Effect of N on the Mechanical Properties of the 308 Type Stainless Steel Weld Metals at Elevated Temperatures

Abstract

The creep and tensile properties of 308 type stainless steel weld metals were studied and following results are obtained.
(1) The amount of scatter in measured value of the creep rupture strength at 550°C, 300hr is about 10 kgf/mm², and that of tensile strength at elevated temperature up to 700°C is about 15 kgf/mm² for the standardized 308 type stainless steel weld metals.
(2) As the quantity of N increases the creep rupture strength, the relation between creep rupture strength σc and N content CN can be expressed as follows, σc=A+B log CN
where A is the constant varing witb composition, welding method, coefficient B indicates the mag- nitude of the effect of N for the creep rupture strength. The same statement is true on the relation between tensile strength and N content.
(3) The addition of about 0.1% of V strengthens the effect of N on creep rupture strength.
(4) N decreases the creep rupture elongation. The addition of about 0.1 %. of V controls the effect of N on the creep rupture elongation.
(5) The tensile rupture elongation decreases at temperature range between 20°C and 500°C, and the elongation increases at temperature above 550°C with increasing temperature. The addition of N above 0.078%, controls the decrease of creep rupture elongation at temperature range between 20°C and 500°C, and decrease the elongation above 600°C, for the 308 type stainless steel weld metals.
(6) The quantity of Cr in δ ferrite is 3 % more than that of austenite, and the quantity of Ni in the δ ferrite is 3% less than that of austenite for the 308 weld metal containing 0.01 % N. In the case of the steel containing 0.253 % N, the quantity of Cr in 6 ferrite is 9 % more than that of austenite, and the quantity of Ni in the δ ferrite is 2% less than that of the austenite. The amount of precipitate formed in δ ferrite of the latter steel is less than that in the former δ ferrite.