Research On Quality Improvement For Forgings In Taiyuan Heavy Industry Casting & Forging Subco

As one of the major products of Taiyuan Heavy Industry Casting & Forging Subco, the heavy forgings are large in dimension, big in weight, many in production cycles. And the preliminary operations are more influential. This paper systematically states the quality improving theory, statistical process control method and the way for quality improving, taking the above-mentioned characteristics of heavy forgings and the major defects found by flaw detection as the entry point. Based on the above-mentioned theory and with the help of technical means, the defected positions of 34CrMo1A rotor forgings have been analyzed by sampling in longitudinal section and cross section through high/low power EM scanning and energy spectrum analysis. Then it is confirmed the inclusions in longitudinal section of the forgings are A-type sulphide inclusions which are distributed strip-like along forging direction. The length of the single strip sulphide is within the scope of 100um .The inclusions in cross section of the forgings are small amount of granular compound inclusions of aluminum oxide and calcium oxide which are distributed separately. The diameter is within the range of 50u?m. For shaft-type forgings, the analysis has been made, taking 42CrMoA roller shafts, the representative heavy forgings made by our company, as the example. Many cracks have been found on the arc surface of the small end after machining. Macroscopic test, chemical composition test, microstructure analysis and SEM analysis test show there is serious spot segregation for macrostructure on the test block in different directions. It is full of big spot segregation between the center part and the surface. And there is dentritic segregation on the test block. The sulphur print level is 4.0. For disc-type forgings, taking 20MnMo tube plate forgings as the example, it is confirmed there are strip-like segregation inside of the forgings through high/low power EM scanning and energy spectrum analysis. Through the above analysis and summary of theoretical analysis for the ways of product quality improving, the measures for improving technology- from improving the purity of liquid steel in the smelting process, improving the design structure of the ingot mould, to improving forging process and strengthen densification, promoting welding of center loose, improving heat treatment process to strengthen uniformity in order to avoid coarse grains as well as for improving management have been obtained. The quality of the forgings has finally been improved.