Constitutive Equation and Hot Processing Map of a Nitrogen-Bearing Martensitic Stainless Steel

Xiao Li,Yinghui Wei,Zhengyan Wei,Lifeng Hou

doi:10.3390/met10111502

Abstract

The hot deformation behavior of a nitrogen-bearing martensitic stainless steel was researched by the isothermal compression test in the temperature range of 950–1150 °C and strain rate range of 0.01–10 s−1 with a Gleeble-3800 thermal-mechanical simulating tester. A strain compensated sine-hyperbolic Arrhenius-type constitutive equation was developed to describe the relationship between true stress and deformation parameters such as temperature, strain rate and true strain. The hot deformation activation energy is calculated to be from 407 to 487 KJ mol−1. It is validated by the standard statistical parameters that the established constitutive equation can accurately predict the true stress. The processing maps at different true strains were constructed based on the dynamic material model (DMM) and the true stress data obtained from the hot compression tests. Two unstable regions which should be avoided during hot working were observed from the processing map. In addition, the optimum hot working parameters are located in the domain of 1000–1150 °C/0.1–1 s−1 with the peak power dissipation efficiency of 39.9%, in which complete dynamic recrystallization (DRX) occurs.

Highlights

Martensitic stainless steels (MSSs) generally possess high hardness and appropriate corrosion resistance, so they are widely applied to machine parts in contact with seawater, bearings used in aerospace, knives and scissors for food contact, medical equipment, etc. [1]
The aim of the present paper is to investigate the hot deformation behavior of the nitrogen-bearing martensitic stainless steel
The experimental steel was melted by argon oxygen decarburization (AOD) furnace and ladle furnace (LF), after which the slab was hot rolled in the temperature range of 1100–1200 ◦ C into a plate with the thickness of 33 mm

Summary

Introduction

Martensitic stainless steels (MSSs) generally possess high hardness and appropriate corrosion resistance, so they are widely applied to machine parts in contact with seawater, bearings used in aerospace, knives and scissors for food contact, medical equipment, etc. [1]. Martensitic stainless steels (MSSs) generally possess high hardness and appropriate corrosion resistance, so they are widely applied to machine parts in contact with seawater, bearings used in aerospace, knives and scissors for food contact, medical equipment, etc. The two most important alloying elements of the conventional MSSs are chromium and carbon, where chromium makes steel stainless while carbon imparts solid solution strengthening. In order to resolve these problems, nitrogen as an important alloying element has been applied to MSSs. Nitrogen is conventionally used in austenitic and duplex stainless steels for its relatively high solubility in these steels. Due to the limited solubility of nitrogen in MSSs, it is very difficult to manufacture nitrogen-bearing MSSs under ambient pressure. There are several approaches to solve this problem, such as alloying with elements (e.g., Cr, Mo and Mn, etc.)

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Conclusion