Hot rolled steel plate for electric resistance welded steel pipe having excellent weldability, and manufacturing method thereof

A hot rolled steel plate for an electric resistance welded steel pipe, the hot rolled steel plate consisting of:

• by wt %, carbon (C):
• 0.05 to 0.14%, silicon (Si):
• 0.1 to 1.0%, manganese (Mn):
• 0.8 to 1.8%, phosphorus (P):
• 0.001 to 0.02%, sulfur (S):
• 0.001 to 0.01%, aluminum (Al):
• 0.1 to 0.3%, chromium (Cr):
• 0.3 to 1.0%, titanium (Ti):
• 0.01 to 0.05%, niobium (Nb):
• 0.025% or less, vanadium (V):
• 0.035% or less, nitrogen (N):
• 0.001 to 0.01%, and the balance of iron (Fe) and inevitable impurities;
• and
• a microstructure comprising:
• a ferrite phase as a matrix phase, a martensite phase, a bainite phase, and a mixture phase composed of a martensite grain and a bainite grain formed inside the martensite grain, wherein the ferrite phase comprises:
• an area fraction of 60 to 85%,
• wherein Mn and Si satisfy the following Relational Expression 1,
• 4<Mn/Si<12 [Relational Expression 1]
• where, Mn and Si refers to a weight content of each element, and
• wherein the microstructure satisfies the following Relational Expression 2,
• SSGM+B/(M+B+SSGM+B)≥0.6 [Relational Expression 2]
• where M, B, and SSGM+B refer to an area fraction of the martensite phase, the bainite phase, and the mixture phase, respectively.