Q620MC straight seam welded steel pipe is a high-strength low-alloy structural steel welded pipe, that is widely used in engineering machinery, mining equipment, bridge construction, high-pressure vessels, and other fields. This steel pipe has become an indispensable and important material in modern industry with its excellent mechanical properties, welding performance, and weather resistance.


First, the material characteristics and standard requirements of Q620MC straight seam welded steel pipe
Q620MC is a low-alloy high-strength structural steel. In its name, "Q" represents yield strength, "620" means the minimum yield strength value is 620MPa, and "MC" indicates that the material is suitable for cold forming. This steel achieves a balance between high strength and good plasticity and toughness by adding trace alloying elements (such as Nb, V, Ti, etc.) and controlling rolling and cooling processes.
According to relevant standards, the main performance indicators of Q620MC straight seam welded steel pipes include:
1. Mechanical properties: yield strength ≥620MPa, tensile strength 700-850MPa, elongation ≥16%
2. Impact toughness: impact energy ≥47J at 0℃
3. Welding performance: carbon equivalent CEV≤0.45%, welding crack sensitivity index Pcm≤0.25%
4. Dimensional accuracy: outer diameter deviation ±0.75%, wall thickness deviation ±10%


Second, the production process of Q620MC straight seam welded steel pipes
The production of Q620MC straight seam welded steel pipes adopts the advanced JCOE forming process (i.e. pre-bending-J forming-C forming-O forming-expansion), and the main process includes:
1. Steel plate pretreatment: Q620MC steel plates produced by the thermomechanical rolling (TMCP) process need to be pre-treated by shot blasting, rust removal, straightening, etc. to ensure that the surface quality reaches Sa2.5 cleanliness.
2. Edge milling: Use a high-precision edge milling machine to process the edge of the steel plate to ensure a groove angle of 30°±5° and a blunt edge height of 1.5-2mm, creating good conditions for subsequent welding.
3. Forming welding:
- Pre-bending: Form a preliminary arc on the edge of the steel plate through multiple progressive bendings
- JCO forming: Use a stepping press to gradually press the steel plate into an open tube
- Seam welding: Use multi-wire submerged arc welding (SAW) for internal and external welds. Typical parameters are: current 600-800A, voltage 28-32V, speed 1.2-1.8m/min
4. Diameter expansion and sizing: Eliminate welding stress through mechanical or hydraulic expansion processes (expansion rate 0.8-1.2%) to improve dimensional accuracy and roundness.


Third, the key technical control points of Q620MC straight seam welded steel pipe
1. Welding process control: Use low-hydrogen welding wire (such as CHW-S3) with neutral flux, and strictly control the interlayer temperature between 150-200℃. For thick-walled pipes (≥20mm), preheating treatment is required (preheating temperature 120-150℃).
2. Residual stress control: By optimizing the expansion process parameters (such as step-by-step expansion, and controlling the expansion speed) and subsequent heat treatment, the residual stress is controlled to less than 20% of the yield strength.
3. Dimensional accuracy control: Use a laser diameter gauge to monitor the pipe diameter in real-time, and cooperate with a hydraulic closed-loop control system to ensure that the finished pipe ovality is ≤0.5%D and the straightness is ≤1.5mm/m.
Fourth, typical application areas of Q620MC straight seam welded steel pipes
1. Engineering machinery:
- Crane boom: Φ219-Φ508mm, wall thickness 12-25mm
- Pump truck boom: Φ168-Φ406mm, wall thickness 8-16mm
- Fatigue life required ≥ 500,000 times, typical service life 8-10 years
2. Mining equipment:
- Hydraulic support column: Φ180-Φ400mm, wall thickness 20-45mm
- Conveyor structure: must meet ISO630 E-level impact requirements
3. Special vehicles:
- Military armored vehicle roll cage: use Φ150-Φ300mm thick wall pipe (10-20mm)
- Fire truck ladder structure: Requires -40℃ impact energy ≥34J


Fifth, the market status and development trend of Q620MC straight seam welded steel pipe
According to industry research data, the market size of Q620MC straight seam welded steel pipe in my country will be about 850,000 tons in 2024. As the equipment manufacturing industry develops towards high-end, the market presents the following trends:
1. Product upgrade:
- Develop Q690MC or even Q890MC products with higher strength levels
- Improve low-temperature toughness (-50℃ impact energy ≥ 60J)
- Develop special pipes resistant to HIC (hydrogen-induced cracking)
2. Process innovation:
- Application of laser-MAG composite welding technology, welding speed increased by 30%
- Intelligent online detection system (AI defect recognition accuracy ≥ 99.5%)
- Green manufacturing process (energy consumption per ton of pipe reduced by 15%)


Sixth, selection and use recommendations
1. Selection principles:
- Select the safety factor according to the working stress state (static load is 1.5-1.8, dynamic load is 2.0-2.5)
- Corrosion environment should consider a 2-3mm corrosion allowance
- The impact test temperature must be specified for use in a low-temperature environment
2. Processing precautions:
- The bending radius during cold bending is ≥ 3 times the pipe diameter
- The welding preheating temperature is 20-30℃ higher than that of conventional Q345
- Avoid long-term heating in the temperature range of 400-600℃


With the advancement of the "dual carbon" strategy, Q620MC straight seam welded steel pipe is developing in the direction of lightweight, long life, and green. In the next five years, it is expected that the demand in the fields of new energy equipment and new infrastructure will maintain an average annual growth of 8-10%, becoming a key basic material for high-end equipment manufacturing. When purchasing, users should focus on the process equipment level, quality assurance system, and engineering application performance of the production enterprise to ensure that the product meets the use requirements of various harsh working conditions.