Mn-Si系, Mn-Si-Cr系およびMn-Si-Mo系鋼におよぼすTiおよびBの影響

Abstract

Effects of addition of Ti and B on Mn-Si, Mn-Si-Cr or Mn-Si-Mo structural steel were studied in this report III, while effects of B and Mo on Mn-Si and Mn-Si-Cr steel had been studied in the last report II (Tets-to-Hagane, 47 (1961) 4, p. 585-591).There were 18 grades of specimens tested. The 1st group contained 6 grades of Mn-Si steel, the 2nd group contained 7 grades of Mn-Si-Cr steel and the 3rd group contained 5 grades of Mn-Si-Mo steel.All samples were melted with a high-frequency induction furnace and cast into about 7kg ingots, and then forged or rolled down to 16 or 35mm_??_ bars.Specimens were tested under various conditions such as air-cooling or furnace-cooling after heating and quench-and-tempering.Tensile strength, yield strength, elongation and reduction of area were determined by tensile test. Hardness-test and microstructure-tests as well as Jominy-end-quenching test to investigate into hardenability of specimens were also made.The results obtained were summarized as follows:(1) Addition of B to Mn-Si steel containning 0·3% Ti, improved hardness, tensile strength and yield point, and decreased elongation and reduction of area only a little, under the condition of air-cooling or quench-and-tempering at a point higher than 600°C.(2) Effects of adding B to Mn-Si-Cr steel with 0·3% Ti on mechanical properties were not recognized apparently.(3) Addition of B (0·0025-0·0050%) to Mn-Si-Mo steel containning 0·13% Ti was effective on improvement of hardness and tensile strength, while decrease of elongation and reduction of area was slight. This tendency was very evident in the condilion of tempering, especially.(4) Ti should be treated as a deoxidizer or denitrider. From the viewpoint of mechanical properties, Ti content should be less than 0·3% in Mn-Si-Cr and Mn-Si-Mo steels.From the viewpoint of hardenability, Ti content should be less than 0.1% in both Mn-Si steel and Mn-Si-Mo steels.(5) Addition of B improved hardenability of Mn-Si, Mn-Si-Cr and Mn-Si-Mo steels.