Piercing Mill Tool Scale Adhesion via Alloy Composition
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Solution Overview
Problem
High-alloy steel seamless pipes require tools with enhanced wear resistance to withstand severe production environments, as existing technologies fail to adequately extend tool lifetime due to excessive oxide scale formation, peeling, and surface deterioration, leading to defects and reduced dimensional accuracy.
Innovation Solution
A tool for a piercing mill with a substrate steel composition containing C, Si, Mn, Cr, Mo, W, Nb, Co, and Ni, featuring a net structure scale layer intertwined with the metal and a ferrite dominant microstructure below the scale layer interface, which improves scale peeling resistance and tool longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If an oxide scale is formed on the tool surface through heat treatment to prevent wear, then the tool lifetime is extended, but excessive oxide scale formation causes peeling, dropping off, and surface deterioration that decreases tool lifetime
Solution Approach 1:
The invention changes the chemical composition parameters of the substrate steel by adding specific amounts of Co (0.1-3.0%) and Ni (0.5-2.5%) along with other alloying elements. This compositional parameter change enables the formation of a net structure scale layer with improved adhesion that prevents peeling while maintaining wear protection, thus extending tool lifetime without compromising surface quality
Solution Approach 2:
The invention creates a composite structure consisting of the substrate steel and the net structure scale layer formed on its surface. The scale layer contains intertwined metal and oxide phases that create a mechanically interlocked structure, forming a composite material system that provides both wear resistance and prevents scale peeling, thereby resolving the contradiction between extending tool life and maintaining surface integrity
2Reliability
If high-alloy steel is used to increase hot deformation resistance, then the seamless pipe quality is improved, but the load on the piercing mill tool increases and tool lifetime decreases
Solution Approach 1:
The invention modifies the substrate steel composition parameters by incorporating Co, Ni, and other alloying elements within specific ranges. This compositional change enhances the tool's hot deformation resistance and wear resistance, enabling it to withstand the increased loads from piercing high-alloy steel seamless pipes while maintaining extended tool lifetime
Solution Approach 2:
The invention forms a composite structure with the net structure scale layer on the substrate steel surface. This composite provides superior resistance to the harsh conditions encountered when piercing high-alloy steel, protecting the tool from excessive wear and thermal damage while maintaining structural integrity under high load conditions
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
Significantly increases the tool's lifetime, reduces production costs, and enhances the productivity and quality of high-alloy steel seamless pipes by preventing scale peeling and maintaining dimensional accuracy.
Implementation Method 1
the wear of a tool for a piercing mill has been prevented by forming an oxide scale having a thickness of several tens of micrometers to several hundred micrometers on a surface of the tool through an oxide scale-forming heat treatment at high temperature
Implementation Method 2
a microstructure containing a ferrite phase at an area fraction of 50% or more, the microstructure being formed on the substrate steel side from the interface of the scale layer
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3(A)~3(C)
AI summary
A tool for a piercing mill with excellent wear resistance and a method for producing the tool for a piercing mill are provided. A scale layer is formed in a surface layer of a substrate steel having a composition containing, on a mass% basis, C: 0.05% to 0.5%, Si: 0.1% to 1.5%, Mn: 0.1% to 1.5%, Cr: 0.1% to 1.5%, Mo: 0.6% to 3.5%, W: 0.5% to 3.5%, and Nb: 0.1% to 1.0% and further containing Co: 0.5% to 3.5% and Ni: 0.5% to 4.0% so as to satisfy 1.0 < Ni + Co < 4.0. The scale layer includes a net structure scale layer that is formed on a substrate steel side, has a thickness of 10 to 200 µm in a depth direction, and is complicatedly intertwined with a metal. A microstructure on the substrate steel side in a range of at least 300 µm in the depth direction from an interface between the net structure scale layer and the substrate steel contains a ferrite phase at an area fraction of 50% or more, the ferrite phase containing 400 /mm2 or more of ferrite grains having a maximum length of 1 to 60 µm. Such a microstructure can be formed by performing a scale-forming heat treatment in which, after heating, cooling to at least 700°C is conducted with first rapid cooling and second slow cooling. Thus, the adhesiveness of the scale layer is improved and the lifetime of the tool for a piercing mill is increased.