纳米贝氏体的热力学分析及强韧化研究

针对目前高碳高硅低温贝氏体(纳米结构贝氏体)相变速度缓慢的现状,采用贝氏体相变热力学理论分析主要合金元素对低温贝氏体相变驱动力的影响,设计了新型纳米结构贝氏体钢成分0.83C-2.44Si-0.43Mn-0.73Al.利用膨胀仪研究该成分贝氏体钢在不同温度下的相变整体动力学,综合使用扫描电子显微镜、X射线衍射、电子背散射衍射等方法研究热处理工艺对实验钢组织和力学性能的影响.结果表明,350℃等温转变贝氏体的抗拉强度为1401 MPa,延伸率为42.21%,强塑积可达59136 MPa·%,在室温拉伸过程中发生明显的相变诱导塑性效应;230℃等温转变组织中贝氏体铁素体片层厚度小于100 nm,抗拉强度达2169 MPa.      

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。     

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。     

Microstructure and properties of hot‐rolled high strength multiphase steels for automotive application

Effects of alloying with combinations of the elements Mo, Cr and B on the bainite transformation behaviour and microstructure of hot‐rolled high strength sheet steels microalloyed with mass contents of Ti and Nb, 0.05 or 0.15 % C and 1.5 % Mn have been studied. The relationships between microstructures formed in the steels coiled at various temperatures and their mechanical properties have been investigated. The 0.15 % C microalloyed steel alloyed with Mo,Cr and B with a complex bainitic microstructure was found to have distinctive high performance behaviour combining continuous yielding, high tensile strength and plasticity after coiling in a wide temperature region. The strain hardening of the micro‐constituents typical for the investigated steels has been analysed to have a better understanding of the mechanical properties of complex phase microstructures in low alloy ferrous alloys. It was found that bainitic ferrite with austenitemartensite islands as a second phase leads to high strength and adequate elongation. The features of the bainite formation in the Mo, Cr and B alloyed CMn steel microalloyed with Ti and Nb during slow cooling from temperatures between 650 and 550 °C was studied by dilatometry.     

硅含量对低碳贝氏体相变动力学和性能的影响

摘要：设计了3种不同Si含量的低碳贝氏体钢,进行了不同温度下等温淬火热处理热模拟实验、X-射线衍射和拉伸实验等,研究Si含量对贝氏体相变动力学和贝氏体钢性能的影响。结果表明,随Si含量增加,贝氏体相变量降低,动力学方程参数b减小,n增大。另外,随贝氏体相变温度增加,参数b减小,n增大。而且在较低相变温度下,因Si含量不同造成参数b和n的值的差异更大,说明低温下Si含量对贝氏体相变动力学的影响更大。此外,Si含量越低,因相变温度不同造成贝氏体相变孕育期和完成时间的差异逐渐增大,表明随Si含量的增加,Si对贝氏体相变动力学的影响降低。最后,随着Si含量的增加,试样抗拉强度和伸长率均逐渐增加。研究结果为优化低碳贝氏体钢成分设计、调控其力学性能提供了参考。     

逆相变退火对连铸坯组织和力学性能的影响

 研究了逆相变退火温度对0.1C5Mn钢连铸坯的组织结构和力学性能的影响规律,采用SEM进行组织结构的表征,利用XRD技术分析连铸坯退火后奥氏体含量,并测试了退火试样的力学拉伸性能。试验结果表明,连铸坯退火过程中发生奥氏体逆转变且在较低退火温度下有少量碳化物析出,随着退火温度升高,奥氏体含量先增加后减少,析出物逐渐溶解消失。提高退火温度可以显著提高试验钢的抗拉强度但却降低它的屈服强度,另外随退火温度升高,断后伸长率和强塑积先增高后降低。在625~650℃退火,可以获得20%~25%的伸长率。研究结果说明利用逆转变退火可以大幅度提高中锰钢铸坯的力学性能。     

2 GPa中碳中锰纳米贝氏体钢的相变和塑性机理

 高碳(质量分数为0.78%~0.98%)高硅(质量分数约为1.5%)钢采用低温贝氏体转变(通常为150~250 ℃),可获得不小于2.0 GPa超高强度,但塑性较低(通常不大于8.0%);同时需要非常长的贝氏体相变时间(通常不小于4 d)。采用降低碳含量(Fe-0.30C-1.5Si-1.5Ni)的成分设计,可以显著加速贝氏体相变(300 ℃等温0.5 d),获得优良强度(抗拉强度(1 138±6) MPa)和塑性(伸长率为18.5%±1.5%)匹配的性能;但很难达到超高强度(1 500 MPa)级别。参考高/中碳贝氏体钢的合金设计、显微组织和力学性能特点,采用“中碳、以铝代硅、以锰代镍”的合金成分(Fe-0.30C-1.2Al-5.0Mn)体系,在M_s(马氏体开始转变温度)温度(300 ℃)附近进行贝氏体相变,可以获得强度为2.0 GPa级((2 029±9) MPa),伸长率超过10.0%(11.5%±1.0%)的高塑性纳米贝氏体钢,同时贝氏体相变时间适中(等温2 d),合金制造成本低廉(镍质量分数约为0.5%)。Fe-0.30C-1.2Al-5.0Mn钢具有超高强度主要是由于硬相组织贝氏体铁素体和马氏体总体积分数为85.1%,其中贝氏体铁素体板条宽度为(85±30) nm。具有较高塑性主要是由于软相组织残留奥氏体的体积分数为14.9%,碳质量分数为1.12%,位于贝氏体铁素体板条之间的薄膜状残留奥氏体尺寸为(30±15) nm;同时碳、锰元素能够增加残留奥氏体稳定性,特别是相对于低锰含量,5%中锰元素对残留奥氏体有更显著的稳定性作用,使其在低应力作用下不容易发生相变,但在高应力过程中持续发生TRIP效应以提高塑性。     

时效温度对贝氏体型冷作强化非调质钢力学性能的影响

 研究了时效温度对一种低碳Mn-B-Ti系贝氏体型冷作强化非调质钢力学性能的影响。结果表明：试验料的强度随时效温度的升高先是增加,并在250℃时存在一个峰值,随后强度又随时效温度的升高而降低,当温度升高到400℃以上时强度明显降低;试验料的塑性和屈强比则随时效温度的升高逐渐增加,其中后者增加的幅度更显著。与未充氢试样相比,试验料拉拔并充氢后的延迟断裂性能显著降低。随着时效温度的升高,充氢试样中的氢含量降低,缺口抗拉强度RBN和延迟断裂强度比R缓慢增加,当时效温度大于200℃时,RBN和R则明显增加。因此,在满足保载永久伸长变形量及强度和塑性要求的前提下,应选择合适的时效温度,以保证材料的延迟断裂性能。     

The Effect of Cold Rolling on Microstructure and Mechanical Properties of a New Cr–Mn Austenitic Stainless Steel in Comparison with AISI 316 Stainless Steel

In the present study the effect of room temperature rolling on microstructure and mechanical properties of a new Cr–Mn austenitic stainless steel (containing 12 %Cr, 23 %Mn and 0.13 %C) and AISI 316 steel was investigated. The specimens of these steels were cold rolled at various thickness reductions of 0, 12, 25, 37 and 50 %. Microstructural investigations were carried out using optical microscopy, magnetic field test and X-ray diffraction technique. Hardness and tensile test methods were also done to evaluate the mechanical properties. Results showed that some of austenite phase transformed to martensite during cold rolling in the 316 steel, while there was no strain induced transformation in the Cr–Mn steel. It was also found that the newly developed steel had higher strength and higher specific strength than those of the 316 steel, while its ductility was the same as that of the 316.     

工艺参数对800 MPa热镀锌双相钢组织性能的影响

 在实验室试制了低Si 的C Mn Cr Mo系的800 MPa级冷轧热镀锌双相钢,研究了卷取温度、退火温度、退火时间等工艺参数对双相钢微观组织和力学性能的影响。试验结果表明：试验用钢在820~850 ℃退火,保温100 s以上,抗拉强度可以达到800 MPa级以上。随着退火温度的升高,强度升高,但综合性能以退火温度为820 ℃时为最佳。在820 ℃退火时,随着保温时间的增加,双相钢的强度显著增加,当保温时间超过100 s以后,强度增加缓慢。690 ℃高温卷取有利于获得最终力学性能良好的双相钢组织。     

Reciprocating Sliding Wear Behavior of Newly Developed Bainitic Steels

The present work discusses the mechanical properties and wear behavior of newly developed bainitic rail steels with nominal composition of 0.71 pct C, 0.35 pct Si, 1.15 pct Mn, 0.59 pct Cr, 0.40 pct Cu, and 0.20 pct Ni (all in wt pct)). Isothermal transformation has been carried out at different time and temperatures for obtaining different bainitic morphologies. Linearly reciprocating sliding wear behavior of the steels has been studied and compared with that of the conventional pearlitic rail steel. Considerable improvement in mechanical properties of the bainitic steels has been noticed. The hardness of the bainitic steels increases with decrease in isothermal transformation temperature. It leads to enhancement of wear resistance of the bainitic steels compared to the conventional rail steel. Finally, it clearly draws correlation between mechanical properties, wear resistance, and microstructural variation of a series of bainitic rail steels.     

Continuously Cooled Ultrafine Bainitic Steel with Excellent Strength–Elongation Combination

Serious efforts have been made to simultaneously improve the strength and ductility of steels for different applications. However, steel with the ultimate tensile strength (UTS) above 1200 MPa with minimum elongation of 20 pct is still difficult to produce. In the current work, an effort has been made to design such a steel that could be directly produced in any hot strip mill, after accelerated cooling on the runout table followed by coiling. Basically this steel consisted of C, Mn, Si, and Cr and the intended final microstructure at room temperature was about 80 pct carbide-free bainite and 20 pct retained austenite. The steel was exposed to a thermal treatment which is generally experienced by a hot strip coil. This newly developed steel possesses an UTS of minimum ~1370 MPa with minimum ~21 pct elongation. The combination of such encouraging mechanical properties can be primarily attributed to the formation of ultrafine bainite plates (~100 to 130 nm) and a high density of dislocations arising out of the bainitic transformation. The presence of sufficient quantity of retained austenite (minimum 21 pct) in the final microstructure could be the reason for the attainment of outstanding ductility values at such a high strength level.     

等温淬火温度对超细贝氏体钢组织及耐磨性的影响

设计了一种0.7C的低合金超细贝氏体钢,并通过膨胀仪、二体磨损实验、光学显微镜、扫描电镜、X射线衍射、激光扫描共聚焦显微镜及能谱仪,研究了不同等温淬火温度对超细贝氏体钢的贝氏体相变动力学、微观组织以及干滑动摩擦耐磨性的影响,揭示超细贝氏体钢在二体磨损条件下的耐磨性能和磨损机理.研究结果表明,不同等温温度下的超细贝氏体钢都由片层状贝氏体铁素体和薄膜状以及块状的残留奥氏体组成;随着等温温度的升高,超细贝氏体的相变速率提高,相变孕育期及相变完成时间缩短,但贝氏体铁素体板条厚度增加,残留奥氏体含量增加,硬度值有所降低;超细贝氏体钢磨损面形貌以平直的犁沟为主,主要的磨损机理为显微切削;不同等温温度下所获得的超细贝氏体的耐磨性能都优于回火马氏体,且随着等温温度的降低,耐磨性能提高.其中在250℃等温所获得的超细贝氏体钢具有最优的耐磨性能,其相对耐磨性为回火马氏体的1.28倍.这主要与超细贝氏体钢中贝氏体铁素体板条的细化及磨损过程中残留奥氏体的形变诱导马氏体相变（TRIP）效应有关.      

超级贝氏体钢的现状和进展

超级贝氏体钢的基本合金元素为C-Mn-Si,通过300～500℃低温相变得到超细贝氏体、马氏体和残余奥氏体组织。为减小临界冷却速度、促进贝氏体转变,部分超级贝氏体钢中添加Cr、Ni、Mo等合金元素,并降低C、Mn含量以改善钢材的焊接性能。超级贝氏体钢具有超高强度和良好的塑性,其屈服和抗拉强度分别达～1 200MPa和1 600～1 700 MPa,总伸长率为～15%。新一代超级贝氏体钢的屈服强度可达1 300 MPa以上,抗拉强度超过1 700 MPa。     

铬对超高强冷轧双相钢相变和组织性能的影响

实验室成功试制C-Si-Mn-Cr-Nb系和C-Si-Mn-Nb系超高强双相钢,利用热膨胀仪研究了铬对超高强双相钢相变规律的影响,利用光学显微镜、SEM以及拉伸试验对双相钢的微观组织和力学性能进行检测。实验结果表明:铬使实验用钢的CCT曲线整体右移,抑制铁素体和珠光体的生成,对铁素体开始转变温度影响不大,升高铁素体的终止转变温度,降低贝氏体转变温度,提高奥氏体的淬透性,在相同的冷速条件下,铬的加入更容易得到铁素体+马氏体的双相组织;合金元素铬显著改善双相钢的显微组织,细化晶粒,双相钢的屈服强度从510 MPa升高到535 MPa,抗拉强度从1 080 MPa升高到1 145 MPa,抗拉强度的增幅高于屈服强度,在抗拉强度提高的同时,伸长率升高。     

硅和铬对超高强双相钢组织和性能的影响

 利用热膨胀仪研究了合金元素硅和铬对C-Si-Mn-Nb系与C-Cr-Mn-Nb系超高强双相钢连续冷却相变规律的影响;采用单向拉伸试验,以及OM、SEM和TEM等方法对比研究了2种DP钢的组织性能与断口形貌。结果表明：硅元素能够提高[Ac1]和[Ac3]点温度,扩大两相区,促进铁素体相变,并能提高马氏体的回火稳定性,改善其形貌和分布;铬元素的添加导致了奥氏体中碳的分布不均匀,使得马氏体内部同时出现了孪晶与板条状精细结构,而且快冷过程中出现了残余奥氏体和马奥岛组织,部分马氏体会在时效过程中发生分解;两钢的抗拉强度均超过1 000 MPa,伸长率超过15%,且含硅的双相钢各项力学性能均要优于含铬的双相钢。     

(C+N)复合强化的Fe-Cr-Mn(W,V)钢高温性能的研究

研究了用于核反应推低放射性结构材料Ｆｅ－Ｃｒ－Ｍｎ（Ｗ,Ｖ）奥氏体钢。通过（Ｃ＋Ｎ）复合强化有效地提高Ｆｅ－１２％Ｃｒ０１５％Ｍｎ（Ｗ,Ｖ）钢高温强度和蠕变断裂寿命,并改善高温塑性。在温度６７３Ｋ以下,合金比ＳＵＳ３１６钢和ＪＰＣＡＳ钢强度和塑性优良。合金强度和塑性与形变的相互关系是和合金形变组织变化;密切相关。对６７３Ｋ以上塑性降低的原因进行断口和显微组织分析,控制晶界碳化物粗化是进一步提高高温     

Effect of BainiticTreatment on Microstructure and Mechanical Properties of TRIP Cold-Rolled Steel Sheets

The effects of bainitic treatment on microstructure and mechanical properties of 0.10C-1.5Mn-l.5Al TRIP-aided cold-rolled steels have been investigated.The samples were heated by intercritical annealing at 820℃for 2 min and quenched in banitic temperature with different hoding time for 5 to 300s,two salt bath were used for the heat treatment.Experimental results show that the yield strength and elongation increase with the increasing of bainitic holding time,while the tensile strength decrease.The volume fraction of retained austenite rise at the beginning of bainitic holding and then reduce,the carbon content of retained austenite increase during the bainitic holding.The tensile strengthen multiply elongation reaches the highest value at 120s.The mechanical stability of retained austenite fits well with strain hardening during deformation.     

重载齿轮钢的高温性能

 通过Gleeble 1500D热模拟试验机高温拉伸试验,对比研究了17Cr2Ni2MoVNb和17Cr2Ni2Mo钢的高温性能。结果表明：因微合金元素V（0.1%,质量分数,下同）、Nb（0.036%）产生细晶强化及固溶强化,17Cr2Ni2MoVNb 钢的抗拉强度比17Cr2Ni2Mo钢稍高。在低N（0.0057%）含量的17Cr2Ni2MoVNb钢中,V和Nb对热塑性的危害很小。而高N（0.0130%）含量的17Cr2Ni2Mo钢在600～900 ℃及1050～1200 ℃温度区间塑性低于17Cr2Ni2MoVNb钢。N含量及相变温度不同导致第二期AlN析出量不同及铁素体先后析出,是造成两试验钢塑性差别的主要原因。     

70Si3MnCrMo钢中贝氏体及其回火稳定性

 对一种新型70Si3MnCrMo钢进行了等温和连续冷却贝氏体相变热处理。利用拉伸和冲击试验研究试验钢的力学行为,利用XRD、SEM和TEM等方法对试验钢进行了相组成分析和微观组织形貌观察。研究结果表明,试验钢经等温贝氏体相变,其最佳综合力学性能出现在200 ℃回火,强塑积为26.4 GPa·%。经连续冷却贝氏体相变,其最佳综合力学性能出现在300 ℃回火,强塑积达到28.6 GPa·%。回火温度较低的情况下,热处理后的组织为由贝氏体铁素体和残余奥氏体组成的无碳化物贝氏体组织,这种无碳化物贝氏体由超细贝氏体铁素体板条而获得超高强度,由一定量的高碳残余奥氏体来保证较高的塑性和韧性。试验钢经连续冷却贝氏体相变,其贝氏体铁素体板条中出现了超细亚单元,并且残余奥氏体呈薄膜状和小块状两种形态分布于贝氏体铁素体板条之间,这两种形态残余奥氏体的稳定性不同。拉伸试样在变形过程中残余奥氏体持续发生TRIP效应,直至全部残余奥氏体都发生转变生成应变诱发马氏体,从而使钢得到更好的强、塑性配合,表现出十分优异的综合性能。