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1.
A medium-Mn steel (Fe–0.3C–4Mn–1.82Al–0.6Si wt-%) was produced by a novel processing route involving twin-roll strip casting, hot rolling and intercritical annealing (IA). Macrosegregation was absent in the as-cast strip. The microstructure of the as-cast strip consisted of martensite and austenite (~10 vol.-%), and the solidification structure was characterised by dendritic structure. With an increase in IA temperature from 680 to 725 and to 755°C, austenite fraction in intercritically annealed steels was increased from 22 to 45% and then decreased to 27%. The 710°C intercritically annealed steel yielded excellent mechanical properties with a tensile strength of ~1007?MPa and total elongation of ~48%, achieved by a high volume fraction of austenite (~42%) with appropriate mechanical stability.  相似文献   

2.
ABSTRACT

The present work reports the effect of different initial microstructures on reverse transformation kinetics and morphologies of austenite formed during intercritical annealing in Fe-0.14C-7Mn-1Si (wt-%) medium Mn steel. Three different initial microstructures were produced by cold-rolling and cold-rolling followed by austenitisation at 820°C and 900°C. The specimen austenitised at higher temperature shows lath-type austenite after intercritical annealing. The difference in austenitisation temperature leads to different Mn distribution in martensitic initial microstructures, thereby leading to a difference in morphology of austenite. The inhomogeneous Mn profiles in initial microstructures also affect reverse transformation kinetics of austenite upon intercritical annealing. The presence of Mn-enriched regions accelerates austenite growth at an early stage of intercritical annealing but retards the transformation kinetics afterwards.

This paper is part of a Thematic Issue on Medium Manganese Steels.  相似文献   

3.
An aluminium-containing medium manganese steel has been designed to undergo intercritical annealing followed by quenching in water and subsequent partitioning. Water quenching, replacing the quenching temperature (QT) between 150 and 300°C in conventional quenching and partitioning steels, is therefore adopted in QP alloys, in order to guarantee the precise QT in practice. The low intercritical annealing temperature of 750°C refines both ferrite and prior austenite grains into submicron size. The large fraction of ultra-fine ferrite, as well as the transformation-induced plasticity effect of retained austenite, improves the overall ductility of this water-quenched and partitioned steel. The alloy has achieved excellent mechanical properties of 1130?MPa ultimate tensile strength combined with 19.2% total elongation.  相似文献   

4.
A novel type of quenching and partitioning steel was developed using direct quenching after hot finishing rolling, followed by intercritical annealing, quenching and partitioning (DQ–Q&P) process. The desirable combination of strength and ductility was obtained. The effect of various intercritical annealing temperatures on the microstructures and mechanical proprieties was studied. With the decreasing intercritical annealing temperature, the amount of acicular retained austenite increased, which exhibited a good work-hardening behaviour resulting in enhanced tensile strength and total elongation. After annealing at 740°C, superior mechanical properties, which were the ultimate tensile strength of 1015?MPa and total elongation of 32.22%, were achieved.  相似文献   

5.
Fine film-like stable retained austenite was obtained in a Fe–0.08C–0.5Si–2.4Mn–0.5Ni in weight percent (wt.%) steel by the two-step intercritical heat treatment. The first step of intercritical annealing creates a mixed microstructure of preliminary alloy-enriched martensite and lean alloyed intercritical ferrite, which is called as “reverted structure” and “un-reverted structure”, respectively. The second step of intercritical tempering is beneficial for producing film-like stable reverted austenite along the reverted structure. The stabilization of retained austenite was studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), dilatometry and X-ray diffraction (XRD) analysis. The two-step austenite reverted transformation associated with intercritical partition of C, Mn and Ni is believed to be the underlying basis for stabilization of retained austenite during the two-step intercritical heat treatment. Stable retained austenite is not only beneficial for high ductility, but also for low temperature toughness by restricting brittle fracture. With 10% (volume fraction) of retained austenite in the steel, high low temperature toughness with average Charpy impact energy of 65 J at −80 °C was obtained.  相似文献   

6.
We elucidate here the role of isothermal hold temperature of 300–500°C after intercritical annealing at 760°C on bainitic transformation and in governing the stabilisation of retained austenite in a 0.23C-1.35Si-1.82Mn steel. A critical analysis was attempted to explain the observations using displacive mechanism of bainite formation in the attempt to endeavour to understand the kinetics of bainitic transformation during isothermal holding. The model predicted that carbon enrichment in austenite was of particular significance in governing the stability of retained austenite. Thus, through the contribution of transformation induced plasticity effect of retained austenite, high tensile strength (964?MPa) and excellent ductility (uniform elongation of 24.5% and total elongation of 32%) was obtained on isothermal holding at 400°C.  相似文献   

7.
采用EMPA,SEM和XRD等手段,研究低碳硅锰钢在双相区保温淬火(I&Q)、双相区保温+奥氏体化+盐浴配分(I&Q&P)和奥氏体化+盐浴配分(Q&P)工艺中的C,Mn元素配分行为及对残余奥氏体的综合作用。结果表明:经I&Q工艺处理后,得到马氏体、铁素体加少量残余奥氏体混合组织,C,Mn在马氏体中出现了富集,并且C富集程度高于Mn;经I&Q&P工艺处理后,C,Mn在板条马氏体中呈现不均匀分布,C的局部富集现象更明显,按C,Mn含量的不同,马氏体可分为"高C高Mn"、"高C低Mn"和"低C低Mn"3种;相比较Q&P工艺中只有C配分作用稳定残余奥氏体,I&Q&P工艺在C,Mn配分综合作用下,能得到更多的残余奥氏体。  相似文献   

8.
The standard heat treatment of PH 13-8 Mo maraging steels consists of solution annealing and subsequent aging. Herein, it is investigated how an additional intercritical annealing step prior to aging affects the microstructure, and, consequently, the mechanical properties of a PH 13-8 Mo maraging steel. In situ techniques by means of high-temperature electron backscatter diffraction and high-temperature X-ray diffraction are applied to study the microstructural changes during intercritical annealing and subsequent aging. In addition, high-resolution investigation methods, such as transmission electron microscopy and atom probe tomography supplemented by transmission Kikuchi diffraction, are used for an in-depth characterization of the microstructure. The results reveal that a diffusion-controlled martensite to austenite transformation accompanied by partitioning of the substitutional atoms Cr, Ni, and Mo takes place during intercritical annealing. As a result of partitioning during intercritical annealing, an inhomogeneous distribution of Ni remains in the microstructure after the martensitic transformation. Consequently, the formation of reverted austenite is facilitated during subsequent aging due to existing Ni-enriched zones in martensite. Since the fracture toughness is significantly enhanced compared to the standard heat treatment, it is suggested that this improvement is related to the increased phase fraction of reverted austenite.  相似文献   

9.
An intercritical annealing pre-treatment was added before the conventional two-step heat treatment process, and the effect of the isothermal bainitic transformation (IBT) time on the steel's microstructure and mechanical properties were investigated. The microstructure was investigated using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, while the mechanical properties were evaluated using tensile testing. The microstructure of the three-step hot-dip galvanised transformation induced plasticity (TRIP) steel consists of ferrite, bainite, retained austenite, and martensite. The mechanical properties of the steel after the three-step heat treatment process are excellent, with a tensile strength above 770?MPa and elongation above 29%. The effect of IBT time on the mechanical properties was insignificant because the intercritical annealing pre-treatment increases the bainitic transformation rate.  相似文献   

10.
采用双相区再加热-淬火-碳配分(IQP)工艺,研究初始组织为铁素体+珠光体的IQP-Ⅰ多相钢和初始组织为马氏体的IQP-Ⅱ多相钢的组织形貌、残留奥氏体及力学性能。结果表明:初始组织为铁素体+珠光体的IQP-Ⅰ多相钢室温组织中,铁素体和马氏体基本呈块状分布,块状残留奥氏体存在于铁素体与马氏体界面处,薄膜状只存在于马氏体内的板条之间,且残留奥氏体含量较少,TRIP效应不明显,其抗拉强度为957 MPa,伸长率只有20%,强塑积为19905.6MPa·%。初始组织为马氏体的IQP-Ⅱ多相钢中铁素体和马氏体大多呈灰黑色的板条状或针状,且细小的针状马氏体均匀地分布在铁素体基体上,残留奥氏体只以薄膜状平行分布在铁素体基体上,体积分数达到了13.2%,且具有较高的稳定性,TRIP效应较明显,强塑积达到21560MPa·%,可以获得强度和塑性的良好结合。  相似文献   

11.
ABSTRACT

We propose an effective heat treatment involving a combination of intercritical hardening and tempering to obtain high strength–high ductility in hot-rolled 0.2C–1.5Al–(6–8.5)Mn–Fe transformation-induced plasticity (TRIP) steels. An excellent combination of high ultimate tensile strength of 1045–1380?MPa and total elongation of 34–39% was obtained when the steels were subjected to intercritical hardening at 630–650?°C and tempered at 200?°C. Intercritical hardening impacted the co-existence of austenite, ferrite and martensite, such that the deformation behaviour varied with the Mn content. The excellent properties of the steels were attributed to cumulative contribution of enhanced TRIP effect of austenite and ferrite and martensite constituents. The discontinuous TRIP e?ect during tensile deformation involves stress relaxation and led to consequent enhancement of ductility.  相似文献   

12.
The microstructure and amount of retained austenite (the austenite remained at room temperature) evolved in Fe–13%Cr–4%Ni martensitic stainless steel during intercritical tempering at 620 °C have been investigated. The amount of retained austenite showed a parabolic trend with increase in tempering time, which can be attributed to the gradual decrease in the thermal stability of the reversed austenite (the austenite formed at high temperature). The influences of chemical composition, morphology of reversed austenite, and mechanical constraints originating from tempered martensite matrix on the thermal stability have been discussed. The precipitation and growth of M23C6 in reversed austenite dilute the carbon concentration in reversed austenite. The spheroidization of lathy reversed austenite during tempering decreases the interfacial energy barrier to the phase transformation of reversed austenite to martensite. Furthermore, the decrease in the strength of martensite matrix lowers the strain energy associated with the transformation of reversed austenite to martensite. All these factors during tempering weaken the thermal stability of reversed austenite and facilitate the phase transformation of reversed austenite to martensite during the cooling step of intercritical tempering.  相似文献   

13.
采用IQP工艺和EPMA、SEM和XRD等手段,研究了3种前驱体对含Cu低碳钢残余奥氏体含量及力学性能的影响。结果表明,双相区保温初期试验钢奥氏体长大由C配分控制,后期由合金元素Mn、Cu配分控制;双相区保温奥氏体化后,双相区配分后形成弥散分布的局部高浓度Mn、Cu区域仍保留富集效果,在随后的淬火-碳配分阶段易于形成残余奥氏体。经IQP处理后,前驱体为P+F的钢室温组织中马氏体板条较粗,原始奥氏体晶界并不明显;前驱体为F+M钢得到的马氏体板条有序细密;前驱体为M的钢室温组织中马氏体板条更加细密。其中,前驱体组织为M的钢中残余奥氏体量最高,延伸率为24.1%,强塑积可达25 338 MPa·%,综合性能最好。  相似文献   

14.
The present work investigates the effect of the initial microstructure on phase transformation after intercritical annealing by measuring the amount of austenite, which was obtained by X-ray diffraction and saturation magnetisation. Pieces of 8?Mn steel were austenitised at 1100°C for 1?h followed by different cooling rates: water, air, and furnace. Samples of each piece were subsequently intercritically annealed from 600 to 800°C followed by air cooling. The microstructure was characterised using scanning electron microscopy and electron backscatter diffraction. Results show how changing the cooling rate affects the temperature of intercritical annealing at which the highest content of retained austenite was obtained.  相似文献   

15.
为了研究22MnB5钢在退火过程中的组织演变规律,细化热冲压成形后马氏体板条束,通过扫描电镜(SEM)、能谱分析、电子背散射衍射(EBSD)分析技术和拉伸实验等方法,研究了不同低温临界区退火时间对22MnB5钢显微组织和力学性能的影响,并阐述了不均匀奥氏体在退火过程中的转变机制及合金元素对粒状珠光体形成的影响.研究表明,经低温临界区不同退火时间保温及随后等温处理后,得到不同的珠光体形态,在770℃保温0.5 h,并在700℃等温处理后,得到铁素体基体上分布颗粒状碳化物的粒状珠光体组织;随着临界区保温时间的延长,奥氏体转变逐渐均匀,使部分奥氏体在随后的等温过程中发生共析转变,得到多边形铁素体+片层状珠光体组织.粒状珠光体组织有利于细化淬火后的马氏体板条束,提高综合力学性能.  相似文献   

16.
We have studied the micromechanical behaviour of two low-alloyed multiphase TRIP steels with different aluminium contents by performing in situ high-energy X-ray diffraction experiments at a synchrotron source under increasing tensile stress levels. A detailed analysis of the two-dimensional diffraction data has allowed us to unravel the interplay between the martensite formation, the texture evolution and the load partitioning, and to correlate the observed behaviour to the macroscopic response of the material. The high aluminium content TRIP steel grade presents a higher volume fraction of retained austenite at room temperature that transforms more gradually into martensite under deformation, providing a larger uniform elongation. The comparison between the observed transformation behaviour and the texture evolution indicates that the 〈1 0 0〉 component along the loading direction corresponds to a low critical stress for the transformation. The evolution of the elastic strains revealed the occurrence of a significant load partitioning before reaching the macroscopic yield strength, which becomes more pronounced in the plastic regime due to the progressive yielding of the different grains in the polycrystalline material. This opens the door to tailor the austenite stability by altering the distribution in grain size, local carbon content, and grain orientation in order to produce the optimal load partitioning and work hardening for improved combinations of strength and formability in low-alloyed TRIP steels.  相似文献   

17.
Abstract

The impact of austenite deformation in the intercritical range on the rate of transformation in continuous cooling to ferrite, pearlite, bainite or martensite has been studied. The austenite associated with the rolled ferrite is much higher in carbon content, which does not influence the pearlite transformation but retards bainite and martensite. Furthermore, in comparison with rolling of stable austenite the increased strain hardening of the intercritically cooled austenite accelerates the formation of ferrite and pearlite (+ 10–30°C) and refines them but retards the bainite and martensite transformations (?20–40°C). At the intermediate cooling rate near 16 K s?1, these several influences combined with near doubling of the ferrite production give rise to the suppression of bainite formation and to maximum increased delay of martensite start.  相似文献   

18.
Bai  Shao-bin  Xiao  Wen-tao  Wang  Yi-de  Li  Da-zhao  Zhuang  Zhi-hua  Zhang  Wang-gang  Liang  Wei 《Journal of Materials Science》2021,56(24):13801-13813

To optimize the formability and strength of hot-rolled Fe-10Mn-0.4C-2Al-0.6 V medium Mn steel, intercritical quenching and tempering processes were carried out. The strength of the steel was enhanced, and the Lüdders platform was eliminated. The higher strength of the steel was attributed to the occurrence of a complex twinning effect, martensitic transformation and V-carbide precipitation during tensile deformation. In particular, the twin martensite structure retained after the quenching-tempering process served as another previous twin to accelerate the generation of nanomechanical twins in recrystallized austenite grain. The occurrence of transformation-induced plasticity (TRIP) of austenite with poor stability in non-recrystallized regions stimulated the TRIP and twinning-induced plasticity (TWIP) effects in austenite with high stability in recrystallized regions. Therefore, two pathways to improve the formability and optimize the mechanical properties of medium Mn steel by adjusting the quenching and tempering processes were proposed in this paper: (1) Manufacturing more martensite twin structures and (2) regulating the balance of austenite stability in both recrystallized and non-recrystallized regions.

  相似文献   

19.
为了提高钢的综合力学性能,用盐浴法对中Mn TRIP钢进行了热处理.采用SEM、TEM、XRD和拉伸测试研究了预奥氏体化处理对中Mn TRIP钢显微组织及力学性能的影响.实验结果表明:全马氏体冷轧态组织经两相区退火处理后,会析出大量渗碳体颗粒,随着退火时间延长,渗碳体颗粒逐渐溶解,马氏体组织逐渐转变为奥氏体和铁素体双相片层状组织;而在两相区退火处理前添加两相区预奥氏体化处理后,渗碳体析出被有效抑制,双相片层组织迅速形成;相比于常规两相区退火处理,预奥氏体化处理能够提高组织中残余奥氏体体积分数和综合力学性能.  相似文献   

20.
We made a quantitative comparison of three different methods, optical microscopy by tint etchant, EBSD phase mapping and dilatometry for analysis of phase fraction in steel subjected to intercritical annealing and isothermal treatment. While the results from optical microscopy and EBSD technique showed quantitative agreement, the dilatometry gave rather higher martensite fraction compared to the microscopic analyses. Nevertheless, all three methods showed qualitative agreement in the variation of martensitic fraction depending on the processing conditions. The analyses revealed that the martensitic fraction in final microstructure decreased as intercritical annealing temperature increased because it deteriorated the hardenability of austenite. Raising the isothermal treatment temperature increases the martensite fraction due to the increases of austenite fraction, which transformed into martensite afterward.  相似文献   

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