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含钼铁素体不锈钢AISI Type444（化学成分力学性能物理性能）节镍高温汽车用不锈钢
发布人：上海艾荔艾金属材料有限公司
更新时间：2013-08-28
AISI Type 444 is a low-carbon, low nitrogen, ferritic stainless steel that provides pitting and crevice corrosion
resistance superior to most ferritic stainless steels.Applications requiring superior corrosion resistance and resistance to chloride stress corrosion cracking are ideal for this alloy. Current uses include food processing, brewery and wine-making equipment; hot-water tanks and heatexchanger tubing and automotive components.
COMPOSITION %
Carbon 0.025 max.
Manganese 1.00 max.
Phosphorus 0.040 max.
Sulfur 0.030 max.
Silicon 1.00 max.
Nitrogen 0.035 max.
Chromium 17.50 - 19.50
Nickel 1.00 max.
Molybdenum 1.75 - 2.50
Titanium + Columbium
0.20+4 x (C+N) min.–0.80 max.
AVAILABLE FORMS
AK Steel produces Type 444 Stainless Steel in coils and cut lengths in thicknesses 0.010" to 0.090" (0.25 mm to
2.29 mm) and widths up to and including 48" (1219 mm).
SPECIFICATIONS
AK Steel Type 444 Stainless Steel sheet and strip is covered by the following
specifications:
ASTM A 268
ASTM A 240
MECHANICAL PROPERTIES
Typical Mechanical Properties
Elongation
UTS 0.2%YS %in2" Hardness
ksi (MPa) ksi (MPa) (50.8 mm) Rockwell
75 (515) 52 (360) 27 B85
Properties Acceptable for Material
Specification
Elongation
UTS 0.2%YS %in2" Hardness
ksi (MPa) ksi (MPa) (50.8 mm) Rockwell
60 (414) 40 (276) 20 min. B90
min. min. max.
PHYSICAL PROPERTIES
Density, 0.28 lbs/in3
7.75 g/cm3
Electrical Resistivity, microhm-in
(microhm-cm) 70°F (21°C) – 22.50 (57)
Specific Heat, BTU/lb/°F (kJ/kg•K)
32 - 212°F (0 - 100°C) – 0.102 (0.427)
Thermal Conductivity, BTU/hr/ft2/ft/°F
(W/m•K)
at 212°F (100°C) – 15.5 (26.8)
Coefficient of Thermal Expansion,
in/in/°F (µm/m•K)
32 - 212°F (0 - 100°C) – 6.1 x 10-6 (11.0)
铁素体不锈钢具有低成本、低热膨胀率和耐高温氧化的优点，所以铁素体不锈钢已广泛应用于汽车排气系统中。传统的奥氏体不锈钢如AISI304和AISI316L被广泛应用于汽车排气系统的高温端排气歧管中，温度可达到1000℃及以上。近年来，Type444等高温端用铁素体不锈钢已大量替代上述奥氏体不锈钢，主要是由于节镍而降低生产成本，同时相比于奥氏体不锈钢其具有较低的热膨胀系数，更好的耐高温氧化性能和高温热疲劳性能。
宝钢研究院的学者采用增重法研究了排气系统用Type444铁素体不锈钢在1000℃空气中的高温抗氧化性能，并结合X射线衍射（XRD）、扫描电镜（SEM）、能谱分析（EDS）及辉光光谱（GDS）分析技术，对氧化膜的形貌和组成进行了分析。结果表明：Type444铁素体不锈钢在1000℃下连续氧化100h，氧化动力学曲线按照抛物线线型氧化规律变化，氧化激活能为（277.5±10）kJ·mol-1，表面氧化膜由连续致密的Cr2O3组成，具有良好的高温抗氧化性能。铌和钼元素扩散至Fe2(Nb, Mo)Laves相，其氧化物颗粒会充当沉淀物从氧化膜表面逆扩散至基体和氧化膜界面处的孔洞里，从而降低了其在高温下的氧化速率，提高了抗高温氧化性能。