Abstract In this study, we consider the mechanism and kinetics of structure formation in the hardened zone during thermal deformation treatment of reinforced steel. Depending on the cooling rate and temperature conditions of austenite decomposition, pearlite and martensitic transformations are shown to occur with the formation of a gradient-layered structure, leading to structure modification of the surface layer of steel at a constant chemical composition, structure, and properties of the central layers of the workpiece. A high cooling rate due to a large temperature gradient near the surface is the reason for the formation of a finely dispersed layered structure. A diffusion-free martensitic transformation develops in the surface zone, leading to the formation of acicular martensite. In the underlying layers, the decomposition of austenite proceeds by diffusion and is accompanied by the formation of a lamellar ferrite–carbide mixture of varying dispersion degrees. An increase in the cooling rate leads to a strong refinement of the structure (grain point according to GOST 5639–82 is 11 in the surface layer and 8 in the core) characterized by an increase in the dispersion degree of the ferrite–carbide mixture, which causes an increase in strength and reduction of the plastic characteristics of steel. It is noted that the formation of a gradient-layered structure in the surface layer of strain-hardened reinforced steel allows excluding a sharp transition from the martensite structure to troosto-martensitic and mixed pearlite structures. This increases the contact-fatigue strength of reinforced steel and its crack resistance.

中文翻译：

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钢筋热变形处理过程中梯度层状结构的形成

摘要 在这项研究中，我们考虑了钢筋热变形处理过程中硬化区组织形成的机制和动力学。根据奥氏体分解的冷却速度和温度条件，珠光体和马氏体转变会随着梯度层状结构的形成而发生，导致钢表层在化学成分、结构和性能不变的情况下发生结构改性工件的中心层。由于靠近表面的大温度梯度导致的高冷却速率是形成精细分散的层状结构的原因。表面区域发生无扩散马氏体转变，导致形成针状马氏体。在底层，奥氏体的分解是通过扩散进行的，并伴随着不同分散程度的层状铁素体-碳化物混合物的形成。冷却速度的增加导致结构的强烈细化（根据 GOST 5639-82 的晶粒点在表面层为 11，在核心层为 8），其特征在于铁氧体-碳化物混合物的分散度增加，这会导致钢的强度增加和塑性降低。注意到在应变硬化增强钢的表层中形成梯度层状结构允许排除从马氏体结构到屈氏马氏体和混合珠光体结构的急剧转变。这增加了增强钢的接触疲劳强度及其抗裂性。