# Microstructure Evolution Control and Performance Degradation of SA-178 Grade C Boiler Tubes Driven by Pearlite Spheroidization

## TL;DR

This study investigates how changes in the microstructure of boiler tubes affect their performance and lifespan.

## Contribution

The study reveals how spheroidization of pearlite in SA-178 grade C boiler tubes leads to performance degradation.

## Key findings

- SAXS and SEM analysis shows lamellar pearlite transforms into spheroidized pearlite over time.
- Tensile strength decreases from 523 MPa to 335 MPa as spheroidization increases.
- Hardness drops from 175 HV to 89 HV with full spheroidization, reducing service life.

## Abstract

SA 178 grade C carbon steel is a material commonly used in boiler tubes. Boilers are crucial in the energy industry; however, their service life degrades over time. If a boiler malfunctions, processing operations must be halted, resulting in financial losses for the company. The aim of this study is to examine the effect of microstructural evolution, especially the transformation of lamellar pearlite into spheroidized pearlite, on the service life degradation of boiler tubes. Understanding these changes is essential for preventing catastrophic system failures. The methodology involves the use of Small-Angle X-ray Scattering (SAXS) supported by metallographic analysis, Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray (EDX) Spectroscopy, and mechanical testing. The SAXS results indicate that the microstructure of SA 178, which initially consisted of ferrite and lamellar pearlite, gradually transforms into spheroidized pearlite. These microstructural changes lead to reductions in tensile strength from 523 MPa for 0% spheroidization to 335 MPa for 100% spheroidization, as well as a reduction in hardness from 175 HV to 89 HV, ultimately decreasing the service life of the boiler tube.