细晶强化和位错强化对中锰马氏体钢的强化作用

 研究了碳和锰含量对淬火中锰马氏体钢的位错密度、残余奥氏体含量、晶粒尺寸等组织结构以及室温力学性能的影响。借助于SEM、EBSD、TEM和XRD表征了材料的微观组织,探讨了马氏体钢的强化机制。结果表明:随着碳含量增加,淬火中锰钢的位错密度和残余奥氏体体积分数逐渐增加,板条束和板条块尺寸逐渐细化,大角晶界百分数逐渐增加,强度逐渐升高;增加锰含量能够提高马氏体钢的位错密度和抗拉强度。分析认为,位错强化和细晶强化是淬火中锰马氏体钢的主要强化机制。马氏体板条尺寸是马氏体抗拉强度的结构控制单元,而原奥氏体晶粒尺寸则是马氏体屈服强度的结构控制单元。     

淬火温度对NM400马氏体耐磨钢残余应力的影响

采用热处理实验、X射线衍射(XRD)、光学显微镜(OM)、扫描电镜观察(SEM)等方法,研究了不同淬火温度对NM400马氏体耐磨钢的组织、硬度与表面残余应力的影响规律。结果表明,随着淬火温度的升高,原始奥氏体逐渐均匀化并粗化长大,实验钢表面轧制方向的残余应力逐渐增大。淬火温度940℃以下,随着温度升高,马氏体板条束逐渐增多,板条块逐渐减少,实验钢硬度随淬火温度的升高而增加;淬火温度1 150℃时,马氏体板条块增多,马氏体板条粗化,表面硬度明显下降。     

高强钢增强韧性的在线淬火技术开发与应用

近年来,广泛应用于中厚板高强钢生产的在线淬火工艺是一种绿色、短流程制造工艺,然而与离线淬火工艺相比,普遍存在强度偏高而冲击韧性较低的问题,阻碍了这种工艺的推广应用。研究发现,产生此类问题的原因是因为轧制过程中奥氏体组织调控不当,使得轧制后钢板的奥氏体晶粒主要呈现出扁平状,这种形态的奥氏体在随后的直接淬火过程中容易形成贯穿原始奥氏体晶粒的马氏体板条,并且取向较为一致,不利于阻止裂纹的拓展。以奥氏体组织调控为基础,钢板轧制后形成细小等轴状态的奥氏体晶粒,并保留部分塑性变形过程的位错,在随后的淬火过程中,形成取向各异的马氏体板条束,这种组织有利于阻止裂纹拓展,从而可有效提升钢材的冲击韧性,不添加昂贵的微合金元素也可实现550 MPa级高强钢的生产,在强度相同的情况下,-20℃冲击韧性大幅度提升到200 J以上,达到离线淬火相当的水平,同时,提高了机组产量;相比于离线淬火,这种工艺下的微合金元素可较多固溶于奥氏体中,随后淬火过程中保留于马氏体中,在回火过程中增强微合金碳氮化物析出强化作用,进一步提高产品的强度,最终采用该工艺所制造的690 MPa级高强钢性能与离线淬火韧性相当且强度略高,为工艺...     

淬火工艺对塑料模具用钢40Cr组织及性能的影响

研究了不同淬火温度、不同淬火介质对塑料模具用钢40Cr组织及力学性能的影响.结果 表明:40Cr钢经水淬后得到组织均为马氏体.随淬火温度的升高,粗针状的马氏体束增多,可降低钢的强度、硬度及韧性;油淬后得到组织均为马氏体+贝氏体+少量铁素体,随着淬火温度的提高,原始奥氏体晶粒长大,马氏体组织含量增多,但获得较粗大的马氏体组织,贝氏体含量逐渐减少;不同淬火温度下,水冷试样硬度均高于油冷试样;水淬试样回火后由于细晶强化作用,使强度、硬度及冲击韧性均高于油淬.840℃水淬试样经过600℃回火可获得最佳综合力学性能.     

电阻焊接用高强Q125级石油套管钢组织及其性能

设计了一种低合金含量的Q125级高强度石油套管用钢,研究了热处理工艺对实验钢组织和力学性能的影响.与870℃淬火+500℃回火工艺相比,实验钢在850℃淬火+500℃回火工艺下具有更好的强韧性配合.与870℃淬火相比,850℃淬火处理的奥氏体晶粒尺寸较小,使决定钢力学性能的晶区、板条束尺寸细化,因此其性能更优异.淬火温度对实验钢的析出行为影响不大.尺寸较大的TiN以及TiC和TiN复合析出物对奥氏体晶界起到钉扎作用,可以抑制奥氏体晶粒的长大;含有Mo的尺寸较小的TiC可以起到钉扎位错的作用,阻止位错移动,对强度的提高贡献很大.      

亚临界区淬火温度对一种新型“锰代镍”低温钢组织演变及力学性能的影响

利用X射线衍射仪(XRD)、电子背散射衍射(EBSD)和透射电子显微镜(TEM)研究了亚临界区淬火温度对一种新型"锰代镍"低温钢组织演变及力学性能的影响。结果表明,随着亚临界区淬火温度的升高,室温亚稳奥氏体的体积分数逐渐降低。当亚临界区淬火温度为700和740℃时,亚稳奥氏体主要以片层状在回火马氏体板条间析出,且排列方向与周围的马氏体板条平行,这种片层状亚稳奥氏体分布较为均匀,尺寸较小,厚度约为100nm,且稳定性较高;当亚临界区淬火温度为780℃时,试验钢中出现尺寸较大的块状奥氏体,在回火马氏体界面的交叉处不均匀析出。分析表明,不同热处理制度下基体"有效晶粒"尺寸、所生成的亚稳奥氏体体积分数及其稳定性的不同是导致不同亚临界区淬火温度下试验钢低温韧性差异的主要原因。     

热处理工艺对NM500耐磨钢组织和力学性能的影响

通过扫描电子显微镜,电子背散射衍射、透射电子显微镜以及力学分析等方法研究了在线淬火-回火(DQ-T)和再加热淬火-回火(RQ-T)对NM500耐磨钢组织和性能的影响,并讨论了不同热处理工艺的强化机理.发现试样经过不同的热处理工艺后在较高的强度下均能保持良好的韧性.由于位错密度的增加和更细的马氏体板条束尺寸,DQ-T试样的抗拉强度和硬度明显高于RQ-T试样,但是强度的增加并没有造成韧性和塑性急剧的降低.再加热淬火温度对RQ-T试样的强度影响较大,当淬火温度较低时,马氏体板条束得到细化,这种细晶强化作用有效地提高了RQ-T试样的强度.      

预备热处理对AMS 6308钢组织及性能的影响

 采用SEM、TEM和力学性能测试等手段,研究了预备热处理对AMS 6308钢组织及性能的影响。结果表明,980 ℃以下正火,随着温度的提高,M6C碳化物逐渐溶解,晶粒细小,淬火后马氏体板条均匀细小,碳化物呈球状或椭球状弥散分布在板条界和晶界上,碳化物体积分数和位错密度较高,强度和冲击值逐渐增加。980 ℃以上正火,M6C碳化物溶解增多,晶粒开始长大,淬火后马氏体板条束尺寸也长大,碳化物体积分数和位错密度下降,强度和冲击值降低。推荐的预备热处理制度：正火温度为980～1 010 ℃,回火温度为680～700 ℃,经性能热处理后,AMS 6308钢体现出良好的强韧性匹配。     

低碳马氏体钢的微观组织及其对强度的影响

利用光学显微镜、扫描电镜、背散射电子衍射(EBSD)以及透射电镜对17CrNiMo6钢经淬火和低温回火后的马氏体组织进行了定量分析,并且研究了其对强度的影响.结果表明:17CrNiMo6钢Packet(板条束)尺寸和Block(相似取向的板条束)宽度随原奥氏体晶粒尺寸的减小而减小,而Lath(板条)宽度在0.3μm左右,对原奥氏体晶粒尺寸变化不敏感.17CrNiMo6钢板条马氏体的屈服强度与原奥氏体晶粒尺寸、Packet尺寸以及Block宽度都符合Hall-Petch关系,而Block宽度是对强度起作用的组织控制因素.     

淬火工艺对高速列车车轴用DZ2钢组织性能的影响

摘要：采用OM、SEM、EBSD、室温拉伸试验和低温冲击试验,揭示了淬火工艺对高速列车车轴用DZ2钢组织和性能的影响。研究结果表明,经850℃两次淬火和650℃回火后,DZ2钢获得了最佳的力学性能。抗拉强度、屈服强度、断后伸长率和-40℃冲击吸收能量分别为874MPa、773MPa、24%和222J。该工艺条件下原始奥氏体晶粒、马氏体板条束和板条块最为细小,其尺寸分别为14.9、6.9和1.32μm,较经950℃淬火和650℃回火后的分别细化了14.3、5.2和0.35μm,可有效抑制裂纹的扩展,提高低温韧性,韧脆转变温度由-103℃显著降低至-136℃。     

Impact Toughness of an NM400 Wear-Resistant Steel

An NM400 wear-resistant steel was hot rolled and then the plates were heat-treated by direct quenching and tempering (DQT) and reheat quenching and tempering (RQT) techniques, respectively. The Charpy impact test was carried out with an instrumented Charpy impact tester. The microstructure and fracture surface were investigated by a combination of optical microscopy, transmission electron microscopy and scanning electron microscopy methods. It was found that the impact toughness of DQT specimen was much higher than that of RQT specimen. The microstructure of both DQT and RQT specimens was characterized by a mixture of tempered lath martensite and lower bainite. The lower bainite in DQT specimen extended into prior austenite grains and the content was higher than that in RQT specimen. The lower bainite in DQT specimen improved the impact toughness by increasing the proportion of large-angle boundaries and relieving the stress concentration at the crack tip. A number of fine and dispersed carbides in DQT specimen also contributed to the improvement of the impact toughness.     

Relationship Among Microstructure and Properties and Heat Treatment Process of Ultra-High Strength X120 Pipeline Steel

 The variation of heat treatments including directed quenching and tempering off-line after controlled rolling (DQT) and quenching off-line and tempering off-line after controlled rolling (RQT) with microstructure and mechanical properties of a low-carbon microalloyed steel was compared and analyzed. For DQT, the quenched steel was obviously banded microstructure, with increasing tempering temperature, lath martensite coarsened, the cusp carbide precipitated at grain boundaries, the yield strength fluctuated slightly, and the fracture-separation was obvious. The impact toughness was better in the steel tempered at 500 ℃ for 1 h. In RQT, with increasing tempering temperature, lath martensite degenerated, intragranular and intergranular finer precipitations with smaller than 30 nm precipitated and grew up and were distributed dispersedly, the stripe-like carbides were distributed at grain boundaries, and the yield strength and tensile strengthen decreased obviously. The impact toughness of RQT process was much better than that of DQT process, and the comprehensive mechanical properties were better for the steel tempered at 500 ℃ for 1 h of RQT process.     

Effect of quenching process on microstructure and properties of DZ2 steel for high speed train axle

The effect of quenching process on the microstructure and properties of DZ2 steel used for high speed train axles is revealed by means of OM, SEM, EBSD, room temperature tensile test and low temperature impact test. The results show that after twice quenching at 850℃ and tempering at 650℃, the optimum mechanical properties of DZ2 steel were obtained. The tensile strength, yield strength, elongation after fracture and impact energy absorption at -40℃ of DZ2 steel are 874MPa, 773MPa, 24% and 222J, respectively. Moreover, the prior austenite grain, martensite packet and block are the finest, with the size of 14.9, 6.9 and 1.32μm, respectively, which are 14.3, 5.2 and 0.35μm finer than those after quenching at 950℃ and tempering at 650℃, respectively. And it is found that finer prior austenite grain boundaries, packet boundaries and block boundaries can effectively inhibit the crack propagation and improve the low temperature toughness, resulting in the ductile brittle transition temperature of DZ2 steel significantly reduced from -103℃ to -136℃.     

回火温度对COST-FB2转子钢析出相与力学性能的影响

 为了调整COST-FB2转子钢的强韧性,采用OM、SEM和TEM等手段研究了回火温度对COST-FB2转子钢的析出相类型与力学性能的影响。结果表明,随着回火温度由350 ℃升高到750 ℃,试验钢的强度、硬度不断下降,塑性和冲击功上升;试验钢350 ℃和570 ℃回火后的高强低韧性可通过再次在700 ℃回火改善。淬火后COST-FB2转子钢中的残余奥氏体,可通过在570 ℃回火消除;在350 ℃和570 ℃回火后马氏体板条内部有大量针状的M₃C,700 ℃回火后的显微组织中M₃C消失,M₂₃C₆在原奥氏体晶界和马氏体板条界上析出,750 ℃回火后晶界上的M₂₃C₆有聚集粗化的现象,部分马氏体板条存在回复现象。     

Effect of Martensite Morphology on Impact Toughness of Ultra-High Strength 25CrMo48V Steel Seamless Tube Quenched at Different Temperatures

A 25CrMo48V steel for ultra-deep oil/gas well casings was quenched at 900-1 200 ℃ and tempered at 650 ℃. The lath martensitic structures were characterized by optical microscope (OM), field emission scanning electron microscopy (FESEM), electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM), and the transverse impact energy at 0 ℃ was measured from the as-quenched and tempered specimens. The results show that with the quenching temperature decreased, the prior austenite grain, martensitic packet and block are refined, while the lath width seems to remain unchanged. The enhancement of impact toughness with the decreasing quenching temperature can be attributed to refinement of the martensitic structure with high-angle boundaries, and the block is the minimum structure unit controlling impact toughness. The transverse impact energy [ECVN (0 ℃) ≥100 J] required for seamless casings with ultra-high strength (Rp0.2≥932 MPa) has been finally achieved with the experimental steel quenched at 900-1 000 ℃ and tempered at 650 ℃.     

常化后冷却工艺对1600MPa级超高强钢组织性能的影响

为改善高强度钢的塑性和韧性,对中碳低合金马氏体高强度钢分别采用常化后空冷＋回火和常化后控冷＋回火工艺,研究常化后冷却工艺对钢中残余奥氏体及力学性能的影响.采用扫描电镜获得钢的组织形态,利用X射线衍射和电子背散射衍射技术分析钢中残余奥氏体的体积分数、形貌和分布.发现两种工艺下均得到板条马氏体＋残余奥氏体组织,残余奥氏体均匀分布在板条之间,随工艺参数不同,其体积分数在3%~10%变化.常化后加速冷却能显著细化马氏体板条,提高钢的屈服强度和抗拉强度100 MPa以上,冲击功下降4 J.残余奥氏体的体积分数随常化控冷终冷温度的升高呈现先升高后降低的变化,常化后的控制冷却也可以作为进一步改善马氏体类型钢组织和性能的方法      

Effect of Martensite Fine Structure on Mechanical Properties of an 1 100 MPa Grade Ultra-high Strength Steel

An 1100 MPa grade ultra-high strength steel with different martensite fine structures,characterized by prior austenite grain size,martensite packet size,block width and lath width,was studied by various heat treatment processes.The result shows that with decreasing prior austenite grain size,both the packet size and block width decrease,while the lath width has virtually no change.Accordingly,both strength and toughness increase,while total elongation decreases.The yield strength has a Hall-Petch type relationship with the prior austenite grain size,packet size and block width,and the block width may be regarded as a key factor influencing strength.On the other hand,the ductile to brittle transition temperature(DBTT)is found to be more related to the packet size,which may be considered as a dominant factor influencing toughness.     

屈服强度1100 MPa级超高强钢热处理组织及性能

摘要：随着工程机械向大型化轻量化方向发展,超高强钢的市场需求越来越大且综合性能要求越来越严格。结合5000mm宽厚板生产线及热处理装备,研究淬火过程中淬火温度对屈服强度1100MPa级超高强度钢组织及力学性能的影响。结果表明,淬火温度决定了合金元素的溶解和分布状态、原始奥氏体晶粒尺寸,影响试验钢的综合力学性能。不同淬火温度下,基本微观组织为板条马氏体。随着淬火温度的升高,原奥氏体晶粒尺寸增大;当淬火温度由840℃升高至990℃时,原奥氏体晶粒平均尺寸由9.0μm增加到22.5μm。采用900～930℃淬火及350℃回火的热处理工艺,试验钢可获得最佳的强韧性匹配,此时屈服强度为1125～1155MPa、抗拉强度为1306～1335MPa、断后伸长率为12.5%～14.0%,布氏硬度为415～419,－40℃冲击功为80～100J,抗拉强度与布氏硬度比值范围在3.10～3.20之间,满足标准GB/T 28909—2012对Q1100E的要求。     

Microstructural basis for the effect of chromium on the strength and toughness of AF1410-based high performance steels

The variation in strength and Charpy impact toughness as a function of tempering temperature in the range of 200 ‡C to 650 ‡C was investigated in AF 1410 and AF 1410 + 1 pct Cr steels produced in a laboratory-scale, and a commercially produced AerMet 100 steel. The tensile test results showed that AF 1410 + 1 pct Cr had lower strength compared to AF 1410, while AerMet 100 had the highest strength of the three steels examined. Transmission electron microscopy (TEM) studies demonstrated that the strength variations among the steels can be attributed to differences in the matrix/carbide coherency strain and the volume fraction of the strengthening M₂C carbides. The toughness values of the three steels were comparable when tempered up to 424 ‡C. Tempering at and above 454 ‡C resulted in a relative enhancement of toughness in AF 1410 + 1 pct Cr steel compared to AF 1410. This toughening was attributed to the destabilization of cementite at lath and prior austenite boundaries and the formation of reverted austenite.