600MPa级冷轧连续退火双相钢临界区加热温度研究

应用光亮连续退火模拟实验机,在300℃过时效的工艺条件下,通过连续退火实验研究了临界区加热温度对600 MPa级冷轧连续退火双相钢组织和性能的影响.结果表明,临界区加热温度越高,第二相组织(贝氏体和岛状马氏体)数量越多,贝氏体组织越粗大,岛状马氏体数量越少;临界加热温度越高,试验钢的强度越高,伸长率越低,屈强比越高;在所设定工艺下,临界区加热温度为780℃时,试验钢的综合力学性能最优.     

退火工艺对低成本980 MPa级冷轧双相钢组织和性能的影响

利用Vatron奥钢联热模拟试验机模拟一种980 MPa级冷轧双相钢连续退火过程,采用拉伸试验机、光学显微镜和扫描电镜研究连续退火工艺中均热温度、缓冷温度、过时效温度和带速对双相钢组织及力学性能的影响。结果表明,当均热温度为820、840和860℃时,随着均热温度的升高,组织中铁素体的比例不断下降,屈服强度不断提高。当均热温度提高到860℃时,组织中出现了一定量的贝氏体,抗拉强度达到了最低值1020 MPa;缓冷温度能够改变马氏体体积分数进而影响双相钢的性能;当过时效温度为250、270、290、310和330℃时,随着过时效温度的升高,马氏体发生软化的程度不断加剧,抗拉强度不断降低,断后伸长率不断升高,过时效温度升高到310℃以上时,马氏体分解加剧同时析出更多第二相,屈服强度先降低后升高。综合不同退火工艺下的冷轧双相钢的性能调控,最终确定均热温度840℃、缓冷温度680℃、过时效温度250℃和带速120 m/min为最佳的工艺参数,强塑积达到了最大值15.6 GPa·%。     

连续退火工艺对Si、Mn系冷轧双相钢组织性能的影响

文章结合工业生产实际采用光学显微镜与扫描电镜观察分析了连续退火过程中退火温度、缓冷温度及快冷段冷速对实验钢组织性能的影响,从而为优化冷轧双相钢实际退火工艺、为同行业工业化生产提供了借鉴。实验表明:退火温度对实验钢性能影响较大,随温度升高强度增加,在770～830℃退火温度范围内组织均为F+M,M含量随温度升高而增加;随着缓冷温度升高强度增加,组织主要为F+M,在660℃出现贝氏体,730℃缓冷时抗拉强度为711 MPa,从该级别钢种看太高;冷速15～30℃/s范围内随冷速增加强度呈上升趋势,马氏体含量呈上升趋势,产品性能均满足600 MPa级性能要求,实验钢对冷速工艺窗口较宽。     

1000 MPa级冷轧双相钢的热处理工艺与性能研究

从高强度冷轧双相钢的冶金成分设计出发,设计了三种不同成分的C-Mn-Si系冷轧双相钢,通过在(α γ)两相区不同温度的加热淬火,获得(Ferrite Martensite)双相组织;探讨了1000 MPa级冷轧双相钢的热处理工艺、性能与组织;研究了退火温度、冷却速度对双相钢性能的影响,分析了双相钢的强化机理,并且优化了退火工艺参数.结果表明,1000MPa级冷轧双相钢最优退火温度为780～800℃,680℃开始快冷,缓冷速度为10℃/s.     

AHSS汽车钢板用高强度钢的连续退火工艺研究

研究了DP双相钢在连续退火工艺中加热温度、退火时间、缓冷温度和过时效温度对其组织和力学性能的影响。结果表明,随着临界区加热温度的升高,DP钢组织中的马氏体逐步转化为由铁素体和贝氏体组成的混合组织,其抗拉强度先升高后降低。随着退火时间的增加,抗拉强度升高而屈服强度和伸长率降低。随着缓冷温度的降低或过时效温度的升高,DP钢抗拉强度和屈服强度呈下降趋势,而伸长率增加。     

980 MPa级冷轧双相钢的热处理工艺优化

利用Gleeble-3500热模拟试验机、光学显微镜和拉伸试验机分析研究了连续退火工艺中均热温度、缓冷温度和过时效温度对DP980钢力学性能及组织的影响。结果表明:随着均热温度的升高DP980钢组织中马氏体含量逐渐增加,规定塑性延伸强度和抗拉强度也随之提高,经分析选取780 ℃为最优均热温度。研究缓冷温度对DP980双相钢力学性能的影响,结合连退产线设备控制能力,选取670 ℃为最优缓冷温度。此外,过时效温度对DP980钢规定塑性延伸强度具有较大调整幅度,能够显著降低其屈强比,随着过时效温度的升高,DP980钢组织中马氏体含量基本不变并伴有少量的碳化物析出,能够降低马氏体的强度即改善双相钢塑性。最终确定均热温度780 ℃、缓冷温度670 ℃和过时效温度320 ℃的最优工艺参数。     

980 MPa级冷轧复相钢力学性能的多元调控

采用Gleeble-3500热模拟试验机、拉伸试验机和光学显微镜研究了连续退火工艺中均热温度、缓冷温度和过时效温度对980 MPa级复相钢力学性能及组织的影响规律。结果表明,经连续退火处理后980 MPa级复相钢组织为典型的铁素体、贝氏体、马氏体组织,随均热温度的提高,贝氏体和马氏体含量逐渐增加,从而提高抗拉强度和规定塑性延伸强度;缓冷温度则能改变新生铁素体晶粒大小及马氏体含量,从而调控复相钢力学性能;随着过时效温度的升高,部分颗粒状碳化物开始析出,能够降低马氏体的强度即改善复相钢塑性。从多元调控的角度逐步优化980 MPa级复相钢的综合力学性能,最终确定均热温度800 ℃、缓冷温度700 ℃和过时效温度340 ℃为最优工艺参数。     

退火工艺对DP590GA双相钢组织和性能的影响

研究退火工艺及快冷工艺对C-Mn系DP590GA双相钢性能和组织的影响。结果表明,该试验钢的规定塑性延伸强度随着均热温度的提高而上升,且温度越高规定塑性延伸强度的增加越显著;而伸长率随着均热温度的提高,先上升后下降;而快冷终止温度提高时,试验钢的强度上升,塑性下降。该试验钢在820 ℃进行退火时,可获得较优的力学性能,规定塑性延伸强度达到400 MPa,抗拉强度达到625 MPa,伸长率达到25.5%。     

退火工艺对冷轧热镀锌DP590组织及性能的影响

文章选用本钢生产的DP590冷硬板,根据实际生产机组的参数,采用热模拟实验对比分析镀前、后形成马氏体和退火工艺对热镀锌双相钢的组织及性能的影响,实验表明:镀后形成马氏体更有利于降低双相钢的屈强比;结合热模拟实验研究不同温度制度对双相钢组织性能的影响,确定最佳的温度组合。     

退火工艺对980 MPa级热镀锌双相钢组织及性能的影响

利用奥钢联热模拟试验机模拟980 MPa级双相钢连续退火镀锌过程,利用拉伸试验机、光学显微镜和扫描电镜研究连续镀锌工艺中均热温度和快冷出口温度对双相钢组织及力学性能的影响。结果表明,经热镀锌退火后,980 MPa级双相钢的微观组织为铁素体+马氏体,组织中有Nb,Ti碳氮化物析出。随着均热温度的升高,马氏体体积分数呈逐渐增加的趋势,屈服强度和屈强比不断升高。快冷出口温度从340 ℃升高到430 ℃,马氏体发生回火分解,降低了试验钢的屈服强度,同时改善了伸长率。快冷出口温度为400 ℃时,强塑积达到最大值13.9 GPa·%。当均热温度为840 ℃,快冷出口温度为460~480 ℃时,可以获得抗拉强度在980 MPa级以上的双相钢。     

退火温度对800MPa级热镀锌双相钢组织性能的影响

在实验室条件下试制800MPa级低硅热镀锌双相钢,研究了双相钢的双相处理工艺、组织和性能。实验结果表明：试样组织为铁素体＋马氏体的双相组织,M的体积含量是15％-20％。通过三种不同的热处理温度获得了不同的F＋M的比例,从而得到不同的力学性能。退火温度从780℃升到850℃,可以获得性能更好的双相钢。     

冷轧耐候双相钢连续冷却转变及过时效工艺研究

为了探索一种冷轧超高强耐候双相钢的连续冷却转变规律以及过时效温度对其组织性能的影响,利用Formaster－FⅡ全自动相变仪和连续退火模拟试验机进行了CCT曲线的测定和连续退火实验。结果表明：实验钢的过冷奥氏体在冷速为0.5 ℃/s时已有马氏体转变的发生,组织为先共析铁素体+贝氏体+马氏体;当冷速为80.0 ℃/s时,仅发生马氏体转变,组织为残留铁素体+马氏体。低温过时效时,马氏体呈板条状结构;过时效温度为350 ℃时,板条马氏体已经出现分解。随着过时效温度的升高,实验钢的屈服强度和抗拉强度呈下降趋势,伸长率则随过时效温度的升高而增加。     

淬火冷却工艺对F460钢调质厚板组织与性能的影响

对120 mm厚的F460钢调质厚板采用相同的淬火回火温度,不同的淬火冷却速度处理,之后对钢板进行组织与性能对比,寻找该钢种的最佳热处理工艺。采用2 ℃/s冷速进行冷却的钢板,回火后强度最高,但是冲击性能不佳;适当降低淬火冷却速度后,钢板回火后强度有一定下降,但是冲击性能得到明显提升;继续降低淬火冷却速度,钢板回火后强度进一步下降,但是冲击性能提升有限。经组织分析,2 ℃/s冷速进行冷却淬火时,钢板回火后的组织为铁素体+贝氏体组织,组织中主要是贝氏体;冷却速度降低以后,钢板回火后组织为铁素体+退化珠光体组织,铁素体含量的增加,有利于钢板韧性的提升,残留奥氏体回火后形成的珠光体组织比较细小,能有效保证钢板的强度。通过对钢板的连续冷却转变曲线进行分析,钢板在冷却过程中先开始进行铁素体相变,溶质元素向奥氏体迁移。在钢板冷速较快时,铁素体中的碳化物迁移较少,奥氏体低温时转变成马氏体或者贝氏体;在钢板冷速较慢时,碳化物迁移到奥氏体内,提高奥氏体稳定性并保留到室温,形成残留奥氏体。残留奥氏体在后续的高温回火过程中,转变成珠光体。块状转变形成的铁素体组织与回火过程中形成的细小珠光体有利于钢板的强韧性匹配。     

A study of microstructure,transformation mechanisms and correlation between microstructure and mechanical properties of a low alloyed TRIP steel

Differently heat treated samples of a low alloyed TRIP steel have been investigated using electron diffraction techniques in SEM and TEM. Aim was, first, to discriminate the microstructure constituents, austenite, ferrite, bainite, and martensite, second to gain information on the γ–α phase transformation mechanisms and third to correlate the mechanical properties and the microstructure of the samples. Bainite always occurs in conjunction with an orientation gradient in the surrounding ferrite matrix. It consists of fine lamellae of ferrite and austenite which show a sharp Kurdjumov–Sachs orientation relationship with each other. This was interpreted in terms of a displacive bainite formation mechanism. The microstructure is formed by growth of γ-grains during intercritical annealing and shrinking of these grains during the subsequent cooling without nucleation of new α-grains. The transformation first occurs reconstructively into ferrite and then, at lower temperature, displacively into bainite. The mechanical properties of differently heat treated samples are most strongly influenced by the amount and distribution of carbon in the retained austenite and by the degree of recovery in bainite and austenite.     

热处理对ZG06Cr13Ni4Mo不锈钢组织与性能的影响

研究了不同正火温度、回火保温时间和冷却方式对低碳马氏体不锈钢ZG06Cr13Ni4Mo组织与力学性能的影响。利用光学金相显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)对材料的微观组织和结构进行了研究。进行了室温拉伸和0℃冲击试验,并用SEM观察了断口形貌。结果表明,正火温度对ZG06Cr13Ni4Mo不锈钢组织与性能有显著影响。在γ+δ两相区正火时,会生成高温δ铁素体,并且δ在随后的热处理中不能被消除,即使很少的铁素体(1%),也会极大损害材料的韧性。采用较快冷却时,材料的韧性较高而强度较低;较长时间的回火保温,材料的强度较低,与较短时间保温下相比韧性没有明显差别。     

Control of Austenite Characteristics and Ferrite Formation Mechanism by Multiple-Cyclic Annealing in Quenching and Partitioning Steel

Quenching and partitioning (Q&P) treatment is a novel method to produce advanced high strength steel with excellent mechanical properties. In this study, combination of multiple-cyclic annealing and Q&P process was compared with traditional cold-rolled Q&P steel to investigate the microstructural characteristics and austenite retention. The results showed that retained austenite in traditional Q&P sample was principally located in the exterior of austenite transformation products, while those in multiple-cyclic annealing samples were mainly distributed inside the transformation products. With the increase in cyclic annealing number, both of austenite fraction and austenite carbon content increased, attributing to higher initial austenite carbon content and larger number of austenite/neighbored phase interface to act as carbon partitioning channel. In traditional Q&P sample, the deformed ferrite was recrystallized by sub-grain coalescence, while the austenite was newly nucleated and grew up during annealing process. As a comparison, the ferrite in multiple-cycle annealing samples was formed by means of three routes: tempered martensite that completely recovered with retention of interior martensite variant, epitaxial ferrite that formed on basis of tempered martensite, ferrite that newly nucleated and grew up during the final annealing process. Both of lath martensite and twin martensite were formed as initial martensite and then tempered during partitioning process to precipitate ε carbide with C enrichment, Mn enrichment and homogeneous Si distribution. Compared with the traditional cold-rolled Q&P steel, the Q&P specimens after multiple-cyclic annealing show smaller strength and much larger elongation, ascribing to the coarser microstructure and more efficient transformation induced plasticity (TRIP) effect deriving from retained austenite with high carbon content and larger volume fraction. The application of double annealing treatment can optimize the mechanical properties of Q&P steel to show a striking product of strength and elongation as about 29 GPa%, which efficiently exploit the potential of mechanical performance in low carbon steel.     

Effect of prior heat treatment on microstructure and mechanical properties of 0·23% carbon dual phase steel

Abstract

The present study is aimed at understanding the effect of prior heat treatment on the microstructure and mechanical properties of 0·23% carbon dual phase steel. The as received steel was subjected to annealing, normalising and hardening treatment before actual dual phase heat treatment. These steels along with the as received steel were intercritically annealed at 745°C followed by water quenching in order to produce a dual phase microstructure consisting of varying quantities and morphologies of ferrite and martensite. Mechanical properties were evaluated by tensile testing and hardness measurement. It was found that prior heat treatment affects the final dual phase microstructure in terms of size and relative amount of ferrite and martensite. It was also found that dual phase treatment resulted in improved mechanical property. Optimum combination of strength and ductility was obtained with the steel subjected to prior hardening (DPLA-3) treatment. The maximum in ultimate tensile strength (762 MPa) was obtained with the steel subjected to prior annealing treatment (DPLA-1). The X-ray diffraction study confirmed the presence of carbides in DPLA-1 steel, which contribute to the increased strength by precipitation hardening.     

非调质NM400复相耐磨钢的相变行为

为进一步优化非调质NM400复相耐磨钢不同组织配比,利用Gleeble-3800热模拟试验机探究了试验钢在连续冷却条件下的组织转变规律,并结合金相法和硬度法,绘制出试验钢的动态连续冷却转变(CCT)曲线。结果表明,当冷速低于1 ℃/s时,试验钢组织为铁素体+粒状贝氏体+珠光体,部分粗大的原奥氏体晶粒转变为粒状贝氏体和珠光体。在冷却速率为5~40 ℃/s时,试验钢不再发生珠光体转变,显微组织均为铁素体+贝氏体+马氏体。并随着冷速的增加,马氏体含量不断增加,硬度升高;此外,不同分段冷却方案下,较低的中冷温度以及较长的空冷时间均有利于铁素体和贝氏体的转变。同时,残留奥氏体含量则随铁素体含量的增大而增大;由于试验钢的Ms点较高,马氏体板条较宽,并且有自回火现象发生。     

变形温度对含Nb双相钢显微组织的影响

通过单道次压缩及连续冷却实验,研究了变形温度(810-720℃)对具有超细原始奥氏体晶粒的含Nb双相钢显微组织的影响.实验结果表明:实验钢最终组织为铁索体加马氏体的双相组织.压缩过程中,实验钢应力-应变曲线上出现峰值,且峰值应力随变形温度的降低先增大后减小;随着变形温度的降低,铁索体的含量先增大再减小,但增减幅度不大,在最低变形温度(720℃)时,铁素体品粒尺寸降低到2.8 μm,弥散分布于铁素体晶界上的马氏体含量达到22.7%;随着变形温度的增加,铁索体晶粒硬度减小,最低可降至230 GPa;EBSD取向分析显示,随着变形温度的降低,组织中小角度晶界增多.