I. Product Introduction

The performance and service life of rolling mill bearings depend to a large extent on the quality of materials and the level of control over heat treatment processes. Under the heavy loads, impact, high temperature and alternating stresses of mill operation, material purity, structural uniformity and hardness distribution directly determine whether bearings can achieve their design service life. NMT has established systematic technical specifications and quality control systems for the material selection and heat treatment processes of rolling mill bearings.

 

Material System: NMT selects different grades of bearing steel according to operating conditions. Conventional hot and cold rolling conditions use GCr15 high-carbon chromium bearing steel, processed through vacuum degassing and electroslag remelting double refining. High-temperature conditions (operating temperatures above 200°C) use M50 high-temperature bearing steel or M50NiL material, with special thermal stabilization treatment. For corrosive media environments, corrosion-resistant bearing steel with special alloying treatment is selected.

 

Heat Treatment Processes: NMT adopts differentiated heat treatment process solutions according to bearing type, size and operating conditions. Controlled-atmosphere quenching, surface carburizing and quenching, and induction hardening are the main process routes. Through precise control of heating temperature, holding time, cooling rate and tempering processes, bearings achieve a “high surface hardness, high core toughness” structure.

 

II. Core Product Advantages

冶炼 Control of High-Purity Materials: NMT implements strict quality control over the冶炼 process of bearing steel. Vacuum degassing is used to remove gases and harmful elements from molten steel, and electroslag remelting (ESR) secondary refining further reduces non-metallic inclusion content and size. For more demanding conditions, vacuum induction melting (VIM) and vacuum arc remelting (VAR) processes are used to reduce oxide inclusions in the steel to extremely low levels. Improved material purity directly extends bearing rolling contact fatigue life.

 

Process Control of Precision Heat Treatment: NMT uses controlled-atmosphere heat treatment equipment to ensure no decarburization or oxidation on bearing surfaces during quenching. Quenching temperature, holding time, cooling medium temperature and circulation rate are monitored and recorded throughout. For carburizing and quenching processes, carburized layer depth and carbon concentration gradient are precisely controlled to ensure hardened layer depth and hardness distribution meet design requirements. Tempering processes relieve quenching stress, stabilize structure and ensure dimensional stability during bearing use.

 

“Hard Surface, Tough Core” Structural Design: NMT rolling mill bearings achieve a uniformly thick high-hardness hardened layer (HRC60-64) on raceway surfaces through surface carburizing or induction hardening, while the core maintains high toughness. This structure enables bearings to resist indentation and spalling on the surface while the core absorbs impact energy under impact loads. For hot rolling conditions, NMT uses materials with special thermal stabilization treatment, controlling retained austenite content at low levels to maintain dimensional stability through repeated thermal cycling.

 

Matching of Materials to Operating Conditions: NMT selects appropriate material grades and heat treatment solutions according to specific mill operating conditions. Hot roughing mill conditions (high temperature, heavy loads, impact) use thermally stabilized high-temperature bearing steel or GCr15 material with carburizing and quenching. Cold rolling mill conditions (high precision, high speed) use GCr15 material with precision controlled-atmosphere quenching for better precision retention. Continuous caster conditions (low speed, heavy loads, water spray) use corrosion-resistant bearing steel or surface-passivated GCr15 material.

 

Completeness of Quality Inspection: NMT performs complete quality inspection on each batch of materials and each heat treatment furnace load. Inspection items include chemical composition analysis, non-metallic inclusion rating, carbide unevenness inspection, surface hardness and core hardness testing, hardened layer depth measurement and metallographic structure inspection. Inspection data for each material batch is traceable, ensuring consistent material and heat treatment quality.

 

III. Typical Application Scenarios

Material and Heat Treatment Solutions for Hot Roughing Mill Bearings——Hot roughing mill bearings withstand high-temperature radiation, thousands of tons of rolling force and frequent impact during billet biting. NMT selects GCr15 material processed through vacuum degassing and electroslag remelting double refining, with surface carburizing and quenching. Carburized layer depth is controlled at 3-5mm, surface hardness HRC60-64, core hardness HRC35-45. Materials undergo special thermal stabilization treatment with retained austenite content controlled at low levels, maintaining dimensional stability at operating temperatures of 150-250°C.

 

Material and Heat Treatment Solutions for Hot Finishing Mill Bearings——Hot finishing mills operate at relatively high speeds, with significant loads and continuous water spray. NMT selects GCr15 material with controlled-atmosphere quenching. After quenching, raceway surface hardness reaches HRC60-64 while the core maintains sufficient toughness. Materials undergo stabilization tempering to maintain structural stability through repeated thermal cycling.

 

Material and Heat Treatment Solutions for Cold Rolling Mill Bearings——Cold rolling mills require high precision retention from bearings. NMT selects high-purity GCr15 material with precision controlled-atmosphere quenching and low-temperature tempering. Quenched structures are fine and uniform, with retained austenite content controlled at low levels to ensure dimensional stability and precision retention during high-speed operation.

 

Material and Heat Treatment Solutions for Sendzimir Mill Bearings——Sendzimir mill bearings承受 high loads and high speeds in compact spaces. NMT selects high-purity materials with precision heat treatment to ensure material consistency and heat treatment uniformity within matched bearing sets. Carburized layer depth and hardness distribution are precisely controlled to meet the dual requirements of high precision and high load capacity.

 

IV. Quality Assurance

Incoming Material Inspection: Each batch of bearing steel material undergoes complete incoming inspection upon arrival at the NMT factory. Inspection内容包括 spectral analysis of chemical composition, microscopic rating of non-metallic inclusions, metallographic inspection of carbide unevenness and acid etching inspection of macrostructure. Inspection data is compared and verified against material certificates to ensure materials meet procurement technical standards.

 

Heat Treatment Process Control: NMT's heat treatment equipment is equipped with advanced process control systems, with quenching temperature controlled within ±5°C and holding time precisely set according to process cards. Quenching medium temperature and circulation rate are continuously monitored. Each heat treatment furnace load is accompanied by complete process records, including temperature curves, time parameters and equipment operating status.

 

Metallographic and Hardness Inspection: Each heat treatment batch undergoes metallographic inspection and hardness testing. Metallographic inspection includes martensite structure grade, retained austenite content and carbide distribution. Hardness testing includes surface hardness and core hardness, with test positions distributed according to standard requirements. Hardened layer depth is measured by microhardness method to ensure design requirements are met.

 

Dimensional Stability Verification: For bearings that have undergone thermal stabilization treatment, NMT performs dimensional stability verification. After multiple thermal cycles at simulated operating temperatures, key dimensional changes are measured to confirm material structure remains stable through temperature cycling.

 

Traceability Management: The material furnace number, heat treatment furnace batch, process parameters and inspection data for each bearing set are recorded and linked to the bearing factory serial number, achieving full traceability of materials and heat treatment processes.

 

V. Product Range

NMT offers the following material and heat treatment related product solutions for steel metallurgical rolling equipment:

 

GCr15 Standard Heat Treatment Solution: Suitable for conventional hot and cold rolling conditions. Vacuum degassing + electroslag remelting double refined material, controlled-atmosphere quenching + tempering, surface hardness HRC60-64.

 

GCr15 Carburizing and Quenching Solution: Suitable for heavy-load impact conditions such as hot roughing mills. Surface carburizing + quenching + tempering, carburized layer depth 3-5mm, surface hardness HRC60-64, core toughness retained.

 

M50 High-Temperature Bearing Steel Solution: Suitable for hot rolling conditions with operating temperatures above 200°C. Special thermal stabilization treatment maintains dimensional stability and hardness retention at high temperatures.

 

Corrosion-Resistant Bearing Steel Solution: Suitable for corrosive media environments (cold rolling emulsion, continuous casting cooling water, etc.). Special alloying treatment or surface passivation treatment resists chemical attack.

 

Sendzimir Mill Precision Heat Treatment Solution: Suitable for high-precision Sendzimir mill bearings. Same furnace number for material and same heat treatment batch within matched sets, ensuring material consistency and heat treatment uniformity.

 

VI. Brand Strength

NMT has accumulated sustained technical experience and data foundations in rolling mill bearing materials science and heat treatment processes.

 

Accumulated Experience in Material Selection: Based on different mill types and operating conditions, NMT has accumulated practical experience in material grade selection, purity requirements and heat treatment solution matching. From GCr15 to M50, from standard quenching to carburizing and quenching, NMT can recommend suitable material and heat treatment combinations according to users' specific operating conditions.

 

Continuous Optimization of Heat Treatment Processes: Based on post-heat-treatment quality inspection data and feedback on actual bearing service life, NMT continuously optimizes heat treatment process parameters. Quenching temperature, holding time, cooling rate, tempering temperature and time are continuously adjusted on the basis of long-term data accumulation to make heat treatment quality more stable.

 

Material Perspective in Failure Analysis: In bearing failure analysis, NMT emphasizes investigation from the material and heat treatment perspective. Whether non-metallic inclusions exceed standards, whether hardened layer depth is insufficient, whether retained austenite content is too high, whether inadequate tempering causes dimensional instability——these material and heat treatment issues are often the underlying causes of premature bearing failure.

 

Completeness of Testing Capability: NMT possesses complete material and heat treatment testing capabilities, including chemical composition analysis, metallographic inspection, hardness testing, hardened layer depth measurement and retained austenite content determination. Testing capabilities cover the entire process from incoming material inspection to finished product出厂.

 

VII. Global Collaboration

NMT provides rolling mill bearing products based on materials science and precision heat treatment to steel mills, non-ferrous metal processors and metallurgical equipment manufacturers worldwide.

 

Service Reach: Material and heat treatment solutions cover bearing products used in various hot rolling, cold rolling, continuous casting and non-ferrous metal rolling equipment.

 

Technical Collaboration: NMT can provide material grade selection recommendations, heat treatment solution design and process parameter recommendations according to users' specific operating conditions. When users have special requirements for bearing life, NMT can provide customized solutions for material upgrades and heat treatment optimization.

 

Quality Support: NMT provides complete material inspection reports and heat treatment process records upon bearing delivery, enabling users to understand the material source and heat treatment quality status of each bearing set.