# Effect of Heat Input on the Hydrogen Embrittlement Sensitivity of CGHAZ of X60 Pipeline Steel

## TL;DR

This study examines how welding heat input affects hydrogen embrittlement in X60 pipeline steel, finding that higher heat input can reduce embrittlement sensitivity.

## Contribution

The study introduces a multi-dimensional approach to evaluate hydrogen embrittlement sensitivity in pipeline steel based on microstructural changes due to welding heat input.

## Key findings

- Higher heat input leads to coarser grains and a transition from bainitic ferrite to granular bainite and polygonal ferrite.
- BF + GB composite structure showed the best resistance to hydrogen embrittlement with 29.8% sensitivity.
- Increased Σ3 grain boundary density at 16 kJ/cm heat input reduced hydrogen enrichment and embrittlement sensitivity.

## Abstract

In the coarse grain heat-affected zone (CGHAZ) of welded pipe steel joints, hydrogen damage is a key factor limiting the high-pressure hydrogen transportation performance of the pipeline. This study employed multi-dimensional characterization methods (including microstructure, mechanical properties, and hydrogen distribution) to investigate the influence of welding heat input on the hydrogen embrittlement (HE) sensitivity of X60 pipeline steel in the CGHAZ. The results showed that as the heat input increased, the grains in the CGHAZ became coarser, and the microstructure changed from bainitic ferrite (BF) to granular bainite (GB) and polygonal ferrite (PF). Among them, the BF + GB composite structure had the best resistance to HE (HE sensitivity was 29.8%). At low heat input, the reversible hydrogen distribution occurred at the interfaces between the grain boundaries and the BF blocks, while at high heat input, it would accumulate around the martensite/austenite (M/A) constituents. For the 16 kJ/cm heat input experimental steel, the increase in Σ3 grain boundary density accelerated hydrogen diffusion and reduced its enrichment, thereby resulting in the lowest HE sensitivity.