High-Strength Welded Steel Pipe Cold Cracking Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-strength steel pipes with tensile strengths above 800 MPa face challenges in preventing weld metal cold cracking and maintaining low-temperature toughness, particularly during the seam welding process, as existing methods like preheating, postheating, and altering the Ms point are inefficient or ineffective.
Innovation Solution
A high-strength welded steel pipe is manufactured using double one-layer submerged arc welding on both internal and external surfaces, with specific chemical compositions for the weld metal and base metal, including C, Si, Mn, Ni, Mo, and V, ensuring a CS value of zero or more to stabilize the ferrite phase in the final solidification mode, preventing transverse cracking and enhancing toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If preheating and post heating are performed to prevent weld metal cold cracking, then cold cracking resistance is improved, but production efficiency decreases
Solution Approach 1:
The invention changes the chemical composition parameters of the weld metal, specifically controlling C content at 0.04-0.09%, Si at 0.30-0.50%, Mn at 1.4-2.0%, Ni at 0.9-4.2%, Mo at 0.4-1.6%, and Cr at less than 0.3%, to achieve high cold-cracking resistance without requiring preheating or post heating processes
Solution Approach 2:
The invention extracts and eliminates the need for preheating and post heating processes from the welding procedure by incorporating specific alloying elements into the weld metal composition, thereby maintaining productivity while achieving the desired cracking resistance
2Reliability
If the Ms point is decreased to induce tensile stress relaxation, then cold cracking resistance is improved, but low-temperature toughness decreases
Solution Approach 1:
Instead of changing the Ms point parameter, the invention changes the chemical composition parameters of the weld metal, specifically controlling C at 0.04-0.09%, Si at 0.30-0.50%, Mn at 1.4-2.0%, and adding Ni (0.9-4.2%) and Mo (0.4-1.6%), to simultaneously achieve both cold cracking resistance and low-temperature toughness
Solution Approach 2:
The invention creates a composite microstructure in the weld metal by combining multiple alloying elements (C, Si, Mn, Ni, Mo, Cr) in specific proportions, resulting in a microstructure that possesses both high cold-cracking resistance and excellent low-temperature toughness without needing to lower the Ms point
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 method achieves high cold-cracking resistance and low-temperature toughness without heat treatment, effectively preventing weld metal cracking and maintaining strength above 800 MPa, as demonstrated by the absence of cracks in weld metal and improved Charpy impact values.
Implementation Method 1
stabilize the ferrite phase in the final solidification mode
Implementation Method 2
final solidification mode
Data Source
Figure 1~2
AI summary
A high-strength steel pipe having a tensile strength of 800 MPa or more that includes a weld metal having high cold-cracking resistance and high low-temperature toughness is provided. The high-strength steel pipe is a high-strength welded steel pipe in which the welded steel pipe is manufactured by double one layer submerged arc welding performed on the internal surface and the external surface of a base metal, both the base metal of the welded steel pipe and a weld metal have a tensile strength of 800 MPa or more, the weld metal contains C: 0.04% to 0.09% by mass, Si: 0.32% to 0.50% by mass, Mn: 1.4% to 2.0% by mass, Cu: less than 0.5% by mass, Ni: more than 0.9% by mass but not more than 4.2% by mass, Mo: 0.4% to 1.5% by mass, Cr: less than 0.5% by mass, V: less than 0.2% by mass, and the remainder of Fe and incidental impurities, and the CS values calculated from the weld metal components using the equation CS = 5.1 + 1.4[Mo] - [Ni] - 0.6[Mn] - 36.3[C] are equal to zero or more at both the internal surface side and the external surface side.