Austenite-type stainless steel hot-rolling steel material with excellent corrosion resistance, proof-stress, and low-temperature toughness and production method thereof

A process for producing an austenitic stainless hot-rolled steel material having a superior corrosion resistance and a low-temperature toughness, comprising:

• C:
• not more than 0.03 mass %;
• Si:
• more than 0.3 mass % and not more than 1.5 mass %;
• Mn:
• 0.1 to 3.0 mass %;
• P:
• not more than 0.05 mass %;
• S:
• not more than 0.003 mass %;
• Ni:
• 15.0 to 21.0 mass %;
• Cr:
• 22.0 to 28.0 mass %;
• Mo:
• 1.5 to 3.5 mass %;
• N:
• 0.15 to 0.35 mass %;
• Al:
• 0.005 to 0.1 mass %;
• O:
• not more than 0.007 mass %;
• and
• a remnant of the steel material comprising Fe and substantially inevitable impurities and a content of intermetallic compounds contained in the steel material is not more than 0.5 mass %, wherein
• a PI value expressed by the following formula ranges from 35 to 40:
• PI=Cr+3.3(Mo+0.5W)+16N;
• and
• a δ cal value expressed by the following formula ranges from −6 to +4:
• δ cal=2.9(Cr+0.3Si+Mo+0.5W)−2.6(Ni+0.3Mn+0.25Cu+35C+20N)−18, wherein
• a value by each element represents the content of the element expressed in terms of mass %, the process comprising:
• performing a homogenizing-heat treatment on a cast steel or a semi-finished product after a rough hot-rolling processing at a temperature of 1200 to 1300° C. for at least one hour in order to reduce the content of the intermetallic compound in the steel material.