The nitrogen content in recarburizers is a critical parameter.

The nitrogen content in recarburizers is a critical parameter that must be strictly controlled in iron foundry production, directly influencing casting quality and performance.

Key Impacts:

1. Excessively High Nitrogen (typically >150 ppm): Dissolved nitrogen in the molten iron can precipitate during solidification, forming nitride inclusions (e.g., with titanium) or nitrogen gas pores. This leads to defects such as pinholes and subsurface blows within or near the casting surface, severely compromising density, mechanical properties, and machining yield.

2. Optimal Nitrogen Range (generally 80-200 ppm): When controlled within a suitable range, nitrogen acts as an effective pearlite stabilizer. It refines the microstructure, promotes pearlite formation, and thereby enhances the tensile strength, hardness, and wear resistance of cast irons (especially gray and ductile iron). It is particularly beneficial for improving hardness uniformity in thin-walled sections.

Selection and Management Advice:
Consequently, selecting a low-nitrogen (e.g., N < 100 ppm) and consistently high-quality recarburizer is paramount. Foundries must determine the optimal type and addition rate through process trials, considering their base charge materials' (pig iron, scrap) nitrogen levels, the target iron grade, and casting wall thickness. This ensures precise control over the total nitrogen in the molten iron, preventing defects while optimizing performance.