日本SUS440C（9Cr18Mo）

440C is a high-carbon chromium steel designed to provide stainless properties with maximum hardness. It has been used primarily as a bearing steel, and is used in the hardened plus tempered condition. When heat-treated, Type 440C attains the highest hardness of any stainless stee (about Rockwell C 60)

This stainless steel principally has been used in bearing assemblies, including bearing balls and races. In addition, it should be considered for cutlery, needle valves, ball check valves, valve seats, pump parts, ball studs, bushings, and wear-resistant textile components.

440C resists corrosion in normal domestic environments and very mild industrial environments, including many petroleum products and organic materials.

This grade is used in the hardened plus tempered condition. Optimum corrosion resistance is obtained by hardening from 2000ºF (1093ºC) to ensure better carbide solution.

However, care should be taken to minimize time at 2000ºF (1093ºC) to avoid excessive grain coarsening. For best corrosion resistance, the tempering temperature should be below about 800ºF (427ºC).

For optimum corrosion resistance, surfaces must be free of scale, lubricants, foreign particles, and coatings applied for drawing and heading. After fabrication of parts, cleaning and/or passivation should be considered.

 

 

 

 

For maximum softness, this steel should be heated uniformly to 1550/1600ºF (843/871ºC). Soak and cool very slowly in the furnace. Brinell hardness approximately 223. Intermediate or process annealing treatment-heat uniformly to 1350/1400ºF (732/760ºC). Air cool. Brinell hardness about 255.

 

Heat to 1850/1950ºF (1010/1066ºC); soak; quench in warm oil or cool in air. Do not overheat. When overheated, full hardness cannot be obtained. See comments under corrosion resistance.

 

Heat to 1850/1950ºF (1010/1066ºC); soak; quench in warm oil or cool in air. Do not overheat. When overheated, full hardness cannot be obtained. See comments under corrosion resistance.

 

 

 

Heat to 1850/1950ºF (1010/1066ºC); soak; quench in warm oil or cool in air. Do not overheat. When overheated, full hardness cannot be obtained. See comments under corrosion resistance.

If annealed for maximum softness, this steel can be moderately cold formed or headed.

For most machining operations, this steel cuts best when in the dead soft annealed condition. Because of its high carbon content it machines somewhat like high-speed steel. Because chips are tough and stringy, chip curlers and breakers are important.
研磨和抛光

In cutlery applications, grinding and polishing are very important. 440C works well in these operations but considerable care must be used not to overheat since both the hardness and corrosion resistance may be lowered.

 

Because of its high-hardness capability, this steel is seldom welded. However, if welding is necessary, the parts should be preheated and maintained at about 500ºF (260ºC), welded, and then immediately given a 6-8 hour anneal at 1350/1400ºF (732/760ºC) with a slow furnace cool. The parts should not be allowed to cool below 500ºF (260°C) between welding and annealing. High welding heat inputs should be used. To obtain mechanical properties in the weld similar to those in the base metal, welding consumables of like composition should be considered. Otherwise, AWS E/ER309 might also be considered.