Maraging Steel Fatigue Strength via TiN Inclusion Control
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Solution Overview
Problem
The existing methods for producing maraging steel result in large variations in fatigue testing due to the size effect, primarily attributed to non-metallic inclusions like TiN and TiCN, which affect the fatigue strength and make it difficult to achieve reliable results, especially in low-cycle fatigue testing.
Innovation Solution
A production method involving the creation of a remelt electrode with specific compositions of Ti, N, Si, Mn, and other elements, followed by vacuum arc remelting to produce a steel ingot with a large diameter, which controls the size and dispersion of Ti-based non-metallic inclusions, reducing the size effect and maintaining high fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If vacuum arc remelting is used to reduce non-metallic inclusions, then fatigue strength is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by adding magnesium oxide to the molten steel before vacuum arc remelting. This pre-treatment step prepares the molten metal by introducing oxide inclusions that will serve as nuclei for inclusion aggregation, making the subsequent vacuum arc remelting process more effective at reducing non-metallic inclusions and improving fatigue strength
Solution Approach 2:
The patent uses magnesium oxide as an intermediary substance. The MgO acts as a mediator that facilitates the aggregation and removal of non-metallic inclusions during vacuum arc remelting. By introducing this intermediate material, the process achieves better inclusion control without requiring overly complex manufacturing equipment
2Measurement precision
If multiple test specimens are used to estimate fatigue strength, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent extracts the source of variability by reducing non-metallic inclusions to a consistent low level through controlled vacuum arc remelting. By removing the harmful variable (inclusion variability) from the test specimens, the fatigue strength results become more consistent and reliable, requiring fewer specimens to achieve statistically significant data
Solution Approach 2:
The patent changes the chemical composition parameters by controlling Ti content (0.03-0.10% by mass) and adding magnesium oxide (0.005-0.05% by mass). These parameter changes ensure that test specimens have uniform inclusion characteristics, reducing the variation in fatigue test results and allowing more accurate estimation with fewer specimens
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 method reduces the variation in fatigue testing results and enhances the fatigue strength of maraging steel by controlling the size and dispersion of Ti-based non-metallic inclusions, providing a more reliable representation of fatigue performance with fewer tests.
Implementation Method 1
remelting the consumable electrode at a higher vacuum than the vacuum in the step of forming the magnesium oxide to decompose the magnesium oxide in the molten metal into magnesium and oxygen
Implementation Method 2
a generally used method for produce a maraging steel includes preparing a consumable electrode for remelting by vacuum melting and using the consumable electrode to produce a maraging steel by vacuum arc remelting
Data Source
AI summary
A production method of a maraging steel includes: the step of producing, by vacuum melting, a remelt electrode which comprises from 0.2 to 3.0% by mass of Ti and from 0.0025 to 0.0050% by mass of N; and the step of remelting the remelt electrode to produce a steel ingot having an average diameter of 650 mm or more; wherein the resulting maraging steel includes from 0.2 to 3.0% by mass of Ti.