Hot-Stamped Steel Surface Layers for Toughness Without Costly Alloying
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Solution Overview
Problem
Current hot stamping processes face challenges in enhancing the toughness of ultra-high strength steel while maintaining economical feasibility, as increasing alloy components lead to higher costs and potential brittleness issues.
Innovation Solution
A hot stamping part is manufactured with a decarburization layer and an inner oxide layer on the surface of a base material, along with a plating layer, which are formed through specific annealing and heating processes to achieve a desired microstructure and hardness distribution, thereby improving toughness and preventing cracks during the hot stamping process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If alloy components are increased to improve toughness, then toughness is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the chemical composition parameters of the steel by precisely controlling the content ranges of alloying elements (C: 0.23-0.45%, Si: 0.015-2.0%, Mn: 1.50-3.00%, P: 0.010-0.050%, S: 0.005-0.030%, Ti: 0.005-0.050%, V: 0.005-0.050%, Nb: 0.005-0.050%, B: 0.0005-0.0050%). This parameter optimization achieves improved toughness through controlled microstructure formation rather than simply increasing alloy content, thereby resolving the contradiction between toughness enhancement and manufacturing cost control
Solution Approach 2:
The patent creates a composite microstructure consisting of martensite, bainite, and retained austenite phases. This multi-phase composite structure provides both high toughness and strength, achieving the desired mechanical properties without requiring excessive alloying, thus addressing the contradiction between toughness improvement and cost increase
2Strength
If alloy components are increased to improve toughness, then toughness is improved, but brittleness increases
Solution Approach 1:
The patent optimizes the balance between alloying elements to achieve the desired microstructure. Specifically, it controls Si content (0.015-2.0%) to suppress excessive carbide precipitation that would increase brittleness, while maintaining adequate Mn (1.50-3.00%) for toughness. The controlled addition of microalloying elements (Ti, V, Nb, B) in small amounts (0.0005-0.050% each) refines the microstructure without causing excessive hardening and brittleness, thus resolving the toughness-brittleness contradiction
Solution Approach 2:
The patent creates a composite microstructure with martensite (for strength), bainite (for toughness), and retained austenite (for ductility and toughness). This multi-phase composite provides a balanced combination of mechanical properties, achieving high toughness while maintaining adequate ductility and avoiding excessive brittleness that would result from single-phase high-strength structures
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 method results in a hot stamping part with enhanced toughness, achieving a tensile strength of 1680 MPa to 2000 MPa, yield strength of 1150 MPa to 1500 MPa, elongation of 4% to 10%, and a VDA bending angle of 60° or more, while maintaining cost-effectiveness by optimizing the depth and hardness of the decarburization and inner oxide layers.
Implementation Method 1
forming a blank by cutting a plated steel sheet having a plating layer formed on at least one surface of a base material; and heating the blank in a heating furnace having a plurality of sections with different temperature ranges, wherein the heating of the blank includes: a multi-stage heating step of heating the blank stepwise; and a soaking step of heating the stepwise heated blank to a temperature of Ac3 to 910° C.
Implementation Method 2
a decarburization layer located on the base material; and an inner oxide layer located on the decarburization layer
Data Source
AI summary
A hot stamping part includes: a base material; a decarburization layer located on the base material; and an inner oxide layer located on the decarburization layer, wherein the hot stamping part has a tensile strength (TS) of 1680 MPa to 2000 MPa, and a hardness of the hot stamping part within a depth of 50 μm from a surface of the hot stamping part in a plate thickness direction of the hot stamping part and an average hardness of the hot stamping part satisfy Relational Expression 1.(A/B)≤0.7<Relational Expression 1>(In Relational Expression 1, A denotes the hardness (Hv(≤50 μm)) within the depth of 50 μm in the plate thickness direction of the hot stamping part, and B denotes the average hardness (Hv(avg.)) of the hot stamping part.)