300M鋼是國內外航空領域廣泛使用的一種中碳低合金超高強度鋼，如波音公司和空客公司生產的最新機型波音-787和空客-380的飛機起落架均采用該鋼來制造，多年來許多學者對300M鋼的組織、性能等方面進行了較全面的研究，而對300M鋼的熱變形行為研究報道相應比較少。而鋼在熱變形過程中發生的動態組織變化(動態回復或動態再結晶過程)，將對鋼的最終性能產生重要影響，因此，要保證鋼在鍛造熱加工后獲得所要求的組織和性能的配合，就要解決鋼在高溫變形過程中的熱加工工藝問題，確定合理的熱變形工藝參數，對改善鋼的組織及提高鋼的性能有重大意義。

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　　實驗用300M鋼的化學成分為(質量分數，%)為：0.40C，0.88Cr，1.84Ni，0.42Mo，1.62Si，0.66Mn，0.08V，0.0024S，0.0048P，0.0008O，0.0019N，余為Fe。試樣加工成Φ10mm×15mm的圓柱形壓縮試樣。在Gleeble-3500熱模擬試驗機上進行軸向壓縮試驗。試樣以10℃/s的加熱速度加熱到1423K，保溫5min，然后以10℃/s的冷卻速度冷卻到不同溫度后進行變形。變形溫度分別為1123、1223、1323和1423K，變形速率分別為0.01、0.1、1和10s-1，最大真應變為1.2，變形后立刻噴水冷卻，以便分析其高溫組織。

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　　在真應變為1.2、溫度為1123～1423K、應變速率為0.01～10s-1的條件下，應變速率一定時，300M鋼的高溫流變應力隨變形溫度的升高而減小;變形溫度一定時，其高溫流變應力隨應變速率的提高而增大。隨變形速率的提高，300M鋼發生完全動態再結晶的臨界溫度也逐漸升高，當變形速率為10s-1時，變形溫度高于1423K，才會發生完全動態再結晶。在變形溫度為1123～1423K、應變速率為0.01～10s-1、真應變為1.2的條件下，300M鋼的熱變形激活能為391.51kJ/mol。

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超高強度鋼300M

Chemistry Data : (化學成分)??
Carbon??0.38 - 0.46??
Chromium??0.7 - 0.95??
Iron??Balance??
Manganese??0.6 - 0.9??
Molybdenum??0.3 - 0.65??
Nickel??1.65 - 2??
Phosphorus??0.01 max??
Silicon??1.45 - 1.8??
Sulphur??0.01 max??
Vanadium??0.05 min??
物理特性
Physical Data :???
Density (lb / cu. in.)??0.283??
Specific Gravity??7.83??
Specific Heat (Btu/lb/Deg F - [32-212 Deg F])??0.116??
Melting Point (Deg F)??2590??
Thermal Conductivity??21??
Mean Coeff Thermal Expansion??6.6??
Modulus of Elasticity Tension??29??
Principal Design Features(主要特點)????300M is a low alloy, vacuum melted, steel of very high strength. Essentially it is a modified AISI 4340 steel with silicon, vanadium and slightly greater carbon and molybdenum content than 4340. 300M has a very good combination of strength (280 to 305 ksi), toughness, fatigue strength and good ductility. It is a through hardening alloy.??
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Applications (應用范圍)?? Applications for 300M steel are those that require strength in the 290 - 300 ksi range, such as aircraft landing gear, high strength bolts and airframe parts.??

Machinability (加工性能)?? Machining is best accomplished with the alloy in the normalized or normalized and tempered condition. Final machining to finish tolerances is done by grinding with care due the hardness of the heat treated alloy (Rockwell C 55). It is important to do a stress relief anneal at 550 F after finish grinding.??
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Forming (成形性能)?? Formability by conventional methods is good in the annealed condition. The alloy behaves much like AISI 4340 steel.??

Welding (焊接性能)?? 300M can be welded by fusion methods or by flash resistance welding. Approved procedures must be used for fusion welding, including pre and post-heating practice, because the alloy will air harden due to heat input from welding. Following welding it is essential to re-normalize or re-normalize and temper prior to the final hardening heat treatment.??
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Heat Treatment??(熱處理)??300M must be normalized at 1700 F before hardening. After the normalizing treatment the alloy is hardened by heating to 1600 F and oil quenching. Tempering is then done last.??

Forging(鍛造性能)????No data. The alloy is forgeable - contact the supplier for details.??
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Hot Working (熱工性能)?? No data. Heat input can cause this alloy to air harden. Contact the alloy supplier for information as to the advisability of hot working.??

Cold Working(冷工性能)????In the annealed or normalized condition the alloy has good ductility and can be readily cold worked by conventional methods.??
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Annealing(退火)????Anneal at 1550 F and slow furnace cool at a rate of less than 50 F per hour down to 600 F. From there it may be air cooled.??

Aging??(時效)??Not applicable to this alloy.??
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Tempering (淬火)??Temper at 600 F to give a nominal 300 ksi strength.??

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Hardening????300M hardens from cold working and by heat treatment. See "Heat Treatment" and "Tempering".??

Other Comments????300M may be joined by Nicer brazing, copper brazing and silver brazing.??

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