Grain-Oriented Steel Slab Heating to Reduce Surface Defects

Solution Overview

Problem

Grain-oriented electrical steel sheets often exhibit surface defects such as cracks and erosion, which affect their magnetic properties and quality, regardless of whether inhibitors are used or not.

Innovation Solution

A method involving specific heating and cooling conditions for the steel slab, including a first heating process below 1300°C, a second heating process at 1300°C or higher with a time gap of 20 seconds or more, and oxygen concentration control in the atmosphere, followed by water cooling at a rate of 3.0°C/s or higher before hot rolling, to reduce surface defects and enhance magnetic properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If high-temperature heating (1300°C or higher) is applied to dissolve inhibitor components, then inhibitors can be finely dispersed in the steel, but surface defects such as cracks and erosion occur on the slab surface

Engineering Contradiction:

Improveinhibitor dispersion uniformityVSAvoidsurface defects

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The heating process is divided into two distinct stages: a first heating process to a temperature below 1300°C, and a second heating process to 1300°C or higher. This segmentation allows the steel slab to undergo different thermal treatments at different times, achieving both inhibitor dissolution and surface quality improvement without the harmful effects of continuous high-temperature exposure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first heating process is performed as a preliminary action before the second heating process. By heating to below 1300°C first and holding for a specified time (20 seconds or more), the steel slab undergoes preparatory thermal treatment that reduces surface defects before the subsequent high-temperature inhibitor dissolution process

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the steel slab is heated to high temperature for inhibitor dissolution, then magnetic properties can be improved, but manufacturing cost and equipment maintenance increase

Engineering Contradiction:

Improvemagnetic propertiesVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The heating process is divided into two distinct stages: a first heating process to a temperature below 1300°C, and a second heating process to 1300°C or higher. This segmentation allows the steel slab to undergo different thermal treatments at different times, achieving both inhibitor dissolution and surface quality improvement without the harmful effects of continuous high-temperature exposure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The heating process employs periodic action by alternating between a first heating process (below 1300°C) and a second heating process (1300°C or higher), with a specific time interval (20 seconds or more) between them. This periodic thermal treatment achieves the desired magnetic properties while reducing the cumulative time at high temperature, thereby lowering manufacturing costs and equipment maintenance requirements

Inventive Principle:

Principle #19Periodic action

3Stability of the object's composition

If continuous high-temperature heating is applied, then inhibitor dissolution is achieved, but temperature differences within the steel slab increase causing non-uniform texture

Engineering Contradiction:

Improveinhibitor dissolutionVSAvoidtexture uniformity

Core Design Contradiction:

Stability of the object's compositionVSManufacturing precision

Solution Approach 1:

The heating process is divided into two distinct stages: a first heating process to a temperature below 1300°C, and a second heating process to 1300°C or higher. This segmentation allows the steel slab to undergo different thermal treatments at different times, achieving both inhibitor dissolution and surface quality improvement without the harmful effects of continuous high-temperature exposure

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first heating process is performed as a preliminary action before the second heating process. By heating to below 1300°C first and holding for a specified time (20 seconds or more), the steel slab undergoes preparatory thermal treatment that reduces surface defects before the subsequent high-temperature inhibitor dissolution process

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This method effectively reduces surface defects and improves the magnetic properties of grain-oriented electrical steel sheets by minimizing temperature differences and scale erosion, leading to a more uniform texture and better recrystallization.

Implementation Method 1

a first heating process of heating the steel slab for grain-oriented electrical steel sheet to a temperature of lower than 1300° C., and a second heating process of heating the steel slab for grain-oriented electrical steel sheet to a temperature of 1300° C. or higher

Methodology Applied

Scientific EffectHeating: Heating

Implementation Method 2

a surface of the steel slab for grain-oriented electrical steel sheet is subjected to water cooling at a cooling rate of 3.0° C./s or higher after the second heating process and before the hot rolling

Methodology Applied

Scientific EffectWater cooling: Cooling

Implementation Method 3

subjecting the heated steel slab for grain-oriented electrical steel sheet to hot rolling to obtain a hot-rolled steel sheet

Methodology Applied

Scientific EffectHot rolling: Deformation

Implementation Method 4

subjecting the cold-rolled steel sheet to decarburization annealing

Methodology Applied

Scientific EffectDecarburization annealing: Heat Treatment

Implementation Method 5

applying an annealing separator to a surface of the cold-rolled steel sheet after the decarburization annealing

Methodology Applied

Scientific EffectAnnealing separator application: Deposition (physical)

Implementation Method 6

subjecting the cold-rolled steel sheet applied with the annealing separator to final annealing

Methodology Applied

Scientific EffectFinal annealing: Annealing

Implementation Method 7

Such a texture is formed by secondary recrystallization in final annealing. As used herein, the secondary recrystallization refers to a phenomenon in which crystal grains with {110} orientation, which is called Goss orientation, preferentially grow into large grains by utilizing grain boundary energy

Methodology Applied

Scientific EffectSecondary recrystallization: Crystallisation

Data Source

PatentUS20240368717A1Method of manufacturing grain-oriented electrical steel sheet

Publication Date: 2024.11.07 JFE STEEL CORP

AI summary

The present disclosure is to reduce the number of surface defects in a grain-oriented electrical steel sheet. When manufacturing a grain-oriented electrical steel sheet, a steel slab is heated before being subjected to hot rolling. The heating includes a first heating process of heating the steel slab to a temperature of lower than 1300° C., and a second heating process of heating the steel slab to a temperature of 1300° C. or higher, where the time from the end of the first heating process to the start of the second heating process is 20 seconds or longer, the oxygen concentration in the atmosphere in the second heating process is 1.0 vol % or less, and the surface of the steel slab is subjected to water cooling at a cooling rate of 3.0° C./s or higher after the second heating process and before the hot rolling.