| "NH4"was a kind of austenitic heat-resistant steel with low nickel, which was developed by Japan in last century. In compare with"Type310SS","NH4"was low cost and better heat-resistant properties. This steel can be used in Chemical Engineering,Furnace and Automobile areas. This paper studied the hot deformation behaviors,high temperature heat resistant properties and strengthen mechanism of"NH4"steel by OM ,SEM,TEM and XRD, throughing heat treatment experimentation,hot simulation experimentation and oxidation experimentation. Getting the following results:Through thermal simulation for"NH4"steel ,Under the strain rate of 0.110s at the temperature range of 900 to 1150℃conditions, the hot deformation activation energy and hot deformation equation was got as follows:The relationship between critical stress for dynamic recrystalization and Zener-Hollomon parameter was determined. (σ|^)c = 24.2ln Z- 810.9The oxide of 1# steel contained more Cerium at 700℃a nd 900℃were composed of two layers. The outer layer was Cr2O3 layer,which is continuum and fine. The main composition of inner layer was SiO2, which is not continuum. At 1000℃, the oxide was a mixture of Cr2O3 and SiO2, the oxide of 2# steel contained less Cerium at 900℃and 1000℃were mainly composed of Cr2O3, including slight SiO2. the oxide is continuum at 900℃, the spalling phenomenon was exist at 1000℃. The heat-resistance property of 1# steel was better than 2# steel."NH4"steel has a nice heat-resistante property, because it contains Ce and enough Cr. The Ce was existed with rare earth sulfide, which can solid sulfur, enhance the adhere force between the oxide and matrix. Cr2O3 was continuum and fine, which can be beneficial for antioxidation properties of"NH4"steel.The main precipitation of"NH4"test steel was M23C6 phase after long time aging. the shape of M23C6 precipitating in grain boundar were short item and thin piece, the size was between 500nm～1.5um. the shape of M23C6 phase precipitating inside the grain was square particle, the size was between 100～600nm.The strengthen of"NH4"steel were solution strengthen and precipitation strengthen. The effect of solution strengthen was attribute to Nitrogen. The effect of precipitation strengthen was attribute to the fine M23C6 phase, which precipitated scattering inside the grain.
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