Maetz J.-Y.,University of British Columbia |
Militzer M.,University of British Columbia |
Goo N.H.,Hyundai Steel Co. |
Kim S.J.,Hyundai Steel Co. |
And 2 more authors.
TMP 2016 - 5th International Conference on ThermoMechanical Processing, Advance Programme | Year: 2016
Precipitation strengthening has been investigated in four Nb-Mo-bearing high strength low alloyed (HSLA) steels. Hot-torsion tests were conducted to simulate a typical hot strip rolling schedule and the as-quenched microstructures were characterized using EBSD, highlighting the effect of Nb and Mo additions on the resulting bainitic ferrite microstructure. Isothermal aging treatments were performed at typical coiling temperatures to quantify the age hardening kinetics. A phenomenological precipitation strengthening model has been developed based on the Shercliff-Ashby approach to determine the coiling temperature and coil cooling to reach maximum precipitation hardening. The results show that the coiling temperature window to fully realize the precipitation strengthening potential in bainite/ferrite HSLA steels is narrower than that of conventional HSLA steels with polygonal ferrite/pearlite microstructures. © 2016, ThermoMechanical Processing (TMP). All rights reserved.
Bian J.,Niobium Technology Asia |
Mohrbacher H.,NiobelCon BVBA |
Zhang J.-S.,Control Iron and Steel Research Institute, China |
Zhao Y.-T.,Shougang Institute of Technology |
And 2 more authors.
Advances in Manufacturing | Year: 2015
The fast-growing economy and the gradually established highway system have boosted the road transportation for both passenger and cargo over the last decade in China. From 2000 to 2010 Chinese GDP increased by around 10.15% annually and the sales of medium and heavy trucks by around 18.87% (sales increased from 0.2 million in 2000 to 1.3 million in 2010) according to the National Bureau of Statistics of People’s Republic of China. Today commercial vehicles consume almost the same amount of fuel as passenger cars in China although the number of commercial vehicles is only about one fourth of passenger cars. It is estimated that around 50% of imported fuel to China each year will be consumed by vehicle transportation. This situation will worsen fuel shortage problems in the long run and at the same time it is partially responsible for the ever-worsening air pollution in China. Due to the widespread overloading in China, lightweight development in commercial vehicles has fallen far behind that of passenger cars with the consequences that Chinese commercial vehicles consume in average about 20% more fuel, especially the heavy trucks, compared to European models. Under these circumstances it is essential to reduce the vehicle fuel consumption and increase the transport efficiency. The key solution thereby is to implement lightweight design in commercial vehicles as it has been successfully practiced over the last decade in the passenger cars. This paper summarizes highlights given in presentations during the “International seminar on the application of high strength steels in light weight commercial vehicles” with the focus on the development and application of Nb alloyed high performance steels made for lightweight commercial vehicles. © 2015, The Author(s).
Zhang S.,University of Science and Technology Beijing |
Zhang S.,Yangtze University |
Huang Y.,University of Science and Technology Beijing |
Sun B.,University of Science and Technology Beijing |
And 8 more authors.
Materials Science and Engineering A | Year: 2015
The effect of Nb addition (0.022, 0.053, 0.078. wt%) on the hydrogen-induced delayed fracture resistance of 22MnB5 was studied by constant load test and electrochemical hydrogen permeation method. It is shown that the appropriate addition of Nb is beneficial to the improvement of the delayed fracture resistance of tested steel, especially when the steel contains high concentration of hydrogen, and the maximum delayed fracture resistance is obtained at a Nb content of 0.053%.The result of hydrogen permeation test shows that the diffusion coefficient of hydrogen in the steel containing niobium is lower than that in steel without niobium, which indicates that it is harder for hydrogen in the steels containing niobium to diffuse and aggregate. In addition, the reason for Nb improving the delayed fracture resistance of steels is discussed from two aspects: hydrogen trap effect and grain refinement effect. The analysis shows that the main reason leading to the improvement of the delayed fracture resistance is the hydrogen trapping effect of NbC while the grain refinement effect of Nb(C,N) secondary. © 2014 Elsevier B.V.
Bian J.,Niobium Technology Asia |
Mohrbacher H.,MobelCon bvba |
Lu H.,CITIC Metal |
Wang W.,CITIC Metal
7th International Conference on High Strength Low Alloy Steels, HSLA Steels 2015, International Conference on Microalloying 2015, Microalloying 2015 and International Conference on Offshore Engineering Steels 2015, OES 2015 | Year: 2015
Press hardening has become the state-of-art technology in the car body manufacturing to enhance safety standard and to reduce CO2 emission of new vehicles. However the delayed cracking due to hydrogen embrittlement remains to be a critical issue. Generally press hardening steel is susceptible to hydrogen embrittlement due to ultra-high strength and martensitic microstructure. The hydrogen charging tests clearly demonstrate that only a few ppm of diffusible hydrogen is sufficient to cause such embrittlement. Currently the hydrogen embrittlement cannot be detected in the press hardened components and the embitteled components could collapse in the crash situation with fatal consequences arisen through dramatic loss in both strength and ductility. This paper introduces a new metallurgical solution to increase the resistance to hydrogen embrittlement of conventional press hardening steel based on 22MnB5 by Nb microalloying. In the hydrogen embrittlement and permeation tests the impact of Nb microalloying on the hydrogen embrittlement behavior was investigated under different hydrogen charging conditions and constant load. The test results revealed that Nb addition increases the resistance to hydrogen embrittlement due to reduced hydrogen diffusivity. The focus of this paper is to investigate the precipitation behavior of microalloying elements by using TEM and STEM and to find out the mechanisms leading to higher performance against hydrogen embrittlement of Nb alloyed steels.
Jian B.,Niobium Technology Asia
SEAISI Quarterly (South East Asia Iron and Steel Institute) | Year: 2013
In order to improve the fuel-efficiency and to reduce the CO2 emission the automotive industry worldwide is pursuing the lightweight technology. With application of advanced high strength steels like DP, TRIP or hot stamping steels a weight reduction about 20% can be achieved for the crash relevant components without safety compromise and cost increase. This paper presents some of the latest developments with regard to the material concepts of some selected 2011 car models from Europe, America and Asia. The focus of the paper is to demonstrate how to use the Nb microalloying to further improve these high strength steels for the automotive application. The strengthening mechanism of advanced high strength steels as well as hot stamping steels is based on higher carbon content and transformation hardening compared to conventional high strength steels. Consequently this leads to on one hand the poor toughness from material side and poor weldability from processing side and on the other hand to the problem of the poor formability due to the inhomogeneity of the mixed microstructure of soft and hard phases. The key to the improvement lies in the grain refinement effect of Nb alloying, because the grain refinement is the only strengthening mechanism which can increase the strength and toughness at the same time. For the medium or high carbon steels like hot stamping steels a better toughness will ensure a better component performance in the crash situation. With the extra strength increase from grain refinement and precipitation hardening due to Nb alloying it is possible to reduce the carbon content in the steel which brings in return a better weldability. Finally the grain refinement can homogenize the microstructure of multiphase steels and reduce or eliminate the banded structure of hard phases like perlite and martensite, which usually causes problems during forming processes especially by bending and hole expansion operations. Finally an innovative alloying design for hot stamping steels with the aim to change the old Manganese -Boron concept will be introduced. Microalloying with Nb can not only upgrade the steel quality but also provide the automotive industry with the most reliable and most economic materials for the lightweight achievement.
Jian B.,Niobium Technology Asia
SEAISI Quarterly (South East Asia Iron and Steel Institute) | Year: 2015
Over the last decades lightweight has become the most important strategy in the car body manufacturing and it can be achieved most economically by using high strength steels in the aspects of material, processing and joining. In some recent car models high strength steels have already reached 80% among which conventional high strength steels like HS-IF, HS-BH and HSLA steels remain to be the most widely used steel grades due to their global availability, reasonable price and easy processing. However advanced high strength steels like DP, CP, MS and press hardening steel will increase application due to their high potential for lightweighting. For the car body engineering mechanical properties like strength and elongation are not solely important criteria. With increasing strength level which generally leads to increase of carbon content other parameters like formability, weldability and crash behaviors of the chosen steel grade become dominate factors to the entire body concept. In order to meet the requirements for the automotive application steel industry has developed appropriate metallurgical solutions to tailor these specific properties. This paper will explain how to use niobium microalloying to optimize automotive high strength steels for an optimum integration of strength, formability, weldability and crash performance.