超细晶钒微合金化双相钢性能

研究了钒微合金化对高强双相钢微观组织及性能的影响。与Fe-0.186C-1.5Mn-0.3Si-0.008N参照钢相比,加入0.14%V带来如下效果:(1)在冷轧及退火状态铁素体晶粒高度细化;(2)严重推迟在连续退火过程中铁素体向奥氏体转变的初始动力学;(3)慢冷条件下铁素体开始转变温度稍微提高,但珠光体和贝氏体转变被抑制,导致淬透性提高;(4)在临界退火温度≤740℃时观察到未溶渗碳体;(5)750℃/180 s退火后铁素体相中发现大量V(C,N)析出(平均直径7.4 nm),而马氏体(奥氏体)中析出物稀少,尺寸更大(平均直径13.4 nm);(6)不含钒参照钢抗拉强度随马氏体体积分数增量为~16 MPa/%,而含钒钢由于晶粒细化和铁素体选择强化,强度随马氏体含量变化增量相当低(~4 MPa/%),在马氏体体积分数45%变软。     

Effect of Mn Addition on Microstructural Modification and Cracking Behavior of Ferritic Light-Weight Steels

In the present study, effects of Mn addition on cracking phenomenon occurring during cold rolling of ferritic light-weight steels were clarified in relation to microstructural modification involving κ-carbide, austenite, and martensite. Four steels were fabricated by varying Mn contents of 3 to 12 wt pct, and edge areas of steel sheets containing 6 to 9 wt pct Mn were cracked during the cold rolling. The steels were basically composed of ferrite and austenite in a band shape, but a considerable amount of κ-carbide or martensite existed in the steels containing 3 to 6 wt pct Mn. Microstructural observation of the deformed region of fractured tensile specimens revealed that cracks which were initiated at ferrite/martensite interfacial κ-carbides readily propagated along ferrite/martensite interfaces or into martensite areas in the steel containing 6 wt pct Mn, thereby leading to the center or edge cracking during the cold rolling. In the steel containing 9 wt pct Mn, edge cracks were found in the final stage of cold rolling because of the formation of martensite by the strain-induced austenite to martensite transformation, whereas they were hardly formed in the steel containing 12 wt pct Mn. To prevent or minimize the cracking, it was recommended that the formation of martensite during the cooling from the hot rolling temperature or during the cold rolling should be suppressed, which could be achieved by the enhancement of thermal or mechanical stability of austenite with decreasing austenite grain size or increasing contents of austenite stabilizers.     

Microstructural Refinement and Strain Hardening Behavior in Low-Density Ultrafine Pearlite Steel

Advanced low-density steels that meet energy shortages and high safety requirements have become a hot research topic in materials science. The addition of light elements with medium-Al content (5 wt%) to ultrahigh-strength pearlite cable steel alloy reduces the material density and causes a microstructural change from traditional θ-pearlite (ferrite + cementite) to θ-pearlite and κ-pearlite (ferrite + cementite + κ-carbide). The results show that the moderate addition of Al and Mn (5 wt%) promotes the formation of κ-carbide, which inhibits the diffusion of C and significantly delays the eutectoid transformation process of pearlite. Meanwhile, the transformation free energy of pearlite increases and obviously refines the lamellar spacing of the ultrafine pearlite by κ-carbide. Simultaneously, the interaction between κ-carbides and dislocations is initiated, which increases the strain hardening rate of ultrafine pearlitic steel.     

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。     

热处理工艺对Fe-Mn-Al-C钢组织和性能的影响

利用SEM、XRD、EPMA等试验方法,对不同退火、固溶以及时效工艺下Fe-Mn-Al-C钢的组织演变规律和力学性能进行研究。结果表明,900～1050℃退火温度对试验钢的组织与性能影响较大,随着退火温度的升高晶粒尺寸增大、碳化物逐渐回溶,强度降低、塑韧性提高,在1050℃保温2 h空冷时抗拉强度为1036 MPa,断后伸长率为39%,冲击功41 J,强塑积40 GPa·%;经1050℃保温2 h水冷固溶后时效处理,试验钢组织为奥氏体+铁素体+κ碳化物,随着时效温度的增高,κ碳化物逐渐析出,使试验钢的强度增加、塑韧性降低。600℃时效时,抗拉强度1145 MPa、断后伸长率22%、冲击功28 J,综合力学性能全部满足设计要求。     

Fe-Mn-Al-C系低密度钢开发中数值模拟的应用

借助FactSage与JMatPro数值模拟软件对Fe-(5～15)Mn-(6～12)Al-(0.5～1.0)C系低密度钢的密度、凝固及冷却路径、相变及析出相进行了研究.利用FactSage软件中的FSstel数据库对该体系的垂直截面相图进行计算,分析了Mn、Al及C元素对凝固及冷却过程中相变及析出相的影响,并得到了F...     

Effects of Annealing Treatment Prior to Cold Rolling on the Edge Cracking Phenomenon of Ferritic Lightweight Steel

Effects of annealing treatment from 923 K to 1023 K (650 °C to 750 °C) prior to cold rolling on the edge cracking phenomenon of a ferritic lightweight steel were investigated. The edge cracking was severely found in the hot-rolled and 923 K (650 °C)-annealed steels after cold rolling, whereas it hardly occurred in the 1023 K (750 °C)-annealed steel. As the annealing temperature increased, lamellar κ-carbides were dissolved and coarsened, and most of the κ-carbides continuously formed along boundaries between ferrite and κ-carbide bands disappeared. Microstructural observation of the deformed region of tensile specimens revealed that the removal of band boundary κ-carbides reduced the difference in tensile elongation along the longitudinal direction (LD) and transverse direction (TD), which consequently led to the reduction in edge cracking. The 1023 K (750 °C)-annealed steel showed fine ferrite grain size, weak texture, and decomposed band structure after subsequent cold rolling and intercritical annealing, because κ-carbides actively worked as nucleation sites of ferrite and austenite. The present annealing treatment prior to cold rolling, which was originally adopted to prevent edge cracking, also beneficially modified the final microstructure of lightweight steel.     

C和Mn元素配分行为对冷轧中锰TRIP钢组织性能的影响

采用冷轧+两相区温轧退火（CR+WR+IA）热处理工艺,研究了两相区退火时间对超细晶铁素体与奥氏体中组织形貌演变、C和Mn元素配分行为以及力学性能的影响。结果表明,冷轧试验钢经两相区形变退火处理后,获得了由铁素体、残余奥氏体或新生马氏体组成的超细晶复相组织。在645℃随退火时间的延长,形变马氏体向逆相变奥氏体配分的C、Mn元素增多,C、Mn元素富集位置增加,同时富Mn区形变马氏体回复再结晶现象明显;伴随少量碳化物溶解,试验钢的屈服强度由741持续降低到325MPa。两相区退火10min时,试验钢力学性能最佳,此时抗拉强度达到最大值1141MPa,断后伸长率及均匀伸长率分别为236%和181%,强塑积达到26928MPa·%。     

碳化物演变对冷轧ART 0-1C-7Mn钢Lüders行为影响

摘要：采用SEM、XRD、力学性能测试等实验分析方法对冷轧中锰钢（0.1C-7Mn）在奥氏体逆相变不同温度退火过程中碳化物演变对Lüders应变的影响进行了分析。结果表明：随着退火温度的升高,碳化物先析出后溶解,在640℃退火时碳化物全部溶解,逆转变奥氏体的稳定性适中,强塑积最高为25GPa·%。退火温度偏低导致奥氏体稳定性过高,同时碳化物会抑制位错运动,使得屈服点延伸较为明显;退火温度适中则高密度位错开始回复,变形时能持续地产生TRIP效应硬化基体,提高材料的综合性能;退火温度偏高时,碳化物的溶解导致位错对消重排,Lüders应变消失,奥氏体稳定性降低,应变诱导马氏体快速形成,导致中锰钢抗拉强度较高但均匀伸长率降低。     

Fe 15C 15Cr 15Al超高碳钢碳化物的球化和力学性能

 对Fe 15C 15Cr 15Al超高碳钢碳化物的球化工艺及力学性能进行了研究。扫描电镜观察表明，加入铝，可抑制锻后空冷条件下先共析网状碳化物的析出；利用铝合金化作用和成分不均匀化奥氏体加热控制，提出了2种无形变球化处理工艺：①离异共析等温球化；②预冷淬火+高温回火。2种球化处理工艺均能获得良好的球化组织和良好的综合力学性能：Rm≥1 000 MPa，Re≥700 MPa，A10=10%~14%。拉伸断口具有明显的缩颈，断口形貌呈具有典型的韧窝特征。     

固溶温度对022Cr22Ni5Mo3N双相不锈钢组织和性能的影响

试验研究了1000℃ 4h和1060℃ 4h固溶处理后022Cr22Ni5Mo3N钢中ϕ75 mm材的组织和力学性能。结果表明,022Cr22Ni5Mo3N钢ϕ75 mm材终锻温度970℃空冷的组织（体积分数)约为铁素体31% ,奥氏体 56%,析出物13%;1 000℃ 4 h固溶后为铁素体38% ,奥氏体60% ,析出物2%;1060℃ 4h固溶后铁素体50%,奥氏体50%,该钢通过釆用1060℃固溶后,拉伸断裂强度731MPa延伸率38%,冲击功AKV(-40℃ ）76~81 J,满足标准要求。     

两相区退火处理含铝中锰钢的组织和力学性能

 为了研究两相区退火处理对冷轧含铝中锰钢(0.2C-0.6Si-5Mn-1.2Al)(质量分数,%)微观组织和力学性能的影响规律,利用SEM、XRD及单轴拉伸等试验方法表征了不同工艺状态后的微观组织及测试了拉伸性能。结果表明,冷轧试验钢在退火过程中组织发生奥氏体逆转变,在退火温度为670 ℃、退火时间为10 min时可获得较佳的力学性能,即抗拉强度达到1 276 MPa,总伸长率达到51.8%,强塑积高达66.1 GPa·%。随着退火温度升高,残余奥氏体组织逐渐粗化且向马氏体组织转变,机械稳定性逐渐降低。残余奥氏体机械稳定性主要受残余奥氏体中碳质量分数及其晶粒尺寸的影响,而残余奥氏体中锰质量分数对其影响较小。     

临界退火中锰钢的组织性能和变形行为

 为了研究临界退火中锰钢的微观组织演变规律以及组织对力学性能和变形行为的影响,对冷轧中锰钢(0.1C-7Mn-0.35Si)在570～650 ℃范围内进行了临界退火处理。研究结果表明,随着退火温度升高,双相“奥氏体+铁素体”组织逐步趋于等轴化且晶粒有粗化的趋势,并且在650 ℃时出现了马氏体组织;试验钢的抗拉强度随温度升高而增加,而伸长率和屈服强度均呈下降趋势,局部不均匀变形带随着退火温度升高逐步弱化,在620和650 ℃时完全消失;在相对较高的退火温度下,粗化的等轴奥氏体晶粒中形变诱导马氏体相变的增强和大尺寸的铁素体晶粒中动态回复的减弱,以及更高温度时马氏体的引入等,均改善了屈服阶段的加工硬化能力,从而有效减弱或抑制吕德斯带的扩展。     

热变形工艺对100Cr6轴承钢线材网状碳化物的影响

利用热膨胀仪、热模拟试验机、金相显微镜、场发射扫描电镜等测定了100Cr6轴承钢的CCT曲线,试验研究了热压缩及控轧控冷对网状碳化物析出行为的影响。结果表明：第二道次压缩温度从850℃降低至700℃时,奥氏体再结晶细化向未再结晶转变,二次碳化物逐步由晶界封闭网状向半封闭条状、短杆状再向沿拉长的奥氏体晶界链状转变,750～800℃内变形碳化物细小、分散;Φ10 mm 100Cr6线材采用910℃降至770℃温度控轧+快速冷却工艺,其热轧态、球化退火及淬回火后碳化物分布均匀性逐步提升,奥氏体晶粒由8.0级细化至10.0级,晶界碳化物由封闭网状向断续条状转变,平均厚度从0.54μm降低至0.11μm,网状级别由3.0级占比33%降低至≤2.0级占比100%,可缩短球化退火时间及提高轴承的疲劳寿命。     

Optimization of Process Conditions for Ultralightweight Steel with More Than 13 wt% of Al and 5 wt% of Cr

An ultralightweight Fe–30Mn–13.2Al–1.6C–5Cr steel, which contains more than 13 wt% of Al and thereby reduces the density by 20%, is developed. The ultralightweight steel, which is very brittle due to high Al content, is fabricated by optimizing hot rolling and heat treatment conditions. Hot rolling is conducted after soaking at the temperature range of 1100–1200 °C for 2 h. The ultralightweight steel is hot-rolled successfully after soaking at 1100 °C, whereas specimens soaked at 1150 and 1200 °C are intergranularly cracked after hot rolling, resulting from coarse grain and a large fraction and size of ferrite, which is transformed to ordered DO₃ phase during cooling, at the grain boundaries. In homogenization heat treatment, water quenching and air cooling are performed, respectively, after holding at 1050 °C for 2 h. The air-cooled steel has inferior tensile property due to the formation of brittle ordered DO₃ phase at grain boundaries. Meanwhile, the water-quenched steel shows an excellent tensile property, which is attributed to a uniform microstructure comprising austenite, fine κ-carbide in austenite, and a very small fraction of the ordered DO₃ phase.     

Electron microstructure and mechanical properties of silicon and aluminium ductile irons

Samples of unalloyed silicon and aluminium spheroidal graphite cast iron have been studied in the austempered condition. Austempering times of up 3 h at 400°C for Al SG and 1 h at 350°C for Si SG gives a typical ADI microstructure consising of carbide-free banitic ferrite and stable, high carbon enriched, retained austenite. This has an attractive combination of elongation and strength. For longer austempering times transition carbides are precipitated in the bainitic ferrite, η-carbide in the upper bainitic range, i.e.400°C for Al SG and 350°C for Si SG, and ϵ-carbide in the lower bainite range. Increasing amounts of transition carbide reduce the ductility and produce a mixed model of fracture. For longer austempring times _X-carbide is precipitated at the ferrite/austenite boundaries leading to a more brittle fracture mode.     

退火温度对冷轧中锰钢组织性能和断裂行为的影响

 为了系统研究临界区退火和全奥氏体区退火对中锰钢性能的影响,为中锰钢的实际应用提供理论基础,在650~900 ℃范围内系统研究了冷轧中锰钢的显微组织和力学性能,并通过断口形貌观察分析了试验钢的断裂特性。结果表明,试验钢在临界区退火的综合力学性能明显优于全奥氏体区退火。650~750 ℃退火时,抗拉强度在1 000 MPa左右,强塑积超过30 GPa·%,发生韧性断裂,宏观上可以观察到明显的层状裂纹,微观下为大量韧窝;在800~900 ℃退火时,抗拉强度在743~1 154 MPa范围内波动较大,强塑积不足10 GPa·%,断口平整,发生脆性沿晶断裂;退火温度为650 ℃时,组织为片层状和等轴状的奥氏体、铁素体双相及大量渗碳体;随着退火温度的升高,渗碳体逐渐溶解消失,等轴状组织所占体积分数明显增加,奥氏体体积分数也不断增加,在750 ℃时达到52.2%;退火温度为800 ℃时,有马氏体产生,奥氏体体积分数下降;退火温度为900 ℃时,组织基本为马氏体,残留奥氏体体积分数仅为14.6%。     

In-situ analysis of retained austenite transformation in high-performance micro-alloyed TRIP steel

Microstructures and mechanical properties of Ti-V micro-alloyed TRIP( transformation-induced plasticity) steel with different compositions were investigated by tensile test,scanning electron microscopy( SEM),transmission electron microscopy( TEM),X-ray diffraction( XRD) and thermodynamic calculation( TC). The results indicated that the steel exhibited high ultimate tensile strength( 1 079MPa),sufficient ductility( 28%) and the highest product of strength and ductility( 30 212 MPa·%) heat treated after intercritical annealing at 800℃ for 3 min and bainitic annealing at 430 ℃ for 5 min. In addition,the change of volume fraction of retained austenite( VF-RA) versus tensile strain was measured using in-situ analysis by X-ray stress apparatus and micro-electronic universal testing machine. It was concluded that a-value could be used to evaluate the stability of retained austenite( S-RA) in the investigated Ti-V micro-alloyed TRIP steel. The smaller a-value indicated the higher stability of retained austenite( S-RA) and the higher mechanical properties of Ti-V micro-alloyed TRIP steel.     

Retained austenite and mechanical properties of 0. 1C- 5Mn steel after intercritical annealing

The effect of annealing temperature on the microstructure, mechanical property and austenite content for 0. 1C- 5Mn steel was studied by ART (Austenite Reverted Transformation) heat treatment process. The morphology, metastable austenite content and mechanical properties of experimental steel were characterized by means of SEM, XRD and tensile testing at room temperature. The results indicate that the structure of experimental steel is composed of ferrite and retained austenite; with the increase of the inintercritical annealing temperature, precipitation and redissolution of carbides are found in experimental steels; simultaneously, the lath- like deformed martensite reverts to form equiaxed ferrite through the recovery and polygonization, and granular austenite undercools to lath- like and blocky martensite; the contents of retained austenite are similar in 630, 645 and 660?? samples, which are 18. 4 vol.%, 19. 5 vol.% and 18. 8 vol.%, respectively; with the increase of the annealing temperature, the volume fraction of the retained austenite suddenly drops and a large amount of reversed austenite changes into martensite; the combination of different annealing temperatures indicates that the experimental steel can obtain the best comprehensive mechanical properties when the annealing temperature is 660??.     

冷轧中锰钢的超塑性与组织结构演化行为

 为了研究含铝冷轧中锰钢的超塑性能和在超塑性变形下的组织结构演化过程,对冷轧含铝中锰钢在800 ℃进行了高温拉伸试验和不同变形量下的微观组织结构表征。研究结果表明,0.05C5Mn2Al、0.10C5Mn2Al和0.15C5Mn3Al钢伸长率分别达到了740%、850%和350%,都获得了超塑性现象,EBSD表征结果表明0.05C5Mn2Al、0.10C5Mn2Al两种冷轧组织均匀细小,在高温拉伸过程中具有较高的稳定性,拉伸过程中铁素体与原奥氏体均匀长大,且最大晶粒尺寸小于10 μm;但0.15C5Mn3Al冷轧组织存在条带状的铁素体,该组织易于通过吞并细小的铁素体和原奥氏体晶粒而异常长大,高温拉伸后的尺寸达到了20 μm。通过对3种含铝冷轧中锰钢的超塑性行为与微观组织结构演化关系分析,认为初始均匀一致的冷轧组织具有高的组织稳定性而有利于超塑性,而具有粗大条带状的铁素体组织易于发生异常长大而不利于超塑性。