AISI 4130 Steel with Minimum Yield Strength of 75,000 psi for Acidic Service Conditions – 75K Low Alloy Steel Forgings
Scope
1.1 AISI 4130 steel with a minimum yield strength of 75,000 psi for acidic service conditions, including 75K low alloy steel forgings and similar alloy steels. 1.2 This specification covers products in the form of free forging, die forging, open-die forging, bars, and rolled sections.
Requirements
a. Chemical Composition: Table 1 provides the chemical composition limits. The manufacturer should analyze each heat, preferably by sampling from the ladle during casting. Elements should be reported in weight percent. Impurities do not need to be reported but must not exceed a total of 1%.
Table 1:
| Element | Range |
|---|---|
| Min | |
| Carbon | 0.26 |
| Silicon | 0.15 |
| Manganese | 0.40 |
| Chromium | 0.80 |
| Phosphorus | – |
| Molybdenum | 0.15 |
| Sulfur | – |
| Nickel | – |
| Vanadium | – |
| Iron | – |
b. Mechanical Properties: Table 2 lists the mechanical property requirements. Testing should be performed on each heat, and the listed mechanical properties should be reported.
Table 2:
| Mechanical Property | Range |
|---|---|
| Tensile Strength, psi (MPa) | Minimum 95,000 (655) |
| Yield Strength, psi (MPa) 0.2% offset | Minimum 75,000 (517) |
| Elongation, 2″ gauge length | Minimum 18% |
| Reduction of Area | Minimum 35% |
| Brinell Hardness (kg/sq mm) | 197-237 |
c. Welding Rules: Steel production can be through continuous argon-oxygen decarburization (AOD) or vacuum treatment (EFVD) electric furnace processes, vacuum induction melting (VIM), vacuum arc remelting (VAR), or electric slag remelting (ESR).
d. Special Requirements:
- I. Bars: For bars larger than 12″ in diameter before quenching and tempering, they must be cut to appropriate lengths, or hardness testing should be performed at the center, outer diameter, or mid-radius. Testing should be done at least 12″ from the original end of the bar (minimum acceptable value HB 197).
- II. Tubes: For tubes with an outer diameter greater than 12″, quenching and tempering must be performed, or hardness testing should be done at the outer diameter or mid-radius. Testing should be done at least 12″ from the original end of the bar (minimum acceptable value HB 197).
- III. All Products: Should be normalized (N), then quenched (Q) and tempered (T) (N+Q&T), except:
- i. If the initial austenite grain size is not less than 5.
- ii. If the forging ratio is equal to or greater than 4:1.
- iii. If the wall thickness is not more than 3″ for rolled or extruded tubes.
- iv. If the diameter is not more than 8″ for bars.
Table 3:
| Process | Medium | Temperature | Time |
|---|---|---|---|
| Normalizing | Air/Nitrogen | Minimum 1600°F (871°C) | Maximum 0.50HR/inch, at least 1 hour; air cooled to below 400°F (204°C) before further processing |
| Austenitizing | Air/Nitrogen | Minimum 1550°F (843°C) | Maximum 0.50HR/inch, at least 1 hour |
| Quenching | Water | Maximum temperature before quenching 100°F (38°C); maximum temperature after quenching 120°F (49°C); Oxygen or Polymer (see Note 2) | See Note 3 |
| Tempering | Air/Nitrogen | Minimum 1200°F (649°C) | Maximum 0.75HR/inch, at least 1 hour; air cooled gradually to room temperature |
Notes:
- Austenitizing temperature should be lower than normalizing temperature.
- Oil and polymer quenchants should start at a minimum temperature of 50°F (10°C) unless the quenchant manufacturer specifies a lower allowable temperature. Starting temperatures for all products should be recorded.
- Temperatures of oil or polymer quenchants before and after quenching should follow heat treatment standards and ensure complete phase transformation. Actual start and completion times for all products should be recorded.
e. Continuous Furnace Heat Treatment: For bars up to 8″ (203mm) in diameter, continuous furnace heat treatment may replace conventional batch heat treatment. Parameters in Table 4 must be followed and reported according to APMS-010 requirements.
Table 4:
| Parameter | Value |
|---|---|
| Minimum temperature of bars in the final zone of the austenitizing furnace | 1525°F (829°C) |
| Minimum time in the austenitizing furnace | 5 minutes (see Note 4) |
| Minimum temperature of bars in the final zone of the tempering furnace | 1200°F (649°C) |
| Minimum time in the tempering furnace | 5 minutes (see Note 4) |
| Maximum temperature of quenching liquid | 120°F (49°C) |
Note 4: The continuous furnace operates through several zones with different temperatures. The temperature of the austenitizing furnace zone should be selected to achieve full austenitization within a relatively short time. Temperatures in the tempering furnace zones should also achieve the desired temper effect within a relatively short time. The duration spent in the austenitizing and tempering furnaces depends on the furnace length and speed. Different diameter bars will have different speeds. Adequate time should be allowed in each furnace to obtain the required mechanical properties equivalent to those achieved with conventional quenching and tempering treatments.
f. Alternate Heat Treatment: For bars up to 4″ (102mm) in diameter, alternate heat treatment can replace conventional bath heat treatment. Parameters in Table 5 must be followed and reported according to APMS-010 requirements.