Effects of Rare Earth on Structure and Mechanical Properties of Clean BNbRE Steel

The mechanisms of RE in clean BNbRE steel were studied by means of experimental measurement, microstructural observation and theoretical analysis. For BNbRE steel, the state and the content of RE were measured, and the effects and the mechanisms of RE on sulfide inclusions, microstructure and properties of steel were determined. On the condition of increasing the cleanliness of steel, the mechanisms of RE in steel were changed to certain degree. Small amount of RE has the effect of cleaning, modifying inclusions and alloying in clean steel, too. With increasing the cleanliness of BNbRE steel, addition of RE should be decreased properly. Under experimental conditions, the optimum addition of RE is -0.01 % （mass fraction） for clean BNbRE steel, while RE can evidently improve plasticity and impact toughness of BNbRE steel.

Reaction mechanism between Al_(2)O_(3)–MgO refractory materials and rare earth high-carbon heavy rail steel

Submerged entry nozzle(SEN)clogging is a major problem affecting the production quality of rare earth steel,and finding a suitable refractory outlet can significantly reduce production costs.To explore the relationship between refractory composition and interface interaction,unprotected coated Al_(2)O_(3)–MgO refractories and SiO2-coated Al_(2)O_(3)–MgO refractories were added to rare earth high-carbon heavy rail steel under laboratory conditions,and the Al_(2)O_(3)–MgO refractory was found to be more suitable.The results show that,from the epoxy resin side to the refractory side,the contour of the refractory interface reaction layer can be divided into two main layers:an iron-rich reaction layer and an iron-poor reaction layer.Calculations based on the spherical model suggest that the adhesion force is proportional to the size of the refractory particles and inclusions,and the same result applies to the surface tension.Controlling the inclusions at a smaller size has a specific effect on alleviating the erosion of refractories.Combined with the erosion mechanism of Al_(2)O_(3)–MgO refractories,the interface reaction mechanism between Al_(2)O_(3)–MgO refractories and molten steel was proposed,which provides ideas for solving SEN clogging.

EFFECTS OF La ON STRUCTURE AND PROPERTIES OF HEAVY RAIL STEEL

The mechanisms of La in heavy rail steel were studied by means of experimental measurements, microstructure observation and theoretical analysis in the present work. For heavy rail steel, the state and the content of La were measured, and the mechanisms and the effects of La on sulfide inclusions, microstracture and properties of steel were determined. Strip-like sulfides disappear in heavy rail steel with La/（O＋S）〉3.50, which is shown that the metallurgical function of modifying sulfide inclusions has been achieved by La. La can fine the grain size of the austenite in heavy rail steel. Under the experimental condition, the plasticity and the impacting toughness of heavy rail steel with 0.005wt% La can evidently be improved.

稀土Ce对DH36船板钢显微组织及耐腐蚀性能的影响研究

针对稀土对钢耐腐蚀性的影响规律及稀土夹杂对船板钢的局部腐蚀机理的研究不足,采用金相显微镜、扫描电子显微镜、激光共聚焦显微镜、电化学工作站研究了在3.5%NaCl溶液中稀土Ce含量对DH36船板钢显微组织和耐腐蚀性能的影响。结果表明,稀土Ce可以细化试验钢的晶粒尺寸,同时降低试验钢的珠光体片层间距。稀土Ce的加入将试验钢中的MnS和Al_(2)O_(3)+MnS夹杂转变为MnS+CeAlO_(3)、Mn-Al-O-Ce、Mn-S-Al-O-Ce夹杂。相比于未添加Ce和添加0.001 0%Ce的试验钢而言,Ce含量为0.009 2%时试验钢的腐蚀速率最低,团絮状腐蚀产物最少,腐蚀坑的尺寸与数量最小,表面粗糙程度较小,且初期仍具有金属光泽;稀土Ce的加入使得试验钢的腐蚀电位升高,腐蚀电流密度降低。腐蚀时间为5 d时,Ce含量为0.009 2%时试验钢的腐蚀电流密度最低(2.225×10^(-5 )A/cm^(2)),腐蚀电压最高(-1.057 V),耐腐蚀性能最佳。

Ce对DH36船板钢显微组织和力学性能的影响

为探究稀土Ce对DH36船板钢显微组织和力学性能的影响,采用真空感应炉熔炼不同Ce含量的DH36船板钢,利用场发射扫描电镜、显微硬度计、冲击试验机、电子万能试验机等设备研究了Ce对DH36船板钢组织、硬度、冲击性能、拉伸性能的影响。结果显示:在DH36船板钢中加入Ce使铁素体和珠光体组织细化。含0.009%Ce的试验钢综合力学性能最好,硬度增幅最大,相比未加Ce的试验钢提升15.6%;抗拉强度由未添加Ce的581.97 MPa提升到643.80 MPa,提升10.6%;冲击功由未添加Ce的162.8 J提升到174.5 J,提升7.2%。加入稀土Ce后,试验钢的拉伸断口和冲击断口形貌得到改善,韧窝数量增多,断口表面的夹杂物类型发生改变,由大尺寸不规则夹杂物变成了小尺寸类球状稀土夹杂物,降低了有害夹杂物引起的应力集中,使断口表面的裂纹源明显减少。

Micro-alloying of Rare Earths in Heavy Rail Steel

In the present study, heavy rail steel was prepared by the process of vacuum induction furnace smelting, forge work and rolling. Effects of Rare earths (RE) on microstructure and mechanical properties of heavy rail steel were systematically investigated by metallographic microscope, SEM, integrated mechanical testing machine, impact tester and so on. Metallographic analysis shows that, a few of RE can evidently delay the growth of austenite grain and fine pearlite. When the RE content is 0.016%, both annealing and normalizing pearlite laminae distances reach the minimum which is 115 nm (annealing) and 104nm (normalizing), respectively. But when the RE content reaches 0.133%, the annealing and normalizing pearlite laminae distance is respectively increased by 40% and 13%. Mechanical properties tests show that, a few of RE has not notable effect on the strength, but both plasticity and ductility can be improved obviously. When the RE content is 0.016%, both plasticity and ductility reach maximum. The maximum of elongation and reduction of area is 13.3% and 29.0%, respectively. However, when the RE content reaches 0.133%, the strength, plasticity and ductility are decreased. Especially, the low temperature (-40 ℃) and room temperature (20 ℃) ballistic work is respectively decreased by 9% and 24.8%.

稀土加入时机对重轨钢成分及夹杂物影响

针对重轨钢“BOF→LF→VD→CC”生产工艺中不同时机添加稀土的效果进行工业试验研究,通过对不同工序加入稀土的重轨钢铸坯进行取样,对样品的稀土含量及夹杂物尺寸、数密度、形貌等进行分析。结果表明:VD后加稀土生产的铸坯中稀土收得率为11.73%,高于LF后加稀土生产的铸坯中稀土收得率2.83%。结合全流程氧含量分析结果,表明稀土加入钢中后就参与脱氧反应,反应产物上浮去除;稀土的加入可有效降低钢中夹杂物尺寸,相较于不加稀土的重轨钢,LF后加稀土和VD后加稀土生产的稀土重轨钢铸坯样品中,夹杂物长度平均值分别由9.28μm降低至7.91、1.42μm,平均宽度由5.71μm降低至4.81、2.27μm;稀土的加入可降低夹杂物评级,对A类、B类、D类夹杂物评级降低效果明显,其中VD后加稀土生产的重轨钢铸坯样品夹杂物评级更优。通过不同工序加入稀土试验对比发现,VD后加稀土的工艺更能提高重轨钢夹杂物变质的能力。SEM及EDS分析结果表明,稀土主要存在于硅钙镁铝系夹杂物中,并使硅钙镁铝系夹杂物由水滴形变为球形,表面发生硫的富集;对硫化锰夹杂分析结果表明,VD后加稀土工艺可使钢中硫化锰与硅钙镁铝系夹杂共生,降低硫化锰对钢带来的危害。

Effects and Mechanisms of RE on Impact Toughness and Fracture Toughness of Clean Heavy Rail Steel

Clean high carbon heavy rail steel was prepared by the process of vacuum induction furnace smelting,forging and rolling.Mechanisms of RE on the impact toughness and fracture toughness for clean high carbon steel were investigated.In addition,the appropriate range of RE content for clean high carbon steel was determined.Both the austenite grain size and pearlite lamellar spacing decreased due to small amount of RE,consequently the impact toughness and fracture toughness were improved evidently.When the RE content exceeded a critical value,the pearlite lamellar spacing was increased,because RE was segregated on the austenite grain boundaries,damaged the orientation relationship of pearlite transformation,caused the disorder growth and morphology degenerating of pearlite.With the increasing of RE content,both the impact toughness and fracture toughness of clean high carbon steel were gradually increased at first and then decreased.It was found that when the RE content was between 0.0081% and 0.0088%,both the impact toughness and fracture toughness of clean high carbon heavy rail steel were the best.The maximum ballistic work was 21.2 J（20 ℃） and 12.2 J（-20 ℃）,respectively.The maximum plane-strain fracture toughness was 45.67 MPa·m1/2（20 ℃） and 37.04 MPa·m1/2（-20 ℃）,respectively.

高碳稀土钢的微观组织

通过真空感应炉模拟实验,结合金相分析,研究稀土对于高碳重轨钢奥氏体晶粒尺寸和珠光体片层间距等的影响作用。研究表明,随着稀土含量的增加,高碳稀土钢的奥氏体晶粒尺寸显著减小,珠光体片层间距先逐渐减小而后开始增大。在本实验条件下,当稀土含量大于0.0050%时,奥氏体晶粒可控制在10μm左右,当稀土含量为0.0061%时,高碳稀土钢的珠光体片层间距达到最小值,分别为0.19μm(正火)和0.26μm(退火)。

稀土在BNbRE重轨钢中的作用机制

通过化学分析、金相观察和理论分析,研究了稀土在BNbRE重轨钢中的存在状态和含量的变化规律,以及它对钢的硫化物夹杂、微观组织和性能的影响机制。研究发现,对于BNbRE重轨钢,加入大量的稀土并不能增加钢中固溶稀土的含量,固溶稀土的含量均保持在0.0012%以下。少量的固溶稀土可以细化BNbRE重轨钢的奥氏体晶粒和珠光体片层结构。在本实验条件下,BNbRE重轨钢的最佳稀土加入量约为0.02%,此时BNbRE重轨钢的塑性和冲击韧性得到显著提高。

稀土在洁净BNbRE重轨钢中的作用机制

通过实验测定、金相观察和理论分析,系统研究了稀土在洁净BNbRE重轨钢中的赋存状态和存量的变化规律,以及其对钢的硫化物夹杂、微观组织及性能的影响作用机制。研究发现,在钢洁净度大幅度提高的条件下,稀土在钢中的作用机制有所变化,微量的稀土起到实现净化钢液、变质夹杂物和微合金化作用,而且作用效果非常稳定。随着钢洁净度的提高,稀土加入量可以适当降低。在本实验条件下,洁净BNbRE重轨钢的稀土最佳加入量为～0.01%,此时洁净BNbRE重轨钢的塑性和冲击韧度得到显著改善。

稀土对重轨钢冲击韧度的影响作用机制

通过实验测定、金相观察和理论分析,研究了稀土对重轨钢冲击韧度的影响作用机制.随着稀土加入量的增加(0～0.06%,ω),重轨钢中的固溶稀土含量均先逐渐增大,达到一定值后开始减小.当稀土加入量为0.01%时,重轨钢的奥氏体晶粒尺寸明显细化,冲击韧度显著改善.稀土在改善重轨钢冲击韧度的同时,可以减小横向冲击功和纵向冲击功之间的差距,消除钢的各向异性,增强钢的各向同性.在本实验条件下,最佳稀土加入量为0.01%.

稀土微合金元素对U71Mn,REⅡ重轨钢动态再结晶的影响

采用Gleeble-1500D热模拟实验机,研究了不同变形条件下U71Mn,REⅡ重轨钢动态再结晶行为及微合金元素RE对其的影响。实验结果表明:变形温度越高,变形速率越低,动态再结晶越容易发生;由于微合金元素RE的作用,使REⅡ的动态再结晶开始时间延长,变形奥氏体的动态再结晶的名义激活能提高,对奥氏体的动态再结晶起到抑制作用。

低成本Q345钢高强度厚板的开发

采用TMCP工艺制备了厚度为85 mm的Q345高强度钢板,通过拉伸和冲击试验、组织及断口形貌观察等对其组织和性能进行了分析。结果表明:制备的Q345钢厚板的表面组织为多边形铁素体+大量贝氏体的混合组织,其余部位均为铁素体+珠光体组织,屈服强度达到320 MPa以上,伸长率在29%以上,冲击韧性良好;该钢不添加微合金元素,轧后不进行热处理,降低了生产成本,实现了强韧性的良好匹配。

稀土对BNbRE重轨钢微观组织的影响

通过实验测定、金相观察和理论分析,系统研究了稀土在BN bRE重轨钢中的赋存状态和存量的变化规律,及其对微观组织的影响作用机制。研究发现,对于BN bRE重轨钢而言,加入大量的稀土并不能增加钢中的固溶稀土含量,固溶稀土含量均保持在0.0012%以下。少量的固溶稀土可以细化BN bRE重轨钢的奥氏体晶粒度和珠光体片层结构。

高强度Q550D钢板的研制及热处理工艺优化

工程机械用低成本高强度Q550D钢板已研制成功。研究了Q550D钢板的显微组织、力学性能和回火工艺。研究结果表明,随着钢板厚度的增加,其组织也发生变化,由回火贝氏体加少量铁素体转变为粒状贝氏体加少量铁素体和少量珠光体。Q550D钢板的屈服强度达600 MPa以上,抗拉强度达700 MPa以上,断后伸长率大于18%,-20℃低温冲击吸收能量大于120 J。热轧后的Q550D钢板应在650℃左右回火。

钇基重稀土对4Cr5MoSiV1钢性能的影响

研究了重稀土对4Cr5MoSiV1钢抗拉强度、冲击韧度、抗冷热疲劳性、抗氧化性和耐磨性的影响。结果表明,4Cr5MoSiV1钢经重稀土处理后,上述性能均有不同程度提高,用该钢制造的热挤压模、压铸模的寿命明显提高。

碳对稀土重轨钢组织和性能的影响

通过真空感应炉模拟实验,结合金相分析和性能测定,研究碳对于稀土重轨钢微观组织、冲击韧性和强度等的影响作用。研究表明,随着碳含量的增加,稀土重轨钢的奥氏体晶粒尺寸和珠光体片层间距逐渐增大,屈服强度和抗拉强度逐渐增大,冲击韧性则逐渐减小。在本实验条件下,将稀土重轨钢的碳含量控制在0.600%-0.650%之间,对于强度的损失并不大,但对于改善冲击韧性具有显著效果。

稀土铈在重轨钢液中行为特性的模型

以重轨钢液为研究对象，建立可以定量描述稀土铈在重轨钢液中行为特性的热力学模型，利用该热力学模型，可以预测在不同洁净度条件下重轨钢液中稀土赋存状态及夹杂物组成的变化规律．结果表明：重轨钢液中初始氧质量分数的增大，有利于稀土氧化物和稀土氧硫化物的析出；钢液中初始硫质量分数的增大，有利于稀土硫化物和稀土氧硫化物的析出；1783K温度条件下重轨钢液中Ce2O3夹杂析出的必要条件为钢中氧硫的活度比大于等于0．19，Ce2S3夹杂析出的必要条件为钢中氧硫的活度比小于等于0．39，CeS夹杂向CeO2S夹杂转变的条件为钢中氧硫的活度比在0．53～0．96之间；随着洁净度的提高，重轨钢液中溶解态稀土的质量分数逐渐增加．

钇基稀土微合金化E36船板钢热模拟焊接探讨

运用Gleeble—3800热模拟机对添加钇基稀土的E36船板钢(以下称E36RE船板钢)进行热模拟试验,研究不同热输入对E36RE船板钢模拟焊接热影响区组织和性能的影响.结果表明,随冷却时间(t8/5)的增加,模拟焊接热影响区组织中贝氏体逐渐减少,板条状贝氏体向粒状贝氏体转变,冷却时间(t8/5)增加到40 s时出现珠光体组织.当模拟热输入线能量为78.37 k J/cm时,模拟焊接热影响区组织细小均匀,具有较好的强韧性,-40℃时冲击韧性为134.6 J.