Size distribution of inclusions in 12%Cr stainless steel with a wide range of solidification cooling rates

The effect of solidification cooling rate on the size and distribution of inclusions in 12%Cr stainless steel was investigated. A wide range of solidification cooling rates（from 0.05 to 106 K·s^-1） was achieved using various solidification processes, including conventional casting, laser remelting, and melt spinning. The size and distribution of inclusions in the steel were observed and statistically collected. For comparison, mathematical models were used to calculate the sizes of inclusions at different solidification cooling rates. Both the statistical size determined from observations and that predicted from calculations tended to decrease with increasing cooling rate; however, the experimental and calculated results did not agree well with each other at excessively high or low cooling rate. The reasons for this discrepancy were theoretically analyzed. For the size distribution of inclusions, the effect of cooling rate on the number densities of large-sized（〉 2 μm） inclusions and small-sized（≤ 2 μm） inclusions were distinct. The number density of inclusions larger than 1 μm was not affected when the cooing rate was less than or equal to 6 K·s^-1 because inclusion precipitation was suppressed by the increased cooling rate.

Distribution behavior of inclusions in compact-strip-produced martensitic steel and its influence on mechanical properties

The distribution behavior of inclusions in martensitic steel produced by compact strip production process(CSP-MS)and its influence on mechanical properties were systematically investigated.The inclusions in the CSP-MS specimen are mainly composed of spherical Al_(2)O_(3)-CaO-CaS,MnS with high aspect ratio and small-sized TiN,whereas many coarse cuboidal TiN inclusions do exist in conventional martensitic steel(Con-MS).The high inclusion density of the CSP-MS specimen resulted in lower total elongation and impact toughness,and the MnS inclusions with high aspect ratio led to significantly stronger mechanical anisotropy than that for Con-MS specimen.The in-situ tensile results indicated that when the fracture direction is parallel to MnS direction,the microcracks induced by MnS inclusions tend to propagate into the matrix,leading to the formation of valley-like features,which significantly deteriorate the properties such as the total elongation and impact toughness.The microcracks caused by TiN inclusions are sharper than those caused by spherical Al_(2)O_(3)-CaO-CaS inclusions,and are easy to propagate into the matrix.This work is expected to guide the optimization of the mechanical properties of martensitic steels produced by CSP process and provide a theoretical basis for the CSP process design.

Estimation of maximum inclusion by statistics of extreme values method in bearing steel

A statistic method, statistics of extreme values （SEV）, was described in detail, which can esti mate the size of maximum inclusion in steel. The characteristic size of the maximum inclusion in a high clean bearing steel （GCrl5） was evaluated by this method, and the morphology and corn position of large inclusions found were analyzed by scanning electron microscopy （SEM）. When standard inspection area （S0） is 280 mm2, the characteristic size of the biggest inclusion found in 30 standard inspection area is 23.93 μm, and it has a 99.9% probability of the characteristic size of maximum inclusion predicted being no larger than 36.85μm in the experimental steel. SEM result shows that large inclusions found are mainly composed of CaS, calcium-aluminate and MgO. Compositing widely exists in large inclusions in high clean bearing steel. Compared with traditional evaluation method, SEV method mainly focuses on inclusion size, and the esti- mation result is not affected by inclusion types. SEV method is suitable for the inclusion eval uation of high clean bearing steel.

Effect of electropulsing treatment on solidification behavior of spring steels in a continuous casting mold simulator

An electropulsing-assisted mold simulator technique was developed to investigate the effects of a pulsed electric voltage on the quality of spring steels during continuous casting by analyzing the mold flux film,shell surface profile,shell micro-structure and inclusion distributions.The results revealed significantly increased crystallization fraction of the mold flux film from 61.2%to 75.3%and finer crystalline phase morphology in the case of electropulsing treatment.The surface of the initially solidified shell could be effectively healed,resulting in smoother shell surface profiles with higher pulsed voltage from 0 to 30V.Furthermore,an increase in the pulsed voltage from 0 to 30V resulted in finer dendritic structures during solidification with decreasing secondary dendrite arm spacing from the values of 17.6-32.2 to 9.7-15.0μm in the direction of shell side toward melt side.In addition,an area scan analysis of inclusions in the as-cast spring steel samples showed that the number of MnS inclusions in the size range of 2.0-4.0μm gradually decreased from 836 to 114 and the number of Al2O3 inclusions in the same size range decreased from 144 to 39,as the voltage increased from 0 to 30V.