Steel Plate Heat Treatment for Soft-Region Shape Accuracy
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Solution Overview
Problem
The existing method for producing steel plate members with hard and soft regions experiences degradation in dimensional accuracy due to thermal deformation during tempering, making it difficult to achieve precise dimensions.
Innovation Solution
A method involving hot press forming, where the steel plate is quenched above the austenite transformation finish temperature and cooled rapidly, followed by a tempering step where only a second region is reheated above the austenite transformation start temperature without reheating the first region, allowing for slower cooling and shape correction within a specific temperature range to form a hard martensite region and a soft ferrite/pearlite region, thereby improving dimensional accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the steel plate member is reheated to a temperature higher than A3 for tempering, then the soft region can be formed, but thermal deformation occurs causing degradation in dimensional accuracy
Solution Approach 1:
The patent applies local quality by reheating only the second region (soft region) to a temperature between A1 and A3, while keeping the first region (hard region) at a lower temperature. This localized heating approach allows the soft region to be formed without subjecting the entire steel plate member to high temperatures that would cause thermal deformation and dimensional accuracy degradation.
Solution Approach 2:
The patent changes the temperature parameter from the conventional A3 or higher to a lower range between A1 and A3 for the tempering process. This parameter change enables the formation of the soft region containing ferrite and pearlite while avoiding the thermal deformation that occurs at higher temperatures, thus maintaining dimensional accuracy.
2Manufacturing precision
If the steel plate member is corrected after tempering, then dimensional accuracy can be improved, but it is difficult to sufficiently improve the accuracy
Solution Approach 1:
The patent performs preliminary action by controlling the tempering temperature to be between A1 and A3, which prevents excessive thermal deformation from occurring in the first place. This preliminary control of heating temperature makes subsequent correction easier and more effective, as the dimensional deviations are minimized before correction is attempted.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively suppresses dimensional degradation by allowing for precise shape correction of the soft region with minimal power, enhancing the accuracy and strength of the steel plate member while maintaining energy efficiency.
Implementation Method 1
heating the steel plate member to a temperature higher than an austenite transformation finish temperature A3 and subsequently cooling the steel plate member at a cooling rate faster than an upper critical cooling rate
Implementation Method 2
reheating a second region of the steel plate member to a temperature higher than an austenite transformation start temperature A1 without reheating a first region of the steel plate member after quenching and subsequently cooling the steel plate member at a cooling rate slower than a lower critical cooling rate, in which a hard region containing martensite is formed in the first region and a soft region containing ferrite and pearlite is formed in the second region
Implementation Method 3
there is a problem that the accuracy of the dimensions in the steel plate member is degraded due to thermal deformation based on a temperature difference between the heated part (the soft region) and the non-heated part (hard region) at the time of tempering
Data Source
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AI summary
A method for producing a steel plate member (SPM) (10), including: a quenching step for heating the SPM to a temperature higher than an austenite transformation finish temperature A3 and subsequently cooling the SPM at a cooling rate (CR) faster than an upper critical CR; and a tempering step for reheating a second region (12) of the SPM to a temperature higher than an austenite transformation start temperature A1 without reheating a first region (11) of the SPM after quenching and subsequently cooling the SPM at a CR slower than a lower critical CR. In the cooling process of the tempering step, the shape of the second region is corrected in a temperature range from a temperature equal to or lower than A1 to a temperature equal to or higher than a temperature at which transformation into ferrite and pearlite is finished while maintaining the CR slower than the lower critical CR.