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Mechanical behavior of ultrafine-grained eutectoid steel containing Nano-cementite particles

机译：含纳米钙铁矿的超细共析钢的力学行为

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摘要

A eutectoid steel with an ultrafine-grained ferrite (a) + submicron/Nano-cementite particle (θ) structure was formed by combining warm deformation of martensite to a strain of 0.36 at 0.1 s~(-1) at 500 ℃ with subsequent annealing at 500 ℃ for 6 h. The characteristics of the microstructure were investigated by means of a scanning electronic microscope and transmission electron microscope, and the corresponding mechanical behavior was analyzed in comparison with that of the eutectoid steel with a typical ultrafine-grained α + θ structure. The results show that both ferrite matrix and cementite particles of the ultrafine-grained a + submicron/Nano-θ steel are finer than that of the ultrafine-grained α + θ steel, i.e., the average size of approximately 0.54 μm vs. 1.0 μm and 0.20 μm vs. 0.56 μm, accompanying with a continuous yielding and a discontinuous yielding, respectively. The yield strength of the ultrafine-grained a + submicron/Nano-θ steel is 264 MPa higher that of the ultrafine-grained α + θ steel, i.e., 884 MPa vs. 620 MPa, resulting from the enhancement caused by refined ferrite grains and cementite particles. The intragranular cementite particles within the ultrafine-grained a + submicron/Nano-θ steel are in Nano-scale, i.e., an average size of approximately 60 nm, resulting in plenty of geometrically necessary dislocations (GNDs) to bring its work-hardening rate higher than that of the ultrafine-grained α + θ steel during uniform deformation. As a result, the stress increments caused by work-hardening are 89 MPa and 155 MPa for the ultrafine-grained α + θ steel and the ultrafine-grained α + submicron/Nano-θ steel, respectively, and their interval length of uniform strain range are nearly equal, i.e., a true strain of approximately 0.08. The work-hardening rate of the ultrafine-grained α + θ steel decline continuously with the increase of tensile strain during uniform deformation. However, the ultrafine-grained α + submicron/Nano-θ steel shows that the work-hardening rate decrease rapidly at the initial stage of work-hardening and then raise within a small strain range, then following by a slowly continuous decline to necking, and, namely, there has a peak of work-hardening rate. Furthermore, the work-hardening rate curve were divided into three stages, and the work-hardening behavior of Stage Ⅰ, Ⅱ and Ⅲ were discussed in view of the evolution of dislocation substructures and the analytical model based on the Kocks-Mecking model.
机译：将马氏体在500℃，0.1 s〜（-1）下的热变形变形为0.36并随后进行退火，从而形成具有超细晶粒铁素体（a）+亚微米/纳米钙钛矿（θ）结构的共析钢。在500℃下6 h。通过扫描电子显微镜和透射电子显微镜研究了显微组织的特征，并与具有典型的超细α+θ结构的共析钢的力学性能进行了比较。结果表明，超细a +亚微米/纳米θ钢的铁素体基体和渗碳体颗粒均比超细α+θ钢的铁素体基体和渗碳体颗粒均细，即平均尺寸分​​别约为0.54μm和1.0μm。和0.20μm对0.56μm，分别具有连续屈服和不连续屈服。超细晶粒a +亚微米/纳米θ钢的屈服强度比超细晶粒α+θ钢高264 MPa，即884 MPa对620 MPa，这是由于精炼的铁素体晶粒和渗碳体颗粒。超细a +亚微米/纳米θ钢中的晶粒内渗碳体颗粒处于纳米级，即平均尺寸约为60 nm，导致大量几何上必需的位错（GND），以提高其加工硬化率均匀变形时，比超细α+θ钢高。结果，超细晶α+θ钢和超细晶α+亚微米/纳米θ钢的加工硬化导致的应力增量分别为89 MPa和155 MPa，并且它们的均匀应变间隔长度范围几乎相等，即大约为0.08的真实应变。随着均匀变形过程中拉伸应变的增加，超细晶α+θ钢的加工硬化率连续下降。但是，超细晶粒α+亚微米/纳米θ钢表明，加工硬化率在加工硬化初期迅速降低，然后在较小的应变范围内升高，然后缓慢连续下降至颈缩，即，工作硬化率达到峰值。此外，将加工硬化率曲线分为三个阶段，并根据位错亚结构的演变和基于Kocks-Mecking模型的解析模型，讨论了阶段Ⅰ，阶段Ⅱ和阶段Ⅲ的加工硬化行为。

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