Piercer Plug Material for Mannesmann Seamless Steel Pipe
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Solution Overview
Problem
Conventional piercer plugs for manufacturing seamless steel pipes suffer from season cracking due to hydrogen embrittlement and high hardness, leading to reduced machinability and shorter lifespan, especially during long-term storage and use in diverse pipe sizes and shapes.
Innovation Solution
A material composition for piercer plugs with a Rockwell hardness of 20 to 40, comprising specific elements like C, Si, Mn, Ni, W, Mo, and controlled diffusible hydrogen levels, subjected to heat treatment conditions that adjust hardness and reduce hydrogen content, resulting in tempered martensite or bainite structure for improved toughness and machinability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength steel with W and Mo is used to raise high temperature deformation resistance, then high temperature deformation resistance is improved, but machinability deteriorates due to high hardness
Solution Approach 1:
The invention changes the material parameters by controlling the carbon content (0.15-0.35%) and adding specific alloying elements (W: 1.00-3.00%, Mo: 1.00-3.00%) to achieve the desired balance between high temperature deformation resistance and machinability. The hardness is controlled to be 20-40 HRC through composition control rather than extreme hardening treatments.
2Duration of action of stationary object
If the piercer plug is stored for long time to obtain inventories, then availability is improved, but season cracking occurs due to hydrogen embrittlement
Solution Approach 1:
The invention extracts and removes hydrogen from the steel material through controlled heat treatment processes. By heating to 550-900°C and holding for 0.5-10 hours, hydrogen is extracted from the material structure, reducing hydrogen embrittlement and preventing season cracking during long-term storage.
Solution Approach 2:
The invention changes the thermal parameters through controlled heat treatment (550-900°C for 0.5-10 hours) to alter the material's hydrogen content and microstructure. This parameter change transforms the material state to be more resistant to season cracking while maintaining storage capability.
3Force
If high contact pressure is applied to the tip during piercing, then piercing force is improved, but the tip melts due to high temperature
Solution Approach 1:
The invention creates a composite material system by combining high carbon steel (0.15-0.35% C) with significant amounts of tungsten (1.00-3.00% W) and molybdenum (1.00-3.00% Mo). These alloying elements form high melting point compounds and strengthen the material structure, allowing the tip to withstand both high contact pressure and high temperatures without melting.
Solution Approach 2:
The invention changes the material's thermal and mechanical parameters through alloying and heat treatment. The addition of W and Mo raises the melting point and thermal stability, while the controlled carbon content and heat treatment (550-900°C for 0.5-10 hours) optimize the strength-temperature resistance balance, enabling the tip to maintain integrity under high contact pressure and temperature conditions.
4Duration of action of stationary object
If the hardness is increased to extend piercer plug life, then durability is improved, but machinability and season cracking resistance deteriorate
Solution Approach 1:
The invention optimizes the hardness parameter to a specific range (20-40 HRC) through controlled composition and heat treatment. This parameter change achieves the triple benefit of extended service life, maintained machinability, and improved season cracking resistance, avoiding the extremes of too hard or too soft material states.
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 solution effectively suppresses season cracking, enhances machinability, and extends the lifespan of piercer plugs, allowing for longer storage and adaptability to various seamless steel pipe sizes and shapes, while maintaining sufficient strength for the Mannesmann process.
Implementation Method 1
performing heat treatment on the cast material for piercer plug under conditions where a heat treatment parameter PH defined by the following formula (1) satisfies the following formula (2) and formula (3)
Implementation Method 2
resulting in tempered martensite or bainite structure for improved toughness and machinability
Implementation Method 3
heat treating by high temperature oxidation a base material which is comprised of high strength steel containing W and Mo
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention relates to a piercer plug which is used when using the Mannesmann process to manufacture seamless steel pipe, more particularly relates to a material for piercer plug for manufacturing seamless steel pipe which is excellent in season cracking resistance and machinability and a method of manufacturing the same. The material for piercer plug comprises as components, by mass%, C: 0.08 to 0.3%, Si: 0.1 to 1.0%, Mn: 0.2 to 1.5%, Ni: 0.2 to 2.0%, and, furthermore, one or both of W and Mo in a total of 1.5% to 8%, a balance of Fe and impurities, wherein the amount of diffusible hydrogen which is contained as an impurity is in 2 ppm or less. The material for piercer plug has a hardness between HRC 6 and 10.