Apparatus for manufacturing compound powder, method of manufacturing iron-boron compound powder by using the apparatus, boron alloy powder mixture, method of manufacturing the boron alloy powder mixture, combined powder structure, method of manufacturing the combined powder structure, steel pipe, and method of manufacturing the steel pipe

[0171]Iron powder having an average particle of 80# to 100# was mixed with boron carbide (B4C) powder having an average particle of 120# or less, which was a boron source material, and Na3AlF6 powder, which was an active agent, to manufacture a mixed powder. An amount of the boron carbide powder was 10 weight %, and an amount of the Na3AlF6 powder was 1 weight % in the mixed powder.

[0172]The mixed powder was loaded into the retort 10 of the apparatus 100 of FIG. 1, and then, the retort 10 was heated at a temperature of 950° C. for 3 hours to boronize iron powder. During heating, the retort 10 was rotated at a rate of 50 rpm.

[0173]When the boronizing was finished, the furnace body 20 was separated from the outer circumference surface of the retort 10, and then, the retort 10 was cooled while rotating, as illustrated in FIG. 3. After the cooling was finished, the powder mixture was unloaded from the retort 10, and then, sieved to divide the powder mixture into the iron-boron compound pow

[0228]78 weight % of the boron iron alloy powder particles having a size of 30 mesh to 100 mesh, 20 weight % of Cr powder having a size of 10 mesh, and 1 weight % of each of KBF4 and AlF3 acting as an active agent were loaded into a retort, and then, the mixture was heated while rotation, and then, maintained at a temperature of 950° C. for 3 hours to perform de-boronizing of the boron iron alloy powder and boronizing of Cr powder, followed by cooling.

[0229]FIGS. 11 and 12 respectively show X-ray diffraction results before and after the de-boronizing and boronizing of the powder mixture. Referring to FIGS. 11 and 12, before the de-boronizing and the boronizing, the powder mixture includes FeB and Cr, and after the de-boronizing and the boronizing, FeB powder is de-boronized and Cr powder is boronized, thereby producing Fe2B and CrB each having a relatively low melting point.

[0230]FIG. 13 shows the cross-section of the de-boronized boron iron alloy powder and EPMA analysis results of th

[0232]90 weight % of waste shot ball formed of carbon steel and 10 weight % of the boron iron alloy powder were mixed, and then, the mixture was heated to de-boronize the ferro-boron and boronize the waste shot ball, thereby manufacturing a powder mixture. 10 weight % borax (Na2B4O710H2O) acting as a flux, was added to 90 weight % of the powder mixture and then, the result was loaded into a mold formed of a carbonaceous material, followed by heating at a temperature of 1250° C. for 10 minutes to manufacture combined powder structure. FIG. 15 shows the micro structure of the combined powder structure. Referring to FIG. 15, the micro structure includes an iron-boron compound (the white region of FIG. 15) and a process solidified structure (the black region of FIG. 15). The combined powder structure was measured by using the Rockwell hardness tester, and the result thereof was a hardness value of HRA 78.