The issues that existing studies on hot working of low-carbon steels mostly focus on low Cu content (≤ 3wt.%), rely on a single analytical method, and insufficiently elaborate on the correlation mechanism between "composition-process-workability" for high Cu content (≥ 5wt.%), this study takes two types of low-carbon steels with representative Cu contents as the research objects, namely 2.3Cu steel (medium–low Cu content) and 6Cu steel (high Cu content). This paper researched the stress–strain curves of two low-carbon steels (2.3Cu steel and 6Cu steel) with different copper contents by analyzing through thermal simulation experiments at temperatures ranging from 950 °C to 1160 °C and strain rates from 0.01 s⁻1 to 7 s⁻1. The workability of both steel types was evaluated based on revised stress–strain curves, hot processing maps, and microstructure analysis. The findings indicated that, above thermal simulation conditions, adding a higher copper content significantly improves yield strength during hot compression, except at a high temperature and a high strain rate (1160 °C, 7 s⁻1). Analysis of the iron-copper phase map suggests that at 1160 °C solid copper in high copper content low-carbon steel transitioned into a liquid phase, resulting in a decreased yield strength. The hot processing maps showed that 2.3Cu steel performs well across the entire processing conditions (950 °C to 1160 °C and 0.01 s⁻1 to 7 s⁻1). In contrast, 6Cu steel showed instability at 1160 °C and 7 s⁻1, although it still retains overall good workability. Further microstructure analysis revealed that, at a strain rate of 7 s⁻1, lower processing temperatures facilitated effective dynamic recrystallization. Notably, higher copper content allowed for lower processing temperatures. Conversely, at high processing temperatures, increased copper content raised atomic activity, leading to faster diffusion rates, which promote grain growth and coarsening. This study not only fills the research gap in the hot working mechanism of high copper (6%) low-carbon steel, but also provides a new view for the machinability evaluation of other alloyed steels, and further offers direct guiding significance for the material selection and hot working technology optimization of high copper low-carbon steel. Graphical Abstract

Characterization of Hot Processing Maps and Microstructure Evolution in Two Types of Steel with Different Cu Contents

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发表日期：

2025年12月12日

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Hong Qin,
Yingxue Teng,
Jing Guo,
Pengyu Wen,
Yuzhen Feng,
Jiashen Yang

摘要

The issues that existing studies on hot working of low-carbon steels mostly focus on low Cu content (≤ 3wt.%), rely on a single analytical method, and insufficiently elaborate on the correlation mechanism between "composition-process-workability" for high Cu content (≥ 5wt.%), this study takes two types of low-carbon steels with representative Cu contents as the research objects, namely 2.3Cu steel (medium–low Cu content) and 6Cu steel (high Cu content). This paper researched the stress–strain curves of two low-carbon steels (2.3Cu steel and 6Cu steel) with different copper contents by analyzing through thermal simulation experiments at temperatures ranging from 950 °C to 1160 °C and strain rates from 0.01 s⁻¹ to 7 s⁻¹. The workability of both steel types was evaluated based on revised stress–strain curves, hot processing maps, and microstructure analysis. The findings indicated that, above thermal simulation conditions, adding a higher copper content significantly improves yield strength during hot compression, except at a high temperature and a high strain rate (1160 °C, 7 s⁻¹). Analysis of the iron-copper phase map suggests that at 1160 °C solid copper in high copper content low-carbon steel transitioned into a liquid phase, resulting in a decreased yield strength. The hot processing maps showed that 2.3Cu steel performs well across the entire processing conditions (950 °C to 1160 °C and 0.01 s⁻¹ to 7 s⁻¹). In contrast, 6Cu steel showed instability at 1160 °C and 7 s⁻¹, although it still retains overall good workability. Further microstructure analysis revealed that, at a strain rate of 7 s⁻¹, lower processing temperatures facilitated effective dynamic recrystallization. Notably, higher copper content allowed for lower processing temperatures. Conversely, at high processing temperatures, increased copper content raised atomic activity, leading to faster diffusion rates, which promote grain growth and coarsening. This study not only fills the research gap in the hot working mechanism of high copper (6%) low-carbon steel, but also provides a new view for the machinability evaluation of other alloyed steels, and further offers direct guiding significance for the material selection and hot working technology optimization of high copper low-carbon steel.

Graphical Abstract