Fe-Mn-Al-C系列低密度高强钢的研究现状

Research Situation of Fe-Mn-Al-C System Low-density High-strength Steel

随着节能环保和经济性的驱动,汽车轻量化已成为汽车行业的迫切需求,Fe-Mn-Al-C系列低密度高强钢因具有低密度与优异的力学性能而受到了学者们的关注。Fe-Mn-Al-C系列低密度钢的出现最早可以追溯到1933年,直到1958年,Fe-Mn-Al-C系列低密度钢才被用于取代Fe-Cr-Ni系列不锈钢(添加过多昂贵的Ni和Cr元素)。目前,Fe-Mn-Al-C系列低密度钢在汽车行业是一种具有高轻量化潜力的钢种,其中添加的Al元素会导致合金密度和杨氏模量的降低。每添加1%(质量分数)的Al,钢密度降低1.3%,杨氏模量降低2%。同时,大量Al、Mn和C元素的添加导致Fe-Mn-Al-C系列钢的冶炼和连铸、成形性和焊接性、微观结构演变和变形机制等与传统钢种大不相同。Fe-Mn-Al-C系列低密度高强钢按合金的成分以及室温下主要的组成相,可分为四类:单一铁素体钢、铁素体基双相钢、奥氏体基双相钢和奥氏体钢。单一铁素体钢拥有200~600 MPa级别的抗拉强度,这与常规的高强度低合金钢(HSLA钢)类似,属于第一代先进高强度钢(1G-AHSS)范畴。铁素体基Fe-Mn-Al-C系双相钢是另一种有潜力的轻量化钢材,其具有较低的合金含量,可以利用铁素体的塑性变形以及残余奥氏体所产生的TRIP或TWIP效应来提高钢的强度与塑性。铁素体基Fe-Mn-Al-C系双相钢与第一代先进的高强度钢相比,具有更优异的强度和延展性,其性能的上限属于第三代先进高强度钢(3G-AHSS)范畴。奥氏体基双相钢与铁素体基双相钢类似,但其合金含量高于铁素体基双相钢,性能的下限属于第三代先进高强度钢(3G-AHSS)范畴。奥氏体Fe-Mn-Al-C系列钢在性能和加工方面是又一个有前途的钢材。奥氏体钢主要组成相为奥氏体、少量的铁素体和κ型碳化物。奥氏体钢的力学性能由奥氏体的变形以及碳化物-奥氏体的相互作用共同决定。奥氏体轻钢的拉伸性能与高锰TWIP钢相似,强度为600~1 500 MPa,塑性可达到30%~80%(甚至可达~100%),属于第二代先进高强度钢(2G-AHSS)范畴。随着钢中Al的添加,Fe-Mn-Al-C系列低密度高强钢层错能(SFE)增大,并析出短程有序(SRO)相和κ型碳化物。高SFE的低密度Fe-Mn-Al-C钢具有多种变形机制,如新型的微带诱导塑性(MBIP)、动态滑移带细化(DSBR)和剪切带诱导塑性(SIP)变形机制以及普遍的相变诱导塑性(TRIP)和孪生诱发塑性(TWIP)变形机制。这些变形机制与Fe-Mn-Al-C钢内的B2及DO3型的有序相、均匀排列的纳米级κ型碳化物、位错滑移、孪晶和相变等有关。其中晶粒内κ′-碳化物析出是含有大量Al和C的奥氏体Fe-Mn-Al-C钢独特的强化机制。然而,由于目前对Fe-Mn-Al-C钢应用性能相关知识的缺乏,其在汽车中的应用仍然不普遍。最重要的原因是这一系列低密度高强钢具有高的Al含量导致其杨氏模量降低,以及高的Mn含量导致其冶炼、连铸和加工难等问题。因此,未来的发展必须集中在提高低密度高强钢的杨氏模量,且将其低合金化和易加工的策略方法上。相信改进后的Fe-Mn-Al-C体系低密度高强钢必将大大推动其在汽车中的应用。本文概述了Fe-Mn-Al-C体系低密度高强钢的研究现状及进展,介绍了Fe-Mn-Al-C体系低密度高强钢的成分设计及其中合金元素的作用,分析了Fe-Mn-Al-C体系低密度高强钢的微观组织特征,揭示了Fe-Mn-Al-C体系低密度高强钢的强韧性形成机理、层错能、物理及力学性能,并讨论了Fe-Mn-Al-C体系低密度高强钢的应用性能。最后,提出了未来Fe-Mn-Al-C体系低密度高强钢的研究方向。

The lightweight of automobile has become more and more widely concerned with the needs of energy conservation,environmental protection and economy.The low density and high strength steel of the Fe-Mn-Al-C system combines the low density and excellent mechanical properties,which complies with this topic.The earliest information on low-density steels dates back to 1933 which was related to the first development of Fe-Mn-Al-C system.Until 1958,the Fe-Mn-Al-C system of low-density steel was developed to replace the Fe-Cr-Ni system of stainless steels(added too many expensive Ni and Cr elements).At present,the Fe-Mn-Al-C system low-density steel is a kind of steel with high lightweight potential in the automotive industry,in which the addition of Al element leads to a decrease in density and Young’s modulus.Adding 1wt%Al,the steel density is reduced by 1.3%,and the Young’s modulus is reduced by 2%.Simultaneously,the addition of a large amount of Al,Mn and C elements resulted in the smelting,continuous casting,formability,weldability,microstructure evolution and deformation mechanism of Fe-Mn-Al-C system steels,which are quite different from those of traditional steels.The lightweight Fe-Mn-Al-C system steel can be classified into four categories:single ferritic steels,ferrite based duplex steels,austenite based duplex steels and austenitic steels,according to the composition of the alloy and the main composition phase of room temperature.The single ferritic steel has similar tensile properties of 200-600 MPa as the conventional high-strength low-alloy steel(HSLA)and belongs to the first generation of advanced high-strength steel(1G-AHSS).Ferrite-based Fe-Mn-Al-C system duplex steels are another promising lightweighting scheme with a lower alloy content that can be produced using ferrite plastic deformation and retained austenite TRIP and TWIP effect to increase steel strength and plasticity.The ferrite based Fe-Mn-Al-C double phase steel has superior strength and ductility compared with the first advanced high strength steel,and the middle and upper level of their performance belongs to the category of the third generation advanced high-strength steel(3G-AHSS).The austenitic-based duplex steel is similar to ferritic-based duplex steel,but it has higher alloy content than ferritic-based dual-phase steel,and its lower limit of performance belongs to the 3G-AHSS category.The austenitic steels are the most promising in terms of properties and processing.The main constituent phases of austenitic steel are austenite,a small amount of ferrite andκ-carbide.The mechanical properties of austenitic steels are determined by the deformation of austenite and the interaction of carbide-austenite.The tensile properties of austenitic light steel are similar to those of high manganese TWIP steel,the strength of 600-1 500 MPa and the plasticity can reach of 30%-80%(even up to^100%),it belongs to the category of the second generation advanced high strength steel(2G-AHSS).The stacking fault energy(SFE)of Fe-Mn-Al-C system low-density high-strength steel increases and short-range ordered(SRO)phase andκ-type carbide are precipitated with the addition of Al content in steel.High-SFE low-density Fe-Mn-Al-C system steel with various deformation mechanisms such as novel microband induced plasticity(MBIP),dynamic slip band refinement(DSBR),shear band induced plasticity(SIP)deformation mechanism,transformation induced plasticity(TRIP)and twinning induced plasticity(TWIP)deformation mechanisms.These deformation mechanisms are consistent with the B2 and DO3 type of ordered phases,uniformly arrange of the intragranular nano-sizedκ-carbides,dislocation slips,twins and phase transitions.The precipitation of intragranularκ-carbide is a unique strengthening mechanism of austenitic Fe-Mn-Al-C steel containing a large amount of Al and C elements.The applications of the Fe-Mn-Al-C system steels in the automobiles are still not prevalent due to the lack of knowledge related to application properties so far.The most important reason is that high Al content leads to high Young’s modulus reduction and high Mn content leads to problems such as smelting,continuous casting,and machining.The future developments will therefore have to concentrate on the alloying and processing strategies and also on the methods to increase the Young’s modulus.An improved processing strategy and a high value for the Young’s modulus will go a long way towards upscaling these steels to real automotive applications.The fundamental research situation and devoment of Fe-Mn-Al-C low-density high-strength steel were summarized.The composition design and the role of alloying elementsof Fe-Mn-Al-C low-density high-strength steel were introduced.The microstructures of Fe-Mn-Al-C low density high strength steel were analyzed.The mechanism of formation of toughness and toughness,stacking fault energy,physical and mechanical properties of Fe-Mn-Al-C series low density and high strength steels were revealed,and the application properties of Fe-Mn-Al-C alloys were discussed.Finally,some future directions of research on Fe-Mn-Al-C system low density steels have been proposed.