Brief Introduction of High Strength Stainless Steel 1Cr15Ni4Mo3N and 07Cr16Ni6

Detailed Summary on 1Cr15Ni4Mo3N and 07Cr16Ni6 Stainless Steels

This summary covers two types of semi-austenitic precipitation-hardening stainless steels critical for the aerospace industry. Through unique heat treatment processes, they transition from an austenitic state (easy to machine) to a high-strength martensitic state, combining excellent mechanical properties with corrosion resistance.

I. Overview and Common Characteristics

1. Type: Both are semi-austenitic precipitation-hardening stainless steels.

2. Core Property: They are sensitive to heat treatment processes. Their shared characteristics are:

• Solution-treated condition: The microstructure is primarily austenite, offering low hardness and good plasticity, making it easy for cold working and forming.

• Aged condition: After specific solution treatment, cold treatment, and aging (tempering), the microstructure largely transforms into martensite, accompanied by the precipitation of intermetallic compounds for strengthening. This results in very high strength, good toughness, and corrosion resistance.

3. Application Field: Primarily used in the aerospace and aviation industries where material performance requirements are extremely high, often for manufacturing key load-bearing structural components.

4. Governing Standards: Their main technical specifications are defined by Chinese National Military Standards, including GJB 8268-2014 "Specification for Precipitation Hardening Stainless Steel Bars for Aviation" and GJB 7960-2012.

II. Detailed Itemized Summary

(A) 1Cr15Ni4Mo3N Stainless Steel (Old Designation: 13Cr15Ni4Mo3N)

1. Composition Characteristics:

• As indicated by the designation, it contains approximately 15% Chromium (Cr), 4% Nickel (Ni), and is alloyed with 3% Molybdenum (Mo) and Nitrogen (N).

• Molybdenum (Mo) significantly enhances the steel's strength, hardness, and resistance to pitting and crevice corrosion. Nitrogen (N) is also an important element for solid solution strengthening and stabilizing austenite.

2. Performance Characteristics:

• After strengthening via heat treatment, the microstructure largely transforms into martensite, achieving high strength while maintaining good plastic toughness and corrosion resistance.

3. Typical Applications:

• Aviation Industry: Used to manufacture critical load-bearing components such as bolts, landing gear joints, and engine fan shafts.

• Precision Machinery: Used for gears and fasteners requiring high precision and high load-bearing capacity.

4. Standard:

• Its composition and mechanical properties strictly adhere to the GJB 8268-2014 standard.

(B) 07Cr16Ni6 Stainless Steel (Old Designation: 0Cr16Ni6)

1. Composition Characteristics (Key Elements):

• Carbon (C): 0.05% ~ 0.09% (Low carbon content helps with corrosion resistance and weldability)

• Chromium (Cr): 15.5% ~ 17.5%

• Nickel (Ni): 5.0% ~ 8.0%

• Impurity Elements: Strict control of elements like Phosphorus (P) ≤ 0.03%, Sulfur (S) ≤ 0.015%.

• Other Elements: Contains limited amounts of Mo, Cu, Ti, W, V, Nb (Niobium ≤ 0.15%).

2. Microstructural Transformation:

• At Room Temperature (solution-treated): Austenite + a small amount of martensite.

• After Cold Treatment: Microstructure transforms to >90% martensite + a small amount of retained austenite. The high martensite content greatly increases strength, while the retained austenite provides good toughness.

3. Mechanical Properties (After Heat Treatment):

   Property	Value
   Tensile Strength (Rm)	≥ 1180 MPa
   Yield Strength (Rp)	≥ 980 MPa
   Elongation after Fracture (A)	≥ 12%
   Reduction of Area (Z)	≥ 55%
   Hardness (HBW, Annealed)	≤ 302
   Impact Energy (KU2, Room Temperature)	≥ 71 J
   Impact Energy (KV2, -192°C)	≥ 55 J (Per GJB 7960-2012)

4. Heat Treatment Process:

• A specific three-step process:

1. Solution Treatment: (975~1000°C) ±10°C, hold for 1 hour, water quench.

2. Cold Treatment: -70°C ~ -80°C, hold for 2 hours, return to room temperature.

3. Aging (Tempering): 350°C ~ 400°C ±10°C, hold for 1~3 hours, air cool.

5. Key Performance Indicators:

• Excellent Comprehensive Performance: Good cold/hot workability, relatively low notch sensitivity, good low-temperature toughness, and good corrosion resistance.

• Notch Sensitivity: The standard GJB 7960-2012 (where it is also coded S-07) specifies the notch tensile sensitivity coefficient (R_mH/R_m). A coefficient >1 indicates higher notch sensitivity (poorer toughness), while<1 indicates lower sensitivity (better toughness). This steel possesses a relatively low notch sensitivity coefficient.

6. Typical Applications:

• Used for force-bearing components in aircraft engines, bolts, and other parts for aircraft and vehicles operating in atmospheres, acetic acid, and salt media.