Effects of MnS on the Heterogeneous Nucleation of Cu Precipitates in Fe-10 and -5mass% Cu Alloys

Abstract

Copper in steel has been thought harmful because of the hot shortness at grain boundaries, but Cu precipitates finely distributed inside of each grain increase the strength. If the problem of hot shortness is solved, scrap recycling will become much easier and even Cu can be used as an important alloying element. It is therefore most important to investigate the behavior of Cu precipitation in Fe-Cu alloys at high temperatures. In this study, in-situ observation of the Cu precipitation on cooling in Fe-10mass%Cu and Fe-5mass%Cu alloys was made using a confocal scanning laser microscope. The precipitates were analyzed by SEM-EDX after in-situ observation experiments.As a result the effect of MnS inclusion on the heterogeneous nucleation of Cu precipitate was made clear. In Fe-10 mass%Cu alloy containing MnS inclusions, the starting temperature of Cu precipitation became higher and its distribution became more uniform than the same alloy without MnS inclusions. In case of Fe-5mass%Cu alloy containing MnS inclusions, some of Cu precipitates appeared in g phase before the g/a phase transformation. In case of the same alloy without MnS inclusions, many fine Cu precipitates appeared in a phase after the g/a phase transformation. The complex precipitate of MnS and Cu was also found indicating that Cu precipitated at MnS inclusion. The reason for these facts was explained by the heterogeneous nucleation theory. The undercooling for the Cu precipitation was estimated to be smaller in the alloy with MnS inclusions than in another case. Based on these results, if the nucleation sites such as MnS inclusions are finely distributed beforehand, the heterogeneous nucleation of Cu precipitates will be accelerated and its distribution will be made very fine.KEY WORDS: in-situ observation; Cu precipitation; MnS inclusions; laser microscope; heterogeneous nucleation.nificantly affects the precipitation behavior. Fe-5mass%Cu alloy and Fe-10mass%Cu alloy were selected in the present study. Figure 1 shows the phase diagram of Fe-Cu-C alloy system. In Fe-10mass%Cu alloys the liquid Cu precipitates appear at 1 526 K in g phase and the g/a phase transformation occurs at 1 130 K in equilibrium state. In Fe-5mass%Cu alloys the solid e-Cu precipitates appear at 1 238 K in g phase and the g/a phase transformation occurs at 1 130 K in equilibrium state. Experimental Methods SamplesAbout 100 g of pure electrolytic iron was melted and alloyed in a tungsten arc furnace under an argon gas atmosphere. The ingot was machined into a disc (4.3 mm in diameter, 2 mm in height) and the surface was mirror polished. The chemical composition of samples is shown in Table 1. Copper content of both samples A and B was the same as about 10 mass% but sample A was without MnS and sample B was with MnS. Copper content of both samples C and D was again the same as about 5 mass% but sample C was without MnS and sample D was with MnS. In order to make clear the effect of MnS on the Cu precipitation, the content of Mn and S in samples B and D was determined to be 0.6...

Evaluation of the Hot Ductility of a C–Mn Steel Produced from Scrap Recycling

“…FeS that could have formed under very high cooling rates during solidification 13,[16][17][18][19] or e-Cu. 20,21) Moreover, 1 100°C leads to a finer grain size (67 mm for the as-cast steel and 55 mm for the as-rolled steel). Therefore, the effect of grain size on the hot ductility will be discussed by the comparison of the hot ductility curves after different reheating treatments.…”

Precipitation Behavior of Copper, Tin and Manganese Sulfide at High Temperature in Fe-10%Cu-0.5%Sn Alloys

“…The principle and the method of operation of the laser microscope have been described in detail elsewhere. 7,[18][19][20][21][22][23][24][25] Fe-10mass%Cu alloys 7,18) and Fe- (Received on August 29, 2005; accepted on October 6, 2005 ) Tramp elements such as Cu or Sn cause a severe hot shortness. Any tramp elements have been rejected and diluted below a certain limit by the use of virgin iron source.…”

“…The manganese (Mn) and sulfur (S) contents are very important and varied from zero to 0.6 % and zero to 0.04 % respectively, given approximately the same Mn/S ratio according to the previous works. 7,18,19) In the previous works Fe-10%Cu alloys were selected so as to investigate the precipitation of liquid Cu in gFe on the basis of the equilibrium phase diagrams of the Fe-Cu binary system. 26) In this study the phase diagram of Fe-0.5mass%Sn-Cu quasi-binary system should be determined.…”

“…In steelmaking process the use of a large amount of virgin iron source is inevitable at any cost to dilute the steel contaminated by tramp elements. Recently, Hasegawa et al 7) has found that MnS precipitates have a good positive effect on the heterogeneous precipitation of Cu in the grains. Therefore it will be expected that steels containing Cu are free from the hot shortness.…”

Dynamic Precipitation Behavior of Secondary M7C3 Carbides in Ti-alloyed High Chromium Cast Iron

“…For instance, Hasegawa et al [18][19][20][21] discussed the in-situ precipitation phenomena in Fe-Cu alloys and Fe-Si alloys by using the ISIJ International, Vol. 53 (2013), No.…”