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以20MnK、Q275两种牌号U型钢进行试验，全面探索了U型钢经亚温淬火及自回火后的强韧性。试验表明，经770～820℃水淬＋300℃自回火处理后，Q275U型钢的屈服强度σ0．2≥440MPa；经790～820℃水淬＋300℃自回火后，20MnKU型钢的屈服强度σ0．2≥520MPa。两种钢的屈服强度均比处理前提高50％以上，而屈强比≤0．75，伸长率δ5≥16％，达到国外同类U型钢的力学性能水平。此外，还对U型钢亚温淬火及自回火工艺的可行性及其强韧化机理进行了初步探讨。
With 20MnK, Q275 two types of U-shaped steel test, a comprehensive exploration of U-shaped steel after sub-tempered quenching and self-tempering toughness. The test shows that the yield strength of Q275U steel is σ0.2≥440MPa after water quenching + 300 ℃ self-tempering at 770 ~ 820 ℃. The yield strength of 20MnKU steel after self-tempering at 790 ~ 820 ℃ and 300 ℃ is σ0. 2 ≧ 520 MPa. The yield strengths of the two steels are both increased by more than 50% compared with those before treatment, while the yield strength ratio is less than or equal to 0.75 and the elongation rate is more than or equal to 16%, which meets the mechanical properties of similar U-shaped steels abroad. In addition, the feasibility of sub-temperature quenching and self-tempering of U-shaped steel and the mechanism of its strengthening and toughening were also discussed.