, and impact toughness of the welded joint were studied. The evolution of the microstructure of the welded joint occurred as follows: welding seam (acicular ferrite+proeutectoid ferrite)→fusion zone (granular bainite-long strip M/A island)→coarse grain zone (granular bainite-long strip or short bar M/A island)→fine grain zone (ferrite+pearlite+blocky M/A island)→mixed grained zone (ferrite+granular bainite+blocky M/A island)→base metal (proeutectoid ferrite+granular bainite-blocky or granular M/A island). Increasing the density of the grain boundaries can effectively improve the impact toughness, and the blocky M/A island hindered crack propagation more effectively than the long strip M/A island. The new hot-rolled 780 MPa super-high strength steel had excellent weldability. The welding technology was applied under the following conditions: welding voltage was 20 to 21 V, welding current was 200 to 210 A, and the gas flow rate was 25 L/min.     

Effect of Boron on CGHAZ Microstructure and Toughness of High Strength Low Alloy Steels

Effect of boron on the microstructure and impact toughness in the coarse-grained heat-affected zone(CGHAZ)of two high strength low alloy steels,boron-free and boron-containing,was investigated by means of weld thermal simulation test.The result shows that,for the boron-free steel,a microstructure consisting of grain boundary ferrite degenerates pearlite and granular bainite for longer t8/5(the cooling time from 800 to 500 ℃),while lath bainite for shorter t8/5.For the boron-containing steel,granular bainite is dominant for a wide range of t8/5.Continuous cooling transformation(CCT)study on the CGHAZ indicates that the transformation start temperature decreases by about 50-100℃under different t8/5,for the boron-containing steel compared with the boron-free steel.The presence of boron suppresses the nucleation of ferrite at prior austenite grain boundaries and hence enlarges the range of t8/5for granular bainite transformation.However,the addition of boron deteriorates the impact toughness of CGHAZ,which may be due to a markedly increased fraction of martensite-austenite(M-A)constituents and decreased fraction of high angle grain boundaries.     

高强度钢韧化机制及与亚结构关系的研究

摘要：以实际生产制备的800MPa级调质态水电钢为研究对象,结合扫描电子显微镜（SEM）、电子背散射衍射（EBSD）和冲击实验等,利用显微组织晶体学结构可视化与定量化方法,研究了钢板厚度方向不同取样位置低温韧性差异的本质原因。结果表明,高强度中厚板厚度方向由表面向心部过渡,显微组织由板条状贝氏体向粒状贝氏体过渡,低温冲击韧性降低,韧脆转变温度（DBTT）升高。随显微组织由表面向心部过渡（冷速降低）,变体选择加强,心部形成了以单一贝恩（Bain）组为主导的相变组织,大角度晶界密度显著降低,且韧脆转变温度的升高与block界面密度降低紧密相关。此外,研究发现奥氏体晶粒内部的block界面和奥氏体晶界可以有效地偏折和阻止裂纹扩展,但由于奥氏体界面密度显著低于block界面,故对冲击实验过程中裂纹扩展阻力的贡献主要来自晶内的block界面。     

增氮对钒微合金钢组织和性能的影响

 通过对不同钒、氮质量分数的试验钢进行热模拟压缩试验和实验室轧制试验,用OM、SEM和TEM分析试验钢的显微组织,研究增氮对钒微合金钢组织和性能的影响。结果表明,普通钒微合金钢为板条贝氏体＋粒状贝氏体组织,增加氮质量分数,可促进晶内铁素体相变,得到针状铁素体组织,使M/A组织细化且弥散分布,改善韧性;而增加钒质量分数,可以增加析出强化作用,提高强度,但组织形态无明显变化,不能提高韧性。增氮钢中的钒在奥氏体内以VN析出,低氮钢内的钒在铁素体内以VC的形式析出,奥氏体-铁素体、VC-铁素体和VN-铁素体的平面点阵错配度分别为6.72%、3.89% 和 1.55%,在奥氏体内析出的VN可以作为铁素体的优先形核位置,促进晶内铁素体相变。     

低成本高焊接性能船板钢EH36的开发

工业化试制了3种厚度规格(20,26和36mm)的新型低成本高焊接性能船板钢EH36。试制钢板的显微组织由多边形铁素体和针状铁素体构成,其力学性能满足EH36级别船板要求并具有优异的低温韧性。采用焊接热模拟评价了钢板的焊接性能,当热输入由30kJ/cm升高至160kJ/cm时,粗晶区原奥氏体晶粒尺寸逐渐增大,其组织也逐渐由粒状贝氏体向晶界铁素体+晶内针状铁素体+晶内多边形铁素体转变,维氏硬度逐渐下降,低温韧性优异。得益于TiN粒子对奥氏体晶粒长大的抑制作用,微量B元素对先共析铁素体转变的抑制作用以及BN粒子对晶内铁素体形核的促进作用,焊接粗晶区获得了有利于韧性的细化组织,保证了粗晶区具有优异的低温韧性。双丝埋弧焊试验也验证了钢板具有优异的焊接性能。     

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。     

屈服强度460MPa级耐候钢及其焊接性能

通过连续冷却相转变行为的研究,利用试验轧机成功试制了24mm厚,屈服强度460MPa级耐候钢板,并分析了钢板微观组织、力学性能、腐蚀性能以及焊接性能。连续相转变行为和钢板试制结果表明:精轧温度不大于850℃,厚度压下率不小于0.6,冷速为4~15℃/s和终冷温度不大于465℃可得到以针状铁素体(3~10μm)和多边形铁素体(5~15μm)为主的钢板,其屈服强度不小于480MPa,抗拉强度不小于635MPa,伸长率不小于23%,-40℃冲击功不小于209J。对试制钢板进行了热输入量为72kJ/cm的双丝埋弧焊接试验,无焊前预热和焊后热处理,得到了无缺陷焊接接头,焊接热影响区-40℃冲击功不小于100J;粗晶区的高韧性与其晶内铁素体为主以及少量晶界铁素体和上贝氏体的微观组织有关。72h周浸试验结果表明:试制钢种的耐大气腐蚀能力比普碳钢Q345B提高了46%。     

微量硼对热轧低焊接裂纹敏感性钢力学性能的影响

采用相同轧制工艺试制低焊接裂纹敏感性钢,对比分析了微量硼元素对显微组织和力学性能的影响.结果表明:含硼钢的屈服强度和抗拉强度比无硼钢分别要高150和105MPa,但冲击韧性明显低于无硼钢.显微组织分析可知,硼的偏聚机制使组织中保留了明显的原始奥氏体晶界,并获得具有较大有效晶粒尺寸的板条贝氏体束,同时在贝氏体板条晶界上分...     

粒状贝氏体组织对低碳钢力学性能的影响

 在化学成分相同的条件下,分别研究了粒状贝氏体、铁素体 珠光体对低碳合金钢强度、塑性、冲击韧性的影响。结果表明：低碳粒状贝氏体钢比铁素体 珠光体钢具有更高的强度和冲击韧性,而且粒状贝氏体组织对钢的强化方式不仅仅是细晶强化和位错强化,弥散强化也是强化方式之一。     

工程机械用高强度钢板控轧控冷工艺的开发

为开发强度级别为６８５ＭＰａ的高强钢板的控轧控冷工艺,研究了终轧温度,未再结晶区累积压下量,终冷温度,冷却速度等工艺参数对钢的显微组织和力学性能的影响。实验结果表明,在控轧控冷条件下,钢的室温显微组织由铁素体和贝氏体组成,贝氏体主要以粒状贝氏体为主,此外,晶粒细化是提高钢的强度和韧性的最有效的手段。     

Recent Development of Air-Cooled Bainitic Steels Containing Manganese

The superiorities of air-cooled bainitic steels were described. A series of air-cooled bainitic steels containing manganese were developed and presented, which include low carbon granular bainitic steels, low carbon grain-boundary allotriomorphic ferrite/granular bainite dual phase steels, medium and medium high carbon bainite/martensite dual phase steel, low carbon carbide free bainite/martensite dual phase steels and casting bainitic steels.The development of ultra-low carbon bainitic steels in China was also introduced.     

水电站用低碳贝氏体钢07MnCrMoVR的组织性能研究

摘要：采用不同的宽展比对水电站用低碳贝氏体钢07MnCrMoVR进行了轧制,对回火前后试验钢的微观组织形貌进行了观察,并对力学性能进行了检验,同时利用EDS能谱分析了回火过程中碳化物析出行为。结果表明：采用较小的宽展比能提高粗轧纵轧阶段的单道次压下率以及变形区系数,有效地破碎奥氏体再结晶晶粒,轧制后获得细小的粒状贝氏体组织,高温回火后析出大量的渗碳体和合金碳化物均匀弥散地分布在贝氏体铁素体基体上。随着回火温度的提高,试验钢强度性能呈现先升高再降低的现象,伸长率和低温冲击韧性持续升高。     

Ni含量对控轧控冷船舶用Nb-Ti微合金化NiCr钢组织和性能的影响

研究了0.31%Ni和0.88%Ni二种控轧控冷Nb-Ti微合金化NiCr钢的组织和性能。结果表明,船舶用钢控轧控冷获得粒状贝氏体、上贝氏体、针状铁素体、多边形铁素体及少量珠光体等组成的复合组织。控轧控冷造成铁素体晶粒尺寸细化,细小M-A岛增多。二种钢均获得较高的抗拉强度、屈服强度、伸长率和硬度,0.88Ni-0.32Cr钢性能优于0.31Ni-0.33Cr钢。船舶用钢-80℃试样纵向冲击功都在200J以上,0.88Ni-0.32Cr钢甚至超过了300J。该钢中最佳的Ni含量为0.88%Ni。由于控轧控冷造成了铁素体细晶强化、M-A岛复合强化、析出强化和位错强化,合金元素镍有效的提高了船舶钢的低温冲击韧性。