Liquid Nitriding

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Liquid Nitriding

Liquid nitriding or salt bath nitriding involves treating ferrous materials in a nitrogen-bearing, fused-salt bath containing either cyanides or cyanates at temperatures ranging from 510°C to 580°C. This process shares a similar temperature range with gas nitriding but differs significantly in its approach and outcomes. Unlike liquid carburising and cyaniding, which also use baths with similar compositions, liquid nitriding is a sub-critical case hardening process. This distinction allows for the processing of finished parts while maintaining dimensional stability. Moreover, liquid nitriding introduces more nitrogen and less carbon into ferrous materials than higher-temperature diffusion treatments.

process

Salt bath nitrocarburising, commonly known as Tufftriding, is typically conducted at a higher temperature of around 580°C for short durations, usually about 90 minutes, with air bubbled into the bath at a fixed rate. This method facilitates the diffusion of carbon and nitrogen into the material’s surface layers. Conversely, liquid nitriding is performed at a lower temperature, usually around 520°C, for extended periods ranging from 12 to 15 hours.

At Metal Technology Engineering, we use two liquid nitriding salt baths:

N1: 700 mm x 1300 mm

N2: 600 mm x 1100 mm

Our high-quality salt is imported from HEF Durferrit in Germany, ensuring superior treatment outcomes.

Benefits

iquid nitriding offers numerous advantages for design and manufacturing engineers seeking to enhance the performance of their products. The benefits include:

Superior Wear Resistance: Wear tests consistently demonstrate that parts treated with salt bath nitriding or nitrocarburising exhibit significantly better wear resistance than those treated with traditional methods, such as induction hardening or hard chrome plating.
Enhanced Fatigue Strength: The process improves fatigue strength for thinner material components, potentially allowing engineers to design lighter parts without compromising durability.
Improved Corrosion Resistance: The process enhances corrosion protection for steel, cast iron, and sintered metal parts. Salt spray test results (per ASTM B 117 and DIN 50021) confirm the superior corrosion resistance of salt bath nitrided parts compared to other processes.
Dimensional Stability: Since liquid nitriding is a sub-critical process, it maintains the dimensional stability of finished parts, reducing the need for post-treatment machining.

Application

Liquid nitriding processes are primarily employed to improve surface wear resistance and increase the endurance limit in fatigue. These processes are particularly effective for:

Steel and Cast Iron Components: Including hydraulic parts, transmission components, and various consumer goods.
Sintered Metals: Enhancing wear resistance and fatigue strength.
Stainless Steels: Increasing surface hardness, although this can reduce corrosion resistance due to the formation of chrome nitride.

Comparison with Gas Nitriding

The applications of liquid nitriding and gas nitriding are often similar and sometimes identical. However, gas nitriding may be preferred for applications requiring deeper case depths. Both processes offer the same advantages, including improved wear resistance, anti-galling properties, increased fatigue resistance, and reduced distortion compared to other case-hardening processes that involve higher temperatures.

Practical Considerations

When choosing between salt bath nitriding/nitrocarburising and other surface engineering processes, consider the following:

Case Depth Requirements: Gas nitriding is suitable for applications needing deeper case depths.
Material Compatibility: Salt bath nitriding/nitrocarburising can be applied to several materials, including unalloyed steels, low-alloy steels, high-alloy steels, cast iron, ductile iron, and sintered metals.
Surface Properties: Liquid nitriding significantly enhances surface hardness and wear resistance while maintaining dimensional stability.

Contact Metal Technology Engineering for Details

Liquid nitriding is a highly effective process for enhancing the surface properties of ferrous materials. Its ability to improve wear resistance, fatigue strength, and corrosion protection makes it an invaluable technique for various industrial applications.

Liquid Nitriding

HEAT TREATMENT services