Launch Of A New Class of 3 rd Generation Cold Formable AHSS

Transcription

1 Launch Of A New Class of 3 rd Generation Cold Formable AHSS D.J. Branagan, C.S. Parsons, T.V. Machrowicz, A.E. Frerichs, B.E. Meacham, S. Cheng, and A.V Sergueeva

2 NanoSteel 3rd Generation AHSS: Reaches Commercial Scale Initial GM delivery of validation material from AK Steel made in April

3 Outline o o o o Overview History / Technological Breakthroughs Current Status NanoSteel 3 rd Generation AHSS Technology Enabling Structures and Mechanisms Performance Characteristics Tensile Properties Bend Performance Bi-Axial Performance Forming Limit Diagram Novel Performance Characteristics Local Formability at Hole Expansion Draw ability & Hydrogen Assisted Delayed Cracking Resistance

4 Overview

5 NanoSteel 3 rd Generation AHSS: Technology Development Pathway Steel Co. Boron-Free Alloy Current Status Steel Co. Analysis -Slab Steel Co. Trials- Boron Alloy Founded NanoSteel R&D Analysis - Slab DOE Research Industrial Coatings Basic Sheet R&D Strip Casting

6 NanoSteel 3 rd Generation AHSS: General Features - Technology Steel Production Using conventional slab production Strength and Ductility Novel combinations 1200 MPa & 50% elongation, 60,000 MPa% Cold Formability High Global, local, and with complex stresses New 3rd Generation AHSS will enable complex geometry for weight savings

7 NanoSteel 3 rd Generation AHSS: Wide Range of Properties NXG 1200 NXG 1200 Technology enables wide range of properties protected by over 300 patents

8 NanoSteel 3 rd Generation AHSS: Steel Making Process NanoSteel s Advanced High-Strength Sheet steels are designed for production in conventional steel mills using existing technology.

9 NanoSteel 3 rd Generation AHSS Technology

10 NanoSteel 3 rd Generation AHSS: Commercial Coil and Structure Example Coil Coil Structure Recrystallized Modal Structure in commercially produced coils is enabling for cold formability

11 NanoSteel 3 rd Generation AHSS: Structural Change During Cold Forming NanoSteel Sheet Final Part Nanophase Refinement & Strengthening through the forming process (e.g. stamping, roll forming etc.) Recrystallized Modal Structure Mixed Microconstituent Structure

12 NanoSteel 3 rd Generation AHSS: Details of Microconstituent #1 General View Nanoscale ferrite grains verified by dark-field TEM Nanoprecipitates verified by high resolution TEM o Microconstituent Area 1 Transformed nanoscale ferrite grains with nanoprecipitates

13 NanoSteel 3 rd Generation AHSS: Details of Microconstituent #2 General View Micron-sized austenitic grains (untransformed) Nanoprecipitates verified by high resolution TEM o Microconstituent Area 2 Untransformed micron sized austenitic grains with nanoprecipitates

14 Performance Characteristics

15 NXG 1200 Performance Characteristics: Properties (Non-mill spec) TEST Average Ultimate Tensile Strength 1188 MPa Yield 0.2% Offset 378 MPa Elongation 54.6% Uniform Elongation 51.5% Young s Modulus 187 GPa Material Density 7.78 g/cm 3 Results from NanoSteel laboratory testing on commercial sheet

16 NXG 1200 Performance Characteristics: Sheet Property Uniformity Tensile Properties in Respect to Rolling Direction Tensile test results did not show any anisotropy in produced coil and along length and width

17 Transverse Longitudinal NXG 1200 Performance Characteristics: Bend Performance Bend 0.34 R/t Enlarged View of 0.34 R/t All specimens pass at 180 (R/t = 0.34) demonstrating exceptional bendability

18 NXG 1200 Performance Characteristics: Bi-Axial Performance - Limiting Dome Height Mechanical Bulge Test Results NanoSteel (1188 MPa UTS) DP980 (1030 MPa UTS) Dome Height NanoSteel DP980 Stopped just before failure (see images) 2.01 (51.1 mm) (28.1 mm) Failed samples 2.26 (57.4 mm) 1.24 (31.5 mm) Test Conditions: 4 ball punch, 10 mm/s punch speed, lubricant Limiting dome height found to be at 2.26 which is superior to existing high strength grades

19 NXG 1200 Performance Characteristics: Forming Limit Diagram NXG 1200 (1188 MPa UTS) DP 980 (1030 MPa UTS) NXG 1200 material has improved formability over DP980 at similar thickness

20 Novel Performance Characteristics

21 NXG 1200 Performance Characteristics: Local Formability at Hole Expansion (λ) Standard View of HER Influences Expanded HER Influences Controlled by: Hole Preparation e.g. die clearance, punch geometry Global Materials Properties: e.g Total elongation, UTS, post uniform elongation Microstructure response to stress adds additional optimization variable Microstructure response to stress provides ability for HER improvement in high strength material

22 NXG 1200 Performance Characteristics: Hole Expansion Performance Example Sample at 46.9% HER ( ) Top View Profile / Side View Sample with punched hole utilized Average HER at ~ 45% High HER / lambda values obtained, high edge formability expected during stamping operations

23 NXG 1200 Performance Characteristics: Hydrogen Assisted Delayed Cracking Resistance Traditional Delayed Cracking Interpretation Expanded Delayed Cracking Criteria Curt D. Horvath et al, Great Designs in Steel, Livonia, Michigan, May 13, 2015 Traditionally, delayed cracking is considered to be affected by & require all 3 criteria Microstructure response provides additional variable to prevent delayed cracking Delayed cracking can be prevented through material response to applied stress

24 NXG 1200 Performance Characteristics: Limiting Draw Ratio Example 1.9 Draw Ratio Cup Drawn Cups in H 2 Atmosphere o Drawing Conditions Cups drawn to LDR at 1.9 draw ratio Cups exposed to 100% hydrogen for 45 minutes Exposed cups monitored in air for over 6 months Delayed cracking avoided at LDR, expected high drawability and crack free during stamping

25 NXG 1200 Performance Characteristics: Additional Testing in Hydrogen Hydrogen Exposed Tensile Testing Hydrogen Exposed Bend Testing Longitudinal, R/t 0.23 Exposure to hydrogen for 10 minutes after each incremental 5% increase in strain Samples exposed to 100% hydrogen while under load for 45 minutes Clamped for >100 hours after exposure without cracking No susceptibility to hydrogen attack / delayed fracture observes at uniaxial tension or bending

26 Conclusions o o o NanoSteel 3 rd Generation AHSS Technology Initial product delivered for OEM testing at 60,000 MPa% Enabled due to unique structures and mechanisms Compelling Performance Characteristics Strength & ductility combination Bend ability with low R/t ratio Bi-axial performance with high Limiting Dome Height Superior Forming Limit Diagram Novel Performance Enabled by Specific Microstructural Response to Stress High local formability for Hole Expansion Avoidance of hydrogen assisted delayed cracking resistance at LDR