Hot-Formed Steel Part Homogeneous Multiphase Microstructure

Solution Overview

Problem

The development of parts made from TRIP or dual-phase steels is limited by the difficulty in controlling springback and achieving homogeneous microstructures, leading to unpredictable behavior and restricted shape options due to high tensile strength and non-uniform deformation during cold-forming processes.

Innovation Solution

A process involving heating a steel blank to a soak temperature between Ac1 and Ac3, followed by hot-forming and controlled cooling to achieve a homogeneous multiphase microstructure comprising ferrite, which ensures consistent mechanical properties and reduces springback, allowing for higher formability and energy absorption capabilities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If cold-forming is used to manufacture parts from TRIP or dual-phase steel, then high tensile strength can be achieved, but springback control becomes difficult and microstructure homogeneity is lost

Engineering Contradiction:

Improvetensile strengthVSAvoidspringback control

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The invention changes the temperature parameter from cold-forming to hot-forming (heating to Ac1-Ac3 range), which fundamentally alters the material's mechanical behavior and microstructure formation, enabling both high strength and controlled springback

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention utilizes phase transition by heating to Ac1-Ac3 temperature range to transform the microstructure to austenite before forming, then controlling the transformation during cooling to achieve homogeneous multiphase microstructure with controlled springback

Inventive Principle:

Principle #36Phase transitions

2Strength

If cold-forming is used to manufacture parts from TRIP or dual-phase steel, then high tensile strength can be achieved, but microstructure homogeneity deteriorates

Engineering Contradiction:

Improvetensile strengthVSAvoidmicrostructure homogeneity

Core Design Contradiction:

StrengthVSStability of the object's composition

Solution Approach 1:

The invention changes the temperature parameter from cold-forming to hot-forming (heating to Ac1-Ac3 range), which fundamentally alters the material's mechanical behavior and microstructure formation, enabling both high strength and controlled springback

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention utilizes phase transition by heating to Ac1-Ac3 temperature range to transform the microstructure to austenite before forming, then controlling the transformation during cooling to achieve homogeneous multiphase microstructure with controlled springback

Inventive Principle:

Principle #36Phase transitions

3Use of energy by moving object

If high tensile strength steel is used, then energy absorption capability improves, but springback effect increases and design complexity increases

Engineering Contradiction:

Improveenergy absorptionVSAvoiddesign complexity

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The invention changes the temperature parameter from cold-forming to hot-forming (heating to Ac1-Ac3 range), which fundamentally alters the material's mechanical behavior and microstructure formation, enabling both high strength and controlled springback

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention performs preliminary heating to Ac1-Ac3 temperature range before forming to establish a controlled microstructure, which then transforms predictably during cooling, allowing high strength with reduced springback and simplified design

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

The process results in parts with improved mechanical properties and reduced springback, enabling the production of a wider variety of shapes with enhanced energy absorption and maintaining known steel characteristics like weldability, while ensuring a homogeneous microstructure throughout the part.

Implementation Method 1

heating a steel blank to a soak temperature between Ac1 and Ac3

Methodology Applied

Scientific EffectPhase transformation (austenite formation): Phase Change

Implementation Method 2

cooling the heated blank at a cooling rate that ensures a homogeneous multiphase microstructure comprising ferrite

Methodology Applied

Scientific EffectPhase transformation (martensite and bainite formation): Phase Change

Data Source

PatentUS10294557B2Method for making a steel part of multiphase microstructure

Publication Date: 2019.05.21 ARCELOR FRANCE SA

AI summary

A steel part having a homogeneous multiphase microstructure in each region of the part, the microstructure containing ferrite, wherein the steel part is obtained by a process involving:cutting a blank from a strip of steel, having a specified composition;optionally, the blank undergoes prior cold deformation;the blank is heated to reach a soak temperature Ts above Ac1 but below Ac3 and held at this soak temperature Ts for a soak time ts adjusted so that the steel, after the blank has been heated, has an austenite content equal to or greater than 25% by area;the heated blank is transferred into a forming tool to hot-form the part; andthe part is cooled within the tool at a cooling rate V such that the microstructure of the steel, after cooling the part, is a multiphase microstructure containing ferrite and being homogeneous in each region of the part.