Test material and heat treatment process
The ingot containing 0.117% Nb (mass fraction) was melted in 15 kg medium frequency induction furnace. The chemical composition of the steel was determined by pmi-masterpro mobile direct reading spectrometer. The ingot was homogenized annealed at 1100 ℃ for 2 h, then quenched and tempered according to the process.
After heat treatment, the ingot was processed into a cuboid of 10 mm × 30 mm × 55 mm, and then the metallographic samples were prepared. The corrosive composition was 1 g picric acid + 5 ml hydrochloric acid + 100 ml ethanol solution.
The size of the sample for corrosion resistance test is 10 mm × 10 mm × 3 mm, which is grinded with 200-2000 alumina sandpaper, degreased with acetone, cleaned with deionized water and dried. The electrode material is self-made by the research group: firstly, the bonding point is determined on the back of the sample, then it is fixed by welding with copper wire, and then encapsulated with epoxy resin, only the working face of 10 mm × 10 mm is exposed. Before use, the sealed working electrode is grinded with alumina sandpaper, cleaned with alcohol and deionized water and dried.
In order to reveal the effect of carbide content on mechanical properties and corrosion resistance of steel, the samples after impact test were extracted by electrolysis. The extractant was composed of 16 g citric acid + 12 ml hydrochloric acid + 375 ml distilled water. When extracting, adjust the rated voltage to 15 V, power on for about 10 h, turn off the power, and put the extract in static precipitation and centrifugal drying. 18kwd / max2500v + / PC type X-ray diffractometer (XRD) was used to analyze the dried powder after extraction. The test angle was 30 ° to 90 ° and the scanning rate was 4 (°) / min. The Rockwell hardness was measured by HBRVU-187.5 Bromwell optical hardness tester, and the test force was 1 471 n. The impact toughness was measured by Feitian series metal pendulum impact testing machine. The sample size was 10 mm × 30 mm × 55 mm.