Mixed Powder for Sintered Bodies Enhancing Compressibility
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for increasing the strength of iron-based powder press-formed products and sintered products, such as those using pre-alloyed and partially diffusion-alloyed steel powders, fail to achieve sufficient compressibility and forming density, limiting their mechanical properties like tensile strength and fatigue resistance.
Innovation Solution
A mixed powder composition comprising an iron-based powder with minimal Si and Mn, and an alloyed steel powder containing Mo, Si, and Mn, with a specific ratio of alloyed steel powder to iron-based powder, along with optional Cu and graphite, to enhance compressibility and mechanical properties during press forming and sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If pre-alloyed steel powder is used to increase strength through complete alloying, then mechanical characteristics are stabilized, but compressibility decreases and forming density is difficult to increase
Solution Approach 1:
The invention applies local quality by creating powder particles with non-uniform alloy distribution - the surface layer contains alloying elements (Mo, Mn, Cr, Si) while the core remains primarily iron with minimal alloy content. This local differentiation allows the surface to provide strength and hardenability while the core maintains compressibility and ductility, resolving the contradiction between mechanical characteristics and compressibility.
Solution Approach 2:
The invention creates a composite powder structure consisting of an iron-based core and an alloyed surface layer. This composite structure combines the advantages of both pre-alloyed powder (uniform strength) and partially diffusion-alloyed powder (good compressibility), achieving high mechanical characteristics while maintaining excellent compressibility during press forming.
2Strength
If Mo is added as alloying element to improve quench hardenability, then transformation toughening and solid solution strengthening are achieved, but production complexity increases
Solution Approach 1:
The invention applies preliminary action by pre-coating the iron powder particles with alloying elements before sintering. The alloying elements are deposited on the powder surface in advance, creating a controlled composition that will diffuse into the core during subsequent heat treatment. This preliminary preparation simplifies the overall production process by eliminating the need for complex multi-step alloying operations while ensuring uniform Mo distribution and desired hardenability.
Solution Approach 2:
The invention utilizes parameter changes by controlling the diffusion process during heat treatment. By adjusting temperature, time, and atmosphere parameters, the alloying elements progressively diffuse from the surface into the core, transforming the powder structure from a coated state to a gradient alloyed state. This controlled parameter change achieves the desired Mo distribution and mechanical properties while keeping the production process manageable.
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 mixed powder achieves higher compressibility and forming density, resulting in sintered bodies with improved tensile strength and mechanical properties, suitable for both single-forming and twice-forming twice-sintering methods.
Implementation Method 1
heating under a non-oxidizing or reducing atmosphere to provide diffusion bonding of alloying element powder on the surface of the pure iron powder or pre-alloyed steel powder
Implementation Method 2
the compressibility of the powder is low, causing a problem that the forming density is difficult to increase during press forming
Implementation Method 3
the formation of ferrite is suppressed and bainite or martensite is generated during hardening treatment, and transformation toughening of the matrix phase is achieved
Implementation Method 4
Mo distributes to the matrix phase to achieve solid solution strengthening of the matrix phase
Data Source
AI summary
Disclosed is a mixed powder for powder metallurgy including: (a) an iron-based powder containing Si in an amount of 0 mass % to 0.2 mass % and Mn in an amount of 0 mass % to 0.4 mass %, with the balance being Fe and inevitable impurities; and (b) an alloyed steel powder containing Mo in an amount of 0.3 mass % to 4.5 mass %, Si in an amount of 0 mass % to 0.2 mass %, and Mn in an amount of 0 mass % to 0.4 mass %, with the balance being Fe and inevitable impurities, wherein a ratio of (b) the alloyed steel powder to a total of (a) the iron-based powder and (b) the alloyed steel powder is from 50 mass % to 90 mass %, and a ratio of Mo to the total of (a) the iron-based powder and (b) the alloyed steel powder is 0.20 mass % or more and less than 2.20 mass %.