The effect of W on mechanical properties of 12% Cr-W-V-Nb heat resistant steel at high temperatures and room temperature is reported.The experimental results indicated that if the W content was about 2.2—3.0 wt-%,the...The effect of W on mechanical properties of 12% Cr-W-V-Nb heat resistant steel at high temperatures and room temperature is reported.The experimental results indicated that if the W content was about 2.2—3.0 wt-%,there was no obviously change of R.T.tensile strength, but impact toughness decreased with the rise of W content.On the other hand,the increase of W content enhanced the short time stress rupture strength,but did not for the long time one. The increase of W have two effects on the precipitation behavior,promoting Laves formation of type Fe_2W,increasing the precipitated phase amount and speeding up the coarsening pro- cess of precipitated phase at high temperatures.The effect of W on the mechanical properties is closely associated with precipitation behaviors.When the rupture life is short,there has no enough time to coarsen the precipitated phases,so the increase of precipitated phases results in strengthening effect,i.e.the W increases the high temperature strength.After prolonged expo- sure,the evident coarsening took plaee,that decreased the effect of precipitation.展开更多
In the last three decades new stronger modified 9%Cr steels have been introduced in new power plants with steam parameters up to 300 bar(1 bar =10~5 Pa) and 600℃. In order to further increase the steam parameters of ...In the last three decades new stronger modified 9%Cr steels have been introduced in new power plants with steam parameters up to 300 bar(1 bar =10~5 Pa) and 600℃. In order to further increase the steam parameters of steel based power plants up to a target value of 650℃/ 325 bar it is necessary to double the creep strength compared with todays strongest 9%Cr steels,and at the same time the resistance against steam oxidation must be improved by adding 12%Cr to the steel. However,so far all attempts to make stronger 12%Cr steels have been unsuccessful because the high chromium content introduced severe microstructure instabilities in the tested steels.Recently,it was found that the microstructure instabilities in 11%- 12%Cr steels can be explained by the precipitation of coarse Cr(V,Nb)N Z-phases, which dissolve fine(V,Nb)N nitrides. A new possibility to use the Z-phase for strengthening of 12%Cr steels has been identified,and the development of stable strong martensitic 12%Cr steels based on this concept is expected to allow the construction of 325 bar/ 650℃steam power plants all based on steel.展开更多
文摘The effect of W on mechanical properties of 12% Cr-W-V-Nb heat resistant steel at high temperatures and room temperature is reported.The experimental results indicated that if the W content was about 2.2—3.0 wt-%,there was no obviously change of R.T.tensile strength, but impact toughness decreased with the rise of W content.On the other hand,the increase of W content enhanced the short time stress rupture strength,but did not for the long time one. The increase of W have two effects on the precipitation behavior,promoting Laves formation of type Fe_2W,increasing the precipitated phase amount and speeding up the coarsening pro- cess of precipitated phase at high temperatures.The effect of W on the mechanical properties is closely associated with precipitation behaviors.When the rupture life is short,there has no enough time to coarsen the precipitated phases,so the increase of precipitated phases results in strengthening effect,i.e.the W increases the high temperature strength.After prolonged expo- sure,the evident coarsening took plaee,that decreased the effect of precipitation.
文摘In the last three decades new stronger modified 9%Cr steels have been introduced in new power plants with steam parameters up to 300 bar(1 bar =10~5 Pa) and 600℃. In order to further increase the steam parameters of steel based power plants up to a target value of 650℃/ 325 bar it is necessary to double the creep strength compared with todays strongest 9%Cr steels,and at the same time the resistance against steam oxidation must be improved by adding 12%Cr to the steel. However,so far all attempts to make stronger 12%Cr steels have been unsuccessful because the high chromium content introduced severe microstructure instabilities in the tested steels.Recently,it was found that the microstructure instabilities in 11%- 12%Cr steels can be explained by the precipitation of coarse Cr(V,Nb)N Z-phases, which dissolve fine(V,Nb)N nitrides. A new possibility to use the Z-phase for strengthening of 12%Cr steels has been identified,and the development of stable strong martensitic 12%Cr steels based on this concept is expected to allow the construction of 325 bar/ 650℃steam power plants all based on steel.
