Research On Ca-treatment Technology Of Cold-heading Steel

Cold forge steel is a kind of special use of steel which can be used to produce the standard part in the room temperature. In the machining process, there would be huge deformation amount of the cold forge steel, and the deformation speed was very quick too. So, the forge steel is required to have the favorable cold forge machining capacity, especial for the impact toughness and deformation ratio. There is high recognition to the production of cold forge steel in many steel corporations, in some way, the quality of cold forge steel show the level of the corporation on production.In present, the most of cold forge steel which is used by domestic standard part producer are import from USA, Japan, Korea, and so on. According to the stationary in 2001, the annual require of cold forge drawing was 100 million ton in China, and the number showed ascend trend. Just in this circs, the research and production of cold forge steel is began in our domestic corporations to replace the import production, and they have gotten some achievement. But there are many problems of the quality of cold forge steel compared with the advance level in foreign, such as CH6A. the main problem is that the surface cracking is relatively severity during the cold forge process, the mechanical property and technical property of cold forge steel are not stabile enough ,and this is badly impact on the quality of production and productivity of cold forge process. Summarizing the experiment of many corporations in domestic, the main reason of this is that the controlling of the inclusion is no good enough. Because the most of cold forge steels are Al-killed steel, Al₂O₃ inclusion will be inevitable found in the steel during Al-killed processing, the cluster Al₂O₃ inclusion which rest in steel could enormously reduce the plasticity, tenacity, weariness intensity and anti-corruption capability of steel, especial, the cluster Al₂O₃ inclusion break the continuity of steel which will lead the cracking during the cold forge processing.Because Ca is a very vivacious element which could react with O and S very easy, Ca could reduce the content of O and S in steel which is harmful to the steel quality, and it could modify the cluster Al₂O₃ inclusion which have the high melting point to the spherical alumina which have the low melting point. Ca-treat could reduce the content of inclusion in steel and control the sharp of inclusion to improve the quality of steel.In present, No.1 Steel Plant of WISCO could product the normal grade cold forge steel, but the production process of high grade cold forge steel, such as CH6A, is still in the research. We must to improve the smelting technique to resolve the quality problem of cold forge steel, such as cold forge cracking and low qualification rate of cold forging. In this paper, the Ca-treat has been researched through the laboratorial research and the production of cold forge steel.1, Through the laboratorial research, we have found the best add amount of the Ca alloy was 0.7721g/kg steel and the best composition of it in laboratory was 18%Ca—82%Fe.2, Through to establishing the heat transfer model and numerical simulation, we have found the melt time of 20%Ca—80%Fe alloy in 1600℃ which is 0.97s. Combining with thepractice of production, we have had the reasonable add speed of the Ca alloy line is a m/s.3 n the result of the thermodynamic calculation and the analysis of production data show that: when T=1600°C and [Al]=0.02⁰.05%, if p/oOJ^^xlO^Tca^OxlO^the Ca-treat could get the perfect effect. To avoid formation CaS at the Ca-treat beginning, the content of sulphur should be lower than 0.009%.4^ The large-sized spherical inclusions which was covered by CaS have being found in the samples which was treated by Ca alloy .We have found another type inclusion —MgOAl2O3. It was combined with the alumina to form the spherical inclusions, whose sizes were larger than 20um. The inclusions like this kind is harmful to the quality of cold forge steel.5 -. Through the theoretical calculation and the analyzing of production data ,and the study of former research, we have analyzed the reasons which was influence the effect of Ca-treat, and we have gotten a series date which was useful to the production.6^ Combined with the practice production , we have made a Ca-treat model:the length ofCa-Fe alloy line Li/m: Li=W(3.054-7633.6[Si]b)the length of Ca-Si alloy line L2/m: L2=W(2.8792+7888.2[Si]b)the model could count the theoretical length of Ca-Fe alloy line and Ca-Si alloy line in the given condition during the low -carbon and low silicon steel production.