ERW Steel Pipe Weld Zone Carbon Control for Fatigue Durability
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Solution Overview
Problem
Conventional electric resistance welded steel pipes or tubes lack fatigue durability, particularly in the electric resistance weld portion, due to insufficient quenching hardness, especially when subjected to rapid and short-time heating quenching treatment, which also fails to prevent decarburization effectively for typical bond widths.
Innovation Solution
The solution involves controlling heating conditions during normalizing heat treatment to ensure sufficient carbon diffusion into the electric resistance weld portion, using a specific chemical composition and atmosphere that prevents decarburization, and performing rapid and short-time heating quenching treatment to enhance quenching hardness and fatigue durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rapid and short-time heating quenching treatment is performed to improve productivity and suppress decarburization, then productivity increases and decarburization is suppressed, but quenching hardness in the electric resistance weld portion becomes insufficient
Solution Approach 1:
The patent applies preliminary action by performing normalizing heat treatment before the final quenching treatment. During this preliminary normalizing step, carbon is allowed to diffuse into the electric resistance weld portion at a slower rate, building up sufficient carbon concentration in advance. This preliminary carbon enrichment enables the weld portion to achieve adequate quenching hardness in the subsequent rapid quenching treatment, resolving the contradiction between productivity and quenching hardness.
2Strength
If heating time is extended to allow carbon diffusion into the electric resistance weld portion, then quenching hardness improves, but decarburization occurs
Solution Approach 1:
The patent performs carbon diffusion as a preliminary action during the normalizing heat treatment step before final quenching. This preliminary carbon enrichment occurs under controlled conditions where carbon can diffuse into the weld portion without excessive decarburization. By completing the carbon diffusion in advance, the subsequent rapid quenching can achieve high hardness without requiring extended heating time that would cause decarburization.
Solution Approach 2:
The patent applies parameter changes by controlling the heating temperature and atmosphere composition during normalizing heat treatment. By optimizing these parameters, the patent creates conditions that favor carbon diffusion into the weld portion while minimizing carbon loss to the atmosphere, thus achieving quenching hardness improvement without significant decarburization.
3Weight of moving object
If conventional electric resistance welded steel pipes are used for hollow parts, then weight reduction is achieved, but fatigue durability is insufficient
Solution Approach 1:
The patent applies preliminary action by performing normalizing heat treatment to pre-enrich carbon in the electric resistance weld portion before the final quenching treatment. This preliminary carbon diffusion ensures that when the rapid quenching is performed, the weld portion has sufficient carbon concentration to form hard martensite structure, thereby achieving high quenching hardness and improved fatigue durability while maintaining the weight benefits of hollow steel pipe structures.
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
This approach effectively increases the quenching hardness of the electric resistance weld portion and prevents decarburization, resulting in improved fatigue durability even for steel pipes or tubes with wider carbon-reduced regions, making them suitable for use in hollow parts like hollow stabilizers.
Implementation Method 1
C enough to ensure sufficient quenching hardness diffuses from the base metal portion into the electric resistance weld portion during heating
Implementation Method 2
electric resistance welded steel pipe or tube that has excellent fatigue durability after rapid and short-time heating quenching treatment
Implementation Method 3
subjecting the steel pipe or tube to quenching or quenching-tempering to impart required strength
Data Source
AI summary
Provided is an electric resistance welded steel pipe or tube having excellent fatigue durability after rapid and short-time heating quenching treatment. An electric resistance welded steel pipe or tube comprises: a base metal being a steel sheet having a specific chemical composition and an electric resistance weld portion having a bond width of 40×10−6 m or more and 120×10−6 m or less, wherein C0-C1 is 0.05 mass % or less, where C0-C1 is a difference between C1 in mass % which is a minimum C content of the electric resistance weld portion and C0 in mass % which is a C content of the steel sheet, and a depth of a total decarburized layer in each of an inner surface layer and an outer surface layer of the electric resistance welded steel pipe or tube is 50×10−6 m or less.