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<p>Surface decarburization during heat treatment critically degrades the fatigue performance of 55SiCr spring steel. The present study systematically investigates the decarburization mechanisms and their dependence on process parameters through thermal analysis, metallographic experiments, and process simulation. Three key findings are revealed: (1) Austenitizing temperature controls decarburization by regulating oxide layer characteristics. Within the 1000–1050&#xa0;°C range, a dense and continuous oxide scale forms that effectively blocks atmospheric ingress, achieving a minimum decarburized layer thickness of approximately 10&#xa0;μm — a mechanism termed oxidation-induced decarburization suppression, directly confirmed by SEM/EDS analysis. At 1100 °C, the scale becomes highly porous and extensively cracked, losing its protective function. (2) The ferrite-austenite two-phase region (730–740&#xa0;°C) is identified as a zone susceptible to decarburization. Here, phase transformation causes a sharp drop in carbon solubility in ferrite while the carbon diffusion coefficient increases by nearly two orders of magnitude, collectively triggering rapid carbon depletion. (3) A cumulative amplification effect is uncovered: even slight carbon inhomogeneity from prior processes is magnified during subsequent two-phase region treatment. Quantitative EPMA/WDS carbon profiling provides direct evidence: after re-austenitization in air, a pre-existing decarburized layer results in a cumulative amplification effect, with the near-surface carbon content averaging approximately 0.32 wt% — significantly below the nominal composition of 0.56 wt%. This finding demonstrates that decarburization control must be maintained throughout the entire production chain. Based on these mechanisms, a prevention-avoidance-control strategy is proposed, providing theoretical guidance and process optimization principles for producing spring steel with high surface quality and superior core toughness.</p>

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Phase-Transformation-Driven Decarburization and its Cumulative Amplification in Multi-Stage Processing of 55SiCr Spring Steel

  • 期刊论文

  • 发表日期：

    2026年6月16日

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  • Y. F. Peng,
  • L. N. Zhang,
  • C. Y. Wei,
  • Z. Yao,
  • H. X. Zheng,
  • F. Jin,
  • X. M. Dong,
  • Z. H. Zhang,
  • G. H. Cao

摘要

Surface decarburization during heat treatment critically degrades the fatigue performance of 55SiCr spring steel. The present study systematically investigates the decarburization mechanisms and their dependence on process parameters through thermal analysis, metallographic experiments, and process simulation. Three key findings are revealed: (1) Austenitizing temperature controls decarburization by regulating oxide layer characteristics. Within the 1000–1050 °C range, a dense and continuous oxide scale forms that effectively blocks atmospheric ingress, achieving a minimum decarburized layer thickness of approximately 10 μm — a mechanism termed oxidation-induced decarburization suppression, directly confirmed by SEM/EDS analysis. At 1100 °C, the scale becomes highly porous and extensively cracked, losing its protective function. (2) The ferrite-austenite two-phase region (730–740 °C) is identified as a zone susceptible to decarburization. Here, phase transformation causes a sharp drop in carbon solubility in ferrite while the carbon diffusion coefficient increases by nearly two orders of magnitude, collectively triggering rapid carbon depletion. (3) A cumulative amplification effect is uncovered: even slight carbon inhomogeneity from prior processes is magnified during subsequent two-phase region treatment. Quantitative EPMA/WDS carbon profiling provides direct evidence: after re-austenitization in air, a pre-existing decarburized layer results in a cumulative amplification effect, with the near-surface carbon content averaging approximately 0.32 wt% — significantly below the nominal composition of 0.56 wt%. This finding demonstrates that decarburization control must be maintained throughout the entire production chain. Based on these mechanisms, a prevention-avoidance-control strategy is proposed, providing theoretical guidance and process optimization principles for producing spring steel with high surface quality and superior core toughness.