Process Parameter Optimization for Surfacing 2Cr13 on 38CrMoAl Substrate

Literature Overview

This 2020 study published in the Journal of Shenyang Ligong University, authored by Zhao Jiaming, Yue Fengli, Chen Zhuojun, and Chen Bin from Shenyang Ligong University and Shenyang Agricultural University, investigates the GTAW (Gas Tungsten Arc Welding) surfacing process for depositing 2Cr13 stainless steel on 38CrMoAl alloy steel substrates. Published in Volume 39, Issue 4 (pages 27-30, ISSN 1003-1251), this research addresses the practical challenge of improving the wear resistance of automotive engine crankshafts through hardfacing weld overlay.

Core Technical Challenge

The study tackles a significant materials engineering challenge: achieving a high-hardness, wear-resistant surfacing layer on a strength-oriented alloy steel substrate while maintaining adequate metallurgical bonding and avoiding defects. The 38CrMoAl substrate is a precipitation-hardening alloy steel widely used in automotive crankshafts due to its excellent fatigue strength and wear resistance. The 2Cr13 surfacing material is a martensitic stainless steel with good wear resistance and moderate corrosion resistance.

The fundamental challenge lies in the dissimilar metal joining: 38CrMoAl contains aluminum for nitriding response and precipitation hardening, while 2Cr13 contains chromium for martensitic transformation and stainless character. The transition zone between these dissimilar materials is critical for both mechanical performance and defect avoidance.

Experimental Parameters and Test Matrix

Parameter	Range	Test Conditions
Welding process	GTAW (TIG)	WSE-350 welding machine
Welding current	110-150 A	Multiple levels tested
Argon gas pressure	5 MPa, 10 MPa	Two levels compared
Base material	38CrMoAl	Crankshaft alloy
Surfacing material	2Cr13 electrode	Martensitic stainless
Hardness test	Hv-1000 microhardness	Cross-section profiling
Wear test	MM-200 machine	900N load, 200 r/min, 300 min
Microstructure	S-3400N SEM	Surface and cross-section

Results and Process Optimization

The study identifies the optimal process parameters as follows:

Condition	Current	Gas Pressure	Transition Layer	Hardness	Wear Amount	Wear Rate	Defects
Optimal	130 A	5 MPa	0.008 mm	3745.4 Hv	15.6 mg	0.052 mg/min	None
Non-optimal	130 A	10 MPa	0.006 mm	3651.4 Hv	23.3 mg	0.078 mg/min	Porosity, craters

The results demonstrate that the 5 MPa gas pressure condition at 130 A current produces superior results compared to 10 MPa pressure at the same current. The lower gas pressure produces a slightly thicker transition layer (0.008 mm vs 0.006 mm) with higher hardness and significantly better wear resistance. The 10 MPa condition, despite producing a thinner transition layer, introduces porosity and crater defects that compromise the overall quality.

Defect Analysis and Process Understanding

The porosity observed under high gas pressure (10 MPa) can be attributed to several mechanisms:

Excessive argon flow disrupts the molten pool surface stability
Higher gas pressure increases the probability of gas entrapment during solidification
The thinner transition layer under high pressure suggests reduced heat input and faster solidification, which does not allow sufficient time for gas bubbles to escape

The crater defect is a typical GTAW phenomenon associated with the "crater shrinkage" that occurs at the end of the weld. Under high gas pressure, the increased cooling rate exacerbates this shrinkage, creating surface irregularities that serve as stress concentrators and reduce the effective wear-resistant area.

Metallurgical Analysis and Performance Mechanism

The 2Cr13 surfacing layer achieves its high hardness (3745.4 Hv) through martensitic transformation during cooling. The microstructure consists of lenticular martensite with retained austenite and carbide precipitates. The chromium content in 2Cr13 promotes the formation of Cr₇C₃ and Cr₂₃C₆ carbides, which provide the primary wear resistance mechanism through hard phase dispersion strengthening.

The transition layer between 2Cr13 and 38CrMoAl is critical for mechanical integrity. At the optimal condition (5 MPa, 130 A), the 0.008 mm transition layer provides adequate metallurgical bonding without excessive dilution that would compromise the hardness of the surfacing layer. The clear and well-defined transition zone indicates good process control and appropriate heat input management.

Engineering Application and FMEA Perspective

For automotive crankshaft repair and refurbishment, this research provides actionable process parameters that can be directly applied in production environments. Applying a Failure Mode and Effects Analysis (FMEA) to this surfacing process:

Failure Mode	Potential Cause	Effect	Prevention
Porosity	High gas pressure (>10 MPa)	Reduced load-bearing area	Maintain 5 MPa gas pressure
Crater formation	Insufficient arc finishing	Stress concentration	Controlled arc termination
Low hardness	Excessive current (>150 A)	Premature wear failure	Current limit at 130 A
Insufficient bonding	Low current (<110 A)	Spalling during service	Minimum current 120 A
Dilution	Excessive heat input	Reduced surface hardness	Multi-pass with controlled overlap

Study Insights and Practical Implications

This research demonstrates that even in well-established welding processes, systematic parameter optimization can yield significant performance improvements. The finding that lower gas pressure (5 MPa) produces better results than higher pressure (10 MPa) challenges the common assumption that more shielding is always better. In reality, excessive gas flow can disrupt the welding process and introduce defects. For engineers working on surface engineering applications in automotive and heavy machinery, this study provides a clear demonstration of how process parameter interactions must be systematically investigated rather than assumed. The excellent wear performance achieved (0.052 mg/min wear rate) validates the 2Cr13/38CrMoAl combination for crankshaft applications where both wear resistance and fatigue performance are required.