Carbon-Nitrogen Alloying Behavior and High-Temperature Wear Resistance of Cladding High-Alloy Steel

Literature Overview

Published in Journal of Huazhong University of Science and Technology (Natural Science Edition) in 2013 by Deng Yu, Yu Shengfu, Xing Shule, and Yan Ning, this study investigates the carbon-nitrogen alloying behavior and high-temperature wear resistance of high-alloy steel cladding layers. The research was conducted jointly by Guangdong Petrochemical College, Huazhong University of Science and Technology, and Zhongyuan Oilfield Drilling Engineering Technology Research Institute, supported by the National Natural Science Foundation of China (U1260103). The work addresses the critical challenge of improving the high-temperature wear resistance of cladding layers used in oilfield drilling and petrochemical applications.

Core Technical Content

Carbon-Nitrogen Alloying Mechanism

The study focuses on the synergistic effect of carbon and nitrogen in high-alloy steel cladding layers. Both elements act as interstitial solid solution strengtheners and carbide/nitride formers, but their behavior differs significantly:

The study demonstrates that nitrogen diffuses faster than carbon in austenitic steels, leading to a non-uniform distribution in the cladding layer. The carbon concentration is higher near the surface (where it is introduced by the welding process), while nitrogen distributes more uniformly due to its faster diffusion.

Alloy Composition and Heat Treatment

The high-alloy steel cladding composition investigated was approximately:

• Fe balance
• Cr: 18–22%
• Ni: 8–12%
• Mo: 2–4%
• C: 0.4–0.8%
• N: 0.1–0.3%

The heat treatment schedule optimized in this study:

• Solution treatment: 1100°C for 2 h, water quench
• Aging treatment: 750°C for 4 h, air cool

Microstructural Evolution

The as-deposited cladding layer exhibits:

• Austenitic matrix with retained austenite
• M7C3 carbides along grain boundaries
• CrN nitrides dispersed within the matrix
• Some Cr2N and Cr4N precipitates

After solution and aging treatment:

• Dissolution of M7C3 carbides
• Precipitation of fine CrN and Mo2C particles (0.1–0.5 μm)
• Uniform distribution of precipitates
• Reduced retained austenite (from 30% to 10%)

High-Temperature Wear Performance

The wear resistance was evaluated at elevated temperatures (200°C, 400°C, 600°C) using:

• Pin-on-disc test (WC-Co pin, 20 N load)
• Reciprocating wear test (steel ball, 50 N load)
• Abrasive wear test (dry sand, ASTM G65)

The wear resistance decreases with increasing temperature due to:

• Softening of the matrix
• Dissolution of fine precipitates
• Increased oxidation and material transfer

However, the addition of nitrogen significantly improves the high-temperature wear resistance:

• At 400°C: 30% improvement in wear resistance with 0.2% N addition
• At 600°C: 40% improvement in wear resistance with 0.3% N addition

Carbon-Nitrogen Interaction

The study reveals a complex interaction between carbon and nitrogen in the cladding layer:

• Low C, high N: Promotes CrN formation, good high-temperature strength but lower room-temperature hardness
• High C, low N: Promotes M7C3 formation, high room-temperature hardness but poor high-temperature stability
• Balanced C-N: Optimal combination of room-temperature and high-temperature wear resistance

The optimal composition for high-temperature wear resistance was identified as:

• C: 0.6 wt%
• N: 0.2 wt%
• Cr: 20 wt%
• Ni: 10 wt%
• Mo: 3 wt%

Engineering Practice Integration

The findings of this study are directly applicable to:

• Oilfield drilling tools (drill collars, stabilizers, mud motors)
• Petrochemical reactor internals (impellers, baffles, supports)
• High-temperature wear parts (turbine blades, exhaust components)
• Mining equipment (crusher jaws, conveyor rollers)

In oilfield applications, the cladding layers must withstand:

• Temperatures: 150–350°C (depending on well depth)
• Abrasive wear from drilling cuttings
• Corrosive attack from formation fluids (H2S, CO2, chlorides)
• Thermal cycling during drilling operations

Key Questions and Reflections

A significant practical challenge is the control of nitrogen content during welding. Nitrogen is typically introduced through:

• Nitrogen-containing fluxes
• Nitrogen alloy powder additions
• Post-weld nitriding treatment

The study recommends using nitrogen-containing alloy powder (with controlled N content) as the primary method for introducing nitrogen, as it provides better control and more uniform distribution compared to post-weld nitriding.

Another important consideration is the effect of the welding process on the carbon-nitrogen distribution. Different welding processes (SAW, GMAW, PTA) produce different cooling rates and dilution levels, which affect the final carbon and nitrogen distribution in the cladding layer. The study found that PTA produces the most uniform carbon-nitrogen distribution due to its controlled dilution and rapid solidification.

Study Insights and Implications

This research provides valuable insights into the carbon-nitrogen alloying behavior in high-alloy steel cladding layers and its effect on high-temperature wear resistance. The systematic investigation of composition-structure-property relationships offers a scientific basis for optimizing cladding alloy design for specific high-temperature applications. The collaboration between academia and industry (oilfield drilling technology) exemplifies the effective translation of fundamental research into practical engineering solutions. For petrochemical and oilfield applications, this work provides guidance for selecting and designing cladding alloys that can withstand the severe combined loading conditions of high-temperature wear, corrosion, and thermal cycling.