碳对马氏体钢显微组织和力学性能的影响

通过固定其它元素的含量,调整碳含量的方式,研究了碳含量对马氏体钢显微组织和力学性能的影响。结果表明,随碳含量增加,马氏体钢的硬度和抗拉强度提高,但冲击韧度下降。     

碳含量对5Cr2MoV系列钢的连续冷却转变行为的影响

通过测定不同碳含量的钢种在不同冷速下的相变点曲线、金相组织和显微硬度，得到了不同碳含量的钢种的过冷奥氏体连续冷却转变曲线(CCT曲线)及其相变点和组织形貌演变；比较分析了不同碳含量下5Cr 2Mo V系列钢CCT曲线的关系。结果表明：随着碳含量的增加，3种钢Ac1点变化不大，Ac3点略有降低，Ms点降低幅度较大；当冷却速度为0.04 ℃/s和0.06 ℃/s时，0.35%C、0.47%C和0.71%C钢的组织由“贝氏体+少量马氏体”构成；0.35%C和0.47%C在大于0.14 ℃/s冷速以上时，贝氏体完全转变为马氏体；0.71%C钢在大于1 ℃/s冷速时，贝氏体完全转变成马氏体；随着碳含量增加，5Cr 2Mo V系列钢的贝氏体转变相区发生左移现象，这与碳在组织转变过程中的扩散有关。     

不同碳含量对中碳低合金钢分级等温淬火组织与性能的影响

以Si、Mn合金钢为对象,研究了不同含碳量对中碳低合金钢分级等温淬火组织和性能的影响,分析贝氏体、马氏体含量与实验钢性能的关系。结果表明,增加含碳量,实验钢中下贝氏体含量下降,马氏体含量增加,实验钢硬度增加,冲击韧度降低;在中碳低合金钢中降低下贝氏体含量或增加马氏体含量可以提高材料硬度,但会引起其冲击韧度的下降。当碳含量在0.48%~0.50%时(下贝氏体含量为30%~40%、马氏体含量为40%~50%),贝/马复相组织强韧性匹配较好,材料具有优异的综合力学性能。     

热镀锌TRIP钢的微观组织结构及演变规律

利用光学显微镜、透射电镜、X射线衍射和相变仪对热镀锌TRIP钢的微观组织进行了定性观察和定量计算,在此基础上对热镀锌TRIP钢残留奥氏体的演变规律和马氏体的精细结构进行了研究。定性观察表明热镀锌TRIP钢的微观组织由铁素体,贝氏体,残留奥氏体和马氏体构成,在贝氏体相变结束后的冷却过程中还存在马氏体相变;通过对微观组织计算发现,受贝氏体等温相变时间影响,热镀锌TRIP钢中的马氏体碳含量在0.80%~1.0%之间,贝氏体等温时间越长,最终组织中马氏体碳含量越高,Ms点越低;在贝氏体相变结束后,部分碳含量不高的奥氏体在随后的冷却过程中发生马氏体相变,以马-奥岛的形式存在,马氏体的精细结构以孪晶马氏体为主,存在少量位错马氏体。     

冷轧双相钢疲劳断裂行为及组织分析

针对不同强度的双相钢开展了疲劳特性分析，选取5种强度的双相钢开展了力学性能和微观组织对比分析；采用MTS 810液压多功能试验机进行了拉-压疲劳测试，获得了应力幅-疲劳寿命(S-N)曲线；对疲劳断口形貌和表面形貌进行了观察；分析了马氏体含量对双相钢疲劳断裂行为的影响；对不同碳含量的双相钢疲劳裂纹扩展速率进行了对比分析，并对裂纹形貌进行了观察，获取影响疲劳寿命的主要因素。结果表明，铁素体先于马氏体发生微观塑性变形而形成可能的裂纹源；随着双相钢强度级别的提高，马氏体含量不断提高，材料的疲劳极限也逐步提高，疲劳极限与马氏体含量之间呈现线性的变化关系；马氏体含量由4%提高到40%左右时，双相钢的疲劳极限提高了约57%;与高碳HC420/780DP相比，低碳HC420/780DP的裂纹扩展速率明显降低，主要由于马氏体岛分布更加弥散细小；低碳HC420/780DP的疲劳裂纹扩展速率比高碳HC420/780DP低。     

耐磨材料与使用工况关系研究

研究比较了高锰钢，马氏体球铁和中碳马氏体钢在二体静载和三体动载条件下的磨损特性，从而找出耐磨材料与使用工况关系。结果表明，在静载条件下，马氏体球铁耐磨性最好；在非强烈冲击条件下，中碳马氏体钢耐磨性最好；在强烈冲击条件下，高锰钢耐磨性最好。     

C同时提高马氏体钢强度和塑性的原理和机制

自从淬火-配分-回火(Q-P-T)工艺被提出以来,本课题组在低C至中C含量的范围内实现了通过增加C含量的同时增强Q-P-T马氏体钢的强度和塑性。最近本课题组致力于将C含量扩大到高C范围。在多次尝试失败的基础上,提出了反相变诱发塑性(anti-TRIP)效应的设计理念,并在该理念指导下进行高碳低合金马氏体钢的成分和工艺设计,使高碳Q-P-T马氏体的强度和塑性均高于中碳Q-P-T马氏体钢,实现了通过C同时增强钢的强度和塑性。本文主要论述anti-TRIP效应提出的背景、高碳Q-P-T马氏体钢成分和工艺的设计及其微观组织、高碳Q-P-T马氏体钢的高强-塑性机制,最后分析Q-P-T工艺使C同时提高马氏体钢的强度和塑性的原理。     

碳含量对低合金耐磨钢组织及耐磨性的影响

研究了碳含量分别为0.31%、0.38%和0.50%的低合金耐磨铸钢热处理后的组织、强韧性及不同磨损条件下的磨损性能。结果表明,试验钢经950℃淬火及250℃回火,显微组织均以板条马氏体为主,随含碳量的增加,组织有所粗化,并且有片状马氏体出现。试验钢的硬度随碳含量的增加而增加,但韧性下降。磨损试验结果表明,冲击磨料磨损条件下,主要表现为凿削磨损,碳含量为0.38%的试验钢具有较好的耐磨性;静磨料磨损条件下,主要表现为切削磨损,耐磨性主要受硬度的影响,碳含量为0.50%试验钢具有较好的耐磨性。     

硅对准贝氏体渗碳钢组织与性能的影响

研究了硅对准贝氏体渗碳钢渗碳组织与性能的影响。试验结果表明，硅降低渗层碳浓度、使渗碳层碳含量的分布平缓，阻碍渗层碳化物析出，渗碳后空冷渗层最外层组织为高碳马氏体和残留奥氏体。硅能显著提高渗碳钢的回火抗力。     

碳含量对热处理低合金耐磨铸钢组织性能的影响

试验研究了碳含量对低合金耐磨铸钢组织和性能的影响。结果表明:随着碳含量的增加,试验钢的硬度总体呈上升趋势,冲击韧度先升高后下降。显微组织由粒状贝氏体+M-A岛+铁素体逐渐向上贝氏体、马氏体、下贝氏体转变,同时出现少量的残余奥氏体。当碳含量为0.40%左右时,碳在钢中的效能得到最大发挥,钢的强韧匹配性最佳。     

Effect of carbon on the plastic strain ratio of low carbon dual-phase steels

The effect of carbon on the plastic strain ratio of low-carbon dual-phase steels was investigated in a series of low C-1.6 Mn-0.3Cr-0.2Mo-0.001B steels with carbon contents ranging from 0.021 to 0.048%. The r_m value of dual-phase steel could be increased by controlling both the carbon content and the martensite morphology. The highest r_m value of 1.23 was obtained in 0.021% C steel annealed at 790 °C according to the typical galvannealing heat cycle. The martensite volume fraction was 5.4%, which was sufficient to eliminate the yieldpoint elongation in as-annealed steel, and this had little deteriorating effect on the r_m value. The fine martensite particles between 0.5 μm and 2.0 μm in size were desirable for a high r_m value in dual-phase steel.     

超高强度钢疲劳塑性区内的应变诱发马氏体相变

对一种低碳马氏体型超高强度钢疲劳断口薄膜试样的电子衍射分析表明,疲劳塑性区内的残余奥氏体在交变应力的作用下转变为马氏体.本文就这种应变诱发相变对疲劳性能的作用机理进行了分析讨论.     

Phase field simulation of the carbon redistribution during the quenching and partitioning process in a low-carbon steel

Phase-field modelling is used to simulate the quenching and partitioning process in a low-carbon transformation-induced plasticity (TRIP) steel, in order to understand the carbon redistribution in the microstructure during the heat treatment. The simulations show that, depending on local characteristics of the microstructure, including phase distributions and carbon-concentration gradients, different features in the carbon evolution during the partitioning step occur that are physically and practically relevant, but are not accessible for experimental observation. The overall carbon partitioning from martensite to austenite occurs not only by direct diffusion from martensite to austenite, but also through the bulk ferrite grains. The simulations also show interface migration driven by the free-energy difference between austenite and martensite, which affects the fractions of phases and the dimensions of the austenite grains. The carbon content of individual austenite, martensite and ferrite grains as well as average values are analysed, showing that the carbon concentration within the austenite grains is strongly inhomogeneous at short partitioning times, which contributes to a variable mechanical stability of individual austenite grains, affecting the occurrence of TRIP.     

马氏体含量对St12Q1和St37-2G双相钢力学性能的影响

将St12Q1和St37—2G钢在两相区不同温度下加热和淬火，可以得到(F M)的双相组织，与此同时研究实验用钢在不同热处理工艺下组织和力学性能的关系。结果表明：其应力一应变曲线表现出屈服点低、连续屈服、没有明显的屈服点等特性；提高两相区的淬火温度，可使马氏体量增多；在相同淬火加热温度下，淬火组织的马氏体量随钢的含碳量增加而增多；双相钢的强度只与它所含的马氏体量有关，而与马氏体中的含碳量无关。     

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.     

一种低碳含钒超高强高锰TRIP钢组织性能的研究

为获得具有优异强塑性匹配的高锰TRIP钢,对固溶处理的低碳含钒高锰钢采用不同压下率的冷轧及600 ℃低温退火处理,利用微观分析和性能测试手段对其微观组织演变和力学性能进行了研究。结果表明,冷轧压下率对低温退火后的低碳含钒高锰钢微观组织和力学性能有重要影响。随着冷轧压下率的增加,该钢低温退火后的晶粒尺寸减小,奥氏体含量增加,马氏体含量减少,其抗拉强度和屈服强度也随之提高。当冷轧压下率为50% 时,该钢低温退火后可获得高强度以及低屈强比,其强塑积可达39.6 GPa·%,主要强化方式为细晶强化、析出强化以及γ ε-M和ε-M α'-M相变强化。     

Strengthening of Ultrafine Lamellar-Structured Martensite Steel via Tempering-Induced Nanoprecipitation

An ultrafine lamellar-structured martensite steel fabricated by heavy warm rolling (HWR) has shown an excellent combination of strength and ductility. By appending tempering at 400 °C to HWR, we show that the comprehensive mechanical property of a lamellar-structured low-carbon martensite steel can be further improved to reach a yield strength of ~ 1.8 GPa, an ultimate tensile strength of ~ 2.0 GPa and a total elongation of ~ 9.3%. This is achieved by tempering the HWR steel from 300 to 750 °C, and the optimum tempering temperature is thus obtained. We find that the tempered ultrafine lamellar martensite contains high-density nanoprecipitates dispersed within the aligned martensite laths with reduced crystallographic variations. The ultrahigh strength of the steel is rationalized as mainly the result of grain boundary strengthening and precipitation strengthening, which contribute to yield stress by 610 MPa and 440 MPa, respectively. The good ductility is believed to be closely related to the capacity of the tempered grains to accommodate dense dislocations upon plastic deformation. The present thermomechanical processing provides a feasible routine for producing steels with ultrahigh-strength and good-ductility.     

800 MPa级热基镀锌复相钢的开发

设计了一种Nb、Ti微合金化低碳复相钢,采用SEM、TEM及力学性能测试等方法研究了退火镀锌过程中热轧复相钢显微组织、析出相和力学性能的演变规律,进行了800 MPa级热基镀锌复相钢工业试制。结果表明,热轧复相钢的显微组织主要由铁素体、马氏体和马/奥岛构成。退火镀锌过程中,马氏体和马/奥岛分解形成高温回火马氏体,铁素体内可动位错密度降低,同时析出纳米级Nb、Ti和Mo的复合碳化物,导致抗拉强度降低、屈服强度和扩孔率显著提高。热基镀锌复相钢的显微组织主要由铁素体和高温回火马氏体构成,屈服强度、抗拉强度、断后伸长率和烘烤硬化值分别为769 MPa、852 MPa、14.5%和43 MPa,扩孔率达到53%,具有良好的力学性能和局部成形性能。