| 摘要 |
PURPOSE:To obtain an abrasion resistant steel plate of fine crystal grains and superior toughness by hot rolling a slab to intermediate thickness steel plates and carburizing these with the carburizers interposed between the plates then hot rolling down to product sizes and hardening the plates under specific conditions. CONSTITUTION:Continuously cast or bloomed slabs are hot-rolled to intermediate thickness steel plates, and plural sheets are superposed means of carburizers added with accelerators. The spaces between the opposite surfaces are hermetically closed with fire bricks, etc. These are heated for 5-15hr at 900-1,300 deg.C in a furnace, whereby the plates carburized on one or both surfaces are obtained. Following this, these are subjected to secondary hot rolling down to product sizes, after which they are immediately cooled down to 600-400 deg.C at >=30 deg.C/sec cooling rate, and are thereafter slowly cooled. Here, if the carburizing temp. is below the lower limit, a long time is required, and above the upper limit, the formation of coarse crystal grains occurs. The carburization time below the lower limit leads to insufficient carburization depth and that at the upper limit to the saturation of effect. In secondary rolling, the structure is made much finer, and the toughness better. The surface hardness is much improved by the cooling. The cooling temp. in excess of the upper limit results in imperfectly hardened structure and that below the lower limit in insufficient slow cooling owing to tempering effect. |
