On the Microstructural Evolution of 4130 Steel During Hot Compression

Mohamadreza      Nourani; Vahid      Sajadifar; Mostafa      Ketabchi; Abbas      S. Milani; Spiro      Yannacopoulos

Abstract

This article first gives a brief patent review of recent trends of steel alloys used in the manufacturing of highpressure gas containers. 4130 steel is among such alloys and has been extensively used in natural gas cylinders that are manufactured through the hot deformation processes. Due to the importance of process parameters such as temperature and strain rate on the ensuing microstructure, primarily grain size, and mechanical properties of the cylinder, the dynamic recrystallization characteristics of 4130 steel are investigated in the second part of this article. Hot compression tests on 4130 steel specimens have been performed at a temperature range of 900-1100°C, strain rate range of 0.001-0.1s-¹ and the strain of 0.9. The resulting flow stress curves show the occurrence of dynamic recrystallization with single or multiple peaks, before reaching the steady state flow at different temperatures and strain rates. The effect of various processing parameters on the microstructure of the alloy is identified by microstructural examination focusing on revealing primary austenite grains using special etchant solutions. It is found that the average grains size of the deformed 4130 steel increases with an increase of the forming temperature and a decrease in the strain rate. The grain size is decreased with an increase of the steady state stress.

Keywords: Austenite grain size, dynamic recrystallization, flow stress, hot compression, microstructure evolution, Zenner-Hollomon parameter, 4130 steel, CNG Cylinders, Hot Deformation, Steel Alloys