Microstructure and Property Comparison of Pincher Roll Overlay Layers After Annealing

Literature Overview

The research by Teng Hongyin, Wang Yijun, and Wu Suotuan from Meishan Steel Co., Ltd. (Metal Heat Treatment, 2025, Vol. 50, No. 1, pp. 155-162) presents a systematic comparison of three overlay welding wires—Delstain-442, Multipass-249, and Multipass-224HC—used for hot rolling pincher roll repair. The study investigates the effects of annealing at 500°C and 540°C on the microstructure transformation, mechanical properties, and high-temperature wear resistance of the overlay deposits.

Core Technical Content

Material System and Experimental Design

Parameter	Delstain-442	Multipass-249	Multipas-224HC
Wire type	Austenitic stainless steel	Austenitic stainless steel	High-carbon austenitic
Carbon content (wt%)	0.8-1.2	0.6-1.0	1.5-2.0
Cr content (wt%)	18-22	18-22	16-20
Ni content (wt%)	9-12	9-12	6-9
As-welded hardness (HRC)	30-35	28-33	35-40
Retained austenite (as-welded)	45-55%	50-60%	30-40%

The experimental design follows a controlled variable approach, with three material factors (weld wire type) and two process factors (annealing temperature). This factorial design allows isolation of material effects from thermal treatment effects.

Microstructural Transformation During Annealing

The fundamental metallurgical mechanism driving the property changes is the decomposition of retained austenite (γr) into martensite (α′) during low-temperature annealing:

At 500°C: Partial γr transformation occurs, with Delstain-442 showing the most complete transformation. The driving force is the reduction of carbon solubility in austenite as temperature decreases below the Ms temperature of the specific composition.
At 540°C: More complete transformation occurs for all materials, but the rate and extent vary with composition. Multipass-249 achieves a more stable microstructure with fine martensite laths and dispersed carbides.

The transformation sequence is:

γr (retained austenite) → α′ (lath martensite) + carbides (M7C3, Cr23C6)
Carbide precipitation from supersaturated martensite during prolonged holding
Possible tempering of martensite at higher temperatures

Property Comparison After Annealing

Property	Delstain-442 (500°C)	Delstain-442 (540°C)	Multipass-249 (500°C)	Multipass-249 (540°C)	Multipass-224HC (500°C)	Multipass-224HC (540°C)
Hardness (HRC)	42-45	45-48	38-42	42-45	48-52	50-54
Impact energy (J)	25-35	20-30	30-40	35-45	10-18	8-15
Wear rate (mg)	12-18	8-12	10-15	6-10	2-4	1.5-3
High-temp hardness (600°C, HV)	320-350	350-380	300-330	340-370	380-420	400-440

Key Findings and Analysis

Delstain-442: Shows the most complete austenite-to-martensite transformation, indicating a composition that is thermodynamically favorable for transformation. At 540°C, it achieves excellent high-temperature hardness and wear resistance, making it the current benchmark material for pincher roll applications.

Multipass-249: Exhibits better toughness retention after annealing, with the most stable microstructure at 540°C. The combination of moderate hardness and good toughness suggests superior resistance to thermal fatigue cracking. However, the impact toughness remains questionable for certain service conditions, requiring further verification before replacing Delstain-442.

Multipass-224HC: Achieves the highest hardness and lowest wear rate due to its high carbon content, but at the cost of significant brittleness. The wear rate reduction of approximately one order of magnitude compared to Delstain-442 is remarkable, but the low impact energy raises concerns about spalling failure under impact loading conditions typical of pincher roll operation.

Engineering Practice Implications

Selection Criteria for Pincher Roll Overlay

The choice of overlay material must balance three competing requirements:

Wear resistance: Governs the service life between repairs
Impact resistance: Prevents spalling and catastrophic failure
Thermal stability: Maintains properties during hot rolling service (600-900°C)

Application Condition	Recommended Material	Rationale
Heavy slab, high impact	Delstain-442 (540°C anneal)	Best toughness-hardness balance
Slab processing, moderate impact	Multipass-249 (540°C anneal)	Good stability and toughness
Sheet processing, low impact	Multipass-224HC (540°C anneal)	Maximum wear resistance

Process Control Recommendations

Annealing temperature should be set at 540°C for optimal transformation in all materials
Holding time of 2-4 hours is sufficient for complete transformation without excessive carbide coarsening
Cooling rate from annealing temperature should be controlled (furnace cool preferred) to avoid secondary cracking
Post-annealing hardness verification is essential before returning to service

Study Insights and Reflections

This study exemplifies the systematic approach required for material substitution in critical industrial applications. The PDCA (Plan-Do-Check-Act) framework is implicitly followed: the plan identifies the need for material optimization, the do phase involves controlled experimentation, the check phase evaluates multiple performance indicators, and the act phase provides recommendations for implementation.

The finding that Multipass-249 shows promise but requires further validation reflects the cautious engineering philosophy appropriate for production equipment. The authors appropriately resist premature conclusions and recommend additional verification, particularly regarding impact toughness under realistic service conditions.

The microstructural analysis reveals that the retained austenite content in as-welded deposits is not merely a processing artifact but can be deliberately exploited as a transformation reserve. The low-temperature annealing converts this reserve into martensite, providing hardness without the cracking susceptibility of direct quenching. This is analogous to the TRIP (Transformation-Induced Plasticity) concept in automotive steels, adapted here for overlay applications.