As-Rolled K55 ERW Pipe Ferrite-Pearlite Structure
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Solution Overview
Problem
It is challenging to produce an as-rolled type electric resistance welded steel pipe with a yield strength comparable to seamless steel pipes while maintaining cost-effectiveness, as the production of hot-rolled steel sheets with the required low yield strength is hindered by high cooling rates during the hot rolling process, which inhibit the formation of ferrite necessary for achieving the desired mechanical properties.
Innovation Solution
An as-rolled type K55 electric resistance welded oil well pipe with a specific chemical composition and metallographic structure, including a ferrite-pearlite structure with a Mn equivalent of 0.50 to 1.20, is developed, which allows for a tensile strength of 655 N/mm2 and yield strength of 379 to 530 N/mm2, along with excellent base metal toughness, using a hot-rolled steel sheet with a similar composition and structure that has been cold-formed into a pipe shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high cooling rate is applied on the run out table during hot rolling to increase productivity, then production cost is reduced, but the formation of ferrite is inhibited and yield strength cannot be sufficiently decreased
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition (C: 0.25-0.45%, Si: 0.05-0.40%, Mn: 0.50-1.20%, and Mn equivalent: 0.50-1.20) and adjusting rolling parameters (finishing temperature: 700-900°C, cooling rate: 5-20°C/s) to achieve the desired ferrite-pearlite structure with appropriate yield strength despite high cooling rates
Solution Approach 2:
The patent creates a composite microstructure consisting of ferrite and pearlite phases through controlled cooling, where ferrite provides ductility and pearlite provides strength, achieving a balanced mechanical property profile suitable for K55 pipe applications
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 enables the production of an as-rolled type K55 electric resistance welded oil well pipe with enhanced base metal toughness and cost-effective production, meeting the mechanical property requirements while maintaining a balance between tensile and yield strengths.
Implementation Method 1
a metallographic structure, at a position to which a distance from a sheet surface is 1/4 a sheet thickness in an L cross-section, is a ferrite-pearlite structure in which prior austenite grains are flattened, includes grain boundary ferrite which is ferrite present in a grain boundary of the prior austenite grains and intragranular ferrite which is ferrite present within the prior austenite grains
Data Source
AI summary
An as-rolled type K55 electric resistance welded oil well pipe includes, in terms of % by mass, 0.30 to 0.50% of C, 0.05 to 0.40% of Si, 0.50 to 1.20% of Mn, 0 to 0.030% of P, 0 to 0.020% of S, 0.002 to 0.080% of Al, 0 to 0.0080% of N, 0 to 0.30% of Cu, 0 to 0.30% of Ni, 0 to 0.30% of Cr, 0 to 0.10% of Mo, 0 to 0.10% of V, 0 to 0.050% of Nb, 0 to 0.030% of Ti, 0 to 0.0100% of Ca, and the balance being Fe and impurities. In the pipe, a metallographic structure at a position of ¼ of a pipe thickness in an L cross-section at a base metal 90° position is a ferrite-pearlite structure in which prior γ-grains are flattened, includes grain boundary ferrite and intragranular ferrite, and has a rate of a total area of the grain boundary ferrite and the intragranular ferrite, of 10 to 30%.