变质处理对高硅铸钢残留奥氏体及力学性能的影响

采用X射线衍射对RE/V/Ti复合变质处理后高硅铸钢等温淬火组织中残留奥氏体量及残留奥氏体含碳量进行了测定.采用透射电子显微镜(TEM)和光学显微镜(OM)对高硅铸钢等温淬火热处理后的显微组织以及残留奥氏体分布形态进行了研究.结果表明,等温温度低于385 ℃时,复合变质处理高硅铸钢中残留奥氏体量及残留奥氏体平均含碳量均低于未变质高硅铸钢;385 ℃等温处理时,两者的残留奥氏体量及残留奥氏体平均含碳量基本相同.等温淬火高硅铸钢显微组织中残留奥氏体呈两种分布形态:薄膜状及块状.在相同的等温温度下,复合变质处理使残留奥氏体薄膜厚度以及贝氏体铁素体板条厚度、长度均大幅度减小,块状残留奥氏体的量大为减少,有利于高硅铸钢综合力学性能的提高.     

C、Mn元素配分对淬火-配分贝氏体钢摩擦磨损的影响

采用淬火-配分-贝氏体区等温(QPB)和双相区保温-淬火-配分-贝氏体区等温(IQPB)两种热处理工艺并进行对比,通过摩擦磨损试验来研究C、Mn元素对残留奥氏体稳定性的影响。采用扫描电镜(SEM)、X射线衍射仪(XRD)、电子探针(EPMA)对试样的显微组织、残留奥氏体含量及C、Mn元素分布进行表征。结果表明:在双相区保温过程中,C、Mn元素发生配分,在奥氏体中富集。摩擦磨损试验后,QPB试样中的残留奥氏体体积分数从7. 24%减少到4. 36%,维氏硬度从417 HV0. 02增加到526 HV0. 02,磨损体积为0. 252 mm~3。IQPB试样中的残留奥氏体体积分数从9.11%减少到7.58%,维氏硬度从384 HV0.02增加到413 HV0. 02,磨损体积为0. 268 mm~3。IQPB试样在摩擦磨损试验前后残留奥氏体体积分数、维氏硬度没有QPB试样变化明显,表明在摩擦磨损过程中,C、Mn元素使残留奥氏体稳定性提高,残留奥氏体不易向马氏体转变。     

C、Mn元素对淬火配分贝氏体钢残留奥氏体稳定性的影响

采用双相区保温-淬火(IQ)、淬火-配分-贝氏体区等温(QPB)和双相区保温-淬火-配分-贝氏体区等温(IQPB)热处理工艺,研究C、Mn元素对残留奥氏体热稳定和机械稳定性的影响。通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)和电子探针(EPMA)对试验钢的组织形貌、残留奥氏体含量及合金元素分布进行表征。结果表明,试验钢在双相区保温过程中C、Mn元素由铁素体向奥氏体扩散,在奥氏体发生富集,使奥氏体的热稳定性增强;在形变过程中由于C、Mn元素的稳定作用使残留奥氏体的机械稳定性提高。试验钢经IQPB工艺处理后,抗拉强度为1098 MPa,伸长率达20%,其强塑积达21 960 MPa·%,与QPB工艺相比,强塑积提高了6840 MPa·%。     

等温淬火工艺对奥-贝铸钢组织和性能的影响

研究等温淬火工艺因素(奥氏体化温度、等温淬火温度、等温淬火时间等)对奥氏体 贝氏体铸钢显微组织和力学性能的影响的试验结果表明,选定成分的高碳(0 75%)高硅(2 4%)铸钢,在280～360℃范围内经等温淬火处理后,可以获得无碳化物析出的奥氏体-贝氏体组织,且随着等温淬火温度的升高,贝氏体形貌由针状下贝氏体逐渐向羽毛状上贝氏体转变。试验结果还表明,等温淬火工艺对力学性能的影响较复杂,奥氏体化温度和时间为900℃×120min、等温淬火温度和时间为320℃、120min时,可以获得较佳的综合力学性能。     

模具钢无碳化物贝氏体的相变行为及其对磨损性能的影响

研究了H13模具钢的常规马氏体(油淬火+580℃回火)和无碳化物贝氏体(300℃等温处理)的相变行为，以及显微组织对其冲击磨损性能的影响。结果表明：试验钢经贝氏体等温后形成了由板条状贝氏体铁素体和残留奥氏体组成的无碳化物贝氏体组织；贝氏体铁素体+残留奥氏体组织的冲击磨损性能在磨损后期(1.5和2.0 h)优于马氏体组织。这是由于马氏体组织容易产生微裂纹，产生大量犁削，从而导致耐磨性能降低，而无碳化物贝氏体组织在冲击磨损过程中使表层发生剧烈的塑性变形，诱导微观组织中的残留奥氏体转变成α相铁素体，能够阻止试验钢基体在冲击磨损过程中产生切削，从而提高其耐磨性。     

低碳Si-Mn系TRIP钢的热处理工艺对组织的影响

低碳Si-Mn系TRIP钢有着复杂的显微组织，主要由多边形铁素体（F）＋无碳贝氏体（B）＋残留奥氏体（AR）组成。本试验采用了彩色金相法，并结合X－ray衍射、SEM和TEM等手段研究了低碳Si-Mn系TRIP钢显微组织与工艺的关系，发现随着两相区退火温度的升高，最终显微组织中铁素体基体体积分数变小，并且贝氏体量增多，残留奥氏体的稳定性呈起伏式变化；在贝氏体转变区的等温温度过高或过低，均使最终显微组织中残留奥氏体体积分数减少；在贝氏体转变区等温时，所形成贝氏体表现出粒状的特征。     

两相区不同等温时间下低碳复相钢的组织与性能

采用两相区保温-淬火-贝氏体区等温-淬火(IQPB)热处理工艺,通过SEM、TEM、XRD、EPMA、室温拉伸等手段,研究了两相区等温时间对低碳贝氏体/铁素体复相钢组织组成、合金元素分布、残留奥氏体形貌、含量及力学性能的影响。结果表明:随两相区等温时间的增加,铁素体逐渐增加,贝氏体逐渐减少;抗拉强度由1116 MPa降低至971 MPa,断后伸长率和残留奥氏体含量呈先升高后降低的趋势,残留奥氏体中的碳含量逐渐增加。由于在拉伸过程中,残留奥氏体发生TRIP效应转变为马氏体,试验钢的强度和塑性得到双重提高。经两相区等温15 min时,强塑积达29 925 MPa·%。     

热处理对含Mo轴承钢组织和性能的影响

研究了含Mo轴承钢的相变规律及热处理制度对其组织和性能的影响,运用SEM和XRD表征了其显微组织,绘制了动态CCT曲线,测试了其硬度、力学性能和耐磨损性能。结果表明,由于钢中含有Mo,推迟了珠光体组织转变,当冷速≥4 ℃/s时冷却过程只发生马氏体相变;淬火+低温回火后,钢的抗拉强度和维氏硬度分别为1850 MPa和785 HV;而经贝氏体等温淬火后钢的抗拉强度和硬度分别达到2160 MPa和735 HV。淬火+低温回火后残留奥氏体的体积分数约为12.68%,而贝氏体等温淬火后约为3.88%。残留奥氏体含量的降低,有助于提高轴承钢的尺寸稳定性。     

低碳贝氏体钢AH80DB过冷奥氏体连续冷却转变与等温转变

利用DIL805A淬火相变膨胀仪测定了AH80DB低碳贝氏体钢的连续冷却转变(CCT)曲线与等温转变(TTT)曲线,并结合金相-显微硬度法确定了过冷奥氏体在不同冷速冷却及不同温度等温时的组织转变。结果表明,连续冷却转变时,在0.2~30℃/s冷速范围内,可得到贝氏体组织;AH80DB钢的等温转变曲线为珠光体区在右,贝氏体区在左的双鼻型,在Ms~600℃等温可获得贝氏体组织。     

等温淬火球墨铸铁热处理工艺研究

系统研究了等温淬火温度和等温时间对传统单步和两步等温淬火工艺处理的等温淬火球墨铸铁(Austempered Ductile Iron,ADI)显微组织与力学性能的影响。结果表明:在280~380℃等温淬火时,随温度升高和时间延长,贝氏体组织逐渐粗化;随等温温度升高,残余奥氏体含量及其含碳量越多。等温淬火温度对ADI力学性能有显著影响,通过调整等温淬火温度可以获得不同力学性能等级的ADI。与传统单步ADI相比,两步工艺等温淬火ADI贝氏体组织更细小,残余奥氏体体积分数和残余奥氏体碳含量更高。两步等温淬火工艺能有效提高ADI抗拉强度和屈服强度,但不利于伸长率和冲击韧性提升。     

Microstructures and Mechanical Properties of Bearing Steels Modified for Preparing Nanostructured Bainite

Mo containing high-C-Cr bearing steel was modified with Si (0.8–1.5 wt.%) and 0.8Si–1.0Al to prepare nanostructured bainite by low-temperature isothermal heat treatment. The modified steels were isothermal held at 220 to 240 °C after partial austenitization in an intercritical gamma+carbide region, and the resultant microstructure and mechanical properties were studied. Carbide-free nanostructured bainite with plate thickness below 100 nm and film retained austenite, as well as a small amount of undissolved carbide particles, was obtained in the modified steels except in 0.8Si steel, in which carbides precipitated in bainitic ferrite. As Si content increased, the mean thickness of bainitic ferrite plates modestly decreased, whereas the fraction of retained austenite markedly increased. The thickness of bainitic ferrite plate and the fraction of retained austenite in Si-Al-modified steel were smaller than those in Si-modified steels. The hardness and elongation of the Si-Al-modified steel were lower than those of Si-modified steels. The yield strength of Si-Al-modified steel was superior to that of Si-modified steels. Mid-level ultimate tensile strength and impact toughness were achieved in Si-Al-modified steel. For bearing applications, Si-modified steels could provide higher hardness and toughness but lower dimensional stability. Meanwhile, Si-Al-modified steel could offer higher dimensional stability but lower hardness and toughness.     

低硅无铝中碳TRIP钢中残留奥氏体的机械稳定性

在GLEEBLE3500热模拟试验机上对两种TRIP( TRansformation Induced Plasticity)钢分别进行不同贝氏体温度的热处理,通过拉伸试验和X射线衍射研究钢板的性能及残留奥氏体转变.结果表明:高的原始残留奥氏体量和残奥中碳含量,可使得钢获得良好的综合性能.另外,建立起残留奥氏体随真应变的转变模型,该模型能较好的预测实验结果.     

Mn含量对0.15C-0.6Si-Mn TRIP钢组织和力学性能的影响

经过在两相区退火和贝氏体区等温处理，研究了两种不同锰含量的低硅TRIP钢的组织和力学性能，试验结果表明，低硅和低锰钢的残留奥氏体量少，力学性能差；增加锰含量，能提高残留奥氏体量及拉伸强度和伸长率，其力学性能与常规低碳Si-MnTRIP钢的水平相关，用电子探针测试了两相区退火钢中锰和硅的分布情况，发现锰在临界区退火时不发生再分配。     

Effect of silicon content and annealing temperature on formation of retained austenite and mechanical properties in multi-phase steels

Cold-rolled and annealed ultra-high strength sheet steels with good ductility accompanied by TRIP of retained austenite have received considerable attention in recent years. This paper discusses the effect of silicon content and annealing temperature on the formation of retained austenite and the mechanical properties in Fe-0.34%C-1.7% Mn steels whose structure consists of ferrite, bainite and retained austenite. Silicon inhibited the cementite formation in bainite during isothermal holding and partitioned carbon from bainite to austenite, resulting in an increase in retained austenite content. When the silicon content was increased to 1.0 wt.% or higher, the amount of retained austenite markedly increased leading to good mechanical properties. 0.34%C-1.03%Si-1.7%Mn steel showed a high tensile strength of 1,030 MPa and a total elongation of 34.5% when annealed at 780°C for 5 min followed by isothermal holding at 400°C for 5 min. In this case, the amount of retained austenite was about 25%. The variation in tensile strength-elongation combination had good correlation with that in the amount of retained austenite with both annealing temperature and silicon content. The most retained austenite was obtained in the steel annealed at just above A_C1 temperature. The annealing temperature which gives the most retained austenite was decreased with decreasing the silicon content.     

不同热处理条件下贝氏体钢的微观组织和疲劳裂纹扩展

以贝氏体钢为研究对象,设计了4种热处理工艺,研究了不同热处理工艺下试验钢的显微组织及疲劳裂纹扩展速率。结果表明,热轧态试验钢的微观组织以粒状贝氏体为主,其上分布有少量的板条贝氏体、马氏体和粗大块状M/A岛,残留奥氏体的体积分数为16.2%,但稳定性较差,裂纹能够直接穿过粗大的块状M/A岛继续扩展,疲劳裂纹扩展速率最快。经900 ℃奥氏体化+空冷后,显微组织以板条贝氏体和马氏体为主,M/A岛仍为粗大的块状,残留奥氏体含量减少至12.3%,疲劳裂纹扩展速率略有降低。经900 ℃奥氏体化+380 ℃盐浴等温30 min +空冷后,显微组织以细密、有序的板条贝氏体为主,残留奥氏体含量减少至10.2%,以薄膜状伴生在板条贝氏体间,板条状贝氏体及板条间的残留奥氏体薄膜会使裂纹端钝化、分叉、偏折,阻碍裂纹扩展的能力增强;经350 ℃回火240 min后,显微组织以马氏体和板条贝氏体为主,残留奥氏体含量比热轧态略微降低,为14.9%;而经450 ℃回火240 min后,显微组织以板条状贝氏体为主,其上分布有少量的马氏体,残留奥氏体体积分数减少至8.6%,也以薄膜状伴生在贝氏体板条间,同时有大量的碳化物析出,裂纹扩展速率最慢。     

EFFECTS OF RETAINED AUSTENITE ON DUPLEX MICROSTRUCTURE OF MARTENSITE AND LOWER BAINITE

ＥＦＦＥＣＴＳＯＦＲＥＴＡＩＮＥＤＡＵＳＴＥＮＩＴＥＯＮＤＵＰＬＥＸＭＩＣＲＯＳＴＲＵＣＴＵＲＥＯＦＭＡＲＴＥＮＳＩＴＥＡＮＤＬＯＷＥＲＢＡＩＮＩＴＥＷＥＮＣｕｉ’ｅ;ＬＩＮＪｉａｎｇｕｏ;ＺＨＯＵＹａｊｉａｎ（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａ...     

Microstructure and Mechanical Properties of Austempered Medium-Carbon Spring Steel

Changes in microstructure and mechanical properties of medium-carbon spring steel during austempering were investigated. After austempering for 1 h at 290 °C or 330 °C, the bainite transformation stabilized austenite, and microstructure consisting of bainitic ferrite and austenite could be obtained after final cooling; the retained austenite fraction was smaller in the alloy austempered at 290 °C because carbon redistribution between bainitic ferrite and austenite slowed as the temperature decreased, and thereby gave persistent driving force for the bainite transformation. The products of tensile strength and reduction of area in the austempered alloy were much larger in the austempered steel than in quenched and tempered alloy, mainly because of significant increase in reduction of area in austempered alloy.     

预相变马氏体对超级贝氏体钢组织热稳定性的影响

为明确超级贝氏体组织失稳机制以及探索提高超级贝氏体钢中残余奥氏体热稳定性的方法,通过预相变马氏体工艺,即在等温贝氏体相变前引入预相变马氏体,制备了中碳超级贝氏体钢。对比分析了回火前后中碳超级贝氏体钢显微组织和力学性能的变化,研究了预相变马氏体对中碳超级贝氏体钢中贝氏体组织及残余奥氏体热稳定性的影响。结果表明：预相变马氏体的存在能够细化贝氏体铁素体板条,提高残余奥氏体含量和热稳定性。预相变马氏体的引入及其对超级贝氏体组织的细化作用使得试验钢的屈服强度超过1 000 MPa,伸长率大于20%;300～600℃回火1 h后,高碳薄膜状残余奥氏体首先发生分解,形成细小的碳化物,然后贝氏体铁素体板条发生回复和再结晶,形成沿原板条方向的铁素体晶粒;600℃回火后试验钢的屈服强度仍与回火前相当,主要是预相变马氏体周围的薄膜状残余奥氏体未发生明显分解,能够抑制相邻贝氏体铁素体板条的回复。     

冷却介质对高强度贝氏体耐磨钢板组织和力学性能的影响

研究了不同冷却介质对贝氏体耐磨钢板组织和力学性能的影响。结果表明,轧制、低温回火及热轧后奥氏体化空冷低温回火耐磨板的组织为板条贝氏体铁素体和残留奥氏体,油冷、水冷热处理耐磨板的组织为板条马氏体和残留奥氏体。经轧制、低温回火及奥氏体化空冷低温回火,新型贝氏体耐磨钢板具有良好的强韧性配合。热轧后用控制奥氏体化介质冷却可以获得不同力学性能的耐磨钢板．     

MECHANICAL PROPERTIES IN AN INTERCRITICALLY HEAT-TREATED BAINITE-TRANSFORMED 2%Si STEEL

A significant amount of austenite can be retained by rapid cooling following intercritical annealing and holding at the bainite transformation range in steel with comparatively low carbon and silicon contents. Retained austenite is blocky and very fine and moderately stabilized due to C enrichment. The elongation and the strength-ductility balance of the steel can be enhanced considerably due to strain-induced martensite transformation and transformation-induced plasticity (TRIP) of retained austenite.