300M钢是国内外航空领域广泛使用的一种中碳低合金超高强度钢，如波音公司和空客公司生产的最新机型波音-787和空客-380的飞机起落架均采用该钢来制造，多年来许多学者对300M钢的组织、性能等方面进行了较全面的研究，而对300M钢的热变形行为研究报道相应比较少。而钢在热变形过程中发生的动态组织变化(动态回复或动态再结晶过程)，将对钢的最终性能产生重要影响，因此，要保证钢在锻造热加工后获得所要求的组织和性能的配合，就要解决钢在高温变形过程中的热加工工艺问题，确定合理的热变形工艺参数，对改善钢的组织及提高钢的性能有重大意义。

　　实验用300M钢的化学成分为(质量分数，%)为：0.40C，0.88Cr，1.84Ni，0.42Mo，1.62Si，0.66Mn，0.08V，0.0024S，0.0048P，0.0008O，0.0019N，余为Fe。试样加工成Φ10mm×15mm的圆柱形压缩试样。在Gleeble-3500热模拟试验机上进行轴向压缩试验。试样以10℃/s的加热速度加热到1423K，保温5min，然后以10℃/s的冷却速度冷却到不同温度后进行变形。变形温度分别为1123、1223、1323和1423K，变形速率分别为0.01、0.1、1和10s-1，最大真应变为1.2，变形后立刻喷水冷却，以便分析其高温组织。

　　在真应变为1.2、温度为1123～1423K、应变速率为0.01～10s-1的条件下，应变速率一定时，300M钢的高温流变应力随变形温度的升高而减小;变形温度一定时，其高温流变应力随应变速率的提高而增大。随变形速率的提高，300M钢发生完全动态再结晶的临界温度也逐渐升高，当变形速率为10s-1时，变形温度高于1423K，才会发生完全动态再结晶。在变形温度为1123～1423K、应变速率为0.01～10s-1、真应变为1.2的条件下，300M钢的热变形激活能为391.51kJ/mol。

超高强度钢300M

Chemistry Data : (化学成分)  
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(主要特点)    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.  
  
Applications (应用范围)   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.  
  
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.  
  
Heat Treatment  (热处理)  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(锻造性能)    No data. The alloy is forgeable - contact the supplier for details.  
  
Hot Working (热工性能)   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.  
  
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  (时效)  Not applicable to this alloy.  
  
Tempering (淬火)  Temper at 600 F to give a nominal 300 ksi strength.  

  
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.