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住友金属工业公司于94年10月7日声称,开发了用作火力发电锅炉的无缝钢管,具有划时代的高温强度的18—8系奥氏体不锈钢“超304H”,并已投放实际应用.“超304H”是以18%Cr钢为基础,添加了9%Ni、3%Cu、、0.08%N、0.4%Nb的18—8系奥氏体不锈钢,在600℃以下的低温区域,由于氮的固溶强化使抗张强度提高,在600℃以上的高温区域,由于适量添加CU、Nb、N导致富Cu相的微细共格析出,使蠕变断裂强度大幅度提高.由添加Cu产生的延性下降,因复合添加Nb和N使晶粒微细化而获得改善.并且,由于晶粒微细化,能确保具有与18—8系不锈钢中耐蚀性最优良的SUS347HTB钢相同的性能.该钢的化学成分范围(重量%)为:CO.07～0.13,Si≤0.30,Mn≤1.00,P≤0.040.S≤0.010,Ni7.5～10.5,Cr17.00～19.00,Cu2.5～3.5,Nb0.3～0.6,NO.05～0.12.室温拉伸性能为:抗张强度≥588MPa,屈服强度≥235MPa,延伸率≥35%.
Sumitomo Metal Industries Co., Ltd. announced on October 7, 1994 that it has developed a seamless steel tube for use as a thermal power generation boiler and has developed ultra-high-strength 18-8 series austenitic stainless steel “Super 304H” which has been put to practical use. “Super 304H” is 18-8 series austenitic stainless steel with 18% Cr steel added with 9% Ni, 3% Cu, 0.08% N and 0.4% Nb. In the low temperature region below 600 ℃, The solid solution strengthening of nitrogen increases the tensile strength, and the addition of Cu, Nb, and N results in the fine coherent precipitation of the Cu-rich phase in a high temperature region of 600 ° C or higher, resulting in a substantial increase in creep rupture strength. Ductility decreases, the grain refinement is improved by the compound addition of Nb and N. Further, due to the grain refinement, it is possible to ensure the same performance as SUS347HTB steel having the most excellent corrosion resistance in 18-8 series stainless steel. The range of the chemical composition of the steel (wt%) is: CO.07 ~ 0.13, Si≤0.30, Mn≤1.00, P≤0.040.S≤0.010, Ni7.5 ~ 10.5, Cr17.00 ~ 19.00, Cu2.5 ~ 3.5 , Nb0.3 ~ 0.6, NO0.05 ~ 0.12. Tensile properties at room temperature: tensile strength ≥ 588MPa, yield strength ≥ 235MPa, elongation ≥ 35%.