Cobalt-Base Oxide Plug for Seamless Steel Pipe Rolling
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Solution Overview
Problem
Conventional methods for extending the life of plugs used in rolling seamless steel pipes, particularly with high-alloy steels, face challenges such as insufficient joint strength, vulnerability to impact, high cost, and thermal fatigue, as well as increased friction leading to deformation.
Innovation Solution
A plug with a cobalt-base oxide layer formed through heat treatment on a ferrous base metal, where the cobalt-base alloy contains 30 mass % or less of nickel, providing a strong and heat-insulating coating that prevents wear and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If a plug composed of iron-base alloy is used for rolling high-alloy steel, then the plug can be manufactured with conventional materials and processes, but the plug life is insufficient due to low high-temperature strength causing deformation and crush
Solution Approach 1:
The invention uses a composite structure consisting of an iron-base alloy base metal and a cobalt-base alloy coating layer. The base metal provides structural integrity and cost-effectiveness, while the cobalt-base alloy coating provides high-temperature strength and wear resistance. This composite approach allows the plug to withstand the high temperatures and loads of rolling high-alloy steel without deforming, thereby extending plug life significantly.
Solution Approach 2:
The invention changes the chemical composition parameters of the surface layer by applying a cobalt-base alloy coating containing specific amounts of nickel (3-30 mass%), chromium (0.5-20 mass%), and other alloying elements. This parameter change in the surface composition provides enhanced high-temperature strength and wear resistance compared to conventional iron-base alloy plugs, allowing the plug to maintain its shape and function under extreme rolling conditions.
2Reliability
If the surface of the plug is protected with oxidized scale by heat treatment, then seizure and deposition are prevented, but the scale layer breaks easily due to plug deformation under high contact load
Solution Approach 1:
The cobalt-base alloy coating layer provides superior high-temperature strength and creep resistance compared to conventional iron-base alloys. This enhanced strength prevents plug deformation and crush under high contact loads, thereby maintaining the integrity of the oxidized scale layer formed on the coating surface. The composite structure ensures that the protective scale layer does not break easily, maintaining reliable protection against seizure and deposition throughout the plug's service life.
Solution Approach 2:
The oxidized scale layer is formed on the cobalt-base alloy coating surface through preliminary heat treatment before the plug is put into service. This pre-formed protective layer provides immediate protection against seizure and deposition when the plug first contacts the heated billet or hollow, while the underlying high-strength cobalt-base alloy coating ensures the scale layer remains intact under subsequent high contact loads during rolling operations.
3Strength
If ceramic or molybdenum alloy is used for the plug tip to increase high-temperature strength, then wear resistance improves, but joint strength between the tip and metallic portion is insufficient and the plug is vulnerable to impact
Solution Approach 1:
The invention uses a composite material system where a cobalt-base alloy coating is applied on an iron-base alloy substrate. The cobalt-base alloy provides high-temperature strength and wear resistance comparable to ceramic or molybdenum alloy, while maintaining metallurgical bonding with the substrate. This eliminates the joint strength problems associated with ceramic or molybdenum alloy tips, as the coating is metallurgically bonded to the substrate throughout its entire area, providing uniform strength and impact resistance.
Solution Approach 2:
The cobalt-base alloy coating is applied locally on the surface of the iron-base alloy plug, particularly on areas subject to high wear and temperature such as the plug tip and cylindrical portion. This localized application provides high-temperature strength and wear resistance exactly where needed, while the bulk of the plug retains the cost-effective iron-base alloy composition. The coating thickness is controlled at 0.1-2.0 mm to provide adequate protection without excessive weight or cost.
4Duration of action of stationary object
If cobalt-base alloy coating is applied to increase wear resistance, then plug life increases, but manufacturing cost increases
Solution Approach 1:
The invention optimizes the composition parameters of the cobalt-base alloy coating, specifically limiting nickel content to 3-30 mass% and chromium to 0.5-20 mass%, while controlling the coating thickness at 0.1-2.0 mm. These parameter optimizations reduce the amount of expensive alloying elements required, thereby lowering material costs. The controlled coating thickness balances wear protection with material consumption, achieving cost-effective plug life extension.
Solution Approach 2:
The composite structure of iron-base alloy substrate with cobalt-base alloy coating allows the use of conventional, cost-effective base materials while adding a relatively thin layer of expensive alloy for wear and temperature protection. This approach is more cost-effective than using expensive materials like ceramic, molybdenum alloy, or full cobalt-base alloy plugs, as the expensive coating is applied only where needed on the surface, minimizing overall material costs while achieving the desired plug life extension.
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 significantly increases the life of the plug by reducing wear damage and maintaining productivity while controlling costs, allowing for the rolling of more billets before replacement.
Implementation Method 1
an oxide layer composed of a cobalt-base oxide on a surface of a coating layer formed by coating a surface of a base metal with cobalt or a cobalt-base alloy
Implementation Method 2
the oxide layer is formed by performing a heat treatment of holding at a high temperature
Implementation Method 3
providing a strong and heat-insulating coating that prevents wear and deformation
Data Source
AI summary
A plug for rolling of a seamless steel pipe, the plug having an oxide layer composed of a cobalt-base oxide on a surface of a coating layer formed by coating a surface of a base metal with cobalt or a cobalt-base alloy, a method for manufacturing the plug and a method for manufacturing a seamless steel pipe using the plug.