Abstract

The phase composition of thin-sheet (0.3 mm thick) austenitic–martensitic VNS9-Sh TRIP steel is studied by X-ray diffraction, and the residual stresses in the steel are determined. This cold-rolled steel is a gradient material with a high content of strain-induced martensite in the near-surface layers. The austenite content in the surface layer is shown to increase from 47% (as-delivered state) to 85% after removing a 10‑μm-thick surface layer. The positive volume effect of the martensitic transformation during cold rolling leads to the relaxation of high tensile stresses up to 850 MPa in the martensite phase and to the formation of compressive stresses up to 950 MPa in austenite in the surface layer. The removal of a 10-μm-thick surface layer brings about a substantial change in the stressed state; in this case, residual tensile stresses prevail in both the phases: 400–800 MPa in martensite and 70–280 MPa in austenite. A technique is proposed for estimating the residual stresses via measuring the lattice parameters for various reflections; it makes it possible to separate the contributions of residual stresses and the solid solution composition with allowance for the elastic anisotropy of the crystal lattice.

中文翻译：

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VNS9-Sh TRIP钢表面层的相组成和残余应力

摘要

通过X射线衍射研究了薄板（0.3毫米厚）奥氏体-马氏体VNS9-Sh TRIP钢的相组成，并确定了钢中的残余应力。这种冷轧钢是一种梯度材料，在近表层中含有大量的应变诱发马氏体。去除10μm厚的表层后，表层中的奥氏体含量从47％（交货状态）增加到85％。冷轧过程中马氏体相变的正体积效应导致在马氏体相中松弛高达850 MPa的高拉伸应力，并在表面层中形成高达950 MPa的压缩应力。去除10μm厚的表面层会导致应力状态发生实质性变化。在这种情况下，残余拉伸应力在两个阶段均占主导：马氏体为400-800 MPa，奥氏体为70-280 MPa。提出了一种通过测量各种反射的晶格参数来估计残余应力的技术。这样可以在考虑晶格的弹性各向异性的情况下分离残余应力和固溶体成分的贡献。