Seamless Steel Pipe Composition for High Strength and Low Temperature Toughness
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Solution Overview
Problem
Seamless steel pipes for crane booms require high tensile strength, toughness at low temperatures, and low weld crack sensitivity (Pcm ≤ 0.30) to meet stringent specifications, while existing methods struggle to balance strength, toughness, and productivity, often resulting in increased energy costs and weldability issues.
Innovation Solution
A seamless steel pipe with a specific chemical composition (C: 0.10-0.20%, Si: 0.05-1.0%, Mn: 0.05-1.2%, and controlled amounts of other elements) and a production process involving hot rolling, cooling, quenching, and tempering to achieve a tensile strength of 980 MPa or more, Charpy impact value of 75 J/cm² at -40°C, and a Pcm value of 0.30 or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength seamless steel pipes are produced using conventional methods with higher alloy content, then tensile strength can be increased, but Pcm value increases leading to poor weldability
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters within specific ranges: C (0.15-0.35%), Si (0.01-2.00%), Mn (0.01-2.00%), Cr (0.10-1.00%), Mo (0.05-0.50%), B (0.0005-0.0050%), and other elements. This compositional parameter control achieves the dual goal of high tensile strength (950 MPa or more) and low Pcm value (0.30 or less), thereby resolving the contradiction between strength and weldability
2Strength
If conventional production methods are used to achieve high strength, then tensile strength can be increased, but energy consumption increases due to complex heat treatment processes
Solution Approach 1:
The patent applies preliminary action by incorporating alloying elements (particularly B, Cr, and Mo) during the steelmaking process that provide ongoing strengthening effects throughout the production and service lifecycle. This preliminary incorporation of strengthening mechanisms reduces the need for extensive subsequent heat treatment operations, thereby lowering energy consumption while maintaining high tensile strength of 950 MPa or more
3Strength
If high strength steel pipes are produced with complex alloy compositions, then tensile strength can be increased, but productivity decreases due to multiple processing steps
Solution Approach 1:
The patent applies the extraction principle by removing unnecessary complex processing steps and focusing on a streamlined production process. By carefully selecting and controlling a specific set of alloying elements within defined ranges, the patent achieves high tensile strength (950 MPa or more) through a simplified process that avoids multiple complex heat treatment and manufacturing steps, thereby improving production efficiency and productivity
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 provides a seamless steel pipe with high strength, excellent low-temperature toughness, and improved weldability, meeting the stringent requirements for crane boom applications while maintaining a low Pcm value and reducing energy costs.
Implementation Method 1
a steel micro-structure includes, in area %, tempered martensite: 90% or more
Implementation Method 2
a quenching process of heating the cooled material pipe to a temperature in a range from an Ac3 point to 950° C., and thereafter rapidly cooling the material pipe; and a tempering process of heating the quenched material pipe to a temperature in a range from 500 to 600° C.
Data Source
AI summary
A seamless steel pipe is provided that has a chemical composition which consists of, by mass %, C: 0.10 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.05 to 1.2%, P≤0.025%, S≤0.005%, Cu≤0.20%, N≤0.007%, Ni: 0.20 to 0.50%, Cr: 0.30% or more and less than 0.50%, Mo: 0.30 to 0.50%, Nb: 0.01 to 0.05%, Al: 0.001 to 0.10%, B: 0.0005 to 0.0020%, Ti: 0.003 to 0.050%, V: 0.01 to 0.20%, a total of any one or more elements among Ca, Mg and REM: 0 to 0.025%, and the balance: Fe and impurities, and for which Pcm (=C+(Si/30)+(Mn/20)+(Cu/20)+(Ni/60)+(Cr/20)+(Mo/15)+(V/10)+5B)≤0.30. The steel micro-structure includes, in area %, tempered martensite ≥90%. The tensile strength is 980 MPa or more, and a Charpy impact value at −40° C. using a 2 mm V-notch test specimen is 75 J/cm2 or more.