The grain size gradient structure is a promising solution to resolve the problem of strength-ductility trade-off. In this work, a gradient micron-structure (GMS) sample was fabricated by applying a laser heat treatment on the surface of a cold-rolled TWIP steel plate. The recrystallized microstructure showed a linear gradient in grain size from ~ 25.5 µm to ~ 13.3 µm throughout the cross section. The yield and ultimate strengths of the GMS sample were 306.3 MPa and 674.1 MPa, respectively, which are lower than those of a sample annealed at 850 °C for 60 min but higher than those of the one annealed at 950 °C for 60 min. It suggests the strengths of the GMS sample obey the rule of mixtures as the coarse grains in the upper surface can be considered as the soft part and the fine grains as the hard ones. However, the GMS sample exhibited a similar tensile elongation (60.7%) as the annealed (850 °C, 1 h) sample does (61.0%). When the strong strain concentration is increased, a large number of small cracks in the lower surface may connect and propagate to the upper side rapidly, resulting in a premature failure.

晶粒尺寸梯度结构是解决强度-延性折衷问题的有前途的解决方案。在这项工作中，通过在冷轧TWIP钢板的表面上进行激光热处理来制造梯度微米结构（GMS）样品。重结晶的显微组织在整个横截面中的晶粒尺寸呈线性梯度，从〜25.5 µm到〜13.3 µm。GMS样品的屈服强度和极限强度分别为306.3 MPa和674.1 MPa，低于在850°C退火60分钟的样品的屈服强度和最终强度，但比在950°C退火60分钟的样品的屈服强度和极限强度高。这表明GMS样品的强度服从混合物的规则，因为上表面的粗晶粒可被视为软质部分，而细晶粒可被视为硬质部分。然而，GMS样品表现出与退火（850°C，1 h）样品（61.0％）相似的拉伸伸长率（60.7％）。当强应变集中度增加时，下表面中的大量小裂纹可能会连接并迅速传播到上侧，从而导致过早失效。