scholarly journals Characterization of the Stretch Flangeabitity of High-Strength Bainitic Steel: The Significance of Variant Pairs

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 276
Author(s):  
Zhiquanquan Wang ◽  
Zifeng Guo ◽  
Chengjia Shang ◽  
Bin Chen ◽  
Yajun Hui
Keyword(s):  
High Strength ◽  
Expansion Ratio ◽  
Influential Factors ◽  
Low Carbon ◽  
High Angle ◽  
Governing Factor ◽  
Stretch Flanging ◽  
Hole Expansion Ratio ◽  
Micro Alloyed Steel

Variant pairs have an indispensable function on mechanical properties such as low impact toughness. Therefore, it was assumed that they would also affect the HER (Hole Expansion Ratio, an indicator to evaluate stretch flanging performance). To clarify this, a comprehensive analysis of the common influential factors in an 800 MPa grade low carbon micro-alloyed steel, i.e., the retained austenite, the M/A (Martensite/Austenite) island, the titanium precipitations, the grain diameter, the density of high angle grain boundaries and the textures, was first conducted. It was found that they did not match well with the HER, suggesting that they were not the governing factor for HER in this steel. However, the dominating crystallography groups and the variant pairing results indicated that they fitted well with the HER. In the samples with high HERs, the CP (Close Packed) groups dominated the transformation, wherein one individual CP group consisted of two or more Bain groups, whereas it evolved into the domination of joint CP groups and Bain groups for the low HER sample. Further analysis on the variant pairing features indicated that a correlation occurred between the HER and the high angle variant pairs. In the steels with high HERs, high-angle variant pairs of V1/V2, V1/V3 that transformed from the same CP group, particularly of V1/V2 pair, were mostly generated. They turned to V1/V9, V1/V10, V1/V12, V1/V15, V1/V17, and V1/V18 pairs from differential CP groups, especially the V1/V12 and V1/V15 pair for low-HER steel. This result showed that V1/V2, V1/V12, and V1/V15 might have accounted most for the HER in this steel. The underlying reason was that the V1/V2 pair was specialized in supplying a slip passage for dislocation transmission across a grain boundary with little resistance, whereas the dislocation transmission ability for V1/V12 and V1/V15 pair was particularly poor. Thus, to efficiently enhance the HER, one should regulate the variant pairs by augmenting the V1/V2 fraction and suppressing the formation of the V1/V12 and V1/V15 pair.

scholarly journals Influence of Ti and Nb on the Strength–Ductility–Hole Expansion Ratio Balance of Hot-rolled Low-carbon High-strength Steel Sheets

2012 ◽  
Vol 52 (1) ◽  
pp. 151-157 ◽  
Author(s):  
Kyohei Kamibayashi ◽  
Yutaka Tanabe ◽  
Yoshito Takemoto ◽  
Ichirou Shimizu ◽  
Takehide Senuma
Keyword(s):  
High Strength Steel ◽  
High Strength ◽  
Expansion Ratio ◽  
Low Carbon ◽  
Hole Expansion ◽  
Steel Sheets ◽  
Hole Expansion Ratio ◽  
Hot Rolled

The Study in Improvement of Hole Expansibility for High-Strength Steel of 980MPa Grade

2018 ◽  
Vol 941 ◽  
pp. 492-497
Author(s):  
Kuo Cheng Yang ◽  
J.F. Tu ◽  
L.J. Chiang ◽  
W.J. Cheng ◽  
C.Y. Huang
Keyword(s):  
Yield Strength ◽  
High Strength Steel ◽  
Dual Phase Steel ◽  
Single Phase ◽  
High Strength ◽  
Expansion Ratio ◽  
High Yield ◽  
Dual Phase ◽  
Hole Expansion ◽  
Hole Expansion Ratio

Recently, due to the requirements of lightweight and safety, the grade of 980MPa high-strength steel has the demand of high hole expansibility and high yield strength. Due to the large difference of hardness between the soft ferrite and hard martensite, the traditional DP980Y dual phase steel has poor hole expansibility. In order to improve the hole expansibility of DP980Y dual phase steel, the best way is to modify the microstructure into a single-phase to eliminate the large difference of hardness. In this paper, the steel of nearly full bainite microstructure with small amount of ferrite and M/A constituents was studied. Compared to the DP980Y dual phase steel, it was found that this modified steel with a single-phase microstructure has the same grade of 980MPa of tensile strength, but can achieve the demand of higher yield strength and hole-expansion ratio. This study shows reducing the amount of ferrite can increase the homogeneity of matrix with the single phase to improve the hole expansibility. In addition, the use of lower bainite transformation temperature and lower carbon content has the higher hole-expansion ratio due to the less amount of M/A constituents.

FE-SEM Study of Fine Nb Precipitates in Carbon Extraction Replicas

2005 ◽  
Vol 500-501 ◽  
pp. 663-668 ◽  
Author(s):  
Rocco Varano ◽  
A.M. Elwazri ◽  
Fulvio Siciliano ◽  
D.Q. Bai ◽  
Raynald Gauvin ◽  
...  
Keyword(s):  
High Strength ◽  
Volume Effect ◽  
Carbon Steels ◽  
Low Carbon ◽  
Thin Foils ◽  
Transmission Electron ◽  
Sem Study ◽  
Before And After ◽  
Linepipe Steel

Precipitation strengthening is an important parameter controlling the mechanical properties of low carbon steels. These precipitates are very fine and are normally analyzed using either thin foils or carbon extraction replicas under a transmission electron microscopy (TEM). In this work, field emission gun scanning electron microscope (FE-SEM) was applied successfully in the characterization of niobium (Nb) carbo-nitride (C,N) precipitates using carbon extraction replicas. FE-SEM observation of high strength linepipe steel replicas before and after aging at 400°C for 1 hr confirmed the presence of Nb(C,N) precipitates in ferrite. The FE-SEM could analyze small particles (below 50 nm) embedded in the steel but the analysis had to be carried out at low voltages to maximize spatial resolution resulting in a poor signal. However, carbon extraction replicas in the FE-SEM can be analyzed using high voltages, since the interaction volume effect is no longer a problem.

scholarly journals Hole Expansion Ratio and Fatigue Properties in Piercing of High-Strength Steel Sheets by PW Punch

2011 ◽  
Vol 52 (606) ◽  
pp. 795-800 ◽  
Author(s):  
Takashi MATSUNO ◽  
Yukihisa KURIYAMA ◽  
Hiroya MURAKAMI ◽  
Shota YONEZAWA ◽  
Naonobu KANAMARU
Keyword(s):  
High Strength Steel ◽  
High Strength ◽  
Expansion Ratio ◽  
Fatigue Properties ◽  
Hole Expansion ◽  
Steel Sheets ◽  
Hole Expansion Ratio

Forming Performance of 800MPa Grade Advanced High Strength Steels

2013 ◽  
Vol 455 ◽  
pp. 173-178 ◽  
Author(s):  
Mei Zhang ◽  
Yu Xiang Ning ◽  
Jun Zhang ◽  
Zi Wan ◽  
Tao Wang
Keyword(s):  
High Strength Steels ◽  
High Strength ◽  
Expansion Ratio ◽  
Hole Expansion ◽  
Advanced High Strength Steels ◽  
Hsla Steels ◽  
Blank Holding Force ◽  
Hole Expansion Ratio ◽  
Test Hole ◽  
Springback Behavior

800MPa grade Advanced High Strength Steels (AHSS), including Complex Phase steel CP800 and Ferrite-Bainite steel FB800, were chosen to test the forming performance in different test conditions and compared with the reference traditional high strength low alloy (HSLA) steels HR700LA. Tensile test, hole expansion (HE) test, and HAT shape stamping test were taken to investigate the forming performance of the materials. Test results indicated that the studied 800MPa grade AHSS showed a better strength ductility balance compared with the reference steel. Among all the steels researched, FB800 showed the best hole expansion ratio (HER), and CP800 the worst. Springback angles of AHSS after HAT shape stamping tests were markedly smaller than those of HR700LA steels, though the springback angles of HR700LA decreased continuously with blank holding force (BHF) increasing. Steel FB800, CP800S and CP800B had much better shape stability compared with steels HR700LA. AHSS showed much smaller springback behavior under the same stamping condition, especially for steels CP800-B, FB800-2 and FB800-1. When increasing the BHF to 100KN, AHSS showed the largest springback deformation. Among the three kinds of CP800 steels researched, steel CP800-B indicated outstanding springback restrain trend in BHF further increasing attempt. So, springback behavior could be restricted obviously by using a larger BHF in AHSS CP800B forming operations.

scholarly journals Microstructures and Properties of Auto-Tempering Ultra-High Strength Automotive Steel under Different Thermal-Processing Conditions

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1121
Author(s):  
Han Jiang ◽  
Yanlin He ◽  
Li Lin ◽  
Rendong Liu ◽  
Yu Zhang ◽  
...  
Keyword(s):  
Great Influence ◽  
High Strength ◽  
Strengthening Mechanism ◽  
Expansion Ratio ◽  
Air Cooling ◽  
Tempered Martensite ◽  
Solid Solution Strengthening ◽  
Heating And Cooling ◽  
Calculation Results ◽  
Hole Expansion Ratio

Automotive steels with ultra-high strength and low alloy content under different heating and cooling processes were investigated. It was shown that those processes exhibited a great influence on the performance of the investigated steels due to the different auto-tempering effects. Compared with the steels under water quenching, there was approximately a 70% increase in the strength and elongation of steels under air cooling, in which the martensite was well-tempered. Although the elongation of the steel with a microstructure composed of ferrite, well-tempered martensite and less-tempered martensite could exceed 15%, the hole expansion ratio was still lower because of the undesirable hardness distribution between the hard phases and the soft phases. It followed from the calculation results based on SEM, TEM and XRD analyses, that for the steel under air cooling, the strengthening mechanism was dominated by the solid solution strengthening and the elongation was determined by the auto-tempering of martensite. Experiments and analyses aimed to explore the strengthening and plasticity mechanisms of auto-tempering steels under the special process of flash heating.

Increasing the Hole Expansion Ability of High Strength Steel Sheet by Improving the Pre-Hole Shearing Process

2019 ◽  
Vol 962 ◽  
pp. 167-174
Author(s):  
Prasan Saengkhiao ◽  
Komgrit Lawanwong ◽  
Pakorn Chumrum
Keyword(s):  
High Strength Steel ◽  
Steel Sheet ◽  
High Strength ◽  
Expansion Ratio ◽  
Expansion Process ◽  
Forming Process ◽  
Research Papers ◽  
Hole Expansion ◽  
Hole Edge ◽  
Hole Expansion Ratio

The hole expansion process is a forming process that the fracture easily occurred on the hole edge. Therefore, many research papers presented various processes to make a precision pre-hole shearing to a hole expansion process such as wire cut, EDM, and laser cut. The purpose of this work is to increase a hole expansion ratio on the high strength steel sheet. The conventional piercing by piercing punch and piercing with a counter punch was used to make a pre-hole shearing process in this research paper. The high strength steel grade 590 and 980 MPa of 1.2 mm of thickness were used in the experiments. From experimental results, it was found that the pre-hole shearing by piercing with a counter punch can be increased a shear surface on cutting edge of workpiece. Moreover, the used piercing with counter punch can improve the hole expansion ratio more than the conventional piercing process because sheared surface around the hole edge was increased.

Microstructural Characterization of New Super-Ferritic-Martensitic Stainless Steel

2016 ◽  
Vol 257 ◽  
pp. 52-55
Author(s):  
Sérgio Souto Maior Tavares ◽  
Adriana da Cunha Rocha ◽  
Manoel Ribeiro da Silva ◽  
Carlos Augusto Silva de Oliveira ◽  
Rachel Pereira Carneiro da Cunha
Keyword(s):  
Stainless Steel ◽  
Corrosion Resistance ◽  
Martensitic Stainless Steel ◽  
High Strength ◽  
Microstructural Characterization ◽  
Low Carbon ◽  
Martensitic Stainless Steels ◽  
Nickel Addition ◽  
High Chloride

The demand for high strength materials with improved corrosion resistance boosted the development of supermartensitic steels from conventional martensitic stainless steels The first alloys were designed with 11-13%Cr, extra-low carbon and nickel addition. More recently, experimental alloys with higher Cr (15-17%) and other ferritizing elements (Mo, W, Nb,…) were developed with the aim of obtain higher corrosion resistance in high chloride environments. In this work, the microstructure features of a new 17%Cr stainless steel were investigated.

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