Q-P-T處理貝氏體-馬氏體復(fù)相高強(qiáng)鋼疲勞斷裂特性研究
發(fā)布人：上海艾荔艾合金股份有限公司www.shailiai.cn
更新時間：2016-07-05
對 20Mn2SiCrNiMo 貝氏體/馬氏體復(fù)相高強(qiáng)鋼進(jìn)行淬火-配分-回火(Q-P-T)工藝處理, 并采用緊湊 拉伸試樣進(jìn)行疲勞實驗.
Q-P-T處理貝氏體-馬氏體復(fù)相高強(qiáng)鋼疲勞斷裂特性研究FATIGUE BEHAVIOR OF BAINITE/MARTENSITE MULTIPHASE
HIGH STRENGTH STEEL TREATED BY
QUENCHING–PARTITIONING-TEMPERING PROCESS 對 20Mn2SiCrNiMo 貝氏體/馬氏體復(fù)相高強(qiáng)鋼進(jìn)行淬火-配分-回火(Q-P-T)工藝處理, 并采用緊湊
拉伸試樣進(jìn)行疲勞實驗. 結(jié)果表明, Q-P-T 工藝參數(shù)對貝氏體/馬氏體復(fù)相高強(qiáng)鋼的疲勞斷裂特性具有顯著
影響, 經(jīng)過合理的 Q-P-T 工藝處理的貝氏體/馬氏體復(fù)相高強(qiáng)鋼具有較高的疲勞門檻值(ΔKth=13.2 MPa·m1/2)
及較低的裂紋擴(kuò)展速率. 顯微組織及裂紋擴(kuò)展路徑觀察顯示, Q-P-T 處理的貝氏體/馬氏體復(fù)相高強(qiáng)鋼的顯
微組織包括貝氏體、馬氏體和殘余奧氏體薄膜, 其中“柳葉狀”貝氏體及納米級殘余奧氏體薄膜可以阻礙裂
紋擴(kuò)展, 迫使裂紋轉(zhuǎn)折、分叉或“間斷”, 這是貝氏體/馬氏體復(fù)相高強(qiáng)鋼疲勞斷裂性能改善的主要因素.
Recently, low-cost advanced high strength steels (AHSS) with high toughness and fatigue limit have
been developed in order to ensure the safety and lightweight of the engineering components. As promising candidates for next generation of AHSS, the bainite/martensite multiphase high strength steels exhibit excellent
combination of strength and toughness due to the refined multiphase microstructure and retained austenite films
located between bainitic ferrite laths. The previous works showed that the mechanical properties of
bainite/martensite multiphase steels can be further improved through quenching- partitioning- tempering (Q-P-T)
process. In the present work, the effect of Q-P-T process on the microstructure and fatigue behaviors of steels was
investigated, and the relationship between the microstructure and the fatigue crack propagation was discussed in
detail. Here, a 20Mn2SiCrNiMo bainite/martensite multiphase steel was treated by Q-P-T processes: (1)
quenching to 200 ℃, partitioning at 280 ℃ for 45 min and finally tempering at 250 ℃ for 2 h (QPT200
sample); (2) quenching to 320 ℃, partitioning at 360 ℃ for 45 min and finally tempering at 250 ℃ for 2 h
(QPT320 sample). Microstructure observation showed that the QPT200 sample consisted of leaf-shaped bainite,
martensite and filmy retained austenite (RA), while some blocky martensite/austenite (M/A) islands were
observed in QPT320 sample. The volume fractions of retained austenite in QPT200 and QPT320 samples are 4.5%
and 9.8%, respectively. The fatigue crack propagation rate da/dN and threshold value of fatigue cracking ΔKth
were measured using compact-tensile specimens. The results showed that the Q-P-T process parameters had a
significant influence on the microstructures and fatigue properties of the bainite/martensite multiphase steels. The
bainite/martensite multiphase steel after appropriate Q-P-T treatment (QPT 200 sample in the present work) has
higher ΔKth and lower da/dN, which originates from the resistance on fatigue crack propagation due to the
presence of leaf-shaped bainite and nanometer-sized retained austenite films. Furthermore, although the volume
fraction of retained austenite in QPT320 sample is higher than that in QPT200 sample, the ΔKth of QPT 320
sample is lower than that of QPT200 sample. It is suggested that the effect of retained austenite on the fatigue
behaviors depends on its volume fraction, size and morphology.
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