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本文在对块规尺寸稳定性进行系统试验过程中获得的初步结果表明:①淬火后经—75℃×1小时冷处理,然后于150℃×3小时回火,这样变温方法能在一两天内模拟出块规数年内的自然时效尺寸变化曲线,从而为建立快速评定块规尺寸稳定性新方法奠定了基础;②通过磁性法与膨胀法相结合证明,回火后施行冷处理没有实际意义。但经150℃回火与120℃长时间时效可分别促使残余奥氏体变达1～1.2%,0.5～1%。③采用860℃×15分淬火——-75℃×60分冷处理——150℃×70分回火(三次)——120℃×48小时时效——精磨——120℃×10小时时效可获0.06(微米/米·年)的尺寸稳定性(硬度在HRC6 64.7～64.9范围内);④磨削后不进行去应力时效会使尺寸膨胀达0.64(微米/米·年);⑤淬火时在马氏体转变区快速冷却会导致前半年内尺寸发生弹性收缩;⑥提高淬火温度不会增加冷处理后残余奥氏体量。但应追加一次回火来降低马氏体正方度,以获得在较低淬火温度下的相同尺寸稳定性。
The preliminary results obtained during the systematic testing of the dimensional stability of block indicate that: ① quenching -75 ℃ × 1 hour cold treatment, followed by tempering at 150 ℃ × 3 hours, so that the temperature change method can be simulated in a day or two The natural aging dimension change curve during the year is laid out, which lays a good foundation for the establishment of a new method for quickly assessing the dimensional stability of block. ② The combination of magnetic method and expansion method proves that it is not practical to apply cold treatment after tempering. However, after aging at 150 ℃ and 120 ℃ for a long time, the retained austenite can reach 1 ~ 1.2% and 0.5 ~ 1% respectively. ③ 860 ℃ × 15 minutes quenching --- 75 ℃ × 60 minutes cold treatment - 150 ℃ × 70 minutes tempering (three times) - 120 ℃ × 48 hours aging - fine grinding - 120 ℃ × 10 hours aging Dimensional stability of 0.06 (μm / m · year) (hardness in the range of HRC6 64.7-64.9); ④ without stress removal after grinding will expand the size of the expansion of 0.64 (μm / m · year); ⑤ quenching Rapid cooling in the martensitic transformation zone will lead to the first half of the size of elastic shrinkage; ⑥ improve the quenching temperature will not increase the amount of retained austenite after cold treatment. However, an additional tempering should be performed to lower the squareness of the martensite to obtain the same dimensional stability at a lower quenching temperature.