Si和Mn含量對超高強度熱成形鋼組織和性能的影響

Si和Mn含量對超高強度熱成形鋼組織和性能的影響Effect of Si and Mn on the microstructure and mechanical properties of ultra-high strength press hardening steel

采用OM、SEM、EBSD和TEM分析技術(shù)，研究了Si、Mn含量對超高強度熱成形鋼在相同的軋制和模擬熱沖壓成形工藝處理后的組織和性能影響。結(jié)果表明，Si、Mn含量對超高強度熱成形鋼熱成形前軋制態(tài)的組織和性能有較大影響，在其它成分相同的情況下，隨著Mn含量由0.57%增加到1.21%，實驗鋼的屈服強度由552 MPa提高到751 MPa，抗拉強度由757 MPa提高到1124 MPa，組織也由貝氏體、鐵素體和珠光體，變成了馬氏體和貝氏體。隨著Si含量由0.25%增加到0.38%，實驗鋼的抗拉強度逐漸升高，屈服強度和伸長率呈波動趨勢。在950 ℃保溫5 min相同的工藝條件下模擬熱沖壓淬火試驗后，四種不同成分實驗鋼的組織均為馬氏體，但馬氏體的精細結(jié)構(gòu)各不相同，平均亞晶粒尺寸大小不一。綜合結(jié)果顯示，含0.34% Si-1.21% Mn的鋼B在950 ℃保溫5 min模擬熱沖壓淬火后的綜合力學性能最優(yōu)，其屈服強度為1161 MPa，抗拉強度為1758 MPa，伸長率為6.5%；熱沖壓成形后的組織為細小的板條馬氏體，馬氏體板條上有大量的位錯，且只有少量的碳化物析出。另外，基于本研究成分設(shè)計的超高強度熱成形鋼，其熱沖壓成形前的組織和性能與熱成形后的力學性能無明顯相關(guān)性，只是最終的馬氏體精細結(jié)構(gòu)略有差別，便于工業(yè)化批量試制零件的性能穩(wěn)定性控制。

It is very important to find out the mechanism of composition in steel. There are many researches which describe the effect of Si and Mn element on the microstructure and mechanical properties of middle Mn steel, TRIP steel and Q&P steel. But fewer studies were focused on the mechanism of Si and Mn content in a press hardening steel. In this work, the microstructures after hot rolled and the fine martensite structure after hot stamping in ultra-high strength press hardening steel (PHS) with different Si and Mn content were studied by OM, SEM, EBSD and TEM. The results showed that there are a great influence of Si and Mn content on the microstructure and mechanical properties of PHS after hot rolled. The yield strength increased from 552 MPa to 751 MPa, the ultimate tensile strength (UTS) increased from 757 MPa to 1124 MPa, the microstructures are different with the Mn content rose from 0.57% to 1.21% of the PHS and the other components remain the same. The UTS of the investigated steels goes up if the Si content goes up from 0.25% to 0.38%, and the yield strength and the elongation show a fluctuation trend. After simulating hot stamping process at 950 ℃ and holding 5 min, the microstructure of the investigated steel with four different components is martensite, but it is different for the fine martensite structure and the average size of sub-grain. Overall consideration, the comprehensive mechanical properties of the steel B with 0.30% C-0.34% Si-1.21% Mn are the most outstanding after hot stamping process by austenitizing at 950 ℃ for 5 min, the yield strength is 1161 MPa, the UTS is 1758 MPa, the elongation is 6.5%. After hot stamping process, the microstructure is fine lath martensite, and there is a large amount of dislocation in the martensite lath, and precipitates a small number of carbide. The ultra-high strength press hardening steels are designed by basing on this work, the mechanical properties before and after hot stamping process is not obvious correlation, it is just a slight difference in martensite fine structure, it is easy to control the performance stability of the mass industrial production.

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