Effect of heat treatment on mechanical and corrosion resistance properties of Fe-25Mn-18Cr-3.5Ni-2Al stainless steel
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摘要: 采用拉伸、冲击和电化学测试方法研究了Fe-25Mn-18Cr-3.5Ni-2Al试验钢不同热处理工艺下的性能，通过SEM，EBSD和XRD等分析表明：奥氏体相体积分数随着固溶温度升高逐渐下降，900、950、1000 ℃固溶后，EBSD分析奥氏体相体积分数依次降低至60.2%，48.7%和20.0%，奥氏体由尖锐的鱼骨状转变为孤立的长针状分布在铁素体晶界上，铁素体相含量上升，试验钢的强度、硬度增加，冲击韧性下降，在900~1000 ℃固溶处理后铁素体相含量依次增大，(001)bcc取向逐渐减弱。经过700 ℃回火后易于在α相内出现弥散分布的NiAl纳米颗粒，导致脆性断裂。极化测试得到点蚀电位随固溶温度升高逐渐正移，1000 ℃固溶处理试样在3.5%NaCl极化测试中出现较长的钝化区和二次钝化，Ecorr=−257 mV，Eb=−46.5 mV，兼具较好耐蚀性能与力学性能，推荐作为实际生产热处理温度。Abstract: The properties of Fe-25Mn-18Cr-3.5Ni-2Al test steel under different heat treatment processes were tested by tensile, impact, and electrochemical methods. The SEM, EBSD, and XRD analysis showed that the volume fraction of the austenite phase decreased gradually with the increase of solid solution temperature. After solid solution at 900, 950 ℃, and 1000 ℃, the volume fraction of the austenite phase separated by EBSD decreased to 60.2%, 48.7%, and 20.0%, respectively. Austenite changes from a sharp fishbone shape to an isolated long needle shape distributed on the ferrite grain boundary. With the increase of ferrite phase content, the strength and hardness of the test steel increase, and the impact toughness decreases. After solution treatment at 900−1000 ℃, the ferrite phase content increases, and the orientation of (001)bcc decreases gradually. After tempering at 700 ℃, only α NiAl nanoparticles with dispersed distribution appear in the phase and show a brittle fracture. The polarization test shows that the pitting potential gradually moves forward with the increase of solution temperature. The sample treated at 1000 ℃ has a long passivation zone and secondary passivation in the 3.5% NaCl polarization test. Ecorr=−257 mV, Eb=−46.5 mV, has good corrosion resistance and mechanical properties and is recommended as the actual production heat treatment temperature.
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Key words:
- stainless steels /
- secondary austenite phase /
- brittle fracture /
- pitting corrosion
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图 2 不同固溶温度下力学性能趋势
(a)工程应力应变曲线；(b)冲击韧性；(c)硬度（HB）
Figure 2. The trend of mechanical properties at different solution temperatures
图 3 XRD衍射图谱
(a)固溶态；(b)第二相颗粒
Figure 3. XRD diffraction pattern (a) solid solution, (b) second phase particles analysis
图 4 固溶态组织金相照片
Figure 4. Metallographic photos of solid solution based microstructure
(a) 900 ℃；(b) 950 ℃；(c) 1 000 ℃
图 5 试验料不同固溶温度处理后EBSD测试相比例与取向成像
Figure 5. EBSD analyze phase propotion maps and orientation maps
(a)、(d) 900 ℃；(b)、(e) 950 ℃；(c)、(f) 1 000 ℃
图 6 不同固溶温度处理后试样的冲击断口形貌及EDS
(a)锻态；(b) 900 ℃固溶；(c) 950 ℃固溶；(d) 1 050 ℃固溶； (e)、(f) EDS谱图
Figure 6. Impact fracture morphology and EDS pictures
图 7 回火态应力-应变曲线(a) 及XRD分析(b)
Figure 7. Tempering state stress-strain curves (a), XRD diffraction patterns (b)
图 8 回火处理后试样SEM组织形貌及其EDS
(a) 500 ℃回火；(b) 600 ℃回火；(c) 700 ℃回火 ；(d) 700 ℃回火局部放大区域；(e)、(f) EDS结果
Figure 8. The state microstructures of tempering treatment
图 9 不同固溶温度下极化曲线及其测试后SEM形貌
Figure 9. Polarization curves at different solution temperatures and corrosion test SEM pictures
(a)、(d) 900 ℃；(b)、(e) 950 ℃；(c)、(f) 1 000 ℃
表 1 试验钢化学成分
Table 1. Chemical composition of tested steel
% C Cr Mn Si Ni Al P S Fe 0.022 17.89 25.83 0.23 3.5 2.06 0.006 0.003 余量 
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