| 摘要 |
PROBLEM TO BE SOLVED: To provide a technology to stably manufacture a refining high tensile strength steel plate excellent in material quality uniformity in a sheet thickness direction.SOLUTION: There is provided a heat treatment method of a refining high tensile strength steel plate to make hardness distribution in a sheet thickness direction of a steel sheet by calculating time change of temperatures of each part in the sheet thickness direction of the steel sheet with a heat conduction calculation in a heat treatment by heating the steel sheet with a heating furnace and extracting with a surface layer part of the steel sheet having higher temperature than an inner of the steel sheet from the heating furnace, dividing the time change of the temperature into time sections, calculating a development type tempering parameter λ by following formulae 1 and 2 from a temperature in such time section T(°C) and length of the time section t(h), predicting hardness of each part in the sheet thickness direction of the steel sheet from a relationship between the development type tempering parameter λ and hardness and setting a heat treatment condition of the heating furnace based on the prediction results. λ=log(10+10+...) Formula 1, λ=log(t)-A/T+50 Formula 2, where A is a constant determined by components of the steel.SELECTED DRAWING: Figure 2 |
