Process Parameter Study for Surfacing 2Cr13 on 38CrMoAl Substrate

Literature Overview

This 2020 paper by Zhao Jiaming et al., published in the Journal of Shenyang Ligong University, Volume 39, Issue 4, pages 27-30, investigates the process parameters for argon arc surfacing (GTAW) of 2Cr13 stainless steel onto 38CrMoAl alloy steel substrates. The authors from Shenyang Ligong University and Shenyang Agricultural University systematically studied the effects of welding current and argon gas pressure on the wear resistance of the surfacing layer, with the application target being automotive engine crankshafts.

Technical Background

Material Selection Rationale

38CrMoAl is a high-strength alloy steel used for automotive crankshafts, characterized by:

• High strength (tensile strength ≥ 980 MPa)
• Excellent fatigue resistance
• Good wear resistance
• Nitriding capability (Al addition promotes AlN formation)
• Typical microstructure: tempered martensite with fine carbides

2Cr13 is a martensitic stainless steel selected for the surfacing layer because:

• High hardness (up to 50 HRC after proper heat treatment)
• Good corrosion resistance (12-14% Cr)
• Excellent wear resistance
• Good hardenability
• Compatible hardness range with the base metal after tempering

The dissimilar metal combination (38CrMoAl + 2Cr13) presents challenges due to:

• Thermal expansion mismatch: Different coefficients of thermal expansion create residual stresses.
• Carbon diffusion: Carbon from 38CrMoAl can diffuse into the 2Cr13 layer, affecting its properties.
• Phase formation: Intermetallic compounds may form at the interface during welding.
• Dilution effects: Base metal dilution affects the composition and properties of the surfacing layer.

Experimental Setup and Parameters

Equipment and Materials

Process Parameter Matrix

Wear Test Conditions

Results Analysis

Optimal Conditions (5 MPa, 130 A)

Suboptimal Conditions (10 MPa, 130 A)

Parameter Effects Analysis

Effect of Welding Current:

• Increasing current from 110 A to 150 A increases heat input, leading to:
• Greater dilution of the surfacing layer by the base metal.
• Coarser microstructure in the weld metal and HAZ.
• Potential for reduced hardness if excessive dilution occurs.
• Increased risk of distortion and residual stress.
• The optimal current of 130 A provides a balance between adequate penetration and controlled dilution.

Effect of Argon Pressure:

• Higher argon pressure (10 MPa vs. 5 MPa) creates:
• Stronger gas flow, which may disrupt the arc stability.
• Increased turbulence in the shielding gas, potentially causing nitrogen pickup or porosity.
• Better slag removal but potentially worse arc confinement.
• The lower pressure (5 MPa) provides adequate shielding without excessive gas dynamics effects.

Microstructural Analysis

SEM Observations

The scanning electron microscopy analysis would reveal:

At optimal conditions (5 MPa, 130 A):

• Uniform distribution of carbides (Cr₇C₃, Fe₃C) in the surfacing layer.
• Fine grain structure in the weld metal.
• Clear and thin transition layer between surfacing and base metal.
• No voids, pores, or microcracks at the interface.
• Good wetting of the surfacing material on the substrate.

At suboptimal conditions (10 MPa, 130 A):

• Gas porosity visible as spherical voids in the weld metal.
• Crater defects at the arc termination point.
• Possible microcracking due to residual stress concentration.
• Potentially coarser microstructure near the surface.

Hardness Distribution

The reported hardness values (3,745.4 HV and 3,651.4 HV) appear exceptionally high for a 2Cr13 surfacing layer. Typical 2Cr13 steel hardness ranges from 40-50 HRC (approximately 400-520 HV). The extremely high values reported may indicate:

1. Measurement at carbide particles: Hardness testing on individual Cr₇C₃ or other hard carbide phases can yield values exceeding 2,000 HV.
2. Localized measurement artifact: The Hv-1000 tester may have been applied to a very small area containing a hard phase.
3. Reporting error or unit confusion: The values may represent a different measurement or scale.
4. Ultrafine microstructure: If the surfacing produced an ultrafine martensitic structure with nanoscale carbides, hardness could be elevated.

For practical purposes, the surfacing layer hardness should be verified using standardized macro-hardness testing (HB or HRC) across the entire layer thickness.

Wear Mechanism Analysis

The wear behavior under the test conditions (900 N, 200 r/min, 300 min) suggests:

• Primary wear mechanism: Abrasive wear from hard carbide particles in the counterface material.
• Secondary mechanism: Possibly adhesive wear at asperity contact points.
• Wear debris: Likely consists of matrix material with embedded carbide particles.
• Wear track morphology: Would show evidence of plowing, micro-cutting, and possible delamination.

The superior wear performance at 5 MPa/130 A is attributed to:

1. Higher hardness: Harder surfaces resist abrasive wear more effectively.
2. Better microstructure: Uniform carbide distribution provides consistent wear resistance.
3. Absence of defects: No porosity or craters to serve as wear initiation sites.
4. Good bonding: Strong interface prevents delamination under load.

Engineering Application to Crankshaft Surfacing

Crankshaft Requirements

Automotive engine crankshafts require:

• Journal surfaces with high hardness and wear resistance.
• Good fatigue strength at stress concentration points.
• Dimensional stability under thermal cycling.
• Corrosion resistance for oil-film environments.

Surfacing Process Integration

For crankshaft production, the surfacing process must be integrated into the manufacturing sequence:

1. Machining: Crankshaft rough machined to near-final dimensions.
2. Heat treatment: Quench and temper to achieve base hardness (typically 28-32 HRC).
3. Surface preparation: Journal surfaces polished to Ra ≤ 0.8 μm.
4. Surfacing: 2Cr13 layer deposited on journal surfaces using GTAW.
5. Post-weld heat treatment: Stress relief and/or tempering to optimize hardness.
6. Final machining: Precision grinding to final dimensions and surface finish.
7. Inspection: Hardness, dimensional, and surface quality verification.

Quality Control Checklist

Study Reflection

This paper demonstrates a systematic approach to process parameter optimization using a well-designed experimental matrix. The selection of 38CrMoAl (a common crankshaft material)