The microstructure and mechanical properties features of laser welded joints of low-carbon tubular steel

ABSTRACT

Technological modes of laser welding is perfected and structural and phase features of the fusion zones structure (ZC) and thermal influence (ZTI) on low carbon steel tube 10G2FBYu is studied. Martensitic structures, characterized by high gradients of microhardness distribution (up to 500–650 HV) are formed in the welding joint after laser welding. This welding joint structure does not exert influence on the specimens mechanical properties under tension (the level of strength properties is 93–97 % of the base material), however, it leads to unsatisfactory indicators of destruction impact strength (KCV) and cold resistance (KCV^{–40 °С} = 50 J/cm²). After annealing at 600 °C, the martensitic structure in the ZC decomposes into less intense tempering martensite and tempering sorbitol at the ZTI. In such a case the microhardness for samples with a welding joints equalizes to 300 HV, the KCV level in the test interval from +20 °С to – 40 °C rises to 200 J/cm², and Tхv shifts to temperatures below – 60°C. Such characteristics are higher than the requirements of the DNV-OS-F101 standard and speak about the efficiency of the laser welding process for two-phase low carbon steel 10G2FBYu.

KEYWORDS:

• Laser welding
• pipe steel 10G2FBYu
• technological modes
• structural-phase
• structure of the fusion zones and heat influence
• mechanical properties of welded joints