Tensile Behavior of Fine-grained Steels
Tensile Behavior of Fine-grained Steels
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DOI：
10.2355/isijinternational.48.1107
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发表时间：
2008-08
影响因子：
1.8
通讯作者：
Y. Tomota;Akinori Narui;N. Tsuchida
中科院分区：
文献类型：
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作者：
Y. Tomota;Akinori Narui;N. Tsuchida
随着铁素体晶粒尺寸的减小，Luders延伸率增大，加工硬化降低，最终导致均匀延伸率的丧失。这个缺点可以通过引入第二相如马氏体或亚稳奥氏体来克服。用细观力学方法中的割线法可以很好地估计第二相对强度和均匀延伸率平衡的改善。两种成分之间的应力分配带来了高的加工硬化，这是由原位中子衍射验证。应变速率和温度的影响用Kocks-Mecking模型描述。结果表明，晶粒细化和上述应力分配对流变应力中的非热应力分量起主要作用。因此，在10 3 /s的高速变形下获得的拉伸性能在细晶粒多相钢中是优异的。以20-30 nm的超细组织为例，研究了抗拉强度大于4 GPa的强拉珠光体钢丝的拉伸行为。尽管具有这样的超高强度，但线材通过位错运动而塑性变形，导致韧窝断裂。强化包括由于微观组织细化引起的各向同性硬化和由中子衍射确定的残余晶间应力引起的各向异性硬化。
With decreasing of grain size in ferritic steels, Luders elongation becomes larger while work-hardening is lowered, finally resulting in loss of uniform elongation. This drawback can be overcome by introducing the second phase like martensite or metastable austenite. The improvement of strength and uniform elongation balance by the second phase can well be estimated by applying the secant method of micromechanics approach. The stress partitioning between two constituents brings high work-hardening, which is verified by in situ neutron diffraction. The influences of strain rate and temperature are described by using the Kocks-Mecking model. It is found that the grain refinement and the above stress partitioning contribute mainly to the athermal stress component of flow stress. Hence the tensile properties obtained at a high speed deformation like 10 3 /s is excellent in fine-grained multi-phase steels. As an example of ultrafine-microstructure with 20-30 nm in size, the tensile behavior of severely drawn pearlite steel wires with tensile strength larger than 4 GPa is investigated. In spite of such ultra-high strength, the wire deforms plastically by dislocation motion resulting in dimple fracture. The strengthening consists of isotropic hardening due to microstructure refinement and anisotropic hardening caused by residual intergranular stresses which are determined by neutron diffraction.