Abstract S500MC high strength low alloy automotive steel is exposed to bulk severe plastic deformation (SPD) via constrained groove pressing (CGP) and surface severe plastic deformation (S2PD) via severe shot peening (SSP) and ultrasonic nanocrystal surface modification (UNSM). SSP and UNSM could create a nanocrystallization layer till 50–100 µm away from outmost surface. EBSD investigations showed average nano-grain size obtained via SSP and UNSM was found to be below 100 nm regime. The strength was improved via 1st to 4th pass of CGP, but elongation percentage decreased abruptly. UNSM achieves both strength-ductility improvement with gradient structure. SSP improves the total elongation however a slight decrease on strength is observed. SSP and UNSM showed better wear and friction resistance particularly at lower loads compared to CGP and untreated specimens. Nevertheless, wear and friction behavior at higher loads showed better responses for Bulk-SPD applications regardless of pass numbers. The frictional load increase played a detrimental role in removing a nanocrystallization surface layer and diminishing the positive influence of SSP and UNSM.

中文翻译：

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约束槽压、剧烈喷丸和超声纳米晶表面改性对S500MC高强低合金汽车钢组织和力学行为的影响

摘要 S500MC 高强度低合金汽车钢通过约束凹槽压制 (CGP) 和表面严重塑性变形 (S2PD) 通过严重喷丸 (SSP) 和超声纳米晶表面改性 (UNSM) 承受大量严重塑性变形 (SPD)。SSP 和 UNSM 可以在距离最外表面 50-100 µm 的地方创建纳米结晶层。EBSD 研究表明，通过 SSP 和 UNSM 获得的平均纳米晶粒尺寸低于 100 nm。CGP的第1～4次强度提高，但伸长率急剧下降。UNSM通过梯度结构实现了强度-延展性的提高。SSP 提高了总伸长率，但观察到强度略有下降。与 CGP 和未经处理的试样相比，SSP 和 UNSM 显示出更好的耐磨性和摩擦性，尤其是在较低载荷下。然而，无论通过次数如何，较高负载下的磨损和摩擦行为对 Bulk-SPD 应用表现出更好的响应。摩擦载荷的增加在去除纳米结晶表面层和减少 SSP 和 UNSM 的积极影响方面起到了不利作用。