Abstract
Requirements for mechanical properties of steels are constantly increasing, and the combination of quenching and tempering is the method generally chosen for achieving high strength in medium carbon steels. This study examines the influence of various silicon contents from 1.06 to 2.49 wt% and the addition of copper (1.47 wt%) on the behavior of 1.7102 steel starting with the as-quenched state and ending with the tempered condition at the temperature of 500 °C. The microstructure was characterized by SEM and TEM, the phase composition and dislocation density were studied by XRD analysis, and mechanical properties were assessed by tensile and hardness testing, whereas tempered martensite embrittlement was assessed using Charpy impact test and the activation energy of carbide precipitation was determined by dilatometry. The benefit of copper consists in the improvement of reduction of area by tempering between 150 and 300 °C. The increase in strength due to copper precipitation occurs upon tempering at 500 °C, where strength is generally low due to a drop in dislocation density and changes in microstructure. The increasing content of silicon raises strength and dislocation density in steels, but the plastic properties of steel are limited. It was found that the silicon content of 1.5 wt% is optimum for the materials under study.
Highlights
Carlos Garcia-Mateo1.7102 steel is a medium carbon steel alloyed with some amount of chrome and silicon.This steel reaches both high strength and toughness and satisfies the requirements for spring materials or for other heavy-duty structural parts [1,2]
(200–450 ◦ C) [6,7,8] when the silicon content is less than 2 wt%, while the monoclinic χcarbides can be formed before θ-cementite in steels alloyed with 2 wt% of silicon [9]
This is consistent with the observed dependence of dislocation density on the tempering temperature (Figure 2) and the conclusions from dilatometry measurement that transition iron carbides, which improve mechanical properties, are formed already at 200 ◦ C, whereas cementite, which could be harmful under certain circumstances, only replaces them on tempering at 400 ◦ C (Figure 3)
Summary
1.7102 steel is a medium carbon steel alloyed with some amount of chrome and silicon This steel reaches both high strength and toughness and satisfies the requirements for spring materials or for other heavy-duty structural parts [1,2]. The typical as-quenched structure of medium carbon steels is lath martensite. The second transformation involves decomposition of retained austenite (200–300 ◦ C), and the third tempering stage is characterized by the transformation of ε- or η-transition carbides to the more stable orthorhombic θ-cementite (200–450 ◦ C) [6,7,8] when the silicon content is less than 2 wt%, while the monoclinic χcarbides can be formed before θ-cementite in steels alloyed with 2 wt% of silicon [9]
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