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Effect of Tempering Temperature on Microstructure and Mechanical Properties of Steel Containing Ni of 9%

ZHAO Xiqing , PAN Tao , WANG Qingfeng , SU Hang , YANG Caifu , YANG Qingxiang

钢铁研究学报(英文版)

Mechanical properties of quenching, intercritical quenching and tempering (QLT) treated steel containing Ni of 9% were evaluated from specimens subject to various tempering temperatures. The detailed microstructures of steel containing Ni of 9% at different tempering temperatures were observed by optical microscope (OM) and transmission electron microscope (TEM). The volume fraction of austenite was estimated by XRD. The results show that high strength and cryogenic toughness of steel containing Ni of 9% are obtained when the tempering temperature are between 540 and 580 ℃. The microstructure keeps the dual phase lamellar structure after the intercritical quenching and there is cementite created in the Nirich constituents when tempering temperature is 540 ℃. When tempering temperatures are between 560 and 580 ℃, the reversed austenites (γ′) grow up and the dual phase lamellar structure is not clear. The γ′ becomes instable at 600 ℃. When tempered at temperature ranging from 500 to 520 ℃, the increase of dislocation density in the lamellar matrix makes both tensile strength and yield strength decrease. When tempered at 540 ℃ and higher temperature, the yield strength decreases continuously because the C and alloying elements in the matrix are absorbed by the cementite and the γ′, so the yield ratio is decreased by the γ′. There are two toughness mechanisms at different tempering temperatures. One is that the precipitation of cementite absorbs the carbon in the steel which plays a major role in improving cryogenic toughness at lower temperature. Another is that the γ′ and the purified matrix become major role at higher tempering temperature. When the tempering temperature is 600 ℃, the stability of γ′ is decreased quickly, even the transformation takes place at room temperature, which results in a sharp decrease of CharpyV impact energy at 77 K. The tempering temperature range is enlarged by the special distribution of cementite and the lamellar structure.

关键词: steel containing Ni of 9% , tempering temperature , cementite , reversed austenite , cryogenic toughness

回火温度对Q960级高强结构钢组织及力学性能的影响

卢峰 , 康健 , 王超 , 王昭东 , 王国栋

钢铁

以屈服强度960MPa级高强调质结构钢板开发为目标，研究了在相同轧制及淬火条件下，回火温度对试验钢显微结构及力学性能的影响。结果表明：随回火温度的升高，试验钢强度下降，韧塑性总体上呈现升高趋势，其中在300~450℃范围内出现一个韧塑性能的恶化区。当回火温度为600℃时，试验钢呈回火索氏体组织，屈服强度为1030MPa，抗拉强度为1080MPa，伸长率为15.9%，-40℃冲击功达144J，各项指标均满足国标GB/T 16270—2009要求。并对试验钢的拉伸力学性能进行了探讨。

关键词: 高强钢 , tempering temperature , quenching and tempering , microstructure , mechanical property

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