17-4PH is martensitic precipitation hardening / aging hardening of stainless steel, with high strength and hardness, but also has a very good corrosion resistance. The material has a good processing performance, while a lower temperature to do a heat treatment can be aging hardening.
chemical component%
| C |
Mn |
Si |
P |
S |
Cr |
Mo |
Ni |
| 0.7 |
0.6~0.9 |
0.15~0.4 |
0.035 |
1 |
15~17.5 |
0.15~0.25 |
1.2~1.5 |
Application
17-4PH Widely used in oil field valve parts, chemical treatment equipment, aircraft joints, fasteners, pump shafts, nuclear reactor parts, gears, paper mill equipment, missile joints, jet engine parts.
At temperatures up to 539 ° C, the 17-4PH still exhibits good oxidation resistance. Precipitation hardening of stainless steel if prolonged exposure to the temperature environment will appear to reduce the toughness of the phenomenon. Sometimes using a higher aging temperature, you can reduce the degree of toughness to a minimum. If the maximum temperature is at least 28 ° C lower than the aging temperature, it is feasible to expose to a high temperature for a short period of time.
Corrosion resistance
17-4PH corrosion resistance is better than 400 series stainless steel, for most corrosive substances, 17-4PH tolerance is close to 302 and 304 stainless steel.
The hardening treatment at 552 ° C or higher provides a good resistance to stress corrosion cracking. As the material has good corrosion resistance and high hardness, 17-4PH can also be well tolerated wear and tear corrosion.
To ensure optimum corrosion resistance, the surface of the material should be thoroughly removed from the debris, lubricants, foreign matter, drawing or forging. After the parts are finished, the parts should be cleaned and passivated.
Comparison of corrosion resistance - mils / year
Heat treatment
The solution material (state A) heated to 482 ° C-621 ° C, according to the temperature need to heat 1-4 hours, and then air cooling, can make the material hardening. The following are a variety of heat treatment methods:
State A (solution or annealing): heated at 1038 ° C +/- 14 ° C for 30 minutes, cooled to below 32 ° C, the material can be fully converted to martensite. Materials with a cross-sectional area of less than 76.2 mm can be quenched with a suitable liquid. Materials with a cross-sectional area exceeding 76.2mm should be air-cooled quickly. State A material stress, prone to stress corrosion cracking, should be used after aging hardening.
State H900 (Precipitation or Aging): Heat the solution material at 482 ° C for 1 hour and then air cool.
Status H925, H1025, H1075, H1100, H1150: The solution material is heated at a specified temperature of +/- 8 ° C for four hours and then air cooled.
Status H1150M: The solution material is heated at 760 ° C +/- 8 ° C for 2 hours, air cooled, and then heated at 621 ° C +/- 8 ° C for 4 hours and air cooled.
Aging deformation
17-4 The material undergoes a slight change in size after precipitation hardening. The solid solution material (state A) precipitates hardened to H900, and the material shrinkage is about 0.0004-0.0006 in / in. The solid solution material (state A) precipitates hardened to H1150, and the material shrinkage is about 0.009-0.0012 in / in.
Processing performance
Thermal processing
17-4 stainless steel forging and hot upsetting. After the hot work must be first solution treatment, do precipitation hardening treatment.
forging
Heated to 1177-1204 ° C, kept for 1 hour, and then forged. Temperature below 1010 ° C can not forge. For optimum grain size and mechanical properties, the forging material should be air cooled to below 32 ° C before proceeding with other processes. Forging materials need to be first solution treatment and then hardening treatment.
Cold working
17-4 The degree of cold work is high until the initial value of yield strength.
Machine plus
17-4 of the solid solution and a variety of aging hardening state can be carried out machine. The processing properties of the solid solution are similar to those of 302 and 304. The higher the hardening temperature, the better the additive performance. H1150M machine with the best performance.
welding
17-4 Available gas protection welding and resistance welding. It is not recommended to use oxyacetylene welding because there is a carbon increase during the welding process. If you need to use electrodes, AWS E / ER630 electrode can be used to match the nature of the weld and the properties of the substrate. The solder joint design should avoid stress concentration, such as sharp corners, threads and partial penetration areas. If the welding strength is not demanding, can also use the standard austenitic stainless steel filler.
In general, solid-state materials are easier to weld. If it is expected to produce a high welding stress, it is best to weld the H1150 state of the material. No preheating is required to prevent cracking.
The solid solution material can be directly treated to the desired strength level after welding. However, in order to take into account the best strength, ductility and corrosion resistance, the need for welding parts first solution treatment, and then do the aging. If the welding is over-aging of the material, welding parts must first solution after aging.
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