Stainless Steel Ferrule Partial Carbonitriding Heat Treatment

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Solution Overview

Problem

Existing partial heat treatment methods for stainless steel ferrules result in uneven hardness distribution, leading to increased rotational torque and reduced corrosion resistance, while traditional carbonitriding processes use harmful cyanide compounds and are difficult to control.

Innovation Solution

A partially carbonitriding heat treatment process using a molten salt solution with a nitrogen-based organic compound like uric acid, which supplies carbon and nitrogen at low temperatures, creating a multilayer structure with a nitrogen-rich surface layer and a carbon-rich deeper layer, preventing chromium precipitation and maintaining corrosion resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If traditional carbonitriding heat treatment is applied to stainless steel ferrule, then surface hardness is improved, but corrosion resistance deteriorates due to chromium precipitation

Engineering Contradiction:

Improvesurface hardnessVSAvoidcorrosion resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent segments the heat treatment process into two distinct stages: first carburizing to form a carbon-rich layer, then nitriding to form a nitrogen-rich layer. This segmentation prevents chromium carbide precipitation by controlling the sequence and conditions of carbon and nitrogen diffusion, thereby maintaining corrosion resistance while achieving surface hardening.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent changes the chemical composition parameters of the molten salt bath, specifically using a cyanide-free composition with controlled carbon and nitrogen content. The salt bath contains specific compounds that provide carbon and nitrogen sources under controlled conditions, preventing uncontrolled chromium precipitation while enabling surface hardening.

Inventive Principle:

Principle #35Parameter changes

2Force

If partial heat treatment is applied to ferrule, then rotational torque is reduced, but hardness distribution becomes uneven

Engineering Contradiction:

Improverotational torqueVSAvoidhardness distribution uniformity

Core Design Contradiction:

ForceVSManufacturing precision

Solution Approach 1:

The patent applies local quality by selectively treating different regions of the ferrule with different heat treatment conditions. The molten salt bath allows selective carbon and nitrogen diffusion into specific areas, creating locally optimized hardness distribution that reduces rotational torque while maintaining overall uniformity.

Inventive Principle:

Principle #3Local quality

3Productivity

If high heat treatment temperature is used, then carbonitriding process is efficient, but harmful chromium precipitation occurs

Engineering Contradiction:

Improvecarbonitriding efficiencyVSAvoidchromium precipitation

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the temperature parameter to a lower range that is sufficient for carbonitriding without causing excessive chromium precipitation. The controlled temperature regime, combined with the specific molten salt composition, maintains process efficiency while preventing harmful side reactions.

Inventive Principle:

Principle #35Parameter changes

4Ease of manufacture

If cyanide compounds are used in carbonitriding, then carbonitriding process is effective, but human safety is compromised

Engineering Contradiction:

Improvecarbonitriding effectivenessVSAvoidhuman safety

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful cyanide-based process into a safe cyanide-free process by using alternative molten salt compositions. The new composition achieves the same carbonitriding effectiveness through different chemical mechanisms, eliminating toxicity while maintaining manufacturing capability.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The process achieves selective hardening of specific ferrule regions, reducing rotational torque, maintaining corrosion resistance, and using a human-safe, cost-effective method, resulting in a ferrule with enhanced strength and corrosion resistance.

Implementation Method 1

diffuse the carbon or nitrogen atoms to the surface of the workpiece. Thereby, the carburizing or nitriding process enables a compound layer having high hardness to be formed on the surface of the workpiece

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

a carbide (Cr3C2) is configured such that chromium is precipitated with respect to carbon

Methodology Applied

Scientific EffectPrecipitation: Precipitation

Data Source

PatentUS9631747B2Partially carbonitriding heat treated stainless steel ferrule and manufacturing method thereof

Publication Date: 2017.04.25 DK LOK CORP

AI summary

This invention relates to a partially carbonitriding heat treated stainless steel ferrule, having a first region with a first hardness and a second region with a second hardness, wherein the first region includes a nitrogen layer having a nitrogen concentration higher than a carbon concentration, and a carbon layer formed under the nitrogen layer and having a carbon concentration higher than a nitrogen concentration, so that the first hardness is greater than the second hardness. Thereby, partial heat treatment is effective at preventing rotational torque of the region, except for the portion to be heat treated, from increasing due to the total hardening.