What are the applications of Si3N4 ferro silicon nitride powder in metallurgy?

Silicon nitride (SiN₄) powder, with Si₃N₄ as its core phase, typically contains 55%-65% Si, 10%-15% N, and 15%-25% Fe, with total impurities (Al, Ca, S, P) ≤3%. Its core characteristics support diverse applications in the metallurgical field:

 Strong Thermodynamic Stability: Si₃N₄ has a melting point of approximately 1900℃ and does not decompose in molten steel/iron below 1600℃, resulting in a mild and controllable reaction.

 Suitable Reactivity: The reaction free energy between Si and O (ΔG₂₀₀₀K = -477 kJ/mol) and between N and O are both low, enabling efficient deoxidation without introducing harmful impurities.

 Excellent Particle Characteristics: Industrial-grade powder has a size of 100-300 mesh (48-150 μm), a large specific surface area, and is easily dispersed in molten metal, resulting in good reaction uniformity.

(1) Steelmaking Deoxidation: Improving the Purity and Stability of Molten Steel

Silicon nitride powder, as a highly efficient composite deoxidizer, has significant advantages over traditional ferrosilicon and aluminum deoxidizers:

Deoxidation Mechanism:

Si₃N₄ reacts with O in molten steel to generate SiO₂ and N₂. SiO₂ has a density of 2.65 g/cm³, far lower than molten steel (7.8 g/cm³), making it easily float and removed with the slag. When N₂ escapes in the form of bubbles, it can carry some small inclusions, further purifying the molten steel.

Suitable Scenarios:

Applicable to low-alloy high-strength steel, bearing steel, spring steel, and other steels with high purity requirements. It can reduce internal porosity and inclusion defects in steel, and improve tensile strength and fatigue life.

(2) Alloying Adjustment: Optimizing the Mechanical Properties of Steel

Si and N work synergistically to achieve a balance between "strengthening and toughening" in steel:

Strengthening Mechanism:

Si dissolves into the iron lattice, causing lattice distortion, hindering dislocation movement, and improving the strength and hardness of steel; N forms fine and dispersed nitrides (such as NbN and VN) with elements such as Nb and V in the steel, producing a precipitation strengthening effect, while refining the grains;

Performance Improvement Data:

When producing high-strength alloy steel, adding 0.4%-0.8% silicon nitride ferro powder increases the yield strength of the steel by 15%-20%, the tensile strength by 10%-15%, and the elongation remains above 18%, balancing strength and plasticity;

(3) Casting Field: Improving Casting Quality and Formability

Silicon nitride iron powder has both inoculation and flowability adjustment functions, suitable for gray cast iron, ductile iron, and precision casting:

Optimized Flowability:

Reduces the surface tension of molten iron, reducing viscosity 15%-20%, improving the filling capacity of molten iron and reducing defects such as "insufficient pouring" and "cold shut";

Grain refinement:

Powder particles act as heterogeneous nucleation cores in molten iron, promoting uniform precipitation of graphite, refining the grain size of castings from 80μm to 30-40μm, increasing strength by 25%-30%, and improving wear resistance;

(4) Special steel production: meeting the performance requirements of high-end scenarios

In the production of special steels such as high-temperature alloys and stainless steel, ferro silicon nitride powder plays a unique role:

High-temperature alloys:

When used in the production of high-temperature alloys for turbine blades of aero-engines, N forms stable nitrides with elements such as Cr and Co, increasing the creep strength of the alloy at 1000℃ by more than 25%, increasing oxidation resistance by 30%, and being able to withstand extreme high temperatures and airflow impact;

Stainless steel:

Adding 0.3%-0.5% powder can optimize the distribution of Cr in stainless steel, avoid the formation of Cr-poor areas, and refine the grains, increasing the salt spray corrosion resistance time from 200h. Extended to over 350 hours, suitable for highly corrosive environments such as chemical equipment and marine engineering;

Other special steels:

In tool steel production, it can improve the red hardness and wear resistance of steel; In low-temperature steel production, it reduces the brittle transition temperature through grain refinement, allowing the steel to maintain good toughness at -60℃.

(1) Addition Amount Control

Steelmaking Deoxidation:

0.3%-0.6% (steel mass), excessive addition can easily lead to excessive N content in the steel (exceeding 0.015%), causing "nitrogen embrittlement";

Casting Inoculation:

0.2%-0.5% (molten iron mass), excessive addition will make the casting too hard, affecting processing performance;

Special Steel Alloying:

0.4%-0.8% (molten steel mass), needs to be precisely adjusted according to the target composition of the steel grade.

(2) Timing and Method of Addition

Steelmaking:

Add during the later stages of furnace charge melting (steel temperature 1500-1600℃) to ensure uniform powder dispersion and avoid local agglomeration;

Casting:

Add 1-2 minutes before tapping the molten iron, or add during the pouring process to improve the inoculation effect.

(3) Material Selection

Purity Requirements:

High-purity FeSi3N4 powder (Si₃N₄ content ≥90%, total impurities ≤1%) is used for high-end steel grades;

Size Selection:

100-200 mesh powder for ordinary steelmaking/casting, 200-300 mesh fine powder for precision casting to ensure uniform reaction.